NOTA MUSCULOSKELETAL SYSTEM 2024 (1).pdf

# Introduction to the musculoskeletal system and bone functions This section introduces the skeletal system, osteology, and the musculoskeletal system, detailing the fundamental functions of bones [1](#page=1). ### 1.1 The skeletal and musculoskeletal systems * The **skeletal system** comprises bones, cartilage, dense connective tissue, epithelium, blood-forming tissue, adipose tissue, and nervous tissue [1](#page=1). * **Osteology** is the study of bone structure and the treatment of bone problems [1](#page=1). * The **musculoskeletal system** is the combination of the skeletal system (bones), muscles, and joints [1](#page=1). ### 1.2 Functions of bones and the skeletal system Bones serve several critical functions within the body [1](#page=1): 1. **Support:** They provide shape to the body, support soft tissues, and offer attachment points for muscles and tendons [1](#page=1). 2. **Protection:** Bones shield vital organs from injury. Examples include the skull protecting the brain, the vertebral column protecting the spinal cord, the ribs protecting thoracic organs, and the pelvis protecting the bladder and internal reproductive organs [1](#page=1). 3. **Movement:** The skeletal system, in conjunction with muscles and joints, enables a wide range of motion [1](#page=1). 4. **Blood cell production:** Red bone marrow in certain bones produces blood cells through a process called hematopoiesis [1](#page=1). 5. **Mineral storage (Mineral Homeostasis):** Bones store essential minerals such as calcium, phosphorus, sodium, potassium, and others, playing a crucial role in mineral balance [1](#page=1). 6. **Fat storage:** The yellow bone marrow, composed of adipose cells, stores triglycerides [1](#page=1). ### 1.3 Classification of bones by shape Bones are primarily classified into five main types based on their shape [1](#page=1): #### 1.3.1 Long bones * Characterized by their length [2](#page=2). * Consist of a diaphysis (shaft) and two epiphyses (ends of the bone) [2](#page=2). * The diaphysis and epiphyses are separated by the epiphyseal cartilage [2](#page=2). * Examples include the humerus, ulna, radius, femur, tibia, fibula, metacarpals, phalanges, metatarsals, and phalanges [2](#page=2). #### 1.3.2 Short bones * Lack a diaphysis [2](#page=2). * Are broad and thick [2](#page=2). * Examples include the carpals (wrist bones) and tarsals (ankle bones) [2](#page=2). #### 1.3.3 Flat bones * Thin and provide protection for organs, as well as broad surfaces for muscle attachment [2](#page=2). * Examples include the sternum, scapula, thoracic (rib) bones, cranial (skull) bones, and ilium [2](#page=2). #### 1.3.4 Irregular bones * Composed of an outer layer of compact bone and an inner layer of cancellous bone [3](#page=3). * Examples include the vertebrae (backbone) and facial bones [3](#page=3). #### 1.3.5 Sesamoid bones * Flat and oval-shaped bones found within specific joints [3](#page=3). * The patella (kneecap) is a prime example [3](#page=3). ### 1.4 Macroscopic structure of bones Bones are composed of several key macroscopic structures [3](#page=3): * **Diaphysis (shaft):** * The long, cylindrical shaft of a long bone [3](#page=3). * Comprises an outer layer of compact bone and an inner layer of cancellous bone [3](#page=3). * Contains the medullary cavity in its center, which houses yellow bone marrow [3](#page=3). * **Epiphysis:** * Derived from the Greek word meaning "to grow upon." [3](#page=3). * Located at the ends of long bones [3](#page=3). * Consists of a thin outer layer of compact bone surrounding cancellous bone, which contains red bone marrow responsible for producing red blood cells, white blood cells, and platelets [3](#page=3). * **Metaphysis:** * The region connecting the diaphysis to the epiphysis [4](#page=4). * This is where bone lengthening occurs. The epiphyseal plate (growth plate), a layer of hyaline cartilage, allows the diaphysis to grow in length until approximately age 17 [4](#page=4). * **Articular cartilage (Hyaline cartilage):** * A thin layer of hyaline cartilage covering the epiphyses at the ends of bones where they articulate with other bones [4](#page=4). * Reduces friction in joints and acts as a shock absorber [4](#page=4). * **Periosteum:** * A strong fibrous membrane that covers all bone surfaces except the epiphyses, which are covered by articular cartilage [4](#page=4). * **Functions:** * Provides protection to the bone [4](#page=4). * Serves as attachment points for ligaments and muscle tendons [4](#page=4). * Contains osteogenic cells (osteoblasts) that build new bone tissue, increasing compact bone thickness and maintaining bone shape [4](#page=4). * Contains nerves, lymphatic vessels, and capillaries that supply nutrients to bone tissue and aid in fracture repair [4](#page=4). * **Medullary cavity:** * The space in the center of the diaphysis that contains yellow bone marrow [5](#page=5). * **Endosteum:** * A membrane that lines the wall of the medullary cavity [5](#page=5). ### 1.5 Microscopic structure of bone Bone tissue is composed of a matrix and various cell types [5](#page=5). * **Matrix:** * Consists of 25% water, 25% collagen fibers, and 50% mineral salts [5](#page=5). * **Bone cells:** There are four primary types of cells in bone tissue [5](#page=5): * **Osteogenic cells:** Mesenchymal stem cells that divide and differentiate into osteoblasts. They are found in the periosteum and endosteum [5](#page=5). * **Osteoblasts:** Non-dividing cells responsible for producing collagen fibers and other organic substances needed to build the extracellular matrix of bone tissue, eventually becoming osteocytes [5](#page=5). * **Osteocytes:** Mature, non-dividing bone cells that maintain bone tissue and carry out daily metabolic functions, such as nutrient and waste exchange between bone and blood. They are the primary cell type found within bone [5](#page=5). * **Osteoclasts:** Found in abundance in the endosteum, these cells are responsible for bone resorption (breaking down the extracellular matrix). They play a critical role in bone development, growth, maintenance, and repair [5](#page=5). > **Tip:** Understanding the roles of osteoblasts (bone builders) and osteoclasts (bone breakers) is crucial for comprehending bone remodeling and repair processes. ### 1.6 Types of bone tissue There are two main types of bone tissue [7](#page=7): * **Compact bone (dense bone):** Appears solid and hard [7](#page=7). * **Cancellous bone (spongy bone/trabecular bone):** Appears porous and sponge-like [7](#page=7). #### 1.6.1 Microscopic structure of compact bone * Compact bone is organized into units called Haversian systems (osteons) [7](#page=7). * Each Haversian system contains [7](#page=7): * **Haversian canals (central canals):** Small canals in the center containing capillaries, lymphatic vessels, and nerves. Blood and lymph supply nutrients to bone cells, while nerves provide stimulation [7](#page=7). * **Lamellae:** Concentric rings of hard matrix surrounding the central canal, providing strength to the bone [8](#page=8). * **Lacunae:** Small cavities between lamellae that house osteocytes, interstitial fluids, and lymph [8](#page=8). * **Canaliculi:** Tiny channels connecting lacunae to each other and to the Haversian canal, allowing for the passage of nutrients, oxygen, and waste products to and from bone cells and blood vessels [8](#page=8). * **Interstitial lamellae:** Bone layers filling the spaces between individual Haversian systems [8](#page=8). * **Volkmann's canals (perforating canals):** These canals connect the medullary cavity, periosteum, and other Haversian canals, running perpendicular to the Haversian canals [8](#page=8). > **Example:** The arrangement of lamellae in concentric circles within osteons gives compact bone its remarkable strength and resistance to bending. #### 1.6.2 Microscopic structure of cancellous bone * Cancellous bone has a spongy appearance with numerous spaces [10](#page=10). * It consists of irregularly arranged lamellae that form separate spaces called trabeculae, resembling a honeycomb structure [10](#page=10). * Microscopically, red bone marrow fills the spaces between the trabeculae, responsible for producing blood cells [10](#page=10). * Osteocytes within lacunae in the trabeculae receive nutrients from blood vessels within the medullary cavity [10](#page=10). * Cancellous bone is typically found in: * Short bones [10](#page=10). * Flat bones [10](#page=10). * Irregular bones [10](#page=10). * The epiphyses of long bones [10](#page=10). * Cancellous bone containing red bone marrow is also found in the pelvic bones, sternum, vertebrae, sternum, and the ends of long bones [10](#page=10). > **Tip:** Red bone marrow, essential for hematopoiesis, is primarily located within the trabeculae of cancellous bone. Bone marrow biopsy sites are often chosen from areas rich in cancellous bone, such as the ilium. --- # Bone development and remodeling processes Bone development encompasses ossification and osteogenesis, vital for embryonic formation, postnatal growth, ongoing remodeling, and repair throughout life. ### 2. Embryonic and fetal bone formation Bone formation in embryos and fetuses begins as early as six weeks of gestation, originating from mesenchymal tissue that provides a scaffold for ossification. There are two primary modes of bone formation: intramembranous ossification and endochondral ossification [11](#page=11). #### 3. Intramembranous ossification Intramembranous ossification is the direct conversion of mesenchymal tissue into bone. This process involves four main stages [11](#page=11): * **I. Development of ossification center:** Mesenchymal cells differentiate into osteogenic cells, which then mature into osteoblasts. Osteoblasts are responsible for producing the organic matrix of the bone [11](#page=11). * **II. Calcification:** The bone matrix is deposited, leading to osteoblasts becoming trapped within lacunae. Their activity decreases, and they mature into osteocytes [11](#page=11). * **III. Formation of trabeculae (spongy bone):** Blood vessels develop, and bone marrow forms between the trabeculae of the developing bone [11](#page=11). * **IV. Formation of periosteum:** The outer surface of the bone forms and is recognized as the periosteum, which contains dense bone tissue [11](#page=11). Intramembranous ossification results in the formation of flat bones, such as the skull, facial bones, mandible, and clavicle [11](#page=11). #### 4. Endochondral ossification Endochondral ossification involves the differentiation of mesenchymal cells into cartilage, which is subsequently replaced by bone. This process is responsible for the formation of most bones in the body. It proceeds through six stages [12](#page=12): * **i. Formation of cartilage model of the "bone":** Mesenchymal cells develop into chondroblasts, forming a cartilage model of the future bone [12](#page=12). * **ii. Growth of cartilage model:** Chondroblasts secrete cartilage matrix, and the cartilage model grows. Chondrocytes mature, and the matrix around them calcifies, leading to chondrocyte death and leaving behind lacunae [12](#page=12). * **iii. Primary ossification center:** The perichondrium delivers a nutrient artery into the disintegrating cartilage. Osteogenic cells from the perichondrium transform into osteoblasts, which deposit bony matrix over the remnants of calcified cartilage, forming spongy bone in the center of the model. As this bone formation begins, the perichondrium is termed the periosteum [13](#page=13). * **iv. Medullary (marrow) cavity:** The spongy bone in the center of the model expands towards the ends. Osteoclasts break down some of this new spongy bone, creating a cavity (marrow cavity) throughout most of the diaphysis. A collar of compact bone replaces most of the diaphysis wall [13](#page=13). * **v. Secondary ossification centers:** Similar to the primary ossification process, nutrient arteries enter the ends (epiphyses) of the bones. Osteoblasts deposit bony matrix, leading to the formation of spongy bone in the epiphyses from the center outwards. This typically occurs around the time of birth [13](#page=13). * **vi. Articular cartilage and epiphyseal cartilage:** The cartilage at the ends of the epiphyses becomes the articular cartilage. The epiphyseal (growth) plate, a region of cartilage, remains between the epiphysis and diaphysis until bone growth ceases [13](#page=13). #### 5. Bone growth Bone growth occurs in two dimensions: length and thickness [14](#page=14). ##### 6. Bone growth in length This process is associated with the activity of the epiphyseal plate. New chondrocytes are formed, and older chondrocytes are replaced by bone. Bone growth in length continues until approximately 18 to 25 years of age. When the epiphyseal plate (which is cartilaginous) is replaced by the epiphyseal line, bone growth in length stops [14](#page=14). ##### 7. Bone growth in thickness On the surface of the bone, the perichondrium divides to form osteoblasts, which then produce bone extracellular matrix and become osteocytes. New lamellae are added to the bone's surface, and new osteons are formed. While bone resorption by osteoclasts also occurs, it does so at a slower rate. Consequently, as the bone's thickness increases, the medullary cavity also enlarges [14](#page=14). #### 8. Bone remodeling Bone remodeling is the continuous process of replacing old bone tissue with new bone tissue. It involves two key activities: bone resorption, where osteoclasts remove minerals and collagen fibers from the bone, and bone deposition, where osteoblasts add minerals and collagen fibers to the bone. Bone resorption leads to the breakdown of the extracellular matrix, while bone deposition involves the formation of new extracellular matrix. Osteoblasts absorb calcium from the blood to build bone tissue (deposition). Conversely, osteoclasts break down bone (resorption) into calcium, which consequently leads to an increase in the size of the medullary cavity [14](#page=14) [15](#page=15). > **Tip:** Bone remodeling is a dynamic process influenced by mechanical stress and hormonal signals, ensuring bone strength and calcium homeostasis. > **Example:** Regular weight-bearing exercise stimulates bone deposition, leading to stronger bones, while a sedentary lifestyle can promote resorption. #### 9. Bone repair Bone repair, or fracture healing, occurs throughout life. The process for healing a fractured bone includes the following steps [14](#page=14): * Phagocytes begin the process by removing dead bone cells [15](#page=15). * Chondroblasts form fibrocartilage at the fracture site, creating a bridge to connect the broken ends [15](#page=15). * Osteoblasts then convert the fibrocartilage into spongy bone [15](#page=15). * Bone remodeling occurs to shape and strengthen the newly formed bone [15](#page=15). * Finally, the spongy bone is remodeled into compact bone for structural integrity [15](#page=15). #### 10. Factors influencing bone development and remodeling The development, formation, and repair of bone are influenced by several factors [15](#page=15): * **Minerals:** Calcium, phosphorus, and magnesium are essential for bone structure and mineralization [15](#page=15). * **Vitamins:** Vitamins A, C, and D play critical roles in bone metabolism and collagen synthesis [15](#page=15). * **Hormones:** Human growth hormone (hGH), estrogen, and androgens are key hormones that regulate bone growth and remodeling [15](#page=15). * **Mechanical stress:** Weight-bearing exercise stimulates bone deposition, contributing to bone strength and density [15](#page=15). --- # Divisions of the skeletal system and joint classifications The skeletal system is divided into axial and appendicular components, and its joints are classified by their structure and function, with synovial joints exhibiting a wide range of movements [15](#page=15). ### 3.1 Divisions of the skeletal system The skeleton is divided into two main categories: the axial skeleton and the appendicular skeleton [15](#page=15). #### 3.1.1 Axial skeleton The axial skeleton consists of bones located around the body's axis [15](#page=15). * **Skull and hyoid bone**: The skull is comprised of eight cranial bones (frontal, two parietal, two temporal, occipital, sphenoid, and ethmoid) and fourteen facial bones (two nasal, two maxilla, two zygomatic, two lacrimal, two palatine, two inferior nasal conchae, one mandible, and one vomer). The hyoid bone is also part of the axial skeleton [15](#page=15) [18](#page=18). * **Vertebrae**: The vertebral column encloses the spinal cord, supports the head, and serves as an attachment point for muscles of the back, ribs, and pelvic girdle. It is divided into regions [19](#page=19): * 7 cervical vertebrae * 12 thoracic vertebrae * 5 lumbar vertebrae * 1 sacrum (fused from S1-S5) * 1 coccyx (fused from 4 coccygeal vertebrae) [19](#page=19). The vertebral column has four normal curves: cervical and lumbar curves are convex (bulging anteriorly), while thoracic and sacral curves are concave (bulging posteriorly). These curves increase strength, aid in balance, and absorb shocks [19](#page=19). * **Cervical vertebrae (C1-C7)**: Often have a bifid spinous process and transverse foramina on transverse processes [19](#page=19). * **C1 (Atlas)**: Articulates with the head and supports it; lacks a body and spinous process [19](#page=19). * **C2 (Axis)**: Possesses a body and spinous process; its dens ("tooth") allows for head rotation [19](#page=19). * **Thoracic vertebrae (T1-T12)**: Larger than cervical vertebrae and have facets for rib articulation [19](#page=19). * **Lumbar vertebrae (L1-L5)**: The largest and strongest, with short and thick spinous processes [19](#page=19). * **Sacrum**: The fused sacral vertebrae form the foundation for the pelvic girdle and contain sacral foramina [19](#page=19). * **Coccyx**: The fused coccygeal vertebrae [19](#page=19). * **Sternum and thorax/ribs**: The thoracic cage consists of the sternum, costal cartilages, ribs, and the bodies of T1-T12 [20](#page=20). * **Sternum**: Composed of the manubrium, body, and xiphoid process, which fuse by approximately age 25 [20](#page=20). * **Ribs**: There are 12 pairs of ribs [20](#page=20). * **True ribs (1-7)**: Articulate directly with the sternum via costal cartilages [20](#page=20). * **False ribs (8-12)**: Do not articulate directly with the sternum via costal cartilages [20](#page=20). #### 3.1.2 Appendicular skeleton The appendicular skeleton includes the bones of the upper and lower limbs, along with the shoulder and hip bones that connect them to the axial skeleton [15](#page=15). * **Pectoral girdle**: Composed of the clavicles (collarbones) and scapulas (shoulder blades), it attaches the bones of the upper limbs to the axial skeleton [20](#page=20) [21](#page=21) [22](#page=22). * **Upper limb**: * **Humerus**: The bone of the arm, articulating with the scapula at the shoulder joint and with the radius and ulna at the elbow [23](#page=23). * **Ulna**: The medial bone of the forearm [23](#page=23). * **Radius**: The lateral bone of the forearm (thumb side) [23](#page=23). * **Wrist and hand**: * **Carpus**: Consists of 8 wrist bones [24](#page=24). * **Metacarpals**: 5 bones forming the palm of the hand, numbered 1-5 starting from the thumb [24](#page=24). * **Phalanges**: 14 bones of the fingers. Each finger (except the thumb) has proximal, middle, and distal phalanges. The thumb has only proximal and distal phalanges [24](#page=24) [25](#page=25). * **Pelvic (hip) girdle**: Comprises two hip (coxal) bones that join anteriorly at the pubic symphysis and attach posteriorly to the sacrum at the sacroiliac joint. The pelvis is formed by the two hip bones, sacrum, and coccyx [25](#page=25). * **False (greater) pelvis**: The superior region, containing abdominal organs [25](#page=25). * **True (lesser) pelvis**: The inferior region, containing the urinary bladder and internal reproductive organs [25](#page=25). Each hip bone is formed by the fusion of three bones by age 23: the ilium (largest and most superior), the ischium (lower posterior part), and the pubis (lower anterior part). The bones meet at the acetabulum, which serves as the socket for the head of the femur [25](#page=25). * **Lower limb**: * **Femur**: The thigh bone, it is the largest bone in the body. It articulates with the hip proximally and the tibia and patella distally. The proximal end features the head (fitting into the acetabulum) and the greater trochanter [26](#page=26). * **Patella**: The kneecap, located anteriorly at the knee joint [26](#page=26). * **Tibia**: The shin bone, the large, medial, weight-bearing bone of the leg [26](#page=26). * **Fibula**: The longest and thinnest bone in the body, located lateral to the tibia and smaller; it does not articulate with the femur [27](#page=27). * **Ankle and foot**: * **Tarsus**: Consists of 7 ankle bones, including the talus (ankle bone) and calcaneus (heel bone) [28](#page=28). * **Metatarsals**: 5 foot bones, numbered 1 to 5 from medial to lateral [28](#page=28). * **Phalanges**: Toe bones, numbered like metatarsals from 1-5. The big toe has proximal and distal phalanges, while other toes have proximal, medial, and distal phalanges [28](#page=28). > **Tip:** Differences exist between male and female skeletons; males generally have heavier bones, while the female pelvis is wider and shallower to accommodate childbirth [28](#page=28). ### 3.2 Joint classifications A joint (or articulation) is the meeting point of two or more bones. Joints can be classified based on their structure or function [29](#page=29). #### 3.2.1 Structural classification of joints Structurally, joints are categorized into fibrous, cartilaginous, and synovial joints [29](#page=29). * **Fibrous joints (synarthroses)**: These are immovable joints where two bones are united by fibrous connective tissue. They are also known as fixed joints [29](#page=29). * **Sutures**: Found between skull bones, e.g., the coronal suture between the frontal and parietal bones [29](#page=29). * **Syndesmoses**: Joints connected by a ligament or interosseous membrane, e.g., the distal tibiofibular joint connected by the anterior tibiofibular ligament, and the interosseous membranes between the radius and ulna or tibia and fibula [29](#page=29). * **Gomphoses**: Joints that anchor teeth into their sockets within the maxilla and mandible [29](#page=29). * **Cartilaginous joints (amphiarthroses)**: These are slightly movable joints where bones are connected by cartilage. Movement is limited, allowing for bending and straightening [29](#page=29) [30](#page=30). * Examples include joints between the bodies of vertebrae and the pubic symphysis [30](#page=30). * **Synovial joints (diarthroses)**: These are freely movable joints characterized by the presence of a synovial membrane that produces synovial fluid. This fluid lubricates the joint, allowing for extensive movement [31](#page=31). **Characteristics of synovial joints**: * Involve two or more bones [31](#page=31). * Articular surfaces of the bones are covered with hyaline cartilage, which smooths the surfaces, reduces friction, withstands weight-bearing, and absorbs shock [31](#page=31). * The joint is enclosed within a fibrous capsule made of connective tissues, providing space for movement and preventing injury [31](#page=31). * The inner surface of the fibrous capsule is lined by a synovial membrane that produces thick, egg-white-like synovial fluid, which accumulates in the synovial cavity [31](#page=31). * **Functions of synovial fluid**: i. Provides nutrients to joint structures [32](#page=32). ii. Acts as a joint lubricant [32](#page=32). iii. Contains phagocytes to remove microbes and debris from the joint [32](#page=32). * **Bursae**: Small sacs filled with synovial fluid that act as cushions between bones and ligaments or tendons, or between bone and skin, particularly near the surface of the skin (e.g., at the knee) [32](#page=32). * Many synovial joints have accessory ligaments, either extracapsular (outside the articular capsule) or intracapsular (between the articular capsule and the synovial cavity), that enhance joint stability [32](#page=32). #### 3.2.2 Functional classification of joints Based on function, joints can be classified as synarthroses (immovable), amphiarthroses (slightly movable), or diarthroses (freely movable). This classification largely overlaps with the structural classification, with fibrous joints typically being synarthroses, cartilaginous joints being amphiarthroses, and synovial joints being diarthroses [29](#page=29) [30](#page=30) [31](#page=31). ### 3.3 Types of movement at synovial joints Movements at synovial joints are categorized into four main groups: gliding movements, angular movements, rotation, and special movements [32](#page=32). #### 3.3.1 Gliding movements Gliding involves the flat articular surfaces of one bone moving over the articular surfaces of another bone, allowing for back-and-forth and side-to-side motion. Examples include movements between carpal bones [32](#page=32). #### 3.3.2 Angular movements Angular movements involve an increase or decrease in the angle between articulating bones [33](#page=33). * **Flexion**: Bending or decreasing the angle between articulating bones; for example, bending the arm at the elbow or the head towards the chest [33](#page=33). * **Extension**: Straightening or increasing the angle between articulating bones; for example, straightening the arm [33](#page=33). * **Abduction**: Moving a bone away from the midline of the body; for example, moving the arm away from the side of the body [33](#page=33). * **Adduction**: Moving a bone towards the midline of the body; for example, bringing the arm back to the side [33](#page=33). * **Circumduction**: The movement of the distal end of a body part in a circular motion, involving a sequence of flexion, extension, adduction, and abduction. An example is the motion made by a baseball pitcher at the shoulder joint [34](#page=34). #### 3.3.3 Rotation Rotation is the movement of a bone around its own axis. For example, shaking the head "no" involves the rotation of the atlas around the dens of the axis [34](#page=34) [42](#page=42). #### 3.3.4 Special movements These are movements that do not fit neatly into the other categories [35](#page=35). * **Inversion**: Turning the sole of the foot inward [35](#page=35). * **Eversion**: Turning the sole of the foot outward [35](#page=35). * **Protraction**: Moving a body part forward; for example, moving the chin forward [35](#page=35). * **Retraction**: The opposite of protraction, moving a body part backward to its anatomical position [35](#page=35). * **Elevation**: Moving a body part upward; for example, shrugging the shoulders [35](#page=35). * **Depression**: Moving a body part downward, the opposite of elevation [35](#page=35). ### 3.4 Types of synovial joints Synovial joints are classified according to the type of movement they allow or the shape of their articulating bone surfaces [36](#page=36). 1. **Ball-and-socket joint**: Allows the widest range of motion among synovial joints, including flexion, extension, abduction, adduction, and rotation. It features a spherical bone head fitting into a socket-like cavity, enabling free, low-friction movement [36](#page=36). * **Locations**: Shoulder joint and hip joint [36](#page=36). * **Shoulder joint**: Involves the scapula and the head of the humerus articulating within the glenoid cavity. The glenoid cavity is deepened by the glenoid labrum, a fibrocartilage rim that enhances stability without restricting movement. The joint capsule is loose inferiorly to allow for free movement, and the tendon of the biceps muscle crosses the joint to further stabilize it [36](#page=36) [37](#page=37). * **Hip joint**: Formed by the head of the femur and the acetabulum of the hip bone. It is stabilized by a strong fibrous capsule and three key ligaments: the iliofemoral ligament (connecting the ilium to the anterior femur, preventing hyperextension), the ischiofemoral ligament (connecting the ischium to the posterior femur), and the pubofemoral ligament (connecting the pubis to the inferior femur). An acetabular labrum also deepens the socket for increased stability [37](#page=37) [38](#page=38). 2. **Hinge joint**: Permits movement in only one plane, allowing for flexion and extension [38](#page=38). * **Locations**: Elbow joint, knee joint, atlanto-occipital joint (between the occipital bone and the atlas), and interphalangeal joints of the fingers [38](#page=38). * **Elbow joint**: Involves the capitulum and trochlea of the humerus articulating with the radial notch of the ulna and the trochlear notch of the ulna, respectively. Flexion is achieved by the biceps and brachialis muscles, while extension is performed by the triceps muscle [38](#page=38). * **Knee joint**: Formed by the medial and lateral condyles of the femur, the condyles of the tibia, and the posterior surface of the patella. It is crucial for weight-bearing and locomotion. Flexion is performed by the gastrocnemius and hamstring muscles, and extension by the quadriceps femoris muscles [39](#page=39). * **Ankle joints**: Involve the distal tibia and medial malleolus, the distal fibula and lateral malleolus, and the talus. Four key ligaments stabilize the joint: posterior, deltoid, medial, and lateral ligaments. Dorsiflexion (flexion) is achieved by the tibialis anterior muscle, while plantar flexion (extension) is performed by the gastrocnemius and soleus muscles [39](#page=39). 3. **Plane/planar joint**: Allows flat articular surfaces to slide or glide over one another, permitting back-and-forth and side-to-side movements [40](#page=40). * **Locations**: Sternoclavicular joint, acromioclavicular joint, joints between carpal bones, and joints between tarsal bones [40](#page=40). 4. **Pivot joint**: Enables rotational movement where one bone pivots around another [40](#page=40). * **Locations**: Proximal and distal radioulnar joints, and the atlantoaxial joint [40](#page=40) [41](#page=41) [42](#page=42). * **Radioulnar joints**: The proximal radioulnar joint involves the head of the radius articulating with the radial notch of the ulna. The distal radioulnar joint involves the head of the ulna articulating with the ulnar notch of the radius, allowing for supination and pronation of the hand [41](#page=41). * **Atlantoaxial (medial) joint**: The atlas rotates over the dens of the axis, allowing for head rotation [42](#page=42). 5. **Condyloid joint (ellipsoidal joint)**: Allows for flexion, extension, abduction, adduction, and circumduction [42](#page=42). * **Examples**: Metacarpophalangeal joints, except for the thumb [42](#page=42). 6. **Saddle joint**: Offers similar movements to condyloid joints, including flexion, extension, abduction, adduction, opposition, and reposition [42](#page=42). * **Example**: Carpometacarpal joint of the thumb [42](#page=42). --- # Muscles: types, functions, and structure This section delves into the three primary types of muscle tissue, their distinct structural characteristics, physiological functions, and related connective tissues like ligaments and tendons. ### 4.1 Muscle functions Muscles are crucial for numerous bodily processes, enabling movement, maintaining posture, generating heat, and facilitating the storage and expulsion of substances [44](#page=44). * **Movement:** All visible and invisible body movements, including cardiac function and digestion [44](#page=44). * **Posture fixation:** Maintaining body position during standing, walking, and sitting [44](#page=44). * **Heat production:** Generated as a byproduct of muscle contraction during activity [44](#page=44). * **Storage and expulsion:** Facilitating the retention and release of substances, such as in the bladder and intestines [44](#page=44). ### 4.2 Types of muscle tissue There are three main types of muscle tissue: skeletal, smooth, and cardiac [44](#page=44). #### 4.2.1 Skeletal muscle Skeletal muscle, also known as voluntary or striated muscle, is under the control of the central nervous system. Its actions are consciously controlled and it is attached to the human skeleton. Skeletal muscle fibers are composed of approximately 75% water, 20% protein (myosin and actin), and 5% minerals, glycogen, and fats [44](#page=44). ##### 4.2.1.1 Microscopic structure of skeletal muscle * **Connective tissue:** Surrounds and protects muscle tissue. Fascia fills spaces between muscle cells and tissues, allowing for movement and serving as a pathway for nerves, blood, and lymphatic vessels [44](#page=44). * **Muscle fibers:** Elongated, cylindrical cells known as muscle fibers, ranging from 10-40 mm in length [44](#page=44). * **Endomysium:** Connective tissue surrounding each individual muscle fiber [44](#page=44). * **Fascicles:** Bundles of muscle fibers covered by perimysium [44](#page=44). * **Epimysium:** Connective tissue covering the entire muscle [44](#page=44). * **Sarcomeres:** The fundamental structural and functional unit of a muscle fiber, demarcated by Z discs [44](#page=44). * **Myofibrils:** Composed of thick (myosin) and thin (actin) filaments that create the striated appearance of muscle fibers [44](#page=44). * **Sarcoplasm:** The cytoplasm within muscle fibers [44](#page=44). * **Nuclei:** Multiple nuclei are located beneath the sarcolemma, the plasma membrane of the muscle cell [45](#page=45). * **Sarcolemma:** The plasma membrane of a muscle cell [47](#page=47). * **Transverse (T) tubules:** Tunnels extending from the sarcolemma's surface to the fiber's center [47](#page=47). * **Sarcoplasmic reticulum:** A network throughout the sarcoplasm that stores calcium ions [47](#page=47). * **Myoglobin:** A red-pigmented protein in the sarcoplasm, similar to hemoglobin, that carries oxygen [47](#page=47). ##### 4.2.1.2 Sarcomere structure and filaments Within sarcomeres, thick and thin filaments overlap in repeating patterns [47](#page=47). * **A band:** The darker area associated with thick filaments [47](#page=47). * **H zone:** Contains no thin filaments [47](#page=47). * **I band:** Contains thin filaments but no thick filaments [47](#page=47). * **Thick filaments (myosin):** Possess movable heads that interact with thin filaments [47](#page=47). * **Thin filaments (actin):** Anchored to Z discs and contain myosin binding sites. They also contain tropomyosin and troponin, which block myosin binding sites when the muscle is at rest [47](#page=47). #### 4.2.2 Smooth muscle Smooth muscle, also known as involuntary or non-striated muscle, is not under conscious control. It is influenced by the autonomic nervous system and hormones. Microscopically, smooth muscle cells are elongated and spindle-shaped, each containing a single nucleus centrally located. They lack a distinct sarcolemma but have a very thin membrane surrounding each fiber. Smooth muscle is found in the walls of blood vessels, lymphatic vessels, the alimentary tract, respiratory tract, bladder, biliary tract, and uterus. Myosin and actin are dispersed within the cytoplasm. Fibers group into bundles, and multiple bundles form muscle layers [47](#page=47) [48](#page=48). ##### 4.2.2.1 Functions of smooth muscle * **Peristalsis:** Responsible for the movement of contents within hollow organs [48](#page=48). #### 4.2.3 Cardiac muscle Cardiac muscle is a specialized type found exclusively in the heart wall. It is involuntary but differs structurally from other involuntary muscles. Cardiac muscle can contract without neural stimulation, though its contractions can be sped up or slowed down by the autonomic nervous system. Microscopically, cardiac muscle is striated like skeletal muscle and consists of cylindrical fibers, each with a single, prominent nucleus that can branch. Cell ends and branches connect tightly to adjacent cells via intercalated discs, which appear thick and dark. These discs facilitate the rapid spread of excitation, crucial for coordinated heart contractions. Fibers are arranged into bundles surrounded by connective tissue [48](#page=48). ##### 4.2.3.1 Functions of cardiac muscle * **Pumping blood:** Contracts rhythmically and automatically to pump blood throughout the body [49](#page=49). ### 4.3 Characteristics of muscles Muscles possess several inherent properties that enable their function. * **Contraction:** Muscles shorten and thicken when adequately stimulated. This occurs due to electrical, mechanical, or chemical stimuli, such as neurotransmitters like acetylcholine. Nerve impulses from the brain and spinal cord trigger this process via motor nerves, releasing acetylcholine at motor fiber endings. Acetylcholine binds to receptors on the muscle membrane, initiating contraction through a sliding mechanism of actin and myosin filaments. Damage to nerve endings can lead to paralysis [49](#page=49). * **Elasticity:** The ability of muscle tissue to stretch and then return to its original size [49](#page=49). * **Muscle tone:** Even at rest, muscles maintain a state of partial contraction, allowing for immediate response when needed [49](#page=49). * **Muscle fatigue:** Repeated muscle contractions lead to a decrease in responsiveness and the loss of the ability to contract effectively. This is due to the depletion of oxygen and glucose, resulting in energy production and the accumulation of lactic acid. Increased lactic acid levels contribute to fatigue. Rest allows for the supply of oxygen and nutrients, enabling muscles to contract again [49](#page=49) [50](#page=50). * **Heat production:** Active muscles generate heat [50](#page=50). > **Tip:** The energy source for muscle contraction is derived from the catabolism of carbohydrates and fats [50](#page=50). ### 4.4 Ligaments and tendons Ligaments and tendons are specialized connective tissues that play vital roles in the musculoskeletal system. #### 4.4.1 Structure and function of ligaments * **Structure:** Composed of thick white fibrocartilage with densely packed collagen fibers. Ligaments are not elastic but are pliable, allowing for joint movement. They attach to bones [50](#page=50). * **Function:** Connect bones to each other near joints, providing stability during movement [50](#page=50). #### 4.4.2 Structure and function of tendons * **Structure:** Made of strong, inelastic fibrous connective tissue with densely packed collagen fibers. The epimysium, perimysium, and endomysium extend from the muscle to form the tendon. Most tendons are covered by a synovial membrane. Tendons can be cord-like or flat (aponeuroses) and are whitish in color [50](#page=50). * **Function:** Attach muscles to bones or muscles to other muscles [50](#page=50). * **Origin:** The attachment point that remains relatively stationary during contraction, typically found in voluntary muscles. Some muscles have one origin, while others have two or more (e.g., biceps) [50](#page=50) [51](#page=51). * **Insertion:** The attachment point on the bone that moves freely. This point moves towards the origin when the muscle contracts [51](#page=51). > **Example:** For a joint to move, one set of muscles (agonists) contracts, while their opposing set (antagonists) relaxes. For example, during elbow flexion, the biceps (flexor) contracts, and the triceps (extensor) relaxes. Conversely, during elbow extension, the triceps contracts, and the biceps relaxes [51](#page=51). ### 4.5 Muscle naming conventions Muscles are named based on various criteria, including their function, location, shape, size, associated bones, fiber direction, or structure [51](#page=51). * **Function:** * Flexor (flexion/bending) [51](#page=51). * Extensor (extension/straightening) [51](#page=51). * Adductor (moving towards midline) [51](#page=51). * Abductor (moving away from midline) [51](#page=51). * **Location/Position:** * Occipitofrontalis (occipital bone to frontal bone) [51](#page=51). * Sternomastoid (sternum to mastoid process) [51](#page=51). * **Shape:** * Trapezius (trapezoidal shape) [51](#page=51). * **Size:** * Maximus (largest) [51](#page=51). * Minimus (smallest) [51](#page=51). * **Associated Bone:** * Temporalis (near temporal bone) [51](#page=51). * **Fiber Direction:** * Rectus abdominis (straight abdominal muscle) [51](#page=51). * Intercostals (between ribs) [51](#page=51). * **Structure (number of tendons/heads):** * Biceps (two heads) [51](#page=51). * Triceps (three heads) [51](#page=51). * Quadriceps (four heads) [51](#page=51). --- # Specific muscles and their actions This section details the location and primary functions of various key muscles in the human body, categorized by anatomical region. ### 5.1 Muscles of the face (head) and neck * **Occipitofrontalis**: Located from the occipital bone to the frontal bone, its main function is to wrinkle the forehead and raise the eyebrows [52](#page=52). * **Levator palpebrae superioris**: Situated from the eye socket to the upper eyelid, its function is to lift the eyelid [52](#page=52). * **Orbicularis oculi**: This muscle encircles the eye and is responsible for closing the eye [52](#page=52). * **Orbicularis oris**: Located around the mouth, it functions to close the mouth [52](#page=52). * **Buccinator**: Found in the cheek area, it pulls the cheeks towards the teeth during chewing, expels air from the mouth, and is sometimes called the trumpeter's muscle [52](#page=52). * **Masseter**: Extends from the zygomatic arch to the angle of the mandible, its function is chewing [52](#page=52). * **Temporalis**: Covers the squamous part of the temporal bone, functioning to close the mouth and aid in chewing [53](#page=53). * **Sternocleidomastoid**: Located in the neck, extending from the sternum to the mastoid process, it assists in tilting and rotating the head from side to side [53](#page=53). * **Trapezius**: The largest muscle in the back of the neck, shoulders, and upper chest, it aids in shoulder movement (elevation and depression) and extending the head backward [53](#page=53). * **Pterygoid**: Extends from the sphenoid bone to the mandible, functioning to close the mouth and protract the lower jaw [53](#page=53). ### 5.2 Muscles of the arm * **Deltoid**: Located on top of the shoulder, its primary function is arm abduction [53](#page=53). * **Biceps**: A powerful flexor muscle with two heads, situated in the upper arm, it flexes the elbow joint [53](#page=53). * **Triceps**: A strong extensor muscle with three heads, located in the upper arm, its main function is the extension (straightening) of the elbow joint [53](#page=53). ### 5.3 Muscles of the back There are six pairs of muscles along both sides of the vertebral column: * Trapezius [54](#page=54). * Teres major [54](#page=54). * Psoas [54](#page=54). * Latissimus dorsi [54](#page=54). * Quadratus lumborum [54](#page=54). * Sacrospinalis [54](#page=54). ### 5.4 Muscles of the trunk * **Pectoralis major**: A fan-shaped muscle on the front of the chest, its primary functions are flexion and adduction of the arm (bringing the arm forward and toward the chest) [55](#page=55). * **Teres major**: Originates from the inferior angle of the scapula and inserts on the humerus below the shoulder joint. Its function is shoulder extension (moving the arm up and backward) [55](#page=55). * **Latissimus dorsi**: Originates from the posterior chest and inserts on the upper humerus. It functions in adduction of the humerus, medial rotation, and assists in arm extension at the shoulder joint [55](#page=55). ### 5.5 Muscles of the abdominal wall The abdominal wall is divided longitudinally by a strong tendon called the Linea alba, extending from the xiphoid process to the pubic symphysis. There are four paired muscle layers [55](#page=55): * **Rectus abdominis**: The outermost muscle layer, it is flat and broad, originating from the pubic bone and inserting on the lower ribs and the xiphoid process medially. The two rectus abdominis muscles are separated by the Linea alba [55](#page=55). * **Internal oblique**: Located deep to the external oblique, it originates from the iliac crest and inserts on the lower ribs and the Linea alba [55](#page=55). * **External oblique**: Originates from the 8th rib and inserts onto the iliac crest and the Linea alba [55](#page=55). * **Transversus abdominis**: The deepest muscle layer, originating from the iliac crest and lumbar vertebrae, it courses across the abdominal wall and inserts onto the Linea alba [56](#page=56). **Main functions of the abdominal wall muscles:** * Form a strong muscular wall for the anterior abdominal cavity [56](#page=56). * Simultaneous contraction of these muscles increases intra-abdominal pressure and causes flexion of the lumbar vertebral column [56](#page=56). ### 5.6 Muscles of the buttocks These muscles are the gluteal muscles, which form the contour of the buttocks. Their fibers originate from the outer surface of the ilium and insert on the greater trochanter of the femur [56](#page=56). * **Gluteus medius**: Abducts the hip joint and medially rotates the thigh [56](#page=56). * **Gluteus maximus**: Extends the hip joint and laterally rotates the thigh [56](#page=56). * **Gluteus minimus**: The deepest gluteal muscle, it abducts the hip joint [56](#page=56). ### 5.7 Muscles of the thigh * **Quadriceps femoris**: Consists of four extensor muscles involved in knee extension: rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius. They are located in the anterior thigh [58](#page=58). * **Sartorius**: The longest muscle in the body. Its main functions include assisting in hip flexion and abduction, and assisting in knee flexion [58](#page=58). * **Hamstring**: Located in the posterior thigh, it comprises three muscles: biceps femoris, semimembranosus, and semitendinosus. Its primary function is knee flexion [59](#page=59). ### 5.8 Muscles of the lower limb (leg) * **Tibialis anterior**: Located on the anterior side of the lower leg (shin), its primary function is foot dorsiflexion (bending the foot upward) [59](#page=59). * **Soleus**: An important muscle in the calf, it is involved in plantar flexion, which is bending the foot towards the sole [59](#page=59). * **Gastrocnemius**: Located on the posterior side of the calf, it is heavily used during walking, running, and jumping. Its main functions are knee flexion and plantar flexion (bending the foot towards the sole) [59](#page=59). ### 5.9 Muscles of the pelvic floor The pelvic floor is divided centrally, with each side containing gluteal muscles and fascia. The primary muscles are the levator ani and coccygeus. Both muscles form the pelvic floor, which is perforated by the urethra and anus in males, and by the urethra, vagina, and anus in females [59](#page=59). * **Levator ani**: A broad, flat muscle forming the anterior part of the pelvic floor. The left and right levator ani muscles meet centrally to form a sling that supports the pelvic organs [60](#page=60). * **Coccygeus**: A triangular muscle located posterior to the levator ani. It originates from the medial surface of the ischium and inserts into the sacrum and coccyx, completing the pelvic floor [60](#page=60). ### 5.10 Muscles of respiration * **Internal intercostals**: Eleven pairs of muscles that run downwards and backward from the lower border of an upper rib to the upper border of the rib below [61](#page=61). * **External intercostals**: Eleven pairs of muscles that run downwards and forward from the lower border of an upper rib to the upper border of the rib below [61](#page=61). * **Diaphragm**: A single, dome-shaped muscle situated between the thoracic and abdominal cavities. Its convex upper surface forms the floor of the thoracic cavity, and its concave lower surface forms the roof of the abdominal cavity. It has a broad, thin central tendon known as the aponeurosis, with muscular fibers originating from the surrounding body [61](#page=61). **Action of intercostal muscles:** * The first rib is fixed, meaning it does not move during respiration [61](#page=61). * During inspiration, contraction of the intercostal muscles pulls the other ribs upwards and outwards, widening the thoracic cavity anteroposteriorly and laterally [61](#page=61). * Intercostal muscle contraction is stimulated by the intercostal nerves during inspiration [61](#page=61). * During exhalation, the intercostal muscles relax, allowing the ribs to return to their original position, thereby decreasing the thoracic cavity volume [61](#page=61). **The diaphragm:** * It has three openings: for the aorta, for the inferior vena cava, and for the esophagus (which is also traversed by the vagus nerve) [62](#page=62). * It receives oxygenated blood from the phrenic arteries and is innervated by the phrenic nerves [62](#page=62). * Superiorly, it is related to the lungs and heart; inferiorly, it is related to the liver, stomach, and spleen [62](#page=62). **Functions of the diaphragm:** * It is the primary muscle of respiration [62](#page=62). * It separates the thoracic and abdominal cavities [62](#page=62). * It aids in defecation and urination by increasing intra-abdominal and pelvic pressure upon contraction [62](#page=62). * It assists in venous return by pressing on the inferior vena cava, promoting blood flow back to the heart [62](#page=62). * It helps prevent venous thrombosis in immobile individuals [62](#page=62). --- ## Common mistakes to avoid - Review all topics thoroughly before exams - Pay attention to formulas and key definitions - Practice with examples provided in each section - Don't memorize without understanding the underlying concepts

| Term | Definition | |------|------------| | Skeletal system | The system of bones, cartilage, dense connective tissue, epithelium, blood-forming tissue, adipose tissue, and nervous tissue that forms the framework of the body. | | Osteology | The study of bones, their structure, and the treatment of bone disorders. | | Musculoskeletal system | The combined system of bones (skeleton), muscles, and joints that enables movement and provides structural support. | | Diaphysis | The shaft or central part of a long bone, typically a hollow cylinder made of compact bone surrounding a medullary cavity. | | Epiphysis | The expanded ends of a long bone, which are covered with articular cartilage and contain spongy bone. | | Epiphyseal plate | A layer of hyaline cartilage in the metaphysis of a long bone that allows for longitudinal growth; also known as the growth plate. | | Articular cartilage | A layer of hyaline cartilage that covers the articular surfaces of bones in synovial joints, reducing friction and absorbing shock. | | Periosteum | A tough, fibrous membrane that covers the outer surface of all bones, except at the surfaces of the joints. It is essential for bone protection, muscle and ligament attachment, and bone cell development. | | Medullary cavity | The central cavity of bone shafts where bone marrow is stored. In adults, it typically contains yellow bone marrow. | | Endosteum | A thin membranous lining of the medullary cavity and the canals of compact bone, containing osteogenic cells. | | Osteogenic cell | An immature bone cell derived from mesenchyme, capable of differentiating into osteoblasts. Found in the periosteum and endosteum. | | Osteoblast | A cell responsible for synthesizing and depositing the organic extracellular matrix of bone tissue; it matures into an osteocyte. | | Osteocyte | A mature bone cell located in a lacuna within the bone matrix, responsible for maintaining bone tissue and regulating its metabolic processes. | | Osteoclast | A large multinucleated cell responsible for bone resorption, breaking down the extracellular matrix of bone. | | Compact bone | A dense, hard type of bone tissue that forms the outer layer of most bones, providing strength and support. It is composed of osteons. | | Cancellous bone (Spongy bone) | A porous, lightweight type of bone tissue found inside bones, characterized by trabeculae and spaces containing bone marrow. | | Osteon (Haversian system) | The basic structural and functional unit of compact bone, consisting of concentric lamellae, a central canal (Haversian canal), lacunae, and canaliculi. | | Haversian canal (Central canal) | A narrow channel in the center of an osteon that contains blood vessels, lymphatic vessels, and nerves, supplying nutrients to the bone cells. | | Lacuna | Small cavities within the bone matrix that house osteocytes. | | Canaliculi | Minute channels that connect lacunae to each other and to the Haversian canal, facilitating the exchange of nutrients and waste products between osteocytes and blood vessels. | | Volkmann canal (Perforating canal) | Channels that run perpendicular to the Haversian canals, connecting them to each other and to the periosteum and medullary cavity, allowing for the passage of blood vessels and nerves. | | Trabeculae | Thin plates or beams that form the framework of spongy bone, providing structural support and containing bone marrow. | | Ossification (Osteogenesis) | The process of bone formation, which occurs during embryonic development, growth, remodeling, and repair. | | Intramembranous ossification | A process of bone formation in which mesenchymal tissue is directly converted into bone, typically forming flat bones. | | Endochondral ossification | A process of bone formation in which a cartilage model is first formed and then gradually replaced by bone, responsible for the development of most bones. | | Bone remodeling | The continuous process of old bone tissue being replaced by new bone tissue through bone resorption and bone deposition. | | Fracture | A break in the continuity of a bone. | | Axial skeleton | The part of the skeleton that lies along the central axis of the body, including the skull, vertebral column, ribs, and sternum. | | Appendicular skeleton | The part of the skeleton that consists of the bones of the limbs and the girdles that attach them to the axial skeleton. | | Fibrous joint | A joint where bones are connected by dense fibrous connective tissue, typically allowing for little to no movement (e.g., sutures of the skull). | | Cartilaginous joint | A joint where bones are united by cartilage, allowing for limited movement (e.g., intervertebral discs, pubic symphysis). | | Synovial joint | A freely movable joint characterized by a joint cavity filled with synovial fluid, surrounded by a joint capsule, and typically lined with articular cartilage. | | Synovial fluid | A viscous fluid produced by the synovial membrane that lubricates synovial joints, reduces friction, and provides nutrients. | | Bursa | A small sac containing synovial fluid, located near joints to reduce friction between tendons, ligaments, bones, and skin. | | Gliding movement | A type of synovial joint movement where flat surfaces of bones slide over each other (e.g., between carpal bones). | | Angular movement | A type of synovial joint movement that changes the angle between articulating bones, including flexion, extension, abduction, and adduction. | | Rotation | A type of synovial joint movement where a bone pivots around its own axis. | | Special movements | Unique movements of synovial joints, including inversion, eversion, protraction, retraction, elevation, and depression. | | Ball and socket joint | A synovial joint that allows for the widest range of motion, including flexion, extension, abduction, adduction, rotation, and circumduction (e.g., shoulder, hip). | | Hinge joint | A synovial joint that permits movement in only one plane, like the hinge of a door, allowing for flexion and extension (e.g., elbow, knee). | | Plane joint (Planar joint) | A synovial joint characterized by flat articulating surfaces that allow for gliding or sliding movements (e.g., intercarpal and intertarsal joints). | | Pivot joint | A synovial joint where a rounded process of one bone fits into a sleeve or ring of another bone, allowing for rotational movement (e.g., radioulnar joints, atlantoaxial joint). | | Condyloid joint (Ellipsoidal joint) | A synovial joint where an oval-shaped condyle of one bone fits into an elliptical cavity of another, allowing for flexion, extension, abduction, adduction, and circumduction (e.g., metacarpophalangeal joints). | | Saddle joint | A synovial joint where the articulating surfaces are shaped like a saddle, allowing for flexion, extension, abduction, adduction, and opposition (e.g., carpometacarpal joint of the thumb). | | Skeletal muscle | A type of muscle tissue that is striated, voluntary, and attached to bones, responsible for body movement. | | Smooth muscle | A type of muscle tissue that is non-striated, involuntary, and found in the walls of internal organs and blood vessels, responsible for peristalsis and regulating blood flow. | | Cardiac muscle | A specialized type of muscle tissue found only in the heart, characterized by striations, involuntary control, and intercalated discs that allow for coordinated contraction. | | Muscle contraction | The process by which muscle fibers shorten and generate force, enabling movement. | | Muscle elasticity | The ability of a muscle to recoil to its original resting length after being stretched. | | Muscle tone | A state of partial contraction in resting muscles that allows for posture maintenance and readiness for action. | | Muscle fatigue | The decline in muscle performance that occurs after prolonged or intense activity, often due to the depletion of energy reserves and accumulation of metabolic byproducts. | | Ligament | A strong band of fibrous connective tissue that connects bone to bone, providing stability to joints. | | Tendon | A strong band of fibrous connective tissue that connects muscle to bone, transmitting the force of muscle contraction to produce movement. | | Acetylcholine | A neurotransmitter released at neuromuscular junctions that triggers muscle contraction. | | Actin | A contractile protein that forms the thin filaments of muscle myofibrils. | | Myosin | A contractile protein that forms the thick filaments of muscle myofibrils and interacts with actin to cause muscle contraction. | | Sarcomere | The basic contractile unit of a striated muscle fiber, composed of overlapping actin and myosin filaments. | | Myoglobin | A red protein found in muscle cells that binds and stores oxygen, similar to hemoglobin. | | Intercalated disc | Specialized junctions between cardiac muscle cells that facilitate rapid electrical impulse transmission, enabling coordinated contraction. | | Peristalsis | Wave-like muscular contractions that move food and waste through the digestive tract and other hollow organs. | | Sarcolemma | The plasma membrane of a muscle fiber. | | Sarcoplasm | The cytoplasm of a muscle fiber. | | Sarcoplasmic reticulum | A specialized endoplasmic reticulum in muscle cells that stores and releases calcium ions, essential for muscle contraction. | | Linea alba | A strong fibrous band running vertically along the midline of the anterior abdominal wall, formed by the aponeuroses of the abdominal muscles. | | Aponeurosis | A broad, flat sheet of connective tissue that connects muscles to bone or to other muscles, similar to a tendon. | | Intercostal muscles | Muscles located between the ribs that play a crucial role in breathing, aiding in inspiration and expiration. | | Diaphragm | A large, dome-shaped muscle located at the base of the thoracic cavity that is the primary muscle of respiration. | | Thoracic duct | The largest lymphatic vessel in the body, which collects lymph from the lower body and the left side of the upper body and empties into the bloodstream. | | Vena cava inferior | The large vein that carries deoxygenated blood from the lower and middle body into the right atrium of the heart. | | Esophagus | The muscular tube connecting the pharynx (throat) with the stomach. | | Vagus nerve | The tenth cranial nerve, which plays a vital role in autonomic functions, including heart rate, digestion, and respiration. | | Arteri frenik | Arteries that supply blood to the diaphragm. | | Saraf frenik | The nerve that innervates the diaphragm, controlling its contractions for breathing. | | Hepar | The liver. | | Gaster | The stomach. | | Limfa | The spleen. | | Defaecation | The process of eliminating feces from the body. | | Venous return | The flow of deoxygenated blood from the peripheral veins back to the heart. | | Venous thrombosis | The formation of a blood clot within a vein. | | Trapezius | A large muscle in the upper back and neck that controls the movement of the shoulders and head. | | Pectoralis major | A large, fan-shaped muscle in the chest that is involved in arm adduction and flexion. | | Latissimus dorsi | A large muscle on the back that is responsible for arm extension, adduction, and medial rotation. | | Quadriceps femoris | A group of four muscles in the front of the thigh that extend the knee. | | Hamstring | A group of three muscles in the back of the thigh that flex the knee and extend the hip. | | Gastrocnemius | The primary calf muscle, located in the posterior leg, involved in plantar flexion of the foot and knee flexion. | | Soleus | A broad, flat muscle beneath the gastrocnemius in the posterior leg, contributing to plantar flexion of the foot. | | Levator ani | A broad, flat muscle that forms the pelvic floor, supporting pelvic organs and contributing to defecation and urination control. | | Coccygeus | A small triangular muscle located in the posterior part of the pelvic floor, contributing to pelvic support. | | Urethra | The tube that connects the bladder to the outside of the body, allowing for the elimination of urine. | | Vagina | The muscular canal extending from the cervix to the outside of the body in females. | | Anus | The opening at the end of the digestive tract through which feces leave the body. | | Internal intercostals | Muscles located between the ribs that contract during forced exhalation to depress the rib cage. | | External intercostals | Muscles located between the ribs that contract during inspiration to elevate the rib cage and expand the thoracic cavity. | | Thorax | The part of the body between the neck and the abdomen, enclosed by the ribs and sternum. | | Thoracic cavity | The space within the thorax that contains the heart, lungs, and major blood vessels. | | Abdomen | The part of the body between the thorax and the pelvis, containing the digestive organs and other viscera. | | Abdominal cavity | The space within the abdomen that houses the digestive organs, kidneys, and other viscera. | | Pelvic cavity | The space within the pelvis that contains the urinary bladder, reproductive organs, and rectum. | | Hepar | The liver. | | Gaster | The stomach. | | Limfa | The spleen. | | Vein | A blood vessel that carries deoxygenated blood from the body's tissues back to the heart. | | Artery | A blood vessel that carries oxygenated blood away from the heart to the body's tissues. | | Nerve | A bundle of fibers that transmits impulses of sensation to the brain or spinal cord, and from the brain or spinal cord to muscles or glands. | | Cranial nerve | One of twelve pairs of nerves that originate directly from the brain, controlling functions of the head and neck. | | Arteri frenik | Arteries that supply blood to the diaphragm. | | Saraf frenik | The nerve that innervates the diaphragm, controlling its contractions for breathing. | | Pelvic floor muscles | A group of muscles that form the base of the pelvic cavity, supporting the pelvic organs and controlling urination and defecation. | | Rectus abdominis | A long, flat muscle on each side of the anterior abdominal wall, responsible for flexing the vertebral column and compressing the abdominal organs. | | Oblique muscles (internal and external) | Muscles in the sides of the abdominal wall that help with rotation, lateral flexion, and compression of the abdomen. | | Transversus abdominis | The deepest abdominal muscle, which encircles the abdominal cavity and compresses its contents. | | Iliac crest | The large, flaring bone that forms the upper part of the pelvis. | | Lumbar vertebra | One of the five vertebrae in the lower back, located between the thoracic and sacral vertebrae. | | Pubic symphysis | The joint where the left and right pubic bones are joined by fibrocartilage. | | Xiphoid process | A small cartilaginous extension at the bottom of the sternum. | | Gluteus muscles (maximus, medius, minimus) | Muscles of the buttocks that are involved in hip extension, abduction, and rotation. | | Femur | The thigh bone, the largest and strongest bone in the body. | | Tibia | The shin bone, the larger of the two bones in the lower leg, located on the medial side. | | Fibula | The smaller of the two bones in the lower leg, located on the lateral side, parallel to the tibia. | | Patella | The kneecap, a small triangular bone located at the front of the knee joint. | | Tarsus | The collection of seven bones in the ankle and heel. | | Metatarsals | The five long bones in the arch of the foot. | | Phalanges | The bones of the fingers and toes. | | Mandible | The lower jawbone. | | Clavicle | The collarbone. | | Scapula | The shoulder blade. | | Humerus | The bone of the upper arm. | | Radius | The lateral bone of the forearm, on the thumb side. | | Ulna | The medial bone of the forearm, on the pinky finger side. | | Vertebrae | The bones of the spinal column. | | Sternum | The breastbone, located in the center of the chest. | | Ribs | The curved bones that form the rib cage, protecting the thoracic organs. | | Cranium | The part of the skull that encloses the brain. | | Facial bones | The bones that form the structure of the face. | | Hyoid bone | A U-shaped bone in the neck that supports the tongue. | | Sacrum | A triangular bone at the base of the spine, formed by the fusion of five vertebrae. | | Coccyx | The tailbone, formed by the fusion of four small vertebrae at the end of the spine. | | Thoracic cage | The structure formed by the ribs, sternum, and thoracic vertebrae, enclosing and protecting the thoracic organs. | | Pectoral girdle | The set of bones that connect the upper limbs to the axial skeleton, consisting of the clavicles and scapulas. | | Pelvic girdle | The set of bones that connect the lower limbs to the axial skeleton, consisting of the hip bones. | | Hip bone (Coxal bone) | Each of the two bones forming the pelvis, composed of the ilium, ischium, and pubis. | | Hip joint | The articulation between the head of the femur and the acetabulum of the hip bone, a ball-and-socket joint. | | Knee joint | The articulation between the femur, tibia, and patella, a complex hinge joint. | | Elbow joint | The articulation between the humerus, ulna, and radius, allowing for flexion and extension. | | Ankle joint | The articulation between the tibia, fibula, and talus, allowing for dorsiflexion and plantar flexion. | | Wrist joint | The articulation between the radius, ulna, and carpal bones, allowing for flexion, extension, abduction, adduction, and circumduction. | | Shoulder joint | The articulation between the head of the humerus and the glenoid cavity of the scapula, a ball-and-socket joint allowing for extensive movement. | | Carpal bones | The eight small bones that make up the wrist. | | Tarsal bones | The seven bones that make up the ankle and heel. | | Metacarpals | The five bones in the palm of the hand. | | Metatarsals | The five bones in the arch of the foot. | | Phalanges of fingers | The bones of the fingers. | | Phalanges of toes | The bones of the toes. | | Tendon | A tough band of fibrous connective tissue that connects muscle to bone. | | Ligament | A tough band of fibrous connective tissue that connects bone to bone at joints. | | Muscle fiber | A single muscle cell. | | Myofibril | A long, filamentous organelle found within muscle cells, composed of actin and myosin filaments. | | Sarcomere | The basic contractile unit of a striated muscle fiber, consisting of actin and myosin filaments. | | Z disc | The boundary structure of a sarcomere, to which thin filaments are anchored. | | A band | The region of a sarcomere containing the thick filaments (myosin). | | I band | The region of a sarcomere containing only thin filaments (actin) and bisected by the Z disc. | | H zone | The central region of the A band that contains only thick filaments. | | Tropomyosin | A protein that wraps around actin filaments and blocks myosin-binding sites when the muscle is at rest. | | Troponin | A protein complex that binds to calcium ions and tropomyosin, regulating muscle contraction. | | Neuromuscular junction | The specialized synapse between a motor neuron and a muscle fiber. | | Motor neuron | A nerve cell that transmits signals from the central nervous system to muscle fibers, causing them to contract. | | Neurotransmitter | A chemical messenger that transmits signals across a synapse, such as acetylcholine at the neuromuscular junction. | | Hormone | A chemical messenger produced by endocrine glands that regulates various bodily functions. | | Human Growth Hormone (hGH) | A hormone produced by the pituitary gland that stimulates growth and cell reproduction. | | Estrogen | A primary female sex hormone involved in the development and regulation of the female reproductive system and secondary sex characteristics. | | Androgen | A male sex hormone, such as testosterone, involved in the development of male reproductive tissues and secondary sex characteristics. | | Weight-bearing exercise | Physical activity that involves supporting one's body weight against gravity, which stimulates bone growth and maintenance. | | Mesenchyme | Embryonic connective tissue that can differentiate into various cell types, including bone cells. | | Chondroblast | A cell that produces cartilage matrix; it matures into a chondrocyte. | | Chondrocyte | A mature cartilage cell found in lacunae within the cartilage matrix. | | Perichondrium | A layer of fibrous connective tissue that surrounds cartilage, containing blood vessels and osteogenic cells. | | Articulation | A joint; the point where two or more bones meet. | | Glenoid cavity | The shallow depression in the scapula that articulates with the head of the humerus. | | Acetabulum | The deep socket in the hip bone that articulates with the head of the femur. | | Labrum glenoid | A rim of fibrocartilage that deepens the glenoid cavity of the shoulder joint. | | Labrum acetabular | A rim of fibrocartilage that deepens the acetabulum of the hip joint. | | Iliofemoral ligament | A strong ligament in the hip that prevents hyperextension. | | Ischiofemoral ligament | A ligament in the hip that connects the ischium to the femur. | | Pubofemoral ligament | A ligament in the hip that connects the pubis to the femur. | | Tibialis anterior | A muscle in the front of the lower leg that dorsiflexes the foot. | | Soleus | A muscle in the posterior lower leg that assists in plantar flexion of the foot. | | Plantar flexion | Movement of the foot downwards, pointing the toes away from the leg. | | Dorsiflexion | Movement of the foot upwards, bending the foot towards the shin. | | Plantar | The sole of the foot. | | Dorsal | The top or back surface of a part of the body. | | Maleolus | A bony prominence at the lower end of the tibia and fibula, forming the ankle. | | Talus | The ankle bone that articulates with the tibia and fibula. | | Calcaneus | The heel bone, the largest bone in the foot. | | Kuneiform bone | One of three wedge-shaped bones in the midfoot. | | Kalkaneum | The heel bone. | | Tendon calcaneus | The Achilles tendon, connecting the calf muscles to the heel bone. | | Pterygoid | Muscles in the side of the skull involved in chewing and moving the jaw. | | Occipitofrontalis | A muscle of the scalp that raises the eyebrows and wrinkles the forehead. | | Levator palpebrae superioris | A muscle that raises the upper eyelid. | | Orbicularis oculi | A muscle surrounding the eye that closes the eyelid. | | Orbicularis oris | A muscle surrounding the mouth that closes the lips. | | Buccinator | A muscle in the cheek that flattens the cheek and is used in blowing. | | Masseter | A powerful muscle of mastication (chewing) located in the jaw. | | Temporalis | A muscle in the temporal bone of the skull used for chewing. | | Sternocleidomastoid | A muscle in the neck that turns and flexes the head. | | Pterygoid | Muscles in the side of the skull involved in chewing and moving the jaw. | | Deltoid | The muscle covering the shoulder joint, responsible for arm abduction. | | Biceps | A muscle in the upper arm that flexes the elbow. | | Triceps | A muscle in the upper arm that extends the elbow. | | Psoas | A muscle of the inner hip that flexes the thigh. | | Latissimus | A large muscle of the back involved in extending, adducting, and medially rotating the arm. | | Quadratus lumborum | A muscle in the lower back that helps with lateral flexion of the trunk. | | Sacrospinalis | A large muscle group along the spine that helps maintain posture. | | Pectoralis major | A large chest muscle involved in arm adduction and flexion. | | Teres major | A muscle of the upper back that assists in extending, adducting, and medially rotating the arm. | | Latissimus dorsi | A large muscle on the back that is responsible for arm extension, adduction, and medial rotation. | | Abdomen | The part of the body between the thorax and the pelvis. | | Trunk | The torso, comprising the chest, abdomen, and pelvis. | | Gluteus muscles | The muscles of the buttocks. | | Gluteus medius | A hip abductor and medial rotator. | | Gluteus maximus | The largest buttock muscle, involved in hip extension and lateral rotation. | | Gluteus minimus | The deepest buttock muscle, involved in hip abduction. | | Thigh | The part of the leg between the hip and the knee. | | Sartorius | The longest muscle in the body, running obliquely across the thigh, involved in hip flexion and abduction, and knee flexion. | | Hamstring | A group of three muscles in the back of the thigh that flex the knee and extend the hip. | | Biceps femoris | A hamstring muscle that flexes the knee and extends the hip. | | Semimembranosus | A hamstring muscle that flexes the knee and extends the hip. | | Semitendinosus | A hamstring muscle that flexes the knee and extends the hip. | | Lower limb | The leg, from the hip to the foot. | | Leg | The part of the lower limb between the knee and the ankle. | | Pelvic floor muscles | Muscles forming the floor of the pelvis. | | Urethra | The tube that carries urine from the bladder out of the body. | | Vagina | The muscular canal connecting the cervix to the exterior in females. | | Anus | The opening at the end of the digestive tract. | | Respiratory muscles | Muscles involved in the process of breathing. | | Diaphragm | The primary muscle of respiration, located below the lungs. | | Internal intercostals | Muscles between the ribs that help with exhalation. | | External intercostals | Muscles between the ribs that help with inhalation. | | Thoracic duct | The largest lymphatic vessel in the body. | | Inferior vena cava | The large vein that carries deoxygenated blood from the lower and middle body into the right atrium of the heart. | | Esophagus | The tube connecting the pharynx to the stomach. | | Vagus nerve | A cranial nerve that influences heart rate, digestion, and other autonomic functions. | | Arteri frenik | Arteries supplying blood to the diaphragm. | | Saraf frenik | The nerve that innervates the diaphragm. | | Hepar | The liver. | | Gaster | The stomach. | | Limfa | The spleen. | | Defecation | The act of eliminating feces. | | Venous return | The flow of blood from the extremities back to the heart. | | Venous thrombosis | The formation of a blood clot in a vein. |