Skeletal and Muscular Systems PDF

The Skeletal System The skeletal system is the framework of the body, providing support, protection, movement, and storage. It interacts closely with the muscular system to facilitate locomotion and other movements. Function - Support: Provides a rigid structure for the body, supporting soft ti...

The Skeletal System The skeletal system is the framework of the body, providing support, protection, movement, and storage. It interacts closely with the muscular system to facilitate locomotion and other movements. Function - Support: Provides a rigid structure for the body, supporting soft tissues. - Protection: Shields vital organs (e.g., brain, heart, lungs) from injury. - Movement: Acts as levers for muscles to pull on, creating movement at joints. - Mineral and Fat Storage: Reservoir for essential minerals like calcium and phosphorus and fat like yellow marrow. - Blood Cell Production: red bone marrow (hematopoiesis, hemopoiesis) Bone Tissue Bone tissue consists of cells and an extracellular matrix of proteins (collagen) and minerals. The matrix includes: - Collagen fibers 25% and water 25%: Provide flexibility and strength. - Also includes minerals; provide strength to bone to withstand sources of stress 2 types of bone: Compact – organized osteons - Makes up bulk of diaphysis in long bones - Protection, support, resistance to external stress Spongy - “trabecular” bone, less organized - Short, flat, irregular bone and epiphysis - Lighter in weight - Red bone marrow - Trabeculae follow lines of stress Types of Bone Cells: How do they contribute to homeostasis? - Osteoblasts: Responsible for bone building by secreting the matrix. Located deep to the periosteum - Osteocytes: Mature bone cells, in the bone matrix. - Osteoclasts: Bone destroying cells - break down matrix, releases minerals to the body Located under endosteum Bone Classification: Classify the bone of skeletal system and provide example of each Classified by their shape: - Long: Long with expended ends (e.g., femur in leg, humerus in arm). Grows at the epiphyseal growth plate (metaphysis region) = growth - Short: Cube-like (e.g., carpals that form wrist, tarsals in ankle). - Sesamoid (round) bones: small, nodular, develops within tendons (e.g., patella) - Flat: Thin, broad surface, protects internal organs (e.g., sternum at the center of chest, ribs, scapula, flattened skull bones). - Irregular: varied shape (e.g., vertebrae, some facial bones). Axial Skeletal System: (Skull, vertebrae, sternum and ribs) Components: 80 bones. - Skull: Cranium (8 bones) and Face (14 bones). - Hyoid: (1 bone) - Auditory ossicles: (6 bones) - Vertebral Column: 26 bones. Makes up the spine o Functions: ▪ Encloses and protects spinal cord ▪ Support the head ▪ Attachment points for rib, pelvic girdle and muscle of the back Spinal curvature:  - Thorax: Sternum (1 bone) and Ribs (24 bones). Entire chest o Functions: ▪ Encloses and protects organ of thoracic cavity and upper abdominal cavity ▪ Provides support for bones of shoulder and upper limb o Ribs: ▪ 12 pairs of ribs Articulate with thoracic vertebrae (T1- T12) ▪ True ribs: 1 to 7 ▪ False ribs: 8 to 10 ▪ Floating ribs: 11 & 12 Appendicular Skeleton: (Shoulders, pelvis, limbs) Attaches bone of upper limbs to the axial skeleton - Components: Clavicle, scapula - 126 bones: o Pectoral Girdle (4 bones): Clavicle, scapula. o Upper Limbs (60 bones): Humerus, radius, ulna, wrist bone (carpals), Bone of the hand (metacarpals, phalanges). o Pelvic Girdle (2 bones): Hip/pelvic bones. o Lower Limbs (60 bones): Femur, patella, tibia, fibula, ankle bone (tarsals), bone of feet (metatarsals, phalanges). Fractures Types of Fractures: o Partial (greenstick): Incomplete break across bone, crack o Complete (transverse): complete break across the bone. o Closed (simple): Fractured bone does not break thought the skin. o Open (Compound): Bone pierces through the skin. Rickets - Caused by Vitamin D or calcium deficiency during childhood. Results in: o Weakened, softer bones. o Bowing or curvature of bones. o Stunted growth. Darker skin tones may have increased risk due to reduced vitamin D synthesis (role of melanin). Joints and Movement Joints (Articulations): Points where bones meet to allow movement and provide stability. - Functions: o Bind bones together. o Permit movement. o Enable bone growth. o Adapt to childbirth by shape changing. Classification of Joints - By Degree of Movement (functionally): o Immovable (Syndesmosis): E.g., sutures in the skull. o Slightly Movable (Amphiarthrosis): E.g., pubic symphysis, intervertebral discs. o Freely Movable (Diarthrosis): Synovial joints, e.g., shoulder. - By Type of Tissue that binds them together (Structurally): o Fibrous: Dense, irregular connective tissue; mostly immovable (e.g., skull sutures, teeth). ▪ Found between bones that lie close in contact, held by dense, irregular connective tissue o Cartilaginous: composed of fibrocartilage and hyaline cartilage (e.g., pubic symphysis) ▪ Tightly connected with little to no movement, intervertebral discs help absorb shocks o Synovial: complex structure; highly movable (e.g., knee, elbow). ▪ Contains capsule filled with synovial fluid ▪ Diarthrotic – allows free movement ▪ Most joints of skeleton are synovial Structure: - The ends of bones in a synovial joint are covered with hyaline (articular) cartilage - Outer layer of dense connective tissue, and an inner layer, called the synovial membrane - secretes synovial fluid, which lubricates the joints - Also consists of ligaments, tendons and bursae to contain and cushion movement Types of Synovial Joints 1. Plane (Planar): Flat surfaces; sliding movements, may also rotate (e.g., Joints between carpals and tarsals). 2. Hinge: Convex surface of one bone fits into concave surface of another; flexion/extension (e.g., elbow, knee, ankle joints). 3. Pivot: Rounded/pointed surface fits into a ring; rotational movement (e.g., atlanto- axial, radioulnar joint). 4. Condyloid: Oval projection fits into oval cavity; angular movements (e.g., wrist, knuckles). 5. Saddle: Saddle-shaped surface; wide range of motion (e.g., thumb joint). 6. Ball-and-Socket: Ball-like surface fits into a cup; greatest range of motion (e.g., shoulder, hip). Types of Movement 3 types: - Gliding: 2 surfaces slide over one another, slight movement (e.g., plane joints). - Rotation: movement around a bone’s own longitudinal axis (e.g., pivot joints). - Angular Movements: Involves increase or decrease of angle between 2 bones o Flexion: Decreasing the angle between two bones. o Extension: Increasing the angle between two bones. o Abduction: Moving away from the midline. o Adduction: Moving toward the midline. o Circumduction: Circular motion combining flexion, extension, abduction, and adduction. Special Movements: o Inversion/Eversion: Sole of foot turns inward/outward.  o Dorsiflexion/Plantarflexion: Bending the foot upward/downward. The Muscular System The muscular system comprises three muscle types: skeletal, cardiac, and smooth. It is responsible for voluntary and involuntary movements, posture, and thermoregulation. Function - Produces body movements. - Stabilizes body position and posture. - Enables movement of internal organs. - Produces heat. - It regulates blood flow. Tissue Types 1. Skeletal Muscle (also called Muscle fibers) - They are organs - Characteristics: Voluntary, somatic nervous system, striated, multinucleated, has all 4 types of tissues - Location: Attached to bones or skin or sphincters by tendons (dense connective tissues) for movement – each in contact with a neuron - cytoplasm is called the sarcoplasm, and the muscle fiber membrane is called the sarcolemma - formed by fusion of multiple myoblasts during development; they end up with multiple nuclei; needed to support protein synthesis. - Do not undergo cell division (mitosis) – instead they contain stem cells called satellite cells which mature into new muscle cells. - Hypertrophy: muscle cells get larger - Atrophy: gets smaller 2. Cardiac Muscle  -Characteristics: Involuntary, autonomic nervous system striated, 1-3 nucleus, intercalated discs. - Location: Found only in the heart. 3. Smooth Muscle - Characteristics: Involuntary, non-striated, single nucleus - Location: Walls of hollow organs (e.g., stomach, blood vessels) Insertion and Origin - Origin: The end of the muscle attached to the stationary bone. - Insertion: The end of the muscle attached to the movable bone. - Belly: Middle of the muscle. Roles in Movement Agonist (Prime Mover): Main muscle responsible for movement. o Example: Biceps brachii during elbow flexion. Antagonist: Causes the opposite movement of the agonist. o Example: If an agonist bends your arm, antagonist straightens your arm. Synergist: Assists the agonist in performing a movement. o Example: Brachialis assisting biceps brachii. Fixator: Stabilizes the origin of the agonist. o Example: Shoulder muscles during bicep curls. Neuromuscular Junction Motor Neurons (somatic efferent neurons): nerve cells whose axons innervate skeletal muscle fibers - Axons of motor neurons are myelinated and the largest-diameter axon in the body - Axon terminals contain vesicles of the neurotransmitter Acetylcholine – Ach - When an action potential moving down a motor neuron reaches the axon terminal, calcium channels open and signal the release of acetylcholine (ACh) across the synaptic cleft to the motor end plate of the muscle: region of the muscle fiber plasma membrane that lies directly under the terminal portion of the axon The synapse between a motor neuron and a skeletal muscle fiber. Key steps include: 1. Release of acetylcholine (ACh) from the neuron into the synaptic cleft. 2. ACh binding to receptors on the muscle fiber, causing depolarization. Opens Na ion channels. 3. Initiation of an action potential that triggers calcium release and muscle contraction. Excitation-Contraction Coupling: The action potential travels along the muscle fiber, reaching the sarcoplasmic reticulum (SR), causing the release of calcium ions (Ca²⁺). Muscle Contraction and Relaxation Skeletal muscle has some defining characteristics: - Multinucleated - Contains many mitochondria - has special structures called transverse tubules (T tubules). - has myofibrils and sarcomeres. - has specific terms for some of the intracellular structures: sarcolemma = plasma membrane sarcoplasm = cytoplasm sarcoplasmic reticulum = smooth ER A muscle cell is also called fiber – arranged into myofibrils - Myofibrils are bundles of contractile filaments that give skeletal and cardiac muscle their characteristic striated appearance. - orderly arrangements of thick and thin filaments: o Actin (thin) – including tropomyosin and troponin proteins o Myosin (thick) When muscles contract, myosin heads bind to actin, causing the thick and thin filaments to slide across one another. This is part of the cross-bridge cycle. Key Steps of the Contraction Cycle: 1. Calcium binds to troponin, moving tropomyosin and exposing actin binding sites. 2. Myosin heads form cross-bridges with actin and perform a power stroke. 3. ATP is required to detach myosin from actin and continuing the cycle until relaxation Cross-Bridge Formation: - Myosin heads, energized by ATP hydrolysis (ATP → ADP + Pi), attach to exposed binding sites on actin. - This forms a cross-bridge Relaxation: - Acetylcholinesterase breaks down ACh. - Calcium ions are pumped back into the sarcoplasmic reticulum. - Actin and myosin return to their resting states.