Muscular and Skeletal Systems: Anatomy, Physiology, and Articulations

Comprehensive review flashcards covering skeletal muscle tissue organization, sarcomere anatomy, sliding filament theory, muscular contraction phases, muscle metabolism, major muscles and their actions, joint classifications, joint anatomy and ligaments, and anatomical movements.

Anaerobic respiration (muscle context)

Production of ATP through glycolysis without directly requiring oxygen; quickly supplies a smaller amount of ATP during intense activity.

Lactate (lactic acid)

A substance produced when pyruvate from glycolysis is converted during high rates of anaerobic glycolysis; allows glycolysis to continue producing ATP by regenerating NAD+ and can also be reused as fuel.

Oxygen debt

A traditional term describing the additional oxygen required during recovery after strenuous exercise to restore normal physiological conditions, replenish oxygen stores, and support recovery.

Myoglobin

An oxygen-binding protein found inside muscle cells that stores oxygen and helps make it available for aerobic metabolism.

Red (slow) fibers

Slow-twitch muscle fibers, also called Type I fibers, that contain abundant myoglobin, many mitochondria, and many capillaries; they contract slowly and resist fatigue.

White (fast) fibers

Fast-twitch muscle fibers, especially Type IIx fibers, that have lower myoglobin content, contract rapidly, produce high force, and fatigue relatively quickly.

Intermediate fibers

Muscle fibers with characteristics between slow-twitch and fast-twitch fibers (commonly Type IIa) that contract relatively quickly and have moderate-to-high fatigue resistance.

Twitch

A brief contraction and relaxation of a muscle fiber in response to a single stimulus.

Latent period

The short delay between the stimulus and the beginning of muscle tension, allowing the electrical signal to spread and calcium to be released before contraction begins.

Contraction phase

The phase of a muscle twitch when muscle tension increases as myosin binds to actin and cross-bridge cycling produces tension.

Relaxation phase

The phase of a muscle twitch when muscle tension decreases as calcium is pumped back into the sarcoplasmic reticulum and cross-bridge activity stops.

Treppe (staircase phenomenon)

A gradual increase in muscle contraction strength when a resting muscle receives repeated stimuli of equal strength after complete relaxation between stimuli.

Wave summation

Increased muscle tension produced when a second stimulus occurs before the muscle has completely relaxed from the first stimulus.

Tetanus

Sustained muscle contraction caused by rapid, repeated stimulation that produces continuous muscle tension without complete relaxation between stimuli.

Electromyography (EMG)

A test that records electrical activity produced by skeletal muscles to evaluate muscle and nerve function.

Muscle tone (tonic contraction)

Continuous, low-level, involuntary partial contraction of muscles at rest that helps maintain posture, balance, and readiness for movement.

Flaccid

A state of abnormally low or absent muscle tone in which muscles become limp and weak and fail to maintain normal resting tension.

Spastic

A state of abnormally increased muscle tone, often involving involuntary muscle stiffness, exaggerated reflexes, and resistance to passive movement.

Isotonic contraction

A type of contraction in which a muscle produces tension while changing its length, creating movement at a joint.

Concentric contraction

An isotonic contraction where the muscle shortens while producing tension to overcome resistance and move a body part.

Eccentric contraction

An isotonic contraction where the muscle lengthens while producing tension to control or slow down movement against resistance.

Isometric contraction (static tension)

A contraction where the muscle produces tension without changing its overall length, maintaining a position without producing joint movement.

Endurance (aerobic) training

Exercise that improves the ability of muscles and the cardiovascular system to sustain physical activity over an extended period by increasing mitochondrial capacity, capillary supply, and oxygen efficiency.

Strength training

Exercise that uses resistance to improve muscular strength, force production, and potentially muscle size.

Hypertrophy

An increase in the size of individual muscle fibers, contributing to greater force-producing capacity.

Atrophy

A decrease in muscle size due to the loss of muscle fiber size, reducing muscle mass and strength.

ATP (adenosine triphosphate)

A molecule that stores and transfers usable energy within cells; provides immediate energy for muscle contraction, including myosin detachment and re-energizing.

Aerobic respiration

A process that produces ATP using oxygen, primarily through cellular respiration in mitochondria, providing large amounts of ATP for prolonged muscle activity.

Skeletal (striated) muscle

Voluntary muscle tissue with long cylindrical fibers, visible striations, and multiple nuclei that produces body movements, maintains posture, and generates heat.

Smooth (visceral) muscle

Involuntary, nonstriated muscle tissue made of spindle-shaped cells with one nucleus; moves substances through internal organs and controls the diameter of hollow structures.

Cardiac muscle

Involuntary, striated muscle tissue with branching cells, usually one nucleus, and intercalated discs; contracts rhythmically to pump blood throughout the body.

Muscle fiber

A single, elongated muscle cell that contracts to generate force and movement.

Sarcolemma

The plasma membrane surrounding a muscle fiber that conducts electrical signals along the muscle cell membrane.

Sarcoplasm

The cytoplasm inside a muscle fiber containing organelles, glycogen, myoglobin, and other substances needed for muscle activity.

Sarcoplasmic reticulum

Specialized smooth endoplasmic reticulum surrounding myofibrils that stores, releases, and reabsorbs calcium ions needed for muscle contraction and relaxation.

Myofibril

Long cylindrical structures inside muscle fibers composed of repeating sarcomeres that produce muscle contraction.

Myofilament

Protein filaments (thin actin and thick myosin) that make up myofibrils and interact with each other to produce contraction.

Sarcomere

The functional contractile unit of striated muscle extending from one Z-line to the next; shortens during contraction as actin slides past myosin.

Structural hierarchy of skeletal muscle

Organization from largest to smallest: 1. Whole muscle -> 2. Fascicle -> 3. Muscle fiber (cell) -> 4. Myofibril -> 5. Sarcomere -> 6. Myofilaments (actin and myosin).

Z-line (Z-disc)

A structure marking the boundaries of a sarcomere; anchors thin actin filaments and helps maintain sarcomere organization.

A-band

The dark region representing the entire length of thick myosin filaments; contains thick filaments and areas where actin overlaps myosin, remaining the same length during contraction.

I-band

The light region containing only thin actin filaments; becomes shorter and narrower as the sarcomere contracts.

H-zone

The central region of the A-band containing only thick myosin filaments with no actin-myosin overlap in a relaxed sarcomere; becomes smaller/narrower or disappears during contraction.

Myosin

The thick filament protein with projecting heads that binds to actin and pulls thin filaments toward the center of the sarcomere, responsible for cross-bridge formation.

Actin

The main protein forming the thin filaments; provides binding sites for myosin and slides toward the center of the sarcomere during contraction.

Troponin

A regulatory protein attached to the thin filament that binds calcium and causes tropomyosin to move away from actin's binding sites.

Tropomyosin

A regulatory protein lying along actin filaments that blocks myosin-binding sites on actin when the muscle is relaxed.

Cross-bridge

A temporary attachment formed when a myosin head binds to an exposed site on actin to pull actin toward the center of the sarcomere during contraction.

Somatic motor neuron

A nerve cell that carries signals from the central nervous system to skeletal muscles to stimulate muscle contraction.

Neuromuscular junction (NMJ)

A specialized communication point between a motor neuron and a skeletal muscle fiber that allows nerve signals to trigger muscle contraction.

Motor end plate

A specialized region of the sarcolemma at the neuromuscular junction containing acetylcholine receptors that receives ACh and initiates an electrical signal.

Acetylcholine (ACh)

A neurotransmitter released by motor neurons at the neuromuscular junction that binds to receptors on the motor end plate to stimulate a muscle action potential.

Motor unit

One somatic motor neuron and all the muscle fibers it controls, allowing the nervous system to control muscle force and movement.

Recruitment

The activation of additional motor units to produce stronger muscle contractions and increase muscle force.

Sliding filament model

An explanation of muscle contraction in which actin filaments slide past myosin filaments, shortening the sarcomere and producing muscle contraction.

Epimysium

The outer layer of dense connective tissue surrounding the entire muscle; protects and supports the muscle and helps transmit force to tendons.

Perimysium

Connective tissue surrounding bundles of muscle fibers (fascicles) that organizes fibers and carries blood vessels and nerves.

Endomysium

A thin layer of connective tissue surrounding each individual muscle fiber that supports fibers and contains small blood vessels and nerve fibers.

Origin

The proximal attachment site of a muscle (e.g., the biceps attaches proximally to the scapula).

Insertion

The distal attachment site of a muscle (e.g., the biceps attaches distally to the radius).

Agonist (muscle)

The primary muscle responsible for producing a specific movement (e.g., biceps brachii produces elbow flexion).

Antagonist (muscle)

The muscle that opposes the action of an agonist (e.g., triceps brachii opposes elbow flexion).

Synergist (muscle)

A muscle that assists the agonist in performing a specific action (e.g., brachialis assists elbow flexion).

Masseter

A muscle located on the side of the jaw that elevates the mandible, closing the jaw during chewing.

Temporalis

A muscle located on the side of the skull above the ear that elevates and retracts the mandible.

Orbicularis oris

A circular muscle surrounding the mouth that closes, compresses, and protrudes the lips (e.g., puckering or kissing).

Buccinator

A muscle located deep in the cheek that compresses the cheek and keeps food between the teeth during chewing, blowing, or whistling.

Platysma

A muscle located in the superficial anterior neck that tenses neck skin and helps depress the lower jaw and lip.

Rectus abdominis

A muscle on the front of the abdomen that flexes the vertebral column and compresses abdominal contents (e.g., sit-ups or crunches).

External oblique

A muscle on the superficial, outer sides of the abdomen that compresses the abdomen, rotates the trunk to the opposite side, and laterally flexes the trunk.

Internal oblique

A muscle deep to the external oblique that compresses the abdomen, rotates the trunk to the same side, and laterally flexes the trunk.

Transversus abdominis

The deepest layer of the abdominal muscles; compresses abdominal contents and stabilizes the trunk.

Trapezius

A large muscle of the upper and middle back extending into the neck; elevates, depresses, retracts, and upwardly rotates the scapula, and helps extend the neck.

Pectoralis major

A large superficial chest muscle that flexes, adducts, and medially rotates the arm (e.g., pushing a door or performing a push-up).

Pectoralis minor

A muscle deep to pectoralis major that protracts and depresses the scapula, stabilizing it against the thoracic wall.

Latissimus dorsi

A large superficial muscle of the lower and middle back that extends, adducts, and medially rotates the arm (e.g., during a pull-up).

Deltoid

A muscle covering the shoulder that primarily abducts the arm; anterior fibers assist flexion and medial rotation, while posterior fibers assist extension and lateral rotation.

Supraspinatus

A rotator cuff muscle on the superior surface of the scapula above the spine that initiates arm abduction and stabilizes the shoulder joint.

Infraspinatus

A rotator cuff muscle on the posterior scapula below the spine that laterally rotates the arm and stabilizes the shoulder joint.

Teres minor

A rotator cuff muscle on the posterior scapula below infraspinatus that laterally rotates and weakly adducts the arm, while stabilizing the shoulder.

Subscapularis

A rotator cuff muscle on the anterior surface of the scapula that medially rotates and assists with adduction of the arm, while stabilizing the shoulder.

Teres major

A muscle located on the inferior lateral border of the scapula that extends, adducts, and medially rotates the arm.

Biceps brachii

A muscle on the front of the upper arm that flexes the elbow, supinates the forearm, and assists with shoulder flexion.

Brachialis

A muscle deep to the biceps brachii that acts as the primary elbow flexor regardless of forearm position.

Brachioradialis

A muscle in the lateral forearm running from humerus to radius that flexes the elbow, especially with the forearm in a neutral position.

Triceps brachii

A muscle on the back of the upper arm that extends the elbow; its long head also assists with shoulder extension and adduction.

Soleus

A muscle in the deep posterior lower leg underneath the gastrocnemius that plantar flexes the foot at the ankle and helps maintain standing posture.

Articulation

Another name for a joint; the point where two or more bones meet to connect bones and potentially allow movement.

Synarthrosis

An immovable joint that provides stability and protection with little or no movement (e.g., sutures between skull bones).

Amphiarthrosis

A slightly movable joint that allows limited movement while maintaining stability (e.g., pubic symphysis, joints between vertebral bodies).

Diarthrosis (synovial joint)

A freely movable joint characterized by a joint cavity containing synovial fluid that allows a wide range of movement (e.g., shoulder, hip, knee, elbow).

Suture

A fibrous joint where bones are tightly connected by dense connective tissue to hold skull bones together and protect the brain.

Gomphosis

A fibrous joint that connects and anchors a tooth to its alveolar socket in the jaw.

Syndesmosis

A fibrous joint where bones are connected by ligaments or an interosseous membrane, providing stability while allowing slight movement (e.g., distal tibiofibular joint).

Synchondrosis

A cartilaginous joint where bones are connected by hyaline cartilage, providing support and potentially allowing bone growth (e.g., epiphyseal growth plate).

Symphysis

A cartilaginous joint where bones are connected by fibrocartilage, providing strength, shock absorption, and slight movement (e.g., pubic symphysis and intervertebral discs).

Hinge joint

A synovial joint that primarily moves in one plane, allowing flexion and extension (e.g., elbow and knee).

Pivot joint

A synovial joint where one bone rotates around another bone or a central axis, allowing rotation (e.g., atlas and axis vertebrae in the neck).

Saddle joint

A synovial joint where both articulating surfaces are saddle-shaped, allowing flexion, extension, abduction, adduction, and circumduction (e.g., carpometacarpal joint of the thumb).

Ball-and-socket joint

A synovial joint where a rounded head of one bone fits into a cup-shaped socket of another bone, allowing the greatest range of motion: flexion, extension, abduction, adduction, rotation, and circumduction (e.g., shoulder and hip).