Muscle Physiology & Major Skeletal Muscles

Vocabulary flashcards covering key physiological terms and major skeletal muscles discussed in lecture, designed for rapid review before exams.

Agonist (Prime Mover)

Main muscle responsible for producing a specific movement.

Antagonist

Muscle that opposes or reverses the action of an agonist.

Synergist

Muscle that assists the agonist by adding force or stabilizing joints.

Origin

Proximal attachment of a muscle; typically the less movable bone.

Insertion

Distal attachment of a muscle; usually the bone that moves.

Motor Unit

A motor neuron and all the skeletal muscle fibers it innervates.

Neuromuscular Junction

Synapse where a motor neuron communicates with a skeletal muscle fiber by releasing acetylcholine.

Motor End Plate

Specialized region of sarcolemma containing ACh receptors at the neuromuscular junction.

T-Tubule

Invagination of sarcolemma that conducts action potentials into the muscle fiber’s interior.

Sarcoplasmic Reticulum

Smooth ER of muscle fibers; stores and releases Ca²⁺ for contraction.

Sarcolemma

Plasma membrane of a muscle fiber.

Sarcoplasm

Cytoplasm of a muscle fiber.

Myofibril

Long contractile organelle composed of repeating sarcomeres in skeletal muscle.

Myofilament

Protein filament (actin or myosin) that slides during contraction.

Actin

Thin filament protein that binds myosin during contraction.

Myosin

Thick filament protein with heads that form cross-bridges with actin.

Cross-Bridge

Connection formed when a myosin head binds to actin.

Troponin

Regulatory protein that binds Ca²⁺ and moves tropomyosin off actin’s binding sites.

Tropomyosin

Strand that blocks actin binding sites until moved by troponin-Ca²⁺.

Excitation-Contraction Coupling

Sequence linking muscle fiber excitation to Ca²⁺ release and contraction.

Fast Glycolytic Fiber

Skeletal muscle fiber that contracts quickly, fatigues rapidly, uses anaerobic metabolism.

Fast Oxidative Fiber

Intermediate fiber; fast contraction and moderate fatigue resistance.

Slow Oxidative Fiber

Fiber that contracts slowly, resists fatigue, relies on aerobic metabolism.

Rigor Mortis

Post-mortem stiffening from ATP depletion, preventing cross-bridge detachment.

Smooth Muscle

Non-striated involuntary muscle with dense bodies, gap junctions, and varicosities.

Dense Body

Protein anchor point in smooth muscle for thin filaments.

Varicosity

Swelling along autonomic axon that releases neurotransmitters to smooth muscle (diffuse junction).

Gap Junction

Protein channel connecting adjacent cells; allows ion flow and coordinated contraction in smooth or cardiac muscle.

Striation

Alternating A and I bands in skeletal & cardiac muscle produced by ordered myofibrils.

Trapezius

Large diamond-shaped back muscle; elevates, retracts, or depresses scapula.

Deltoid

Triangular shoulder muscle; prime mover of arm abduction.

Pectoralis Major

Broad chest muscle; flexes, adducts, and medially rotates humerus.

Pectoralis Minor

Deep chest muscle; protracts scapula or elevates ribs during inhalation.

Sternocleidomastoid

Neck muscle; flexes, laterally rotates head, known as the "birth-control" (just-say-no) muscle.

Diaphragm

Primary breathing muscle; contraction flattens dome for inspiration.

External Intercostals

Superficial rib muscles; elevate ribs for inspiration.

Internal Intercostals

Deep rib muscles; depress ribs for forced expiration.

External Oblique

Outermost abdominal muscle; fibers run "hands-in-pockets"; flexes & rotates trunk.

Internal Oblique

Middle abdominal layer; fibers run perpendicular to external oblique; flexes & rotates trunk.

Rectus Abdominis

"Six-pack" muscle; flexes lumbar spine.

Transversus Abdominis

Deep abdominal layer; compresses abdominal contents.

Latissimus Dorsi

Broadest back muscle; extends, adducts, and medially rotates humerus ("lat pull-down" muscle).

Levator Scapulae

Neck/back muscle; elevates scapula.

Rhomboids (Major & Minor)

Deep back muscles; retract and downward-rotate scapula.

Supraspinatus

Rotator-cuff muscle superior to scapular spine; initiates arm abduction.

Infraspinatus

Rotator-cuff muscle inferior to spine; laterally rotates humerus.

Teres Minor

Rotator-cuff muscle; lateral rotation of humerus.

Teres Major

Not rotator cuff; extends and medially rotates humerus.

Biceps Brachii

Two-headed anterior arm muscle; flexes elbow and supinates forearm.

Brachialis

Deep anterior arm muscle; prime mover of elbow flexion.

Brachioradialis

Forearm muscle on radial side; synergist in elbow flexion.

Triceps Brachii

Three-headed posterior arm muscle; prime mover of elbow extension.

Pronator Teres

Forearm muscle that pronates forearm.

Flexor Carpi Radialis

Anterior forearm; flexes and abducts wrist.

Palmaris Longus

Anterior forearm; flexes wrist; absent in ~15 % of people.

Flexor Carpi Ulnaris

Anterior forearm; flexes and adducts wrist.

Flexor Digitorum Superficialis

Intermediate anterior forearm; flexes fingers 2-5 at PIP joints.

Flexor Digitorum Profundus

Deep anterior forearm; flexes distal phalanges 2-5.

Flexor Pollicis Longus

Deep anterior forearm; flexes thumb.

Extensor Carpi Radialis Longus

Posterior forearm; extends and abducts wrist.

Extensor Carpi Radialis Brevis

Shorter companion to ECRL; extends/abducts wrist.

Extensor Digitorum

Posterior forearm; extends fingers 2-5.

Extensor Carpi Ulnaris

Posterior forearm; extends and adducts wrist.

Supinator

Deep posterior forearm; supinates forearm ("I am the SUPINATOR").

Abductor Pollicis Longus

Posterior forearm; abducts thumb.

Extensor Pollicis Longus

Posterior forearm; extends thumb ("thumbs-up" muscle).

Gluteus Maximus

Largest gluteal muscle; extends and laterally rotates hip.

Gluteus Medius

Middle gluteal; abducts hip and stabilizes pelvis.

Gluteus Minimus

Deepest gluteal; assists in hip abduction.

Iliotibial (IT) Tract

Thick lateral fascia from ilium to tibia; receives insertion of gluteus maximus & tensor fasciae latae.

Hamstrings

Posterior thigh group—biceps femoris, semitendinosus, semimembranosus; extend hip & flex knee.

Biceps Femoris

Lateral hamstring; two heads; extends hip, flexes knee.

Semitendinosus

Superficial medial hamstring with cord-like tendon; extends hip, flexes knee.

Semimembranosus

Deep medial hamstring; broad, flat; extends hip, flexes knee.

Iliopsoas

Major hip flexor formed by psoas major and iliacus.

Psoas Major

Part of iliopsoas; originates on lumbar vertebrae; flexes hip.

Iliacus

Part of iliopsoas; originates on iliac fossa; flexes hip.

Epicranius (Occipitofrontalis)

Frontal & occipital bellies linked by galea aponeurotica; raises eyebrows, wrinkles forehead.

Temporalis

Fan-shaped muscle over temporal bone; elevates mandible.

Masseter

Powerful jaw muscle; prime mover of mandible elevation (chewing).

Orbicularis Oculi

Circular muscle around eye; forceful eye closure, winking.

Orbicularis Oris

Circular muscle around mouth; puckers lips (kissing muscle).

Zygomaticus Major/Minor

Corner-of-mouth to zygomatic bone; elevate corners for smiling.

Buccinator

Cheek muscle; compresses cheeks during chewing or blowing.

Corrugator Supercilii

Deep eyebrow muscle; draws eyebrows medially, creates frown wrinkles.

Levator Scapulae

Neck muscle elevating scapula; assists downward rotation.