Muscle Anatomy & Physiology – Sarcomere to Whole-Muscle Lecture

These vocabulary flashcards review key anatomical structures, connective tissues, molecular components, neural elements, muscle actions, and representative skeletal muscles discussed throughout the lecture video. They provide concise definitions to reinforce recognition and understanding for exam preparation.

Sarcomere

Smallest contractile unit of a myofibril; spans from one Z line to the next.

Z line (Z disc)

Boundary of a sarcomere; anchoring point for thin filaments and appears zig-zagged.

A band

Dark region of a sarcomere containing the entire length of thick filaments (myosin).

I band

Light region containing only thin filaments on either side of the Z line.

H zone

Central part of the A band where thick filaments have no thin-filament overlap.

M line

Midline of the sarcomere; proteins that hold thick filaments in place.

Zone of overlap

Area where thick and thin filaments interdigitate; increases during contraction.

Thin filament

Filament made primarily of actin plus regulatory proteins; appears red on model.

Thick filament

Filament composed of myosin molecules and their projecting heads; appears blue.

Actin

Globular protein forming two twisted chains; main component of thin filaments.

Myosin

Motor protein forming thick filaments; has projecting heads that bind actin.

Myosin head

Movable projection of myosin that attaches to actin to generate force.

Tropomyosin

Long regulatory strand that blocks myosin-binding sites on actin at rest.

Troponin

Three-part protein that controls tropomyosin position and regulates contraction.

Sarcoplasmic reticulum

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

T tubule

Invagination of sarcolemma that brings action potentials into the fiber interior.

Myofibril

Cylindrical bundle of sarcomeres inside a muscle fiber.

Muscle fiber

Single skeletal muscle cell; wrapped in endomysium.

Fascicle

Bundle of muscle fibers surrounded by perimysium.

Epimysium

Connective tissue sheath encasing an entire skeletal muscle.

Perimysium

Connective tissue layer surrounding a fascicle.

Endomysium

Delicate connective tissue around an individual muscle fiber.

Neuromuscular junction

Point where a motor neuron communicates with a muscle fiber.

Axon

Long neuronal process transmitting impulses toward terminals.

Axon terminal

Distal portion of axon that forms synapses with a muscle fiber.

Synaptic end bulb

Bulbous enlargement at axon terminal containing synaptic vesicles.

Synapse (synaptic cleft)

Tiny space between neuron and motor end plate where neurotransmitter diffuses.

Motor end plate

Folded region of sarcolemma that houses ACh receptors at NMJ.

Sarcolemma

Plasma membrane of a muscle fiber.

Myelin sheath

Insulating wrapping around axons formed by Schwann cells.

Schwann cell

Glial cell that produces myelin around peripheral axons.

Terminal branches

Small branches of an axon leading to individual synaptic bulbs.

Synaptic vesicles

Membranous sacs storing neurotransmitter (ACh) in the synaptic bulb.

Flexion

Movement that decreases the angle between two bones.

Extension

Movement that increases the angle between two bones.

Hyperextension

Extension beyond the anatomical position.

Abduction

Movement away from the midline of the body.

Adduction

Movement toward the body’s midline.

Circumduction

Circular, cone-shaped motion combining flexion, extension, abduction, adduction.

Rotation

Bone turns around its own longitudinal axis.

Elevation

Lifting a body part superiorly (e.g., shrugging).

Depression

Moving a body part inferiorly.

Protraction

Anterior movement in a transverse plane (e.g., mandible forward).

Retraction

Posterior movement in a transverse plane.

Inversion

Turning sole of foot medially.

Eversion

Turning sole of foot laterally.

Dorsiflexion

Lifting foot so superior surface approaches shin.

Plantar flexion

Pointing foot downward, increasing angle at ankle.

Supination

Forearm rotation that turns palm anteriorly (radius & ulna parallel).

Pronation

Forearm rotation that turns palm posteriorly (radius crosses ulna).

Opposition

Thumb movement toward fingers enabling grasping.

Aponeurosis

Broad, flat tendon sheet connecting muscles to each other or bone.

Epicranial aponeurosis (Galea aponeurotica)

Tendon sheet linking frontalis and occipitalis across the skull roof.

Occipitofrontalis

Two-part scalp muscle consisting of frontalis and occipitalis bellies.

Frontalis

Anterior belly that raises eyebrows and wrinkles forehead.

Occipitalis

Posterior belly that pulls scalp posteriorly.

Temporalis

Fan-shaped muscle over temporal bone; elevates mandible for chewing.

Orbicularis oculi

Circular muscle around the eye; closes eyelids.

Nasalis

Muscle over bridge of nose; flares nostrils.

Orbicularis oris

Circular muscle around mouth; purses lips.

Masseter

Powerful jaw elevator on cheek; major muscle of mastication.

Platysma

Thin superficial neck muscle that tenses skin of neck and depresses mandible.

Sternocleidomastoid

Neck muscle from sternum & clavicle to mastoid; flexes & rotates head.

Deltoid

Triangular shoulder muscle; abducts arm.

Pectoralis major

Large chest muscle; flexes, adducts, and medially rotates arm.

Serratus anterior

Saw-toothed muscle on ribs; protracts scapula.

Biceps brachii

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

Brachialis

Deep anterior arm muscle; primary elbow flexor.

Triceps brachii

Three-headed posterior arm muscle; extends elbow.

Pronator teres

Forearm muscle that pronates the forearm.

Brachioradialis

Forearm muscle that flexes elbow and aids in pronation/supination.

Flexor carpi radialis

Anterior forearm muscle; flexes and abducts wrist.

Flexor digitorum superficialis

Anterior forearm; flexes fingers 2-5 at middle phalanges.

Flexor carpi ulnaris

Anterior forearm; flexes and adducts wrist.

Latissimus dorsi

Broad back muscle; extends, adducts, and medially rotates arm.

Rectus abdominis

Straight abdominal muscle; flexes vertebral column.

External oblique

Superficial lateral abdominal muscle; rotates trunk & compresses abdomen.

Tensor fasciae latae

Lateral hip muscle; tenses iliotibial tract & abducts thigh.

Iliopsoas

Combined psoas major + iliacus; primary hip flexor.

Pectineus

Short groin muscle; flexes and adducts thigh.

Adductor longus

Medial thigh muscle; adducts and flexes hip.

Sartorius

Longest muscle; crosses hip & knee, producing flexion & lateral rotation.

Gracilis

Thin medial thigh muscle; adducts thigh and flexes knee.

Rectus femoris

Middle quadriceps muscle; extends knee & flexes hip.

Vastus medialis

Medial quadriceps muscle; extends knee.

Vastus lateralis

Lateral quadriceps muscle; extends knee.

Tibialis anterior

Anterior leg muscle; dorsiflexes and inverts foot.

Fibularis (Peroneus) longus

Lateral leg muscle; everts and plantar-flexes foot.

Gastrocnemius

Calf muscle with two heads; plantar-flexes ankle & flexes knee.

Soleus

Deep calf muscle; plantar-flexes ankle.

Calcaneal (Achilles) tendon

Common tendon of gastrocnemius & soleus inserting on calcaneus.

Trapezius

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

Splenius capitis

Posterior neck muscle; extends & rotates head.

Gluteus maximus

Largest buttock muscle; extends and laterally rotates thigh.

Gluteus medius

Deep to maximus; abducts and medially rotates thigh.

Biceps femoris

Lateral hamstring; extends hip & flexes knee.

Semitendinosus

Superficial medial hamstring; extends hip & flexes knee.

Semimembranosus

Deep medial hamstring; extends hip & flexes knee.

Plantaris

Small posterior leg muscle; weak plantar flexor with long tendon.

Flexor digitorum longus

Deep posterior leg; flexes toes 2-5.