Anatomy Lesson 4 – The Muscular System

Vocabulary flashcards summarizing key terms, structures, movements, and representative muscles from the lecture on the human muscular system.

Excitability

Capacity of a muscle fiber to respond to stimulation.

Contractility

Ability of muscle cells to generate tension and shorten when stimulated.

Elasticity

Muscle’s tendency to recoil to resting length after contraction or stretch.

Extensibility

Capability of a muscle cell to lengthen in response to opposing force.

Body Movement (muscle function)

Skeletal muscles pull on bones to create voluntary motion.

Maintenance of Posture

Continuous contraction of skeletal muscles that keeps the body upright.

Temperature Regulation

Heat produced by muscle contractions helps maintain body temperature.

Storage and Movement of Materials

Skeletal muscles regulate passage of substances by sphincters.

Support (muscle function)

Muscles stabilize and protect soft organs.

Fascia

Sheet of connective tissue separating, supporting and binding muscles.

Superficial Fascia

Areolar & adipose layer beneath skin that separates it from muscles.

Deep Fascia

Dense irregular connective tissue that envelops and groups muscles with similar functions.

Epimysium

Connective tissue layer surrounding an entire skeletal muscle.

Perimysium

Connective tissue sheath surrounding a fascicle (bundle) of muscle fibers.

Endomysium

Innermost delicate connective tissue surrounding each muscle fiber.

Fascicle

Bundle of skeletal muscle fibers within a muscle.

Sarcolemma

Plasma membrane of a muscle fiber.

Sarcoplasm

Cytoplasm of a muscle cell.

Transverse (T) Tubules

Invaginations of sarcolemma that conduct action potentials into the cell interior.

Sarcoplasmic Reticulum

Smooth-ER-like organelle that stores and releases Ca²⁺ for contraction.

Myofibril

Cylindrical contractile organelle composed of myofilaments inside a muscle fiber.

Myofilament

Protein filament (actin or myosin) that slides to produce contraction.

Actin

Protein forming the bulk of thin filaments in skeletal muscle.

Myosin

Motor protein forming thick filaments that pull on actin.

Sarcomere

Smallest functional contractile unit of a muscle fiber.

Motor Unit

Single motor neuron and all skeletal muscle fibers it innervates.

Origin (muscle)

Fixed, usually proximal attachment of a muscle to bone.

Insertion (muscle)

Movable, usually distal attachment pulled toward the origin.

Belly (muscle)

Thick central portion of a muscle between origin and insertion.

Tendon

Dense regular connective tissue cord connecting muscle to bone.

Aponeurosis

Broad sheet-like tendon connecting muscle to bone or other muscles.

Axial Muscles

Muscles that move the head, neck and trunk and support visceral organs.

Appendicular Muscles

Muscles that move the limbs and stabilize pectoral & pelvic girdles.

Flexion

Angular movement decreasing the joint angle; brings bones closer.

Extension

Angular movement increasing joint angle; straightens articulating bones.

Hyperextension

Extension of a joint beyond 180°.

Lateral Flexion

Bending trunk or neck away from midline in coronal plane.

Abduction

Movement of a limb away from the midline; “to take away.”

Adduction

Movement toward the midline; “to bring together.”

Circumduction

Distal end of limb moves in a circle combining flexion, extension, abduction & adduction.

Rotation

Bone revolves around its longitudinal axis.

Pronation

Forearm rotation so palm faces posteriorly (prone position).

Supination

Forearm rotation so palm faces anteriorly (supine position).

Elevation

Lifting a body part superiorly.

Depression

Moving a body part inferiorly.

Protraction

Anterior movement in the transverse plane (e.g., jutting jaw forward).

Retraction

Posterior movement back to anatomical position.

Inversion

Turning sole of foot medially; weight on outer edge.

Eversion

Turning sole laterally; weight on inner edge.

Dorsiflexion

Lifting foot so superior surface approaches shin.

Plantar Flexion

Pointing foot downward (standing on tip-toes).

Opposition

Thumb movement across palm to touch fingertips.

Gliding Movement

Sliding motion between flat bone surfaces as in carpal joints.

Excitation–Contraction Coupling

Sequence linking muscle fiber excitation to actin–myosin sliding and force generation.

Sliding Filament Theory

Model describing how myofilaments slide past each other to shorten sarcomeres.

Calcium (role in contraction)

Ion released from SR that binds troponin, enabling actin–myosin cross-bridging.

Muscle Action (nomenclature)

Naming criterion referring to primary movement a muscle produces (e.g., flexor).

Specific Body Region (nomenclature)

Muscle name indicating region it occupies (e.g., femoris on thigh).

Muscle Attachments (nomenclature)

Names that include origin and/or insertion sites (e.g., sternocleidomastoid).

Orientation of Fibers (nomenclature)

Names describing fiber direction, e.g., rectus (straight).

Shape and Size (nomenclature)

Names referencing form—deltoid (triangle), maximus (large), brevis (short).

Heads/Tendons of Origin (nomenclature)

Names indicating number of origins, e.g., biceps (2), triceps (3).

Sternocleidomastoid

Neck muscle originating on sternum & clavicle, inserting on mastoid; flexes and rotates head.

Trapezius

Large superficial back muscle that elevates, retracts & rotates scapula and extends neck.

Deltoid

Shoulder muscle that abducts arm and assists in flexion and extension.

Latissimus Dorsi

Broad back muscle extending, adducting & medially rotating the arm.

Pectoralis Major

Chest muscle flexing, adducting & medially rotating humerus.

Supraspinatus

Rotator-cuff muscle that abducts arm and stabilizes shoulder joint.

Infraspinatus

Rotator-cuff muscle that laterally rotates arm and stabilizes shoulder.

Subscapularis

Rotator-cuff muscle that medially rotates arm and stabilizes shoulder.

Teres Minor

Rotator-cuff muscle that laterally rotates & adducts arm; shoulder stabilizer.

Quadriceps Femoris

Group of four anterior thigh muscles extending the knee.

Hamstrings

Posterior thigh muscles (biceps femoris, semitendinosus, semimembranosus) that flex knee & extend hip.

Gastrocnemius

Superficial calf muscle that plantar-flexes foot and flexes knee.

Soleus

Deep calf muscle that plantar-flexes foot; postural when standing.

Tibialis Anterior

Anterior leg muscle dorsiflexing and inverting foot.

Fibularis (Peroneus) Longus

Lateral leg muscle everting and plantar-flexing foot.

Diaphragm

Primary muscle of inhalation; depresses floor of thorax.

External Intercostals

Muscles between ribs that elevate ribs during quiet inspiration.

Internal Intercostals

Muscles that depress ribs during forced expiration.

Rectus Abdominis

Anterior abdominal muscle flexing vertebral column and compressing abdomen.

External Abdominal Oblique

Superficial abdominal muscle involved in trunk flexion, rotation & compression.

Motor Nerve

Nerve carrying impulses from CNS to muscles to initiate contraction.

Selective Contraction

Ability to activate specific motor units for graded force production.