Muscular System

A set of vocabulary flashcards covering key terms from the lecture notes on the Muscular System, including muscle structure, types, attachments, contraction mechanisms, neuromuscular physiology, energy systems, and abdominal anatomy.

Skeletal muscle

Organ of the muscular system composed of muscle tissue, connective tissue, nerves, and blood vessels; attached to bones; voluntary and striated.

Myocyte

Muscle cell; in skeletal muscle these are long, multinucleate cells also called fibers.

Fascicle

Bundle of muscle fibers surrounded by perimysium.

Perimysium

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

Endomysium

Loose connective tissue surrounding each muscle fiber; rich in capillaries and nerves.

Epimysium

Dense irregular connective tissue surrounding the entire muscle; continuous with tendons.

Tendon

Dense regular connective tissue that links muscle to bone and transmits force.

Aponeurosis

Flat, sheet-like tendon for broad attachment of flat muscles.

Origin

Muscle attachment that is less movable (usually proximal) during contraction.

Insertion

Muscle attachment that is more movable (usually distal) during contraction.

Agonist

Muscle primarily responsible for producing a given movement.

Antagonist

Muscle that opposes the action of the agonist.

Synergist

Muscle that assists the agonist by preventing undesired movements.

Flexor

Muscle that decreases the angle of a joint (bends a limb).

Extensor

Muscle that increases the angle of a joint (straightens a limb).

Adductor

Muscle that moves a limb toward the midline.

Abductor

Muscle that moves a limb away from the midline.

Sphincter

Muscle that encircles an opening and constricts it.

Striated

Muscle tissue with visible bands; includes skeletal and cardiac muscle.

Smooth muscle

Non-striated, involuntary muscle; spindle-shaped; lacks T-tubules; Ca++ largely from outside; cells can function as a unit.

Single-unit (visceral) smooth muscle

Most smooth muscle type; cells connected by gap junctions and contract as a unit (peristalsis).

Multiunit smooth muscle

Smooth muscle with individualized innervation and finer control (iris, ciliary body).

Sarcolemma

Plasma membrane of a muscle fiber.

T-tubule

Transverse invagination of the sarcolemma that conducts action potentials into the fiber.

Sarcoplasmic reticulum

Intracellular Ca++ store (endoplasmic reticulum) in muscle fibers.

Triad

Structure consisting of a T-tubule and two terminal cisternae of the sarcoplasmic reticulum; key to excitation-contraction coupling.

Calcium (Ca++)

Ion essential for muscle contraction; binds troponin to allow cross-bridge cycling.

Troponin

Ca++-binding protein on thin filaments that regulates tropomyosin blocking of myosin binding sites.

Tropomyosin

Protein that covers actin binding sites; moved by troponin to expose sites for myosin.

Actin

Thin filament; polymer whose binding sites interact with myosin heads.

Myosin

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

Cross-bridge

Myosin head binding to actin and generating force during the power stroke.

Sliding filament model

Contraction mechanism where myosin heads pull on actin, shortening the sarcomere.

Sarcomere

Functional unit of a striated muscle from one Z-line to the next.

Z-line

Boundary of a sarcomere; anchors actin filaments.

I-band

Region with only thin (actin) filaments; light band.

A-band

Region including thick (myosin) filaments and overlapping thin filaments; dark band.

Troponin-Tropomyosin complex

Regulatory proteins that block or expose myosin-binding sites on actin depending on Ca++.

Excitation-contraction coupling

Process linking an action potential to muscle contraction via Ca++ release from the SR.

Neuromuscular junction

Synapse between a motor neuron and a muscle fiber; releases acetylcholine to trigger depolarization.

Acetylcholine

Neurotransmitter released at the NMJ to stimulate muscle contraction.

Nicotinic acetylcholine receptor

Ligand-gated Na+ channel on the muscle fiber that responds to ACh.

DHPR (dihydropyridine receptor)

Voltage-gated receptor on the T-tubule that triggers Ca++ release from the SR.

Ryanodine receptor (Ca++ release channel)

Ca++ channel on SR that releases Ca++ into the cytoplasm when activated.

ATP

Adenosine triphosphate; energy source for muscle contraction and relaxation.

Creatine phosphate (CP)

Immediate high-energy phosphate reservoir to rapidly regenerate ATP.

Glycogen

Stored glucose in muscle for rapid ATP production via glycolysis.

Glycolysis

Anaerobic breakdown of glucose to pyruvate/lactate to generate ATP.

Oxidative phosphorylation

Aerobic production of ATP in mitochondria via Krebs cycle and electron transport.

Type I fibers

Slow-twitch, oxidative fibers; red (myoglobin-rich); fatigue-resistant.

Type II fibers

Fast-twitch, glycolytic fibers; fatigue-prone; larger diameter.

Motor unit

A motor neuron and all the muscle fibers it innervates.

Recruitment

Activation of additional motor units to increase contraction strength.

Tetanus

Sustained maximal contraction due to high-frequency stimulation with little to no relaxation.

Denervation

Loss of nerve supply to a muscle, leading to neurogenic atrophy.

Neurogenic atrophy

Muscle wasting due to loss of neural input.

Intercalated discs

Cell-to-cell junctions in cardiac muscle that enable synchronized contraction and electrical coupling.

Cardiac muscle

Striated, branched muscle with single or few nuclei and intercalated discs; autonomic control.

Intercostal muscles

Muscles between ribs (external and internal) involved in breathing.

Diaphragm

Primary muscle of respiration; separates thoracic and abdominal cavities.

Linea alba

Midline tendinous seam of the abdominal wall where aponeuroses fuse.

External abdominal oblique

Abdominal wall muscle with fibers running ventrad and caudad; lateral trunk flexion.

Internal abdominal oblique

Abdominal wall muscle with fibers running ventrad and cranial.

Rectus abdominis

Vertical abdominal muscle that flexes the trunk.

Transversus abdominis

Abdominal wall muscle with horizontal fibers; stabilizes the trunk.

Inguinal canal

Slit-like passage in the ventral abdominal wall; transmits spermatic cords or round ligament.

Inguinal ring

Openings in the abdominal wall through which structures pass; related to hernias.