Muscular System - Anatomy and Physiology

Vocabulary flashcards covering muscular system concepts, structural anatomy, physiological processes, and major muscle groups from Chapter 7 of Seeley's Essentials of Anatomy & Physiology.

Skeletal Muscle

A type of striated muscle attached to bones that is under voluntary control and constitutes approximately $40\%$ of body weight.

Cardiac Muscle

A type of striated muscle located in the heart that is involuntarily controlled and autorhythmic.

Smooth Muscle

A type of non-striated muscle located in blood vessels and hollow organs that is involuntarily controlled.

Contractility

The ability of a muscle to shorten forcefully, or contract.

Excitability

The capacity of a muscle to respond to a stimulus.

Extensibility

The ability of a muscle to be stretched beyond its normal resting length and still be able to contract.

Elasticity

The ability of a muscle to recoil to its original resting length after being stretched.

Epimysium

The connective tissue sheath that surrounds an entire skeletal muscle.

Fascicles

Subdivided groups of muscle cells within a skeletal muscle.

Perimysium

The connective tissue covering that surrounds each muscle fascicle.

Endomysium

The connective tissue covering surrounding an individual muscle fiber (cell).

Sarcolemma

The cell membrane of a skeletal muscle fiber.

Transverse Tubules (T tubules)

Tubelike inward folds of the sarcolemma occurring at regular intervals that extend into the center of the muscle fiber.

Sarcoplasmic Reticulum

Enlarged smooth endoplasmic reticulum in a muscle fiber that stores a high concentration of $\text{Ca}^{2+}$, playing a major role in muscle contraction.

Terminal Cisternae

Enlarged portions of the sarcoplasmic reticulum associated with T tubules.

Muscle Triad

A structure formed by a T tubule connecting to two adjacent terminal cisternae.

Sarcoplasm

The cytoplasm of a skeletal muscle fiber.

Myofibrils

Bundles of protein filaments (myofilaments) running through the sarcoplasm, composed of actin and myosin.

Sarcomere

The basic structural and functional unit of a skeletal muscle capable of contracting, extending from one Z disk to the next.

Z Disks

A network of protein fibers that serves as an anchor for actin myofilaments and separates one sarcomere from the next.

I Bands

Light-staining bands in a sarcomere consisting only of actin myofilaments.

A Bands

Dark-staining bands in a sarcomere that extend the full length of the myosin myofilaments.

Actin Myofilament

Thin myofilaments composed of actin strands, troponin (with binding sites for $\text{Ca}^{2+}$), and tropomyosin (blocking myosin binding sites).

Myosin Myofilament

Thick myofilaments resembling bundles of tiny golf clubs, whose heads contain ATP binding sites, ATPase activity, and actin attachment spots.

Resting Membrane Potential

The electrical charge difference across the cell membrane of an unstimulated cell, inside negative relative to the outside.

Depolarization

An increase in positive charge inside the cell membrane caused by the influx of $\text{Na}^+$ down its concentration gradient.

Threshold

The specific membrane potential value that depolarization must reach to trigger an action potential.

Action Potential

A rapid change in electrical charge across the cell membrane that triggers a muscle contraction.

Repolarization

The return of the membrane potential to resting conditions caused by the closure of gated $\text{Na}^+$ channels and outward diffusion of $\text{K}^+$.

Motor Neuron

A nerve cell that stimulates muscle cells.

Neuromuscular Junction

The specialized synapse where an axon fiber of a nerve connects with a muscle fiber.

Synapse

A cell-to-cell junction between a nerve cell and another nerve cell or effector cell (e.g., muscle or gland).

Motor Unit

A group of muscle fibers stimulated by a single motor neuron.

Presynaptic Terminal

The enlarged distal end of a neuron cell axon fiber at a synapse.

Synaptic Cleft

The microscopic space separating the presynaptic terminal from the postsynaptic membrane.

Postsynaptic Membrane

The specialized region of the muscle fiber membrane (sarcolemma) at the neuromuscular junction.

Synaptic Vesicle

A membrane-bound vesicle in the presynaptic terminal storing chemical neurotransmitters.

Neurotransmitter

A chemical agent released by a presynaptic terminal to stimulate or inhibit a postsynaptic cell.

Acetylcholine (ACh)

The specific neurotransmitter that stimulates skeletal muscle fibers.

Acetylcholinesterase

An enzyme that breaks down acetylcholine in the synaptic cleft, closing $\text{Na}^+$ channels and terminating muscle contraction.

Rigor Mortis

Rigidity in muscles occurring after death because no ATP is available to release myosin heads from actin cross-bridges.

Cross-Bridge Movement

The sequence where myosin heads bind exposed actin sites, undergo a power stroke to slide actin filaments, bind ATP to release, and hydrolyze ATP during the recovery stroke.

Muscle Twitch

A single contraction of a muscle fiber in response to a stimulus, consisting of lag (latent), contraction, and relaxation phases.

Lag Phase

The brief time period between the application of a stimulus and the onset of muscle contraction.

Summation

Process by which individual muscle twitches combine to generate a more forceful overall muscle contraction.

Tetanus

A sustained, steady muscle contraction produced when the frequency of stimulation is rapid enough that no relaxation occurs between stimuli.

Recruitment

The activation of additional motor units to produce greater muscle force.

Slow Twitch Fibers

Muscle fibers that contract and fatigue slowly, contain abundant myoglobin, utilize aerobic respiration, are dark in color, and excel in endurance activities.

Fast Twitch Fibers

Muscle fibers that contract and fatigue quickly, rely on anaerobic respiration and glycogen, are light in color, and excel in sprinting.

Muscle Fatigue

A temporary state of reduced work capacity caused by factors like acidosis, ATP depletion, oxidative stress, and local inflammatory reactions.

Isometric Contraction

A muscle contraction in which muscle tension increases while muscle length remains constant.

Isotonic Contraction

A muscle contraction in which muscle length changes while tension remains constant.

Concentric Contraction

An isotonic contraction in which muscle tension increases as the muscle shortens.

Eccentric Contraction

An isotonic contraction in which tension is maintained while an opposing force causes the muscle to lengthen.

Muscle Tone

The constant baseline tension maintained by muscles over long periods of time, responsible for posture.

Intercalated Disks

Specialized cell junctions in cardiac muscle containing desmososomes and gap junctions that allow direct electrical communication.

Tendon

A cordlike band of connective tissue that attaches muscle to bone.

Aponeuroses

Broad, sheetlike tendons that attach muscles to bones or neighboring structures.

Retinaculum

A band of connective tissue holding down tendons at the wrist or ankle.

Origin

The fixed or least mobile attachment site of a skeletal muscle.

Insertion

The movable end of a muscle attached to the bone undergoing the greatest movement.

Belly

The central, fleshy part of a muscle located between its origin and insertion.

Agonists

A group of muscles working together to accomplish a primary body movement.

Antagonists

A muscle or group of muscles that oppose specific action movements.

Diaphragm

The primary thoracic muscle responsible for quiet breathing.

Quadriceps Femoris

A four-part anterior thigh muscle group composed of rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.