BIOL 2251: Chapter 10 (Muscle Tissue) & Chapter 12 (Neuron Structure & Physiology)

Comprehensive vocabulary flashcards covering the key terms and concepts of Chapter 10 (Muscle Tissue) and Chapter 12 (Neuron Structure & Physiology).

Skeletal Muscle

Striated, voluntary muscle attached primarily to bones; produces rapid, forceful contractions.

Cardiac Muscle

Striated, involuntary muscle found only in the heart.

Smooth Muscle

Nonstriated, involuntary muscle found in walls of hollow organs and blood vessels.

Excitability (Responsiveness)

Ability of a muscle cell to receive and respond to a stimulus.

Contractility

Ability of muscle to shorten forcibly and generate tension.

Extensibility

Ability of muscle tissue to be stretched.

Elasticity

Ability of muscle tissue to recoil toward its resting length after being stretched.

Origin

Attachment of a muscle to the less movable or relatively fixed bone.

Insertion

Attachment of a muscle to the more movable bone.

Tendon

Ropelike connective tissue structure that attaches muscle to bone.

Aponeurosis

Broad, sheetlike connective tissue attachment of a muscle.

Epimysium

Dense connective tissue surrounding the entire skeletal muscle.

Perimysium

Connective tissue surrounding a fascicle.

Endomysium

Fine connective tissue surrounding each individual muscle fiber.

Fascicle

Bundle of skeletal muscle fibers wrapped by perimysium.

Muscle Fiber

A single, elongated muscle cell.

Sarcolemma

The plasma membrane of a muscle fiber.

Sarcoplasm

The cytoplasm of a muscle fiber.

Myofibril

Rod-like contractile structure composed of repeating sarcomeres.

Sarcomere

The functional contractile unit of a myofibril extending from one Z disc to the next.

Z Disc

Boundary of a sarcomere where thin filaments are anchored.

A Band

Dark region that contains the full length of the thick filaments; its length does not change during contraction.

I Band

Light region containing thin filaments only; shortens during contraction.

H Zone

Lighter region in the center of the A band where thin filaments do not overlap thick filaments; narrows or disappears during contraction.

M Line

Protein structure at the center of the sarcomere that stabilizes and aligns thick filaments.

Actin

Major thin-filament protein; contains binding sites for myosin.

Myosin

Major thick-filament protein; myosin heads bind actin and hydrolyze ATP to generate force.

Troponin

Regulatory protein complex that binds $\text{Ca}^{2+}$ and initiates movement of tropomyosin.

Tropomyosin

Regulatory protein that blocks myosin-binding sites on actin in a relaxed muscle fiber.

Titin

Elastic protein that stabilizes thick filaments, helps the sarcomere recoil, and resists overstretching.

Dystrophin

Structural protein that helps link thin filaments to proteins of the sarcolemma.

Sarcoplasmic Reticulum (SR)

Specialized smooth ER that stores, releases, and re-sequesters $\text{Ca}^{2+}$.

Terminal Cisternae

Expanded sacs of the SR located next to a T tubule; major $\text{Ca}^{2+}$ storage/release sites.

T Tubules

Invaginations of the sarcolemma that carry the muscle action potential deep into the fiber.

Triad

One T tubule flanked by two terminal cisternae; key structural unit for excitation-contraction coupling.

Neuromuscular Junction (NMJ)

Synapse between a somatic motor neuron and a skeletal muscle fiber.

Motor End Plate

Specialized region of sarcolemma at the NMJ containing many acetylcholine receptors.

Synaptic Cleft (NMJ)

Narrow fluid-filled space between the motor neuron axon terminal and the muscle fiber.

Synaptic Vesicle (NMJ)

Membrane-bound vesicle in the axon terminal that stores acetylcholine.

Acetylcholine (ACh) [Excitation-Contraction Coupling]

Neurotransmitter released by somatic motor neurons that initiates depolarization of the muscle fiber.

ACh Receptor

Chemically gated receptor/channel on the motor end plate that opens when ACh binds.

Acetylcholinesterase (AChE) [NMJ]

Enzyme in the synaptic cleft that breaks down ACh and helps terminate NMJ signaling.

End-Plate Potential

Local graded depolarization of the motor end plate produced by ACh receptor activation.

Ryanodine Receptors

$\text{Ca}^{2+}$ release channels in the SR that open during excitation-contraction coupling.

Excitation-Contraction Coupling

Sequence linking a muscle action potential to SR $\text{Ca}^{2+}$ release and activation of contraction.

Sliding Filament Model

Muscle contraction occurs as thin filaments slide past thick filaments, increasing overlap without changing filament length.

Cross-Bridge

Connection formed when a myosin head binds to an exposed binding site on actin.

Power Stroke

Pivoting of an attached myosin head that pulls the thin filament toward the M line.

Cross-Bridge Cycle

Repeating sequence of myosin binding, power stroke, ATP-dependent detachment, and ATP hydrolysis/cocking.

ATP in Contraction

ATP is required to detach myosin from actin and to re-energize the myosin head; ATP also supports $\text{Ca}^{2+}$ pumping back into the SR.

Rigor Mortis

Postmortem muscle stiffness caused largely by lack of ATP, preventing cross-bridge detachment.

Isotonic Contraction

Muscle changes length because tension exceeds the load.

Concentric Contraction

Type of isotonic contraction in which the muscle shortens while generating force.

Eccentric Contraction

Type of isotonic contraction in which the muscle lengthens while still generating force.

Isometric Contraction

Muscle develops tension without appreciable change in length.

Motor Unit

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

Recruitment (Multiple Motor Unit Summation)

Increasing force by activating additional motor units.

Size Principle

Smaller motor units are recruited first; progressively larger motor units are added as more force is required.

Muscle Twitch

Brief contraction-relaxation response of a muscle fiber to a single action potential.

Latent Period

Brief interval between stimulation and development of measurable tension; excitation-contraction coupling occurs here.

Contraction Period

Phase of a twitch during which cross-bridge activity increases tension.

Relaxation Period

Phase of a twitch during which $\text{Ca}^{2+}$ returns to the SR and tension falls.

Wave Summation

Increased tension when a second stimulus arrives before the muscle has completely relaxed from the first.

Incomplete (Unfused) Tetanus

Sustained but fluctuating contraction caused by high-frequency stimulation with partial relaxation between stimuli.

Tetanus / Fused Tetanus

Smooth, sustained maximal contraction produced when stimuli arrive so rapidly that relaxation disappears.

Threshold Stimulus

Minimum stimulus strength that produces the first observable contraction.

Maximal Stimulus

Stimulus strength at which all recruitable motor units are active and no further increase in force occurs.

Length-Tension Relationship

Relationship between sarcomere length and force; force is greatest when thick and thin filament overlap is near optimal.

Muscle Tone

Continuous low-level contraction produced by alternating motor unit activity; helps maintain readiness and posture.

Muscle Fatigue

Physiological inability to maintain contraction despite continued stimulation.

Slow Oxidative Fibers

Slow, fatigue-resistant fibers rich in mitochondria, capillaries, and myoglobin; specialized for endurance and posture.

Fast Oxidative Fibers

Fast fibers with substantial aerobic capacity and intermediate fatigue resistance; suited for moderate-intensity activity.

Fast Glycolytic Fibers

Fast, powerful fibers relying heavily on anaerobic glycolysis; fatigue relatively quickly.

Hypertrophy

Increase in muscle fiber size with repeated loading or training.

Excess Postexercise Oxygen Consumption (EPOC)

Elevated oxygen use after exercise that supports restoration of ATP/creatine phosphate, oxygen stores, and other recovery processes.

Sensory Input

Information gathered by sensory receptors about changes inside or outside the body.

Integration

Processing and interpretation of sensory information by the nervous system.

Motor Output

Activation of effectors, such as muscles and glands, to produce a response.

Central Nervous System (CNS)

Brain and spinal cord; major integration and control center.

Peripheral Nervous System (PNS)

Nervous system structures outside the CNS, especially nerves and ganglia.

Sensory (Afferent) Division

PNS division that carries information from receptors toward the CNS.

Motor (Efferent) Division

PNS division that carries commands from the CNS to effectors.

Somatic Nervous System

Motor division that controls skeletal muscle; commonly associated with voluntary control.

Autonomic Nervous System (ANS)

Motor division that regulates cardiac muscle, smooth muscle, and glands.

Nuclei

Clusters of neuron cell bodies within the CNS.

Ganglia

Clusters of neuron cell bodies within the PNS.

Tracts

Bundles of axons within the CNS.

Nerves

Bundles of axons within the PNS.

Gray Matter

CNS regions containing many neuron cell bodies, dendrites, and nonmyelinated processes.

White Matter

CNS regions containing dense collections of myelinated axons.

Neuron

Excitable cell specialized to receive, process, and transmit electrical and chemical signals.

Cell Body (Soma/Perikaryon)

Biosynthetic and metabolic center of the neuron; contains the nucleus and most organelles.

Dendrites

Receptive processes that receive incoming signals and conduct graded potentials toward the cell body.

Axon

Conductive process that carries action potentials away from the cell body.

Axon Hillock

Cone-shaped region where the axon begins; graded potentials are integrated near this region.

Axon Collateral

Branch extending from the main axon.

Axon Terminal (Terminal Bouton/Synaptic Knob)

Distal ending of an axon that releases neurotransmitter.

Axolemma

Plasma membrane of the axon.

Synapse

Junction where a neuron communicates with another neuron or an effector cell.

Presynaptic Neuron

Cell that sends information toward a synapse.