Muscular and Nervous Systems Study Guide

Comprehensive vocabulary flashcards covering skeletal muscle organization, excitation-contraction coupling, levers, neuroglia, membrane potentials, neurotransmission, brain regions, and spinal cord pathways based on the Muscular and Nervous Systems study guide.

Epimysium

Dense irregular connective tissue surrounding the entire skeletal muscle.

Perimysium

Fibrous connective tissue surrounding individual muscle bundles called fascicles.

Endomysium

A fine sheath of loose connective tissue (reticular fibers) surrounding each individual muscle cell (fiber).

Sarcolemma

The plasma membrane of a muscle fiber.

Sarcoplasm

The cytoplasm of a muscle fiber containing myoglobin for oxygen storage and glycosomes for glycogen storage.

Sarcoplasmic Reticulum (SR)

Smooth endoplasmic reticulum specialized for storing and releasing $Ca^{2+}$, characterized by paired terminal cisternae.

Triad

A structural unit at skeletal muscle A-I junctions consisting of one central T-tubule flanked on both sides by two terminal cisternae of the sarcoplasmic reticulum.

Sarcomere

The functional contractile unit of striated muscle extending from one Z-disc to the next Z-disc.

Tropomyosin

A regulatory muscle protein that physically blocks the myosin-binding sites on actin myofilaments in a resting muscle fiber.

Troponin

A three-subunit protein complex on thin filaments that binds $Ca^{2+}$ (troponin C), binds tropomyosin (troponin T), and binds actin (troponin I) to inhibit myosin binding.

Motor Unit

A single motor neuron and all individual muscle fibers it innervates.

Latent Period

The brief time interval immediately following stimulus application at a skeletal muscle cell during which acetylcholine diffuses across the synaptic cleft and excitation-contraction coupling occurs before tension develops.

Muscle Tone

A state of sustained, involuntary partial contraction of resting skeletal muscles maintained by spinal reflexes.

Isotonic Concentric Contraction

A muscle contraction where the muscle generates force while shortening to move a load.

Isotonic Eccentric Contraction

A muscle contraction where the muscle generates force while lengthening against a load.

Creatine Kinase

The enzyme that catalyzes the rapid reversible transfer of a high-energy phosphate group from creatine phosphate to ADP, regenerating ATP during early exertion.

Excess Post-Exercise Oxygen Consumption (EPOC)

The extra volume of oxygen required post-exercise to restore myoglobin, resynthesize ATP and creatine phosphate, and convert lactic acid back to glucose in the liver.

Calmodulin

A calcium-binding regulatory protein utilized in smooth muscle that activates myosin light chain kinase (MLCK) when bound to $Ca^{2+}$.

Myosin Light Chain Kinase (MLCK)

An enzyme activated by $Ca^{2+}$-calmodulin in smooth muscle that phosphorylates myosin heads to initiate cross-bridge cycling.

First-Class Lever

A lever system where the fulcrum is located between the effort and the load (E-F-L), exemplified by backward neck extension.

Second-Class Lever

A lever system where the load lies between the fulcrum and the effort (F-L-E), consistently operating at a mechanical advantage ($\text{MA} > 1$), exemplified by standing on tiptoes.

Third-Class Lever

A lever system where the effort is applied between the fulcrum and the load (F-E-L), operating at a mechanical disadvantage for force ($\text{MA} < 1$) but enabling rapid, large-range movements.

Rigor Mortis

Post-mortem muscle stiffening caused by the cessation of ATP synthesis, which prevents active pumping of $Ca^{2+}$ into the SR and prevents myosin heads from detaching from actin until protein structures degrade ($3-4\,\text{days}$).

Astrocytes

The most abundant CNS neuroglia; they form blood-brain barrier perivascular feet and regulate extracellular chemical balance by mopping up excess potassium ions ($K^+$).

Microglia

Resident macrophage neuroglial cells of the CNS that phagocytize microbes and cellular debris.

Ependymal Cells

Ciliated CNS neuroglial cells lining the brain ventricles and central canal that produce and circulate cerebrospinal fluid (CSF).

Oligodendrocytes

Neuroglial cells that form insulating myelin sheaths around multiple axon segments within the Central Nervous System.

Schwann Cells

Neuroglial cells that form myelin sheaths around individual axons in the Peripheral Nervous System and guide nerve fiber regeneration.

Satellite Cells

PNS neuroglial cells that surround and support neuron cell bodies within ganglia.

Nissl Bodies

Dense aggregates of rough endoplasmic reticulum and free ribosomes (chromatophilic substance) in the neuron soma dedicated to protein synthesis.

Kinesin

The motor protein responsible for driving anterograde axonal transport from the neuronal cell soma toward the axon terminal.

Dynein

The motor protein responsible for driving retrograde axonal transport from the axon terminal back to the cell soma.

Resting Membrane Potential (RMP)

The baseline electrical potential of $-70\,\text{mV}$ across a resting neuronal membrane, generated primarily by $K^+$ leakage out of the cell and maintained by the $Na^+/K^+$ ATPase pump.

Absolute Refractory Period

The period following an action potential when voltage-gated $Na^+$ channels are inactivated, preventing the generation of another action potential and enforcing unidirectional propagation.

Relative Refractory Period

The interval after the absolute refractory period during which voltage-gated $K^+$ channels remain open and the membrane is hyperpolarized, requiring a larger-than-normal stimulus to reach threshold.

Saltatory Conduction

The fast mode of nerve impulse transmission in myelinated axons, characterized by action potentials jumping between consecutive Nodes of Ranvier.

Excitatory Postsynaptic Potential (EPSP)

A local, graded depolarization of the postsynaptic membrane caused by the influx of $Na^+$ through chemically gated ion channels.

Inhibitory Postsynaptic Potential (IPSP)

A local, graded hyperpolarization of the postsynaptic membrane caused by $Cl^-$ influx or $K^+$ efflux, moving the potential further away from threshold.

Temporal Summation

The addition of postsynaptic potentials occurring when a single presynaptic axon fires impulses in rapid succession onto a postsynaptic neuron.

Spatial Summation

The addition of postsynaptic potentials occurring when multiple distinct presynaptic terminals fire simultaneously at different locations on the postsynaptic neuron.

Ionotropic Receptor

A ligand-gated ion channel receptor that opens directly upon neurotransmitter binding to produce rapid, brief postsynaptic potentials.

Metabotropic Receptor

A G-protein coupled neurotransmitter receptor that operates via intracellular second messenger cascades to trigger slower, long-lasting modulatory effects.

Gamma-Aminobutyric Acid (GABA)

The principal inhibitory amino acid neurotransmitter in the brain.

Precentral Gyrus

The cortical ridge of the frontal lobe that contains the primary motor cortex and pyramidal Betz cells, controlling skilled voluntary movements.

Postcentral Gyrus

The cortical ridge of the parietal lobe that houses the primary somatosensory cortex, which receives and processes general sensory inputs.

Broca's Area

A motor speech area located in the inferior frontal gyrus (typically of the left hemisphere) that coordinates the muscular movements required for speech production.

Wernicke's Area

A cortical association region located in the temporal and parietal lobes (typically of the left hemisphere) that coordinates language comprehension.

Thalamus

A diencephalic structure that functions as the primary sensory relay gateway, sorting, editing, and routing sensory information to the cerebral cortex.

Hypothalamus

The primary visceral and autonomic control center of the diencephalon, regulating body temperature, thirst, hunger, sleep-wake cycles, and pituitary endocrine function.

Epithalamus

The dorsal posterior component of the diencephalon that houses the pineal gland, which secretes melatonin to regulate sleep-wake patterns.

Corpora Quadrigemina

Four midbrain dorsal protrusions comprising the superior colliculi (visual reflex centers) and the inferior colliculi (auditory reflex centers).

Substantia Nigra

A midbrain nucleus containing dopamine-releasing neurons whose degeneration leads to the motor manifestations of Parkinson's disease.

Medulla Oblongata

The inferior brainstem segment containing pyramidal decussation along with vital regulatory centers for heart rate, blood pressure, and basic respiratory rhythm.

Decussation of Pyramids

The crossover point of approximately $85\text{–}90\%$ of descending corticospinal motor fibers located on the anterior inferior surface of the medulla oblongata.

Reticular Activating System (RAS)

A functional brainstem network that filters sensory inputs and maintains cerebral cortex wakefulness, alertness, and consciousness.

Arbor Vitae

The distinctive tree-like branching pattern of inner white matter observed in a sagittal section of the cerebellum.

Purkinje Cells

Large, highly branched neurons in the cerebellar cortex that provide the sole inhibitory (GABAergic) output for precise motor coordination.

Conus Medullaris

The tapered, cone-shaped inferior termination of the spinal cord proper, situated at the $L_1-L_2$ vertebral level.

Filum Terminale

A delicate fibrous extension of the pia mater that extends from the conus medullaris to anchor the spinal cord to the coccyx.

Cauda Equina

The collection of spinal nerve roots situated within the subarachnoid space inferior to the conus medullaris below the $L_2$ level.

Lateral Spinothalamic Tract

An ascending spinal tract that decussates in the spinal cord and transmits pain and temperature sensations to the somatosensory cortex.

Direct (Corticospinal) Pathway

A descending motor pathway originating from pyramidal neurons in the precentral gyrus that transmits signals for skilled, voluntary skeletal muscle movements.