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A vocabulary set of key terms and their concise definitions based on the lecture notes.
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Neuron
Basic structural unit of the nervous system; has a cell body (soma), dendrites, and an axon; the same basic structure is found throughout the body.
Soma (cell body)
Contains the nucleus; from it radiate dendrites and the axon.
Dendrites
Receivers of impulses; carry impulses toward the cell body.
Axon
conducts impulses away from the cell body; begins at the axon hillock and ends at axon terminals with neurotransmitters.
Axon hillock
Region where the axon begins and where action potentials are typically initiated.
Resting membrane potential (RMP)
Difference in electrical charge across the cell membrane, about −70 mV; polarized due to ion distribution.
Sodium (Na+) and potassium (K+) gradients
High Na+ outside, high K+ inside; Na+ channels closed at rest, K+ channels open, contributing to RMP.
Sodium-potassium pump (Na+/K+ pump)
Maintains gradients by moving 3 Na+ out and 2 K+ in, contributing to resting membrane potential.
Depolarization
Inside of the cell becomes less negative (−70 mV toward 0 mV); Na+ influx initiates the process.
Hyperpolarization
Inside of the cell becomes more negative (toward −90 mV); K+ efflux makes it harder to fire another impulse.
Threshold
Critical membrane potential (~−55 mV) that must be reached to trigger an action potential.
Graded potentials
Localized changes in membrane potential that can be excitatory (depolarizing) or inhibitory (hyperpolarizing) and influence whether an AP occurs.
Action potential (AP)
Rapid, large depolarization that travels along the axon; lasts about 1 ms; follows the all-or-none rule.
Absolute refractory period
During depolarization when Na+ channels are inactivated; neuron cannot fire another AP.
Relative refractory period
During repolarization when a stronger stimulus is needed; Na+ channels may reopen and K+ channels remain open.
Myelin
Fatty sheath around axons (produced by Schwann cells) that speeds conduction; segmented by nodes of Ranvier.
Saltatory conduction
Propagation of an AP by jumping from node to node across myelinated segments.
Nodes of Ranvier
Gaps in the myelin sheath where the axon is exposed; sites of rapid AP regeneration.
Propagation speed
Increases with larger axon diameter and with myelination.
Synapse
Junction between neurons where the AP is transmitted; transmission can be electrical to chemical to electrical.
Presynaptic neuron
Neuron sending the signal; contains synaptic vesicles with neurotransmitters.
Postsynaptic neuron
Neuron receiving the signal; has receptors for neurotransmitters.
Synaptic cleft
The gap between the presynaptic and postsynaptic membranes.
Neurotransmitters
Chemical messengers; >50 known; include small-molecule transmitters and neuropeptides; include acetylcholine and norepinephrine.
Acetylcholine (ACh)
Neurotransmitter at the neuromuscular junction; excitatory and mediates parasympathetic effects.
Neuromuscular junction (NMJ)
Specialized synapse between a motor neuron and a muscle; ACh is released and causes muscle depolarization.
Motor end plate
Postsynaptic region of the muscle fiber at the NMJ where ACh receptors are located.
Excitatory postsynaptic potential (EPSP)
Depolarizing postsynaptic potential that makes an AP more likely; summation can trigger an AP.
Inhibitory postsynaptic potential (IPSP)
Hyperpolarizing postsynaptic potential that makes an AP less likely; summation can prevent an AP.
Sensory division (afferent)
Transmits information from the periphery to the brain; major receptor types include mechanoreceptors, thermoreceptors, nociceptors, photoreceptors, chemoreceptors.
Mechanoreceptors
Receptors sensitive to physical forces such as touch, pressure, and stretch.
Thermoreceptors
Receptors sensitive to temperature changes.
Nociceptors
Pain receptors.
Photoreceptors
Receptors sensitive to light (in the visual system).
Chemoreceptors
Receptors sensitive to chemical stimuli (e.g., changes in blood or tissue chemistry).
Muscle spindle
Intrafusal fibers sense muscle length and rate of length change; innervated by gamma motor neurons; trigger reflexes and contribute to force production.
Golgi tendon organ
Tendon-tension receptor; inhibits agonists and excites antagonists to prevent injury during high tension.
Kinesthetic receptors (joint receptors)
Joint receptors sensitive to joint angles and the rate of angle change; sense joint position.
Gamma motor neurons
Innervate intrafusal fibers to adjust spindle sensitivity.
Alpha motor neurons
Innervate extrafusal muscle fibers to generate contraction.
Motor unit
A motor neuron and all the muscle fibers it innervates; fiber numbers per unit affect fine versus gross motor control; fibers within a unit are of the same type.
Primary motor cortex
Frontal lobe region responsible for conscious control of skeletal muscle movement; corticospinal tract involvement.
Basal ganglia
Deep cerebral structures that help initiate and regulate sustained or repetitive movements and posture.
Primary sensory cortex
Parietal lobe area responsible for processing somatosensory information.
Thalamus
Major sensory relay center; contributes to conscious awareness of sensory input.
Hypothalamus
Maintains homeostasis; regulates visceral functions; controls neuroendocrine activity (appetite, thirst, sleep, BP, HR, breathing, temperature).
Cerebellum
Coordinates rapid, complex movements; refines timing, sequence, and motor corrections; integrates input from motor cortex.
Brain stem
Midbrain, pons, and medulla oblongata; houses reticular formation for motor tone and autonomic control; contains analgesia system.
Spinal cord
Continues from the medulla; contains ascending (sensory) and descending (motor) tracts for two-way conduction.
Central nervous system (CNS)
Brain and spinal cord.
Peripheral nervous system (PNS)
All nerves outside the CNS; connects CNS to limbs and organs; includes sensory and motor divisions.
Somatic nervous system
Voluntary nervous system; controls skeletal muscles.
Autonomic nervous system
Involuntary nervous system; regulates visceral functions; has sympathetic and parasympathetic divisions.
Sympathetic nervous system
Fight-or-flight response; increases heart rate and force, blood flow to muscles, bronchodilation, metabolic rate, and mental activity.
Parasympathetic nervous system
Rest-and-digest actions; promotes digestion and energy conservation; generally decreases heart rate and may constrict bronchi.
PGC-1α (peroxisome proliferator–activated receptor-γ coactivator 1α)
A transcriptional coactivator upregulated with exercise; associated with NMJ adaptations such as increased presynaptic branching and acetylcholine receptor density.
Reflex activity
A motor reflex is an instant, preprogrammed response to a stimulus; occurs without conscious awareness and is mediated at lower, simple levels of the CNS.
Afferent feedback (Group III/IV)
Group III: thinly myelinated mechanosensitive fibers; Group IV: unmyelinated, chemically sensitive; convey signals to CNS to aid performance and fatigue management.