PY3.1-12 | Nerve and Muscle Physiology — Glossary

The functional unit of the nervous system; a specialised cell for generating and transmitting electrical signals, consisting of a cell body (soma), dendrites, axon, and axon terminals

The region of the neuron cell body where the axon begins; contains the highest density of voltage-gated Na+ channels and serves as the trigger zone where action potentials are initiated

An insulating lipid-rich layer formed by Schwann cells (PNS) or oligodendrocytes (CNS) that wraps around axons, enabling saltatory conduction and greatly increasing conduction velocity

The gap between adjacent myelin segments where voltage-gated Na+ channels are concentrated; the site where action potentials are regenerated during saltatory conduction

The electrical potential difference across the cell membrane at rest, typically -70 mV in neurons (inside negative), maintained by K+ leak channels, Na+/K+-ATPase, and trapped intracellular anions

An equation that calculates the equilibrium potential for a single ion species: E = (RT/zF) × ln([ion]outside/[ion]inside); EK = -90 mV, ENa = +60 mV

The Goldman-Hodgkin-Katz equation that calculates the membrane potential accounting for the permeabilities and concentrations of multiple ions (K+, Na+, Cl-); gives the actual RMP of -70 mV

A rapid, all-or-none reversal of membrane potential (from -70 mV to +30 mV and back) lasting 1-2 ms, generated by sequential opening of voltage-gated Na+ and K+ channels

The membrane potential (~-55 mV) at which enough voltage-gated Na+ channels open to create a self-sustaining positive feedback of Na+ influx and depolarisation, triggering an action potential

The period during and immediately after an action potential when voltage-gated Na+ channels are inactivated and no stimulus, regardless of strength, can trigger another AP; ensures unidirectional propagation

The rapid jumping of action potentials from one node of Ranvier to the next in myelinated nerve fibres, achieving conduction velocities up to 120 m/s compared to 0.5-2 m/s in unmyelinated fibres

The junction between two neurons or between a neuron and an effector cell where signal transmission occurs, either electrically (gap junctions) or chemically (neurotransmitter release)

A chemical messenger released from presynaptic vesicles into the synaptic cleft that binds postsynaptic receptors to generate excitatory or inhibitory postsynaptic potentials

Excitatory postsynaptic potential; a graded depolarisation of the postsynaptic membrane caused by Na+ influx through ligand-gated channels, bringing the membrane closer to threshold

Inhibitory postsynaptic potential; a graded hyperpolarisation of the postsynaptic membrane caused by Cl- influx or K+ efflux, moving the membrane away from threshold

The chemical synapse between a motor neuron axon terminal and a skeletal muscle fibre at the motor end plate, using acetylcholine as the neurotransmitter acting on nicotinic receptors

The enzyme in the synaptic cleft that rapidly hydrolyses acetylcholine into choline and acetate, terminating neuromuscular transmission; inhibited by neostigmine (used in myasthenia gravis)

An autoimmune disease caused by antibodies against nicotinic acetylcholine receptors at the NMJ, resulting in progressive skeletal muscle weakness and fatigability; treated with AChE inhibitors

The functional unit of skeletal and cardiac muscle contraction, extending from one Z-line to the next, containing interdigitating thick (myosin) and thin (actin) filaments

The mechanism of muscle contraction where thin filaments slide over thick filaments, shortening the sarcomere without the filaments themselves changing length; driven by myosin cross-bridge cycling

The process linking the electrical signal (action potential in sarcolemma/T-tubules) to the mechanical response (contraction), mediated by Ca2+ release from the sarcoplasmic reticulum

A regulatory protein complex on the thin filament with three subunits: TnC (binds Ca2+), TnI (inhibits actin-myosin binding), TnT (binds tropomyosin); Ca2+ binding to TnC initiates contraction

Sustained maximal muscle contraction resulting from high-frequency stimulation where successive twitches fuse; fused tetanus has no relaxation between stimuli and produces maximum force

Non-striated involuntary muscle in visceral organs and blood vessels that uses calmodulin-MLCK pathway for contraction and can maintain sustained tone efficiently via the latch mechanism

A high-energy phosphate compound in muscle that provides the fastest source of ATP regeneration via the creatine kinase reaction (PCr + ADP → Cr + ATP); fuels the first 8-10 seconds of intense activity