Nerve Impulses and Synaptic Transmission

Myelinated nerve fibre

Nerve fibre with insulating myelin sheath.

Unmyelinated fibres

Nerve fibres lacking myelin sheath.

Dendrites

Short processes receiving impulses towards cell bodies.

Action potential

Electrical impulse traveling along nerve cells.

Resting membrane potential

Polarized state of nerve cell membrane.

Sodium (Na+)

Main extracellular cation in nerve cells.

Potassium (K+)

Main intracellular cation in nerve cells.

Depolarisation

Rapid influx of Na+ causing nerve impulse.

Repolarisation

Return of membrane potential to resting state.

Refractory period

Time during which restimulation is not possible.

Sodium-potassium pump

Transport mechanism restoring Na+ and K+ balance.

Nodes of Ranvier

Gaps in myelin sheath for ion movement.

Saltatory conduction

Impulse jumps between nodes, speeding transmission.

Continuous conduction

Impulse travels along entire unmyelinated fibre.

Diameter of neurone

Larger diameter increases conduction speed.

Fastest conduction speed

Up to 130 m/s in myelinated fibres.

Slowest conduction speed

As low as 0.5 m/s in unmyelinated fibres.

Synapse

Junction between presynaptic and postsynaptic neurones.

Synaptic knobs

Terminal boutons releasing neurotransmitters.

Synaptic cleft

Space between presynaptic and postsynaptic neurones.

Neurotransmitters

Chemicals transmitting signals across synapses.

Exocytosis

Process of neurotransmitter release into synaptic cleft.

Receptor sites

Locations on postsynaptic membrane for neurotransmitter binding.

Enzymatic inactivation

Process of neurotransmitter breakdown after action.

Noradrenaline

Neurotransmitter involved in arousal and alertness.

Adrenaline

Hormone and neurotransmitter for fight-or-flight response.

Dopamine

Neurotransmitter linked to pleasure and reward.

Serotonin

Regulates mood, sleep, and appetite.

GABA

Inhibitory neurotransmitter reducing neuronal excitability.

Acetylcholine

Neurotransmitter at neuromuscular junctions.

Enkephalins

Neuropeptides involved in pain modulation.

Endorphins

Natural painkillers released during stress.

Substance P

Neurotransmitter involved in pain transmission.

Somatic nerves

Carry impulses to skeletal muscles.

Neuromuscular junctions

Synapses between motor neurones and muscles.

Autonomic nervous system

Controls involuntary body functions.

Preganglionic neurone

First neurone in autonomic pathway.

Postganglionic neurone

Second neurone in autonomic pathway.

Efferent impulses

Nerve signals traveling away from the CNS.

Nerve structure

Bundles of neurones with protective coverings.

Tracts

Bundles of nerve fibres in CNS.

Sciatic nerve

Largest nerve in the human body.