#nervefiber

Chemical Synapse

Action potential travels down axon of presynaptic neuron

Vesicle fuses with plasma membrane and releases neurotransmitter into the synaptic cleft

Neurotransmitters bind to ligand-gated ion channels, opening them

Ions entering through the open channels cause a depolarization of the membrane, opening voltage-gated ion channels

Ions pass through these voltage-gated ion channels, causing further depolarization of the membrane

This depolarization (action potential) travels along the membrane as more voltage-gated ion channels are opened

Electrical Synapse

Cytoplasms of adjacent neurons are connected, allowing ions (and action potentials) to travel directly to the next cell

Degree of myelination affects action potential conduction speed

Bare plasma membrane – After stimulus, voltage quickly degrades as ions leak across the membrane

Non-myelinated axon – While voltage still quickly degrades, the action potential is regenerated as new voltage-gated ion channels are opened; conduction speed is slow because it takes time to open new channels

Myelinated axon – Due to myelin insulating the membrane, voltage does not degrade as quickly; new voltage-gated ion channels are only opened at the Nodes of Ranvier so the conduction speed is faster (because the action potential appears to "jump" from Node to Node, it is called saltatory conduction)

Gasser Classification of Nerve Fibers

Group A – Largest diameter, thick myelin sheaths, conduction speeds of up to 120m/s

Group B – Intermediate diameter, lightly myelinated, conduction speeds of around 10m/s