Nerve impulse

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The pre- and post-synaptic axons are separated by a short distance known as the synaptic cleft. Neurotransmitter released by pre-synaptic axons diffuse through the synaptic clef to bind to and open ion channels in post-synaptic axons.
When an action potential arrives at the end of the pre-synaptic axon (yellow), it causes the release of neurotransmitter molecules that open ion channels in the post-synaptic neuron (green). The combined potentials of the inputs can begin a new action potential in the post-synaptic neuron.
Approximate plot of a typical action potential

A nerve impulse is the way nerve cells (neurons) communicate with one another. Nerve impulses are mostly electrical signals along the dendrites to produce a nerve impulse or action potential.[1]

The action potential is the result of ions moving in and out of the cell.[2] Specifically, it involves potassium (K+) and sodium (Na+) ions. The ions are moved in and out of the cell by potassium channels, sodium channels and the sodium-potassium pump.

Axons of neurons are wrapped by several myelin sheaths, which shield the axon from extracellular fluid. There are short gaps between the myelin sheaths known as nodes of Ranvier where the axon is directly exposed to the surrounding extracellular fluid.

Special faster connections[change | change source]

Electrical synapses between excitable cells are much faster than chemical synapses

Faster electrical synapses are used in escape reflexes, the retina of vertebrates, and the heart. They are faster because they do not need the slow diffusion of neurotransmitters across the synaptic gap. Therefore, electrical synapses are used whenever fast response and coordination of timing are crucial.

These synapses connect the presynaptic and postsynaptic cells directly together.[3] When an action potential reaches such a synapse, the ionic currents cross the two cell membranes and enter the postsynaptic cell through pores known as connexons.[4] Thus, presynaptic action potential directly stimulates the postsynaptic cell.

References[change | change source]

  1. The Mind Project Glossary.
  2. Eastern Kentucky University: Neurons and the nervous system.
  3. Zoidl G. & Dermietzel R. (2002). "On the search for the electrical synapse: a glimpse at the future". Cell Tissue Res. 310 (2): 137–42. doi:10.1007/s00441-002-0632-x. PMID 12397368.
  4. Brink P.R; Cronin K. & Ramanan S.V. (1996). "Gap junctions in excitable cells". J. Bioenerg. Biomembr. 28 (4): 351–8. doi:10.1007/BF02110111. PMID 8844332.