MCAT Content / Nerve Cell / Synapse Site Of Impulse Propagation Between Cells

Synapse: site of impulse propagation between cells

Topic: Nerve Cell

A synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell; varieties of synapses are electrical and chemical.

In the nervous system, a synapse is a structure that permits the electrical or chemical conduction from one cell to another. Chemical synapses rely on the secretion of neurotransmitters across a synaptic cleft from the pre synaptic neuron. The neurotransmitter moves over the synaptic cleft to the post synaptic neuron. Receptors on the post-synaptic neuron bind these neurotransmitters and induce a signaling response. On the post-synaptic nerve cell, the plasma membranes bind the neurotransmitters to receptors opening protein channels which causes the diffusion of ions across the plasma cell membrane. This movement of ions propagates the impulse in the postsynaptic neurone. 

The vast majority of synapses in the mammalian nervous system are axo-axonal (axon synapsing with another axon) or axo-dendritic synapses (axon synapsing upon a dendrite). However, a variety of other arrangements exist.

Electrical synapses are very rapid, allowing for faster signal processing than chemical synapses. However, due to their nature, electrical synapses cannot induce the gain of signal strength. Chemical synapses are slower than electrical synapses but allow for gain or amplification of a signal.


Key Points

• In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell.

• The neuron conducting impulses towards the synapse is called a pre-synaptic neuron. The neuron transmitting the electrical impulse away from the synapse is called a post-synaptic neuron.

• There are two varieties of synapses: electrical and chemical synapse based on the type of transmission.

• Chemical synapses rely on the secretion of neurotransmitters across a synaptic cleft between cells. Receptors on the post-synaptic cell bind these neurotransmitters and induce a signaling response.

• Electrical synapses form when the plasma membranes of two neurons are fused, and punctured by gap junction proteins, allowing for the diffusion of ions across the plasma cell membrane.

• Chemical synapses are slower than electrical synapses but allow for gain or amplification of a signal.


Key Terms

axon: A long, slender projection of a nerve cell, or neuron, that typically conducts electrical impulses away from the neuron’s cell body.

synapse: A structure that permits a neuron to pass an electrical or chemical signal to another cell

synaptic cleft: a space that separates two neurons

neurotransmitters: a type of chemical messenger which transmits signals across a chemical synapse

post-synaptic: the neurone that is on the other side of the synaptic cleft which receives the impulse

pre-synaptic neuron: is the neuron conducting impulses towards the synapse

axo-axonal: axon synapsing with another axon

axo-dendritic: axon synapsing to a dendrite



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