Synapses

Synapses- contact between neurons where information is passed from one neuron to the next.

Synapses form between axons and dendrites, consist of a presynaptic neuron, synaptic cleft, and a postsynaptic neuron.

axodendritic synapses—synapses of axon terminal buttons on dendrites.

axosomatic synapses— synapses of axon terminal buttons on somas (cell bodies).

axoaxonic synapses - can mediate presynaptic facilitation and inhibition.

Dendrodendritic- connections between the dendrites of two different neurons.

Dendroaxonic- a dendrite communicates with axon (rare).

Presynaptic Inhibition-inhibitory neuron provides synaptic input to the axon of another neuron (axo-axonal synapse).

Postsynaptic Inhibition-postsynaptic receptors are attached to neurons. As a result, the postsynaptic neuronal membrane’s sensitivity to certain ions will be altered.

directed synapses—synapses at which the site of neurotransmitter release and the site of neurotransmitter reception are in close proximity

Nondirected synapses - synapses at which the site of release is at some distance from the site of reception.

Chemical Events at the Synapse:

1. The neuron synthesizes chemicals that serve as neurotransmitters.
2. Neurons store neurotransmitters in axon terminals or transport them there.
3. An action potential triggers the release of neurotransmitters into the synaptic cleft.
4. The neurotransmitters travel across the cleft and attach to receptors on the postsynaptic neuron.
5. The neurotransmitters separate from the receptors.
6. The neurotransmitters are taken back into the presynaptic neuron, diffuse away, or are inactivated by chemicals.
7. The postsynaptic cell may send negative feedback to slow the release of further neurotransmitters.

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