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In the nervous system, a synapse [1] is a structure that allows a neuron (or nerve cell) ... all have the same deleterious effects on neuronal integrity. Furthermore ...
Not all animals have neurons; Trichoplax and sponges lack nerve cells altogether. Neurons may be packed to form structures such as the brain of vertebrates or the neural ganglions of insects. The number of neurons and their relative abundance in different parts of the brain is a determinant of neural function and, consequently, of behavior.
Electrical synapses can exist between two axons, two dendrites, or between an axon and a dendrite. [30] [31] In some fish and amphibians, electrical synapses can be found within the same terminal of a chemical synapse, as in Mauthner cells. [32]
Immature synapses are multiply innervated at birth, due to the high propensity for new axons to innervate at a pre-existing synapse. As the synapse matures, the synapses segregate and eventually all axonal inputs except for one retract in a process called synapse elimination.
When the wave reaches a synapse, it provokes release of a puff of neurotransmitter molecules, which bind to chemical receptor molecules located in the membrane of another neuron, on the opposite side of the synapse. In neuroscience, Dale's principle (or Dale's law) is a rule attributed to the English neuroscientist Henry Hallett Dale.
However, the difference in speed between chemical and electrical synapses is not as marked in mammals as it is in cold-blooded animals. [12] Because electrical synapses do not involve neurotransmitters, electrical neurotransmission is less modifiable than chemical neurotransmission. The response always has the same sign as the source.
Synapses will strengthen for a short time because of an increase in the amount of packaged transmitter released in response to each action potential. [22] Depending on the time scales over which it acts synaptic enhancement is classified as neural facilitation , synaptic augmentation or post-tetanic potentiation .
The three models explaining synaptic pruning are axon degeneration, axon retraction, and axon shedding. In all cases, the synapses are formed by a transient axon terminal, and synapse elimination is caused by the axon pruning. Each model offers a different method in which the axon is removed to delete the synapse.