Transcript The Synapse
Neural communication How do neurons send messages to each other? The Synapse • Two neurons meet at a synapse. • Children have roughly 1016 synapses. Adults somewhere from 1-5 1015 • A typical synapse is about 20nm wide (20 billionths of a meter). This is called the synaptic cleft Neurotransmitter • Neurons communicate by sending chemical messages called neurotransmitters to other neurons. • These neurotransmitters travel from axon to either the dendrite or the cell body across the synapse. • Where a synapse is depends on what the connection type is – Excitatory: Axon to dendrite – Inhibitory: Axon to cell body Neurotransmitter release • Neurotransmitters are held in the terminal button in synaptic vesicles. • The action potential opens voltage-gated Ca+ channels in the terminal. • This causes the vesicles to bind with the cell membrane, which allows neurotransmitter to be released into the synaptic cleft. Neurotransmitter absorbtion • On the post-synaptic side of the synaptic cleft, neurotransmitters bind to chemical receptors that open chemically-gated ion channels. • Some of these ion channels are K+ channels, which allow K+ ions to leave the cell. This has the effect of hyperpolarizing the area, which inhibits the post-synaptic cell. • Others are Na+ channels, which allow sodium into the cell, depolarizing the area. This excites the post-synaptic cell. Re-uptake • Once the neurotransmitter has done its job, it binds to a protein on the pre-synaptic membrane. • This process allows the pre-synaptic cell to recycle the neurotransmitter, ensuring each action potential will generate the same sized signal in the synapse. • It also lessens the effect of the neurotransmitter so that the receiving cell does not become desensitized to its effects, unless a rapid sequence of action potentials causes neurotransmitter to be continually present.