Transmission Across Synapses
Transmission across synapses. Certain chemicals, called neurotransmitters, transmit nerve impulses across synapses. When an impulse reaches the end of an axon, a neurotransmitter is released into the synaptic cleft. The neurotransmitter moves to the dendrites of the next nerve cell and causes certain pores of the nerve membrane to open. Ions move through these pores, and a voltage change, called a postsynaptic potential, results. The postsynaptic potential is either excitatory or inhibitory. An excitatory postsynaptic potential spreads to the axon of a nerve cell and tends to produce another action potential. An inhibitory postsynaptic potential tends to prevent the axon from producing another action potential. Not every impulse that reaches a synapse is transmitted to the next neuron. The synapses thus help regulate and route the constant flow of nerve impulses throughout the nervous system.