The membrane of a postsynaptic fibre has many different kinds of receptors, and some presynaptic terminals release more than one type of neurotransmitter. For example, norepinephrine, a common neurotransmitter in the autonomic nervous system, binds to some receptors that excite nervous transmission and to others that inhibit it. This process causes a series of brief transmission events, each one taking place in only 0.5 to 4.0 milliseconds.Ī single neurotransmitter may elicit different responses from different receptors. Once they have been released and have bound to postsynaptic receptors, neurotransmitter molecules are immediately deactivated by enzymes in the synaptic cleft they are also taken up by receptors in the presynaptic membrane and recycled.

If the net flow of positively charged ions into the cell is large enough, then the PSP is excitatory that is, it can lead to the generation of a new nerve impulse, called an action potential. This sudden shift of electric charge across the postsynaptic membrane changes the electric polarization of the membrane, producing the postsynaptic potential, or PSP. Electrically charged ions then flow through the channels into or out of the neuron. The chemical binding action alters the shape of the receptors, initiating a series of reactions that open channel-shaped protein molecules. This substance transmits the nerve impulse to the postsynaptic fibre by diffusing across the synaptic cleft and binding to receptor molecules on the postsynaptic membrane. The arrival of a nerve impulse at the presynaptic terminals causes the movement toward the presynaptic membrane of membrane-bound sacs, or synaptic vesicles, which fuse with the membrane and release a chemical substance called a neurotransmitter. The typical synaptic cleft is about 0.02 micron wide. A synaptic connection between a neuron and a muscle cell is called a neuromuscular junction.Īt a chemical synapse each ending, or terminal, of a nerve fibre (presynaptic fibre) swells to form a knoblike structure that is separated from the fibre of an adjacent neuron, called a postsynaptic fibre, by a microscopic space called the synaptic cleft. Synapse, the site of transmission of electric nerve impulses between two nerve cells (neurons) or between a neuron and a gland or muscle cell (effector). New study suggests enhanced mitochondrial fusion fuels nerve cell function and plasticity

Free nerve endings of sensory neurons