The junction between the terminal buttons of one neuron and the cell membrane of another neuron, muscle or gland is called a synapse. Synapses are the way in which neurons communicate with one another in the nervous system.
How Does a Neuron Communicate With Another Neuron?
The neuron is made up of a cell body, an axon, terminal buttons and dendrites. When a neuron is activated, a signal is sent down the axon, toward its terminal button endings. These terminal buttons belong to the presynaptic neuron, that is, the neuron that is sending the message.
When the terminal buttons are activated, a chemical substance called a neurotransmitter is released into a small, fluid-filled gap, called a synaptic cleft, where it binds to the postsynaptic neuron, that is, the neuron receiving the message. The terminal buttons on the presynaptic neuron form synapses with the dendrites on the postsynaptic neuron.
Motor Neurons
The terminal buttons on a motor neuron form synapses with muscle fibers found in muscles, and as a result, control muscle contractions. As such, when the axon of a neuron fires, the muscle fibers that it's synapsed with, will move. A muscle contains many muscle fibers and is therefore controlled by numerous motor neurons. The degree to which a muscle will contract depends on an axon's rate of firing. If axonal firing is weak, muscle contraction will be weak, however, if firing is strong, muscle contraction will also be strong.
Excitatory and Inhibitory Synapses
According to Carlson & Buskist, a synapse can be either excitatory or inhibitory. An excitatory synapse is formed when the terminal buttons on a presynaptic neuron release a chemical substance that excites the postsynaptic neuron, making it more likely to fire. In contrast, an inhibitory synapse is formed when the terminal buttons on a presynaptic neuron release neurotransmitters that inhibit the postsynaptic neuron, making it less likely to fire.
The excitatory and inhibitory responses of a neuron occur because of tiny receptors that are located on the cell membrane of a postsynaptic neuron. When a neurotransmitter is released into the synaptic cleft, it binds to receptors located on the receiving neuron, that recognize for that neurotransmitter. This activates the receptors causing either excitatory or inhibitory currents along the cell membrane. Receptor activation causes ion channels to open, which either allows sodium ions to enter the neuron, causing excitation, or causes potassium ions to exit the neuron, resulting in inhibition.
Reuptake
Excitatory and inhibitory synapses are brief events which cease by a process called reuptake. When the terminal buttons release a neurotransmitter, they quickly retrieve the substance, meaning that the receptors on the postsynaptic neuron will only be stimulated for a brief amount of time. The quicker the substance is retrieved, the shorter stimulation will be.
Sources
- Carlson, N., & Buskist, W. (1997). Psychology: The Science of Behavior. 5th Ed. A Viacom Company. MA.
- Siegal, A., & Sapru, H. (2011). Essential Neuroscience. 2nd Ed. Lippincott Williams & Wilkins, MD
Katherine Dowling - Currently working as a freelance writer. Hold a B.Science (Psychology)
