The combination of the neurotransmitter molecules to receptor cell molecules in the postsynaptic cell membrane produces a change of potential in the postsynaptic cell membrane called the postsynaptic potential (PSP). (Molecules of the neurotransmitter that do not bind to receptors in the postsynaptic neuron are taken up again by the presynaptic neuron, a process called reuptake). Most of the released neurotransmitters bind with molecules at special sites, receptors, on the dendrites of the postsynaptic neuron. Stimulation of the presynaptic neuron to produce an action potential causes the release of neurotransmitters into the synaptic cleft. The axon of the presynaptic neuron does not actually touch the dendrites of the postsynaptic neuron and is separated from them by a space called the synaptic cleft. Neurotransmitters are stored in small containers ( vesicles) located in knoblike structures ( terminal buttons) on the axon tips. The action potential causes information to be transmitted from the axon of the first neuron ( presynaptic neuron) to the dendrites or cell body of the second neuron ( postsynaptic neuron) by secretion of chemicals called neurotransmitters. The synapse is the name given the junction between neurons where information is exchanged. After the refractory period, the neuron will fire when the neural threshold is reached. It is followed by the relative refractory period, during which a stronger than usual stimulus is required to trigger the action potential before the neuron returns to resting state. The absolute refractory period lasts for only a short time. During the first part of the refractory period (the absolute refractory period), the neuron will not fire again no matter how great the stimulation. Once triggered, the action potential continues the length of the axon without diminishing because the action potential depends upon cell membrane permeability, a cell characteristic, and not upon the strength of the triggering stimulus.Īfter the action potential occurs, however, there is a short period of refractoriness, which affects neuron firing. The relationship between the level of stimulation and the production of a neural impulse is called the all or none principle. If the threshold is reached or exceeded, the amplitude of the action potential is the same regardless of the level of stimulation. That is, if the neural threshold is not reached, the neuron will not fire. The rate of neural transmission, however, is independent of the level of stimulation. ![]() The neuron then returns to its resting electrical state, the resting potential, until stimulated again. Alteration of membrane permeability (polarization) allows a change of electrical charges (negative to positive) that runs along the entire cell membrane. When unstimulated, a neuron is like a small battery and has a measurable negative electrical charge (about 70 millivolts) called the resting potential.Īction potential is the potential produced when appropriate stimulation is high enough to reach the neural threshold and causes the neuron to fire, that is, alters the membrane permeability. Resting potential is the potential maintained by the inactive neuron. The neural threshold must be reached before a change from resting to action potential occurs (Figure 1). Neurons have two types of potentials, a resting potential and an action potential. The term potential refers to a difference in electrical charges. When a neuron is sufficiently stimulated to reach the neural threshold (a level of stimulation below which the cell does not fire), depolarization, or a change in cell potential, occurs. (The type of stimulation necessary to produce firing depends on the type of neuron.) The fluid inside a neuron is separated from that outside by a polarized cell membrane that contains electrically charged particles known as ions. Activation (firing) of the neuron takes place when the neuron is stimulated by pressure, heat, light, or chemical information from other cells. Neural transmission occurs when a neuron is activated, or fired (sends out an electrical impulse). ![]() The function of a neuron is to transmit information within the nervous system. Legal Aspects of Psychological Disorders.Development in Early & Middle Adulthood.Developmental Psychology: Age 13 to 65+.Psychology: Biological Bases of Behavior.
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