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Axon Terminal

contain hundreds of tiny vesicles, or membranous sacs, that contain chemicals called neurotransmitters


a chemical that is released from a nerve cell which thereby transmits an impulse from a nerve cell to another nerve, muscle, organ, or other tissue. A neurotransmitter is a messenger of neurologic information from one cell to another

Synaptic Cleft

a tiny gap between neurons at a nerve synapse across which a nerve impulse is transmitted by a neurotransmitter


the place at which a nervous impulse passes from one neuron to another usually by a chemical neurotransmitter

Myelin Sheath

encloses the axon


the plasma membrane surrounding a Schwann cell of a myelinated nerve fiber and separating layers of myelin

Nodes of Ranvier

gaps or indentations in the myelin sheath


small collections of cell bodies found in a few sites outside the CNS in the PNS


bundles of nerve fibers running through the CNS (tracts) in the PNS (nerves)

White Matter

consists of dense collections of myelinated fibers

Gray Matter

contains mostly of unmyelinated fibers and cell bodies

Association or Interneurons

third category of neurons. They connect the motor and sensory neurons in neural pathways


there are fewer positive ions sitting on the inner face of the neuron's plasma membrane than there are on its outer face in the tissue fluid that surrounds it


inward rush of sodium ions that changes the polarity of the neuron's membrane at the site

Action Potential

a long distance signal. The change in electrical potential that occurs between the inside and outside of a nerve or muscle fiber when it is stimulated, serving to transmit nerve signals


outflow of positive ions from the cell restores the electrical conditions at the membrane to the polarized or resting state


are rapid, predictable, and involuntary responses to stimuli

Autonomic Reflexes

regulate the activity of smooth muscles, the heart, and glands

Somatic Reflexes

include all reflexes that stimulate the skeletal muscles

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