Nervous System Terms

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Interneurons

Neurons that conduct impulses from afferent neurons to or toward motor neurons. They lie in the CNS.

Efferent Neuron

Neurons that transmit nerve impulses away from the brain or spinal cord toward muscles or glands.

Afferent Neuron

Neurons that transmit nerve impulses to the spinal cord or brain.

Unipolar Neuron

A neuron that has a single process extending from the cell body. This single process branches to form a central process and a peripheal process. These processes combine to form an axon.

Bipolar neuron

A neuron found in the retina of the eye that has only one axon and one branched dendrite. Least numerous type of neuron.

Multipolar Neuron

A neuron that has only one axon but several dendrites. Mostly found in the brain and spinal cord.

Axon

They conduct impulses away from the cell body. They vary in length and diameter; a single process that branches.

Temporal Summation

When synaptic knobs stimulate postsynaptic neurons in rapid succession, their effects can add up to produce an action potential.

Neurons

Excitable cells that conduct the impulses that make possible all nervous system functions.

Parasympathetic Division

Involved in coordinating the body's normal resting activities

Sympathetic Division

Involved in preparing the body to deal with immediate threats to the internal environment.

ANS

Part of the nervous system that carries information to the visceral effectors (smooth muscles, cardiac muscle)

Somatic Nervous System

Part of the nervous system that carries information to the skeletal system.

Efferent Division

Consists of all of the outgoing motor pathways of the nervous system.

Afferent Division

Consists of all of the incoming sensory pathways of the nervous system.

Spatial Summation

What it is called when voltage gated channels in the axon membrane open because the sum of the local potentials reaches the threshold potential.

Chemical Synapse

A synapse that uses a chemical transmitter to send a signal from the presynaptic cell to the postsynaptic cell.

IPSP

A temporary hyperpolarization when the inside of the axon membrane is more negative than the resting potential.

Soma

Cell Body

EPSP

A temporary depolarization when both Na channels and K channels open.

Neurotransmitter

The chemicals by which neurons communicate.

Relative Refractory Period

The few milliseconds after the absolute refractory period-when the membrane is repolarizing and restoring the resting potential.

Myelin

A white, fatty substance.

Schwann Cells

Found only in the PNS, support nerve fibers by forming a myelin sheath around them.

Oligodendrocytes

Cells that have few uses. Some lie clustered around nerve cell bodies. Some are arranged in rows between nerve fibers in the brain and spinal cord.

Ependymal Cells

Glia that form thin sheets that line fluid-filled cavities in the brain and spinal cord. Some produce this fluid.

Endoneurium

A delicate layer of fibrous connective tissue surrounding each nerve fiber.

Nerves

Bundles of peripheal nerve fibers held together by several layers of connective tissues.

Synapse

The place where nerve information is transmitted from one neuron to another.

Reflex Arc

A signal conduction route to and from the CNS.

Satellite Cell

Special Schwann cells that surround the cell body of a neuron.

Nodes of Ranvier

Microscopic gaps in the myelin sheath between adjacent Schwann cells.

PNS

The existing nerve tissues that reside in the body besides the CNS.

CNS

The brain and the spinal cord.

Threshold Potential

A limit of local depolarization. If surpassed, it causes Na channels to open.

Action Potential

The membrane potential of an active neuron conducting an impulse.

Absolute Refractory Period

When the Threshold Potential is surpassed, for about half a millisecond, the axon will not respond to any stimulus.

Membrane Potential

A difference in electrical charge across an axon's plasma membrane.

Gray Matter

Cell bodies and unmyelinated fibers.

White Matter

Bundles of myelinated fibers.

Tracts

The name for nerves located in the CNS.

Epineurium

A fibrous coat that holds together numerous fascicles to create a nerve.

Perineurium

A connective tissue layer that holds together fascicles.

Fascicles

Bundles of fibers each with its own endonerium.

Nissel Bodies

A structure formed from ribosomes that provide protein molecules needed for the sending of nerve signals from one neuron to another.

Microglia

Small, stationary cells found in the CNS. They engulf and destroy microorganisms and cellular debris.

Astrocytes

Star shaped cells that are the largest and most numerous type of glia. They feed neurons by using glucose and converting it to lactic acid.

Glia

Cells that do not conduct information but support the neurons in various ways.

Hyperpolarization

Movement of the membrane potential away form zero.

Depolarization

Movement of the membrane potential toward zero.

Local Potential

A slight shift away from the resting membrane potential in a specific region of the plasma membrane.

Resting Membrane Potential

The membrane's potential maintained by a nonconducting neuron's plasma membrane.

Dendrites

Receptors that receive the stimuli that initiate nerve signals. They receive the stimuli and conduct electrical signals toward the axon of the neuron. They branch from the main body.

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