9.1 INTRODUCTION Neurons: masses of nerve cells. Structural and functional units of the nervous system. Specialized to react to physical and chemical changes in their surroundings. Nerve impulses: electrochemical changes neurons transmit. NEURONS Cell body: rounded area
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ORGANS OF NERVOUS SYSTEM
MOTOR FUNCTIONS OF THE PERIPHERAL NERVOUS SYSTEM
Ependymalcells: form an ephithelia-like membrane that covers specialized brain parts (choroid plexuses) and forms the inner linings that enclose spaces within the brain (ventricles) and spinal cord (central canal).
Schwanncells: neuroglial cells that form a myelin sheath around axons.
Interneurons: (association or internuncial neurons) lie within the brain or spinal cord. Multipolar, link other neurons.
As long as a nerve cell membrane is undisturbed, the membrane remains in this polarized state.
As sodium ions diffuse inward, the membrane loses its negative electrical charge and becomes depolarized.
Rapid sequence of depolarization and repolarization, 1/1000 of a second, called action potential.
Speed of nerve impulse conduction is proportional to the diameter of the axon.
The resulting action potential causes a local bioelectric current that stimulates adjacent portions of the membrane.
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Inhibitory: neurotransmitters that make it less likely that threshold will be reached. Lessens the chance that a nerve impulse will occur.
When an action potential reaches the membrane of a synaptic knob, it increases the membrane’s permeability to calcium ions by opening the membrane’s calcium ion channels.
Decomposition or removal of neurotransmitters prevents continuous stimulation of postsynaptic neurons.