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Chapter 12
Intro to the Nervous System
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The Nervous System• The most complex system• Coordinates activities of all body systems• Two divisions:
The Central Nervous System (CNS) = brain & spinal cordThe Peripheral Nervous System (PNS) = all neural tissue not included in CNS
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Histology of Nervous Tissue
2 cell types:• Neurons
transmit nerve impulses
• Neuroglia:support neurons
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Neurons• Very long lived• Amitotic
mature neurons lose the ability to divide
• High metabolic rateneed a large supply of O2 and C6H12O6
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Neuron Structure• Cell Body = Soma
contains the usual cellular organelles
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• Dendritesshort, highly branched extensions from the somatransfer information to the cell body
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• Axontransmits information away from the somaends in many branches (axon terminals)
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• Action potentials (nerve impulses) start at the axon hillock & travel along the axon to the axon terminal
• Arrival of action potential causes the release of neurotransmitters across a synapse to the dentrites of the next neuron
• Neurotransmitters can excite or inhibit the next neuron
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• Myelin sheath = lipid-rich covering on axons, myelinated fibers conduct impulses 10-150x faster than unmyelinated fiber
Nodes of Ranvier = gaps between myelin; impulses jump from node to node
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Functions of the Nervous System• Sensory Input
Sensory neurons deliver info (stimulus) from sensory receptors to the CNS
• IntegrationInterneurons in the CNS process & interpret sensory stimulus
• Motor Output Motor neurons cause response by carrying info from
the CNS to various effector organs
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Sensory Neuron
Interneuron
Motor Neuron
Muscle Contracts
Synapse Synapse
Synapse
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NERVES
Nerves = bundles of neurons• Can contain all motor neurons, all sensory
neurons, or be mixed