chapter 12 intro to the nervous system. the nervous system the most complex system coordinates...
TRANSCRIPT
Chapter 12
Intro to the Nervous System
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
Histology of Nervous Tissue
2 cell types:• Neurons
transmit nerve impulses
• Neuroglia:support neurons
Neurons• Very long lived• Amitotic
mature neurons lose the ability to divide
• High metabolic rateneed a large supply of O2 and C6H12O6
Neuron Structure• Cell Body = Soma
contains the usual cellular organelles
• Dendritesshort, highly branched extensions from the somatransfer information to the cell body
• Axontransmits information away from the somaends in many branches (axon terminals)
• 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
• 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
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
Sensory Neuron
Interneuron
Motor Neuron
Muscle Contracts
Synapse Synapse
Synapse
NERVES
Nerves = bundles of neurons• Can contain all motor neurons, all sensory
neurons, or be mixed