chapter 12 intro to the nervous system. the nervous system the most complex system coordinates...

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