Intro to the
Nervous
System
Chapter 12
The Nervous System
• The most complex system
• Coordinates activities of all body systems
• Two divisions:
The Central Nervous System (CNS) = brain &
spinal cord
The 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 rate
need a large supply of O2 and C6H12O6
Neuron Structure
• Cell Body = Soma
contains the usual cellular organelles
• Dendrites
short, highly branched extensions from the soma
transfer information to the cell body
• Axon
transmits information away from the soma
ends 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
• Integration
Interneurons in the CNS process & interpret sensory
stimulus
• Motor Output
Motor neurons cause response by carrying info from
the CNS to various effector organs
Interneuron
Synapse
Synapse
Motor
Neuron
Sensory
Neuron
Synapse
Muscle
Contracts
NERVES
Nerves = bundles of neurons
• Can contain all motor neurons, all sensory
neurons, or be mixed