chapter 12 nervous tissue - mr. meagher's science · copyright 2009 john wiley & sons,...
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Copyright 2009 John Wiley & Sons, Inc. 1
Chapter 12
Nervous Tissue
Terms to Know
CNS
PNS
Afferent division
Efferent division
Somatic nervous system
Autonomic nervous system
Sympathetic nervous system
Parasympathetic nervous system
Axons
Dendrites
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Overview of Major Structures Twelve pairs of cranial
nerves.
Thirty-one pairs ofspinal nerves.
Ganglia, small masses of nerve tissue, located outside the brain and spinal cord.
Sensory receptorsmonitor changes in the internal or external environment.
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Functions of Nervous System Sensory function: to
sense changes in the
internal and external
environment through
sensory receptors.
Sensory (afferent)
neurons serve this
function.
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Functions of Nervous System Integrative function: to
analyze the sensory
information, store some
aspects, and make
decisions regarding
appropriate behaviors.
Association or
interneurons serve this
function.
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Functions of Nervous System Motor function is to
respond to stimuli by
initiating action.
Motor(efferent)
neurons serve this
function.
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Nervous System Divisions
Central nervous system
(CNS)
consists of the brain and
spinal cord
Peripheral nervous system
(PNS)
connects CNS to
muscles, glands & all
sensory receptors
What does a neuron look like?
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What does a neuron look like?
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Subdivisions of the PNS
Somatic (voluntary) nervous system (SNS)
neurons from sensory receptors to the CNS
motor neurons to skeletal muscle tissue
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Subdivisions of the PNS
Autonomic (involuntary) nervous systems
motor neurons to smooth & cardiac muscle and glands
sympathetic division (speeds up heart rate)
parasympathetic division (slow down heart rate)
Enteric nervous system (ENS)
involuntary sensory & motor neurons control GI tract
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Subdivisions of the PNS
Speed: speed of neuron signal is affected by axon diameter, temperature, and myelin.
Neurotransmitters: examples
include; acetylcholine,
glutamate, aspartate, gamma
aminobutyric acid, glycine,
norepinephrine, epinephrine,
and dopamine.
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Structural Classification of Neurons
Multipolar Bipolar Unipolar
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Neuroglia of the CNS
Most common glial
cell type
Each forms myelin
sheath around
more than one
axons in CNS
Analogous to
Schwann cells of
PNS
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Neuroglia of the CNS
Cells encircling
PNS axons
Each cell produces
part of the myelin
sheath surrounding
an axon in the PNS
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Neuroglia of the CNS
Schwann cells myelinate (wrap around) axons in the PNS during fetal development
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Myelinated and unmyelinated axons
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Organization of the Nervous System
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Electrical Signals in Neurons
Communicate with 2 types
of electric signals
action potentials that
can travel long
distances
graded potentials that
are local membrane
changes only
In living cells, a flow of
ions occurs through ion
channels in the cell
membrane
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Types of Ion Channels
Leakage (nongated) channels are always open nerve cells have more K+ than Na+ leakage channels
Ligand-gated channels open and close in response to a stimulus results in neuron excitability
Voltage-gated channels respond to a direct change in the membrane potential.
Mechanically gated ion channels respond to mechanical vibration or pressure.
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Generation of Action Potentials
An action potential (AP) or impulse is a sequence of rapidly occurring
events that decrease and eventually reverse the membrane potential
(depolarization) and then restore it to the resting state (repolarization).
During an action potential, voltage-gated Na+ and K+ channels open in sequence
According to the all-or-none principle, if a stimulus reaches threshold, the action
potential is always the same.
A stronger stimulus will not cause a larger impulse.
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Signal Transmission at the Synapse
2 Types of synapses
electrical
ionic current spreads to next cell through gap junctions
chemical
one-way information transfer from a presynaptic neuron to a
postsynaptic neuron
axodendritic -- from axon to dendrite
axosomatic -- from axon to cell body
axoaxonic -- from axon to axon
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Chemical Synapses Action potential reaches end and voltage-gated Ca+ 2
channels open
Ca+2 flows inward triggering release of neurotransmitter
Neurotransmitter crosses synaptic cleft
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Neurotransmitter Effects
Agonist - anything that enhances a transmitters effects
Antagonist - anything that blocks the action of a
neurotransmitter
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