Download Nervous System Intro

Chapter 7
The Nervous System
General overview of the nervous
system functions
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Sensory input (info travels “in” along afferent pathways)
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Integration (information is processed)
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Sensory neurons
Spinal cord and brain
Motor output (info results in a response, travels along
efferent pathways)
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Stimulation of muscle and glands
General Overview
Nervous Tissue
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2 kinds of cells
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neurons
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supporting cells: glia or neuroglia = “nerve glue”
CNS Neuroglia
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astrocytes
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microglia
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phagocytes: dispose of debris
ependymal cells
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barrier between nerves and capillaries
help circulate cerebrospinal fluid (CSF)
oligodendrocytes
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produce myelin sheaths on CNS nerve fibers
CNS Neuroglia
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blue = nerve
PNS also has neuroglia
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Schwann cells - form myelin sheaths on PNS nerve
fibers
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Satellite cells – cushion PNS nerves
PNS Neuroglia
Neurons
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specialized cells that
transmit messages
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cell body
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Nissl substance
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rough ER
neurofibrils
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intermediate filaments
Nerve Anatomy: Processes
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dendrites
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convey incoming messages
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many per cell
axons
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conduct messages away from cell body
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one per cell
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axon terminals
Nerve Anatomy
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axon terminal can connect to another neuron
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synapse = junction between neurons
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gap = ?
Nerve Anatomy
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myelin: whitish, fatty, waxy
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protects and insulates fibers
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increases rate of impulse
transmission
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Schwann cells - PNS
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nodes of Ranvier
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Oligodendrocytes - CNS
Schwann Cells & Nodes of Ranvier
Peripheral nerve regeneration is
assisted by the Schwann cells
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Multiple Sclerosis
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myelin sheaths gradually destroyed
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loss of muscle control
Nerve Anatomy
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nuclei: clusters of cell bodies in CNS
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ganglia: clusters of cell bodies in PNS
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tracts: bundles of fibers in CNS
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nerves: bundles of fibers in PNS
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white matter: myelinated fibers in CNS
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gray matter: unmyelinated fibers in CNS
Neurons can be
classified by function
Neurons can be
classified by structure
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based on # of processes
that extend from the cell
body
Nerve Physiology
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Overview:
If neurons are excitable cells…
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What does this mean?
How are they different from other cells in the
body?
Have we talked about a model in another cell
for propagation of an impulse?
The cell membrane is where all the
action occurs.
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Remember the chemical composition of the cell
membrane?
How does the chemical composition promote a
separation of ions?
Which ions are in greater concentration inside
the cell? Outside the cell?
So far we know the following:
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For an inactive nerve cell:
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Intracellular fluid contains a high concentration of
K+
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Extracellular fluid contains a high concentration of
Na+
Inside of cell has fewer cations than outside…
therefore the membrane is polarized
In a resting neuron…
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Na+ cannot normally diffuse through membrane
What would happen if the cell membrane were
freely permeable?
When a neruon is stimulated…
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Na+ gates open and Na+
diffuses into where?
the polarity of the
membrane is changed
graded potential:
membrane is depolarized
in one area
If stimulus is strong enough…
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action potential (nerve impulse) is generated
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long distance signal
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all or none
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propagates over entire axon
Action Potential
Repolarization
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Na+ rushing into cell triggers another change in
membrane permeability
membrane is no longer permeable to Na+, but
IS permeable to K+
K+ diffuses out of the cell rapidly
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restores electrical conditions
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until restored, neuron cannot conduct impulse
Repolarization
After repolarization
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how do Na+ and K+ get back to original resting
ionic conditions?
Saltatory conduction
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saltare = “dance, leap”
myelin sheaths insulate
membrane
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no current flow
nerve impulse jumps
from node to node
fast!
What happens at the synapse?
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conduction of electrical impulse to another
nerve via a neurotransmitter
if enough neurotransmitter is released, action
potential is generated
electrochemical
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electro = transmission down neuron membrane
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chemical = transmission at synapse
What is happening when…
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hands get cold?
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foot goes numb?
Lab Exercise 13
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Turn in:
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Activities 1, 2, 3
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Review Sheet on pp. 291-294