Transcript Nervous System Ch 10 Notes - Reading Community Schools

Chapter 10
Nervous System I
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Divisions of the
Nervous System
• Central
Nervous
System
•Brain and spinal cord
•All sensations have to be
relayed here to be acted
on
•Muscle & gland
stimulation
•Control center for the
entire system
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Divisions of the
Nervous System
• Peripheral Nervous
System
• Connection between
and CNS & receptors,
muscles, and glands
• Nerves
• Cranial nerves
• Spinal nerves
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Divisions of Peripheral
Nervous System
• Sensory Division
•Afferent System
• Picks up sensory information and delivers it to
the CNS
• Motor
Division
•Efferent System
• Carries information to muscles and glands
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Divisions of Peripheral
Nervous System
• Divisions of the Motor Division
– Somatic (SNS)
• Carries information to skeletal muscle
• Voluntary
– Autonomic (ANS)
• Carries information to smooth muscle,
cardiac muscle, and glands
• Involuntary
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Divisions Nervous System
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Functions of Nervous System
Sensory Function
• sensory receptors gather
information
• information is carried to the
CNS
Integrative Function
• sensory information used to
create
• sensations
• memory
• thoughts
• decisions
Motor Function
• decisions are acted
upon
• impulses are
carried to effectors
Most rapid
means of
maintaining
homeostasis in
your body
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Nervous System Cytology
Two Types of Cells
• Neurons
• Conduct nerve
impulses from one
part of the body to
another
• Information
Processing Units
• Neuroglial cells
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Neuron Structure
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Neuron Structure
• Cell Body
• Large nucleus
surrounded by
granular
cytoplasm
• Dendrites
• Thick branched
divisions of cell body
• Bring nerve
impulses toward the
cell body
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Neuron Structure
• Axon
• Usually a single,
longer process that
conducts nerve
impulses from the cell
body
• Terminates at another
neuron, muscle or
gland
• May be up to a meter
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Neuron Structure
• Axon
• Axon terminal
• End of an axon
with many
branching fibers
• End expands to
form synaptic end
bulb
• Nerve Fiber
• Common name for
an axon and its
myelin sheath
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Myelination of Axons
• Myelin sheath
• Formed by neuroglial
cell
• Phospholipid segment
that wraps around
axon
• Provides protection
for axon
• Increases speed of
impulse along axon
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Myelination of Axons
• Myelin sheath
• Schwann cells
• Form myelin
sheath
• Found ONLY in
peripheral nervous
system
• Assist in repair of
damaged axons,
provides tube for
axon or dendrite
to grow
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Myelination of Axons
• Myelin sheath
• Production begins
during 1st year of life
• Amount increases
from birth to
maturity
• This is why adults
react quicker to
certain stimuli
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Myelination of Axons
• Myelin sheath
• Nodes of Ranvier
• Segments on axon that
are not myelinated
• Gaps in sheath
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Myelination of Axons
White Matter
• contains myelinated
axons
Gray Matter
• contains
unmyelinated
structures
• cell bodies, dendrites
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Classification of Neurons –
Structural Differences
Bipolar
• Two processes
• One axon, one
dendrite
• Eyes, ears, nose
Unipolar
• One process that
branches in two
• Ganglia
• Specialized
masses of nerve
tissue outside
brain & spinal
cord
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Classification of Neurons –
Structural Differences
• Multipolar
• Many processes
• Only one axon
•
Most neurons of CNS
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Classification of Neurons –
Functional Differences
Sensory Neurons
• Afferent
• Carry impulse to CNS
• Dendrites act as sensory
receptors
• Most are unipolar
• Some are bipolar
Interneurons
• Link neurons
• Multipolar
• In CNS
Motor Neurons
• multipolar
• carry impulses
away from CNS
• Carry impulses to
effectors (muscles
or glands)
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Classification of Neurons –
Functional Differences
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Types of Neuroglial Cells
in the PNS
Schwann Cells
• Produce myelin found on peripheral
myelinated neurons
• Speed neurotransmission
Satellite Cells
• Support ganglia in PNS
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Types of Neuroglial Cells
in the CNS
Astrocytes
• CNS
• Scar tissue in CNS
• Regulate ion
concentrations (K+)
• Induce synapse
formation
• Connect neurons to
blood vessels
Oligodendrocytes
• Form myelin in CNS
• Myelinating cell
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Types of Neuroglial Cells
in the CNS
• Microglia
• CNS
• Phagocytic cell
• Proliferate w/ CNS
injury
• Ependyma
• CNS
• Cuboidal or
columnar
• Ciliated
• Line central canal of
spinal cord
• Line ventricles of
brain
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The Synapse
• Junction between
two neurons
• Also called synaptic clefts
• Essential in
homeostasis because of
the ability to transmit
some impulses while
inhibiting others
•
Brain disease & many
psychiatric disorders
result from bad synaptic
communication
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The Synapse
• 2 Types
• Electrical & Chemical
• Most in CNS are
chemical
• Function
• Neuron secretes
neurotransmitters across
synaptic cleft
• Post-synaptic neuron
has receptors to match
transmitter
• When they match,
impulse continues
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Resting Membrane Potential
• Inside is negative
relative to the outside
• Polarized membrane
• Due to distribution
of ions
• Unequal
distribution of Na+
and K+ ions
• K+ 28x greater
inside
• Na+ 14x greater
outside
• Na+/K+ pump
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Sodium/Potassium Pump
• Fights osmosis
• Transports 3 Na+ out
& 2 K+ into a resting
neuron
• Active Process
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Local Potential Changes
• Caused by various
stimuli
• Temperature changes
• Light
• Pressure
• Environmental changes
affect the membrane
potential by opening a
gated ion channel
•Allows Na+ to diffuse in
& K+ to diffuse out
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Local Potential Changes
• If membrane potential becomes more negative, it has
hyperpolarized
• If membrane potential becomes less negative, it has
depolarized
• Summation can lead to threshold stimulus that starts an
action potential
• Multiple impulses often needed to reach threshold
stimulus
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Local Potential Changes
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Action Potentials
• At rest membrane
is polarized
• Threshold stimulus
reached
• Na+ channels open
and membrane
depolarizes
• Na+ enters cell
• K+ leaves cytoplasm
and membrane
repolarizes
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Action Potentials
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Action Potentials
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All-or-None Response
• If a neuron responds at all, it responds completely
• A nerve impulse is conducted whenever a stimulus of
threshold intensity or above is applied to an axon
• All impulses carried on an axon are the same strength
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Refractory Period
• Absolute
– Time when threshold stimulus does not start another action
potential
• Relative
– Time when stronger threshold stimulus can start another action
potential
• Under normal conditions each fiber may conduct 10-500
impulses per second
• Larger neurons conduct up to 2500 per second
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Impulse Conduction
• Nerve cell membrane maintains resting potential by
diffusion of Na+ and K+ down their concentration
gradients as the cell pumps them up the gradients
• Neurons receive stimulation, causing local
potentials, which may sum to reach threshold
• Sodium channels in a local region of the membrane open
• Sodium ions diffuse inward, depolarizing the membrane
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Impulse Conduction
• Potassium channels in the membrane open
• Potassium ions diffuse outward, repolarizing the
membrane
• The resulting action potential causes an electric
current that stimulates adjacent portions of the
membrane
• Series of action potentials occurs sequentially along
the length of the axon as a nerve impulse
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Saltatory Conduction
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Saltatory Conduction
• Impulse along myelinated fiber
• Sheath inhibits movement of ions
• Nodes of Ranvier allow generation of action
potentials and conduction
• Ionic current flows through extra-cellular fluid
& triggers impulse at next node
• Impulse mechanism is the same, BUT impulse skips
from one node to the next.
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Saltatory Conduction
• Valuable to Homeostasis
• Speed of impulse greatly increased
• Low ATP expenditure by Na-K pump due to little
exposed membrane
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Clinical Application
Drug Addiction
• Occurs because of the complex interaction of
neurons, drugs, and individual behaviors
• Understanding how neurotransmitters fit receptors
can help explain the actions of certain drugs
• Drugs have different mechanisms of action
• Several questions remain about the biological
effects of addiction, such as why some individuals
become addicted and others do not
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