CHAPTER 10 The Nervous
System
Hole’s Human
Anatomy and Physiology
Tenth Edition
10-1
Chapter 10: Nervous System I
• Cell Types of Neural Tissue
• neurons
• neuroglial cells
10-2
Divisions of the Nervous System
• Central Nervous System
• brain
• spinal cord
• Peripheral Nervous System
• peripheral nerves
• cranial nerves
• spinal nerves
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Divisions of Peripheral Nervous
System
Sensory Division
• picks up sensory information and delivers it to the
CNS
Motor Division
• carries information to muscles and glands
Divisions of the Motor Division
• Somatic – carries information to skeletal muscle
• Autonomic – carries information to smooth
muscle, cardiac muscle, and glands
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Divisions Nervous System
10-5
Functions of Nervous System
• Motor Function
• decisions are acted upon
• impulses are carried to effectors
• Sensory Function
• sensory receptors gather information
• information is carried to the CNS
• Integrative Function
• sensory information used to create
•
•
•
•
sensations
memory
thoughts
decisions
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Neuron Structure
10-7
Myelination of Axons
• White Matter
• contains myelinated axons
• Gray Matter
• contains unmyelinated
structures
• cell bodies, dendrites
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Classification of Neurons
• Bipolar
• two processes
• eyes, ears, nose
• Unipolar
• one process
• ganglia
• Multipolar
• many processes
• most neurons of CNS
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Classification of Neurons
• Sensory Neurons
• afferent
• carry impulse to CNS
• most are unipolar
• some are bipolar
• Interneurons
• link neurons
• multipolar
• in CNS
• Motor Neurons
• multipolar
• carry impulses away from
CNS
• carry impulses to effectors
10-10
Types of Neuroglial Cells
• Schwann Cells
• peripheral nervous system
• myelinating cell
• Oligodendrocytes
• CNS
• myelinating cell
• Microglia
• CNS
• phagocytic cell
• Astrocytes
•
•
•
•
•
CNS
scar tissue
mop up excess ions, etc
induce synapse formation
connect neurons to blood
vessels
• Ependyma
• CNS
• ciliated
• line central canal of spinal
cord
• line ventricles of brain
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Types of Neuroglial Cells
10-12
Regeneration of A Nerve Axon
10-13
Resting Membrane Potential
• Inside is negative
relative to the
outside
• polarized
membrane
• due to distribution
of ions
• Na+/K+ pump
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Potential Changes
• At rest membrane is
polarized
• Threshold stimulus
reached
• Sodium channels open
and membrane
depolarizes
• Potassium leaves
cytoplasm and
membrane repolarizes
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Local Potential Changes
• Occur on membranes of dendrites and cell bodies
• Caused by various stimuli
•
•
•
chemicals
temperature changes
mechanical forces
• If membrane potential becomes more negative, it has
hyperpolarized
• If membrane potential becomes more positive, it has
depolarized
• graded
• summation can lead to threshold stimulus that starts an
action potential
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Action Potentials
•
•
•
•
Nerve impulse
Occur on axons
All-or-none
Refractory period
•
absolute - time when threshold stimulus does not start another action
potential
• relative – time when stronger threshold stimulus can start another
action potential
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Action Potentials
10-18
Impulse Conduction
10-19
Saltatory Conduction
10-20
The Synapse
• Nerve
impulses pass
from neuron
to neuron at
synapses
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Synaptic Transmission
Neurotransmitters
are released
when impulse
reaches
synaptic knob
10-22
Synaptic Potentials
• EPSP
•
•
•
•
excitatory postsynaptic potential
graded
depolarizes membrane of postsynaptic neuron
action potential of postsynaptic neuron becomes more
likely
• IPSP
•
•
•
•
inhibitory postsynaptic potential
graded
hyperpolarizes membrane of postsynaptic neuron
action potential of postsynaptic neuron becomes less likely
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Summation of
EPSPs and IPSPs
• EPSPs and IPSPs
are added together
in a process called
summation
• More EPSPs lead
to greater
probability of
action potential
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Neurotransmitters
Acetylcholine
•Acetylcholine is a neurotransmitter in both the peripheral nervous
system, where it activates the muscles, and the central nervous system,
where it acts as a neuromodulator upon plasticity, arousal and reward. It is
one of many neurotransmitters in the autonomic nervous system and the
only neurotransmitter used in the motor division of the somatic nervous
system.
Dopamine
•Dopamine is produced in quite a few areas of the brain, including the
substantia nigra and the ventral tegmental area. Dopamine is also a
neurohormone released by the hypothalamus. Its principle hormonal role
is to inhibit the release of prolactin from the anterior lobe of the pituitary.
Dopamine has important roles in behavior and cognition, voluntary
movement, motivation, punishment and reward, sleep, mood, attention,
working memory and learning.
Neurotransmitters
Serotonin
•Serotonin is a monoamine neurotransmitter, usually found in the
gastrointestinal tract, platelets and the central nervous system. This
chemical is also known as the “happiness hormone”, because it
arouses feelings of pleasure and well-being. Low levels of
serotonin are associated with increased carbohydrate cravings,
depression, sleep deprivations and hypersensitivity to pain.
Gamma Aminobutyric Acid (GABA)
•Gamma Aminobutyric Acid is a protein that in humans is encoded
by the GABRA1 gene. GABA acts at inhibitory synapses in the
brain by binding to specific transmembrane receptors in the plasma
membrane of both pre and postsynaptic neuronal processes. The
primary role of this neurotransmitter is to slow down the neuron
activity.
Neurotransmitters
Glutamate
•This is the most abundant excitatory neurotransmitter in the vertebrate nervous
system. It is also the major excitatory transmitter in the brain, and major mediator
of excitatory signals in the mammalian central nervous system, involved in most
aspects of normal brain functions including cognition, memory and learning.
Epinephrine and Norepinephrine
•These are separate but related hormones secreted by the medulla of the adrenal
glands. These chemicals are also produced at the ends of sympathetic nerve fibers,
where they serve as chemical mediators for conveying the nerve impulses to
effector organs. They are responsible for concentration, attention, mood and both
physical and mental arousal.
Endorphins
•Endorphins are produced by the pituitary gland and the hypothalamus in
vertebrates during exercise, excitement, pain, consumption of spicy food,.
Endorphins contribute to the feeling of well-being and act similarly to opiates.
They are also known to reduce pain and anxiety.
Neurotransmitters
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Impulse Processing
• Neuronal Pools
• groups of interneurons that make synaptic
connections with each other
• interneurons work together to perform a common
function
• each pool receives input from other neurons
• each pool generates output to other neurons
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Convergence
• neuron receives input
from several neurons
• incoming impulses
represent information
from different types of
sensory receptors
• allows nervous system
to collect, process, and
respond to information
• makes it possible for a
neuron to sum impulses
from different sources
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Divergence
• one neuron sends
impulses to several
neurons
• can amplify an
impulse
• impulse from a single
neuron in CNS may be
amplified to activate
enough motor units
needed for muscle
contraction
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Clinical Application
Multiple Sclerosis
• Symptoms
• blurred vision
• numb legs or arms
• can lead to paralysis
• Treatments
•
•
•
•
no cure
bone marrow transplant
interferon (anti-viral drug)
hormones
• Causes
• myelin destroyed in
various parts of CNS
• hard scars (scleroses)
form
• nerve impulses
blocked
• muscles do not receive
innervation
• may be related to a
virus
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