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Nervous System
Chapter 7
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Outline
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Functions of the Nervous System
Nervous Tissue: Neuron Structure and Types
The Nerve Impulse
Synaptic Transmission
System Organization: Main Divisions of the
Nervous System
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Central Nervous System
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Brain
Spinal Cord
Peripheral Nervous System
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Central Nervous System (CNS)
Peripheral Nervous System (PNS)
(Spinal Cord), Nerves and Ganglia
Homeostasis
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Functions of the Nervous System
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Helps coordinate all the other systems of the body
in conjunction with the endocrine system.
Helps govern all organ function and the
composition of blood.
Helps coordinate movement.
Helps regulate blood pressure, heart rate,
breathing rate.
Helps regulate peristalsis in digestive tract.
Involved in reproduction.
Involved in control of urination and defecation.
Provides us with the ability to reason and
communicate.
Allows positive interaction with environment.
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Nervous Tissue: Neuron Structure and Types
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Nervous Tissue contains two types of cells.
– Neurons transmit nerve impulses between
parts of the nervous system.
– Neuroglia support and nourish neurons.
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Types of Neuroglial Cells
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Central Nervous System Neuroglia
1.
Astrocytes- most abundant; have projections around
2.
3.
4.
neurons & blood capillaries, anchor neurons to nutrient
supply, help determine capillary permeability, control
chemical environment of the neurons
Microglia- spider-like phagocytes, remove debris &
bacteria
Oligodendrocytes- wrap plasma membranes around
neurons, create myelin sheath for CNS neurons,
increases conduction speed of neuronal impulse
Ependymal Cells- line cavities in the brain, cilia
circulates the cerebrospinal fluid- cushioning fluid in
the brain
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Figure 7.3 Supporting (glial) cells of nervous tissue.
Capillary
Myelin sheath
Neuron
Process of
oligodendrocyte
Nerve
fibers
Astrocyte
(a) Astrocytes are the most abundant
and versatile neuroglia.
(d) Oligodendrocytes have processes that form
myelin sheaths around CNS nerve fibers.
Satellite
cells
Neuron
Microglial
cell
(b) Microglial cells are phagocytes that
defend CNS cells.
Fluid-filled cavity
Ependymal
cells
Brain or
spinal cord
tissue
(c) Ependymal cells line cerebrospinal
fluid-filled cavities.
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Cell body of neuron
Schwann cells
(forming myelin sheath)
Nerve fiber
(e) Satellite cells and Schwann cells (which
form myelin) surround neurons in the PNS.
Types of Neuroglial Cells (Cont.)
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Peripheral Nervous System Neuroglia
1.
Schwann Cells- wrap plasma membranes around
2.
neurons, create myelin sheath for PNS neurons,
increases conduction speed of neuronal impulse
Satellite Cells- act as protective, cushioning cells
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Figure 7.5 Relationship of Schwann cells to axons in the peripheral nervous system.
Schwann cell
cytoplasm
Axon
Schwann cell
plasma membrane
(a)
Schwann cell
nucleus
(b)
Neurilemma
Myelin
sheath
(c)
© 2015 Pearson Education, Inc.
Figure 7.3 Supporting (glial) cells of nervous tissue.
Capillary
Myelin sheath
Neuron
Process of
oligodendrocyte
Nerve
fibers
Astrocyte
(a) Astrocytes are the most abundant
and versatile neuroglia.
(d) Oligodendrocytes have processes that form
myelin sheaths around CNS nerve fibers.
Satellite
cells
Neuron
Microglial
cell
(b) Microglial cells are phagocytes that
defend CNS cells.
Fluid-filled cavity
Ependymal
cells
Brain or
spinal cord
tissue
(c) Ependymal cells line cerebrospinal
fluid-filled cavities.
© 2015 Pearson Education, Inc.
Cell body of neuron
Schwann cells
(forming myelin sheath)
Nerve fiber
(e) Satellite cells and Schwann cells (which
form myelin) surround neurons in the PNS.
Neuron Structure
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Neurons contain three basic parts.
– Cell body contains nucleus and other
organelles.
– Dendrites receive signals from sensory
receptors or other neurons.
– Axon conducts nerve impulses to another
neuron.
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Figure 7.4a Structure of a typical motor neuron.
Mitochondrion
Dendrite
Cell body
Nissl substance
Axon hillock
Axon
Neurofibrils
Nucleus
Collateral
branch
One Schwann cell
Axon
terminal
(a)
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Node of Ranvier
Schwann cells,
forming the myelin
sheath on axon
Neuron Types
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Neurons are classified according to function.
– Sensory neurons take impulses from sensory
receptors to the CNS.
– Interneurons receive input from sensory neurons,
and other neurons, and then communicate with
other interneurons connected to the brain and
with motor neurons.
– Motor neurons take nerve impulse away from the
CNS to an effector that carries out responses to
environmental change.
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Types of Neurons
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Figure 7.6 Neurons classified by function.
Central process (axon)
Sensory
Spinal cord
Cell neuron
(central nervous system)
body
Ganglion
Dendrites
Peripheral
process (axon)
Afferent
transmission
Interneuron
(association
neuron)
Peripheral
nervous system
Receptors
Efferent transmission
Motor neuron
To effectors
(muscles and glands)
© 2015 Pearson Education, Inc.
The Nerve Impulse
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The nervous system uses the nerve impulse
to convey information.
– Resting potential is the voltage level when
an axon is not conducting an impulse.
Sodium-potassium pump (requires ATP)
causes greater concentration of Na+ outside
the axon, and greater concentration of K+
inside the axon.
– Unequal ion distribution causes inside of
axon to be negative relative to the
outside.
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Action Potential
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An action potential is a rapid change in
polarity across an axomembrane as the
nerve impulse occurs.
– All-or-none once threshold is reached.
+
 Sodium gates open, allowing Na to
move inside the axon.
+
 Potassium gates open, allowing K to
move outside the axon.
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Propagation of an Action Potential
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Each preceding portion causes an action
potential in the next portion of an axon.
– As soon as an action potential has moved
on, the previous portion of an axon
undergoes a refractory period in which the
sodium gates are unable to open.
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Maintenance of the Resting
Membrane Potential
Bio 130 Human Biology
Figure 11.3
Resting and Action Potential
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Interstitial fluid
Interstitial fluid
Axon cytoplasm
Axon cytoplasm
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REPOLARIZATION
• Sodium channels close
• Potassium channels open
• Potassium diffuses out
• Membrane repolarizes
DEPOLARIZATION
• Sodium channels open
• Sodium diffuses in
• Membrane depolarizes
Membrane potential (mV)
+30
0
PNa
Threshold
PK
–70
0
1
2
3
4
5
6
Time (milliseconds)
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RESTING POTENTIAL
• Sodium and potassium channels closed
• Na+-K+ pump matches rate of leakage
REESTABLISHMENT OF RESTING
POTENTIAL
• Potassium channels close
Interstitial fluid
Interstitial fluid
Axon cytoplasm
Axon cytoplasm
Figure 11.5
Transmission Across a Synapse
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Synapse is point of interaction between neurons.
Not a direct interaction; a space between called
synaptic cleft.
Transmission across a synaptic cleft is carried out
by chemicals called neurotransmitters stored in
synaptic vesicles.
Neurotransmitter binds to receptor on postsynaptic
membrane.
Depending on the neurotransmitter and the
receptor, response of postsynaptic neuron can be
towards excitation or inhibition.
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Figure 7.10 How neurons communicate at chemical synapses.
Axon of
transmitting
neuron
Receiving
neuron
1 Action
potential
arrives.
Vesicles
Dendrite
Axon terminal
Synaptic
cleft
2 Vesicle Transmitting neuron
fuses with
4 Neurotrans3 Neurotrans- mitter binds
plasma
membrane.
mitter is
released into
synaptic cleft.
to receptor
on receiving
neuron’s
membrane.
Neurotransmitter
Na+
Receptor
Synaptic
cleft
Ion
channels
Receiving neuron
© 2015 Pearson Education, Inc.
Neurotransmitter
is broken down
and released.
Na+
Neurotransmitter
molecules
5 Ion channel opens.
6 Ion channel closes.
System Organization Details
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brain
Central Nervous System (CNS)
cranial nerves
brain
spinal cord
spinal cord
spinal nerves
Peripheral Nervous System (PNS)
sensory (afferent) nerves —
carry sensory information
into brain and spinal cord
somatic sensory
nerves: signals
from skin,
muscles,
joints, special
senses
a.
The two divisions of the nervous system.
b.
autonomic
visceral sensory
nerves:
signals from
body organs
motor (efferent) nerves —
carry motor information
from CNS to effectors
somatic motor
nerves: signals
to skeletal
muscles,
voluntary
autonomic motor
nerves: signals
to smooth
muscle, cardiac
muscle, glands,
involuntary
sympathetic
division
“fight or flight”
parasympathetic
division
“rest and digest”
System Organization
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Central Nervous System
– The central nervous system (CNS) is made
up of the spinal cord and the brain.

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Both are wrapped in protective membranes, meninges,
with spaces between meninges filled with
cerebrospinal fluid.
CNS is composed of two types of nervous
tissue.
Gray matter – Cell bodies and short, nonmyelinated
fibers.
 White matter - Myelinated axon bundles or tracts.

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CNS: The Brain
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The Cerebrum.
– The cerebrum, telencephalon, is the
largest portion of the human brain.
 Communicates with, and coordinates
activities of, other parts of the brain.
 Divided into left and right cerebral
hemispheres.
 Divided by longitudinal fissure.
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The Human Brain
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Lobes of Cerebral Hemisphere
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The Brain
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Diencephalon is made up of hypothalamus and
thalamus, and circles the third ventricle.
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Hypothalamus: Hunger, sleep, thirst, body temperature, water
balance; control pituitary gland
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Thalamus: Visual, auditory, somatosensory
Cerebellum is separated from the brain stem by
the fourth ventricle.
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Input from eyes, ears, joints, muscles for maintenance of posture
and balance; coordinated voluntary movements
The brain stem contains the midbrain, pons,
medulla oblongata, reticular formation.
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Medulla oblongata: Regulation of heartbeat, breathing,
vasoconstriction
Reticular formation is a complex network of nuclei and fibers in the
brain stem; regulates alertness, waking up.
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CNS & PNS
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Functions of the Spinal Cord.
– The spinal cord extends from the base of
the brain through the foramen magnum
into the vertebral canal.
– The spinal cord provides a means of
communication between the brain and the
peripheral nerves that leave the cord, and
is a center for reflex actions.
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CNS & PNS: Spinal Cord and Spinal Nerves
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CNS & PNS: Spinal Cord; Reflex Arc
Reflex Arc
Animation
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System Organization
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CNS & PNS: Spinal Cord and Spinal Nerves
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Peripheral Nervous System
– The peripheral nervous system (PNS) is composed of
nerves and ganglia.

Nerves are bundles of axons.
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Both sensory and motor axons exist in the nerves.
Ganglia are areas of nerves containing collections of cell
bodies.
The sensory neurons are subdivided into two
categories: 1. somatic sensory (head, body wall, limbs, special
senses), 2. autonomic sensory (visceral organs)
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The motor neurons are subdivided into two categories:
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Somatic motor (skeletal muscle; voluntary)
Autonomic motor (smooth, cardiac muscle, glands;
involuntary)

The autonomic motors are subdivided into two categories:
 Sympathetic division (fight or flight)
 Parasympathetic division (rest and digest)
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Somatic sensory &
Autonomic sensory
Somatic motors
Autonomic motors
Sympathetic
Parasympath.
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PNS: Autonomic System
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Autonomic system regulates the activity of cardiac
and smooth muscles and glands.
This system covers all motor output to all the
organs and blood vessels of the body.
Broken down to two divisions, both use two
neurons and one ganglion.
– Sympathetic division brings about “fight or flight”
responses; ganglion close to spinal cord.
– Parasympathetic division brings about “rest or
digest”, vegetative responses; ganglion close to
or within effector organ.
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Sympathetic Division
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Parasympathetic Division
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Homeostasis
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Helps coordinate all the other systems of the body
in conjunction with the endocrine system.
Helps govern all organ function and the
composition of blood.
Helps coordinate movement.
Helps regulate blood pressure, heart rate,
breathing rate.
Helps regulate peristalsis in digestive tract.
Involved in reproduction.
Involved in control of urination and defecation.
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Need to Know
Functions of the Nervous System
1.
A.
B.
C.
D.
E.
F.
G.
2.
Coordination of body functions; assisted by endocrine
system
Govern organ function
Regulation of heart rate, breathing, blood pressure
Regulation of coordinated movement
Provides ability to reason and communicate
Regulation of peristalsis
Regulation of urination and defecation
Neuron types
A.
Sensory neurons
B.
Interneurons
C.
Motor neurons
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Need to Know (Cont.)
3.
Nervous System Organization
A.
CNS; brain and spinal cord
B.
PNS; nerves and ganglia
C.
Sensory neurons; somatic & autonomic;
dorsal-root ganglia
D.
Motor neurons; somatic and autonomic
E.
Autonomic motor neuron divisions;
sympathetic and parasympathetic
F.
Placement of ganglia in sympathetic and
parasympathetic divisions
G.
Functionality of both divisions (sympathetic &
parasympathetic)
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4.
5.
Need to Know (Cont.)
Spinal Cord Organization
A.
White and gray matter, what are they?
B.
Dorsal-root ganglia and dorsal roots and
ventral roots
C.
Spinal cord reflex arcs, understand how
they work
Brain
A.
Function of hypothalamus, cerebellum,
medulla oblongata
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