Transcript HS 120 Anatomy and Physiology I Douglas Turner Apr09

Chapter 8
The Nervous System
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
Copyright © 2005, Elsevier, Inc. All rights reserved.
0
Slide 0
Learning Objectives
•
•
•
List the organs and divisions of the nervous
system and describe the generalized functions of
the system as a whole
Identify the major types of cells in the nervous
system and discuss the function of each
Identify the anatomical and functional components
of a three-neuron reflex arc. Compare and contrast
the propagation of a nerve impulse along a nerve
fiber and across a synaptic cleft
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
1
Learning Objectives (cont’d.)
•
•
•
Identify the major anatomical components of the
brain and spinal cord and briefly comment on the
function of each
Compare and contrast spinal and cranial nerves.
Discuss the anatomical and functional
characteristics of the two divisions of the
autonomic nervous system
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
2
Physiology of the Nervous System
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
Copyright © 2005, Elsevier, Inc. All rights reserved.
3
Slide 3
Question
What are the two
principal divisions of
the nervous system?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
4
Organs and Divisions of the Nervous System
• Central nervous system (CNS): Brain
and spinal cord
• Peripheral nervous system (PNS): All nerves
 Autonomic nervous system (ANS)
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
5
Divisions of the Nervous System
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
6
Cells of the Nervous System
• Neurons
 Consist of three main parts
 Dendrites
 Cell body
 Axon
 Classified according to function
 Sensory
 Motor
 Interneurons
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
7
Cells of the Nervous System (cont’d.)
Neuron
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
8
Cells of the Nervous System (cont’d.)
 Schwann cells form myelin sheaths
of axons in the peripheral nervous system (PNS).
 What is the purpose of a myelin sheath?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
9
Cells of the Nervous System (cont'd.)
• Glia (neuroglia)
 Support cells, bringing the cells of nervous tissue
together structurally and functionally
 Three main types of glial cells of the CNS
 What are they?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
10
Answer

Astrocytes

Microglia

Oligodendrocytes
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
11
Cells of the Nervous System (cont'd.)
Glia
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
12
Nerves
• Nerve: Bundle of peripheral axons
 Tract of central axons
 White matter: Tissue composed primarily
of myelinated axons (nerves or tracts)
 Gray matter: Tissue composed primarily
of cell bodies and unmyelinated fibers
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
13
Nerves (cont'd.)
• Nerve coverings: Fibrous connective tissue
 Endoneurium: Surrounds individual fibers within a
nerve
 Perineurium: Surrounds a group (fascicle)
of nerve fibers
 Epineurium: Surrounds the entire nerve
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
14
Question
What is a reflex arc?
What purpose does it
serve?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
15
Reflex Arcs
• Nerve impulses are conducted from receptors to
effectors over neuron pathways or reflex arcs
• Conduction by a reflex arc results in a reflex, either
contraction by a muscle or secretion by a gland
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
16
Reflex Arcs (cont'd.)
• Simplest reflex arcs are two-neuron arcs; they consist
of sensory neurons synapsing in the spinal cord with
motor neurons
• Three-neuron arcs consist of sensory neurons
synapsing in the spinal cord with interneurons that
synapse with motor neurons
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
17
Question
What is a nerve
impulse?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
18
Nerve Impulses
• Self-propagating waves of electrical disturbances that
travel along the surface of a neuron membrane
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
19
Nerve Impulses (cont'd.)
• Mechanism
 Stimulus triggers the opening of Na+ channels in
the plasma membrane of the neuron
 Inward movement of positive sodium ions leaves a
slight excess of negative ions outside at a
stimulated point
 Marks beginning of a nerve impulse
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
20
Conduction of Nerve Impulses
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
21
The Synapse
• Chemical compounds are released from axon
terminals (of a presynaptic neuron) into
a synaptic cleft
• Neurotransmitters bind to specific receptor molecules
in the membrane of a postsynaptic neuron
 Open ion channels, stimulate impulse conduction
by the membrane
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
22
Question
What are examples
of
neurotransmitters?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
23
The Synapse (cont'd.)
• Types of neurotransmitters
 Acetylcholine
 Catecholamines (norepinephrine,
dopamine, and serotonin)
 Other compounds
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
24
Components of a Synapse
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
25
Structure of the Nervous System
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
Copyright © 2005, Elsevier, Inc. All rights reserved.
26
Slide 26
Central Nervous System
• Divisions of the brain (What do they each do?)
 Brainstem

Medulla oblongata

Pons

Midbrain
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
27
Central Nervous System (cont'd.)
 Diencephalon
 Hypothalamus
 Thalamus
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
28
Central Nervous System (cont'd.)
 Cerebellum

Second largest part of the human brain

Helps control muscle contractions to produce
coordinated movements so that we can maintain
balance, move smoothly, and sustain posture
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
29
Central Nervous System (cont'd.)
 Cerebrum

Largest part of the human brain

Outer layer of gray matter is the cerebral cortex,
composed mainly of dendrites and cell bodies of
neurons

Interior of the cerebrum composed mainly of
white matter (nerve fibers arranged in bundles
called tracts)
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
30
Central Nervous System (cont'd.)
The Cerebrum
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
31
Central Nervous System (cont'd.)
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
32
Question
What is the function of
the spinal cord?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
33
Central Nervous System (cont'd.)
• Spinal cord
 Outer part composed of white matter made up of
many bundles of axons called tracts
 Interior is composed of gray matter made up
mainly of neuron dendrites and cell bodies
 Functions as the center for all spinal cord reflexes
 Sensory tracts conduct impulses to the brain

Motor tracts conduct impulses from the brain
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
34
Question
What is a meninge?
What are the three layers of
meninges?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
35
Central Nervous System (cont'd.)
• Coverings and fluid spaces of the brain
and spinal cord
 Coverings
 Cranial bones and vertebrae
 Cerebral and spinal meninges—dura mater,
arachnoid mater, and pia mater
 Fluid spaces—subarachnoid spaces
of meninges, central canal inside cord,
and ventricles in the brain
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
36
Central Nervous System (cont'd.)
Flow of Cerebrospinal Fluid
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
37
Peripheral Nervous System
• Cranial nerves
 Structure—12 pairs are attached to the
undersurface of the brain
 Function—conducts impulses between the brain
and structures in the head and neck and in the
thoracic and abdominal cavities
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
38
Peripheral Nervous System (cont’d.)
• Spinal nerves
 Structure—contains dendrites of sensory neurons
and axons of motor neurons
 Functions—conducts impulses necessary
for sensations and voluntary movements
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
39
Cranial Nerves
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
40
Question
What’s the purpose
of the ANS?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
41
Autonomic Nervous System
• Motor neurons that conduct impulses from
the central nervous system to cardiac muscle, smooth
muscle, and glandular epithelial tissue
• Regulates the body’s autonomic or involuntary
functions
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
42
Autonomic Nervous System (cont'd.)
Innervation of the Major Target Organs by the Autonomic
Nervous System
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
43
Autonomic Nervous System (cont'd.)
• Autonomic neurons
 Preganglionic autonomic neurons conduct from
spinal cord or brainstem to autonomic ganglia
 Postganglionic neurons conduct from autonomic
ganglia to cardiac muscle, smooth muscle, and
glandular epithelial tissue
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
44
Autonomic Nervous System (cont'd.)
• Autonomic or visceral effectors
 Tissues to which autonomic neurons conduct
impulses
• Autonomic conduction paths
 Consist of two-neuron relays
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
45
Autonomic Nervous System (cont'd.)
• Sympathetic nervous system
 Structure
 Sympathetic preganglionic neurons have
dendrites and cell bodies in gray matter
of thoracic and upper lumbar segments
of the spinal cord

Sympathetic postganglionic neurons have
dendrites and cell bodies in sympathetic ganglia
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
46
Autonomic Nervous System (cont'd.)
• Sympathetic nervous system:
 Functions

Serves as the emergency or stress system

Group of changes induced by sympathetic
control is called the fight-or-flight response
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
47
Autonomic Nervous System (cont'd.)
• Parasympathetic nervous system:
 Structure
 Parasympathetic preganglionic neurons have
dendrites and cell bodies in the gray matter of
brainstem and sacral segments of the spinal
cord
 Parasympathetic preganglionic neurons
terminate in parasympathetic ganglia located in
the head and the thoracic and abdominal
cavities close to visceral effectors
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
48
Autonomic Nervous System (cont'd.)
• Parasympathetic nervous system
 Function

Dominates control of many visceral effectors
under normal, everyday conditions
What are examples of
parasympathetic responses?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
49
Autonomic Nervous System (cont'd.)
Autonomic Conduction Paths
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
50
Autonomic Nervous System (cont'd.)
• Autonomic neurotransmitters:
 Cholinergic fibers

Preganglionic axons of parasympathetic and
sympathetic systems and parasympathetic
postganglionic axons

Release acetylcholine
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
51
Autonomic Nervous System (cont'd.)
• Autonomic neurotransmitters
 Adrenergic fibers

Axons of sympathetic postganglionic neurons

Release norepinephrine (noradrenaline)
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
52
Autonomic Nervous System (cont'd.)
• Autonomic nervous system as a whole
 Regulates the body’s autonomic functions
in ways that maintain or quickly restore
homeostasis
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
53
Chapter 8
Let’s Review!
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
Copyright © 2005, Elsevier, Inc. All rights reserved.
54
Slide 54
Question
Some individuals who are depressed have
an abnormally small amount of the
neurotransmitter serotonin at certain
synapses in the brain. One category of
antidepressant drugs is called selective
serotonin reuptake inhibitors. Can you
deduce what action this drug has at a
synapse to increase the amount of
serotonin present in the synaptic cleft?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
55
Answer
• The name of the drug category tells you that the drug
decreases the amount of serotonin that is taken back
into the presynaptic knob after a nerve impulse has
caused its release into the synaptic cleft. Because the
amount of serotonin being taken from the synaptic cleft
decreases, the amount remaining in the synaptic cleft
increases. This restores the chemical imbalance
associated with depression and hopefully relieves the
symptoms. (Hint: The name of the drug is a clue, as is
the discussion in the section about the synapse on pp.
193-195 in the text.)
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
56
Question
Another type of antidepressant
inhibits the enzymes that naturally
break down serotonin at the
synaptic cleft. Can you explain
how this might reduce the
symptoms of depression?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
57
Answer
As explained in the text, some neurotransmitter
molecules are taken back into the presynaptic
knob, whereas others are broken down by
specific enzymes. This particular category of
antidepressants inhibits the breakdown of
serotonin after it is released. Such inhibition of
serotonin destruction increases the amount of
serotonin present in the synaptic cleft, restoring
the original balance and removing the chemical
basis for depression.
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
58
Question
What are the functions of
the medulla oblongata?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
59
Answer
The medulla oblongata is an enlarged
upward extension of the spinal cord that
lies inside the cranial cavity above the hole
in the occipital bone. It is the lowest part of
the brainstem. It has a two-way conduction
pathway between the spinal cord and
higher brain centers, such as the cardiac,
respiratory, and vasomotor centers.
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
60
Question
What are the functions
of the cerebellum?
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
61
Answer
The cerebellum is the secondlargest part of the brain. It plays
an essential part in smooth
coordinated movement,
maintaining equilibrium, and
sustaining normal posture.
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
62
???????????????????????
• Questions???????????
Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.
63