Transcript 08_NervousSystem

Essentials of Anatomy & Physiology, 4th Edition
Martini / Bartholomew
8
The Nervous
System
PowerPoint® Lecture Outlines
prepared by Alan Magid, Duke University
Slides 1 to 145
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Nervous System
Two Organ Systems Control All
the Other Organ Systems
• Nervous system characteristics
• Rapid response
• Brief duration
• Endocrine system characteristics
• Slower response
• Long duration
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The Nervous System
Two Anatomical Divisions
•
Central nervous system (CNS)
•
•
•
Brain
Spinal cord
Peripheral nervous system (PNS)
•
•
•
All the neural tissue outside CNS
Afferent division (sensory input)
Efferent division (motor output)
• Somatic nervous system
• Autonomic nervous system
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PERIPHERAL
NERVOUS
SYSTEM
Receptors
Somatic sensory
receptors (monitor
the outside world
and our position
in it)
Visceral sensory
receptors (monitor
internal conditions
and the status
of other organ
systems)
“INPUT”
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Figure 8-1
2 of 7
PERIPHERAL Sensory information
NERVOUS
within
SYSTEM
afferent division
Receptors
Somatic sensory
receptors (monitor
the outside world
and our position
in it)
Visceral sensory
receptors (monitor
internal conditions
and the status
of other organ
systems)
“INPUT”
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Figure 8-1
3 of 7
CENTRAL NERVOUS SYSTEM
Information
Processing
PERIPHERAL Sensory information
NERVOUS
within
SYSTEM
afferent division
Receptors
Somatic sensory
receptors (monitor
the outside world
and our position
in it)
Visceral sensory
receptors (monitor
internal conditions
and the status
of other organ
systems)
“INPUT”
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Figure 8-1
4 of 7
CENTRAL NERVOUS SYSTEM
Information
Processing
PERIPHERAL Sensory information
NERVOUS
within
SYSTEM
afferent division
Motor commands
within
efferent division
Receptors
Somatic sensory
receptors (monitor
the outside world
and our position
in it)
Visceral sensory
receptors (monitor
internal conditions
and the status
of other organ
systems)
“INPUT”
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“OUTPUT”
Figure 8-1
5 of 7
CENTRAL NERVOUS SYSTEM
Information
Processing
PERIPHERAL Sensory information
NERVOUS
within
SYSTEM
afferent division
Motor commands
within
efferent division
includes
Somatic
nervous
system
Receptors
Effectors
Somatic sensory
receptors (monitor
the outside world
and our position
in it)
Visceral sensory
receptors (monitor
internal conditions
and the status
of other organ
systems)
“INPUT”
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Skeletal
muscle
“OUTPUT”
Figure 8-1
6 of 7
CENTRAL NERVOUS SYSTEM
Information
Processing
This diagram is
on next test.
You need to fill
in the boxes
and know the
function of
each branch.
PERIPHERAL Sensory information
NERVOUS
within
SYSTEM
afferent division
Motor commands
within
efferent division
includes
Somatic
nervous
system
Autonomic
nervous system
Parasympathetic
division
Receptors
Figure 8-1
7 of 7
Sympathetic
division
Effectors
Somatic sensory
receptors (monitor
the outside world
and our position
in it)
Visceral sensory
receptors (monitor
internal conditions
and the status
of other organ
systems)
“INPUT”
Smooth
muscle
Skeletal
muscle
Cardiac
muscle
Glands
Adipose
tissue
“OUTPUT”
Nervous System Overview
Red = CNS
Blue = PNS
The Autonomic Nervous System
Autonomic Nervous System
Branch of nervous system that
coordinates cardiovascular,
digestive, excretory, and
reproductive functions
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Autonomic Nervous System
Neural Tissue Organization
Two Classes of Neural Cells
• Neurons
• For information transfer, processing,
and storage
• Neuroglia
• Supporting framework for neurons
• Phagocytes = eat up microbes
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Neural Tissue Organization
Neuroglia in the CNS
Figure 8-4
Neural Tissue Organization
Three Classes of Neurons
• Sensory neurons
• Deliver information to CNS
• Motor neurons
• Stimulate or inhibit peripheral tissues
• Interneurons (=association neurons)
• Located between sensory and motor
neurons
• Analyze inputs, coordinate outputs
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Neural Tissue Organization
Neuron Anatomy
• Cell body
• Nucleus
• Mitochondria, RER, other organelles
• Dendrites
• Several branches
• Signal reception and transmission
toward cell body
• Axon
• Signal propagation Away from cell body
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Neural Tissue Organization
Anatomy of a Motor Neuron
This diagram is
on next test.
You need to
label the parts.
Figure 8-2
Neural Tissue Organization
Two Types of Neuroglia in the PNS
• Satellite cells
• Surround cell bodies
• Schwann cells
• Surround all peripheral axons
• Form myelin sheath on myelinated axons
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Neural Tissue Organization
Schwann Cells and
Axons of Peripheral
Neurons
Figure 8-5
Neural Tissue Organization
Key Note
Neurons perform all of the communication,
information processing, and control
functions of the nervous system. Neuroglia
outnumber neurons and have functions
essential to preserving the physical and
biochemical structure of neural tissue and
the survival of neurons.
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Neuron Function
The Membrane Potential
• Resting Membrane Potential (RMP)
• Excess negative charge inside the neuron.
Excess positive charge outside.
• Maintained by Na+/K+ ion pump (uses ATP)
• Negative voltage (potential) inside
• -70 mV (0.07 Volts)
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Neuron Function
The Cell Membrane at the
Resting Potential
This diagram
is on next
test. You
need to label
each item in
this diagram.
There will be
a checklist of
parts to assist
you.
Figure 8-7
Neuron Function
Changes in Membrane Potential
• Result from changes in ion movement
• Ions move thru trans-membrane channels
• Some membrane channels can open or close.
• Some membrane channels are always open
(=“leak channels.”)
• If Na+ channels open  positive charges enter
cell  membrane potential becomes more (+).
(This is called depolarization.)
• If K+ channels open  positive charges leave
cell  membrane potential becomes more (-).
(This is called hyperpolarization.)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Neuron Function
Key Note
A membrane potential exists across the cell
membrane because (1) the cytosol and the
extracellular fluid differ in their ionic
composition, and (2) the cell membrane is
selectively permeable to these ions. The
membrane potential can quickly change, as
the ionic permeability of the cell membrane
changes, in response to chemical, pressure,
light, sound, etc stimuli.
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Neuron Function
Generation of Action Potential
• Gradual depolarization of membrane until it
reaches the threshold
• Rapid opening of voltage-gated Na+ channels
• Na+ entry causes rapid depolarization (spike in
graph)
• Then voltage-gated K+ channels open
• K+ ions exit causing rapid repolarization
• Refractory period ends as membrane restores
the RMP, thanks to the Na+/K+ pumps.
• An action potential is all-or-none!
Depolarization to threshold
Sodium ions
Local
current
Transmembrane potential (mV)
+30
DEPOLARIZATION
0
_ 60
_ 70
Threshold
1
Resting
potential
0
1
2
Time (msec)
3
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Figure 8-8
2 of 5
Depolarization to threshold
Activation of voltageregulated sodium channels
and rapid depolarization
Sodium ions
Local
current
Potassium ions
Transmembrane potential (mV)
+30
DEPOLARIZATION
0
2
_ 60
_ 70
Threshold
1
Resting
potential
0
1
2
Time (msec)
3
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Figure 8-8
3 of 5
Depolarization to threshold
Activation of voltageregulated sodium channels
and rapid depolarization
Sodium ions
Local
current
Potassium ions
Inactivation of sodium
channels and activation of
voltage-regulated
potassium channels
Transmembrane potential (mV)
+30
DEPOLARIZATION
3
REPOLARIZATION
0
2
_ 60
_ 70
Threshold
1
Resting
potential
0
1
2
Time (msec)
3
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Figure 8-8
4 of 5
Depolarization to threshold
Activation of voltageregulated sodium channels
and rapid depolarization
Sodium ions
Local
current
Potassium ions
+30
Transmembrane potential (mV)
This graph is
on the second
test. You need
to know what is
occurring
during each
phase of the
graph and why
it is occurring.
Inactivation of sodium
channels and activation of
voltage-regulated
potassium channels
DEPOLARIZATION
REPOLARIZATION
0
2
_ 60
_ 70
The return to normal
permeability and resting state
Threshold
1
4
Resting
potential
REFRACTORY PERIOD
0
Figure 8-8
5 of 5
3
1
2
Time (msec)
3
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Neuron Function
Propagation of an Action Potential
• “Continuous” propagation
• Involves entire membrane surface
• Proceeds in series of small steps (so it’s slower)
• Occurs in unmyelinated axons
• “Saltatory” (= leaping/hopping) propagation
• Involves patches of membrane exposed at nodes
(spaces between myelin sheath)
• Proceeds in series of large steps (so it’s faster)
• Occurs in myelinated axons
Neuron Function
The Propagation of
Action Potentials over
Unmyelinated Axons
Figure 8-9(a)
Neuron Function
The Propagation of
Action Potentials
over Myelinated
Axons
Figure 8-9(b)
Neuron Function
Key Note
“Information” travels within the nervous
system primarily in the form of
propagated electrical signals known as
action potentials. The most important
information (e.g., vision, balance,
movement), is carried by myelinated
axons.
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Neural Communication
Synapse Basics
• Intercellular communication
• Axon terminal
• Input to next cell
• Chemical signaling
• Neurotransmitter release
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Neural Communication
Structure of a Synapse
• Presynaptic components
• Axon terminal
• Synaptic knob
• Synaptic vesicles
• Synaptic cleft
• Postsynaptic components
• Neurotransmitter receptors
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Neural Communication
The Structure of a Typical Synapse
Figure 8-10
Neural Communication
Synaptic Function and Neurotransmitters
• Cholinergic synapses
• Release neurotransmitter acetylcholine
• Enzyme in synaptic cleft
(acetylcholinesterase) breaks it down
• Adrenergic synapses
• Release neurotransmitter norepinephrine
• Dopaminergic synapses
• Release neurotransmitter dopamine
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An action potential arrives and
depolarizes the synaptic knob
PRESYNAPTIC
NEURON
Synaptic vesicles
Action potential
EXTRACELLULAR
FLUID
ER
Synaptic
knob
AChE
CYTOSOL
POSTSYNAPTIC
NEURON
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Figure 8-11
2 of 5
Extracellular Ca2+ enters the synaptic
cleft triggering the exocytosis of ACh
An action potential arrives and
depolarizes the synaptic knob
PRESYNAPTIC
NEURON
Synaptic vesicles
Action potential
EXTRACELLULAR
FLUID
ACh
ER
Synaptic
knob
Ca2+
Synaptic
cleft
Ca2+
AChE
CYTOSOL
POSTSYNAPTIC
NEURON
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Chemically regulated
sodium channels
Figure 8-11
3 of 5
Extracellular Ca2+ enters the synaptic
cleft triggering the exocytosis of ACh
An action potential arrives and
depolarizes the synaptic knob
PRESYNAPTIC
NEURON
Synaptic vesicles
Action potential
EXTRACELLULAR
FLUID
ACh
ER
Synaptic
knob
Ca2+
Synaptic
cleft
Ca2+
AChE
CYTOSOL
Chemically regulated
sodium channels
POSTSYNAPTIC
NEURON
ACh binds to receptors and depolarizes
the postsynaptic membrane
Initiation of
action potential
if threshold
is reached
Na2+ Na2+
Na2+
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Na2+ Receptor
Na2+
Figure 8-11
4 of 5
Extracellular Ca2+ enters the synaptic
cleft triggering the exocytosis of ACh
An action potential arrives and
depolarizes the synaptic knob
PRESYNAPTIC
NEURON
Synaptic vesicles
Action potential
EXTRACELLULAR
FLUID
ACh
ER
Synaptic
knob
Ca2+
Synaptic
cleft
Ca2+
AChE
CYTOSOL
Chemically regulated
sodium channels
POSTSYNAPTIC
NEURON
ACh is removed by AChE
(acetylcholinesterase)
ACh binds to receptors and depolarizes
the postsynaptic membrane
Initiation of
action potential
if threshold
is reached
Propagation of
action potential
(if generated)
Na2+ Na2+
Na2+
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Na2+ Receptor
Na2+
Figure 8-11
5 of 5
Neural Communication
Key Note
A synaptic terminal releases a neurotransmitter that binds to the postsynaptic
cell membrane. The result is a brief, local
change in the permeability of the
postsynaptic cell. Many drugs affect the
nervous system by stimulating
neurotransmitter receptors and thus
produce complex effects on perception,
motor control, and emotions.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Neural Tissue Organization
Anatomic Organization of
CNS Neurons
• Nucleus—A center with a
discrete anatomical
boundary
• Gray matter covering of brain
portions. Made up of neuron
cell bodies
• White matter—Bundles of
axons (tracts) that share
origins, destinations, and
functions
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Neural Tissue Organization
Anatomic Organization of PNS Neurons
• Ganglia—Groupings of neuron cell bodies
• Nerve—Bundle of axons supported by
connective tissue
• Spinal nerves
• To/from spinal cord
• Cranial nerves
• To/from brain
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Neural Tissue Organization
The Anatomical Organization of the
Nervous System
Figure 8-6
The Central Nervous System
Meninges—Layers that surround and
protect the brain and spinal cord (CNS)
• Dura mater (“tough mother”)
• Tough, fibrous outer 2 layers. Dural sinus
between them contains CSF.
• Epidural space above dura of spinal cord
• Arachnoid (“spidery”)
• Subarchnoid space
• Cerebrospinal fluid
• Pia mater (“delicate mother”)
• Thin inner layer
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The Central Nervous System
The Cranial Meninges
Figure 8-13(a)
The Central Nervous System
The Spinal Meninges
Figure 8-13(b)
The Central Nervous System
Spinal Cord Basics
• Relays information to/from brain
• Processes some information on
its own
• Divided into 31 segments
• Each segment has a pair of:
• Dorsal root ganglia
• Dorsal roots
• Ventral roots
• Gray matter appears as horns
• White matter organized into
columns
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The Central Nervous System
Gross Anatomy of
the Spinal Cord
Figure 8-14(a)
The Central Nervous System
Gross Anatomy of the Spinal Cord
Red rectangles indicate structures to memorize.
Figure 8-14(b)
The Central Nervous System
Functional Anatomy of the Spinal Cord
Figure 8-15(a)
The Central Nervous System
Sectional Anatomy of the Spinal Cord
Figure 8-15(b)
The Central Nervous System
Key Note
The sensory and motor nuclei (gray matter)
of the spinal cord surround the central canal.
Sensory nuclei are dorsal, motor nuclei are
ventral. A thick layer of white matter
consisting of ascending and descending
axons covers the gray matter. These axons
are organized into columns of axon bundles
with specific functions. This highly organized
structure can enable a clinician to predict the
impact of a particular injury.
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The Central Nervous System
Brain Regions
•
•
•
•
•
Cerebrum
Midbrain
Pons
Medulla oblongata
Cerebellum
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The Central Nervous System
Superior View of Brain
Figure 8-16(a)
The Central Nervous System
Lateral View of Brain
Figure 8-16(b)
The Central Nervous System
Mid-sagittal
Section of Brain
Figure 8-16(c)
The Central Nervous System
Brain Ventricles —The four hollow
chambers in the center of the brain
filled with cerebrospinal fluid (CSF)
• CSF circulates
• From ventricles and central canal
• To subarachoid space
• Accessible by lumbar puncture
• To blood stream
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The Central Nervous System
The Ventricles of the Brain
Figure 8-17
The Central Nervous System
Functions of the Cerebrum
•
•
•
•
Conscious thought
Intellectual activity
Memory
Origin of complex patterns of movement
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The Central Nervous System
Anatomy of Cerebral Cortex
• Highly folded surface (increases S.A.)
• Elevated ridges (gyri) = “hills”
• Shallow depressions (sulci) = “valleys”
• Cerebral Hemispheres
• Longitudinal fissure
• Central sulcus (very impt landmark)
• Boundary between frontal and parietal lobes
• Lateral sulcus – separates temporal lobe.
• Other lobes (temporal, occipital)
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The Central Nervous System
Functions of the Cerebral Cortex
• Hemispheres serve opposite body sides
• Primary motor cortex (pre-central gyrus)
• Directs voluntary movement
• Primary sensory cortex (post-central gyrus)
• Receives somatic sensation (touch, pain,
pressure, temperature)
• Association areas
• Interpret sensation
• Coordinate movement
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The Central Nervous System
The Surface of the Cerebral Hemispheres
Figure 8-19
The Central Nervous System
Hemispheric Lateralization
• Left hemisphere
• General interpretative and speech centers
• Language-based skills
• Right hemisphere
• Spatial relationships
• Logical analysis
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The Central Nervous System
Hemispheric
Lateralization
Figure 8-20
The Central Nervous System
Brain Waves
(Electroencephalogram)
Figure 8-21
The Central Nervous System
Anatomy and Function of the Cerebellum
• Oversees postural muscles (these are the
muscles that maintain posture and correct
body position in different situations.)
• Stores patterns of movement
• Fine tunes most movements/balance
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The Central Nervous System
Functions of the Medulla Oblongata
• Controls crucial organ systems by reflex
• Cardiovascular centers (regulation of heart
rate)
• Respiratory rhythmicity centers (regulation of
breathing rate)
• very important for overall homeostasis
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The Central Nervous System
Key Note
The brain, a large mass of neural tissue,
contains internal passageways and
chambers filled with CSF. The six major
regions of the brain have specific functions.
As you ascend from the medulla oblongata
to the cerebrum, those functions become
more complex and variable. Conscious
thought and intelligence are provided by the
cerebral cortex.
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The Peripheral Nervous System
PNS Basics
• Links the CNS with the body
• Carries all sensory information and motor
commands
• Axons bundled in nerves
• Cell bodies grouped into ganglia
• Includes cranial nerves (12 pairs) and
spinal nerves (31 pairs)
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The Peripheral Nervous System
The Cranial Nerves
Someday you may
have to learn
these names.
Figure 8-25(a)
The Peripheral Nervous System
Key Note
The 12 pairs of cranial nerves are
responsible for the special senses of
smell, sight, and hearing/balance, and
control movement of the eye, jaw, face,
tongue, and muscles of the neck, back,
and shoulders. They also provide
sensation from the face, neck, and
upper chest and autonomic innervation
to thoracic and abdominopelvic organs.
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The Peripheral Nervous System
Dermatomes
•very important!
•each shaded region
corresponds to a specific
spinal nerve
•diagram enables diagnosing
problems in a specific nerve
or nerve root
Left side of picture =
anterior view
A dermotome =
a region of the
body surface
monitored by a
pair of spinal
nerves
Right side of picture =
posterior view
Figure 8-27
The Peripheral Nervous System
Reflex—An automatic involuntary motor
response to a specific stimulus
• The 5 steps in a reflex arc
1. Arrival of stimulus and activation of
receptor
2. Activation of sensory neuron
3. CNS processing of information
4. Activation of motor neuron
5. Response by effector (muscle or gland)
• See the next 5 slides for examples of these.
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Arrival of
stimulus and
activation of
receptor
Stimulus
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Figure 8-27
2 of 6
Arrival of
stimulus and
activation of
receptor
Activation of a
sensory neuron
Dorsal
root
Receptor
Stimulus
KEY
Sensory neuron
(stimulated)
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Figure 8-27
3 of 6
Arrival of
stimulus and
activation of
receptor
Activation of a
sensory neuron
Sensation
relayed to
the brain by
collateral
Dorsal
root
Receptor
Stimulus
Information
processing
in CNS
KEY
Sensory neuron
(stimulated)
Excitatory
interneuron
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Figure 8-27
4 of 6
Arrival of
stimulus and
activation of
receptor
Activation of a
sensory neuron
Receptor
Sensation
relayed to
the brain by
collateral
Dorsal
root
REFLEX
ARC
Stimulus
Ventral
root
Activation of a
motor neuron
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Information
processing
in CNS
KEY
Sensory neuron
(stimulated)
Excitatory
interneuron
Motor neuron
(stimulated)
Figure 8-27
5 of 6
Arrival of
stimulus and
activation of
receptor
Activation of a
sensory neuron
Receptor
Sensation
relayed to
the brain by
collateral
Dorsal
root
REFLEX
ARC
Stimulus
Effector
Response
by effector
Ventral
root
Activation of a
motor neuron
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Information
processing
in CNS
KEY
Sensory neuron
(stimulated)
Excitatory
interneuron
Motor neuron
(stimulated)
Figure 8-27
6 of 6
The Peripheral Nervous System
Examples of Reflexes
• touching hot stove (a “withdrawal” reflex)
• “stretch reflex” - regulates muscle length
and tension (example: patellar reflex aka
“knee jerk reflex”)
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Stretching of muscle tendon
stimulates muscle spindles
Muscle spindle
(stretch receptor)
Stretch
Spinal
cord
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Figure 8-29
2 of 3
Stretching of muscle tendon
stimulates muscle spindles
Muscle spindle
(stretch receptor)
Stretch
Spinal
cord
REFLEX
ARC
Contraction
Activation of motor
neuron produces reflex
muscle contraction
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Figure 8-29
3 of 3
The Peripheral Nervous System
The Flexor Reflex, a Type of Withdrawal
Reflex
Figure 8-30
The Peripheral Nervous System
Key Note
Reflexes are rapid, automatic responses
to stimuli that “buy time” for the planning
and execution of more complex
responses that are often consciously
directed.
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The Autonomic Nervous System
Divisions of the ANS
• Sympathetic division
• Preganglionic neurons in the thoracic and
lumbar segments of the spinal cord
• “Fight or flight” system
• Parasympathetic division
• Preganglionic neurons in the brain and
sacral segments
• “Rest and digest” system
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The Autonomic Nervous System
Key Note
The two divisions of the ANS operate
largely without our awareness. The
sympathetic division increases
alertness, metabolic rate, and
muscular abilities; the
parasympathetic division reduces
metabolic rate and promotes visceral
activities such as digestion.
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The Autonomic Nervous System
The Somatic and
Autonomic Nervous
Systems
The Organization of
the Somatic and
Autonomic Nervous
System
Figure 8-33(b)
The Autonomic Nervous System
The Sympathetic Division
Figure 8-34
The Autonomic Nervous System
Effects of Sympathetic Activation
•
•
•
•
•
•
Generalized response in crises
Increased alertness
Feeling of euphoria and energy
Increased cardiovascular activity
Increased respiratory activity
Increased muscle tone
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The Autonomic Nervous System
The Parasympathetic Division
Figure 8-35
The Autonomic Nervous System
Effects of Parasympathetic Activation
• Relaxation
• Food processing
• Energy absorption
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The Autonomic Nervous System
Relationship between the Two Divisions
• Sympathetic division reaches visceral and
somatic structures throughout the body
• Parasympathetic division reaches only
visceral structures via cranial nerves or in
the abdominopelvic cavity
• Many organs receive dual innervation
• In general, the two divisions produce
opposite effects on the their target organs
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings