Chapter 7 jk converted

Functions of the Nervous System
 Sensory input – gathering information
 To monitor changes occurring inside and outside
the body
 Changes = stimuli
 Integration
 To process and interpret sensory input and decide
if action is needed
 Motor output
 A response to integrated stimuli
 The response activates muscles or glands
Slide 7.2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Structural Classification of the Nervous
System
 Central nervous system (CNS)
 Brain and Spinal cord
 Acts as integrating and command center – interpret
incoming sensory information and issue instructions
based on past experiences and current conditions
 Peripheral nervous system (PNS)
 Nerves outside the brain and spinal cord
 Link all parts of the body by carrying impulses to the
CNS and back
Slide 7.3

Functional Classification of the
Peripheral Nervous System
 Sensory (afferent) division
Nerve fibers that carry information to the
central nervous system
Figure 7.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.4

 Motor (efferent) division
Nerve fibers that carry impulses away from
the central nervous system
Figure 7.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.5

 Motor (efferent) division
Two subdivisions
 Somatic nervous system = voluntary
nervous system
 Skeletal muscle reflexes such as stretch
reflex are initiated involuntarily by same
fibers
 Autonomic nervous system = involuntary
nervous system
 Sympathetic and parasympathetic
divisions
Slide 7.6

Organization of the Nervous System
Figure 7.2
Slide 7.7

Nervous Tissue: Support Cells
(Neuroglia) - glia
 Astrocytes
 Abundant, star-shaped cells
 Brace neurons
 Form barrier
Slide 7.8
between capillaries
and neurons and make
exchanges between
the two
 Control the chemical
environment of
the brain by capturing ions and
neurotransmitters
Figure 7.3a

Slide 7.9
 Microglia
 Spider-like phagocytes
 Dispose of debris –
dead cells and bacteria
 Ependymal cells
 Line cavities of the
brain and spinal cord
 Circulate
cerebrospinal
fluid with cilia
Figure 7.3b, c

 Oligodendrocytes
Wrap their flat
extensions tightly
around the nerve
fibers
Produce myelin
sheath around nerve
fibers in the central
nervous system
Figure 7.3d
Slide 7.10

 Satellite cells
 Protect neuron cell bodies
 Schwann cells
 Form myelin sheath in the peripheral nervous
system
 Neuroglia are not able to transmit nerve impulses but
do not lose their ability to divide, unlike neurons
Figure 7.3e
Slide 7.11

Nervous Tissue: Neurons
 Neurons = nerve cells
Cells specialized to transmit messages
Major regions of neurons
Cell body – nucleus and metabolic center
of the cell
Processes – fibers that extend from the
cell body
Slide 7.12

Neuron Anatomy
 Cell body
Nissl
substance –
specialized
rough
endoplasmic
reticulum
Neurofibrils –
intermediate
cytoskeleton
that maintains
cell shape Figure 7.4a
Slide 7.13

Neuron Anatomy
 Cell body
Nucleus
Large
nucleolus
Figure 7.4a
Slide 7.14

Neuron Anatomy
 Extensions
outside the cell
body
 Dendrites –
conduct
impulses toward
the cell body
 Axons – conduct
impulses away
from the cell
body
Figure 7.4a
Slide 7.15

Axons and Nerve Impulses
 Axons end in axonal terminals
 Axonal terminals contain vesicles with
neurotransmitters
 Axonal terminals are separated from the
next neuron by a gap
Synaptic cleft – gap between adjacent
neurons
Synapse – junction between nerves
Slide 7.16

Nerve Fiber Coverings
 Schwann cells –
produce myelin
sheaths in jelly-roll
 Nodes of Ranvier –
gaps in myelin
sheath along the
axon
Slide 7.17
Figure 7.5

Neuron Cell Body Location
 Most are found in the central nervous system in
clusters called nuclei
 Bundles of nerve fibers in CNS = tracts
Gray matter – cell bodies and
unmyelinated fibers
White matter – myelinated fibers
 Bundles of nerve fibers in PNS = nerves
 Ganglia – collections of cell bodies outside the
central nervous system Slide 7.18

Functional Classification of Neurons
 Sensory (afferent) neurons
 Cell bodies in a ganglion outside the CNS
 Carry impulses from the sensory receptors to CNS
 Cutaneous (skin) sense organs
 Proprioceptors – detect stretch or tension in
muscles, tendons, joints
 Motor (efferent) neurons
 Cell bodies found in the CNS
 Carry impulses from the central nervous system
Slide 7.19

Functional Classification of Neurons
 Interneurons (association neurons)
Found in neural pathways in the central
nervous system
Cell bodies in the CNS
Connect sensory and motor neurons
Slide 7.20

Neuron Classification
Figure 7.6
Slide 7.21

Structural Classification of Neurons
 Multipolar neurons – many extensions
from the cell body
Figure 7.8a
Slide 7.22

 Bipolar neurons – one axon and one
dendrite
 Rare in adults – in eye and ear only
Figure 7.8b
Slide 7.23

 Unipolar neurons – have a short, single
process leaving the cell body
 Axon conducts nerve impulses both to and
from the cell body
Figure 7.8c
Slide 7.24

Functional Properties of Neurons
 Two main functions
 Irritability – ability to respond to stimuli
 Conductivity – ability to transmit an
impulse
 The plasma membrane at rest is polarized
Fewer positive ions (usually K+) are inside the
cell than outside the cell (usually Na+)
Slide 7.25

Starting a Nerve Impulse
 Depolarization – a
stimulus depolarizes the
neuron’s membrane
 A deploarized membrane
allows sodium (Na+) to
flow inside the membrane
 The exchange of ions
initiates an action
potential (nerve impulse)
in the neuron
Figure 7.9a–c
Slide 7.26

The Action Potential
 If the action potential (nerve impulse) starts, it is
propagated over the entire axon – all-or-none
response
 Potassium ions rush out of the neuron after
sodium ions rush in, which repolarizes the
membrane
 The sodium-potassium pump restores the
original configuration
This action requiresATP
Until repolarization occurs, a neuron cannot
conduct another impulse
Slide 7.27

Nerve Impulse Propagation
 The impulse continues to
move toward the cell body
 Impulses travel faster
when fibers have a myelin
sheath
 Nerve impulse literally
jumps from node to
node because it cannot
cross myelin insulation
Figure 7.9c–e
Slide 7.28

Continuation of the Nerve Impulse
between Neurons
 Impulses are unable to cross the synapse to
another nerve
Neurotransmitter is released from a nerve’s axon
terminal
The dendrite of the next neuron has receptors
that are stimulated by the neurotransmitter
An action potential is started in the dendrites of
the next neuron
Transmission of an impulse is an electrochemical
event Slide 7.29

How Neurons Communicate at
Synapses
Figure 7.10
Slide 7.30

The Reflex Arc
 Reflex – rapid, predictable, and
involuntary responses to stimuli
 Reflex arc – direct route from a sensory
neuron, to an interneuron, to an effector
Figure 7.11a
Slide 7.31

Simple Reflex Arc
Figure 7.11b,c
Slide 7.32

Types of Reflexes and Regulation
 Autonomic reflexes
 Smooth muscle regulation
 Size of eye pupils
 Heart and blood pressure regulation
 Regulation of glands and sweating
 Digestive system and elimination regulation
 Somatic reflexes
 Activation of skeletal muscles
Slide 7.33

Types of Reflexes and Regulation
 Reflex arcs have a minimum five elements
 A sensory receptor – reacts to stimuli
 An effector receptor – muscle or gland
stimulated
 Afferent and efferent neurons connecting
the two
 The CNS integration center
Slide 7.34

Central Nervous System (CNS)
 CNS develops from the embryonic neural
tube – a simple tube
The neural tube becomes the brain and spinal
cord
The opening of the neural tube becomes the
ventricles
Four chambers within the brain
Filled with cerebrospinal fluid
Slide 7.35

Regions of the Brain
 Cerebral hemispheres
 Diencephalon
 Brain stem
 Cerebellum
Slide 7.36
Figure 7.12

Cerebral Hemispheres (Cerebrum)
 Paired (left
and right)
superior parts
of the brain
 Include more
than half of
the brain
mass
Figure 7.13a
Slide 7.37

Cerebral Hemispheres (Cerebrum)
 The surface is
made of
elevated ridges
(gyri) and
shallow grooves
(sulci)
Figure 7.13a
Slide 7.38

Lobes of the Cerebrum
 Fissures (deep grooves) divide the
cerebrum into lobes
 Surface lobes of the cerebrum – named for
cranial bone over them
Frontal lobe
Parietal lobe
Occipital lobe
Temporal lobe
Slide 7.39

Lobes of the Cerebrum
Figure 7.15a
Slide 7.40

Specialized Areas of the Cerebrum
 Somatic sensory area in parietal lobe –
receives impulses from the body’s sensory
receptors (except special senses)
 Occipital lobe – vision and temporal lobe
– auditory
 Primary motor area – sends impulses to
skeletal muscles – frontal lobe
 Broca’s area – involved in our ability to
speak – base of the precentral gyrus
Slide 7.41

Sensory and Motor Areas of the
Cerebral Cortex
Figure 7.14
Slide 7.42

Specialized Area of the Cerebrum
 Cerebral areas involved in special
senses
Gustatory area (taste)
Visual area
Auditory area
Olfactory area
Slide 7.43

 Interpretation areas of the cerebrum
Speech/language region
Language comprehension region
General interpretation area
Slide 7.44

Figure 7.13c
Slide 7.45

Layers of the Cerebrum
 Gray matter
Outermost layer
Composed
mostly of neuron
cell bodies
Cerebral cortex
Figure 7.13a
Slide 7.46

 White matter
Fiber tracts
inside the gray
matter
Example:
corpus callosum
connects
hemispheres
Figure 7.13a
Slide 7.47

 Basal nuclei –
internal islands
of gray matter
 Helps regulate
voluntary motor
activities by
modifying
instructions sent
to the skeletal
muscles Figure 7.13a
Slide 7.48

Diencephalon - interbrain
 Sits on top of the brain stem
 Enclosed by the cerebral hemispheres
 Made of three parts
Thalamus
Hypothalamus
Epithalamus
Slide 7.49

Diencephalon
Figure 7.15
Slide 7.50

Thalamus
 Surrounds the third ventricle of the brain
 The relay station for sensory impulses
passing upward to the sensory cortex
 Transfers impulses to the correct part of
the cortex for localization and
interpretation
Slide 7.51

Hypothalamus
 Under the thalamus
 Important autonomic nervous system
center
Helps regulate body temperature
Controls water balance
Regulates metabolism
Slide 7.52

Hypothalamus
 An important part of the limbic system
(emotions) – emotional-visceral brain
 The pituitary gland is attached to and
regulated by the hypothalamus
Slide 7.53

Epithalamus
 Forms the roof of the third ventricle
 Houses the pineal body (an endocrine
gland)
 Includes the choroid plexus – forms
cerebrospinal fluid
Slide 7.54

Brain Stem
 Attaches to the spinal cord
 Parts of the brain stem
Midbrain
Pons
Medulla oblongata
Slide 7.55

Brain Stem
Figure 7.15a
Slide 7.56

Midbrain
 Mostly composed of tracts of nerve fibers
 The cerebral aqueduct – canal that connects
the 3rd ventricle of the diencephalon to the 4th
ventricle
 Has two bulging fiber tracts – cerebral
peduncles – convey ascending and descending
impulses
 Has four rounded protrusions – corpora
quadrigemina – Reflex centers for vision and
hearing
Slide 7.57

Pons
 The bulging center part of the brain
stem
 Mostly composed of fiber tracts
 Includes nuclei involved in the control of
breathing
Slide 7.58

Medulla Oblongata
 The lowest part of the brain stem
 Merges into the spinal cord
 Includes important fiber tracts
 Contains important control centers
Heart rate control
Blood pressure regulation
Breathing
Swallowing
Vomiting
Slide 7.59

Reticular Formation
 Diffuse mass of gray matter along the
brain stem
 Involved in motor control of visceral
organs
 Reticular activating system plays a role in
awake/sleep cycles and consciousness
 Damage here results in a permanent
coma
Slide 7.60

Reticular Formation
Figure 7.15b
Slide 7.61

Cerebellum
 Two hemispheres with convoluted
surfaces
 Provides involuntary coordination of body
movements – of skeletal muscles, balance
and equilibrium
 Automatic pilot – continually comparing
brain’s intentions with actual body
performance
Slide 7.62

Cerebellum
Figure 7.15a
Slide 7.63

Protection of the Central Nervous
System
 Scalp and skin  Cerebrospinal fluid
 Skull and vertebral  Blood brain barrier
column
 Meninges
Figure 7.16a
Slide 7.64

Meninges
 Dura mater
Double-layered external covering the brain
Periosteum – attached to surface of the
skull
Meningeal layer – outer covering of the
brain and continues as the dura matter of
the spinal cord
Folds inward in several areas that
attaches the brain to cranial cavity
Slide 7.65

Meninges
 Arachnoid layer
 Middle layer that is web-like
 Pia mater
 Internal layer that clings to the surface of the brain
following every fold
Subarachnoid space filled with cerebrospinal
fluid
 Arachnoid villi – projections of arachnoid
membrane protruding through the dura matter
Slide 7.66

Cerebrospinal Fluid
 Similar to blood plasma composition
 Less protein, more vitamin C, different ions
 Formed by the choroid plexus
 Forms a watery cushion to protect the brain
 Circulated in arachnoid space, ventricles,
and central canal of the spinal cord
Slide 7.67

Ventricles and Location of the
Cerebrospinal Fluid
Figure 7.17a
Slide 7.68

Ventricles and Location of the
Cerebrospinal Fluid
Figure 7.17b
Slide 7.69

Blood Brain Barrier
 Includes the least permeable capillaries of
the body – only H2O, glucose, and essential
amino acids get through
 Excludes many potentially harmful
substances
 Useless against some substances
Fats and fat soluble molecules
Respiratory gases
Alcohol
Nicotine
Anesthesia Slide 7.70

Traumatic Brain Injuries
 Concussion
 Slight brain injury – dizzy or lose consciousness
briefly
 No permanent brain damage
 Contusion
 Nervous tissue destruction occurs - does not
regenerate
 If cortex is damaged, coma for hours or life
 Cerebral edema
 Swelling from the inflammatory response
 May compress and kill brain tissue Slide 7.71

Cerebrovascular Accident (CVA)
 Commonly called a stroke
 The result of a clot or a ruptured blood
vessel supplying a region of the brain
 Brain tissue supplied with oxygen from
that blood source dies
 Loss of some functions or death may
result
Slide 7.72

Alzheimer’s Disease
 Progressive degenerative brain disease
 Mostly seen in the elderly, but may
begin in middle age
 Structural changes in the brain include
abnormal protein deposits and twisted
fibers within neurons
 Victims experience memory loss,
irritability, confusion and ultimately,
hallucinations and death
Slide 7.73

Spinal Cord
 Extends from the
medulla oblongata to
the region of T12
 Below T12 is the cauda
equina (a collection of
spinal nerves)
 Enlargements occur in
the cervical and lumbar
regions
Figure 7.18
Slide 7.74

Spinal Cord Anatomy
 Internal gray matter - mostly cell bodies
that surround the central canal of the cord
Dorsal (posterior) horns
Anterior (ventral) horns
Contains motor neurons of the somatic
nervous system, which send their axons out
the ventral root
Together they fuse to form the spinal nerves
Nerves leave at the level of each vertebrae
Slide 7.75

Spinal Cord Anatomy
 Cell bodies of sensory neurons, whose fibers
enter the cord by the dorsal root, are found in an
enlarged area called the dorsal root ganglion
 Damage to this area causes sensation from the
body area served to be lost
Figure 7.19
Slide 7.76

Spinal Cord Anatomy
 Exterior white mater – conduction tracts
 Posterior, lateral, and anterior columns
 Each contains a number of fiber tracts make
up of axons with the same destination and
function
Figure 7.19
Slide 7.77

Spinal Cord Anatomy
 Central canal filled with cerebrospinal
fluid
Figure 7.19
Slide 7.78

 Nerves and ganglia outside the central
nervous system
 Nerve = bundle of neuron fibers
 Neuron fibers are bundled by a
connective tissue sheath
Slide 7.79

Structure of a Nerve
 Endoneurium
surrounds each fiber
 Groups of fibers are
bound into fascicles
by perineurium
 Fascicles are bound
together by
epineurium
Slide 7.80
Figure 7.20

Classification of Nerves
 Classified according to the direction in
which they transmit impulses
 Mixed nerves – carry both sensory and
motor fibers – spinal nerves
 Afferent (sensory) nerves – carry
impulses toward the CNS
 Efferent (motor) nerves – carry impulses
away from the CNS
Slide 7.81

Cranial Nerves
 12 pairs of nerves that mostly serve the
head and neck
 Numbered in order, front to back – names
reveal structures they control
 Most are mixed nerves, but three are
sensory only
 Optic, olfactory, and vestibulocochlear
Slide 7.82

Distribution
of Cranial
Nerves
Figure 7.21
Slide 7.83

Cranial Nerves
 I Olfactory nerve – sensory for smell
 II Optic nerve – sensory for vision
 III Oculomotor nerve – motor fibers to
eye muscles
 IV Trochlear – motor fiber to eye
muscles
Slide 7.84

Cranial Nerves
 V Trigeminal nerve – sensory for the
face; motor fibers to chewing muscles
 VI Abducens nerve –
motor fibers to eye muscles
 VII Facial nerve – sensory for taste;
motor fibers to the face
 VIII Vestibulocochlear nerve –
sensory for balance and hearing
Slide 7.85

Cranial Nerves
 IX Glossopharyngeal nerve – sensory
for taste; motor fibers to the pharynx
 X Vagus nerves – sensory and motor
fibers for pharynx, larynx, and viscera
 XI Accessory nerve – motor fibers to
neck and upper back
 XII Hypoglossal nerve – motor fibers to
tongue
Slide 7.86

Spinal Nerves
 There is a pair of spinal nerves at the
level of each vertebrae for a total of 31
pairs
 Spinal nerves are formed by the
combination of the ventral and dorsal
roots of the spinal cord
 Spinal nerves are named for the region
from which they arise
Slide 7.87

Spinal Nerves
Slide 7.88
Figure 7.22a

Anatomy of Spinal Nerves
 Spinal nerves divide
soon after leaving the
spinal cord
 Dorsal rami – serve the
skin and muscles of the
posterior trunk
 Ventral rami – forms a
complex of networks
(plexus) for the anterior,
which serve the motor
and sensory needs of
the limbs
Figure 7.22b
Slide 7.89

Examples of Nerve Distribution
Figure 7.23
Slide 7.90

Autonomic Nervous System
 The involuntary branch of the nervous
system
 Consists of only motor nerves
 Divided into two divisions
Sympathetic division – mobilizes the body
Parasympathetic division – allows body to
unwind
Slide 7.91

Differences Between Somatic and
Autonomic Nervous Systems
 Nerves
Somatic – one motor neuron – axons extend
all the way to the skeletal muscle they serve

postganglionic nerves
 Effector organs
Somatic – skeletal muscle
Autonomic – smooth muscle, cardiac muscle,
and glands
Slide 7.92

Differences Between Somatic and
 Nerurotransmitters
Somatic – always use acetylcholine
Autominic – use acetylcholine, epinephrine,
or norepinephrine
Slide 7.93

Comparison of Somatic and
Slide 7.94
Figure 7.24

Anatomy of the Parasympathetic
Division
 Originates from the brain stem and S2 –S4
 Neurons in the cranial region send axons out
in cranial nerves to the head and neck organs
 They synapse with the second motor neuron
in a terminal ganglion
 Terminal ganglia are at the effector organs
 Always uses acetylcholine as a
neurotransmitter
Slide 7.95

Anatomy of the Sympathetic
Division – thoracolumbar division
 Originates from T1 through L2
 Preganglionic axons leave the cord in the ventral root,
enter the spinal nerve, then pass through a ramus
communications, to enter a sympathetic chain
ganglion at the sympathetic chain (trunk) (near the
spinal cord)
 Short pre-ganglionic neuron and long postganglionic
neuron transmit impulse from CNS to the effector
 Norepinephrine and epinephrine are neurotransmitters
to the effector organs
Slide 7.96

Sympathetic Pathways
Figure 7.26
Slide 7.97

Anatomy of the Autonomic Nervous
System
Figure 7.25
Slide 7.98

Autonomic Functioning
 Sympathetic – “fight-or-flight”
Response to unusual stimulus
Takes over to increase activities
Remember as the “E” division = exercise,
excitement, emergency, and
embarrassment
Slide 7.99

Autonomic Functioning
 Parasympathetic – housekeeping
activites
Conserves energy
Maintains daily necessary body functions
Remember as the “D” division - digestion,
defecation, and diuresis
Slide 7.100

Development Aspects of the
Nervous System
 The nervous system is formed during the
first month of embryonic development
 Any maternal infection can have extremely
harmful effects
 The hypothalamus is one of the last areas of
the brain to develop – contains centers for
regulating body temperature
Slide 7.101

Development Aspects of the
Nervous System
 No more neurons are formed after birth,
but growth and maturation continues for
several years largely due to myelination
 The brain reaches maximum weight as
a young adult
Slide 7.102

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