chapter © 2011 the mcgraw-hill companies, inc. all rights reserved. 25 the nervous system

CHAPTER

© 2011 The McGraw-Hill Companies, Inc. All rights reserved.

25The Nervous

System


25-2

Learning Outcomes

25.1 Explain the difference between the central nervous system and the peripheral nervous system.

25.2 Describe the functions of the nervous system.

25.3 Describe the structure of a neuron.

25.4 Describe the function of a nerve impulse and how a nerve impulse is created.


25-3

Learning Outcomes (cont.)

25.5 Describe the structure and function of a synapse.

25.6 Describe the function of the blood-brain barrier.

25.7 Describe the structure and functions of meninges.

25.8 Describe the structure and functions of the spinal cord.


25-4


25.9 Describe the location and function of cerebrospinal fluid.

25.10 Define reflex and list the parts of a reflex arc.

25.11 List the major divisions of the brain and give the general functions of each.

25.12 Explain the functions of the cranial and spinal nerves.


25-5


25.13 Describe the differences between the somatic nervous system and autonomic nervous system.

25.14 Explain the two divisions of the autonomic nervous system.

25.15 Describe the causes, signs and symptoms, and treatments of various diseases and disorders of the nervous system.


25-6

Introduction

• Highly complex system of two parts

– Central nervous system (CNS)

– Peripheral nervous system (PNS)

• Controls all other organ systems and is important for maintaining balance within those systems

Disorders are numerous and often difficult to diagnose and treat

Disorders are numerous and often difficult to diagnose and treat


25-7

General Functions of the NS

• CNS– Brain– Spinal cord

• PNS– Peripheral nerves– Two sections

• Somatic nervous system (SNS)

– Skeletal or voluntary muscles

• Autonomic nervous system (ANS)

– Automatic functions


25-8

General Functions (cont.)

• Three types of neurons– Afferent or sensory nerves

• Sensory information from environment or inside body to CNS for interpretation

– Efferent or motor nerves• Impulses from CNS to PNS to allow for movement

or action

– Interneurons • Interpretive neurons between afferent and efferent

nerves in the CNS


25-9

Apply Your Knowledge

Match the following:

___ Somatic nervous system A. Motor nerves

___ Autonomic nervous system B. Governs skeletal or voluntary muscles

___ Afferent nerves C. Governs respiratory and GI systems

___ Efferent nerves D. Go-betweens or interpreters

___ Interneurons E. Sensory nerves

C

A

E

D

B

ANSWER:


25-10

Neuron Structure

• Functional cells of NS

• Transmit electrochemical messages called nerve impulses to – Other neurons – Effectors (muscles

or glands)


25-11

Neuron Structure (cont.)

• Neurons lose their ability to divide – If destroyed, not replaced

• Neuralgia– Support cells for neurons that can divide– Astrocytes – anchor blood vessels to nerves– Microglia – act as phagocytes– Oligodendrocytes – assist with production of

myelin sheath


25-12


Neurons have a cell body and processes called nerve fibers that extend from the cell body.

Neurons have a cell body and processes called nerve fibers that extend from the cell body.

Dendrites – short Receive nerve impulses

for the neuron

Axons – long Send nerve impulses

away from the cell body


25-13


• White matter – axons with myelin sheath – Schwann cells

• Wrap around some axons

• Cell membranes contain myelin

• Myelin insulates axons and enables axons to send nerve impulses more quickly

• Gray matter – axons without myelin sheath

Schwann cells

Axon

Dendrites


25-14


True or False:

___ Effectors are neurons.

___ Neurons can reproduce.

___ Astrocytes anchor blood vessels to nerve cells.

___ Microglia act as phagocytes.

___ Oligodendrocytes are reproductive cells.

___ Repolarization is the return to the resting state.

F

T

T

F

T

F

ANSWER:

They are the muscles or glands.

Neurons cannot reproduce.

They take part in myelin production.

GOOD JOB!


25-15

Nerve Impulse • Membrane potential

– Neuron cell membrane at rest is in a polarized state• Inside of cell membrane is negative• Outside of cell membrane is positive due to more Na+ and K+

– As Na+ and K+ move into the cell, the membrane becomes depolarized

• Inside becomes more positive• Action potential (nerve impulse) is created

– Repolarization occurs when K+ and later Na+ move to the outside of the cell membrane

• Return of the cell to polarized (resting) state


25-16

Nerve Impulse (cont.)

• Impulse travels down axon to synaptic knob – Vesicles or small sacs in synaptic knob

• Produce chemicals called neurotransmitters

– Neurotransmitters are released by synaptic knob• Allow impulse transmission to postsynaptic

structures– Dendrites– Cell bodies– Axons of other neurons


25-17

Nerve Impulse (cont.)

• Functions of neurotransmitters– Cause muscles to contract or relax

– Cause glands to secrete products

– Activate or inhibit neurons


25-18


What is the function of neurotransmitters?

ANSWER: Neurotransmitters cause muscles to contract or relax, cause glands to secret products, activate neurons to send nerve impulses, or inhibit neurons from sending them.

Right!


25-19

Central Nervous System

• Includes the spinal cord and brain

• Blood-brain barrier– Protects layers of the membranes

of the CNS– Formed by tight capillaries

• Prevents unwanted substances from entering the CNS tissues

• Inflammation can make more permeable


25-20

Central Nervous System (cont.)

• Meninges –protect brain and spinal cord– Dura mater

• Tough outer layer

– Arachnoid mater • Middle layer (web-like)

– Pia mater • Innermost and most

delicate• Directly on top of brain

and spinal cord• Holds blood vessels on the

surface of these structures


25-21

Central Nervous System (cont.)

– Epidural space • Above dura mater

– Subdural space• Below dura mater

– Subarachnoid space • Between arachnoid mater and pia mater• Contains cerebrospinal fluid (CSF) • Cushions CNS


25-22

Spinal Cord• Slender structure continuous with

the brain

• Descends into the vertebral canal and ends around the level of the first or second lumbar vertebra

• 31 spinal segments: – 8 cervical segments – 12 thoracic segments – 5 lumbar segments – 5 sacral segments– 1 coccygeal segment


25-23

Spinal Cord (cont.)


25-24

Spinal Cord (cont.)

• Gray matter – Inner tissue with darker color

– Contains neuron cell bodies and their dendrites

– Divisions are called horns

– Central canal runs down the entire length of the spinal cord through the center of the gray matter

Spinal Cord/Nerve


25-25

Spinal Cord (cont.)

• White matter

– Outer tissue

– Contains myelinated axons

– Divisions are called columns (funiculi)• Columns contain groups of axons called

nerve tracts

Spinal Cord/Nerve

Spinal Cord/Nerve


25-27

Spinal Cord (cont.)

• One function of the spinal cord is to carry sensory information to and from the brain

• Ascending tracts – Carry sensory information up to the brain

• Descending tracts – Carry motor information down from the brain

to muscles and glands


25-28

Spinal Cord (cont.)

• Reflexes – Another function of the spinal cord is to

participate in reflexes – Reflex – a predictable, automatic response to

stimuli

Receptor Sensory Neurons

Effectors Motor Neurons

Interneurons


25-29

Brain

• Four sections

–Cerebrum

–Diencephalon

–Brain stem

–Cerebellum


25-30

Cerebrum

• Largest section• Two cerebral hemispheres

– Connected by a thick bundle of nerve fibers called the corpus callosum

– Longitudinal fissure between hemispheres

• Sulci – grooves on surface

• Gyri or convolutions – bumps of brain matter between sulci

Brain


25-31

Cerebrum (cont.)

• Lobes– Frontal

• Motor areas for voluntary body movements

– Parietal • Somatosensory – interprets

sensations

– Temporal • Auditory – interprets sounds

– Occipital • Interprets what a person

sees

Frontal Parietal

OccipitalTemporal


25-32

Cerebrum (cont.)

• Cortex– Outer layer – gray

matter• Contains about 75%

of all neurons

– Inner layer – white matter

– Functions• Interpret sensory

information• Initiate body

movements• Stores memories and

creates emotions

• Ventricles– Interconnected

cavities within the brain

– Filled with CSF


25-33

Diencephalon

• Between the cerebral hemispheres superior to the brain stem

• Thalamus

– Relay station for sensory information going to the cerebral cortex for interpretation

• Hypothalamus

– Maintains homeostasis by regulating vital activities

Brain


25-34

Brain Stem

• Connects the cerebrum to

the spinal cord• Midbrain

– Just beneath diencephalon

– Controls both visual and auditory reflexes

• Pons – Rounded bulge on

underside of brain stem– Between midbrain and

medulla oblongata– Regulates respiration

• Connects the cerebrum to

the spinal cord• Midbrain

– Just beneath diencephalon

– Controls both visual and auditory reflexes

• Pons – Rounded bulge on

underside of brain stem– Between midbrain and

medulla oblongata– Regulates respiration

• Medulla oblongata – Inferior portion of brain

stem– Directly connected to

spinal cord– Controls many vital

activities, such as heart rate, blood pressure, and breathing

Brain


25-35

Cerebellum

• Location– Inferior to the occipital lobes of the

cerebrum– Posterior to the pons and medulla

oblongata

• Coordinates – Complex skeletal muscle contractions that

are needed for body movements– Fine movements

Brain


25-37

Preventing Brain and Spinal Cord Injuries• Wear appropriate

protective gear for sports

• Avoid diving into unknown waters

• Always wear seat belts

• Follow safety rules on playgrounds

• Children should be in car seats appropriate for age and weight

• Know how to get help quickly in emergencies

• Follow traffic rules and signs while walking, biking, or driving


25-38



___ Meninges A. Carry motor information from brain

___ Ascending tracts B. Stores memories and creates emotions

___ Descending tracts C. Grooves on the surface of the cerebrum

___ Cerebral cortex D. Carry sensory information to the brain

___ Hypothalamus E. Predictable, automatic response to stimuli

___ Sulci F. Maintains homeostasis

___ Cerebellum G. Coordinates skeletal muscle contractions

___ Reflexes H. Protects the brain and spinal cord

B

F

C

G

E

D

A

H

SUPER!


25-39

Peripheral Nervous System

• Nerves that branch off the CNS

• Peripheral nerves– Two types:

• Cranial nerves

• Spinal nerves


25-40

Cranial NervesI. Olfactory nerves

– Carry smell information to the brain for interpretation

II. Optic nerves – Carry visual information to the brain for

interpretation

III. Oculomotor nerves – Found within the muscles that move the eyeball,

eyelid, and iris

IV. Trochlear nerves – Act in the muscles that move the eyeball.


25-41

Cranial Nerves (cont.)

V. Trigeminal nerves – Carry sensory information from the surface

of the eye, the scalp, facial skin, the lining of the gums, and the palate to the brain for interpretation

– Also found within the muscles needed for chewing

VI. Abducens nerves – Act in the muscles that move the eyeball


25-42


VII. Facial nerves – Found in the muscles of facial

expression as well as in the salivary and tear glands

– Also carry sensory information from the tongue

VIII. Vestibulocochlear nerves – Carry hearing and equilibrium

information from the inner ear to the brain for interpretation


25-43


IX. Glossopharyngeal nerves – Carry sensory information from the throat

and tongue to the brain for interpretation– Also act in the muscles of the throat

X. Vagus nerves – Carry sensory information from the

thoracic and abdominal organs to the brain for interpretation

– Also found within the muscles in the throat, stomach, intestines, and heart


25-44


XI. Accessory nerves – Found within the muscles of the throat,

neck, back, and voice box

XII. Hypoglossal nerves – Found within the muscles of the tongue


25-45

Spinal Nerves• Peripheral nerves originating from the

spinal cord

• 31 pairs of spinal nerves– 8 pairs of cervical nerves (C1 through C8) – 12 pairs of thoracic nerves (T1 through

T12)– 5 pairs of lumbar nerves (L1 through L5) – 5 pairs of sacral nerves (S1 through S5) – 1 pair of coccygeal nerves (C0) Spinal

Nerves


25-46

Spinal Nerves (cont.)

• Dermatome – Skin segment innervated by spinal nerve– C1 is not associated with a dermatome

• Ventral root– Axons of motor neurons only

• Dorsal root– Axons of sensory neurons only– Dorsal root ganglion

• Contains cell bodies of sensory neurons


25-47

Spinal Nerves (cont.)

• Main portions of spinal nerves fuse to form nerve plexuses– Cervical – supply skin and muscles of neck

• Phrenic nerve originates from this plexus and controls the diaphragm

– Brachial – control muscles in the arms– Lumbosacral – lower abdomen, external

genitalia, buttocks, thighs, legs, and feet• Sciatic nerve originates from this plexus and

controls muscles of legs

Spinal Nerves


25-49

Somatic Nervous System • Nerves that connect the CNS to skin and

skeletal muscle

• “Voluntary” nervous system – Controls skeletal muscles, which are under voluntary

control


25-50

Autonomic Nervous System • Nerves that connect the CNS to organs and

other structures

• “Involuntary” nervous system

• Motor neurons located in ganglia

– Neuron cell bodies outside the CNS


25-51

Autonomic Nervous System (cont.)

• Sympathetic division– “Fight or flight” – Prepares body for stressful

or emergency situations– Neurons release neurotransmitter

norepinephrine• Increases heart and breathing rates• Slows down muscles of the stomach and intestines• Dilates pupils• Constricts blood vessels – increases blood

pressure


25-52

Autonomic Nervous System (cont.) • Parasympathetic division

– Prepares body for rest and digesting– Controls most of the body’s organs– Releases acetylcholine

• Slows heart and breathing rates• Constricts pupils• Activates muscles of stomach and intestine

– No communication with blood vessels

• Sympathetic and parasympathetic divisions are antagonistic


25-53


What is the difference between the sympathetic and parasympathetic nervous systems?

ANSWER: The sympathetic nervous system prepares the body for stress. It releases norepinephrine, causing an increase in heart and respiratory rate, slows down the GI system, and dilates pupils. The sympathetic system also controls constriction of blood vessels.

The parasympathetic system prepares the body for resting and digesting. It releases acetylcholine, which slows heart and respiratory rates, constricts pupils, and stimulates the GI system. It has no effect on most blood vessels.


25-54

Neurologic Testing

• Typical neurologic examination– State of consciousness

– Reflex activity

– Speech patterns

– Motor patterns


25-55

Diagnostic Procedures• Lumbar puncture

• Magnetic resonance imaging (MRI)

• Positron emission tomography (PET) scan

• Cerebral angiography

• Computerized tomography (CT) scan

• Electroencephalogram (EEG)

• X-ray


25-56

Cranial Nerve Tests

• Olfactory nerves (Cranial nerve I)– Have patient smell various substances

• Cranial nerves III, IV, and VI– Have patient track movement of finger

• Cranial nerve V– Have patient clench teeth, feel jaw muscles


25-57

Cranial Nerve Tests (cont.)

• Cranial nerve VII– Check patient’s facial expression

• Cranial nerve XII– Have patient extend his tongue and move it

from side to side


25-58

Reflex Testing

• Areflexia– Absence of a reflex

• Hyporeflexia– Decreased reflex

• Hyperreflexia– Stronger-than-normal reflex


25-59

Reflex Testing (cont.)

• Biceps reflex – Absence indicates spinal cord damage in

the cervical region

• Knee reflex – Absence may indicate damage to lumbar or

femoral nerves

• Abdominal reflexes– Used to evaluate damage to thoracic spinal

nerves


25-60



___ State of consciousness A. Determines the health of peripheral nerves

___ Reflex activity B.Loss of balance,

abnormal posture

___ Speech patterns C.Stupor, delirium,

vegetative

___ Motor patterns D.Loss of ability to form words

A

D

B

C

ANSWER:


25-61

Common Diseases and Disorders

Disease/Disorder Description

Alzheimer’s disease

Progressive, degenerative disease of the brain

Amyotrophic lateral sclerosis (ALS)

Lou Gehrig’s disease

Degeneration of neurons in the spinal cord and brain

Bell’s palsy Weak or paralyzed facial muscles


25-62

Common Diseases and Disorders (cont.)


Brain tumors and cancers

Abnormal growths

Can be primary or secondary tumors

Most common – gliomas

Epilepsy and seizures

Occurs as a result of bursts of electrical signals that disrupt normal brain functioning

Guillain-Barré Syndrome

Body’s immune system attacks the PNS


25-63



HeadachesTension

Migraines

Cluster

Episodic or chronic

With aura/without aura

Form of migraines; occurs in groups

Meningitis Inflammation of meninges

Multiple sclerosis (MS)

Chronic disease of CNS

Myelin is destroyed


25-64



Neuralgias Disorders causing nerve pain

Parkinson’s disease

Progressive and degenerative motor system disorder

Sciatica Damage to sciatic nerve

Stroke Brain cells die because of an inadequate blood flow; “brain attack”


25-65


True or false:

___ Alzheimer’s disease is a progressive degenerative disease of the brain.

___ Epilepsy is due to degenerative neurons in the spinal cord and brain.

___ Neuralgias are motor system disorders.

___ Stroke occurs when brain cells die because of inadequate blood flow.

F

F

T

Due to a burst of electrical signals that disrupt brain function.

They are group of disorders referred to as nerve pain.

T

ANSWER: Bravo!


25-66

In Summary

25.1 The central nervous system is composed of the brain and spinal cord. The peripheral nervous system consists of the peripheral nerves located throughout the body. The peripheral nervous system is further divided into two distinct systems: the somatic and autonomic nervous systems.

25.2 There are three separate types of neurons to carry out the functions of the nervous system. The afferent (sensory) nerves, the efferent (motor) nerves, and the interpretive interneurons that act as “interpreters” between the afferent and efferent nerves.


25-67

In Summary (cont.)

25.3 All neurons are composed of a cell body, the shorter and more numerous dendrites that receive information for the cell body, and the longer axons that bring an impulse from the cell body to the dendrite of the next neuron.

25.4 The function of a nerve impulse is the sending of information either from the CNS to the PNS or vice versa.

At rest, a neuron is said to be in a polarized state, and when it responds to stimuli, depolarization takes place.

Repolarization occurs after the electrical current (impulse) has passed.


25-68

In Summary (cont.)

25.5 A synapse is the space between the axon of one neuron and the dendrite of the next. At the end of each axon is the synaptic knob, which contains vesicles that produce neurotransmitters. These are released by the synaptic bulb to allow impulse transmission to continue to the next neuron.

25.6 The blood-brain barrier is a layer of tightly woven capillaries that protects the delicate tissues of the CNS. This barrier prevents certain substances, such as various waste products and drugs, from easily crossing this barrier and entering the brain tissues.


25-69

In Summary (cont.)

25.7 The meninges, a triple-layered membrane protecting the brain and spinal cord, are composed of the following layers:

The tough outer layer is the dura mater.

The space between the cranium and the dura mater is called the epidural space.

Below the dura mater is the subdural space.

The middle layer is the arachnoid, and below it is the subarachnoid space, which contains cerebrospinal fluid (CSF).

The innermost layer is the pia mater.


25-70

In Summary (cont.)

25.8 The spinal cord is continuous with the brain and consists of 31 spinal segments:

8 cervical 5 sacral

12 thoracic 1 coccygeal

5 lumbar

The basic function of the spinal cord is to carry sensory information from the body to the brain and motor information from the brain to the muscles and glands of the body.


25-71

In Summary (cont.)

25.9 Cerebrospinal fluid (CSF) is located within the subarachnoid space of the brain and within the central canal of the spinal cord. It cushions the brain and spinal cord.

25.10A reflex is a predictable automatic response to a stimulus. A typical reflex flows as follows: Sensory receptors send information (impulse) to the interneurons, which in turn send the information on to the effectors of the motor neurons, producing a response.


25-72

In Summary (cont.)

25.11The cerebrum is the largest part of the brain and is divided into two hemispheres subdivided into four lobes: frontal, parietal, temporal and occipital.

The diencephalon contains the thalamus and hypothalamus.

The brain stem consists of three parts: the midbrain, pons, and medulla oblongata.

The cerebellum is the final area of the brain.


25-73

In Summary (cont.)

25.12Twelve cranial nerves carry sensory information:

Olfactory Optic Oculomotor

Trochlear Trigeminal Abducens

Facial Vagus Vestibulocochlear

Glossopharyngeal Accessory Hypoglossal

There are 31 pairs of spinal nerves, each except C1 innervating a dermatome. Refer to Figure 25.8 for a map of the spinal nerves.


25-74

In Summary (cont.)

25.13The somatic nervous system connects the CNS to the skin and skeletal muscle (voluntary functions).

The autonomic nervous system connects the CNS to the internal organs (involuntary functions).

25.14The autonomic nervous system is divided into the sympathetic system, which prepares the body for “fight or flight” (stressful) situations, and the parasympathetic system, which is the body’s everyday “resting” system for normal situations.


25-75

In Summary (cont.)

25.15There are many and varied diseases and disorders related to the nervous system. The signs, symptoms, and treatments of these diseases are as varied as the diseases themselves. Many of the more common diseases are included in the Pathophysiology section at the end of this chapter.


25-76

Activity of the nervous system improves the capacity for activity, just as exercising a muscle makes it stronger.”

~ Dr. Ralph Gerard

End of Chapter 25

chapter © 2011 the mcgraw-hill companies, inc. all rights reserved. 25 the nervous system

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