the nervous system - welcome to mrs. cassidy's...

ELAINE N. MARIEB

EIGHTH EDITION

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

PowerPoint® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University

ESSENTIALS

OF HUMAN

ANATOMY

& PHYSIOLOGY

The Nervous System


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


Functions of the Nervous System

Motor output

A response to integrated stimuli

The response activates muscles or glands


Structural Classification of the Nervous

System

Central nervous system (CNS)

Brain

Spinal cord

Peripheral nervous system (PNS)

Nerve outside the brain and spinal cord


Figure 7.1

Functional Classification of Neurons

Sensory (afferent) division

Nerve fibers that carry information to the

central nervous system


Figure 7.1


Motor (efferent) division

Nerve fibers that carry impulses away

from the central nervous system


Figure 7.1


Motor (efferent) division

Two subdivisions

Somatic nervous system = voluntary

Autonomic nervous system = involuntary



Interneurons (association neurons)

Found in neural pathways in the central

nervous system

Connect sensory and motor neurons

99% of neurons in body


Organization of the Nervous System

Figure 7.2


Nervous Tissue: Neurons

Neurons = nerve cells

Cells specialized to transmit messages

Amitotic but extreme longevity (100 yrs. with

proper nutrition)

High metabolic rate (require large amounts of O2

& C6H12O6)

Major regions of neurons

Cell body – nucleus and metabolic center of the cell

Processes – fibers that extend from the cell body


Neuron Anatomy

Cell body (soma)

Nucleus

Large nucleolus

Figure 7.4a–b


Neuron Anatomy

Extensions outside

the cell body –

increase surface area

Dendrites –

conduct impulses

toward the cell

body

Axons – conduct

impulses away

from the cell

body

Figure 7.4a


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


Nerve Fiber Coverings

Myelin sheath – fatty

husk surrounding nerve

fibers (insulator)

Schwann cells –

produce myelin

sheaths in jelly-roll

like fashion

Nodes of Ranvier – gaps

in myelin sheath along

the axon (increases speed

of a nerve impulse)

Figure 7.5


Neuron Cell Body Location

Most are found in the central nervous system

Gray matter – cell bodies and unmylenated

fibers

Nuclei – clusters of cell bodies within the

white matter of the central nervous system

Ganglia – collections of cell bodies outside

the central nervous system


Neuron Classification

Figure 7.6


Starting a Nerve Impulse (Action Potential)

Depolarization – a

stimulus depolarizes the

neuron’s membrane

(inside membrane

becomes more +)

A deploarized membrane

allows Na+ to flow inside

the membrane

The exchange of ions

initiates an action

potential in the neuron

Figure 7.9a–c


The Action Potential If the action potential (nerve impulse) starts, it is

propagated over the entire axon

Eventually the concentration gradient resists more Na+ and Na+ gates close

K+ gates open and K+ ions rush out of the neuron after Na+ ions rush in, which repolarizes the membrane

The Na+/K+ pump restores the original configuration

– Na+ out, K+ in (3Na+:2K+)

This action requires ATP

***Whole process takes a few milliseconds***


Nerve Impulse Propagation

The impulse

continues to move

away from the cell

body

Impulses travel faster

when fibers have a

myelin sheath

Figure 7.9d–f


Continuation of the Nerve Impulse

between Neurons

Impulses are able to cross the synapse to another nerve

Neurotransmitter is released from a nerve’s axon terminal (ie. ACh)

The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter

An action potential is started in the dendrite


How Neurons Communicate at Synapses

Figure 7.10

ELAINE N. MARIEB

EIGHTH EDITION



ESSENTIALS

OF HUMAN

ANATOMY

& PHYSIOLOGY

The Nervous System


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


Simple Reflex Arc

Figure 7.11b–c


The Brain

Intricate mass of soft,

highly developed,

complex nervous tissue

Females = 3 lbs.

(1450g)

Males = 3.5 lbs.

(1600g)


Regions of the Brain

Cerebral hemispheres

Diencephalon

Brain stem

Cerebellum

Figure 7.12b


Cerebral Hemispheres (Cerebrum)

Paired (left and

right) superior

parts of the brain

Approx 83% of

brain mass

Most conscious

behavior

“Executive Suite”

Figure 7.13a


Cerebral Hemispheres (Cerebrum)

The surface is

made of ridges

(gyri “twisters”)

and grooves

(sulci “furrows”)

Figure 7.13a


Lobes of the Cerebrum

Fissures (deep grooves) divide the cerebrum into

lobes

ie. longitudinal & transverse

Surface lobes of the cerebrum

Frontal lobe – controls voluntary motor

functions (right controls left)

Parietal lobe – receives/interprets impulses for

pain, touch, heat, cold, distances, size & shapes

Occipital lobe – controls eye sight

Temporal lobe – auditory & olfaction area


Lobes of the Cerebrum

Figure 7.15a


Specialized Areas of the Cerebrum

Somatic sensory area – receives impulses

from the body’s sensory receptors

Primary motor area – sends impulses to

skeletal muscles

Broca’s area – involved in our ability to speak

Directs muscles of tongue, throat & lips to

articulate words

Recognition of words, interpret meaning

(spoken or written)


Sensory and Motor Areas of the Cerebral

Cortex

Figure 7.14



Cerebral areas involved in special senses

Gustatory area (taste)

Visual area

Auditory area

Olfactory area



Interpretation areas of the cerebrum

Speech/language region

Language comprehension region

General interpretation area



Figure 7.13c


Layers of the Cerebrum

Gray matter

Outer layer, 2-4

mm thick

Composed

mostly of neuron

cell bodies

Figure 7.13a


Layers of the Cerebrum

White matter

Myelinated

fibers inside the

gray matter

Example:

corpus

callosum -

connects

hemispheres

Figure 7.13a


Diencephalon

Sits on top of the brain stem – central core

Enclosed by the cerebral hemispheres

Made of three parts

Thalamus

Hypothalamus

Epithalamus


Diencephalon

Figure 7.15


Thalamus

Egg-shaped mass of gray matter that

surrounds the third ventricle

Makes up 80% of diencephalon

The relay station for sensory impulses

Transfers impulses to the correct part of the

cortex for localization and interpretation

“Gateway to the cerebral cortex”


Hypothalamus

Below the thalamus

Forms the lateral walls & floor of 3rd ventricle

Important autonomic nervous system (bp, heart rate

peristalsis, respiratory rate, pupil size, etc) center

Helps regulate body temperature

Controls water balance (thirst)

Regulates metabolism

Appetite control

Biological clock


Hypothalamus

An important part of the limbic system

(emotions)

The pituitary gland is attached to the

hypothalamus


Epithalamus

Forms the roof of the third ventricle

Houses the pineal body (an endocrine gland

that secretes melatonin)

Includes the choroid plexus – forms

cerebrospinal fluid


Brain Stem

Attaches to the spinal cord

Parts of the brain stem

Midbrain

Pons

Medulla oblongata


Brain Stem

Figure 7.15a


Midbrain

Mostly composed of tracts of motor nerve

fibers

Reflex centers for vision and hearing (startle

reflex)


Pons

The bulging center part of the brain stem

Bridge between medulla oblongata &

midbrain

Forms wall of 4th ventricle

Mostly composed of two-way fiber tracts

Includes nuclei involved in the respiratory

center


Medulla Oblongata The most inferior part of the brain stem

Merges into the spinal cord

Forms wall of 4th ventricle

Contains important control centers

Cardiac center

Vasomotor center

Respiratory center

Swallowing, vomiting, hiccupping , coughing, sneezing


Cerebellum Two hemispheres with convoluted surfaces “Small

brain”

11% of brain’s mass

Provides involuntary coordination of body movements

Balance

Muscle tone

Muscle coordination (speaking, walking, writing)

Thin outer gray matter & internal “arbor vitae” white matter


Cerebellum

Figure 7.15a

ELAINE N. MARIEB

EIGHTH EDITION



ESSENTIALS

OF HUMAN

ANATOMY

& PHYSIOLOGY

The Nervous System


Protection of the Central Nervous System

Scalp and skin

Cranial/facial bones and vertebral column

Meninges – forms partitions in skull

Figure 7.16a


Protection of the Central Nervous System

Cerebrospinal fluid (CSF) – liquid cushion (reduces

weight by 97%)

Blood brain barrier – inhibits passage of materials

from blood into brain

Figure 7.16a


Meninges

Dura mater – “tough mother”

Double-layered external covering

Periosteum – attached to surface of the skull

Meningeal layer – outer covering of the brain

Folds inward in several areas


Meninges

Arachnoid layer – “spider layer”

Middle layer

Loose brain covering with large blood vessels

Filled with CSF

Pia mater – “gentle mother”

Internal layer

Clings to the surface of the brain

Delicate connective tissue

Richly vascularized


Cerebrospinal Fluid

Similar to blood plasma composition

Formed by the choroid plexus – capillary

knot that protrudes into ventricles

Forms a watery cushion to protect & nourish

the brain

Circulated in arachnoid space, ventricles, and

central canal of the spinal cord


Ventricles and Location of the

Cerebrospinal Fluid

Figure 7.17a–b


Ventricles and Location of the

Cerebrospinal Fluid

Figure 7.17c


Blood Brain Barrier

Includes the least permeable capillaries of the body

Excludes many potentially harmful substances

Useless against some substances

Fats and fat soluble molecules

Respiratory gases

Alcohol

Nicotine

Anesthesia


Traumatic Brain Injuries Concussion

Slight brain injury – “seeing stars”

No permanent brain damage

Contusion

Nervous tissue destruction occurs

Nervous tissue does not regenerate

Cerebral edema

Swelling from the inflammatory response

May compress and kill brain tissue


Cerebrovascular Accident (CVA)

Commonly called a stroke

Most common NS disorder – 3rd leading

cause of death in U.S.

The result of a ruptured/blocked 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


Alzheimer’s Disease

Progressive degenerative brain disease resulting in dementia

Mostly seen in the elderly, but may begin in middle age

Structural changes (shrinking gyri) in the brain include abnormal protein deposits and twisted fibers within neurons

Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death


Developmental Disorders

Cerebral Palsy – caused by a difficult birth

with a temporary lack of oxygen

Volunatry muscles are poorly controlled or

paralyzed

Results in seizures, mental retardation,

deafness & visual impairments

Does not worsen over time

Affects 6 out of 1000 births


Nervous System Disorders

Meningitis- inflammation of meninges

Bacterial or viral

Mild symptoms include headache, fever & stiff

neck

Severe symptoms include paralysis, coma &

death

Encephalitis – inflammation of brain

Caused by chemicals or virus

Symptoms include fever, lethargy, extreme

weakness & visual difficulties


Nervous System Disorders Epilepsy – excessive discharge of neurons

Cause is unknown

Symptoms include convulsions, hallucinations & loss of consciousness

Poliomyelitis – disease of neural pathways in sc that causes paralysis

Vaccine has almost eliminated disease in U.S.

Hydrocephalus – increased volume of CSF in ventricles

Caused by blockage of 3rd/4th ventricle

Enlarged head at birth


Nervous System Disorders Parkinson’s Disease – characterized by tremors,

shuffling gait, pin-rolling & muscular rigidity

Causes decrease in dopamine (neurotransmitter)

Multiple Sclerosis – chronic inflammation of CNS where WBC’s attach to sheaths of myelin (creates scar tissue)

Scar tissue delays/blocks nerve impulses

Cause of inflammation is unknown

Symptoms include weakness in extremities, numbness, double-vision, tremors in eyes, speech problems, loss of coordination & paralysis


Nervous System Disorders

Dementia – loss of at least 2 complex

behaviors (ie. language, memory, visual &

spatial abilities or judgment)

Brain tumors – overproduction of cells in the

brain

Hematoma – localized mass of blood

Caused by head trauma


Diagnostic Procedures

Lumbar puncture – a long needle is inserted

between L3 & L4 & CSF is removed

Knee-jerk response

Pneumoencephalography – X-ray of

ventricles

Used for hydroencephaly

CSF is withdrawn & air is injected into

subarachnoid space to float upward into

ventricles



Cerebral angiogram – views arteries

Injected dye, X-ray given to see blood

clots & arteriosclerosis

CT Scan (computed tomography) aka

CAT Scan (computerized axial tomography)

X-ray projects beams in all directions

Images are slices the thickness of a dime

Used to find tumors, lesions & dead tissue



PET Scan (Positron Emission Tomography)

Injection of a radioisotope tagged for

biological molecules (ie. glucose)

High E rays are produced as the body

metabolizes the molecule

Scanner provides a picture of brain’s

biochemical activities

Used for seizures, Alzheimer’s & brain

illnesses


Diagnostic Procedures MRI (Magnetic Resonance Imaging)

Uses a magnetic field 60,000x stronger than the Earth’s

Patient lays in a large chamber with a huge magnet

H+ molecules spin in the magnetic field & their E is enhanced by radio waves

Radio waves are turned off and the remaining E is released into an image

Detects degenerative diseases & can easily distinguish soft tissues

Problems include removal of dental fillings, pacemakers & shrapnel & large room to contain machine

ELAINE N. MARIEB

EIGHTH EDITION



ESSENTIALS

OF HUMAN

ANATOMY

& PHYSIOLOGY

The Nervous System


Spinal Cord

Extends from the medulla oblongata to the region of T12

42 cm (17 in) long; 1.8 cm (.75 in) thick

Below T12 is the cauda equina (a collection of spinal nerves)

Enlargements occur in the cervical and lumbar regions Figure 7.18


Spinal Cord Anatomy

Exterior white mater – conduction tracts

Internal gray matter - mostly cell bodies

Central canal filled with cerebrospinal fluid

Figure 7.19


Spinal Cord Anatomy

Meninges cover the spinal cord

Nerves leave at the level of each vertebrae


Peripheral Nervous System

Nerves and ganglia outside the central

nervous system

Nerve = bundle of neuron fibers

Neuron fibers are bundled by connective

tissue


Structure of a Nerve

Endoneurium surrounds

each fiber

Groups of fibers are

bound into fascicles by

perineurium

Fascicles are bound

together by epineurium

Figure 7.20


Classification of Nerves

Mixed nerves – both sensory and motor fibers

Afferent (sensory) nerves – carry impulses

toward the CNS

Efferent (motor) nerves – carry impulses

away from the CNS


Distribution of Cranial Nerves

Figure 7.21


Spinal Nerves

Figure 7.22a


Examples of Nerve Distribution

Figure 7.23


Autonomic Nervous System

The involuntary branch of the nervous system

Consists of only motor nerves

Divided into two divisions

Sympathetic division

Parasympathetic division


Figure 7.24

Comparison of Somatic and Autonomic

Nervous Systems


Anatomy of the Autonomic Nervous

System

Figure 7.25


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


Autonomic Functioning

Parasympathetic – housekeeping activities

Conserves energy

Maintains daily necessary body functions

Remember as the “D” division - digestion,

defecation, and diuresis


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


Development Aspects of the Nervous

System

No more neurons are formed after birth, but

growth and maturation continues for several

years

The brain reaches maximum weight as a

young adult

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