Nervous System

The Neuron

• Also called the nerve cell

• It is the basic structural unit of the nervous system

The Neuron• Part of the Neuron

– Cell Body– Nucleus (inside the cell body)– Nerve Fibers

Nerve Fibers• Dendrites

– Carries impulses TOWARD the cell body

• Axon– Single nerve fiber that carries impulses

AWAY from the cell body

Nerve Fibers• Myelin Sheath

– Lipid (fat) cover over the axon– Increases the rate of transmission of an

impulse– Insulates and protects the axon

Nerve Impulses

• Axon of a neuron lies close to the dendrites of many other neurons

• Synapse– Space between dendrites of one neuron and

axon of another neuron– Impulses “jump” the synapse

Nerve Impulses

• Neurotransmitters– Special chemicals located at the end of each

axon

– Allows the nerve impulse to pass from one neuron to another via the synapse or synaptic cleft

– Synapse is the space between the axon of one neuron and the dendrites of the next

Nerves

• Bundle of nerve fibers (neuron, dendrites, axons, etc) enclosed by connective tissue

• Nerve impulses travel to and from the brain at the rate of 170 mph

Types of Nerves

• AFFERENT/Sensory– Carries messages from all parts of the body

(sensory organs) to the brain and spinal cord

• EFFERENT/Motor– Carries messages from the brain and spinal

cord to muscles and glands

Division of the Nervous System

• Two main divisions– Central Nervous System

• Brain and Spinal Cord

– Peripheral Nervous System• Made up of the nerves in the body• Broken down into Autonomic and Somatic

divisions

Central Nervous System

• Brain– Mass of nerve tissue– Protected by membranes and the cranium

(skull)

Central Nervous SystemCEREBRUM• Largest and highest

section of the brain• Has convolutions (folds)• Separated into lobes

which are named from the skull bones that surround them– Frontal (1 lobe)– Parietal (2 lobes)– Temporal (2 lobes)– Occipital (2 lobes)

Central Nervous SystemCerebellum• Section below the

cerebrum• Responsible for

coordination of muscles, balance and posture, and muscle tone

Diencephalon• Located between the

cerebrum and midbrain• Contains two structures

– Thalamus – acts as relay center

– Hypothalamus – regulates Autonomic Nervous System

Central Nervous System

• Midbrain– Located below the

cerebrum at the top of the brain stem

– Responsible for conducting impulses between brain parts

– Responsible for certain eye reflexes

Central Nervous System• Pons

– Located below the midbrain in the brain stem

– Responsible for conducting messages to other parts of the brain

– Responsible for certain reflex actions including chewing, tasting, production of saliva

– Assists with respirations

Central Nervous System• Medulla Oblongata

– Lowest part of the brain stem

– Connects with the spinal cord

– Responsible for regulating the heart beat, respirations, swallowing, coughing, and blood pressure

Central Nervous System

• Corpus Callosum: bundle of nerve fibers that connect R and L hemispheres of brain

• Choroid Plexus: network of capillaries that produce cerebral spinal fluid

Central Nervous System

• Spinal Cord– Continues down from the medulla oblongata– Ends at the 1st or 2nd lumbar vertebra– Surrounded and protected by the vertebrae– Carries AFFERENT (sensory) messages to

the brain– Carries EFFERENT (motor) messages from

the brain to the nerves that go to muscles and glands

Central Nervous System• Meninges

– Three membranes that cover and protect the brain and spinal cord

– Dura mater• Thick, tough outer layer

– Arachnoid• Middle, delicate web like layer

– Pia mater• Innermost layer• Closely attached to the brain and spinal cord• Contains blood vessels that nourish the nerve tissues

Central Nervous System

Peripheral Nervous System

• Consists of cranial nerves and spinal nerves

• 12 Cranial Nerves– On Old Olympus Towering Tops A Finn

Versus German Viewed All Hops– See worksheet

• Spinal nerves– 31 pairs and their branches– Carries messages to and from the spinal cord

Peripheral Nervous System

• Spinal nerves– 31 pairs and their branches– Carries messages to and from the spinal

cord– Plexus

• Each nerve goes directly to a particular part of the body or network with other spinal nerves

• Supplies sensation to large segments (Dermatomes) of the body

PlexusCervical

Brachial

Lumbar

Sacral

Dermatomes

Autonomic Nervous System

• Important part of the Peripheral Nervous System

• Helps maintain a balance in the involuntary functions– Heart rate, respirations, temperature,

digestion, etc.

• Allows the body to react in times of emergency

Autonomic Nervous System

• Two divisions– Sympathetic Nervous System– Parasympathetic Nervous System

• Two systems work together to– Maintain HOMEOSTASIS (balanced state)– Control involuntary body functions at proper

rates

Autonomic Nervous System

• Sympathetic Nervous System– “Fight or Flight” – Acts in times of emergencies– Prepares the body to act– Increases heart rate, respirations, and blood

pressure– Slows down the digestive tract

Autonomic Nervous System

• Parasympathetic Nervous System– Counteracts the actions of the Sympathetic

system after an emergency– Lowers heart rate, respirations, and blood

pressure– Increases activity of the digestive tract

Pathophysiology - CVA• Cerebrovascular Accident (CVA)

– Also called Stroke– Blood flow to the brain has been interrupted resulting in lack of

oxygen to the brain and therefore destruction of brain tissue– Causes

• Cerebral hemorrhage from hypertension, aneurysm (weak blood vessel), trauma

• Occlusion (blockage) caused by atherosclerosis (fat build up) or

thrombus (blood clot)

Pathophysiology - CVA

• Symptoms– Varies depending on the area of the brain affected

and the amount of brain tissue damaged

– Loss of consciousness

– Dizziness

– Weakness

– Paralysis on one side of the body (hemiplegia)

– Mental confusion

– Visual disturbances

– Aphasia (speech and language impairment)

– Incontinence

Treatment - CVA

• Like a heart attack, the quicker treatment is administered the less the damage occurs

• Within first three hours give thrombolytic (clot bursting) drugs such as TPA

• CT scan done first because if caused by hemorrhage cannot give thrombolytic

• Angioplasty – opens cerebral artery, dissolves clot and restores blood flow

Treatment - CVA

• Long term treatment depends on the damage that has occurred

• Often need therapies such as physical, occupational, and speech therapies

• May need assistive devices such as canes, walkers, and braces

• Prevention of blood clots – thin blood– Take ASA, Coumadin, etc for the rest of your life

• Treat underlying conditions such as high blood pressure, atherosclerosis, diabetes, etc

Pathophysiology – Parkinson’s Disease

• Chronic, progressive condition involving degeneration of brain cells

• Usually occurs in persons over 50 years of age but not always

Pathophysiology – Parkinson’s Disease

Cause:• Nerve cells use a brain chemical called

dopamine to help control muscle movement. • Nerve cells in the brain that make dopamine

are slowly destroyed. • This leads to the loss of muscle function. • The damage gets worse with time. • Exactly why these brain cells waste away is

unknown.

Pathophysiology – Parkinson’s Disease

Symptoms:– Tremors, stiffness, and muscular

rigidity– Forward leaning position and a

shuffling gait– Difficulty in stopping while

walking– Loss of facial expression and

drooling• Parkinson’s Mask

– Mood swings, behavioral changes, and frequent depression

Treatment – Parkinson’s Disease

• No known cure

• Medication to lessen symptoms and possibly slow progression– Levodopa – synthetic dopamine

• Physical therapy and assistive devices to limit the muscular rigidity

ParalysisParalysis• Usually results from brain Usually results from brain

or spinal cord injuryor spinal cord injury– HemiplegiaHemiplegia

• Paralysis on one sideParalysis on one side

- ParaplegiaParaplegia- Paralysis of the lower Paralysis of the lower

extremitiesextremities

– Quadriplegia Quadriplegia • Paralysis of the arms, legs, Paralysis of the arms, legs,

and body below the spinal and body below the spinal cord injurycord injury

• No cure, treatment is No cure, treatment is supportivesupportive

Multiple SclerosisMultiple Sclerosis

• Chronic, progressive Chronic, progressive disabling condition resulting disabling condition resulting from degeneration of the from degeneration of the myelin sheathmyelin sheath

• Occurs between the ages of Occurs between the ages of 20 and 40. 20 and 40.

• Cause is unknownCause is unknown• Progresses at different rates Progresses at different rates

depending on the persondepending on the person• Periods of remissionPeriods of remission• No cureNo cure

Amyotrophic Lateral Sclerosis (ALS)

• aka “Lou Gehrig’s disease”• Cause unknown• Chronic, degenerative• Nerve cells that control

voluntary movement degenerate = atrophy of the muscles they control

• Eventual total body paralysis

• Mental acuity is unaffected• Usually fatal within 4-6

years of symptom onset

Carpal Tunnel Syndrome• Repetitive movement

of the wrist causes swelling which puts pressure on the nerves

• Sx: Pain, numbness, and tingling in the thumb, ring finger, and middle finger

• Tx: NSAIDS, splinting, surgery

DementiaDementia

• General term defining a loss in at least two General term defining a loss in at least two areas of complex behavior such as language, areas of complex behavior such as language, memory, visual/spatial abilities or judgmentmemory, visual/spatial abilities or judgment

• Does not mean that everyone that is forgetful Does not mean that everyone that is forgetful has dementiahas dementia

Shingles

• Herpes zoster• Inflammation of nerve cells caused by herpes virus• Same virus that causes chicken pox• Occurs in thoracic area on one side of the body and follow path of affected nerves• Itching, fever, increased skin sensitivity• Treatment is to relieve pain and itching until

inflammation subsides, antiviral (acyclovir)

Other Diseases of the Nervous Other Diseases of the Nervous SystemSystem

• Encephalitis = inflammation of the brain caused by virus, bacteria, or chemical agent. (The virus can be contracted from a mosquito bite)

• Meningitis = inflammation of the meninges of the brain caused by a bacteria, virus, fungus, or toxin

Other Diseases of the Nervous Other Diseases of the Nervous SystemSystem

• Hydrocephalus = excessive accumulation of cerebrospinal fluid in the ventricles

Other Diseases of the Nervous Other Diseases of the Nervous SystemSystem

• Neuralgia = nerve pain

• Epilepsy = condition involving abnormal electrical impulses in the brain resulting in convulsions or seizure

• Cerebral palsy = disturbance in voluntary muscle action caused by brain damage

Diagnostic Tests

• EEG: electroencephalogram– Measures and records

the electrical activity of the brain

– Special sensors, called electrodes, are attached to your head and hooked by wires to a computer

Diagnostic Tests

• Lumbar Puncture: (Spinal Tap)– Procedure to collect CSF