Health Occupations

Nervous System

Nervous System

Complex & highly organized Coordinates all of the many activities of

the body Allows body to respond and adapt to

changes that occur both inside and outside of the body

Neuron

Also called nerve cell Basic structural unit of nervous system Parts of neuron

– Cell body– Nucleus inside cell body– Nerve fibers

• Dendrites – carry impulses to cell body• Axon – carry impulses away from cell body

– Many covered with myelin sheath (fat covering)– Increases rate of transmission of impulses– Insulates & maintains the axon

Neuron

Axon lies close to dendrites of many other neurons– Synapse – space between neurons– Impulses coming from an axon jump synapse to

get to the dendrite of a neuron that will carry the impulses in the right direction

– Neurotransmitters – special chemicals located at end of axon to allow impulses to pass from neuron to another

– Impulses may follow many different routes

1. Dendrites

2. Cell body

3. Nucleus

4. Axon

5. Myelin Sheath6. Terminal branches

Nerves

Combination of many nerve fibers Located outside brain & spinal cord Afferent – sensory

– Messages to brain & spinal cord Efferent – motor

– Messages from brain & spinal cord Associative – both sensory & motor

Divisions of nervous system

Central nervous system– Brain– Spinal cord

Peripheral nervous system– Nerves– Autonomic nervous system

• Separate division of peripheral nervous system• Controls involuntary body functions

Central nervous system

Brain– Mass of nerve tissues– Protected by membranes & cranium– Cerebrum

• Largest & highest section of brain• Convolutions – folds found on outer part• Lobes

– Frontal, parietal, temporal, occipital– Named after bones that surround them

• Responsible for reasoning, thought, memory, speech, sensation, sight, smell,hearing, & voluntary body movement

Brain

Cerebellum– Below back of cerebrum– Responsible for coordination of muscles, balance,

posture, muscle tone Diencephalon

– Between cerebrum & midbrain– Thalamus

• Relay center to direct sensory impulses to cerebrum

– Hypothalamus• Regulates & controls ANS, temperature, appetite, water

balance, sleep, constriction & dilation of blood vessels, anger, fear, pleasure, pain, affection

Brain

Midbrain– Below cerebrum at top of brain stem– Responsible for conducting impulses

between brain parts & eye reflexes Pons

– Below midbrain in brain stem– Responsible for conducting messages to

other parts of brain & reflexes like chewing, tasting, production of saliva, respiration

Brain

Medulla oblongata– Lowest part of brain stem– Connects with the spinal cord– Responsible for regulating heartbeat,

respiration, swallowing, coughing, & blood pressure

VentriclesConvolutions

Midbrain

Pons

Medulla oblongata

Cerebellum

Spinal cord

Cerebrum

Spinal cord

Continues down from the medulla oblongata Ends at L1 or L2 Surrounded & protected by vertebrae Responsible for many reflexes Carries sensory messages to brain (afferent) Carries motor messages away from brain

(efferent)

Meninges

3 membranes Cover & protect brain & spinal cord Dura mater – thick, tough outer layer Arachnoid membrane – middle layer, delicate

& weblike Pia mater – innermost layer

– Closely attached to brain & spinal cord– Contains blood vessels that nourish nerve tissue

Ventricles 4 hollow spaces located in brain Connect with each other & with subarachnoid space Filled with CSF

– Fluid circulates continually between ventricles & through subarachnoid space

– Serves as shock absorber– Carries nutrients to brain & spinal cord– Helps remove metabolic products & wastes– Produced by choroid plexuses in ventricles– After circulating, absorbed into blood vessels of the dura

mater & returned to bloodstream through arachnoid villi

Peripheral Nervous System

Made up of all the nerves Consists of cranial nerves & spinal nerves Cranial nerves

– 12 pairs & branches– Responsible for special senses like sight, hearing,

taste, smell– Receive general sensations like touch, pressure,

pain, temperature– Send out impulses for voluntary & involuntary

muscle control

Peripheral Nervous System

Spinal nerves– 31 pairs & branches– Carry messages to & from spinal cord– Sensory & motor– 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 pair of

coccygeal spinal nerves– Each nerve goes directly to a particular part of the

body or networks with other spinal nerves to form a plexus, supplying sensation to a larger segment of the body

Autonomic Nervous System

Part of PNS Helps maintain a balance in the involuntary

functions of body, but allows body to react in emergency

2 divisions – sympathetic & parasympathetic– Usually 2 systems work together– Maintain homeostasis– Controls involuntary body functions at proper rates

Autonomic Nervous System

Sympathetic– Acts in time of emergency – fight/flight– Prepares body to act– Increases heart rate, respirations, BP– Slows activity in digestive tract

Parasympathetic– Counteracts actions of sympathetic after emergency is

over– Slows heart rate, respirations– Lowers BP– Increases digestive activity

Diseases & Abnormal Conditions

Cerebral Palsy– Disturbance in voluntary muscle action– Caused by brain damage

• Lack of oxygen to brain &/or birth injury• Prenatal rubella (German measles) & infections

– Spastic, athetoid, & atactic (most common)– Symptoms

• Exaggerated reflexes & seizures• Tense muscles & contractures• Speech impairment• Muscle spasms & tremors• Mental retardation in some cases

Cerebral palsy Treatment but no cure

– PT, OT, & speech tx– Muscle relaxants & anticonvulsive druges– Casts & braces– Orthopedic surgery for severe contractures

Cerebrovascular Accident (CVA)

Stroke, apoplexy Blood flow to brain is impaired resulting in lack

of oxygen & destruction of brain tissue Causes

– Cerebral hemorrhage• HTN• Aneurysm• Weak blood vessel

– Occlusion or blockage• Atherosclerosis• Thrombosis (blood clot)

CVA

Symptoms – vary depending on area & amount of brain tissue damaged– Loss of consciousness– Weakness & vertigo– Hemiplegia (paralysis on 1 side)– Dysphagia (difficulty swallowing)– Visual disturbances & difficulty swallowing– Aphasia (speech impairment)– Incontinence

CVA

Immediate treatment– 1st THREE hours– Thrombolytic (clot busting) drugs– Angioplasty of cerebral arteries– CT scans needed to determine cause– Neuroprotective agents can be used to

prevent permanent brain damage to neurons

CVA

Treatment– Depends on symptoms present– Directed toward helping person recover

from OR adapt to symptoms present– PT, OT, speech therapy ESSENTIAL

Encephalitis

Inflammation of brain caused by virus, bacteria, or chemical agent

Mosquitoes are common vector Symptoms vary – fever, extreme weakness,

lethargy, visual changes, HA, N & V, stiff neck & back, seizures, coma

Treatment – supportive– Antiviral & antiseizure meds– Maintenance of fluids & electrolytes– Monitoring of respiratory & kidney function

Epilepsy

Brain disorder associated with abnormal electrical impulses in neurons of brain

Causes – brain injury, birth trauma, tumors, toxins (lead & carbon monoxide)

Many cases are idiopathic Absence (Petit mal) seizures

– Milder, characterized by loss of consciousness lasting several seconds

– Common in children– Usually disappears by late adolesence

Epilepsy

Tonic-clonic (grand mal) seizures– Most severe– Loss of consciousness lasting at least several

minutes– Convulsions with violent thrashing movements &

shaking– Hypersalivation, foaming at mouth– Loss of body functions

Treatment – antiseizure medications

Hydrocephalus Excessive accumulation of CSF in ventricles &

subarachnoid space Usually caused by congenital defect, infection, or

tumor that obstructs the flow of CSF Symptoms –

– Abnormally large head & prominent forehead with bulging eyes

– Irritability– Distended scalp veins– Retardation when pressure prevents proper

development of brain

Hydrocephalus Treatment – surgical implantation of a

shunt between ventricles & veins, heart, or abdominal peritoneal cavity to drain excess CSF

Meningitis

Inflammation of meninges of brain &/or spinal cord caused by bacteria, fungus, virus, or toxins (lead, arsenic)

Symptoms– High fever– HA, back & neck pain, stiffness– N & V– Delirium & confusion– Coma & death if untreated

Treatment – antibiotics, anticonvulsants, meds for pain & cerebral edema

Multiple Sclerosis

Chronic, progressive, disabling condition resulting from degeneration of the myelin sheath in the CNS

Usually occurs between 20 – 40 Unknown cause Progresses at different rates Early symptoms

– Visual disturbances– Weakness, fatigue– Poor coordination– Tingling & numbness

Multiple sclerosis

Later symptoms– Tremor, spasticity of muscles– Paralysis– Speech impairment– Emotional swings– incontinence

Treatment – PT, muscle relaxants, steroids, psychological counseling

Goal is to maintain functional ability

Neuralgia

Nerve pain Caused by inflammation, pressure,

toxins, & other diseases Treatment directed towards eliminating

cause

Paralysis

Brain or spinal cord injury destroys neurons & results in loss of function & sensation below level of injury

Hemiplegia – paralysis on 1 side of body Paraplegia – paralysis in lower extremities Quadriplegia – paralysis of arms, legs, &

body No cure, research being done towards repair Treatment – supportive, PT, OT

Parkinson’s Disease

Chronic progressive condition involving degeneration of brain cells

Usually occurs in people over 50 Symptoms

– Tremors, stiffness, muscle rigidity– Forward leaning position & shuffling gait– Difficulty stopping when walking– Loss of facial expression & drooling– Mood swings with frequent depression– Behavior changes

Parkinson’s Disease

Treatment but no cure– Levodopa used to relieve symptoms– In selected cases, surgery to selectively

destroy a small area of brain to control involuntary movements or implant a device

– PT to treat rigidity

Shingles or herpes zoster

Acute inflammation of nerve cells Caused by herpes virus, similar to chicken pox Characteristically, occurs in thoracic area on 1

side of body & follows path of the affected nerves

Symptoms – fluid filled vesicles, severe pain, redness, itching, fever, abnormal skin sensations

Treatment – relief of pain & itching until inflammation subsides, usually 1-4 weeks