The NervousSystem

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Functions

Sensory– Detects changes that occur inside and outside

of the bodyIntegrative– Sensory inputs are put together to create

sensation, produce thought, create memoryMotor– Sends signals to glands or muscles to

produce an action

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Organization

Divisions of the Nervous System– Central Nervous System (CNS)

Receives and processes information and regulates body activityConsists of brain and spinal cord

– Peripheral Nervous System (PNS)Carries information to and from the CNSConsists of cranial and spinal nerves, plexuses, and peripheral nerves

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Nerve Cells

Neurons– Base cell of the nervous system– Carry impulses throughout the body in a

particular direction

Dendrites Cell Body Axon

– CNS neurons do not replicate – not replaceable

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Nerve Cells

Neuron structure– Cell body

Central portion where the nucleus is locatedAll processes extend from it

– DendritesRoot-like processes that receive impulses and conduct them to the cell body

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Neuron structure (con’t)– Axon

Process that conducts impulses away from the cell bodyCan be more than 3 feet longSometimes covered in a myelin sheathEnds in Terminal End Fibers

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Neurons

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Nerve Cells– A synapse is the space between the terminal

end fibers of one neuron and the dendrites of another OR the space between the terminal end fibers of one neuron and a receptor organ

Each neuron can have any number of synapses with other cells

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Nerve Cells– Neurotransmitters are

chemicals that carry information across a synapse from the neuron to the target receptor

Ex endorphins, serotonin, dopamine, epinephrine

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Nerves

Nerves (neur/o) are bundles of neurons, joined end-to-end, that travel together like strands of rope– Two types of nerves are defined according to

function and the direction of impulseAfferent nerves (Sensory)Efferent nerves (Motor)

Nerves and neurons are the parenchymal tissues of the Nervous System

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Nerves

– Tract – bundle of nerve fibers located within the brain or spinal cord

– Ganglion – cluster of nerve cell bodies outside of the CNS

– Plexus – network of intersecting nerves

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Nerve Cells

Stromal Tissues of the Nervous System– Glial Cells

AKA neuroglia supportive and connective cells of the nervous systemDo not conduct impulsesCan replicate-glia comes from the Greek word that means glue

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Nerve Cells

Myelin sheath– White protective covering

along the axons of some neurons

– Functions to provide insulation and to make signal transmission more efficient

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Nerve Cells– White matter is the name given

to the portion of nerve cells that have a myelin sheath

Most peripheral nerves, and portions of the nerves in the spinal cord and brain

– Grey matter is the name given to the portion of nerve cells that do not have a myelin sheath

Portions of the nerves in the spinal cord and brain

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Nerves– Innervation is the supply of nerves to a body

part– Receptors are sites that receive sensory

stimulation and send messages through the sensory neurons to the brain

Stimulus – anything that excites a nerve and creates an impulseImpulse – wave of excitation transmitted through a nerve

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Central Nervous System

Brain– Encephal/o means brain– Located within the cranial vault– Parts of the brain

CerebrumThalamusHypothalamusCerebellumBrainstem

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Central Nervous System

Cerebrum– Largest and uppermost portion of the brain– Responsible for thought, memory, sensation,

language, intelligence, etc– Cerebr/o means cerebrum (and sometimes

brain)

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– The outer layer of the cerebrum is a sheet of grey matter called the cerebral cortex

Arranged in folds called gyri separated by grooves called sulci

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Central Nervous System– Cerebrum is divided into two

hemispheresReferred to as the left and right brainConnected by the corpus callosum - thick band of nerve fibers

– Each hemisphere is further divided into lobes

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Central Nervous SystemFrontal Lobe– Skilled motor functions,

memory, behaviour, personality

Parietal Lobe– Sensation (tongue, skin,

muscles)Occipital Lobe– Vision

Temporal Lobe– Hearing, smell, ability to

create, store and access new information, language

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Central Nervous System

Inside the cerebrum are four spaces called ventricles which produce and contain cerebrospinal fluid

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Central Nervous System

Thalamus (thalam/o)– Relays information

from the sense organs and cerebellum to the cerebrum

– Controls perception of pain

– Located below the cerebrum– Together with the hypothalamus, make up the

diencephalon

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Central Nervous SystemHypothalamus

– Located below the thalamus– Seven major functions

1. Regulates the autonomic nervous system

2. Regulates emotional response3. Regulates body temperature4. Controls hunger sensation5. Regulates water balance and thirst6. Regulates sleep-wake cycle7. Regulates endocrine system function

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Central Nervous SystemCerebellum– Cerebell/o means

cerebellum– Located at the back of the

brain below the cerebrum– Motor center of brain –

produces smooth, coordinated movement, maintains balance and posture

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Central Nervous System

Brainstem– Connects cerebral

hemispheres with the spinal cord

– Three parts:MidbrainPonsMedulla Oblongata

– Provide conduction pathways and basic life functions like breathing, heart rate, blood pressure, coughing and sneezing, swallowing, vomiting

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Central Nervous System

Meninges (mening/o, meningi/o)– Three layers of connective tissue membrane

that enclose the brain and spinal cord

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Meninges– Dura Mater – tough, outermost covering

located just inside the cranial vault and spinal column

– Arachnoid Membrane – connected with thin attachment strands that resemble spider webs (arachn/o means spider)

– Pia Mater – very thin, adhered to the surface of the brain and spinal cord (rich supply of blood vessels)

Thec/o (sheath) can also be used to refer to the meninges

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Central Nervous System

Spaces between the meninges– Subdural space – located between the dura

mater and the arachnoid (“potential space”)– Epidural space – located above the dura

mater in the spinal column (contains fat and connective tissue to cushion)

– Subarachnoid space – located between the arachnoid and the pia mater (contains cerebrospinal fluid)

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Central Nervous System

Cerebrospinal Fluid– Produced in the ventricles of the brain– Clear, colourless, watery– Nourishes, cools, and cushions the brain and

spinal cord– Transports nutrients and chemical

messengers throughout the brain and spinal cord

Blood-brain barrier*

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Central Nervous SystemSpinal Cord (myel/o)– Pathway for impulses going to

and from the brain– Surrounded by meninges and

CSF– Inner portion is made up of grey

matter and outer portion is white matter

– Extends from the base of the skull to the first lumbar vertebra, then becomes the cauda equina

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Peripheral Nervous System

Consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves plus branchesCranial Nerves– Originate from the undersurface of the brain– One member of each pair serves one half of

the body– Identified by roman numerals

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I. SmellII. VisionIII. Eye movementIV. Eye movementV. Sensory info from face and

head, muscles for chewingVI. Eye movementVII. Taste, facial expression,

sensory info from earVIII. Hearing, balanceIX. Taste, swallowingX. Sensation and control of

organsXI. Head movementXII. Tongue movement

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Peripheral Nervous System

Spinal Nerves– 31 pairs – grouped together based on region

they innervateCervical C1-C8Thoracic T1-T12Lumbar L1-L5Sacral S1-S5 1 Coccygeal

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Spinal Nerves

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Autonomic Nervous System

Controls involuntary actions of the bodyDivided into two systems that work together to regulate homeostasis– Sympathetic Nervous System

Prepares the body for emergencies by increasing breathing and heart rate, and blood flow to muscles (fight-or-flight response)

– Parasympathetic Nervous SystemReturns the body to normal after a response to stressMaintains normal body functions

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Medical SpecialtiesAnesthesiologist– Specializes in administering anesthetic agents before

and during surgery– Esthesi/o means feeling or sensation

Anesthetist– Person trained in administering anesthetic agents, but

is not necessarily a physicianNeurologist– Specializes in diagnosing and treating disorders of

the nervous system

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Symptoms

Pain– -algia and –dynia mean pain– -algesia means sensitivity to pain

Movement– Kines/o, kinesi/o mean movement

BradykinesiaHyperkinesiaDyskinesiaAkinetic

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Symptoms

Seizures– Electrical disturbance in the brain caused by

high fever, brain injury or lesionsLoss of consciousness with twitching or shakingLess observable staring spells

– May be generalized (affect the whole body) or focal (only affect one part or side of the body)

– -lepsy means seizure

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Symptoms

Weakness– -paresis means weakness or partial loss of

movement– Due to nerve damage

HemiparesisMonoparesisParaparesis

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Symptoms

Paralysis– Loss or impairment of the ability to move parts

of the body-plegia means paralysis

– Quadriplegia– Paraplegia– Hemiplegia

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Symptoms

Speech disorders– -phasia means speech

Aphasia– Motor aphasia– Sensory aphasia

Control of movement– -praxia means action

Apraxia – Tax/o means coordination

Ataxia

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Symptoms

Syncope– AKA fainting– Brief loss of consciousness– Caused by decreased flow of blood to the

brain

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Symptoms

Levels of Consciousness– Conscious means being alert, aware– Unconscious is the state of being unaware –

unable to respond to stimuli– Lethargy

Lowered level of consciousness characterized by listlessness, drowsiness, and apathy

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Symptoms– Stupor

Impaired awareness - mind and senses are dulled to stimuli

– ComaState of deep unconsciousnessAbsence of spontaneous eye movement, no response to pain, no vocalization

– Persistent Vegetative StateType of comaPatient exhibits a sleep-wake cycle, but is unconscious even when apparently awake

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SymptomsSomnolence– Condition of unnatural sleepiness or

semiconsciousness approaching coma– Usually can be aroused by verbal stimuli

Delirium– Sudden onset of confusion, anxiety and cloudiness– Associated with high fever, intoxication, shock– Potentially reversible

Dementia– Slowly progressing decline in mental abilities

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Congenital Disorders

Anencephaly– Occurs due to a defect in the first month of

pregnancy– Most of the cerebrum does not form, and the

rest of the brain is often not covered by bone or skin

– Detectable with amniocentesis and prenatal ultrasound

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Congenital Disorders

Hydrocephalus– Abnormally increased amount

of CSF within the ventricles of the brain

– Due to blocked circulation, tumours, infection

– Pressure may be relieved with a catheter or “shunt”

– May also occur later in life

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Congenital Disorders

Spina Bifida– Occurs when vertebrae do not fuse (normally

in lumbar region)Originates in the first four weeks of pregnancyOpening allows damage to spinal nervesDefect may be covered over with skin (Occulta), or may be visible because the meninges and/or the spinal cord protrude through the openingMeningocele, Myelomeningocele

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Congenital Disorders

Encephalocele– Herniation of the brain through a gap in the skull

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Congenital Disorders

Cerebral Palsy– Condition of poor muscle control, spasticity,

speech defects, and other neurological deficiencies

– Due to damage that affects the cerebrum– Occurs most often in premature or low-

birthweight babies– Usually caused by an injury that occurs during

pregnancy, birth or soon after

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Degenerative and Movement Disorders

Alzheimer’s Disease (AD)– Degenerative changes in

the brain structure lead to symptoms like progressive memory loss, impaired cognition, personality changes

Cognition is thinking, learning, and memory

– Early onset AD has a genetic basis

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Degenerative and Movement Disorders

Parkinson’s Disease– Chronic, degenerative CNS disorder – Progressive loss of control over movement– Thought to be due to inadequate levels of

dopamine in the brain– Characterized by tremors, rigidity and

shuffling gaitGenetic link in 15% of cases

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Degenerative and Movement Disorders

Bell’s Palsy– Temporary paralysis of the seventh cranial

nerve (likely due to viral infection)– Causes facial drooping on the

side affectedMay also cause pain, tearing, drooling, impairment of taste, etc

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Degenerative and Movement Disorders

Amyotrophic Lateral Sclerosis (ALS)– AKA Lou Gehrig’s Disease– Degenerative disease of the motor nerve cells

of the brain and spinal cord– Patients become progessively weaker until

they are completely paralyzed

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Degenerative and Movement Disorders

Multiple Sclerosis– Progressive autoimmune disorder

characterized by scattered patches of demyelination of nerve fibers in the brain and spinal cord

– Repeated episodes of nerve inflammation disrupt transmission of nerve impulses and cause symptoms including loss of balance, fatigue, paralysis, speech disturbances

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Infectious Disease

Meningitis– Inflammation of the meninges– Symptoms include fever,

headache, photophobia, stiff neck

– Usually caused by bacterial or viral infection

– Diagnosed using a Lumbar Puncture

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Infectious Disease

Encephalitis– Inflammation of the brain– Due to bacterial or viral infection, or secondary to

other diseases such as influenza

Tetanus– AKA Lockjaw– Infection of the CNS – can be fatal– Bacterial, acquired through deep wounds

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Infectious Disease

Reye’s Syndrome– Commonly occurs during recovery from a viral

infection– Symptoms include persistent vomiting,

listlessness, disorientation– Harmful to organs, especially brain and liver;

may be fatal

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Infectious Disease

Poliomyelitis– AKA Polio– Highly contagious viral infection that inflames

the spinal cord and brainstem, resulting in paralysis

– Prevented through immunization– Symptoms can recur later in life

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Other Inflammatory Conditions

Radiculitis– AKA pinched nerve– Inflammation of the root of a spinal nerve

Sciatica– Inflammation of the sciatic nerve– Results in pain, burning, and tingling along

the thigh and leg

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Other Inflammatory Conditions

Tic douloureux– AKA trigeminal neuralgia– Inflammation of the fifth cranial nerve– Sudden, intense pain on one side of the face

and affecting the lips, gums, or cheek– Attacks can be triggered by touch or

movement, and may come and go throughout the day or last for weeks or months at a time

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Traumatic Disorders

Amnesia– Memory disturbance– Can be caused by injury, illness,

psychological disturbanceConcussion– Jarring or shaking up of the brain– May cause a loss of awareness or function

(temporary)

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Traumatic Disorders

Cerebral Contusion– Bruising of the brain tissue– May cause swelling of the

brainCranial Hematoma– Collection of blood trapped

in the tissues of the brain

– Examples: epidural, subdural, etc

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Vascular Disorders

Cephalgia– AKA headache– Migraine headache – syndrome

characterized by sudden, throbbing, sharp pain – often accompanied by nausea and photosensitivity

– Cluster headache – characterized by concentrated pain on one side of the head – very painful, and occur one or more times daily for weeks or months

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Vascular Disorders

Cerebrovascular Accidents (CVA’s)– AKA stroke– damage to the brain caused by disruption of

blood flow (blockage or rupture of a blood vessel)

– Ischemic strokes – most common type of stroke in the elderly

Occur when blood flow is blocked due to narrowing of the carotid artery or cerebral thrombosisAffects the cerebrum and damages the control of movement, senses, and speech

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Vascular Disorders

Transient Ischemic Attack (TIA)– Temporary interruption in blood flow– Symptoms: numbness, blurred vision,

dizziness, loss of balance– Warning sign of stroke risk

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Vascular Disorders

Hemorrhagic Stroke– Occurs when a blood vessel in the brain leaks

or ruptures (often due to an aneurysm)– Often fatal – affects the area of the brain

damaged by the leaking blood

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Sleep Disorders

Insomnia– Prolonged abnormal inability to sleep’– Usually a symptom of depression, pain,

excessive caffeineSomn/i, somn/o mean sleep

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Sleep Disorders

Narcolepsy– Sleep disorder consisting of recurring

episodes of falling asleep during the dayOften also suffer from cataplexy (respond to emotional stimuli by suddenly falling to the ground without losing consciousness)Narc/o means stupor, -lepsy means seizure

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Sleep Disorders

Somnambulism– AKA Sleepwalking– Condition of walking or performing some other

activity without wakingAmbul/o means walk

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Seizure Disorders

Epilepsy– Group of disorders characterized by recurrent

episodes of seizures or convulsions– Grand Mal Epilepsy

Severe form characterized by generalized seizures (sudden loss of consciousness and sudden, violent, involuntary contraction of a group of muscles)

– Petit Mal EpilepsyMilder form characterized by frequent but partial seizures (brief loss of consciousness, but no convulsions)

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Abnormal Sensation

Causalgia– Persistent, severe, burning pain following

injury to a sensory nerveHyperesthesia– Excessive sensitivity to stimuli

Paresthesia– Abnormal sensation in the extremities due to

neurological disease or nerve damage

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Diagnostic Procedures

Electroencephalography (EEG)– Recording the electrical activity of the brain

through electrodes attached to the scalpMyelography– Radiographic study of the spinal cord with

contrast media injected through a lumbar puncture

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Treatment Procedures

Pain Control– Transcutaneous electronic nerve stimulation

(TENS)

Application of electrical impulses to the nerve endings through the skin

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Treatment Procedures– Analgesic – medication that relieves pain– Sedative – medication that depresses the

CNS to produce calm and diminished responsiveness

– Hypnotic – medication that depresses the CNS and produces sleep

– Anticonvulsant – medication that prevents seizures and convulsions

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Treatment Procedures

Anesthesia– Absence of normal sensation– Induced by the administration of a medication

called an anestheticTopical anesthetic – numbs only the tissue surfaceLocal anesthetic – causes loss of sensation in a limited area by injecting anesthetic solution near the area

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Treatment Procedures

– Regional anesthetic - causes temporary interruption of nerve conduction produced by injecting anesthetic solution near the nerves to be blocked

– General anesthesia – total loss of body sensation and consciousness induced by anesthetic agents inhaled or injected intravenously

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Treatment Procedures

Electroconvulsive therapy (ECT)– AKA electroshock therapy– Controlled convulsion produced by the

passage of an electric current through the brain

Lobectomy– Surgical removal of a portion of the brain to

treat brain cancer or seizure

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Treatment Procedures

Neuroplasty– Surgical repair of a nerve

Neurorrhaphy– Surgically suturing together the ends of a

severed nerveNeurotomy– Surgical incision or the dissection of a nerve