NERVOUS SYSTEM

I. Anatomy and Physiology of the Nervous System

• Neuron• Is the basic functional unit of the brain. It has three main

parts: cell body, dendrite nad axon. • Dendrite• Is a branch-type structure with synapses that are used

for receiving electro chemical messages.• Axon• A long projection that carries impulses away from the cell

body.

Cells of the Nervous System

• Cell body

• If occuring in clusters are called ganglia or nuclei. A cluster of cell bodies with a common function is called a center.

• Neuroglial cells

• A type of nerve cell that support, protect and nourish neurons.

• Neurotransmitters• Are substances that communicate

messages from one neuron to another or from a neuron to a specific target tissue. These are manufactured and stored at the synaptic vesicles. When released binds to the specific receptor at the postsynaptic cell membrane. It acts to potentiate, terminate or modulate specific action and can either excite or inhibit the target cells activity.

• Receptors• There are two types of receptors the

direct and the indirect. • Direct Receptors (Inotropic)• They are linked to the channels and allow

passage of ions when opened. • They can be excitatory or inhibitory• Rapid acting (measured in milliseconds)• Indirect Receptors• Affect metabolic process in the cell, w/c

can take from seconds to hours to occur.

• Nervous System• Divided into Central and Peripheral Nervous

System. • The Central nervous system is composed of

the brain and the spinal cord. • The Peripheral nervous system is

composed of the cranial nerves, spinal nerves, and the autonomic nervous system.

• Brain

• The brain accounts for approximately 2% of the total body weight.

• In an average young adult (Brain weight is approximately 1,400g)

• In an average elderly person (Brain weight approximately 1,200 g)

• The brain is divided into three major areas:

• Cerebrum

• Brainstem

• Cerebellum

Cerebrum• Composed of two hemispheres • (Thalamus, Hypothalamus, and the Basal

Ganglia).• Connections for the olfactory (CN II) and Optic

(CN III) nerves are found in the Cerebrum.• Consists of 2 hemispheres that are incompletely

separated by the great longitudinal fissure.

• Longiotudinl fissure – separates the cerebrum into the right and left hemispheres.

• The 2 hemispheres are joined at the lower portion ofg the fissure by the Corpus Callosum.

• Gyri – wrinkled appearance in the outer surface of the hemisphere which increase the surface area of the brain

• Cerebral Cortex – the external or outer portion of the cerebrum – Made up of gray matter approximately 2 to 5

mm in depth– Gray matter contains of billions of

neutrons/cell bodies giving it a gray appearance.

– White Matter – makes up the innermost layer and is composed of nerve fibers and neuroglia (support tissue) that form tracts of pathways connecting various parts of the brain with one another (transverse and association pathways) and the cortex to lower portions of the brain and spinal cord (projection fibers).

– The cerebral hemisp[heres are divided into pairs of frontal, parietal, temporal, and occipital lobes.

• Frontal – the largest lobe

Located in the front of the skull

FRONTAL LOBE

• Major functions concentration, abstract thought, information storage or memory and motor function.

• Contains broca’s area, critical for motor control or speech.

• Frontal lobe also responsible in large part for a person’s affect judgement, personal;ity, and inhibitions.

Parietal

• Predominantly sensory lobes located near the crown of the head.

PARIETAL LOBE

• This lobe analyzes sensory information and relays the interpretation of this information to the thalamus and other cortical areas.

• Also essential to a person’s awareness of the body in space, as well as orientation in space, and spatial relations.

Temporal

• Contains the3 auditory receptive areas located around the temples.

TEMPORAL

• Contains a vital area called the interpretative area that provides integration of somatization, visual and auditory areas

• Plays the most dominant role of any area of the cortex in thinking.

Occipital

• Posterior lobe of the cerebral hemisphere located at the lower back of the head.

• Is responsible for visual interpretation.

The Corpus Callosum

• Is a thick collection of nerve fibers that connects the 2 hemispheres of the brain

• Responsible for the transmission of information from one side of the brain to another.

• Information transferred includes sensation, memory and learned discrimination.

TRIVIA

• Right-handed people and some left-handed people have cerebral dominance on the left-side of the brain for verbal, linguistic, arithmetical, calculating, and analytic functions.

• The non-dominant hemisphere (Right Hemisphere) is responsible for geometric, spatial, visual, pattern, and musical functions.

Basal Ganglia

• Are masses of nuclei located deep in the cerebral hemispheres that are responsible for control of fine motor movements, including those of the hands and lower extremities

Thalamus

• Lies on either side of the third ventricle and acts primarily as a relay station for all sensation except smell.

• All memory sensation and pain impulses also pass through this section of the brain

Hypothalamus

• Located anterior and inferior to the thalamus

• Lies immediately beneath and lateral to the lower portion of the wall of the third ventricle

hypothalamus

• It includes the optic chiasm (the point at which the two optic tracts cross) and the mamillary bodies (involved in Olfactory reflexes and emotional response to odors)

• The hypothalamus plays an important role in endocrine system because it regulates the pituitary secretion of hormones that influence metabolism, reproduction, stress, response, and urine production.

Hypothalamus

• It works with the pituitary to maintain fluid balance and maintains temperature regulation by promoting vasoconstriction or vasodilation

• Hypothalamus is the site of hunger center and is involved in appetite control

Hypothalamus

• It contains centers that regulate the sleep-wake cycle, blood pressures, aggressive and sexual behavior and emotional responses

• Also controls and regulates the automatic nervous system

Pituitary Gland

• Located in the Sella Tursica at the base of the brain and is connected to the hypothalamus.

• Common site of brain tumors in adults.

Brainstem

• Consists of the midbrain, pons, and medulla oblongata

Midbrain

– Connects the pons and the cerebellum with the cerebral hemispheres,

– It contains sensory and motor pathways and serves as the center for auditory and visual reflexes

– Cranial nerves III and IV originate in the midbrain

Pons

– Is situated in the front of the cerebellum between the midbrain and the medulla and is a bridge between the two halves of the cerebellum, and between the medulla and the cerebrum.

– Cranial nerves V through VIII connect to the brain in the pons.

– Pons contains motor and sensory pathways– Also control the heart respiration and blood pressure.

Medulla Oblongata

– Contains motor fibers from the brain to the spinal cord and sensory fibers from the spinal cord to the brain.

– Cranial nerves IX through XII connect to the brain in the medulla.

Cerebellum

• The cerebellum is separated from the cerebral hemisphere by a fold of dura matter, the Tentorium Cerebelli

• Has both excitatory and inhibitory actions and is largely responsible for coordination of movement, balance, position (postural), sense or proprioception (awareness of where each part of the body is) and integration of sensory input.

Structures that protect the brain

• Skull – is dived into four pairs of bones, the Frontal, parietal, occipital, and temporal bones.

• Meninges – This is has three layers: the dura matter, Arachnoid matter, and pia matter.

• Dura

• The outermost layer

• Covers the brain and the spinal cord

• It is tough, thick, inelastic, fibrous, and gray

• Arachnoid

• The middle membrane

• An extremely thin, delicate membrane that closely resembles a spider web

• It appears white because it has no blood supply

• It contains the choroids plexus which is responsible for the production of CSF

• Pia Mater

• The innermost membrane

• A thin, transparent layer that hugs the brain closely and extends into every folds of the brain’s surface.

• Cerebrospinal Fluid (CSF)• A clear and colorless fluid with a specific

gravity of 1.007• It is produced in the choroids plexus of the

lateral, third, and fourth ventricle.• The ventricular and subarachnoid system

contains approximately 150 ml of fluid; 15 to 25 ml of CSF is located in each lateral ventricle.

• Cerebral Circulation

• Receives approximately 15 % of the cardiac output, or 750 ml per minute.

• The brain’s blood pathway is unique because it flows against gravity; its arteries fill from below and the veins drain from above

• Blood Brain Barrier

• This is formed by the endothelial cells of the brain’s capillaries, which form continuous tight junctions, creating a barrier to macromolecules and many compounds.

ANATOMY OF THE SPINAL CORD

• The spinal cord and medulla form a continuous structure extending from the cerebral hemisphere and serving as the connection between the brain and the periphery.

• It is approximately 45 cm (18 in) long and about the thickness of a finger.

• It is also consists of gray and white matter. Gray mater is in the center and is surrounded on all sides by white matter.

• It is surrounded by the meninges, dura, arachnoid, and pia layers.

THE PERIPHERAL NERVOUS SYSTEM

• The peripheral nervous system includes the cranial nerves, the spinal nerves and the autonomic nervous system.

CRANIAL NERVES

• There re 12 pairs of cranial nerves that emerge from the lower surface of the brain and pass through the foramina in the skull

• Three are entirely sensory ( I, II, VIII)

• Five are motor (III, IV, VI, XI, and XII)

• Four are mixed (V, VII, IX, and X)

• The cranial nerves are numbered in order in which they arise from the brain

• Most cranial nerves innervate the head, neck, and special sense structures.

SPINAL NERVES

• The spinal cord is composed of 31 pairs of spinal nerves : 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.

• Each spinal nerve has a ventral root and a dorsal root.

• The dorsal root are sensory and transmit sensory impulses from specific areas of the body known as dermatomes to the dorsal ganglia.

• The ventral roots are motor and transmit impulses from the spinal cord to the body.

AUTONOMIC NERVOUS SYSTEM

• Regulates the activities of internal organs such as the heart, lungs, blood vessels, digestive organs, and glands.

• It is also responsible for the maintenance and restoration of internal homeostasis

• It is divided into two: the sympathetic and parasympathetic systems, which generally acts in opposition to each other.

• It innervates most body organs.

Sympathetic Nervous System• Known for its role in the body’s “fight” or

flight”response.• The sympathetic neurotransmitter is

norepinephrine.• Under stress conditions from either

physical or emotional causes, sympathetic impulses increase greatly

• The sympathetic neurons are located in the thoracic and the lumbar segments of the spinal cord

Parasympathetic Nervous System

• Functions as the dominant controller for most visceral effectors.

• During quiet, nonstressful condition, impulses from parasympathetic fibers (cholinergics) predominate.

• The fibers of the parasympathetic system are located in two sections, one in the brain stem and the other from the spinal segments below L2.

• The parasympathetic nerves arise from the midbrain and the medulla oblongata.

II. ASSESSMENT: NEUROLOGICAL FUNCTION

• HEALTH HISTORY• An important aspect of the neurologic

assessment is the history of the present illness. The initial interview provides an excellent opportunity to systematically explore the patients condition and related events while simultaneously observing overall appearance, mental status, posture movement and affect. Depending on the condition the nurse may need to rely on yes-or-no answer to questions, on a review of the medical record, or input from the family or a combination of these.

Neurologic disorders

• Alzheimer’s disease• Amyotrophic lateral sclerosis• Epilepsy• Friedrich ataxia• Huntington disease• Myotonic dystropy• Spina bifida • Tourette syndrome

Nursing assessments• FAMILY HISTORY ASSESSMENT• Assess for other similarly affected relatives with

neurologic impairment• Inquire about age onset (present at birth-spina

bifida; developed in childhood-Duchene muscular dystrophy; developed in Adulthood-Huntington disease, Alzheimer’s disease, amyotrophic lateral sclerosis)

• Inquire about the presence of related conditions such as mental retardation and/or learning disabilities (neurofibromatosis type I ).

• PHYSICAL ASSESSMENT

• Assess for the presence of other physical features suggestive of an underlying genetic condition, such as skin lesion seen in neurofibromation type I (café-au-lait spots)

• Management specific to genetics• Inquire whether DNA mutation or other genetic

testing has been performed on affected family members.

• If indicated refer for further genetic counseling and evaluation so that the family members can discuss inheritance, risk to other family members, availability of genetic testing and gene-based interventions.

• Offer appropriate genetics information and resources.

• Assess Patient’s understanding of genetics information.

• Provide to support families with newly diagnosed genetic related neurologic disorders.

• Participate in management and coordination of care of patients with genetic conditions and individuals predisposed to develop or pass on genetic conditions.

CLINICAL MANIFESTATION• PAIN

– Pain is considered an unpleasant sensory perception and emotional experience associated with actual or potential tissue damage or described in terms of such damage.

• SEIZURES– Seizures are the result of abnormal

paroxysmal discharges in the cerebral cortex, which then manifest as an alteration in sensation, behavior, movement, perception, or consciousness.

• DIZZINESS– Dizziness is an abnormal sensation of

imbalance or movement.

• VISUAL DISTURBANCES– Decreased visual acuity associated with

aging to sudden blindness caused by glaucoma.

– Abnormalities of eye movement can also compromise by causing diplopia or double vision.

• WEAKNESS– Weakness, specifically muscle weakness, is

a common manifestation of neurologic disease.

• ABNORMAL SENSATION– Numbness, abnormal sensation, or loss of

sensation is a neurologic manifestation of both central and peripheral nervous system disease. Both numbness and weakness can significantly affect balance and coordination.

• PHYSICAL EXAMINATION– The neurologic examination is a systemic

process that includes a variety of clinical tests, observations, and assessment designed to evaluate a complex system.

Assessing cerebral function• Cerebral abnormalities may cause

disturbances in mental status. Intellectual functioning and thought content and in patterns of emotional behavior. There may also be alterations in perception, motor and language abilities as well as life style.

• Mental status• Intellectual function• Thought content• Emotional status• Perception • Motor ability• Language ability• Impact on lifestyle• Documentation of findings

EXAMINING THE CRANIAL NERVES

• Cranial Nerves

• Assessment Techniques

• (I) Olfactory Nerve-smell, not usually tested

• patient should close both eyes and occlude one nostril

• identify the odor of a common object placed under each nostril

• objects frequently used include coffee, cloves, lemon or soap (avoid ammonia or harsh soaps)

• (II) Optic Nerve-visual acuity and visual fields

• a. Visual Acuity – Snellen eye chart at 14" – counting fingers covering one eye at a time

• b. Visual Fields – patient covers one eye

– examiner moves fingers of left hand and then right into patient view

– patient identifies when fingers can be seen – repeat with patient covering the opposite eye

• (III) Oculomotor, (IV) Trochlear, and (VI) Abducens

• CN III controls pupillary reactions (pupillary light reflex and accommodation), eyelid elevation, eye movements up, down, and medially

• CN IV controls eye movement down and in toward nose

• CN VI controls eye movement laterally toward temporal field

• (CN III, IV, and VI function together to control eye movement)

a. Pupillary reaction (CN III) – instruct the patient to fix both eyes on an

object – shine the beam of a light directly into each

pupil – note the size, shape, and reaction of the

pupils – (may see "PERRLA" in chart notations)

b. Ocular movement (CN III, IV, and VI)– instruct the patient to follow your finger

without moving head – examiner moves finger up, down, left, right – note the presence of nystagmus, limited eye

movement

• (V) Trigeminal Nerve-sensation of face, corneal reflex, muscles of mastication (jaw movement) (has both motor and sensory functions)

a. Motor function testing– ask the patient to open mouth as wide as

possible – observer attempts to close mouth by placing

one hand under chin and the other on top of head

• (VII) Facial Nerve-controls facial muscles, supplies taste fibers to the anterior 2/3 of tongue, controls eyelid closure (has both motor and sensory functions)

a. Motor function testing– have patient wrinkle forehead, smile showing

teeth, and wink eyes – note any asymmetrical movement or facial

drooping

• (VIII) Auditory or Acoustic Nerve-controls hearing and sense of balance

• test using Rinne and Weber tests with tuning fork

• test gross hearing by holding a watch or rubbing fingers together close to ears

• (IX) Glossopharyngeal Nerve and (X) Vagus Nerve-control cough, gag, swallow, articulation, and phonation

• CN IX also controls posterior 1/3 of tongue

• CN X also controls autonomic function

• (have both motor and sensory functions)

• instruct patient to open mouth and say "ahhh"

• look for elevation of soft palate and uvula in the midline

• assess gag reflex by stimulating back of pharynx with tongue depressor

• note any difficulties in articulation and/or speech

• (XI) Spinal Accessory Nerve-controls trapezius and sternocleidomastoid muscles, movement of shoulder and head, shoulder shrugging

a. Trapezius testing

1. patient raises both shoulders while examiner applies resistance

b. Sternocleidomastoid testing

1. patient turns head to left and then to right while examiner applies resistance

• (XII) Hypoglossal Nerve-controls tongue movement and strength

• a. patient protrudes tongue

• b. normally should be midline, note deviation to the right or left

EXAMINING THE MOTOR SYSTEM

• Motor Function– Abnormalities of the motor system are

assessed by evaluating the patient’s muscle size, tone, tenderness, strength and involuntary or abnormal muscle movements (chorea, athetosis). Both primary muscle diseases and diseases of nerves innervating muscles can cause weakness and atrophy. Muscle tone can be decreased (flaccid) or increased (spasticity).

• Reflex Function– Evaluation of deep tendon reflexes (DTRs)

examines the spinal reflex arc. DTRs are usually tested by tapping on a tendon with fingers or a reflex hammer. This causes a stretching of certain muscles and results in contraction. When damage occurs to higher centers (upper motor neurons), the spinal reflex arc is uninhibited and the DTRs are hyperactive.

Reflexes

• Assessment Techniques– Reflexes are graded on a scale of 0 to 4. A stick

figure typically appears in the chart to designate the elicited reflexes.

• 0 ............Not present• 1+ ..........Present but diminished• 2+.......... Normal• 3+ ..........Hyperactive, may have clonus but not

sustained• 4+...........Hyperactive with sustained clonus

• BICEP REFLEX

• TRICEP REFLEX

• BRACHIORADIALIS REFLEX

• PATELLAR REFLEX

• ANKLE REFLEX

• CLONUS

• SUPERFICIAL REFLEX

• Sensory Function– The primary sensations include pain, touch,

vibration, joint position sense (JPS) and thermal. Pain is conveyed by small unmyelinated fibers and is tested with a pinprick (PP). Light touch (LT) is mediated by a combination of small and larger nerve fibers and is tested with a wisp of cotton. Vibration and JPS are mediated by large myelinated fibers. Vibration is tested with a tuning fork.

DIAGNOSTIC EVALUATION• Computed Tomography ScanningNursing Interventions:

•Prepare the patient for the procedure and monitor patient.•Instruct patient about the procedure. Tell the patient to lie quietly still without talking or moving the face throughout the procedure.•Sedation can be used if agitation, restlessness or confusion.•Assess patient for an iodine/shellfish allergy before CT Scan, if contrast agent is used.•Monitor the patient who receive contrast agent for any allergic reactions during and after the procedure.

• Positron Emission TomographyNursing Interventions:

•Prepare the patient for the procedure.•Explain about inhalation techniques and the sensation that may occur.•Teach relaxation technique to reduce anxiety

Single Photon Emission Computed Tomography

Nursing Interventions:• Prepare and monitor the patient.• Premenopausal women are advised to practice

effective contraception before and for several days after testing.

• A woman who is breastfeeding is instructed to stop nursing for the period of time.

• Accompany and monitor the patient during transport to the nuclear medicine department for the scan.

Monitor patient during and after procedure for allergic reactions.

Magnetic Resonance ImagingNursing Interventions:

•Prepare the patient to the procedure.•Teach relaxation techniques.•Tell the patient that he will be able to talk to the staff by means of microphone located inside the scanner.•Before entering the MRI room, all metals and credit cards should be removed.•Obtain patient history to determine the presence of any metal objects such as aneurysm clips.

Cerebral Angiography

Nursing Interventions:• Patient should be well hydrated and clear liquids are permitted up

to the time of the procedure.• Instruct patient to void.• Prepare and shave the groin.• Marked with a felt-tip pen the location of the appropriate

peripheral pulses.• Instruct patient to remain immobile during the procedure.• Tell patient to expect a brief feeling of warmth in the face, behind

the eyes/jaw, teeth, tongue, lips, and a metallic taste when the contrast agent is injected.

• Administer local anesthetics.• Introduced catheter to femoral artery, flushed with heparinized

saline.• Observe signs and symptoms of altered cerebral blood flow after

procedure.• Observe the injection site for hematoma.

MyelographyNursing Interventions:

• Clarify the explanations given by the physician and answer the questions of the patient.

• Inform about what to expect after procedure and should be aware that changes in the position may be made during the procedure.

• Regular meal is omitted before the procedure.• Administer sedative as ordered.• Lie patient on bed with head bed elevated 30-45

degrees.• Advised patient to remain on bed in recommended

position for 3 hours or as prescribed by physician.• Encouraged patient to drink liberal amounts of fluid.• Monitor vital signs as well as ability to void.

Noninvasive Carotid Flow Studies

• It use ultrasound imagery and Doppler measurements of the arterial blood flow.

• Graph produced indicates carotid velocity.

• It is obtained before angiography.

• It use ultrasound imagery and Doppler measurements of the arterial blood flow.

• Graph produced indicates carotid velocity.

• It is obtained before angiography.

•

Transcranial DopplerNursing Interventions:

• Described the procedure to the patient.• Inform that a hand-held Doppler will be placed

over the neck and orbits of the eyes and some water-soluble jelly is used on the transducer.

• Tell patient that it can be performed at the patient’s bedside.

ELECTROENCEPHALOGRAPHY(EEG)

NURSING INTERVENTION• To increase the chances of recording seizure activity, it is

sometimes recommended that the patient be deprieved of sleep on the night before the EEG. Antiseizure agents, tranquilers, stimulants, & depressant should be withheld 24-48 hrs. before EEG. This meds. Can alter the EEG patterns or mask the abnormal wave pattern of seizure disorders.

• Coffee, tea, chocolate & cola drinks are omitted in the mail before the test because of their stimulating effects.

• Meal is not omitted because an altered blood glucose levels can also causes changes in the brain wave pattern.

• Standard EEG takes 45-60 minutes & EEG requires patient cooperation & ability to lie quietly during the test.

• Patient assumed that the procedure does not cause an electric shock, this is not a form of treatment but this is a diagnostic test.

• Sedation is not advisable because it may lower the seizure threshold in patient with seizure disorder& alters brain wave activity in all patients

ELECTROMYOGRAPHY (EMG)

NURSING INTERVENTION• The patient is warned to expect a sensation

similar to that of an intramuscular injection as the needle is inserted into the muscles.

• Muscles examined may ache for a short time after the procedure

NERVE CONDUCTION STUDIES

• Performed by stimulating the peripheral nerve at several points along its cause & recording the muscles action potential or the sensory action potential that results.

EVOKED POTENTIAL STUDIES

NURSING INTERVENTION• There is no specific preparation other tha

explain the procrdure & reassure the patient, encourage the patient to relax.

LUMBAR PUNCTURE

• CSF ANALYSIS

• CSF should be clear and colorless, pink, blood-tinged or grossly bloody CSF may indicate a cerebral contusion, laceration or subarchnoid hemorrhage.

• CSF pressure normally 70-200 mm H2O.

Nursing Intervention• After LP the patient should lie prone for 2-3 hours to

separate the alignment of the dural and arachnoid needle puncture in the meninges to reduce the leakage of CSF.

• Monitor for the complication like headache, notify the physician.

• Encourage fluid intakr to reduce the risk of post-procedure headache, keeping the patient flat overnight may reduce the incidence of headache.

Nerve Cells and Astrocyte

Structure of a neuron and the direction of

nerve message transmission.

Cross section of myelin sheaths that surround axons

Structure of a nerve bundle.

A synapse.

Areas of the brain.

Parts of the brain as seen from the middle of the brain.

•THE END