Neurological System PDF

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Review Chapter 24 NUR 325 Neurologic System Structure and Function Nervous system divided into two parts:  Central nervous system (CNS), which includes brain and spinal cord  Peripheral nervous system (PNS), which includes all nerve fibers outside brain and spinal cord o Includes 12 pairs of cranial nerves, 31 pairs of spinal nerves, and all their branches o Carries sensory (afferent) messages to CNS from sensory receptors o Motor (efferent) messages from CNS to muscles and glands, as well as autonomic messages that govern internal organs and blood vessels Central Nervous System

Cerebral Cortex  Cerebral cortex is cerebrum’s outer layer of nerve cells.  Cerebral cortex is center of functions governing thought, memory, reasoning, sensation, and voluntary movement. o Each half of cerebrum is hemisphere. o Each hemisphere divided into four lobes: frontal, parietal, temporal, and occipital Lobes of the Cerebral Cortex  Lobes have areas that mediate specific functions: o Frontal lobe concerned with personality, behavior, emotions, and intellectual function  Broca’s area in frontal lobe mediates motor speech o Parietal lobe’s postcentral gyrus is primary center for sensation o Occipital lobe is primary visual receptor center o Temporal lobe behind ear, has primary auditory reception center, taste, and smell o Wernicke’s area in temporal lobe associated with language comprehension Damage to Cerebral Cortex

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Damage to specific cortical areas produces a corresponding loss of function: o Motor weakness o Paralysis o Loss of sensation o Impaired ability to understand and process language Damage occurs when highly specialized neurologic cells are deprived of blood supply, such as when a cerebral artery becomes occluded.

Cerebral Cortex

Central Nervous System Components  Basal ganglia o Gray matter in two cerebral hemispheres that form subcortical associated motor system (extrapyramidal system)  Thalamus o Main relay station where sensory pathways of spinal cord, cerebellum, and brainstem form synapses  Hypothalamus o Major respiratory center with basic function control and coordination  Cerebellum o Concerned with motor coordination and muscle tone of voluntary movements  Brainstem o Central core of the brain—contains midbrain, pons and medulla  Spinal cord o Main pathway for ascending and descending fiber tracts that connect brain to spinal nerves

Brainstem

Midbrain—The most anterior part of the brainstem that still has the basic tubular structure of the spinal cord. o It merges into the thalamus and hypothalamus. o It contains many motor neurons and tracts.  Pons—The enlarged area containing ascending sensory and descending motor tracts. o It has two respiratory centers (pneumotaxic and apneustic) that coordinate with the main respiratory center in the medulla.  Medulla—The continuation of the spinal cord in the brain that contains all ascending and descending fiber tracts. o It has vital autonomic centers (respiration, heart, gastrointestinal function) and nuclei for cranial nerves VIII through XII. Pyramidal decussation (crossing of the motor fibers) occurs here Pathways of CNS  Crossed representation is notable feature of nerve tracts. o Left cerebral cortex receives sensory information from and controls motor function to right side of the body. o Right cerebral cortex likewise interacts with left side of body.  Knowledge of where fibers cross midline will help interpret clinical findings. Sensory Pathways  Sensation travels in afferent fibers in peripheral nerve through posterior (dorsal) root and into spinal cord.  There, may take one of two routes: anterolateral (spinothalamic) tract or posterior (dorsal) columns  Anterolateral tract o Contains sensory fibers that transmit sensations of pain, temperature, and crude or light touch  Posterior (dorsal) columns o These fibers conduct sensations of position, vibration, and finely localized touch. o Position (proprioception), vibration, and finely localized touch (stereognosis) Sensory Pathways 

Motor Pathways

Corticospinal or pyramidal tract o Fibers mediate voluntary movement, particularly very skilled, discrete, purposeful movements. o Motor nerve fibers travel to brainstem crossing to opposite, contralateral side, (pyramidal decussation) and then pass down in lateral column of spinal cord.  Extrapyramidal tracts include o motor nerve fibers originating in motor cortex, basal ganglia, brainstem, and spinal cord outside pyramidal tract. o subcortical motor fibers that maintain muscle tone and control body movements, especially gross automatic movements, such as walking.  Cerebellar system o Coordinates movement, maintains equilibrium and posture o Receives information on position of muscles and joints, body’s equilibrium, and kind of motor messages sent from cortex to muscles o Integrates information using feedback pathway to exert control Upper Motor Neurons  Complex of descending motor fibers that can influence or modify lower motor neurons  Located completely within CNS; convey impulses from motor areas of cerebral cortex to lower motor neurons  Examples of upper motor neuron diseases are cerebrovascular accident, cerebral palsy, and multiple sclerosis. Lower Motor Neurons  Final common pathway, providing final contact with muscle  Located in anterior gray column of spinal cord, but nerve fibers extend to muscle  Movement must be translated into action by lower motor neuron fibers. o Examples of lower motor neurons are cranial nerves and spinal nerves of peripheral nervous system. o Examples of lower motor neuron diseases are spinal cord lesions, poliomyelitis, and amyotrophic lateral sclerosis. Motor Pathways 

Reflexes

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Reflexes: basic defense mechanisms of nervous system o Involuntary; below level of conscious control permitting quick reaction to potentially painful or damaging situations Three types of reflexes: o Stretch on/deep tendon (myotatic), e.g., knee jerk  DTR has 5 components: intact sensory (afferent) nerve, functional synapse in the cord, intact motor (efferent) nerve, neuromuscular junction and competent muscle o Superficial (cutaneous), e.g., plantar reflex o Visceral (organ), e.g., pupillary response to light and accommodation

Reflex Arc

Cranial Nerves  LMNs that enter and exit brain rather than spinal cord: o CN I and II extend from cerebrum. o Cranial nerves III to XII extend from midbrain and brainstem.  12 pairs of cranial nerves supply primarily head and neck, except vagus nerve, which travels to heart, respiratory muscles, stomach, and gallbladder. Cranial Nerves: Pathways

Cranial Nerves

Spinal Nerves  31 pairs of spinal nerves arise from length of spinal cord and supply rest of body.  Named for region of spine from which they exit o 8 cervical 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal  “Mixed” nerves o Contain both sensory and motor fibers  Each innervates particular segment of body.  Dermal segmentation o Cutaneous distribution of various spinal nerves Spinal Nerves

Dermatomes

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Dermatome o Circumscribed skin area supplied mainly from one spinal cord segment through particular nerve o Dermatomes overlap; if one nerve is severed, most of sensations are transmitted by one above and one below. Useful landmark dermatomes o Thumb, middle finger, fifth finger are C6, C7, and C8 o Axilla at T1 o Nipple at T4 o Umbilicus at T10 o Groin in region of L1 o Knee at L4

Autonomic Nervous System  Peripheral nervous system composed of cranial nerves and spinal nerves  Carry fibers divided functionally into two parts: o Somatic fibers innervate skeletal (voluntary) muscles. o Autonomic fibers innervate smooth (involuntary) muscles, cardiac muscle, and glands.  Autonomic system mediates unconscious activity. Developmental Competence: Infants  Neurologic system is not completely developed at birth. o Movement is directed primarily by primitive reflexes. o Persistence of primitive reflexes is an indication of CNS dysfunction. o Sensory and motor development proceed with gradual acquisition of myelin needed to conduct most impulses. o As myelinization develops, infant is able to localize stimulus more precisely and make more accurate motor response. Developmental Competence: Aging Adult  Atrophy with steady loss of neuron structure in brain and spinal cord  Velocity of nerve conduction decreases making reaction time slower in some older persons.  Increased delay at synapse results in diminished sensation of touch, pain, taste, and smell.  Motor system may show general slowing down of movement, muscle strength, and agility decrease.  Progressive decrease in cerebral blood flow and oxygen consumption may cause dizziness and loss of balance.

Culture and Genetics

Racial/ethnic disparity noted relative to strokes o 5th most common cause of death in the United States o Screening for hyperlipidemia and HTN with statin treatment  Geographic disparity noted relative to strokes o Existence of “Stroke Belt” —8 states with increased stroke mortality  Nationwide burden of stroke o Higher for African Americans and Hispanic populations  Global concern o Research evidence indicates that 90% of stroke burden due to modifiable factors. Subjective Data  Headache  Head injury  Dizziness/vertigo  Seizures  Tremors  Weakness  Incoordination  Numbness or tingling  Difficulty swallowing  Difficulty speaking  Patient-centered care  Environmental/occupational hazards 

Subjective Data Questions  Headache: Ask about o onset, frequency, and severity. o location, quality description, and associated factors. o A patient who says, “This is the worst headache of my life,” needs emergency referral to screen possible stroke.  Head injury: Ask about o event history, type and description. o loss of consciousness and recall of event. o Concussion comes from a direct blow that causes rotation of the brain inside the skull and shear injury.  Dizziness/vertigo: Ask about o onset, duration, description, and frequency. o associated with change in position. o vertigo characteristics—objective or subjective vertigo. o Syncope is a sudden loss of strength, a temporary loss of consciousness (a faint) caused by lack of cerebral blood flow, e.g., low BP. o True vertigo is rotational spinning caused by neurologic disease in the vestibular apparatus in the ear or the vestibular nuclei in the brainstem.  Seizures: Ask about o course and duration. o motor activity in body.

associated clinical presentations. postictal phase. precipitating factors. medication therapy. coping strategies. Aura is a subjective sensation that precedes a seizure; it could be auditory, visual, or motor. Tremors: involuntary shaking, vibrating, or trembling. Ask about o onset, type, duration, and frequency. o precipitating and alleviating factors. Weakness: Ask about o localized or generalized, distal or proximal. o impact on mobility or ADLs. o Paresis is a partial or incomplete paralysis. o Paralysis is a total loss of motor function caused by a lesion in the neurologic or muscular system or loss of sensory innervation. Incoordination: Dysmetria is the inability to control the distance, power, and speed of a muscular action. Ask about o problems with balance while standing or ambulating. o lateral drifting, stumbling, or falling. o legs giving way and/or clumsy movements. Numbness or tingling: Paresthesia is an abnormal sensation (e.g., burning, tingling). Ask about o onset, duration, and location. o whether it occurs with activity. Difficulty swallowing: Dysphagia. Ask about o With solids or liquids o Drooling Difficulty speaking: Dysarthria is difficulty forming words; dysphasia is difficulty with language comprehension or expression. Ask about o onset, pattern, and duration. o forming words or saying what you want to say. Patient-centered care: Ask about o information regarding past pertinent medical history. Environmental and occupational hazards: Ask about o exposure history. o medication history: Rx and OTC. o alcohol history. o substance abuse/drug history. o Review anticonvulsants and anti-tremor, antivertigo, and pain medication. o Review moderate to heavy alcohol use. o o o o o o

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Additional History: Infants and Children Ask about

 maternal and/or fetal problems during pregnancy and delivery.  gestational status, birth weight, and Apgar score.  reflexes and motor performance.  presence of seizure activity.  meeting developmental milestones.  environmental exposure to lead.  learning problems identified.  significant family history.  participation in sports—injury history. Additional History: Aging Adult  Dizziness: Ask about o association with positional change or activity or medication. o impact on ADLs. o safety modifications.  Memory: Ask about o decrease in mental function or confusion. o onset, duration, and frequency.  Tremor: Ask about o location. o precipitating and alleviating factors. o impact on ADLs.  Sudden vision change: Ask about o onset, duration, and frequency. o loss of consciousness and safety. o impact on ADLs. Objective Data: Preparation  Perform screening neurologic examination on well persons with no significant findings from history.  Perform complete neurologic examination on persons with neurologic concerns (e.g., headache, weakness, loss of coordination) or who have shown signs of neurologic dysfunction.  Perform neurologic recheck examination on persons with demonstrated neurologic deficits who require periodic assessments (e.g., hospitalized people or those in extended care)  Integrate steps of neurologic examination with examination of particular part of body.  Use following sequence for complete neurologic examination: o Mental status o Cranial nerves o Motor system o Sensory system o Reflexes Screening Neurological Examination

1. Mental status (level of alertness, appropriateness of responses, orientation to date and place) 2. Cranial nerves: o II–visual acuity, pupillary light reflex; o III, IV, VI–eye movements o VII–facial strength (smile, eye closure) o VIII–hearing 3. Motor function: Strength (shoulder abduction, elbow extension, wrist extension, finger abduction, hip flexion, knee flexion, ankle dorsiflexion); coordination (fine finger movements, finger to nose); gait (casual, tandem) 4. Sensation (one modality at toes can be light touch, pain/temperature, or proprioception) 5. Reflexes: Deep tendon reflexes (biceps, patellar, Achilles); plantar responses Objective Data: Equipment  Penlight  Tongue blade  Cotton swab  Cotton ball  Tuning fork: 128 Hz or 256 Hz  Percussion hammer Cranial Nerve Testing  Cranial nerve I: olfactory nerve (not tested routinely) o Test sense of smell in those who report loss of smell, head trauma, and abnormal mental status, and when presence of intracranial lesion suspected. o With the person's eyes closed, occlude one nostril and present an aromatic substance. Use familiar, obtainable, and nonnoxious smells such as coffee, toothpaste, orange, vanilla, soap, or peppermint. Alcohol wipes smell familiar and are easy to find.  Cranial nerve II: optic nerve o Test visual acuity and visual fields by confrontation. o Using ophthalmoscope, examine ocular fundus to determine color, size, and shape of optic disc.  Cranial nerves III, IV, and VI: oculomotor, trochlear, and abducens nerves o Check pupils for size, regularity, equality, direct and consensual light reaction, and accommodation. o Assess extraocular movements by 6 cardinal positions of gaze. o Assess for nystagmus (back-and-forth oscillation of the eyes)  Cranial nerve V: trigeminal nerve o Motor function: assess muscles of mastication by palpating temporal and masseter muscles as a person clenches his or her teeth

Decreased strength on one or both sides. Asymmetry in jaw movement. Pain with clenching of teeth. Unilateral weakness occurs with lesion of the pons (same side) and cancer metastases to skull. o Sensory function: with a person’s eyes closed, test light touch sensation by touching a cotton wisp to designated areas on a person’s face: forehead, cheeks, and chin  Decreased or unequal sensation. With a stroke, sensation of face and body is lost on the opposite side of the lesion. Hemiparesis and aphasia often are associated. o Assess corneal reflex if the person has abnormal facial sensations or abnormalities of facial movement. o Tests all three divisions of CN V: ophthalmic, maxillary, and mandibular. 

Motor

Sensory

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Cranial nerve VII: facial nerve o Motor function:  Note mobility and facial symmetry as a person responds to selected movements.  Have the person puff cheeks, then press puffed cheeks in, to see that air escapes equally from both sidesMuscle weakness is shown by flattening of the nasolabial fold, drooping of one side of the face, lower eyelid sagging, and escape of air from only one cheek that is pressed in.  Loss of movement and asymmetry of movement occur with both CNS lesions (e.g., stroke that affects lower face on one side) and peripheral nervous system lesions (e.g., Bell palsy that affects the upper and lower face on one side). o Sensory function: (not tested routinely)  Test only when you suspect facial nerve injury.  When indicated, test sense of taste by applying cotton applicator covered with solution of sugar, salt, or lemon juice to tongue and ask the person to identify taste.

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Cranial nerve VIII: acoustic nerve (vestibulocochlear) o Test hearing acuity by ability to hear normal conversation and by whispered voice test. Cranial nerves IX and X: glossopharyngeal and vagus nerves o Motor function  Depress tongue with tongue blade and note pharyngeal movement as the person says “ahhh” or yawns; uvula and soft palate should rise in midline, and tonsillar pillars should move medially.  Touch posterior pharyngeal wall with tongue blade, and note gag reflex; voice should sound smooth, not strained.  Absence or asymmetry of soft palate movement or tonsillar pillar movement. Following a stroke, dysfunction in swallowing increases risk for aspiration.  Hoarse or brassy voice occurs with vocal cord dysfunction; nasal twang occurs with weakness of soft palate. o Sensory function  Cranial nerve IX does mediate taste on posterior one third of tongue, but technically too difficult to test. Cranial nerve XI: spinal accessory nerve o Examine sternomastoid and trapezius muscles for equal size. o Check equal strength by asking the person to rotate head against resistance applied to side of chin. o Ask the person to shrug shoulders against resistance.  Atrophy. Muscle weakness or paralysis occurs with a stroke or following injury to the peripheral nerve (e.g., surgical removal of lymph nodes). Cranial nerve XII: hypoglossal nerve o Inspect tongue; no wasting or tremors should be present. o Note forward thrust in midline as the person protrudes tongue. o Ask the person to say “light, tight, dynamite,” and note that lingual speech (sounds of letters l, t, d, n) is clear and distinct.  Tongue deviates to side when stroke affects the hypoglossal nerve (when this occurs, deviation is toward the paralyzed side).

Inspect and Palpate Motor System: Muscles  Size (atrophy or hypertrophy) o Inspect all muscle groups for size noting bilateral comparison.  Strength (Paresis or weakness) o Test muscle groups of extremities, neck, and trunk.  Tone: normal tension in relaxed muscles (Flaccid, spastic, or rigid; pain or limited ROM) o Persuade the person to relax completely and move each extremity smoothly through a full range of motion; normally note mild, even resistance to movement.  Involuntary movements (Tic, tremor, fasciculation, myoclonus, chorea) o Normally none occur; if present, note location, frequency, rate, and amplitude; note if movements can be controlled at will. Cerebellar Function: Coordinati...