Neurological System Overview

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Neurological System Overview

Central Nervous System (CNS)

  • Composed of the brain and spinal cord.

Peripheral Nervous System (PNS)

  • Includes cranial and spinal nerves.

  • Divisions:

    • Autonomic System

    • Somatic System

Basic Functional Unit

  • Neuron: responsible for transmitting signals throughout the nervous system.

Anatomy of the Brain

Frontal Lobe

  • Largest lobe of the brain.

Major Functions

  • Concentration.

  • Abstract thought.

  • Information storage/memory.

  • Motor function.

  • Affect, judgment, personality, inhibitions.

Parietal Lobe

Major Functions

  • Sensory discrimination.

  • Analysis of sensations (pain, heat, cold, pressure).

  • Recognition of size, shape, and texture of objects.

  • Proprioception and spatial perception.

Occipital Lobe

  • Responsible for visual interpretation.

Cerebellum

Major Functions

  • Responsible for excitatory and inhibitory actions.

  • Coordination of movement and balance.

  • Proprioception and sensory input integration.

Temporal Lobe

Major Functions

  • Auditory receptive areas.

  • Comprehension of spoken and written language.

  • Dominant role in thinking and interpretation.

Brain Stem

Components and Functions

  • Midbrain:

    • Connects pons and cerebellum with hemispheres.

    • Contains sensory and motor pathways.

    • Center for auditory and visual reflexes (CN III & IV).

  • Pons:

    • Acts as a bridge between various structures.

    • Contains CN V-VIII, motor and sensory pathways, controls heart rate (HR), respiration (R), and blood pressure (BP).

  • Medulla Oblongata:

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

    • Contains cranial nerves IX-XII.

Cerebral Circulation

  • The brain receives 750-800 mL of blood per minute, accounting for 15-20% of total resting cardiac output.

  • High metabolic demand, with no nutrient storage.

  • Arteries fill from below; veins (without valves) drain from above, not following arterial circulation which results in poor collateral flow.

  • Major neck arteries/veins include:

    • 2 internal carotids.

    • 2 vertebral arteries.

  • Circle of Willis:

    • Located at the base of the brain, a ring of arteries that can provide collateral flow if blockage occurs.

    • Can be a site for aneurysm formation.

Cranial Nerves Overview

  • I Olfactory Nerve:

    • Function: Smell.

  • II Optic Nerve:

    • Function: Vision.

  • III Oculomotor Nerve:

    • Functions: Eye movements, control of pupil size.

  • IV Trochlear Nerve:

    • Function: Eye movement.

  • V Trigeminal Nerve:

    • Function: Sensory for the head & face, motor for chewing and tongue movement.

  • VI Abducens Nerve:

    • Function: Movement of eye muscle.

  • VII Facial Nerve:

    • Function: Motor supply to most facial muscles for facial expression.

  • VIII Vestibulocochlear Nerve:

    • Function: Hearing and balance.

  • IX Glossopharyngeal Nerve:

    • Functions: Taste, motor for swallowing, sensory to tongue and throat.

  • X Vagus Nerve:

    • Functions: Inner workings of abdominal and thoracic organs, gag reflex.

  • XI Accessory Nerve:

    • Function: Motor to two neck muscles.

  • XII Hypoglossal Nerve:

    • Function: Motor to tongue muscles.

Transient Ischemic Attack (TIA)

  • Definition: Temporary neurologic deficit resulting from a temporary impairment of blood flow.

  • Characteristics:

    • Lasts less than 24 hours, most resolve in less than 1 hour.

    • Sudden loss of motor, sensory, and visual function.

    • Considered a warning sign for an impending stroke.

Stroke

  • Definition: Sudden loss of function resulting from disruption of blood supply to a part of the brain, also known as a brain attack.

  • Stroke is the primary cerebrovascular disorder and the third leading cause of death in the U.S.

  • Types of Stroke:

    • Ischemic Stroke (80-85%):

    • Caused by obstruction that leads to infarction of brain tissue.

    • Hemorrhagic Stroke (15-20%):

    • Caused by bleeding into the brain.

Prevention of Stroke

Major Risk Factors

  • Hypertension: The primary risk factor for stroke.

    • Other risk factors include:

    • Cardiovascular disease.

    • Elevated cholesterol or hematocrit.

    • Obesity.

    • Diabetes.

    • Oral contraceptive use.

    • Smoking and drug/alcohol abuse.

Tests to Diagnose Cerebrovascular Accident (CVA)

CT Scan of Head

  • The single most important diagnostic test for possible CVA.

  • Critical to rule out hemorrhage.

  • Must be performed within 25 minutes of arrival to the Emergency Department, read in another 20 minutes and treatment initiated within 1 hour.

  • May appear normal for a few hours initially.

  • Ischemic brain is typically damaged and begins to swell after 6-12 hours.

NIH Stroke Scale

  • A 15-item neurologic examination stroke scale used to evaluate the effect of acute cerebral infarction.

  • Ratings for each item are scored 0 (normal) to 3-5 grades with allowance for untestable items.

  • The single client assessment requires less than 10 minutes to complete.

  • Important for assessing eligibility for tissue plasminogen activator (t-PA) treatment.

    • Must be given within 3 - 4.5 hours after symptom onset.

Stroke Interventions

Immediate Actions

  • Identify the onset of symptoms.

  • Support vital functions.

  • Rapid transport to a certified stroke center.

  • Maintain adequate oxygenation (O2).

  • Elevate head of bed (HOB) by 30 degrees.

  • Initiate seizure precautions.

  • Call the (AHA) stroke team.

    • Blood pressure (BP) is usually elevated.

    • NPO until evaluated.

    • Avoid dextrose or hypertonic fluids.

Cerebrovascular Terms

  • Hemiplegia: Paralysis of one side of the body.

  • Hemiparesis: Weakness of one side of the body.

  • Dysarthria: Disturbance in the muscular control of speech.

  • Apraxia: Loss of the ability to execute skilled movements and gestures.

  • Aphasia:

    • Expressive aphasia: Loss of ability to produce language.

    • Receptive aphasia: Loss of comprehension.

    • Global aphasia: Total inability to communicate.

  • Hemianopsia: Loss of vision in half of the visual field of one or both eyes.

Comparison of Hemispheric Strokes

Left Sided Stroke

  • Symptoms include:

    • Paralysis/weakness on the right side.

    • Right visual field deficit.

    • Impulsivity and lack of awareness of deficits.

    • Altered intellectual ability.

    • Slow and cautious behavior.

Right Sided Stroke

  • Symptoms include:

    • Paralysis/weakness on the left side.

    • Left visual field deficit.

    • Spatial-perceptual deficits.

    • Increased distractibility.

Ischemic Stroke

  • Definition: Disruption of blood supply due to an obstruction leading to infarction of brain tissue caused by either thrombus or emboli.

  • Symptoms depend on location and size of affected area.

  • Recovery depends on the location and size of infarction after edema has disappeared.

  • The acute phase may last 1-3 days.

Manifestations of Ischemic Stroke

  • Numbness or weakness of face, arm, or leg, especially on one side.

  • Confusion or change in mental status.

  • Trouble speaking or understanding speech.

  • Difficulty in walking, dizziness, or loss of balance or coordination.

  • Sudden, severe headache and perceptual disturbances.

Treatment of Ischemic Stroke

  • Health maintenance measures such as healthy diet, exercise, and prevention of periodontal disease.

  • Carotid endarterectomy: Surgical procedure that involves removing plaque from the carotid arteries.

  • Anticoagulant therapy: Use of medications to prevent blood clotting.

  • Antiplatelet therapy: Including aspirin, dipyridamole (Persantine), clopidogrel (Plavix), and ticlopidine (Ticlid).

  • Statins and antihypertensive medications: For long-term management of blood pressure and cholesterol levels.

Hypertension Management

  • Management of systolic BP > 220 and diastolic BP > 120 is critical.

  • Gradual 20% lowering of BP is recommended.

    • Note: Providing proper control of Intracranial Pressure (ICP) usually results in decreased BP.

  • Thrombolytics are contraindicated if BP is greater than 185/110.

  • Recommended antihypertensive:

  • Labetalol (Normodyne, Trandate): Preferred due to limited effect on cerebral vessels with no reflex tachycardia.

  • Enalapril (Vasotec) and using nitroglycerin paste: 1-2 inches may also be beneficial.

Thrombolytic Therapy

Alteplase (t-PA)

  • Administered within a 3-4.5 hour window from symptom onset when deemed a candidate

  • If eligible, no other anticoagulants are to be administered for 24 hours.

  • Control BP carefully during treatment; maintain SBP < 180 mmHg and DBP < 105 mmHg.

  • Common side effect includes bleeding: assess all sites and avoid invasive procedures for 24 hours, e.g., insertion of catheter, NG, arterial lines.

Hemorrhagic Stroke

Definition and Causes

  • Definition: Intracranial or subarachnoid bleeding due to aneurysm or arteriovenous malformation (AVM), especially in younger people.

  • Risk factors include:

    • Hypertension, age greater than 55, male gender, use of phenylpropanolamine (PPA).

  • Presents with increased mortality, more significant deficits, and longer recovery time compared to ischemic stroke.

Manifestations

  • Sudden severe headache, loss of consciousness, nuchal rigidity, and visual disturbances.

  • Diagnosis through CT scan and lumbar puncture if no signs of increased intracranial pressure (IICP).

Hemorrhagic Stroke Management

  • Managing complications such as vasospasm which can lead to increased mortality 4-14 days post-initial bleed.

  • Treatment options include:

    • Aneurysm clips, calcium channel blockers, and