Chapter 14: Nervous System Disorders

Anatomical and Functional Features of the Brain

• Anatomical Structures of the Brain

  • A: Motor cortex (Identified as letter A)

  • B: Central sulcus (Identified as letter B)

  • C: Sensory cortex (Identified as letter C)

  • D: Parietal lobe (Identified as letter D)

  • E: Visual area (Identified as letter E)

  • F: Occipital lobe (Identified as letter F)

  • G: Cerebellum (Identified as letter G)

  • H: Medulla (Identified as letter H)

  • I: Pons (Identified as letter I)

  • J: Temporal lobe (Identified as letter J)

  • K: Lateral sulcus (Identified as letter K)

  • L: Frontal lobe (Identified as letter L)

  • M: Premotor cortex (Identified as letter M)

• Functional Features and Corresponding Locations

  • Intellect and personality (N): Primary characteristic of the Frontal lobe.

  • Broca's speech area (O): Located in the frontal lobe, responsible for expressive speech.

  • Auditory area (P): Located in the temporal lobe.

  • Memory (Q): Supported extensively by the temporal lobe.

  • Reticular activating system—RAS (R): Vital for maintaining alertness and consciousness.

  • Vital centers (S): Located in the brainstem (Medulla/Pons).

  • Balance, equilibrium, and coordination (T): Primary function of the Cerebellum.

  • Visual association area (U): Located in the occipital/parietal regions.

  • Wernicke's area (V): Located in the temporal-parietal region, responsible for language comprehension.

• Summary of Lobe Functions

  • Frontal Lobe: Essential for personality, judgment, voluntary movement, and expressive speech.

  • Parietal Lobe: Responsible for processing sensation.

  • Temporal Lobe: Supports hearing, language, and memory.

  • Occipital Lobe: Responsible for processing vision.

Understanding Aphasia

• Definition: Aphasia is the impaired ability to speak, understand, read, or write resulting from damage to the brain's language areas.

• Expressive (Broca) Aphasia

  • Pathology: Caused by damage to Broca’s area in the frontal lobe.

  • Presentation: The individual understands language but experiences significant difficulty producing words.

  • Characteristics: Speech is described as slow, limited, and frustrating for the speaker.

• Receptive (Wernicke) Aphasia

  • Pathology: Caused by damage to Wernicke’s area in the temporal-parietal region.

  • Presentation: The individual can speak fluently, but the words may not make sense (often called "word salad").

  • Characteristics: Significant difficulty understanding spoken or written language.

• Global Aphasia

  • Pathology: Extensive damage involving both major language areas (Broca and Wernicke).

  • Presentation: Severe impairment in both understanding and producing language.

Manifestations of Increased Intracranial Pressure (ICP)

• Headache: Occurs because pressure stretches pain-sensitive tissues and blood vessels.

• Vomiting: Result of pressure stimulating the vomiting center in the brain; notably, it may occur without preceding nausea.

• Decreasing Consciousness: Caused by reduced cerebral perfusion and pressure on the Reticular Activating System (RAS), which impairs alertness.

• Pupil Changes: Occurs as pressure compresses cranial nerve III (Oculomotor nerve).

• Blurred Vision or Papilledema: Pressure is transmitted directly to the optic nerve.

• Weakness or Abnormal Posturing: Caused by the compression of motor pathways.

• Seizures: Result from irritated cerebral neurons discharging abnormally.

• Cushing Triad: A late and dangerous indicator of high ICP, characterized by:

  • Increased systolic blood pressure and a widened pulse pressure.

  • Bradycardia (slow heart rate).

  • Irregular respirations.

• Abnormal Breathing: Occurs as brainstem respiratory centers become compressed.

Brain Tumors: General and Location-Specific Manifestations

• General Manifestations (Resulting from increased ICP)

  • Headache, which is often significantly worse in the morning.

  • Nausea and vomiting.

  • Papilledema.

  • Seizures.

  • Cognitive or personality changes.

  • Fatigue.

  • Altered consciousness.

• Location-Specific Manifestations

  • Frontal Lobe: Personality changes, impaired judgment, expressive aphasia, and motor deficits.

  • Parietal Lobe: Sensory deficits, difficulty recognizing objects (agnosia), and neglect of one side of the body.

  • Temporal Lobe: Receptive aphasia, memory problems, hearing disturbances, and seizures.

  • Occipital Lobe: Visual field defects and other visual disturbances.

  • Cerebellum: Ataxia (loss of muscle coordination), balance problems, and nystagmus (involuntary eye movement).

  • Brainstem: Cranial nerve deficits, swallowing difficulty (dysphagia), and respiratory or cardiac problems.

  • Pituitary: Hormonal changes and visual field defects, specifically bitemporal hemianopia.

Cerebrovascular Disorders: TIA and Stroke

• Transient Ischemic Attack (TIA)

  • Definition: A temporary interruption of blood flow to the brain.

  • Manifestations: Sudden onset of one-sided weakness/numbness, facial drooping, difficulty speaking or understanding speech, temporary vision loss/blurring, dizziness, loss of balance, confusion, and sudden severe headache.

  • Duration and Outcome: Symptoms typically resolve within minutes because blood flow returns; there is no permanent infarction.

  • Significance: Serves as a vital warning sign of a potential future stroke.

• Stroke (Cerebrovascular Accident)

  • Definition: Prolonged blockage or bleeding leading to brain cell injury or death.

  • Duration and Outcome: Symptoms continue without treatment, and neurological deficits may persist permanently.

  • Significance: Represents actual cerebral injury.

• Common Categories of Stroke

  1. Thrombotic Stroke: A clot forms directly in a cerebral artery, usually over an atherosclerotic plaque. This is the most common single type of stroke.

  2. Embolic Stroke: A clot travels from another location (e.g., the heart) and blocks a cerebral artery.

  3. Hemorrhagic Stroke: A cerebral blood vessel ruptures.

• Statistics and Broader Classifications

  • Ischemic Strokes: Include both thrombotic and embolic categories; these account for approximately $87\%$ of all strokes.

• Pathophysiology of Ischemic Stroke

  1. Thrombus or embolus obstructs a cerebral artery.

  2. Oxygen and blood cannot reach the affected brain tissue.

  3. Brain cells lose ATP (Adenosine Triphosphate).

  4. Ion pumps fail, leading to cell swelling.

  5. Excitatory neurotransmitters and inflammation cause further secondary injury.

  6. The central area of the obstruction becomes infarcted (dead tissue).

  7. Penumbra: The surrounding tissue that is at risk but potentially salvageable with rapid medical treatment.

• Pathophysiology of Hemorrhagic Stroke

  1. A blood vessel ruptures.

  2. Blood enters the brain tissue or subarachnoid space.

  3. Blood acts as a toxin, directly damaging neurons.

  4. A hematoma and cerebral edema (swelling) develop.

  5. Intracranial Pressure (ICP) rises, which may lead to brain herniation.

• Prognosis of Hemorrhagic Stroke

  • Generally worse than ischemic stroke because it can directly destroy tissue, rapidly increase ICP, cause severe edema, continue bleeding, and cause vasospasms. Blood is toxic to brain tissue and compresses nearby structures.

Specific Stroke Presentation: Left Frontal and Parietal Thrombotic Stroke

• General Rule: The left cerebral hemisphere controls the right side of the body and usually houses the major language centers.

• Probable Manifestations:

  • Right-sided weakness or paralysis (Hemiplegia).

  • Right-sided sensory loss.

  • Right facial drooping.

  • Expressive aphasia (from frontal lobe involvement).

  • Difficulty reading, writing, or calculating (dyscalculia).

  • Apraxia: Difficulty planning movements.

  • Poor judgment or personality changes.

  • Right visual-field loss.

  • Difficulty recognizing body position or objects.

Shingles (Herpes Zoster)

• Cause: Reactivation of the varicella-zoster virus (the virus that causes chickenpox).

• Pathology: After the initial chickenpox infection, the virus remains dormant in the sensory nerve ganglia.

• Manifestation Factors: Reactivation typically occurs years later due to increasing age, stress, immunosuppression, or serious illness.

• Clinical Presentation: A painful, blistering rash that follows a specific dermatomal pattern.

Spinal Cord Injury (SCI)

• Manifestations (Dependent on injury level and completeness):

  • Neck or back pain.

  • Weakness or paralysis.

  • Loss of sensation below the level of injury.

  • Spinal Shock: Loss of reflexes immediately following injury; spasticity may develop later.

  • Loss of bowel and bladder control.

  • Neurogenic Shock: Characterized by hypotension (low blood pressure) and bradycardia (slow heart rate).

  • Difficulty breathing (specifically with cervical injuries).

  • Priapism.

  • Loss of temperature regulation and inability to sweat below the lesion site.

Neurological Terminology

• Ptosis: Drooping eyelid.

• Agnosia: Inability to recognize everyday objects.

• Contralateral: Relating to the opposite side of the body.

• Dysarthria: Difficulty pronouncing words due to muscle weakness.

• Paraplegia: Paralysis affecting the lower half of the body.

• Aphasia: Inability to express or comprehend speech.

• Photophobia: Increased sensitivity to light.

• Quadriplegia: Paralysis of all four limbs.

• Ipsilateral: Relating to the same side of the body.

• Hemiplegia: Paralysis of one side of the body.

• Bitemporal hemianopia: Loss of lateral vision from both visual fields.

• Glioma: A brain tumor originating in neurologic (glial) cells.

• Contusion: Bruising of the brain tissue.

Seizure Disorders

• Pathophysiology

  1. A group of neurons becomes abnormally excitable.

  2. The normal balance between excitation and inhibition is disrupted.

  3. Neurons fire excessively and synchronously.

  4. Abnormal activity may remain focal or spread through both hemispheres.

• Absence (Petit Mal) Seizure

  • Characteristics: Brief staring episodes, cessation of movement or speech, and possible eyelid fluttering or minor automatisms.

  • Duration: Often lasts less than $20\,seconds$; may occur many times per day.

  • PostictalState: Usually no collapse, no convulsion, and no postictal confusion.

• Prodromal Signs vs. Aura

  • Prodromal Signs: Nonspecific changes (irritability, mood changes, headache, sleep disturbance) occurring hours or days before a seizure.

  • Aura: A sensation that occurs immediately before or at the very beginning of the seizure.

• Tonic-Clonic Seizure Phases

  • Tonic Phase: Sudden loss of consciousness, body stiffness, air leaving lungs (cry), cessation of breathing, and falling.

  • Clonic Phase: Repetitive rhythmic jerking, possible tongue biting, excessive salivation, and possible urinary incontinence.

  • Postictal Phase: Confusion, sleepiness, headache, muscle soreness, and temporary weakness.

  • Total Duration: The convulsive portion usually lasts approximately $1-3\,minutes$.

Parkinson's Disease

• Pathologic Changes

  1. Degeneration of dopamine-producing neurons in the substantia nigra.

  2. Decrease of dopamine in the striatum.

  3. Relative dominance of acetylcholine activity.

  4. Basal ganglia circuits fail to smoothly regulate and start movement.

  5. Presence of Lewy bodies containing abnormal alpha-synuclein.

• Early Manifestations

  • Unilateral resting "pill-rolling" tremor.

  • Bradykinesia (slow movement) and rigidity.

  • Reduced arm swing and shuffling gait.

  • Masklike facial expression, small handwriting (micrographia), and soft voice.

• Late Manifestations

  • Postural instability leading to falls; freezing of gait.

  • Dysphagia (difficulty swallowing) and drooling.

  • Orthostatic hypotension, constipation, and urinary dysfunction.

  • Cognitive impairment, dementia, and depression.

Comparative Disease Matrix: ALS, MG, and Huntington's

• Amyotrophic Lateral Sclerosis (ALS)

  • Etiology: Mostly sporadic; some inherited genetic forms.

  • Pathophysiology: Degeneration of both upper and lower motor neurons.

  • Manifestations: Progressive weakness, muscle atrophy, fasciculations (twitching), spasticity, and respiratory failure. Sensation is usually preserved.

  • Treatment: Riluzole, edaravone, and respiratory/nutritional support.

  • Prognosis: Progressive and ultimately fatal.

• Myasthenia Gravis (MG)

  • Etiology: Autoimmune; antibodies against ACh receptors or MuSK proteins.

  • Pathophysiology: Reduced functioning of Acetylcholine (ACh) receptors impairs neuromuscular transmission.

  • Manifestations: Fluctuating skeletal muscle weakness, ptosis, diplopia (double vision), and facial weakness. Symptoms improve with rest.

  • Treatment: Pyridostigmine, corticosteroids, thymectomy, or IVIG/plasma exchange.

  • Prognosis: Often manageable, but myasthenic crisis is life-threatening.

• Huntington's Disease

  • Etiology: Autosomal dominant mutation with an expanded CAG repeat in the HTT gene.

  • Pathophysiology: Degeneration of neurons in the caudate and putamen; reduced GABA; altered basal ganglia circuits.

  • Manifestations: Chorea (involuntary movements), poor coordination, personality changes, psychiatric issues, and cognitive decline.

  • Treatment: Tetrabenazine or deutetrabenazine (for chorea), psychiatric meds, and supportive care.

  • Prognosis: Progressive and fatal; symptoms progress over $10-30\,years$.

Alzheimer's Disease

• Diagnostic Brain Changes

  • Beta-amyloid plaques located between neurons.

  • Tau neurofibrillary tangles located inside neurons.

  • Loss of synapses and neuronal death.

  • Reduced acetylcholine activity.

  • Atrophy of the hippocampus and progressive cortical atrophy.

  • Enlarged ventricles resulting from tissue loss.

• Clinical Stages of Alzheimer's

  • Early: Short-term memory loss, repeating questions, word-finding difficulty, getting lost, and poor judgment.

  • Middle: Increasing confusion, wandering, sleep disturbances, personality changes, difficulty recognizing people, and requiring assistance with Activities of Daily Living (ADLs).

  • Late: Severe memory loss, loss of speech, inability to recognize family, dysphagia, incontinence, immobility, and total dependence with high infection risk.