Nervous System Disorders Notes (Chapter 14)

Review of the Nervous System

  • CNS = brain and spinal cord; integrates inputs, processes, and coordinates responses.

  • PNS = cranial nerves, spinal nerves, sensory receptors, enteric plexuses, sensory neurons, neuromuscular junctions.

  • Fundamental divisions: Central nervous system (brain, spinal cord) vs Peripheral nervous system (cranial/spinal nerves, sensory receptors).

Brain: Structure and Function

  • Brain as communication and control center: receives inputs, processes/evaluates, decides action, initiates response.

  • Actions: involuntary (homeostasis; autonomic nervous system regulation) and voluntary; includes reflexes.

Protection of the Brain

  • Meninges: three layers surrounding brain and spinal cord

    • Dura mater: outer layer closest to bone; contains subdural space.

    • Arachnoid: middle layer; subarachnoid space contains CSF.

    • Pia mater: adheres to brain surface.

  • Spaces:

    • Epidural space (between skull/bone and dura in some contexts)

    • Subdural space

    • Subarachnoid space (CSF)

  • Key note: All are protected structures; pathology often involves these spaces.

Cerebrospinal Fluid (CSF) and Homeostasis

  • CSF functions:

    • Cushion for brain and spinal cord; similar to plasma but with different electrolyte, glucose, protein levels.

    • Diagnostic changes in CSF characteristics indicate pathology.

  • CSF production and flow:

    • Formed by choroid plexuses of the ventricles; flows through ventricles into subarachnoid space.

    • Equal production and reabsorption are required to maintain intracranial pressure (ICP).

  • CSF values (normal):

    • Appearance: ext{Clear and colorless}

    • Pressure: 9-14 ext{ mmHg} or 150 ext{ mm H}_2 ext{O}

    • Red blood cells: 0

    • White blood cells: occasional

    • Protein: 15-45 ext{ mg/dL}

    • Glucose: 45-75 ext{ mg/dL}

    • Sodium: 140 ext{ mEq/L}

    • Potassium: 3 ext{ mEq/L}

    • Specific gravity: 1.007

    • pH: 7.32-7.35

    • Volume in system at one time: 125-150 ext{ mL}

    • Volume formed in 24 hours: 500-800 ext{ mL}

Blood–Brain Barriers

  • Blood-brain barrier (BBB):

    • Located at brain capillaries; restricts entry of most substances; maintains CNS electrolyte, glucose, and protein balance.

    • Lipid-soluble substances pass readily.

    • Poorly developed in neonates.

  • Blood–CSF barrier: located at choroid plexus; regulates CSF constituents.

Functional Areas of the Brain

  • Major regions: Cerebral hemispheres, diencephalon, brain stem, cerebellum.

  • Frontal lobe functions: intellect, personality; prefrontal area (left cortex) – higher cognitive function; premotor cortex – skilled movements; motor cortex – voluntary movements; Broca’s area (left cortex) – speech expression.

  • Parietal lobe: somatosensory area – sensation; sensory sorting.

  • Occipital lobe: visual cortex – vision.

  • Temporal lobe: auditory cortex; olfactory cortex; Wernicke’s area (left cortex) – language comprehension.

  • Diencephalon: thalamus (sensory relay); hypothalamus (homeostasis, autonomic/endocrine regulation, body temperature, fluid intake, temperature, sleep cycles, stress, hormones); epithalamus.

  • Limbic system: emotion and memory integration.

  • Brainstem: vital center control (respiration, cardiovascular); cranial nerve nuclei; conduit between brain and spinal cord.

  • Cerebellum: balance, posture, coordination; input from pyramidal (corticospinal) system and proprioceptors; integrates visual and vestibular information.

  • Reticular activating system (RAS): arousal and awareness; connected to many brain regions.

Cerebral Hemispheres and Lateralization

  • Structure: cortex (gray matter, nerve cell bodies) and corpus callosum (white matter, myelinated tracts connecting hemispheres).

  • Hemispheric dominance: language usually left-hemisphere dominant; Broca’s area (speech expression) and Wernicke’s area (language comprehension).

  • Right hemisphere: may emphasize music/art appreciation, spatial abilities; may show behavioral differences when dominant side is injured.

  • Prefrontal cortex: coordinates complex cognitive behavior and personality.

  • Basal nuclei: extrapyramidal system (EPS) – motor control/coordination of skeletal muscle activity.

  • Limbic system: emotions, memory, and behavior.

Brain Stem and Cerebellum

  • Brain stem includes midbrain, pons, medulla oblongata; connects brain to spinal cord; houses many autonomic and cranial nerve nuclei.

  • Midbrain: RAS, arousal and awareness; site of many neural pathways; drug effects can alter consciousness via RAS.

  • Pons: bridge between cerebellum and cerebrum; houses cranial nerve nuclei.

  • Medulla oblongata: respiratory and cardiovascular control centers; coordinates cough, swallow, vomiting reflexes; cranial nerve nuclei present.

  • Cerebellum: coordinates movement, balance, posture; integrates proprioceptive input with visual and vestibular information.

Blood Supply to the Brain

  • Major arteries:

    • Internal carotid and vertebral arteries; each internal carotid divides into anterior and middle cerebral arteries.

    • Anterior cerebral artery supplies frontal lobe; middle cerebral artery supplies lateral hemispheres; basilar artery gives branches to brainstem and cerebellum; posterior cerebral arteries arise distally.

  • Circle of Willis: arterial circle formed by anastomoses; anterior communicating artery connects the two anterior cerebral arteries; posterior communicating arteries link middle/posterior regions.

  • Autoregulation: cerebral arteries maintain constant blood flow; high CO2, low pH, or low BP cause local vasodilation; baroreceptors and chemoreceptors contribute to rapid responses.

  • Venous drainage: brain venous blood drains into dural venous sinuses and then to the internal jugular veins.

Cranial Nerves

  • 12 pairs; originate from various brain regions; named I–XII and numbered from ventral to dorsal.

  • Nerve types: motor, sensory, or mixed; many carry autonomic fibers as well.

  • Table highlights (major components):

    • I Olfactory: sensory; smell.

    • II Optic: sensory; vision.

    • III Oculomotor: motor; extrinsic eye muscles, pupil constriction, accommodation.

    • IV Trochlear: motor; superior oblique muscle.

    • V Trigeminal: mixed; mastication and facial sensation.

    • VI Abducens: motor; lateral rectus.

    • VII Facial: mixed; facial expression; lacrimal and salivary glands.

    • VIII Vestibulocochlear: sensory; hearing and balance.

    • IX Glossopharyngeal: mixed; taste, gag reflex, throat sensation.

    • X Vagus: mixed; autonomic control of viscera, speech, swallowing.

    • XI Spinal accessory: motor; head/neck movement.

    • XII Hypoglossal: motor; tongue movements.

  • Note: Detailed motor/sensory roles for each nerve are provided in the table (Table 14-3).

Spinal Cord and Spinal Nerves

  • Spinal cord anatomy:

    • Protected by vertebral column; continuous with the medulla; ends at L1-L2; cauda equina extends inferiorly as nerve roots.

    • White matter contains ascending (sensory) and descending (motor) tracts; gray matter includes anterior horns (motor neurons), posterior horns (interneurons), and lateral horns (visceral motor neurons).

  • Spinal nerves: 31 pairs; named by vertebral level; connected to the cord via ventral (motor) and dorsal (sensory) roots.

  • Reflexes: automatic, rapid responses to stimuli; involve receptors, afferent fibers, spinal cord synapses, efferent impulses, and interneurons in many cases.

Neurons and Conduction of Impulses

  • Neurons: highly specialized, largely nondividing; require glucose and oxygen.

  • Structure: cell body, axons (conduct away from cell body), dendrites (receptive, conduct toward cell body).

  • Myelination:

    • Myelin insulates axons; speeds conduction.

    • PNS: Schwann cells form myelin; CNS: oligodendrocytes form myelin.

    • Nodes of Ranvier: gaps in myelin that enable saltatory conduction.

  • Glial cells (support cells):

    • Astroglia (astrocytes): contribute to BBB.

    • Oligodendroglia: myelinate CNS axons.

    • Microglia: phagocytic.

    • Ependymal cells: line ventricles; part of choroid plexus.

Regeneration and Conduction

  • Regeneration: if neuronal cell body is damaged, neurons die; distal axon may regenerate in the PNS via Schwann cell guidance; CNS regeneration is limited.

  • Conduction basics:

    • Stimulus increases membrane permeability; Na+ influx causes depolarization and action potential.

    • Repolarization via outward K+ flow; Na+/K+ pump restores ions.

    • Myelination enables saltatory conduction (rapid conduction).

  • Synapses and neurotransmitters:

    • Synapse: presynaptic axon terminal with neurotransmitter vesicles, synaptic cleft, postsynaptic receptor.

    • Neurotransmitters: released, act on receptors, then inactivated by enzymes or reuptake.

    • Examples: acetylcholine (excitatory; neuromuscular junction, ANS, brain); norepinephrine and epinephrine (excitatory; SNS); dopamine/serotonin (excitatory; brain); GABA (inhibitory; brain); glycine (inhibitory; spinal cord).

Autonomic Nervous System (ANS)

  • Two divisions: Sympathetic (SNS) and Parasympathetic (PNS); motor and sensory innervation; generally involuntary; effects are antagonistic and help maintain homeostasis.

  • Preganglionic fibers: in brain or spinal cord; postganglionic fibers: outside CNS.

  • Sympathetic nervous system:

    • Fight-or-flight; increases overall activity; preganglionic from thoracic and first two lumbar segments; ganglia in sympathetic trunks.

    • Neurotransmitters:

    • Preganglionic: acetylcholine (ACh)

    • Postganglionic: norepinephrine (NE)

    • Receptors: alpha and beta (e.g., B-1, B-2, α-1).

  • Parasympathetic nervous system:

    • Originates in brainstem and sacral segments; dominates digestive system; promotes recovery after sympathetic activity.

    • Ganglia near/in target organs; neurotransmitter: acetylcholine (ACh) for both pre- and postganglionic neurons.

    • Receptors: nicotinic and muscarinic.

  • Table of ANS effects (highlights): cardiovascular, respiratory, eye, digestive, urinary, and other organ system effects, with specific receptor involvements.

Functional Imaging and Assessment of Brain Function

  • Level of Consciousness (LOC): Decreased LOC can indicate acute brain disorders; signs include confusion, memory loss, unresponsiveness, or coma.

  • Glasgow Coma Scale (GCS): A practical tool to quantify LOC. Components and scoring:

    • Eye opening: 4 spontaneous, 3 to speech, 2 to pain, 1 none.

    • Verbal response: 5 oriented, 4 confused, 3 inappropriate words, 2 incomprehensible sounds, 1 none.

    • Motor response: 6 obeys commands, 5 localizes pain, 4 normal flexion, 3 abnormal flexion (decorticate), 2 abnormal extension (decerebrate), 1 none.

    • Total score: E + V + M = 15 ext{ (normal)}; ranges indicate level of impairment.

  • Vegetative state and locked-in syndrome are critical LOC-related conditions; brain death criteria require EEG, brainstem reflexes, spontaneous respiration status, cause confirmation, and physician verification.

Sensory and Perceptual Deficits

  • Visual pathways: optic nerve, optic chiasm (partial crossover), optic tract, occipital lobe; damage yields various field losses (hemianopia) depending on lesion site.

  • Language disorders (aphasia):

    • Expressive (Broca’s): left frontal lobe; speech production impaired.

    • Receptive (Wernicke’s): left temporal lobe; comprehension impaired.

    • Global: damage to both areas; communication severely affected.

    • Dysarthria: motor dysfunction affecting articulation due to cranial nerve/muscle impairment.

    • Agraphia: impaired writing; Alexia: impaired reading; Agnosia: failure to recognize objects.

  • Seizures:

    • Generalized (e.g., absence, tonic-clonic, myoclonic) vs. partial (simple/complex, psychomotor).

    • Status epilepticus: continuous seizures; life-threatening if not controlled.

    • Triggers: infections, hypoxia, trauma, metabolic disturbances, stimuli (lights/noise).

    • Treatment: antiseizure medications; emergency management for ongoing seizures.

Increased Intracranial Pressure (ICP)

  • ICP rises when brain volume increases, CSF dynamics are disrupted, or blood volume changes.

  • Early signs: decreased LOC, pupillary changes, severe headache, vomiting, papilledema.

  • Cushing reflex: hypertension with bradycardia in attempts to preserve cerebral perfusion; vasomotor and chemoreceptor responses.

  • Pupil signs: CN III involvement can cause fixed and dilated pupils with progressive ICP.

  • CSF changes and imaging: CSF pressure elevation; CSF can appear pink, cloudy, or show abnormal protein/cell content depending on cause.

  • Herniation risk: transtentorial, uncal, infratentorial (cerebellar/tonsillar) herniations can compress brainstem or vascular structures and be fatal.

Diagnostic Tests for Neurological Disorders

  • CT scans, MRI for structural imaging.

  • Cerebral angiography, Doppler ultrasound for blood flow; EEG for electrical activity.

  • Radionuclide perfusion imaging.

  • Lumbar puncture to assess CSF pressure and composition.

Acute Neurologic Problems

  • Brain tumors: space-occupying lesions causing increased ICP; gliomas most common primary malignant tumors; metastases from breast/lung; pathology often invasive with poorly defined margins; treatment includes surgery, radiotherapy, chemotherapy.

  • Vascular disorders: TIAs, CVAs (strokes), cerebral aneurysms.

  • Infections: meningitis, brain abscess, encephalitis, and other infection-related syndromes.

  • Brain injuries and spinal cord injuries: concussion, contusion, open/closed head injuries; primary and secondary injury processes; hematomas (epidural, subdural, intracerebral, subarachnoid).

  • Congenital disorders: hydrocephalus, spina bifida, cerebral palsy.

  • Degenerative and inflammatory diseases: MS, Parkinson’s, ALS, myasthenia gravis, Huntington’s disease, dementias (Alzheimer’s, vascular dementia, CJD, AIDS dementia).

  • Mental disorders: schizophrenia, depression, panic disorders.

  • Herniated intervertebral discs: nucleus pulposus protrusion, nerve root compression; diagnostic imaging; conservative and surgical treatments.

Brain Tumors and Vascular Disorders (Key Points)

  • Brain tumors:

    • Primary malignant tumors often gliomas; margins are not well defined; invasive growth.

    • Secondary tumors arise from metastasis elsewhere (e.g., breast, lung).

    • Symptoms depend on tumor location; seizures common; headaches due to ICP.

  • TIAs vs CVAs:

    • TIAs: temporary ischemic episodes; warning sign for potential stroke; etiology includes atherosclerosis, emboli, vasospasm.

    • CVAs (strokes): infarction due to occlusion or hemorrhage; time-sensitive treatment; NIH Stroke Scale used in assessment.

  • Aneurysms:

    • Berry aneurysms at circle of Willis; rupture leads to subarachnoid hemorrhage and rapid ICP rise; treatment focuses on clipping and reducing ICP/vasospasm risk.

Infections and Infection-Related Syndromes

  • Meningitis: bacterial meningitis; neonates (E. coli), children/adults (Neisseria meningitidis, Haemophilus influenzae), older adults (Streptococcus pneumoniae).

  • Encephalitis: viral causes (e.g., West Nile, St. Louis, Western/Eastern equine encephalitis); sometimes Lyme disease or herpes simplex encephalitis.

  • Brain abscess: localized infection (frontal/temporal lobes) with edema and necrosis; may arise from infection in ear, throat, sinuses, or septic emboli; surgical drainage and antibiotics.

  • Other infections: rabies, tetanus, poliomyelitis; post-infection syndromes (Guillain-Barré, Reye’s syndrome, shingles, PPS, etc.).

Infection-Related Syndromes and Degenerative Disorders

  • Guillain-Barré syndrome: acute inflammatory PNS process; demyelination; ascending paralysis; life-threatening if respiration involved; supportive care.

  • Hydrocephalus: noncommunicating (obstructive) vs communicating; ventricular dilation and ICP changes; etiology includes developmental stenosis/atresia, tumors, infections.

  • Spina Bifida: occulta, meningocele, myelomeningocele; prenatal AFP screening and ultrasound diagnosis; surgical repair and long-term therapy.

  • Cerebral Palsy: motor impairment with multiple etiologies (hypoxia, ischemia, infection, metabolic issues); management includes multidisciplinary therapy.

  • Dementias: Alzheimer’s disease (amyloid plaques and neurofibrillary tangles; acetylcholine deficits), vascular dementia, Creutzfeldt-Jakob disease; AIDS dementia.

  • Schizophrenia, Depression, Panic disorders: DSM-5 classifications; neurochemical and structural associations; treatment involves medications (antipsychotics, antidepressants), psychotherapy.

Motor and Movement Disorders

  • Parkinson’s disease: progressive degeneration of the extrapyramidal motor system; resting tremor, rigidity, bradykinesia, gait/posture abnormalities; etiology includes idiopathic and secondary causes; treatment with levodopa, MAO-B inhibitors, anticholinergics, and supportive therapies.

  • Amyotrophic Lateral Sclerosis (ALS): degeneration of upper and lower motor neurons; progressive weakness and respiratory failure; treatment focuses on slowing progression and supportive care.

  • Myasthenia Gravis: autoimmune antibodies to ACh receptors; muscle weakness worsens with use; treatment includes anticholinesterase, immunosuppression, plasmapheresis, thymectomy.

  • Huntington’s disease: autosomal dominant; progressive degeneration of basal ganglia and frontal cortex; depletion of GABA; choreiform movements; behavioral changes and dementia; genetic testing (DNA analysis).

Demyelinating and Degenerative Conditions (Summary)

  • MS: demyelination in CNS; plaques form near lateral ventricles, brainstem, optic nerves; relapsing-remitting course; MRI used for diagnosis; no curative therapy; disease-modifying therapies and supportive rehabilitation improve quality of life.

  • Other dementias: vascular dementia, CJD, AIDS dementia; management is largely supportive and includes addressing underlying etiologies.

Spinal Cord Injury (SCI) and Complications

  • SCI results from vertebral fracture/dislocation; injury may be cervical (high risk for respiratory compromise) or other levels; primary injury may cause direct tissue damage; secondary injury includes edema, ischemia, vasospasm, infection.

  • Spinal shock: loss of reflexes below injury; flaccid paralysis initially; autonomic function loss; gradual return of reflexes may occur with hyperreflexia later.

  • Autonomic dysreflexia: massive reflex sympathetic discharge below the injury; triggers include infection or bladder distention; leads to hypertension and tachycardia; requires removal of stimulus and medical management.

  • Vertebral fracture types: simple, compression, wedge, dislocation; pathophysiology includes axonal damage and demyelination; dermatomal assessment helps determine extent of injury and recovery.

  • Management: immobilization, imaging, surgical intervention if needed, glucocorticoids to reduce edema, prevention of complications (infection, pressure ulcers, pulmonary issues).

Congenital Neurologic Disorders

  • Hydrocephalus: as above (noncommunicating vs communicating); signs depend on age; imaging (CT/MRI) for diagnosis; treatment may include shunting or endoscopic procedures.

  • Spina Bifida: occulta, meningocele, myelomeningocele; prenatal screening; surgical repair; ongoing therapy to maximize function.

  • Cerebral palsy: classification by symptomatology (spastic, dyskinetic, ataxic); management includes early stimulation, speech-language therapy, physical and occupational therapy, assistive devices.

Seizures and Epilepsy

  • Seizures: abnormal, excessive neuronal discharge; may be localized or generalized; triggers include genetic predisposition, brain injury, or metabolic disturbances.

  • Seizure management: identify and treat underlying cause; anticonvulsant medications; emergency management for ongoing seizures.

Practical and Clinical Connections

  • Many neurologic disorders share common themes: ICP management, impaired conduction due to demyelination, loss of neuronal function from ischemia or hemorrhage, autoimmune etiologies, and neurodegenerative progression.

  • Therapeutic approaches are often multidisciplinary: pharmacologic (drugs targeting neurotransmitters or immune modulation), surgical interventions (tumor resection, aneurysm clipping, decompression), and rehabilitative therapies (PT/OT/SLP).

  • Diagnostic tools (CT/MRI, EEG, angiography, CSF analysis) guide treatment decisions and prognosis.

  • Ethical and practical implications include end-of-life decisions in severe brain injury or brain death, vaccination strategies to prevent CNS infections, and long-term support for chronic neurodegenerative diseases.

LaTeX-formatted references and key values

  • CSF normal values summary: ext{Appearance} = ext{Clear and colorless}, \ ext{Pressure} = 9-14~\text{mmHg}~(150~\text{mm H}_2\text{O}), \ ext{RBCs} = 0, \ ext{WBCs} = ext{occasional}, \ ext{Protein} = 15-45~\text{mg/dL}, \ ext{Glucose} = 45-75~\text{mg/dL}, \ \text{Na}^+ = 140~\text{mEq/L}, \ \text{K}^+ = 3~\text{mEq/L}, \ \text{Specific gravity} = 1.007, \ \text{pH} = 7.32-7.35, \ \text{Volume in system} = 125-150~\text{mL}, \ \text{Volume formed in 24 h} = 500-800~\text{mL}.

  • Glasgow Coma Scale (example): E=4, V=5, M=6 \text{Total} = E+V+M = 15. This represents normal LOC.

  • Autonomic nervous system receptor examples (summary):

    • SNS receptors: \alpha1, \beta1, \beta_2, \text{(various targets listed in Table 14-4)}

    • PNS receptors: \text{nicotinic}, \text{muscarinic}