Lecture 11: Nervous System Disorders

Overview

This study guide covers major disorders affecting the nervous system, relevant medical terminology, and the actions of various drugs on nervous function. It is designed for Anatomy & Physiology students preparing for exams or seeking a concise review of nervous system pathology.

Disorders of the Nervous System

Poliomyelitis

Poliomyelitis is a viral disease caused by the polio virus that can result in deformity and paralysis. The virus attacks motor neurons at the neuromuscular junction, leading to muscle weakness and loss of motor function.

• Prevention: Vaccination is highly effective in preventing poliomyelitis.

• Pathophysiology: Destruction of motor neurons impairs voluntary muscle control.

• Example: Outbreaks in unvaccinated populations can lead to widespread paralysis.

Gliomas

Gliomas are primary brain tumors originating from glial cells. The most common type is an astrocytoma.

• Treatment: May include surgery, chemotherapy, or radiation therapy.

• Clinical significance: Gliomas can cause neurological deficits depending on their location and size.

Multiple Sclerosis (MS)

Multiple Sclerosis is an autoimmune disorder that attacks the myelin sheath surrounding axons in the central nervous system (CNS).

• Symptoms: Numbness, behavioral and cognitive problems, and paralysis.

• Pathophysiology: Demyelination slows action potential propagation.

• Example: Relapsing-remitting MS is a common clinical course.

Schizophrenia

Schizophrenia is a psychiatric disorder characterized by repetitive psychotic episodes, believed to result from excessive release of dopamine.

• Management: Involves blocking postsynaptic dopamine receptors with antipsychotic drugs.

• Symptoms: Hallucinations, delusions, and disorganized thinking.

Depressive Disorders

Depressive disorders are thought to be caused by decreased synaptic transmission of serotonin, norepinephrine, and dopamine.

• Treatment: Antidepressants such as selective serotonin reuptake inhibitors (SSRIs) prolong the lifespan of neurotransmitters.

• Example: Major depressive disorder is treated with SSRIs like fluoxetine (Prozac).

Anxiety Disorders

Anxiety disorders are linked to abnormal transmission of norepinephrine, serotonin, and GABA.

• Treatment: Antidepressant drugs enhance GABA activity and modulate norepinephrine transmission.

• Symptoms: Excessive worry, restlessness, and physical symptoms.

Bipolar Disorder

Bipolar disorder involves episodes of abnormally elevated mood (mania) followed by depression.

• Treatment: May involve sodium channel blockers to stabilize mood.

Epileptic Seizures

Epileptic seizures are recurrent episodes of disorganized electrical activity in the brain.

• Symptoms: Loss of consciousness and uncontrolled muscle activity.

• Pathophysiology: Sudden bursts of excitatory electrical activity within a neuronal pool.

Infectious Meningitis

Meningitis is inflammation of the meninges and subarachnoid space due to viral or bacterial infection.

• Symptoms: Headaches, lethargy, stiff neck, and fever.

• Diagnosis: Examination of cerebrospinal fluid (CSF) samples.

Parkinson's Disease

Parkinson's disease is characterized by difficulty initiating and terminating movement, minimal facial expression, shuffling gait, and resting tremors.

• Cause: Degeneration of dopamine-secreting neurons in the substantia nigra.

Tay-Sachs Disease

Tay-Sachs disease is caused by deficiency of the enzyme hexosaminidase-A, resulting in buildup of gangliosides around neurons in the brain.

• Symptoms: Blindness, loss of coordination, dementia, and death by age 3.

Amyotrophic Lateral Sclerosis (ALS)

ALS (Lou Gehrig's Disease) degenerates cell bodies of alpha-motor neurons in the anterior horn of the spinal cord and upper motor neurons of the cerebral cortex.

• Symptoms: Muscle weakness and death within 5 years.

Spina Bifida

Spina bifida occurs when vertebrae fail to enclose the spinal cord, potentially causing paralysis and urinary infections.

• Prevention: Folic acid (Vitamin B9) supplementation prior to conception reduces risk.

Dementia and Alzheimer's Disease

Dementia is a progressive loss of recent memory, cognitive functions, and personality changes. Alzheimer’s disease is the most common form, marked by memory loss, neurofibrillary tangles, and senile plaques.

• Symptoms: Impairment in attention, language skills, and visual-spatial abilities.

Huntington’s Disease

Huntington’s disease is a hereditary disorder causing exaggerated unwanted movements (chorea) and failing of the limbs.

• Symptoms: Involuntary movements and cognitive decline.

Dyskinesias

Dyskinesias are abnormal difficulties in initiating movement, often produced by lesions in the basal nuclei.

Broca’s and Wernicke’s Aphasia

• Broca’s Aphasia: Inability to produce speech, but language comprehension remains intact.

• Wernicke’s Aphasia: Inability to understand language; patients speak fluently with adequate grammar and syntax.

Coma

Coma is an unarousable unconsciousness with no response to stimuli, though brainstem reflexes may remain intact.

Medical Terminology and Diagnostics

Electroencephalogram (EEG)

An electroencephalogram measures electrical activity in the form of brain waves using electrodes.

• Wave Types:

  • Alpha waves: Low amplitude, high frequency; present when awake and engaged in mental activity.

  • Beta waves: Normal in children and drowsy or sleeping adults.

  • Delta waves: Present in awake infants and adults during deep sleep.

• REM Sleep: Characterized by rapid eye movements and is the stage when most dreams occur.

Drugs Affecting Nervous Function

Prozac (Fluoxetine)

• Mechanism: Blocks serotonin uptake for treatment of depression.

Monoamine Oxidase Inhibitors (MAOIs)

• Mechanism: Inhibit breakdown of monoamine neurotransmitters, increasing their levels.

Amphetamines

• Mechanism: Resemble norepinephrine and dopamine, associated with elevated mood.

Cocaine

• Mechanism: Blocks reuptake of dopamine, resulting in high levels of dopamine and stimulation of postsynaptic receptors.

• Effects: Produces a rush of good feelings; loss of neurotransmitter increases receptors, leading to anxiety and depression.

Caffeine

• Mechanism: Competes with adenosine, which inhibits ACh release by cholinergic neurons. Caffeine binds to adenosine receptors but does not inhibit ACh release, resulting in increased alertness.

Summary Table: Major Nervous System Disorders

Key Equations

• Nerve Conduction Velocity: where is velocity, is distance, and is time.

• Neurotransmitter Reuptake Inhibition: when reuptake is blocked.

Additional info: Some details and terminology were expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.