Lecture 11: Nervous System Disorders

Overview

This lecture covers major disorders affecting the nervous system, their underlying mechanisms, clinical features, and relevant medical terminology. It also discusses the effects of various drugs on nervous system function.

Objectives

• Identify and describe major nervous system disorders, including multiple sclerosis, meningitis, sciatica, spinal cord trauma, spina bifida, Tay-Sachs disease, Alzheimer’s disease, Huntington’s disease, and Parkinson’s disease.

• Define medical terminology associated with the nervous system.

• Describe the actions and effects of various drugs on nervous system function.

Disorders of the Nervous System

Poliomyelitis

Poliomyelitis is a viral disease caused by the poliovirus that primarily affects motor neurons.

• Etiology: Infection with poliovirus.

• Clinical Features: May result in deformity and paralysis due to destruction of motor neurons at the neuromuscular junction.

• Prevention: Vaccination is highly effective.

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

Gliomas

Gliomas are primary brain tumors arising from glial cells, which support and protect neurons.

• Types: The most common glioma is an astrocytoma, originating from astrocytes.

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

• Example: Patients with gliomas may present with headaches, seizures, or neurological deficits.

Multiple Sclerosis (MS)

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

• Pathophysiology: Demyelination slows action potential propagation.

• Clinical Features: Numbness, behavioral and cognitive problems, and paralysis.

• Example: MS often presents with relapsing-remitting neurological symptoms.

Schizophrenia

Schizophrenia is a psychiatric disorder characterized by repetitive psychotic episodes.

• Neurochemical Basis: Believed to result from excessive release of dopamine.

• Management: Involves blocking postsynaptic dopamine receptors (antipsychotic drugs).

• Example: Patients may experience 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: SSRIs like Prozac are commonly prescribed for depression.

Anxiety Disorders

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

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

• Example: Benzodiazepines increase GABAergic activity to reduce anxiety.

Bipolar Disorder

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

• Treatment: May involve sodium channel blockers (e.g., lithium).

• Example: Patients alternate between manic and depressive episodes.

Epileptic Seizures

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

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

• Clinical Features: Loss of consciousness and uncontrolled muscle activity.

• Example: Generalized tonic-clonic seizures affect the entire brain.

Infectious Meningitis

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

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

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

• Example: Bacterial meningitis requires prompt antibiotic treatment.

Parkinson's Disease

Parkinson's disease is a neurodegenerative disorder affecting movement.

• Symptoms: Difficulty initiating and terminating movement, minimal facial expression, shuffling gait, reduced arm swing, and resting tremors.

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

• Example: Patients may benefit from dopamine replacement therapy.

Tay-Sachs Disease

Tay-Sachs disease is a genetic disorder caused by deficiency of the enzyme hexosaminidase-A.

• Pathophysiology: Buildup of gangliosides around neurons in the brain inhibits nerve conduction.

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

• Example: Most common in certain ethnic populations (e.g., Ashkenazi Jews).

Amyotrophic Lateral Sclerosis (ALS, Lou Gehrig's Disease)

ALS is a progressive neurodegenerative disease affecting motor neurons.

• Pathophysiology: Degeneration of cell bodies of alpha-motor neurons in the anterior horn of the spinal cord and upper motor neurons in the cerebral cortex.

• Symptoms: Muscle weakness and death within 5 years.

• Example: ALS leads to progressive paralysis and respiratory failure.

Spina Bifida

Spina bifida is a congenital defect where vertebrae fail to enclose the spinal cord.

• Incidence: Occurs in 1:1,000 babies.

• Complications: Paralysis, urinary infections, renal failure.

• 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 of dementia.

• Pathology: Neurofibrillary tangles, senile plaques, degeneration of cortical neurons and synaptic connections.

• Symptoms: Memory loss, impaired attention, language skills, critical thinking, and visual-spatial abilities.

• Example: Early signs include forgetfulness and difficulty with daily tasks.

Huntington’s Disease

Huntington’s disease is a hereditary neurodegenerative disorder.

• Symptoms: Exaggerated unwanted movements (chorea), flailing of the limbs.

• Genetics: Autosomal dominant inheritance.

• Example: Onset typically occurs in mid-adulthood.

Dyskinesias

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

• Example: Parkinson’s disease and Huntington’s disease are associated with dyskinesias.

Broca’s Aphasia

Broca’s aphasia is the inability to produce speech, while language comprehension remains intact.

• Location: Lesion in Broca’s area of the frontal lobe.

• Example: Patients understand language but struggle to speak.

Wernicke’s Aphasia

Wernicke’s aphasia is the inability to understand language, despite fluent speech with adequate grammar and syntax.

• Location: Lesion in Wernicke’s area of the temporal lobe.

• Example: Patients speak fluently but produce nonsensical sentences.

Coma

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

• Example: Severe traumatic brain injury may result in coma.

Medical Terminology and Neurophysiology

Electroencephalogram (EEG)

An electroencephalogram (EEG) measures electrical activity in the form of brain waves using electrodes placed on the scalp.

• 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; majority of dreams occur during this stage. light sleep

• NON-Rem sleep: very tired, no dreams, there is no rapid eye movement

Drugs Affecting Nervous System Function

Prozac (Fluoxetine)

Prozac is a selective serotonin reuptake inhibitor (SSRI) used to treat depression.

• Mechanism: Blocks serotonin uptake, increasing its availability in the synaptic cleft.

Monoamine Oxidase Inhibitors (MAOIs)

MAOIs interfere with the breakdown of monoamine neurotransmitters by inhibiting monoamine oxidase.

• Effect: Increases levels of serotonin, norepinephrine, and dopamine.

Amphetamines

Amphetamines resemble norepinephrine and dopamine, leading to elevated mood.

• Effect: Stimulate release of these neurotransmitters.

Cocaine

Cocaine blocks reuptake of dopamine, resulting in high levels of dopamine stimulating postsynaptic receptors.

• Effect: Produces a rush of good feelings; loss of neurotransmitter leads to increased receptors, causing anxiety and depression.

Caffeine

Caffeine competes with adenosine, which normally inhibits acetylcholine (ACh) release by cholinergic neurons.

• Effect: Caffeine binds to adenosine receptors but does not inhibit ACh release, resulting in increased alertness.

Summary Table: Major Nervous System Disorders

Additional info: Academic context and expanded explanations have been added to ensure completeness and clarity for college-level Anatomy & Physiology students.