Disorders and Clinical Terms of the Nervous System

Chapter 12: The Central Nervous System

Neurological Disorders and Conditions

This section covers several disorders and clinical terms related to the central nervous system, focusing on developmental, genetic, and acquired conditions that affect brain function and structure.

• Autism Spectrum Disorder: A group of developmental neurological conditions, typically appearing in the first three years of life. Characterized by difficulty in communicating, forming relationships, and responding to external stimuli. Caused by mutations in functionally related genes. Occurs in about 2 per 1000 people. Early behavioral intervention is beneficial.

• Cordotomy: A surgical procedure in which a tract in the spinal cord is severed, usually to relieve unremitting pain.

• Dyslexia: A learning disability affecting 5–15% of the population, specifically impairing the ability to read. Results from errors in visual symbol and language processing, often arising in one hemisphere. Several genes predispose children to dyslexia, but it can also be acquired by brain injury or degeneration.

• Encephalopathy: Any disease or disorder of the brain. The term encompasses a wide range of conditions, from infections to degenerative diseases.

• Hypersomnia: A condition in which affected individuals sleep as much as 15 hours daily. May be associated with neurological or metabolic disorders.

• Microcephaly: Condition involving the formation of a small brain, evidenced by reduced skull size. Most microcephalic children are intellectually disabled. Can be caused by Zika virus infection during gestation.

Example: Microcephaly is a prominent concern during Zika virus outbreaks, as prenatal infection can lead to severe developmental delays.

Chapter 13: The Peripheral Nervous System and Reflex Activity

Peripheral Nervous System Disorders and Clinical Terms

This section introduces terminology and disorders related to the peripheral nervous system, including sensory, motor, and autonomic dysfunctions.

• Analgesia: Reduced ability to feel pain without losing consciousness. Analgesics are drugs that relieve pain.

• Dysarthria: Difficulty in articulating speech due to motor pathway disorders, resulting in weakness, uncoordinated motion, or altered respiration/rhythm. Lesions of cranial nerves IX, X, and XII cause nasal, breathy speech; upper motor pathway lesions produce a hoarse, strained voice. Not to be confused with dysphasia or aphasia, which are disorders of language processing.

• Dystonia: Impaired muscle tone, often resulting in abnormal posture or movement.

• Nerve Conduction Studies: Diagnostic tests assessing nerve integrity by measuring conduction velocities. The nerve is stimulated at one point, and activity is recorded at a second point a known distance away. Used to assess suspected peripheral neuropathies.

• Neuralgia: Sharp, spasm-like pain along the course of one or more nerves, often caused by inflammation or injury (e.g., trigeminal neuralgia).

• Paresthesia: Abnormal sensation (burning, numbness, tingling) in the absence of stimuli, usually caused by a sensory nerve disorder.

• Peripheral Neuropathy: Disorder of the peripheral nerves characterized by weakness, numbness, and pain, typically in the hands and feet. Often caused by diabetes, infections, or trauma.

Example: Nerve conduction studies are commonly used to diagnose carpal tunnel syndrome, a type of peripheral neuropathy.

Autonomic Nervous System Disorders

These terms describe conditions affecting the autonomic nervous system, which controls involuntary bodily functions.

• Atonic Bladder: A condition in which the urinary bladder becomes flaccid and overfills, allowing urine to dribble through the sphincters. Results from temporary loss of the micturition reflex following spinal cord injury.

• Horner’s Syndrome: Caused by damage to the superior sympathetic trunk on one side of the body. Symptoms include drooping upper eyelid (ptosis), constricted pupil, and lack of sweating on the affected side of the head.

• Vagotomy: Surgical cutting or severing of the vagus nerve to decrease secretion of gastric juice. Used as treatment for peptic ulcers unresponsive to medication.

• Vasovagal Syncope: Also called neurocardiogenic syncope, it is the most common cause of fainting. Provoked by emotional stress, pain, or dehydration, but typically occurs during prolonged standing. Fainting results from a drop in blood pressure, decreasing blood flow to the brain.

Example: Vasovagal syncope is often seen in medical settings when patients faint during blood draws or after standing for long periods.

Summary Table: Selected Nervous System Disorders

Term	Definition	Key Features	Causes
Autism Spectrum Disorder	Developmental neurological condition	Communication, social, and behavioral difficulties	Genetic mutations
Dyslexia	Learning disability affecting reading	Visual symbol and language processing deficit	Genetic, brain injury
Microcephaly	Small brain and skull size	Intellectual disability	Zika virus, genetic
Neuralgia	Sharp nerve pain	Spasm-like pain along nerves	Inflammation, injury
Horner’s Syndrome	Autonomic dysfunction	Ptosis, pupil constriction, no sweating	Sympathetic trunk damage
Vasovagal Syncope	Fainting due to low blood pressure	Loss of consciousness, triggered by stress	Emotional stress, prolonged standing

Additional info:

• Many of these disorders are diagnosed using clinical history, physical examination, and specialized tests such as nerve conduction studies.

• Early intervention and targeted therapies can improve outcomes for developmental disorders like autism and dyslexia.

• Autonomic nervous system disorders often require multidisciplinary management, including neurology, urology, and cardiology.