Module 7 Chapter 11: Pathophysiology of Neurologic Conditions

Objectives

Module Objectives: By the end of this module, you should be able to:

• Describe etiologies of disorders of the neurologic system, including genetic, environmental, and lifestyle factors.

• Explain clinical signs and symptoms of disorders that affect the neurologic system, recognizing the importance of early diagnosis and intervention.

Book Objectives:

• Discuss normal neural anatomy and physiology, focusing on the functional significance of various brain structures.

• Describe and compare congenital neurologic disorders, detailing how they affect development and function.

• Compare and contrast traumatic neurologic disorders, considering the impact of the injury's mechanism on recovery outcomes.

• Compare and contrast infectious neurologic disorders, highlighting key pathophysiological mechanisms.

• Describe and compare vascular neurologic disorders, discussing factors such as ischemia and hemorrhage.

• Compare and contrast chronic degenerative neurologic disorders and their long-term management strategies.

• Compare and contrast types of dementia, examining risk factors and symptomatic progression.

• Describe and compare cancers of the nervous system, including primary and metastatic tumors, and their impact on function.

The Central Nervous System (CNS)

Main Areas of the CNS:

• Cerebrum: Responsible for higher brain functions, including thought, action, and emotion;

• Thalamus/Hypothalamus: Plays a crucial role in sensory processing and homeostasis;

• Brain Stem: Controls basic bodily functions, including autonomic behaviors;

• Cerebellum: Essential for coordination, balance, and fine motor skills.

Protection:

• The CNS is encased by three protective membranes known as meninges (dura mater, arachnoid mater, pia mater).

• Cerebral spinal fluid (CSF), secreted by the choroid plexus, cushions the brain and spinal cord; it flows freely to help maintain intracranial pressure during varying conditions.

Ventricles:

• There are four ventricles that hold CSF; they play a key role in maintaining the homeostasis of the cranial cavity and facilitating nutrient transport to the brain. The flow of CSF is critical during instances of increased intracranial pressure (ICP).

Regeneration:

• Unlike the Peripheral Nervous System (PNS), CNS tissue has limited ability to regenerate following injury. The mechanisms of repair and regeneration are areas of active research.

The Cerebrum

Hemispheres:

• Divided into right and left hemispheres, which specialize in different cognitive and motor functions; the right hemisphere is often associated with creativity and spatial ability, while the left is linked to analytical and verbal tasks.

Lobes and Functions:

• Frontal Lobe: Facilitates voluntary motor activity, influences personality traits, decision making, and impulse control; suffers significant impairment in conditions like frontal lobe syndrome.

• Parietal Lobe: Receives and processes sensory input, except smell, hearing, and vision; involved in spatial awareness and sensations of touch, temperature, and pain.

• Occipital Lobe: Processes and interprets visual information, playing a critical role in vision-related disorders.

• Temporal Lobe: Essential for hearing, memory, and language comprehension; lesions can lead to conditions such as Wernicke's aphasia.

Functions of the CNS Structures

• Cerebral Cortex: Receives sensory information and sends messages to skeletal muscles, influencing voluntary movement and sensory integration.

• Basal Nuclei: Integrates and modulates nerve impulses, involved in the control of movement and coordination; dysfunction is seen in conditions like Parkinson's disease.

• Thalamus: Acts as a relay station for sensory info to the cerebral cortex, playing a role in consciousness and alertness.

• Hypothalamus: Controls autonomic functions such as temperature, hunger, thirst, fatigue, sleep, circadian rhythms, and hormone secretion.

• Brainstem: The origin of cranial nerves; regulates vital functions such as heart rate, respiration, and consciousness; damage can lead to life-threatening conditions.

• Cerebellum: Coordinates subconscious muscle movements, posture, and balance; crucial for motor learning and adaptation.

The Peripheral Nervous System (PNS)

Components:

• Consists of cranial and spinal nerves (12 pairs cranial, 31 pairs spinal), connecting CNS to limbs and organs.

Nerve Types:

• Sensory (Afferent): Carry impulses from sensory receptors to the brain, essential for nociception (pain perception).

• Motor (Efferent): Carry impulses from the brain to effectors (muscles and glands); direct control of muscle movement.

Regeneration:

• Severed peripheral nerves have the potential to regenerate, reestablishing connections with target organs or muscles; influenced by factors like the type of nerve injury and timing of intervention.

Cranial Nerves

• Facilitate vital functions, including sensory perception, motor control, and autonomic activities; some carry sensory fibers, some carry motor fibers, and others carry both types.

Autonomic Nervous System

Functionality:

• Manages unconscious activities such as heart rate, blood pressure, and intestinal motility, influencing homeostasis.

Subdivisions:

• Sympathetic Nervous System: Responds to stress and emergencies, triggering the fight-or-flight response.

• Parasympathetic Nervous System: Supports rest-and-digest responses, promoting energy conservation and recovery; these systems work antagonistically to maintain homeostasis.

Conditions of the Neurologic System

Increased Intracranial Pressure (ICP)

• Definition: An abnormal increase in volume within the cranial cavity, which can lead to brain displacement and damage.

• Causes: Include traumatic brain injury (TBI), tumors, hydrocephalus, cerebral edema, and hemorrhage; prompt identification and treatment are critical to prevent permanent injury.

• Monro-Kellie Hypothesis: Describes the compensatory mechanisms among blood, CSF, and brain tissue to maintain ICP.

Clinical Manifestations of Increased ICP

• Cushing’s Triad: A classic late sign of increased ICP, characterized by hypertension, bradycardia, and irregular respirations (e.g., Cheyne-Stokes).

• Compensatory Mechanisms: Include autoregulation of cerebral blood flow and Cushing’s reflex, which increases sympathetic stimulation to preserve perfusion.

Glasgow Coma Scale (GCS)

• Purpose: A scale used to assess the level of consciousness and responsiveness after an injury, crucial for determining the severity of brain injury.

• Components: Evaluates eye opening, verbal response, and motor response, with scores helping guide treatment decisions.

Meningitis

• Definition: Inflammation of the meninges, subarachnoid space, and possibly the CSF, which can lead to severe neurological impairment.

• Causes: Include bacterial or viral infections; bacterial meningitis often presents more severely.

• Complications: Potentially life-threatening, including permanent neurologic damage, seizures, and septicemia.

• Manifestations: Common signs include fever, chills, mental status changes, headache, neck stiffness, and photophobia.

Encephalitis

• Definition: Inflammation of the brain and spinal cord, typically caused by infection and associated with significant morbidity.

• Causes: Can be viral (e.g., herpes simplex), bacterial, or result from autoimmune reactions.

• Manifestations: Flu-like symptoms, altered mental status, confusion, seizures, and neurological deficits.

Traumatic Brain Injury (TBI)

• Types: Includes closed injuries (e.g., concussions, contusions) and open injuries, where the skull is breached.

• Common Causes: Falls, vehicle accidents, sports injuries, or violence; prevention strategies are crucial.

• Residual Effects: Can include confusion, memory loss, disturbances in concentration, and chronic headaches.

Hydrocephalus

• Definition: An abnormal accumulation of fluid within the ventricles of the brain, leading to increased cranial pressure.

• Infant Presentation: Enlarged head size, bulging fontanelles, high-pitched crying as a result of brain distortion.

• Adult Presentation: Symptoms include persistent headaches, confusion, and difficulties with balance and walking.

Cerebral Aneurysm

• Definition: A localized outpouching or dilation of a cerebral artery caused by a weakness in the arterial wall.

• Manifestations: Often asymptomatic until rupture; severe headaches (thunderclap headache) can indicate a critical event, leading to stroke or death.

Seizure Disorders

• Definition: Involve abnormal electrical activity in the brain that leads to transient changes in behavior, sensation, or consciousness.

• Causes & Types: Can result from a wide range of factors, including head injuries, infections, or genetic conditions.

• Epilepsy: Characterized by recurrent seizures with no identifiable precipitating cause.

• Management: Involves immediate interventions during seizures and long-term medications to control seizure frequency and severity.

Other Neurologic Disorders

• Cerebral Palsy: A group of disorders affecting posture and movement caused by developmental malformations or neurological damage.

• Multiple Sclerosis: An autoimmune condition resulting in the demyelination of nerve fibers in the CNS, leading to various neurological symptoms and disability.

• Myasthenia Gravis: An autoimmune disorder that interrupts communication between the nerve and muscle, resulting in muscle weakness.

• Parkinson’s Disease: A progressive neurodegenerative disorder characterized by the degeneration of dopamine-producing neurons, leading to motor control issues, such as tremors and rigidity.

• Dementia: A decline in cognitive function due to various pathologies, with Alzheimer’s Disease being the most prevalent, impacting memory, thinking, and behavior.