Chapter24_Neurological

Chapter 24: Neurologic System

Overview of the Nervous System

The nervous system is intricately divided into two primary components, each playing a crucial role in human physiology:

1. Central Nervous System (CNS): This core system includes the brain and spinal cord, serving as the main control center for processing information, coordinating actions, and responding to stimuli.

2. Peripheral Nervous System (PNS): Comprising all nerve fibers outside the brain and spinal cord, the PNS includes 12 pairs of cranial nerves (which primarily serve the head and neck) and 31 pairs of spinal nerves, along with their branches. This system is essential for transmitting sensory (afferent) messages to the CNS, and motor (efferent) messages from the CNS to muscles and glands, facilitating a vast array of bodily functions.

Anatomy of the Central Nervous System

Key Structures:

• Brain: The brain is subdivided into several parts:

  • Cerebrum: Responsible for higher brain functions such as movement, memory, learning, judgment, and emotion, containing both the cerebral cortex and subcortical structures.

  • Cerebellum: Coordinates voluntary movements, balance, and posture, ensuring smooth and accurate motor performance.

  • Brainstem: Comprising the midbrain, pons, and medulla oblongata, it regulates vital functions including heart rate, respiration, and blood pressure.

• Spinal Cord: A tubular structure extending from the brainstem down the vertebral column, functioning as the main pathway for transmitting neural signals between the brain and body.

Protective Structures:

• Meninges: The CNS is encased by three protective membranes: Dura Mater, Arachnoid, and Pia Mater, which provide support and protection.

• Cerebral Spinal Fluid (CSF): Cushions the brain, prevents injury from trauma, and aids in waste removal.

Functional Areas of the Cerebrum

Homunculus Representation:

• Frontal Lobe: Governs personality, behavior, emotional expression, intellectual functions, and decision-making skills. Includes the Precentral Gyrus (primary motor area) and Broca's Area (motor speech production).

• Temporal Lobe: Processes auditory information and sensory inputs like taste and smell; includes sensory areas for the face, lips, tongue, and hands.

• Parietal Lobe: Responsible for sensation and perception of touch; features the Postcentral Gyrus (primary sensory area) and Wernicke's area (speech comprehension).

• Occipital Lobe: Dedicated to visual reception and processing.

Damage and Functional Loss

Damage to specific cortical areas can lead to various deficits, including:

• Motor weakness or paralysis

• Loss of sensation

• Impairments in language processing

Additional CNS Components

• Basal Ganglia: Involved in motor control, cognition, emotions, and learning, regulating voluntary movements.

• Thalamus: Acts as a relay station for sensory and motor signals.

• Hypothalamus: Regulates essential functions like hunger, thirst, and body temperature.

Nerve Pathways

Crossed Representation:

The left hemisphere controls the right side of the body, and vice versa, facilitating coordinated responses to stimuli.

Sensory Pathways

• Afferent Fibers: Transmit sensory information from the body to the spinal cord.

  • Anterolateral (Spinothalamic) Tract: Carries pain, temperature, and crude touch sensations.

  • Posterior (Dorsal) Columns: Conducts position, vibration, and fine touch sensations.

Major Motor Pathways

• Corticospinal Tract: Facilitates voluntary movement; connects directly to spinal motoneurons.

• Extrapyramidal Tracts: Assist in regulating muscle tone and body movements.

Lower and Upper Motor Neurons

• Upper Motor Neurons (UMN): Convey messages from the brain to lower motor neurons, affected by conditions like strokes and multiple sclerosis.

• Lower Motor Neurons (LMN): Provide the final link to muscles, impacted by diseases such as spinal cord lesions and poliomyelitis.

Spinal Nerves

31 pairs of nerves emerge from the spinal cord, each classified as mixed nerves containing both sensory and motor fibers, serving distinct body areas.

Dermatome Reference

• Dermatome Areas: Specific regions of the skin supplied by certain spinal nerves.

  • Examples:

    • Thumb: C6

    • Nipple: T4

    • Umbilicus: T10

Autonomic Nervous System

Divided into somatic (voluntary) and autonomic (involuntary) fibers, regulating bodily functions without conscious control.

Developmental Considerations

• Fetal and Infancy: Rapid growth of the neurologic system occurs, yet it is incomplete at birth. Movements are guided by primitive reflexes.

• Childhood Development: Assessment includes observing movement and coordination, often using tools like the Denver II to screen motor skills.

Neurologic Changes in Pregnancy and Aging

• Pregnant Women: Normal changes may include a slight loss of tone and hyperactive reflexes due to hormonal shifts.

• Aging Adults: Changes can include muscle bulk loss, delayed reflexes, and increased rates of senile tremors.

Assessment Techniques

Structured assessments of neurologic exams focus on:

• Mental status

• Cranial nerves

• Motor and sensory systems

• Reflexes

Glasgow Coma Scale

Assesses consciousness based on eye, verbal, and motor responses, with scores ranging from 1 to 15.

Neurologic Diseases

• Stroke: Acute condition causes sudden loss of brain function due to disrupted blood flow.

• Alzheimer's Disease: A progressive disorder resulting in memory loss and cognitive decline.

Reflex Testing and Responses

Reflexes are involuntary responses that indicate neurologic function quality.

• Deep Tendon Reflexes (DTRs): Graded responses (0-4) where:

  • 4 = very brisk

  • 2 = normal

  • 0 = no response