Lab 4: The Nervous System

Nervous System Overview

• Components of the Nervous System:

  • Central Nervous System (CNS):
  • Comprises the brain and spinal cord.
  • Peripheral Nervous System (PNS):
  • Comprises cranial and spinal nerves.

• Types of Nerves:

  • Sensory (Afferent): Transmit sensory information to the CNS.
  • Motor (Efferent): Transmit commands from the CNS to muscles and glands.
  • Somatic Nervous System: Controls voluntary skeletal muscles.
  • Autonomic Nervous System: Controls involuntary functions, subdivided into:
    • Parasympathetic: Rest and digest functions.
    • Sympathetic: Fight or flight responses.

General Functions of the Nervous System

• Functions to control, communicate, and coordinate all body activities rapidly.

Meninges

• Three Menigeal Layers:
  • Dura Mater:
  • Tough, outermost layer; consists of two layers (periosteal and meningeal).
  • Arachnoid Mater:
  • Middle layer characterized by web-like extensions; spans subarachnoid space filled with cerebrospinal fluid (CSF).
  • Pia Mater:
  • Innermost layer that tightly clings to the brain surface.

Neuron Structure

• Key Components:
  • Dendrites: Receive messages from other neurons.
  • Cell Body (Soma): Contains nucleus and organelles.
  • Axon: Transmits electrical impulses away from the cell body.
  • Myelin Sheath: Fatty layer around axons created by:
  • Schwann Cells: In the peripheral nervous system.
  • Oligodendrocytes: In the CNS.
  • Node of Ranvier: Gaps in the myelin sheath allowing for saltatory conduction.

Brain Structure

• Four Principal Parts of the Brain:

  1. Cerebrum: Contains cerebral hemispheres involved in sensory processing, motor commands, and higher-order functions.
  2. Diencephalon: Includes thalamus, hypothalamus, and epithalamus.
  3. Brain Stem: Comprises medulla oblongata, pons, and midbrain.
  4. Cerebellum: Coordinates balance and fine motor skills.

• Hemispheric Lateralization:

  • Left Hemisphere: Language, logic, analytical skills.
  • Right Hemisphere: Spatial abilities, artistic skills, intuition.

• Cerebrum Structure:

  • Comprised of gyri (ridges) and sulci (grooves) to increase surface area.

Brain Function

• Thalamus: Relay station for all sensory info to the cerebral cortex except smell.
• Hypothalamus: Maintains homeostasis, regulates temperature, hunger, and thirst.
• Brain Stem:
  • Midbrain: Reflex center for eye and head movements.
  • Pons: Relay bridge, regulates respiration.
  • Medulla Oblongata: Controls vital autonomic functions (e.g., heart rate, breathing).

Cranial Nerves

• 12 Cranial Nerves:
  1. Olfactory (I): Smell.
  2. Optic (II): Vision.
  3. Oculomotor (III): Eye movement.
  4. Trochlear (IV): Eye movement.
  5. Trigeminal (V): Face sensations and chewing.
  6. Abducens (VI): Eye movement.
  7. Facial (VII): Facial expressions, taste.
  8. Vestibulocochlear (VIII): Hearing and balance.
  9. Glossopharyngeal (IX): Taste and swallowing.
  10. Vagus (X): Controls heart, lungs, and digestive tract.
  11. Accessory (XI): Shoulder and head movement.
  12. Hypoglossal (XII): Tongue movements.

Spinal Cord and Reflex Arc

• Spinal Cord Overview:

  • Continuous with the brain, approximately 18 inches long, gives rise to 31 pairs of spinal nerves.

• Reflex Arc:

  • Components: Sensory receptor, sensory neuron, interneuron, motor neuron, effector organ.
  • Example: Knee-jerk reflex involves rapid response to a stimulus without direct involvement of the brain.

Autonomic Nervous System

• Sympathetic vs. Parasympathetic Responses:

  • Sympathetic: Prepares the body for emergency situations (fight or flight).
  • Parasympathetic: Conserves energy and maintains bodily functions at rest.

• Functions of the Autonomic System:

  • Regulates visceral functions: heart rate, digestion, respiratory rate, etc.

Dermatome

• Specific skin sensation areas supplied by individual spinal nerves, useful for determining nerve function.