Lecture on the Nervous System

Importance for Nurses

• Nurses encounter patients with altered neurologic function.
• Requires understanding of nervous system anatomy and physiology.

Functions of the Nervous System

• Control and integration of body activities (motor, sensory, autonomic, cognitive, behavioral).

Divisions of the Nervous System

• Central Nervous System (CNS):
  • Comprises the brain and spinal cord.
• Peripheral Nervous System (PNS):
  • Includes cranial and spinal nerves, autonomic and somatic systems.

Neurons

• Basic functional unit of the nervous system.
• Supported by glial cells.
• Communicate via neurotransmitters.
  • Neurotransmitters can excite/inhibit target cells (imbalances can cause disorders).
  • Communication components:
    • Dendrites: Receive messages.
    • Axon: Carries impulses away from the cell body.
    • Myelination: Increases speed of conduction.
    • Signal Transmission: Via synaptic terminals.

Protection of the CNS

• Brain Protection:
  • Enclosed in the skull - 8 cranial and 14 facial bones.
  • Foramen magnum - link to spinal cord.
• Spinal Cord Protection:
  • Surrounded by vertebral column (7 cervical, 12 thoracic, 5 lumbar vertebrae).
  • Sacrum: 5 fused vertebrae; Coccyx: 4 fused vertebrae.
  • Includes intervertebral discs.

Meninges

• Three protective layers: Pia mater, arachnoid mater, dura mater.
  • Pia Mater: Innermost, thin layer.
  • Arachnoid Mater: Middle layer, spider web-like.
    • Subarachnoid space contains cerebrospinal fluid (CSF).
  • Dura Mater: Outermost, tough layer.

Cerebrospinal Fluid (CSF)

• Cushions brain and spinal cord.
• Circulates in subarachnoid space.
• Clear, colorless, about 100-200 ml total volume.
• Produced in ventricles, reabsorbed by arachnoid villi.
• Important for immune/metabolic functions.
• Sampling: Lumbar puncture or intraventricular catheter.

Blood Supply to the Brain

• Brain requires constant oxygen, receives 15% of cardiac output.
• Arterial supply from common carotid artery.
  • Anterior Cerebral Arteries: Frontal lobe.
  • Middle Cerebral Arteries: Outer frontal, parietal, superior temporal lobes.
  • Posterior Cerebral Arteries: Occipital, inferior temporal lobes.
• Circle of Willis: Collateral circulation.

Venous Flow and Blood-Brain Barrier

• Venous Flow: Through internal jugular veins, relies on gravity.
• Blood-Brain Barrier:
  • Physiologic barrier by brain capillaries.
  • Tight junctions prevent macromolecules from entering brain tissue.
  • Can be affected by trauma, cerebral edema, hypoxemia.

Conclusion

• End of part one, continuation in next lecture.