Physiology Long Test 4: Basic Features of the Nervous System

Basic Features of the Nervous System

• The nervous system consists of two key systems: Central Nervous System (CNS) and Peripheral Nervous System (PNS).
• CNS consists of the brain and spinal cord, encased in bone.

Central Nervous System (CNS)

• Brain:
  • Made up of neurons, glia, and other supporting cells.
  • Receives approximately 20% of the blood flow from the heart, continuously.
  • Most protected organ in the body, encased in a tough, bony skull and floating in a pool of cerebrospinal fluid (CSF).
  • Chemically guarded by the blood-brain barrier.
  • Can store only a small amount of glucose and cannot function without oxygen.
  • 1-second interruption of blood flow uses up much of the dissolved oxygen, and 6-second interruption produces unconsciousness.
• Spinal cord:
  • Contained within the vertebral column.

Peripheral Nervous System (PNS)

• Consists of:
  • Cranial nerves
  • Spinal nerves
  • Peripheral ganglia

Anatomical Directions

• Anterior vs. Posterior: front end vs. tail end
• Rostral vs. Caudal: toward nose and mouth vs. toward tail
• Dorsal vs. Ventral: back/top surface vs. belly/front surface
• Superior vs. Inferior: above (brain-specific) vs. below (brain-specific)
• Lateral vs. Medial: toward the side vs. toward the middle
• Neuraxis: imaginary line drawn through the length of the CNS, from the lower end of the spinal cord up to the front of the brain.

Brain Sections

• Cross-sections (frontal section): sliced like bread, dividing into front and back halves
• Horizontal sections: parallel to the ground, dividing into upper and lower halves
• Sagittal sections: parallel to the neuraxis, dividing into right and left halves
• Midsagittal plane: splits the brain symmetrically

Meninges

• Protective sheaths around the brain and spinal cord
• Three layers:
  • Dura mater (outer layer): durable, thick, tough, and flexible but unstretchable
  • Arachnoid membrane (middle layer): soft and spongy, with arachnoid trabeculae
  • Pia mater (inner layer): closely attached to the brain and spinal cord, with smaller surface blood vessels

Ventricular System and CSF Production

• Ventricular system: series of interconnected chambers filled with CSF
• Ventricles:
  • Produce and contain CSF
  • Lateral ventricles: largest chambers of the ventricular system
• Cerebral aqueduct: connects third ventricle to fourth ventricle
• Choroid plexus: special tissue with rich blood supply, manufactures CSF, and protrudes into all four ventricles
• Total CSF volume: ~125 ml
• Half-life of CSF: ~3 hours
• CSF flow: produced in lateral ventricles, flows to third ventricle, passes through cerebral aqueduct to fourth ventricle, and circulates around CNS before being reabsorbed into blood.

Cerebrospinal Fluid (CSF)

• Reduces brain's effective weight from ~1,400 g to ~80 g
• Cushions brain, reducing impact from sudden movements
• May cause hydrocephalus (obstructive) if CSF flow is blocked