Neurophysiology Summary

The Nervous System

• Consists of:
  • Central Nervous System (CNS): Brain and Spinal Cord
  • Peripheral Nervous System (PNS):
    • Sensory (afferent) neurons: brings information to the CNS
    • Motor (efferent) neurons: carries information away from CNS
      • Somatic (voluntary - skeletal muscles)
      • Autonomic (involuntary - smooth & cardiac muscles, glands)
        • Sympathetic
        • Parasympathetic

CNS: Grey and White Matter

• GREY MATTER:
  • Unmyelinated nerve cell bodies
  • Clusters of cell bodies in the CNS are nuclei
  • Dendrites
  • Axon terminals
• WHITE MATTER:
  • Myelinated axons
  • Axon bundles connecting CNS regions are tracts
  • Contains very few cell bodies

Central Nervous System (CNS)

• Brain:
  • Cerebrum
  • Diencephalon
  • Cerebellum
  • Brain Stem
• Spinal Cord:
  • Ascending tracts (Sensory)
  • Descending tracts (Motor)
  • Sensory nuclei
  • Motor nuclei

CNS: Protection

• Bone & Meninges:
  • Brain is encased in bony skull, or cranium
  • Spinal cord runs through vertebral column
  • Meninges lie between bone and tissues to stabilize neural tissue and protect from bruising
    1. Dura mater
    2. Arachnoid membrane
    3. Pia mater
• CSF (Cerebrospinal Fluid):
  • Formed in the choroid plexuses in the ventricles of the brain
  • Functions:
    1. Cushions the brain and spinal cord
    2. Transports ions & nutrients
• BBB (Blood-Brain Barrier):
  • Selective permeability barrier
  • Protects the brain from harmful substances in the bloodstream while allowing essential nutrients to pass through
  • Maintains the brain's stable environment
  • Tight junction prevents solute movement between endothelial cells.

Brain

• Cerebrum:
  • Two cerebral hemispheres with four cortical lobes
• Diencephalon:
  • Thalamus: Relay and integration center for sensory & motor information
  • Hypothalamus: Homeostasis; Contains control centers for hunger, thirst, temperature, sleep, $H_20$ balance, BP; Controls release of hormones from pituitary gland
  • Pineal gland: Melatonin secretion
  • Pituitary gland: Hormone secretion; Links nervous and endocrine system
• Cerebellum:
  • Planning, initiation and coordination of voluntary movements
  • Maintenance of balance
  • Regulation of muscle tone
• Brainstem:
  • Midbrain: Eye movement
  • Pons: Relay station between cerebrum and cerebellum; Coordination of breathing
  • Medulla Oblongata: Control of involuntary functions
  • Reticular formation (not shown): Arousal, sleep, muscle tone, pain modulation

Spinal Cord

• Organization:
  • Grey matter: Consists mostly of cell bodies; Nuclei = clusters of nerve cell bodies in the CNS; Consists of sensory and motor nuclei.
  • White matter: Consists of tracts of axons carrying information to and from the brain.
    • Ascending tracts: carry sensory information to the brain.
    • Descending tracts: carry commands to motor neurons.

Peripheral Nervous System

• Consists of:
  • Ganglia: clusters of nerve cell bodies in the PNS
  • Nerve fibres
  • 31 pairs of spinal nerves
  • 12 pairs of cranial nerves
• Spinal Nerves:
  • C1-C8 (8 cervical)
  • T1-T12 (12 thoracic)
  • L1-L5 (5 lumbar)
  • S1-S5 (5 sacral)
  • 1 Coccygeal nerve
• Cranial Nerves:
  • Originate from brain stem
  • Some nerves purely sensory or motor
  • Some contain motor and sensory fibres (mixed nerves)

Neural Reflexes

• A reflex arc consists of:
  1. A sensory receptor (sense organs)
  2. An afferent neuron (sensory neuron)
  3. A center in the CNS (brain / spinal cord)
  4. An efferent neuron (motor neuron)
  5. An effector (muscle / gland)
• Spinal reflex:
  • Spinal cord as integrating centre
  • Sensory neuron through spinal grey matter to efferent neuron
  • Important in coordination and movement