Equilibrium Pathways

Overview:

• Focus on equilibrium pathways similar to other special senses.
• Hair cells detect equilibrium and generate action potentials.
• Neurons synapse with hair cells, belonging to the vestibular nerve.

Vestibular Nerve:

• Combined with cochlear nerve to form Cranial Nerve 8 (vestibulocochlear nerve).
• Transmits information from hair cells.

Ganglia:

• Collection of neuron cell bodies outside the CNS is known as ganglia.
• Vestibular ganglia are formed by neuron cell bodies.

Pathway of Signal Transmission:

• From Hair Cells:

  • Action potentials generated by hair cells are transmitted through neuron fibers.
  • Signals pass through vestibular ganglia.
  • Bundled as vestibular nerve.

• To the Brain:

  • Vestibulocochlear nerve sends signals to the vestibular nucleus.
  • Vestibular nucleus is located in the brain stem.

Vestibular Nucleus:

• Collection of cell bodies within the CNS.
• Transmits equilibrium information to various brain areas and spinal cord.
• Functions:
  • Integrates equilibrium information from both ears.
  • Relays information to cerebral cortex for conscious awareness of head position and movement.
  • Sends motor commands to muscles (head, neck, limbs, eyes) to maintain balance, posture, and focus.

Eye Movement and Balance:

• Normal Eye Movement:

  • Eyes move back and forth when spinning, maintaining focus.
  • Jumping between points is normal, known as nystagmus.

• Abnormal Nystagmus:

  • Occurs when eyes move back and forth without spinning.
  • Indicates potential damage to inner ear or brain stem.

Motion Sickness:

• Occurs due to conflicting sensory information (ears vs. eyes).
• Common situations include being on a boat or reading in a moving car.
• Treatment:
  • Medications like Dramamine depress vestibular nucleus activity.

Conclusion:

• Understanding equilibrium pathways is crucial for diagnosing issues like motion sickness and nystagmus.