Medulla and Cranial Nerves

Medulla Features

• Outside features of the medulla are visible upon observation.
• Inside features include the pyramids.

Pyramids

• Made up of pyramidal axons.
• Carry descending information from the thalamus towards the spinal cord.

Olive

• Bulge on the medulla.
• Responsible for relaying information to the cerebellum.

Cranial Nerve 12 (Hypoglossal Nerve)

• Supplies all muscles of the tongue except one.

Nuclei of Termination

• Found where the cell body for a neuron is located.
• Associated with sensory functions within the Central Nervous System (CNS).
• Cranial nerve nuclei can be identified as nuclei of origin or termination based on the cell bodies found within them.

Cranial Nerve Nuclei Organization

• The nervous system is bilaterally symmetrical.
• Each cranial nerve nucleus has a corresponding nucleus on both sides of the brain.
• On diagrams:
  • Right side shows the name of the nucleus with an abbreviation.
  • Left side indicates the Roman numeral of the associated cranial nerve.
  • Color-coding indicates the type of information processed by the nucleus.

Sensory Functions (Posterior Columns)

• Special Sensory (Posterior column):
  • Deals with special sensory information.
• Somatic/General Sensory (Posterior columns):
  • Deals with somatic or general sensory information.
• Visceral Sensory (Posterior columns):
  • Deals with visceral sensory information.

Motor Functions (Anterior Columns)

• Visceral/Autonomic (Anterior column):
  • Deals with visceral and autonomic information.
  • Terms are used interchangeably.
  • Nuclei contain cell bodies of preganglionic parasympathetic fibers.

Cranial Nerves

Olfactory Nerve (I) and Optic Nerve (II)

• Sensory related.
• No specific nuclei of termination are identified.

Oculomotor Nerve (III)

• Purely motor.
• Oculomotor Nucleus:
  • Nucleus of origin.
  • Contains cell bodies of lower motor neurons.
    • Each lower motor neuron innervates lots of fibers.
• Supplies four out of the six muscles that move the eyes.
• Innervates the levator palpebrae superioris muscle (responsible for holding eyelids up).
• Parasympathetic Pathway:
  • Preganglionic parasympathetic fibers have long axons.
  • Postganglionic parasympathetic fibers have short axons.
  • Synapse in a ganglion between the two fibers.
  • Target muscles are inside the eyes.

Accommodation

• Process of changing focal distance to focus on objects at different distances.
• Requires changing the shape of the lens (making it more convex to focus on closer objects).

Pupillary Constriction

• Pupil constricts when exposed to bright light.
• Dilation is the opposite.

Nearsightedness and Farsightedness

• Relate to the ability to focus light on the retina.
  {Nearsightedness: Light focused too far anterior}
  {Farsightedness: Light focused too far back}
• Can be due to the shape of the eye or the lens's ability to focus.

Astigmatism

• Irregularity in the shape of the cornea.

Trochlear Nerve (IV)

• Purely motor.
• Trochlear Nucleus:
  • Nucleus of origin.
  • Supplies one muscle (one of the six muscles that move the eyes).
• Mesencephalic Nucleus:
  • Nucleus of termination.