Neuroanatomy 4 - CN's nuclei and central connections

Question 1

What is each component i.e. motor, sensory, parasympathetic etc in a CN associated with ?

Answer 1

A streak of grey matter in the brain/ brain-stem which serves on function e.g. motor or sensory etc

• Motor components of a CN will be associated with motor nuclei (groups of efferent nerve cells which send their axons into a CN)
• Sensory components will be associated with sensory nuclei (groups of nerve cells upon which the sensory neurons of the CN’s synapse) The soma (body) of the sensory nerve cells will be found in ganglia outside of the CNS (as there then projecting axons to then synapse onto these nuclei)

Question 2

What are the CN’s which only carry motor fibres ?

Answer 2

CN III, IV, VI, XI & XII

Question 3

What is the nuclei of origin for the oculomotor nerve & where is this nuclei situated ?

Answer 3

Nuceli of origin = superior colliculus, located in the midbrain

Question 4

What is the nuclei of origin for the trochlear nerve & where is this nuclei situated ?

Answer 4

Nuclei of origin = inferior colliculus, located in the midbrain

Question 5

What is the nuclei of origin for the abducent nerve & where is this nuclei situated ?

Answer 5

Nuclei of origin = abducens nucleus, located at the pontomedullary junction

Question 6

What is the nuclei of origin for the hypoglossal nerve & where is this nuclei situated ?

Answer 6

Nuclei of origin = hypoglossal nucleus, located in the medulla

Question 7

Go over this pic of some of the CN’s positions

Question 8

What are the 3 nuclei which make up the sensory nucleus of the trigeminal nerve and what sensations are sent to each of the nuclei?

Answer 8

1. Mesencephalic nucleus - sensations of proprioception from muscles of mastication sent here
2. Pontine nucleus - discriminative touch & vibration sensations sent here
3. Spinal nucleus - pain & temp sensations sent here

Note the trigeminal sensory nucleus stretches from midbrain down to the upper 2 segments of the spinal cord, also V3 of the trigeminal nerve will have associated motor nuclei (i think)

Question 9

What is unusual about the mesencephalic nucleus ?

Answer 9

This is the only site in the CNS where the cell bodies of the primary afferent neurons live inside the CNS. It is essentially a ‘retained’ sensory ganglion.

Question 10

What are the 3 components (nuclei) for the facial nerve ?

Answer 10

1. Facial motor nucleus
2. Salivary nucleus
3. Solitary nucleus

Question 11

What are the 4 components (nuclei) for the glossopharyngeal nerve ?

Answer 11

1: Solitary nucleus - Gustatory nucleus – taste, v Commissural nucleus- visceral information
2. Spinal trigeminal nucleus (small region of somatosensation associated with the ear).
3. Inf. Salivatory n. (parasymp)
4. Nucleus ambiguus (stylopharyngeus muscle

Question 12

What are the 4 components (nuclei) for the vagus nerve ?

Answer 12

1. Dorsal (motor) Nucleus (parasymp)
2. Solitary -taste Commissural – visceral information
3. Spinal trigeminal nucleus (pain from dura and small region of somatosensation associated with the ear).
4. Nucleus Ambiguus (motor)

Question 13

Are several nuclei shared by > 1 CN?

Answer 13

Yes!

• Solitary nucleus (taste and visceral sensory information) CNs VII, IX, X,
• Sup. and Inf. Salivatory nuclei (parasympathetic efferents to ganglia of salivary glands and pterygopalatine ganglion) CNs VII and IX
• Nucleus ambiguus (motor efferents to muscles of pharynx, larynx and upper oesophagus) CN’s IX and X (and cranial part of XI)

Pic simply to show that solitary nucleus has different CN’s involved and its runs from upper to lower medulla

Question 14

What is the location of the nucleus ambigus ?

Answer 14

lower pons/upper medulla.

Question 15

Describe the motor input to CN’s via the corticobulbar tract

Answer 15

• The corticobulbar tract is the part of the pyramidal tract that is motor to cranial nerves.
• This includes fibres to the motor nuclei of CN’s V, VII, X, and XII.
• Interestingly, many of these cortical inputs are bilateral. However the input to the facial nucleus is only bilateral to that part that controls muscles of the upper face (forehead and around the eyes).

Question 16

Describe the motor input to CN’s containing parasympathetics?

Answer 16

• Input mainly from the hypothalamus whose efferents reach the preganglionic autonomic neurons both directly and via synapses in the reticular formation.
• Hypothalamus influenced by physiological status and input from many brain regions.

Question 17

What is the recticular formation and its function ?

Answer 17

The reticular formation is a network of loosely aggregated cells with cell bodies, axons and dendrites intermingling in the central core of the brainstem. It is distinct from the long pathways (like the medial lemniscus, or the corticospinal tract) and the specific distinct cell groups (like cranial nerve nuclei).

The reticular formation includes centres that:

• •Integrate cranial nerve reflexes.
• •Participate in conduction and modulation of pain.
• •Influence voluntary movement.
• •Regulate autonomic activity.
• •Integrate some basic functions, like respiration and
• sleep.
• •Activate the cerebral cortex: major component of the Ascending Reticular Activating System (a medial bilateral lesion of the brainstem reticular formation at or above the upper pons causes irreversible coma).