Neuroscience - Gall - Brainstem Lecture 3

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What are the four branchiomeric CNs?

CNs 5,7,9,10.

What is a branchiomeric CN?

CN that innervate branchial arch-derived structures.

These are mixed nerves with both afferent and efferent components.

Are associated with multiple CN nuclei.

Have overlapping functions, esp CN 7, 9, and 10. [These three are involved in taste. All go to the same nucleus in the brainstem called the nucleus solitarius).

What are branchial arches?

Structures which develop in head and neck. These are similar to gills in a fish.

These structures reorganize to form cartilage, nerve, muscle, and arteries in the head and neck region.

It forms much of the muscular in the head and some of the neck.

Note: branchial arch = pharyngeal arch.

What are the muscles of the branchial arches innervated by?

Cranial nerves!

Which CN innervates the first, second, third, and fourth branchial arch?

First arch - CN 5

Second arch - CN 7

Third arch - CN 9

Fourth arch - CN 10

How many functional components and nuclei are associated with CN 5?

The trigeminal nerve has four functional components and is associated with 4 nuclei. Three of the nuclei are sensory, one of them is motor.

What are the four functions of the trigeminal CN and what nuclei does each function go to?

1. Crude touch, pain and temp - for the head, neck, mouth and teeth. This is GSA. The afferents go to the spinal trigeminal nucleus which is located from the SC to the mid pons.

2. Two point discrimination - for the head, neck and mouth. This is GSA. Afferent for to the chief/principal trigeminal nucleus in the mid pons.

3. Proprioceptive information of jaw muscles. This is monitoring the tension in the jaw muscles. This is GVA. Afferent go to the mesencephalic nucleus of 5, which is from the mid pons through the mesencephalon.

4. Innervation to muscles of mastication. This is SVE. Efferents from the motor nucleus of 5.

What sensation can you only have in the teeth?

Pain.

Where is the motor nucleus of CN 5 with respect to the other sensory nuclei? Where would you find the motor nucleus of 5?

The motor nucleus is found medial, which the sensory nuclei are more lateral.

The motor nucleus of 5, along with the chief nucleus, is located in the mid pons.

Where in a cross section of the midbrain would you see the trigeminothalamic tract and the trigeminal lemniscus?

Both are laterosuperior to the red nucleus. Just above the location of the medial lemniscus. Also medioinferior to the spintothalamic tract. These three are all bunched together lateral to the red nucleus.

TQ = the axons of both of these tracts go to the VPM of the thalamus. This is unlike the medial lemniscus and spinothalamic tracts which went to the VPL.

Wherein a cross section of the midbrain would you find the mesencephalic trigeminal nucleus?

Located at the border between the tectum and the ventricle. At the lateral superior edges.

What is the corneal reflex used for?

Used to test the integrity of the trigeminal nerve.

CN5 is the sensory component, CN7 is the motor component.

So this tests the trigeminal nerve, the chief trigeminal nucleus and the spinal trigeminal nucleus, the facial motor nucleus, and the facial nerve.

TQ = The right cornea tests the ipsilateral trigeminal nerve.

What is trigeminal neuralgia?

Have intense pain in the maxillary and mandibular field.

Describe the location of the spinal trigeminal nucleus throughout the medulla.

You can see this nucleus throughout the medulla since it goes from the SC to the mid pons.

Since this is a sensory nucleus, alar plate derived, it is expected to be lateral in all slides.

In the SC it is in the upper middle right. In the low medulla is in the upper middle right above the reticular formation. In the middle medulla it is in the upper middle right above the reticular formation. In the upper medulla (can only see a little of the olive) it is in the upper middle right.

Describe the location of the motor nucleus of 5 and the chief trigeminal nucleus.

These will both be found in the mid pons.

Will be located in the very upper right of the bonds at the edge of the cerebellar peduncles. So it's regions before the lateral dark rectangles.

Given the developmental setup, the motor nucleus is medial to the sensory nucleus.

Describe the location of the Mesencephalic trigeminal nucleus.

This is found in the rostral pons or in the mesencephalon.

In the rostral pons it is at the lateral edge of the diamond for the ventricle. The axon will decussate over the bridge formed by the ventricle.

What does the facial nerve do with respect to taste? Where do the afferents terminate?

It provides taste for the anterior 2/3 of the tongue.

The afferents in the rostral nucleus solitarius.

What are the motor functions of the facial nerve? Where do the efferents originate?

It controls the muscles of facial expression and also dampens sounds.

The efferents arise from the facial motor nucleus to the facial muscles and the stapedius.

What are the secretory functions of the facial nerve? Where do the efferents originate?

It controls secretions via parasym to the lacrimal, submandibular and submaxillary glands.

The efferents arise from the superior salivatory nucleus.

What touch sensation does the facial nerve have? Where do the afferents terminate?

Touch sensation from region around ear.

The afferents will terminate in the spinal nucleus of 5.

What are the internal sensation functions of the glossopharyngeal nerve? Where do the afferents terminate?

It controls sensation form the larynx/pharynx, oral cavity, and carotid body (baroreceptors, chemoreceptors).

The afferents terminate in the caudal nucleus solitarius. (Gag reflex).

What does the glossopharyngeal nerve do with respect to taste? Where do the afferents terminate?

It does taste for the posterior 1/3 of the tongue.

The afferents terminate in the rostral nucleus solitarius.

What touch sensation goes the glossopharyngeal nerve do? Where do the afferent terminate?

Touch sensation from region around ear.

Afferents terminate in the spinal nucleus of 5.

What secretions does the glossopharyngeal control? Where do the efferents originate?

Controls secretions via parasym to the parotid glands.

Efferents from the inferior salivatory nucleus.

What internal muscles does the glossopharyngeal nerve control? Where do the efferents originate?

Branchial motor controls of muscles of larynx/pharynx.

Efferents form the nucleus ambiguus.

What parasym functions does the vagus nerve have? What nucleus is involved?

Parasym control of heart, lungs, GI

Dorsal motor nucleus of the vagus

What internal muscles does the vagus nerve control? Where do the efferents originate?

Branchial motor controls of muscles of larynx/pharynx.

Efferents form the nucleus ambiguus.

What touch sensation goes the vagus nerve do? Where do the afferent terminate?

Taste from epiglottis.

Afferents to the rostral nucleus solitarius.

What touch sensation goes the vagus nerve do? Where do the afferent terminate?

Touch sensation from region around ear.

Afferents terminate in the spinal nucleus of 5.

What are the internal sensation functions of the vagus nerve? Where do the afferents terminate?

Sensation from the larynx/pharynx, meninges and aortic arch.

Afferents to the caudal nucleus solitarius.

To what nucleus does taste information go to?

Rostral nucleus solitarius.

What CNs are involved in taste sensation and where in the body do they sense taste?

Anterior 2/3 of tongue = facial nerve.

Posterior 1/3 of tongue = glossopharyngeal nerve.

Epiglottis = vagus nerve.

Note: the CNs going to the rostral nucleus solitarius all are ipsilateral.

To what nucleus does touch sensation from around the ear go?

Which CNs are involved in this sensation?

To the spinal trigeminal nucleus.

This is considered crude touch.

CNs 7,9, and 10.

To what nucleus does sensory afferents from the larynx, pharynx, caudal oral, nasal cavities, and aortic arch go to?

Which CNs are involved in this sensation?

Caudal nucleus solitarius.

CNs 9 and 10. (9 is more important)

From what nucleus does efferent to the muscles of the larynx and pharynx originate?

Which CNs are involved in this function?

Nucleus ambiguus.

CNs 9 and 10. (10 is more important). So if have damage to CN 10 will have difficulty in swallowing! = TQ.

Note: these are to branchial muscles, SVE.

TQ = what are the four CNs that carry sensory axons that terminate in the spinal trigeminal nucleus?

CNs 5,7,9, and 10.

What are the autonomic preganglionic components of CNs 7,9, and 10?

7 - Superior salivatory nucleus.

9 - Inferior salivatory nucleus.

10 - Dorsal motor nucleus of vagus.

What are the branchial efferents of CNs 7,9, and 10?

7 - Facial motor nucleus.

9 - Nucleus ambiguus

10 - Nucleus ambiguus

What are the visceral sensory for CNs 7,9, and 10?

7 - none.

9 - Caudal nucleus solitarius.

10 - Caudal nucleus solitarius.

Where do the afferents for taste terminate in CNs 7,9, and 10?

7 - Rostral nucleus solitarius.

9 - Rostral nucleus solitarius.

10 - Rostral nucleus solitarius.

Where do the somatic afferents around the ear terminate for CNs 7, 9, and 10?

7, 9, and 10 - Spinal trigeminal nucleus.

Describe the nucleus solitarius.

Long nucleus, VA column thorugh medulla.

Looks like eyes with dark pupils.

Describe the spinal trigeminal nucleus.

Dorsolateral sector, away from ventricle.

Long, extends from upper spinal cord to mid pons.

Medial to the spinal trigeminal tract.

Describe the nucleus ambiguus.

Long nucleus, SVE column, medullary tegmentum.

Embedded in the reticular formation, can't ID.

Describe the facial motor nucleus.

SVE column, in the pontine tegmentum.

Looks like square shaped.

Describe the dorsal motor nucleus of the vagus.

Extends through the medulla, generally myelin free axons so it looks pale.

Describe the superior and inferior salivatory nuclei.

Small, cannot identify in cross section.

Embedded in the reticular formation.

Where are motor and sensory nuclei located with respect to the sulcus limitans?

Motor is medial, sensory is lateral to the sulcus limitans.

How do you identify the nucleus solitarius in a slide of the medulla?

Superiolateral to the reticular formation. Looks like an eyeball, which a dark center and pale around it.

How do you identify the spinal trigeminal nucelus in a slide of the medulla?

Superiomediolateral to the reticular formation.

Doesn't look like much.

How do you identify the dorsal motor nucleus of the vagus in a slide of the medulla?

It is pale, in the most superior aspect at the edge of the open ventricle.

How do you identify the nucleus ambiguus in a slide of the medulla?

It is in the middle of the reticular formation.

How do you identify the facial nucleus in a slide of the mid pons?

Facial nucleus is in the lateral aspect prior to the darkening of the cerebellar peduncles.

It's axon goes concave in superior and wraps around the nucleus abducens and comes out lateral to the axon of the abducens.

To where in the thalamus does taste go?

VPM of thalamus.

Where is the taste cortex?

Lateral to the poster central gyrus, above the temporal lobe, next to the insula.

Located on both sides of the brain.

Describe the central taste pathway.

From CNs 7,9,and 10 the axon goes to the rostral nucleus solitarius (in the medulla). Also called the gustatory nucleus. It is ipsilateral because at CN nuclei are ipsilateral.

The central tegmental tract is the name of the axon after the rostral nucleus solitarius. It bifurcates and goes to the VPM nucleus of the thalamus. It is bilateral to function as a safety.

What is the span of the central tegmental tract?

It is a structure that begins in the medulla and goes up the mesencephalon.

So starts at the rostral nucleus solitarius.

What is Bell's palsy?

Impaired function of the 7th cranial nerve. Will have ipsilateral facial paralysis.

What are the three major branches of the peripheral trigeminal nerve? Where do these nerve terminate their sensory projections?

1. Mandibular

2. Maxillary

3. Opthalmic

Sensory projections terminate to both the chief and spinal trigeminal nuclei since they do fine and crude tough respectively.

What is unique about the mesencephalic trigeminal nucleus?

It is composed to pseudounipolar (ganglion-like) neurons with the peripheral process innervating the periphery and the central process terminating in the brainstem.

What happens if you have a lesion in the motor trigeminal nucleus?

Will have weakness in chewing.

What is the difference between damage a nerve or a nucleus?

Damage to a nerve will damage all components of the nerve. Both motor and sensory.

Damage to one nucleus will damage only the specific function of that nucleus, be it motor or sensory.

Where do the chief and spinal trigeminal nuclei terminate?

In the VPM of the thalamus.

Where is the VPM located with respect to the VPL?

VPM is medial, VPL is lateral.

Where do axons in the trigeminal lemniscus arise from?

Where do they cross and then ascend to?

Axons in the trigeminal lemniscus arises in the Chief sensory nucleus.

These axons cross the midline at the level of the Pons, courses near the medial lemniscus, and terminate in the VPM.

Where do axons in the trigeminothalamic tract arise from?

Where do they cross and then ascend to?

Axons in the trigeminothalamic tract arises in the Spinal Trigeminal nucleus.

Cross the midline at levels encompassed by that long nucleus (in the medulla) and ascend next to the spinothalamic tract to terminate in the VPM.

Describe the location of the dorsal motor nucleus of vagus on brainstem cross sections.

This nucleus is located lateral to the hypoglossal nucleus and medial to the sulcus limitans.

Describe the gag reflex. Explain the reflex arc.

Gag reflex can be elicited by touching the posterior pharynx with a cotton swab.

This stimulates a reflex that involves CN 9 as the afferent arc and CN 10 as the efferent arc, eliciting a gag.

If the reflex is absent you know that there is a problem with one of these nerves or with the associated brainstem nuclei (afferents terminate in the caudal nucleus solitarius, efferents arise from nucleus ambiguus) = TQ!

Describe the ascending projections in the taste system.

The rostral nucleus Solitarious receives taste information via cranial nerves 7, 9, and 10.

This nucleus gives rise to ascending projections to the ventroposteromedial (VPM) thalamus.

The VPM thalamus then projects to the ipsilateral insular/gustatory neocortex.

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