Lab 3

Question 2

Identify the structures

Answer 2

1. Tectum
2. Cerebral Aquaduct (aka mesecephalic aquaduct)
3. Tegmentum

Question 3

Label the structures

Answer 3

1. Tectum
2. Cerebral aquaduct
3. Tegmentum

Question 4

Identify the structures

Answer 4

1. Rostral colliculus
2. Crus Cerebri
3. Cerebral aquaduct
4. Tectum
5. Tegmentum
6. Medial geniculate nucleus of the thalamus

Question 5

Identify the structures

Answer 5

1. Rostral colliculus
2. tectum
3. tegmentum
4. crus cerebri
5. cerebral aquaduct
6. medial geniculate nucleus of the thalamus

Question 6

What major midbrain structures represent the tectum?

Answer 6

Rostral and caudal colliculi

(tectum means “roof” -think of it as the roof of the cerebral aquaduct)

Question 7

What functional defecits would you expect with a lesion of the internal capsule?

Answer 7

Lesions involving the internal capsule affect both sensory (diminished perception, localization of pain, tactil, thermal, proprioceptive, auditory and visual), and motor functions (weakness in motor control)

(see page 16)

Question 8

Where is a lesion in the dog displaying ventrolateral strabismus of the right eye?

Answer 8

R oculomotor nerve

The oculomotor n. emerges from the ventral midbrain medial to the crus cerebri (there are conflicting statements about the nuclei of CN III emerging from either the rostral colliculi vs. the tegmentum - I’m not sure which is correct, they’re both in the text, I think it’s just important to remember that there is a separate nucleus for the motor and parasympathetic functions of CN III).

Question 9

What clinical signs would you see if the oculomotor nerve is damaged?

Answer 9

Ventrolateral strabismus, ptosis, puillary dilation

Question 10

What geniculate nucleus works closely with the occipital lobe?

Answer 10

Lateral geniculate nucleus (part of the thalamus) - received fibers of the optic tract, then projects visual signals to the visual cortex. Also connected with the visual reflex center fo the midbrain (the rostral colliculus).

Question 11

If the eyes fail to follow your moving hand in front of the animal’s face, what nerve(s) could be injured?

Answer 11

Oculomotor, optic, abducent, maybe trochlear, but it would be very hard to tell in a dog - not likely

Question 12

Identify these structures of the cerebellum

Answer 12

1. Cerebellar hemisphere
2. Vermis

Question 13

Identify the structures

Answer 13

3. nodulus
4. cerebelar peduncles
5. flocculus
6. flocculonodular peduncle
7. vermis

Question 14

Identify the structures

Answer 14

1. Cerebellar peduncles
2. fourth ventricle
3. fasiculus cuneatus
4. spinal tract of the trigeminal nerve
5. vestibular nuclei

in purple - medlla oblongata

in red - the area of the pons - easier seen on a lateral view - see pages 42-43 in the book

Question 15

What are the cerebellar peduncles?

Answer 15

These peducnles are formed from cerebellar afferent and efferent fibers and they connect the cerebellum to the rest of the CNS. The names rostra, midle and caudal stem from where their fibers originate or terminate.

See page 40 for more information

Question 16

1. Which side of the body will be affected by a lesion of the right cerebellum?
2. What kind of functional deficits would you expect to see?

Answer 16

1. Ipsilateral side
2. Loss of smooth execution of movment, increased muscle tone, loss of equilibrium and posture. A lesion of the flocculonodular nobe induces a oss of equilibrium, head tilt, abnormal nystagmus

Question 17

Identify the structures

Answer 17

1. CN VII - Facial n
2. pyramid
3. pyramidal decussation
4. also pyramidal decussation… sorry!
5. trapezoid body
6. CN VI - Abducent n.

In red - area of the pons

In blue - area of the medulla

Question 18

Label cranial nerves II-XII (except CN IV - you can’t see that here)

Answer 18

Question 19

Virtual Slide 07b (caudal end of the meddula) - also see pages 229-233 in book

Identify the structures

Answer 19

1. pyramidal decussation
2. pyramid
3. lateral corticospinal tract - to the contralateral spinal cord
4. ventral corticospinal tract - to the ipsilateral spinal cord

I’m not sure if we have to know the names of the spinal tracts, but I think we do need to understand that at the pyramidal decussation, some fibers cross to the contralateral side while some remain ipsilateral

Question 20

Where do fibers of the pyramid originate?

Answer 20

In the cerebral cortex

The pyramids are a pair of descending motor tracts on the vetral medulla oblongata - they descend as part of the internal capsule, form the crus cerebri at the ventral midbrain, run through the pons, and reappear to form the pyramid. 75% of the fibers cross to the contralateral side at the pyramidal decussation - these fibers descend in the lateral funiculus. Those that do not cross over descend in the ventral funiculus.

image is for reference so you can trace the course of these fibers

Question 21

What clinical sign would you expect if the right pyramid is damaged?

Answer 21

Contralateral hemiparesis (weakness) with defecits in gait and postural reactions - remember that some fibers remain ipsilateral so the clinical signs would likely be mild

Question 22

Identify the structures

Answer 22

1. tegmentum - extends from the midbain to the caudal end of the pons
2. basilar pons

Question 23

If an animal shows a loss of balance and right facial paralysis, what area of the brain is most likely inovlved?

Answer 23

R side of the medulla oblongata - these nuclei are rostral to the pyramidal decussation so innervation is all ipsilateral - my group originally said trapezoid body in lab but I don’t think this is correct because the vestibular nuclei are not in the trapezoid body, they are lateral to the fourth ventricle, but correct me if I’m wrong! Although maybe trapezoid body is also correct because both nerves emerge at/near the trapezoid body? Idk this question confuses me…

Question 24

If you see paresis of the left limba and medial strabismus of the right eye, what area of the brain is most likely involved?

Answer 24

The right pyramid

Descending motor tracts that originate in the cerebral cortex - this would cause paresis of the L limbs, however the abducent nerve doesn’t techincally emerge from the pyramid, it emerges at the junction of the pyramid and trapezoid body, so it migt be a good idea to say, “at the junction of the right pyramid and trapezoid body”

Question 25

If touching the medial canthus does not induce eye blinking, what nerves could be injured?

Answer 25

Trigeminal (ophthalmic), facial

The ophthalmic nerve detects tactile stimulus, these signals are sent to the motor nucleus of the facial nerve, which innervates the orbicularis oculi, and the eye blinks if everything is working

Question 26

Where is the lesion if a dog shows a loss of facial tone and drooped lip on the right side?

Answer 26

It could be at the genu of the facial nerve deep in the medulla, or it could be to the right facial nerve itself. Either way, the lesion would be on the same side as the facial paralysis

Question 27

Where is the lesion if the dog tends to fall to the right side?

Answer 27

On the right side of the medulla - the vestibular nuclei occupy the lateral floor of the fourth ventricle on either side of the medulla

Or, right vestibular organ

Or, right vestibular nerve

Or, right vestibulospinal tract

See Lecture 7

Question 28

Although it is rare to see an injury to the accessory nerve, compare the clinical signs induced by injury to the spinal root or cranial root of the accessory nerve.

Answer 28

cranial root - innervates the larynx and esophagus - potential problems swallowing

spinal root - innervates muscles of neck and shoulder - ipsilateral muscle atrophy of trapezius, cleidomastoideus, sternomastoideus - twisting of neck and an unnatural position of the head

Question 29

A patient shows slow onset of hearing loss in the right ear. MRI suggests Schwanoma of the right facial nerve in the cranium. If this condition is allowed to progress, what other clinical signs could potentially develop with time?

Answer 29

You would expect to see vestibular symptoms since the vestibulocochlear nerve courses with the facial nerve and they both exit the cranium through the internal acoustic meatus - loss of balance, falling, etc.

Also damage to the facial nerve - facial paralysis, no palpebral reflex, lack of blinking, reduced or absent lacrimation