Fine structure of the midbrain

Question 1

I. What are the characteristics of the midbrain

Answer 1

• The mesencephalon (midbrain) has a tegmentum and a tectum (quadrigeminal plate).
• We also have a crus – the crus cerebri. Have a special area around the cerebral aqueduct, the periaqueductal gray matter.

Question 2

II. Crus
1. Which tracts can you find in the crus?

Answer 2

Made up of the corticospinal tract, and 2 separate parts of the corticopontine tract:
- Fronto-pontine tract (Arnold) (fibers arising from frontal lobe)
- Temporo-parieto-occipitio-pontine tract (Türk) (fibers arising from temporal/parietal/occipital lobe)
=> The corticospinal tract terminates in the spinal cord, the corticopontine tracts in the
nucleic pontis

Question 3

II. Crus
2. Which tracts can you find inside the corticospinal tract?

Answer 3

Inside the corticospinal tract, also the corticonuclear or corticobulbar tracts are
present

Question 4

II. Crus
3. Which structure can you find closed to the corticospinal tract?

Answer 4

We can find the susbtantia nigra close to the corticospinal tract, which will contain
those dopaminergic neurons that provide dopaminergic monoamine pathway of the
brainstem. They will go to the striatum and the limbic system

Question 5

III. Tegmentum
1. Which tract and nuclei can you find in tegmentum?

Answer 5

• We can still find the medial lemniscus and the red nucleus (where the rubrospinal
  tract arises from in the extrapyramidal system)
• Can still find the tectospinal tract
• Can find the medial longitudinal fascicle near the periaqueductal grey matter
  (besides the oculomotor and trochlear nucleus)

Question 6

IV. Periaqueductal grey matter
1. What is the feature of periaqueductal grey matter?

Answer 6

• ## It Is composed of many special reticular formation nuclei, it is where the analgesic pathway (pain-relieving) is regulated the most

Question 7

IV. Periaqueductal grey matter
2. Which tract and reflex can you find here?

Answer 7

Here we also have the mesencephalic trigeminal tract + nucleus, which will carry the proprioceptive reflex arch for the masticatory muscles

Question 8

IV. Periaqueductal grey matter
3. Which nuclei can you find here?

Answer 8

1. The Edinger-Westphal nucleus is the visceromotor nucleus for the
   oculomotor nerve (accommodation
   of the eye) -> fibers from the
   nucleus leave as the oculomotor nerve
2. Very close to the cerebral aqueduct,
   we can find the dorsal longitudinal
   fascicle (Schütz). Has a lot of
   connections with the hypothalamus
   and the central autonomic nervous
   system

Question 9

IV. Periaqueductal grey matter
3. What can we find At the brachium of the inferior colliculus?

Answer 9

At the brachium of the inferior
colliculus, we can find the medial
geniculate body. It is a part of the
auditory pathway, so the lateral
lemniscus will arrive here