Midbrain

Question 1

What markes the division between dorsal and ventral midbrain?

Answer 1

The aqueduct.

Question 2

What is the dorsal part behind the the aqueduct called?

Answer 2

Tectum.

Question 3

What is Tectum composed of?

Answer 3

1-2 superior colliculli
2 inferior colliculi

Question 4

What is the function of the superior and the inferior colliculli?

Answer 4

Superior= centre of vision
Inferior = centre of hearing

Question 5

What is the posterior part of the ventral midbrain called ( som sitter ihop med tectum)?

Answer 5

Its called midbrain tegmentum and is the prolongation of the pontine tegmentum.

Question 6

What are the three compartments of the ventral midbrain from anterior to posterior?

Answer 6

1. Crus cerebri
2. Substantia nigra (ser ut som en linje mellan främre o bakre delen)
3. Tegmentum.

Question 7

What is crus cerebri made of?

Answer 7

Entirely pyramidal and cortico-pontiine fibres.

Question 8

What is Substantia Nigra made off?

Answer 8

Deeply pigmented grey matter.

Question 9

What centre is substantia nigra?

Answer 9

Its an extrapyramidal motorcentre

Question 10

What does midbrain tegmentum contain?

Answer 10

• ascending tracts
• certain nuclei
• decussation and reticular formation of the midbrain.

Question 11

What structures lie at the plane of caudal midbrain?

Answer 11

• Inferior colliculus
  — Efferents from inferior colliculus to geniculate nucleus of thalamus (and from there to auditory cortex in temporal lobe)
• The cerebral aqueduct SURROUNDED BY GREY MATTER - periaqueductal grey matter
• Trochlear nucleus Ventral to the peri-aqueductal grey matter (send efferents cross over and forward to sup oblique.)
• Decussation of superior cerebellar peduncles - in the central part of tegmentum.
• Medial lemniscus - just posterior of substantia nigra
• Spinal lemniscus just posterior to the medial lemniscus
• trigeminal lemniscus just posterior to the spinal lemniscus
• Lateral lemniscus - just posterior to the trigeminal lemniscus

Question 12

Main structures of rostral midbrain at the level of the superior colliculus

Answer 12

• Superior colliculus
• Pretectal nucleus
• Peri-aqueductal grey matter
• Oculomotor nucleus and Edinger Westphal
• Red nucleus

Question 13

What reflex centre is localized in the inferior colliculus of midbrain?

Answer 13

The reflex centre of hearing.

Question 14

What three cranial nerves’ nuclei lie close to the MEDIAL LONGITUDINAL FASCICULUS?

Answer 14

• Occulomotor, Trochlear and Abducent nuclei.

Question 15

From what CN nuclei does the medial longitudinal fasciculus recieve fibres and to what CN nuclei does it send efferents?

Answer 15

FROM the Vestibular nuclei.
TO the Occulomotor nuclei, the trochlear nuclei and abducent nuclei.

Question 16

Where are efferents send from the 4 nuclei composing the vestibular nuclei near to vestibular area of floor of 4th ventricle in tegmental, caudal pons ?

Answer 16

1. Via the medial longitudinal fasciculus to:
   * abducent nuclei
   * trochlear nuclei
   * occulomotor nuclei
2. Via the inferior cerebellar peduncle to cerebellar cortex.
3. Via medial and lateral vestibulospinal fasciculus to ?
4. Direct to the reticular formation of pons.

Question 17

What two structures decussate and then form aschending Fs of the medial lemniscus?

Answer 17

Gracile and Cuneate tracts. (contralateral)

Question 18

Connections of hearing sensory input from cochlear nerve to primary ausitory cortex

Answer 18

cochlear nerver to ventral and dorsal cochlear nucleus (ventrally and dorsally of inferior cerebellar peduncle). From both to the trapezoid body (? or superior olivary nucleus) crossing in the trapezoid decussation and up through lateral lemniscus via the nucleus of the lateral lemniscus to the inferior colliculus of the midbrain tectum.
From there via inferior brachium to medial geniculate body.
Then via the auditory radiation to auditory area of cerebral cortex.

There are also fibres that go straight from ipsilateral dorsal and ventral cochlear nucleus to inferior colliculus and even straight to auditory radiation. There are also fibres crossing after the inferior colliculus.

Question 19

Between what structures does the medial longitudinal fasciculus span?

Answer 19

From level of inferior colliculus in midbrain and down into the spinal cord.

Question 20

What is the function of the medial longitudinal fasciculus?

Answer 20

To control gaze by coordination of eye, head and neck movement.

Question 21

What information is carried in the medial lemniscus?

Answer 21

Proprioception and fine touch sensation of contralateral side.

Question 22

What part of substantia nigra consists of pigmented melanin-containing neurones?

Answer 22

Pars Compacta

Question 23

To where does pars compacta project?

Answer 23

• Caudate nucleus and Putamen (Basal Ganglia in the forebrain)

Question 24

What two sets of fibres does the pyramidal tract of crus cerebri contain?

Answer 24

1- Cortico-bulbar fibres
2 - Cortico-spinal fibres

Question 25

What more than the pyramidal tract does crus Cerebri contain?

Answer 25

* Cortico-pontine (-cerebellar) * Temporo-pontine (-cerebellar) * Fronto-pontine (-cerebellar) fibres. - Involve in coordination of movement.

Question 26

What type of function does pars compacta involve?

Answer 26

Extra-Pyramidal motor functions.

Question 27

What centre is the superior colliculus?

Answer 27

A centre of visual reflexes: Control movements of eyes and accomodation reflex.

Question 28

What are the main afferent Fs to Superior colliculus?

Answer 28

Cortico-tectal Fs. - From visual cortex occipitally - Frontal eye field frontally

Question 29

Where is the pretectal nucleus situated?

Answer 29

close to superio-lateral superior colliculus.

Question 30

What are the important connections of pretectal nucleus?

Answer 30

* Visual Fs from the optic tract just rostral to sup.colliculus end in the pretectal nucleus. * Connections w the Edinger Westphal nucleus.

Question 31

What is the function of Edinger Westphal nucleus?

Answer 31

It is the parasympathic nucleus of the oculomotornerve, controlling sphincter pupillae (smooth muscle) and mediate pupillary light reflex (together w pretectal nucleus).

Question 32

what is the function of the red nucleus?

Answer 32

It is involved in motor control.

Question 33

From where does the red nucleus recive afferents?

Answer 33

From motorcortex of the frontal lobe.

Question 34

To where does nucleus ruber send efferents?

Answer 34

1. To the spinal cord - as rubro-spinal tract. It cross in ventral tegmental decussation. 2. To the inferior olivary nucleus as rubro-olivary Fs via central tegmental tract.

Question 35

What does internuclear ophthalmoplegia (INO)mean?

Answer 35

Det påverkade ögat (contralateralt till hjärnstamslesionen) kan inte conjugera med det andra ögat i medial blickriktning för det skadade ögat utan tittar istället rakt fram. Dock KAN det påverkade ögat adducera (ställa sig medialt) tillsammans med det andra ögat vid convergence.

Question 36

Signs of unilateral brain stem lesion:

Answer 36

1. ipsilateral CN dysfunction (ipsil facial paresis) 2. Contralateral spatic hemiparesis 3. Hyperreflexia (especially in the contralateral limbs) 4. Positive babinski reflex in contralateral side. 5. contralateral hemisensory loss (ipsilateral facial) 6. Ipsilateral incoordination 7. Internuclear opthalmoplegia

Question 37

What structure in the brain stem is damaged to produce INO? (internuclear opthalmoplegia)

Answer 37

The medial longitudinal fasciculus.