Brainstem II: Midbrain

Question 1

3 components of midbrain

Answer 1

Tectum (2 suprior colliculi, 2 inferior colliculi)

Tegmentum (cerebral aqueduct, periaqueductal grey, red nucleus, decussation of SCPs, substantia nigra that separates tegmentum and crus cerebri)

crus cerebri (CBT and CST)

Cerebral peduncle = everything except tectum

Question 2

What CN can you see exiting dorsally right below the inferior colliculus?

Answer 2

CN IV! (the only one that you can’t see from the front), comes out from dorsal part of brainstem

Question 3

CNs associated with midbrain

Answer 3

CN III and IV

Question 4

Match CNs in midbrain with which colliculus they associate with

Answer 4

CN III - superior colliculus

CN IV - inferior colliculus

Question 5

Inferior colliculus important for what kind of pathways?

Answer 5

AUDITORY

Question 6

Input and output for inferior colliculus?

Answer 6

Input from lateral leminiscus - originating from the superior olivary nucleus of the pons, and cochlear nuclei of medulla

Output to medial geniculate nucleus of thalamus

Question 7

What is the periaqueductal grey rich in?

Answer 7

Enkephalins for modulation of autonomics and pain, closely associated with reticular system

Question 8

Medial longitudinal fasiculus (MLF)

Answer 8

located right under nucleus of CN IV) , plays role in vision has fibers that go to III and IV and VI, helps coordinate muscles of eye with muscles of neck

Question 9

What is the reticular formation/activating system for?

Answer 9

Important in wakefulness, serotonin, at the level of inf colliculus

Question 10

Where does the decussation of the SCP occur?

Answer 10

Inferior colliculus (traveling to red nucleus and ventrolateral nucleus of thalamus

Question 11

What important NTs are in substantia nigra?

Answer 11

Dopamine (important in Parkinsons) and GABA (from pars reticulata)

Question 12

If you see the red nucleus and nuclei of CN III, what level of midbrain are you at?

Answer 12

superior colliculus

Question 13

Superior colliculus is associated with what kind of pathways?

Answer 13

VISUAL

Question 14

Inputs and outputs of superior colliculus?

Answer 14

Input from retina

output to cervical muscles for coordination of visual tracking

Question 15

Superior colliculus contains nucleus of which CN?

Answer 15

CN III

Question 16

Red nucleus

Answer 16

Prominent in superior colliculus.

Receives fibers from SCP (important for motor activity) and projects to flexor muscles as well as inferior olivary nucleus

Question 17

Pretectal area is an important area in which location with respect to colliculi?

Answer 17

Above. at the extreme rostral end of the midbrian.

important in coordinating structures of eye

Question 18

Edinger Westphal nucleus

Answer 18

presynaptic parasympathetic fibers of III to ciliary ganglion for pupillary constriction of pupillary light reflex as well as accomodation for near vision

Question 19

Posterior commissure important for what?

Answer 19

coordinated movement of both eyes. (i.e. bilateral pupillary constriction when light is shined in one eye)

Question 20

Weber’s syndrome

Answer 20

ipsilateral oculomotor (CN III) paralysis with contralateral upper motor neuron lesion (this is because decussation of CST is down in the medullary pyramids), hyperreflexia Results form vascular insufficiency in medial aspect of midbrain at level of superior colliculus

Question 21

Benedikt’s syndrome

Answer 21

ipsilateral III paralysis with contralateral tremor (from substantia nigra) and possible contralateral somatosensory loss.

Vascular lesion to III and red nucleus and SCP, and medial leminiscus (dorsal columns) and possible STT

Question 22

Gaze palsy (Parinaud’s syndrome)

Answer 22

from pineal tumor which affects pretectal area and posterior commissure. Upward gaze paralysis, large pupil, abnormal elevation of upper eyelid and paralysis of accommodation