Exam 1 (Lecture 4) - Midbrain Flashcards
What part of the neural tube is the midbrain derived from?
Mesencephalon
Which structure is the pretectal nucleus part of? What does it do?
1) Part of the rostral colliculus
2) It receives input from the optic nerve; responsible for pupil constriction
- use PLR to asses (Pupillary Light
Reflex)
What is the function of the rostral colliculus?
Mediates visual reflexes (body ocular reflex)
What is the function of the caudal colliculus?
Mediates auditory reflexes (startle reflex)
Where does the tectospinal tract run and what is its function?
1) Tract from tectum to spinal cord
2) Mediates head movement
What does the trochlear nerve innervate? What is its function? Which nucleus gives rise to which trochlear nerve?
1) Innervates the dorsal oblique of the eye
2) It rotates the eye toward the midline (intorsion of the eye)
3) Nucleus on the right give rise to the left trochlear nerve (and vice versa)
What midbrain structures can be seen on the midsagittal view of the brain?
1) Tectum
2) Tegmentum
3) Cerebral aqueduct
What midbrain structures can be seen on the ventral view of the brain?
1) Oculomotor nerve (emerges from crus cerebri)
2) Crus cerebri
3) Pyramids
Which nuclei and nerves are responsible for VOLUNTARY movement of the eyes?
Midbrain:
1) Motor nucleus of III –> CN III
(Oculomotor nerve)
2) Motor nucleus of IV –> CN IV
(Trochlear nerve)
Medulla Oblongata:
1) Motor nucleus of VI –> CN VI
(Abducens)
What clinical sign(s) would you expect to see with a lesioned oculomotor nerve? Explain.
1) Lateral strabismus, pupillary dilation, and droopy eyelid.
You would see these signs because CN III (oculomotor) innervates the medial rectus (that pulls the eye medially), pupillary sphincter muscle (that constricts the pupil), and the levator palpebrae superioris (that opens the eyelid)
What clinical sign(s) would you expect to see with a lesioned trochlear nerve? Explain.
You would see extorsion of the eye.
You would see this sign because CN IV (trochlear) nerve innervates the dorsal oblique (which pulls the eye toward the medial side)
What clinical sign(s) would you expect to see with a lesioned abducent nerve?
You would see medial strabismus and absence of the 3rd eyelid reflex.
You would see these signs because CN VI (abducens) innervates lateral rectus muscle (pulls the eye to the lateral side) and the retractor bulbi muscle (retracts the eye, initiating the 3rd eyelid response)
