Midbrain CN III and CN IV* Flashcards
What does the midbrain consist of?
- The cerebral peduncles
- The tectum
What do the cerebral peduncles comprise?
- Motor axons traveling from the cortex to the brainstem and spinal cord.
- Sensory axons traveling from the brainstem and spinal cord to the cortex.
What is the tectum formed by?
The superior colluculi and the inferior colliculi.
What is the superior colliculi?
It centres for co ordination of the eye, head and body movements to follow objects in the visual field.
What is the inferior colliculi?
It centres for co ordination of the head, eye and body movements towards a source of sound.
What two pairs of nuclei are located within the anterior part of the midbrain?
- The red nucleus
- the substantia nigra
What 4 extraocular muscles does the oculomotor nerve supply (motor)?
Medial rectus – turns the eye medially.
Superior rectus – turns the eye superiorly and medially.
Inferior rectus – turns the eye inferiorly and medially.
Inferior oblique – turns the eye upwards and laterally.
It also supplies the levator palpebrae superioris that elevates the upper eyelid.
What parasympathetic nerves does CN III supply?
The ciliary muscles - focus on close objects.
The constrictor pupillae muscles - constrict pupil and decrease the light on retina.
What happens if the oculomotor nerve (CN III) is damaged?
It can cause double vision and pupillary dilation.
How is the pupillary light reflex tested?
Shining a torch into each eye. If reflex does not occur in either eye then optic nerve should be suspected. If only one eye then the oculomotor should be expected.
What is the trochlear nerve (CN IV)?
They are very slender and supply one muscle in each orbit (superior oblique). This muscle turns the eye downwards and laterally.
What happens if the trochlear nerve is injured?
It is rarely injured alone. It could be damaged whiplash.
