Brain Stem: Midbrain Flashcards
what are the 3 general layers of the Midbrain?
- Tectum = dorsal
- Tegmentum = intermediate
- Crus Cerebri = ventral
what structures are on the tectum of the Midbrain?
(dorsal layer)
Corpus quadrigemina = S/I colliculi
what is the superior colliculi responsible for?
visual reflex response to unexpected stimuli in visual field
what is the inferior colliculi responsible for?
auditory reflex respone
what is the tegmentum of the midbrain a continuation of?
the pontine tegmentum
what are the cerebral peduncles?
crus + tegmentum
what is the cerebral aqueduct?
connection between the 3rd and 4th ventricle
what are the fiber tracts within the tectum of the midbrain?
posterior commisure
what does the posterior commissure do?
coordinate eye movements
list the fiber tracts in the tegmentum at the level of the inferior colliculus
- decussation superior cerebellar peduncle
- medial longitudinal fasciculus
- lateral lemniscus
- medial lemniscus
- trigeminothalamic
- spinothalamic
what info is carried in the decussation of the superior cerebellar peduncle?
efferent output from cerebellum crosses here
what info is carried in the medial longitudinal fasciculus?
balance with efferent limb of balance reflex
what info is carried in the lateral lemniscus?
afferent to inferior colliculus for auditory reflex
list the tracts located in the tegmentum of the midbrain at the level of the superior colliculus
- medial longitudinal fasciculus
- medial lemniscus
- trigeminothalamic
- spinothalmic
what are the crus cerebri?
descending axons from cerebrum that form corticospinal or corticobulbar tracts
divided into 4 segments

tracts in the most lateral segment of the crus cerebri are coming from where?
descending from parietal, temporal, and occipital cortex to pontine nuclei/cerebellum
tracts in the most medial segment of the crus cerebri are coming from where?
descending from frontal lobe to pontine nuclei/cerebellum
where is the corticospinal tract located in the crus cerebri
lateral middle segment
where is the corticobulbar tract located in the crus cerebri?
median middle segment
what nuclei are located in the tectum of the midbrain?
- inferior colliculus (auditory reflex)
- superior colliculus (visual reflex)
- pretectal region
what supplies the input to the inferior colliculus?
afferent input from:
cochlear, superior olivary, trapezoid nuclei via
lateral lemniscus
efferent output from the inferior colliculus heads where?
thalamus
via brachium of inferior colliculus (tectospinal)
what supplies the input to the superior colliculus?
retina
efferent output from the superior colliculus heads where?
cervical spine
via tectospinal for head turning, and tracking

