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Let’s start our USMLE Review with Anatomy from the Gold Standard USMLE Step 1 Audio Review program.
Play USMLE Audio MP3 26 13 Midbrain (3_5) Below
Begin 26 13 Midbrain (3_5) Transcription
Now we’re going to look at the superior collicular level of the midbrain. Refer to figure 9.2.
In which of the three midbrain structures is the visual reflex center located?
- In the tectum.
The visual reflex center is in a tectal midbrain structure. Student doctor, more specifically where in the tectal midbrain structure is the visual reflex center located?
- In the superior colliculus.
Please describe the overall function of the superior colliculus?
- The superior colliculus is involved in the relay of the visual reflexes from the retina and the frontal eye field to the occipital eye field.
What is the name of the commissure that interconnects the left and right superior colliculi?
- This is the commissure of the superior colliculus.
Student doctor, what is the major function of the brachium of the superior colliculus?
- The brachium of the superior colliculus is involved in optic and pupillary reflexes.
What additional functions are served by the brachium of superior colliculus?
- In addition to being involved in the optic and papillary reflexes, the brachium of the superior colliculus also conducts retinal and corticotectal fibers to the superior colliculus and pretectum.
Student doctor, please pause if you wish and describe the location of the nucleus of the oculomotor nerve?
- The nucleus of the oculomotor nerve is located near the midline of the caudal midbrain in the anterior part of the central gray.
Student doctor, what are the four extraocular muscles innervated by the oculomotor nerve?
- Please list these in alphabetical order.
- First, the inferior oblique.
- Second, the inferior rectus.
- Third, the medial rectus. And
- four, the superior rectus.
Student doctor, what is the structure adjacent to the lateral border of the oculomotor nucleus which contains the vestibular fibers that coordinates eye movement?
- This is the medial longitudinal fasciculus.
What is the abbreviation for this?
- The MLF.
Student doctor, what structure in the dorsolateral tegmentum carries information from the dorsal column to the ventroposterolateral nucleus of the thalamus?
- This is the medial lemniscus.
How many divisions are there of the fibers arranged in the medial lemniscus?
- There are two divisions of them, what are they? The lateral division and the medial division.
What is the function of the lateral division of fibers in the medial lemniscus?
- The lateral division of fibers in the medial lemniscus carries information from the lower extremities.
And what is the function of the medial division. The medial division of the medial lemniscus carries information from the upper extremities.
Student doctor, what structure in the anterior tegmentum gives rise to a cross rubrospinal tract and an uncrossed rubroolivary tract?
- This is the red nucleus.
The red nucleus is part of what system?
- The extrapyramidal system.
The red nucleus receives input from what two parts of the brain?
- From the cerebral cortex and from cerebellar nuclei.
What kind of input does the red nucleus receives from the cerebral cortex?
- Bilateral input.
And what type of input does the red nucleus receive from the cerebellar nuclei?
- Contralateral input.
Student doctor, what is the large dopaminergic nucleus located at the base of both the rostral and caudal midbrain?
- The substantia nigra.
What are the two parts of the substantia nigra?
- The pars compacta and the pars reticularis.
Student doctor, please name the two types of fibers found in the central tegmental tract. Rubroolivary and reticulothalamic fibers.
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