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Questions and Answers
What is the name of the substance pierced by a number of blood vessels?
What is the name of the substance pierced by a number of blood vessels?
Which nerves emerge at the medial margin of each crus cerebri?
Which nerves emerge at the medial margin of each crus cerebri?
What is the name of the structure that winds on the lateral side of each crus cerebri?
What is the name of the structure that winds on the lateral side of each crus cerebri?
What is located between the two crura?
What is located between the two crura?
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What is the name of the two pairs of small elevations on the dorsal surface of the midbrain?
What is the name of the two pairs of small elevations on the dorsal surface of the midbrain?
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What is connected to the lateral geniculate body by the superior brachium?
What is connected to the lateral geniculate body by the superior brachium?
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Which cranial nerve is the smallest and arises from the dorsal surface of the brainstem?
Which cranial nerve is the smallest and arises from the dorsal surface of the brainstem?
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What is the name of the part that is posterior to the aqueduct and is made of four colliculi?
What is the name of the part that is posterior to the aqueduct and is made of four colliculi?
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Where is the red nucleus positioned?
Where is the red nucleus positioned?
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What does the substantia nigra do?
What does the substantia nigra do?
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What is the main function of the crus cerebri?
What is the main function of the crus cerebri?
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What is the function of the medial lemniscus?
What is the function of the medial lemniscus?
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What is the function of the trigeminal lemniscus?
What is the function of the trigeminal lemniscus?
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What is the function of the spinal lemniscus?
What is the function of the spinal lemniscus?
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What is the function of the medial longitudinal bundle?
What is the function of the medial longitudinal bundle?
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What type of matter is the Sup.Colliculus Section composed of?
What type of matter is the Sup.Colliculus Section composed of?
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Where is the tectospinal decussation located?
Where is the tectospinal decussation located?
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What is the function of the nucleus of the inferior colliculus?
What is the function of the nucleus of the inferior colliculus?
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What is the function of the mesencephalic nucleus of CN V?
What is the function of the mesencephalic nucleus of CN V?
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What is the function of the trochlear nerve nucleus?
What is the function of the trochlear nerve nucleus?
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What is present in the same location as the reticular nuclei and substantia nigra?
What is present in the same location as the reticular nuclei and substantia nigra?
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What is the function of the rubrospinal decussation?
What is the function of the rubrospinal decussation?
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What is present in the inf. colliculus section of the white matter?
What is present in the inf. colliculus section of the white matter?
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Where is the rubrospinal decussation located?
Where is the rubrospinal decussation located?
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What is the function of the nucleus of superior colliculus?
What is the function of the nucleus of superior colliculus?
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Where is the pretectal nucleus located?
Where is the pretectal nucleus located?
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What type of fibers are found in the superior colliculus?
What type of fibers are found in the superior colliculus?
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Which tract receives auditory fibers from the lateral lemniscus?
Which tract receives auditory fibers from the lateral lemniscus?
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What is the function of the Edinger-Westphal nucleus?
What is the function of the Edinger-Westphal nucleus?
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What is the function of the superior colliculus?
What is the function of the superior colliculus?
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Where is the motor nucleus of CN III located?
Where is the motor nucleus of CN III located?
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Which nucleus is involved in pupillary light reflexes?
Which nucleus is involved in pupillary light reflexes?
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What type of information does the mesencephalic nucleus of CN V receive?
What type of information does the mesencephalic nucleus of CN V receive?
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What is the result of damage to the pretectal nucleus?
What is the result of damage to the pretectal nucleus?
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What is the function of the reticular nuclei?
What is the function of the reticular nuclei?
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Which tract carries efferent fibers from the colliculi to the spinal cord?
Which tract carries efferent fibers from the colliculi to the spinal cord?
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Where are the reticular nuclei located?
Where are the reticular nuclei located?
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What is the function of the inferior colliculus?
What is the function of the inferior colliculus?
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Study Notes
Brainstem Surface Features
- The ventral surface of the brainstem converges towards the upper border of the pons, with a posterior perforated substance between the crura cerebri.
- The III and IV nerves emerge at the medial margin of each crus cerebri.
- The optic tract curls around each crus cerebri.
Midbrain (Mesencephalon)
- The midbrain has a dorsal surface featuring two pairs of small elevations called the superior and inferior colliculi.
- The superior colliculi are connected to the lateral geniculate body by the superior brachium (visual).
- The inferior colliculi are connected to the medial geniculate body by the inferior brachium (auditory).
- The IV nerve leaves the dorsal surface just below the inferior colliculus.
- The superior cerebellar peduncles converge from the cerebellum into the dorsal surface of the midbrain.
Parts of the Midbrain
- Tectum: a small part posterior to the aqueduct, consisting of four colliculi.
- Cerebral peduncles: one on each side, anterior to the cerebral aqueduct, subdivided into:
- Crus cerebri (anterior)
- Substantia nigra (middle)
- Tegmentum (posterior)
Superior Colliculus Section
Grey Matter
- Nucleus of superior colliculus: involved in general visual reflexes, located in the tectum (posterior lateral).
- Pretectal nucleus: involved in pupillary light reflexes, located just cranial to the superior colliculus at the junction of the midbrain and diencephalon.
- Motor nucleus of CN III: motor to extraocular muscles, located ventromedial to the aqueduct.
- Edinger-Westphal nucleus: involved in pupillary light reflexes, located posterior lateral to the CN III motor nucleus.
- Mesencephalic nucleus of CN V: receives proprioception from the masticatory, facial, ocular, and lingual muscles, located lateral to the aqueduct.
- Reticular nuclei: control alertness, circadian rhythm, etc., located lateral to the central grey matter.
- Red nucleus: part of the extrapyramidal system, located paramedian behind the substantia nigra.
- Substantia nigra: gives Negrostriate fibers, secretes dopamine, located between the tegmentum and crus cerebri.
White Matter
- Crus cerebri: contains descending tracts (frontopontine, corticospinal, corticonuclear, temporopontine), located ventral to the substantia nigra.
- Medial lemniscus: ascending for proprioception and most of touch, located posterior lateral to the red nucleus.
- Trigeminal lemniscus: carries opposite fibers for facial pain and temperature, located posterior lateral to the medial lemniscus.
- Spinal lemniscus: ascending for pain, temperature, and some touch, located posterior lateral to the trigeminal lemniscus.
- Medial longitudinal bundle: connects the vestibular nuclei with the III, IV, VI, and spinal XI nuclei, and reticular nuclei to coordinate eye movement and audiovisual reflexes of the head and neck.
Decussations
- Tectospinal decussation: decussating descending fibers from the colliculi (tectum) to the spinal cord and medulla, located at the midline ventral to the medial longitudinal bundle.
- Rubrospinal decussation: decussating descending fibers from the red nucleus to the spinal cord, located at the midline between the two red nuclei.
Inferior Colliculus Section
Grey Matter
- Nucleus of inferior colliculus: involved in general auditory reflexes, located in the tectum (posterior lateral).
- Mesencephalic nucleus of CN V: receives proprioception from the masticatory, facial, ocular, and lingual muscles, located lateral to the aqueduct.
- Trochlear nerve nucleus: motor neurons to the superior oblique muscle, located ventromedial to the aqueduct.
White Matter
- Lateral lemniscus: ascending auditory fibers from the cochlear nuclei to the inferior colliculus and thalamus, located dorsal to the spinal lemniscus.
- Tectospinal tract: descending fibers from the colliculi (tectum) to the spinal cord, located ventral to the medial longitudinal bundle.
Functions
- The superior colliculus receives visual fibers from the optic tract and visual cortex, and gives efferent to the motor nuclei of the cranial and spinal nerves for reflex movements of the eyes, head, neck, and limbs away from or towards light stimuli.
- The inferior colliculus receives auditory fibers from the lateral lemniscus and sends efferent to the reticular formation and the medial geniculate body.
- The pretectal nucleus is involved in pupillary light reflexes, receiving visual afferent from the optic tract and occipital cortex, and sending efferent to the Edinger-Westphal nuclei of both sides. Damage to the pretectal nucleus causes Argyll-Robertson pupil, where the light reflex is lost but the accommodation reflex is present.
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Description
This quiz covers the anatomy of the cerebral crura, including the optic tract, III and IV nerves, and surrounding structures like the interpeduncular fossa.
