08: Midbrain

Midbrain

This is the most rostral transverse segment of the brainstem that contains a cavity called the cerebral (Sylvian) aqueduct or Iter

Midbrain-diencephalic junction

This junction demarcates midbrain ↔ diencephalon and is an imaginary line from Mammillary Body (ventral) to Posterior Commissure (dorsal)

Rostral tip of the cerebral aqueduct and Caudal tip of the third ventricle

Midbrain-diencephalic junction passes through these 2 structures

Ponto-midbrain junction

This junction demarcates pons↔midbrain and is an imaginary line from superior pontine sulcus to the rostral tip of the cerebellum

Caudal end of the Cerebral Aqueduct and Rostral part of the Fourth Ventricle

What structrues are passed by the Ponto-midbrain junction?

Ponto-medullary junction

This junction demarcates pons↔ medulla and is an imaginary line from Pontomedullary Sulcus (inferior pontine sulcus) to the Fastigium of the Fourth Ventricle

Tectum of the midbrain (Corpora quadrigemina)

This roofs cerebra aqueduct; lies dorsal to cerebral aqueduct

4 rounded bodies: a pair of superior and inferior colliculi

What are teh round bodies that forms the tectum?

Tegmentum of the midbrain

This is located ventral to the cerebral (Sylvian) aqueduct and dorsal to the basis

III & IV & Mesencephalic nucleusof CN V

What cranial nerves nuclei are under the midbrain tegmentum?

Substancia nigra

Demarcates the junction of the midbrain tegmentum from the basis

Midbrain

The Trapezoid body is to the Pons, as the Substantia nigra is to the to what structure

Reticular formation nuclei

This is found throughout the tegmentum of the brainstem and play an important role in the state of consciousness and arousal (maintains an alert wakeful state)

Ascending sensory tracts

What part of the tegmentum does it passes through it to get to thalamus

Descending subcortical motor tracts

What part of the tegmentum originate from structures in the brainstem and descend toward the spinal motor neurons

Corticospinal

This part of the basis lies above the pyramidal decussation and conveys voluntary movement and is responsible for movement of the contralateral side of the body

Corticobulbar/Corticonuclear

This part of the basis contains cranial nerve motor nucle

Corticopontine

This part of the basis terminates at the pontine nuclei and projects through the middle cerebellar peduncle to the opposite cerebellum via the pontocerebellar fibers

Crus cerebri

This can be found in the basis of the midbrain only

Basis pedunculi

This can be found in the basis and Substantia nigra of the midbrain only

Cerebral peduncle

This can be found in the basis and Entire Tegmentum of the midbrain only

Superior pontine sulcus

This is the caudal limit of the midbrain and marks the ponto-midbrain junction ventrally

Optic chiasm & tract

This is the rostral limit of the midbrain and encircles the rostal part of the midbrain

Pair of crura cerebri

This is part of teh midbrain that is a diverging in V-shaped configuration from the upper limit of the pons

Interpeduncular fossa

This is part of teh midbrain that is the space in between the 2 crura that contains diencephalic (particularly hypothalamic) structures

CN III

This is part of the midbrain that emerges medial to the crus cerebri from within the interpeduncular fossa

CN IV

This is part of the midbrain that hugs the lateral aspect of the crus cerebri

true

(T/F) Corpora quadrigemina is seen in the dorsal surface of the midbrain

Marks the caudal limit of midbrain & Rostral limit of the pons, dorsally

What is being marked bythe exit of the trochlear nerve?

diencephalon

The rostral limit of the midbrain, dorsally, will be by the structures belonging to the this structure?

Inferior colliculus (IC)

This is the auditory relay nucleus of the midbrain where lateral lemniscus fibers will end

inferior quadrigeminal brachium

Inferior colliculus (IC) must connect with the medial geniculate via the ______________________

Medial geniculate

This structure is specific for pecific for Thalamic nucleus hearing

Superior colliculus (SC)

This structure mediates visual reflexes, it has to have connections with the visual pathway (through superior quadrigeminal brachium)

Lateral geniculate body (LGB)

This structure is part of the visual pathway specifically the thalamic nucleus for vision where the optic tract fibers terminate

Superior Quadrigeminal Brachium

This structure connects the superior colliculus to the lateral geniculate body.

Inferior Quadrigeminal Brachium

This structure connects the inferior colliculus to the medial geniculate body.

Tectum

This structure is the dorsal part of the midbrain and contains the corpora quadrigemina/ quadrigeminal plate (superior and inferior colliculi)

Cerebral Peduncle

This structure is located ventral to the tegmentum

Trochlear Nerve (CN IV)

This structure exits at the dorsal aspect of the midbrain, then runs laterally and ventrally, winding/hugging over the lateral surface of the midbrain.

Level of Superior Colliculus

At what level is theupper ½ of the midbrain that has a wider interpeduncular fossa

Level of Inferior Colliculus

At what level is the lower ½ of the midbrain that has a narrower interpeduncular fossa

DORSAL = DOWN, VENTRAL = UP For CT scan and MRI

What is the direction of the clinical ?

Decussation of the Brachium Conjunctivum

Anatomical basis for communication between one cerebellar hemisphere with the opposite cerebral hemisphere

CN III (the rest), IV (superior oblique), VI (lateral rectus)

What are the Three CN which supply extraocular muscles:

Weakness of superior oblique

What happens if there is a CN IV lesion?

Tectum

This is the Dorsal to the line along the (midline) plane of the cerebral aqueduct

Tegmentum

This is the ventral to the line along the (midline) plane of the cerebral aqueduct

Substantia nigra

Structure in the tegmentum that is most ventrally placed and houses the largest nucleus of the midbrain

crus cerebri

The basis is called

Inferior Colliculus

This is the Auditory relay nucleus in the midbrain that receives ascending projections of the lateral lemniscus (principal ascending auditory pathway) that was formed in the pons

Lateral lemniscus

____________ terminates in the inferior colliculus

Medial geniculate body

Inferior Colliculus projects to this structure via inferior quadrigeminal brachium

Superior colliculus

Inferior Colliculus projects to this structure above for audio-visual refle

Inferior colliculus in the midbrain and Superior olivary nucleus in the pons

What are the 2 auditory relay nuclei in the brainstem

Corticospinal tract & Corticobulbar tract

What comprises the pyramidal tract taht forms 3/5 of crus of ceribri

Corticopontine tract

What forms the Medial and lateral 1/5 of Crus Cerebri?

Arnold’s bundle (Frontopontine)

Corticopontine tracts that from the frontal lobe and Medial 1/5 of Crus Cerebri

Turck’s bundle (Parieto-occipito-temporopontine)

Corticopontine tracts from the parietal, occipital, and temporal lobes and Lateral 1/5 of Crus Cerebri

Substantia Nigra

This is the largest nucleus of the Midbrain and lies at the boundary of the tegmentum and basis

False, Pars Compacta (dorsal): Contains Dopamine and Pars Reticulata (ventral): Contains GABA

Pars compacta a component of the Substantia Nigra contains GABA

Substantia Nigra

This structure is Important for the modulation and regulation of movement that if it is destroyed, decreases dopamine input leads to Parkinson's disease

Ascending Sensory Fiber tracts

What groups together to form the Lemniscal Crescent?

Medial lemniscus

This ascending sensory fiber tract is for conscious proprioception, vibration, fine touch from the opposite side

Spinal lemniscus

This ascending sensory fiber tract is for pain, temperature, and crude touch from the opposite side

Trigeminal lemniscus

This ascending sensory fiber tract is for various sensory modalities from the opposite side of the face

Lateral lemniscus

This ascending sensory fiber tract is for ascending auditory pathway which will terminate at the inferior colliculus

PAG (Periaqueductal Gray)

This structure surrounds the cerebral aqueduct

Mesencephalic nucleus of V

This structure is embedded inside the periaqueductal gray primarily found in the upper half of the pons but extends to the midbrain

F. none. Conveys nonconscious proprioception from the muscles of mastication

(T/F) Mesencephalic nucleus of V has a synaptic connection with the CN nuclei of the midbrain

Medial longitudinal fasciculus

This structure is located ventral to the periaqueductal gray and functions to conjugate gaze

Central tegmental tract

This structure is located ventral to the medial longitudinal fasciculus (MLF)

Decussation of SCP

anatomical basis for communication between one cerebellar hemisphere with the opposite cerebral hemisphere

Trochlear nucleus

This structure is located and embedded at the most ventral part of the periaqueductal gray and gives rise to the trochlear nerve root

substance of the midbrain

Trochlear nucleus decussate completely within this structure

trochlear nerve

The ________________ seen dorsally is actually a nerve that has already decussated

Trochlear nerve

This isthe only cranial nerve that exits dorsally and only cranial nerve that decussates completely

Superior Colliculus

This structure is for visual reflexes, but not vision and facilitates visual orientation and tracking

superior quadrigeminal brachium

Superior Colliculus receives fibers from retina via this structure

superior quadrigeminal brachium

Superior Colliculus receives fibers from retina via this structure that connects the superior colliculus with the lateral geniculate body (termination of optic tract)

Inferior colliculus

Superior Colliculus receives fibers from inferior colliculus for audiovisual reflexes via the _________________- for visual

tectospinal tract

Superior Colliculus projects to Spinal cord via ______________

Ventral Tegmental Area (VTA) of Tsai

This structrue is located only in the upper half of tegmentum and consists of dopaminergic neurons, which is another source of dopamine aside from the substantia nigra

ventral striatum

Ventral Tegmental Area (VTA) of Tsai projects to the nucleus accumbens of the ___________

Ventral Tegmental Area (VTA) of Tsai

Plays a role in the reward pathway which is the basis of addiction

Lemniscal Crescent

Occupies the lateral portion of the upper half of tegmentum that consists of:

○ Trigeminal lemniscus

○ Spinal lemniscus

○ Medial lemniscus

Red Nucleus

Theis structure of the tegmentum is located at the ventromedial aspect of tegmentum and receives axons of the deep cerebellar nuclei from the contralateral cerebellar hemisphere via the superior cerebellar peduncle

cerebellar relay nucleus

Red nucleus is what type of nucleus?

RIGHT red nucleus (upper ½) and RIGHT thalamus → RIGHT cerebral hemisphere

Where will the red nucleus fibers go after deussation?

Rubro-Olivary Tract and Rubrospinal Tract

Whata re the 2 Descending Projections of the Red Nucleus divisions

Parvocellular

This gives rise to the descending rubro-olivary tract that does not decussate

Rubro-Olivary Tract

This descending tract descends through the central tegmental tract (CTT) and terminates at the inferior olivary nucleus in the medulla on the same side

Magnocellular

This gives rise to the descending rubrospinal tract and does not decussate

ventral tegmental

Rubrospinal Tract decussates first in the ________________decussation before descending and synapse with contralateral spinal motor neurons

tectospinal tract decussation

This decussation originates from the superior colliculus, crosses at the dorsal tegmental decussation (Meynert) in the midbrain, and then descends to the spinal cord.

Somatic Cell Column

Part of the oculomotor nuclear complex that supplies skeletal muscles

Visceral Cell Column (Edinger-Westphal Nucleus)

Part of the oculomotor nuclear for parasympathetic function

CN III Nerve Root

Emerges ventrally from within the interpeduncular fossa medial to the crux cerebri