midbrain

What is the midbrain?

The most rostral part of the brainstem

What are the main external parts of the midbrain? (3)

Tectum, tegmentum and cerebral peduncles

What is the tectum?

dorsal part of the midbrain

hat structures form the tectum?

Superior and inferior colliculi

What is the tegmentum?

central part of the midbrain

сверху вниз

tectum, tegmentum, basis

What is the cerebral aqueduct?

canal connecting the 3rd and 4th ventricles

What are the cerebral peduncles?

Major fiber bundles connecting the cerebrum with the brainstem and spinal cord

tectum, red nucleus, substantia nigra, crus cerebri

What are the main structures seen in the caudal midbrain? (4)

Inferior colliculus, PAG, CN 4 nucleus and substantia nigra

What are the main structures seen in the rostral midbrain? (4)

Superior colliculus, CN 3 nucleus, red nucleus and substantia nigra

What is the inferior colliculus?

relay nucleus in the auditory pathway

What is the superior colliculus?

elay nucleus in the visual reflex pathway

What is the main function of the superior colliculus?

Visual reflexes and orienting movements

What is the main function of the inferior colliculus?

Auditory processing and reflexes

What is the periaqueductal gray (PAG)?

Gray matter surrounding cerebral aqueduct

What is the main function of the PAG?

Modulates pain and affective responses

What is the substantia nigra?

midbrain structure involved in motor control

What is the clinical significance of substantia nigra degeneration?

Parkinson disease

What is the red nucleus?

motor-related nucleus in the rostral tegmentum

What is the main function of the red nucleus?

Influences motor control, upper-limb flexors

Which cranial nerve nucleus is found in the caudal midbrain?

CN 4 nucleus

Which muscle is innervated by CN 4?

Superior oblique

What is unique about CN 4?

the only cranial nerve to exit dorsally

сверху вниз

trochlear nerve, trochlear nerve nucleus, lemnisci

Which cranial nerve nucleus is found in the rostral midbrain?

CN 3 nucleus

Which muscles are NOT supplied by CN 3?

lateral rectus and superior oblique

What is the Edinger-Westphal nucleus?

parasympathetic nucleus of CN 3

сверху вниз

oculomotor nucleus, oculomotor nerve

What does the Edinger-Westphal nucleus control?

Pupillary constriction and accommodation

What is the pretectal nucleus?

midbrain nucleus involved in the pupillary light reflex

optic chiasm, edinger westphal nucleus, pretectal olivary nucleus

Where is the pretectal nucleus located?

Rostral and lateral to the superior colliculus

What is the afferent input to the pretectal nucleus?

retina

Where does the pretectal nucleus project?

Edinger-Westphal nuclei

What reflex is mediated by the pretectal nucleus?

Pupillary light reflex

What is the ventral tegmental area (VTA)?

dopamine-producing region of the midbrain

What functions are associated with the VTA?

Motivation, emotion, drive and reward

What are raphe nuclei associated with?

Serotonergic signaling and modulation

What is the main arterial supply of the midbrain?

Branches of the posterior cerebral artery (PCA)

What is Weber syndrome?

CN 3 palsy with contralateral hemiparesis

сверху вниз

parinaud’s syndrome, benedikt’s, weber’s

Which structures are affected in Weber syndrome? (3)

CN 3, cerebral peduncle and substantia nigra

What is the main eye finding in Weber syndrome?

Ipsilateral oculomotor paresis

What motor deficit occurs in Weber syndrome?

Contralateral hemiparesis

What other feature can occur in Weber syndrome?

Contralateral parkinsonism

Which artery is classically affected in Weber syndrome?

Superficial penetrating branches of PCA

What is Benedikt syndrome?

CN 3 palsy with contralateral sensory and motor deficits

Which structures are affected in Benedikt syndrome? (4)

CN 3, cerebral peduncle, substantia nigra and ventral tegmentum

What sensory deficit occurs in Benedikt syndrome?

Contralateral loss of vibration, touch and proprioception

What movement abnormalities occur in Benedikt syndrome?

Contralateral ataxia, tremor and involuntary movements

Which pathway causes the sensory loss in Benedikt syndrome?

Medial lemniscus

Which artery is classically affected in Benedikt syndrome?

Deeper penetrating branches of PCA

What is Parinaud syndrome?

disorder of vertical gaze due to dorsal midbrain damage

Which region is affected in Parinaud syndrome?

Pretectal/dorsal midbrain region

what is the classic eye movement deficit in Parinaud syndrome?

Paralysis of upward gaze

What other eye finding occurs in Parinaud syndrome?

Central nystagmus

What happens to saccades in Parinaud syndrome?

They become impaired

Which artery is associated with Parinaud syndrome?

PCA

What is the medial lemniscus in the midbrain?

An ascending pathway carrying fine touch, vibration and proprioception

What does the trigeminal lemniscus carry?

ensory information from the face

What does the spinal lemniscus carry?

Pain, temperature and crude touch from the body

Which major structures surround the cerebral aqueduct?

Periaqueductal gray

What is the difference between the rostral and caudal midbrain?

Rostral contains the superior colliculus; caudal contains the inferior colliculus

Which colliculus is involved in visual reflexes?

Superior colliculus

hich colliculus is involved in auditory pathways?

Inferior colliculus

Which midbrain structure is strongly associated with dopamine?

substantia nigra

Which midbrain structure is strongly associated with reward?

ventral tegmental area

Which midbrain structure is strongly associated with pain modulation?

periaqueductal gray

Which midbrain structure is strongly associated with upper-limb motor control?

Red nucleus

Which midbrain structure is involved in pupillary light reflex?

Pretectal nucleus

Why can midbrain lesions cause ipsilateral CN 3 deficits and contralateral body deficits?

Cranial nerve fibers are ipsilateral; long motor/sensory pathways cross