Midbrain Flashcards
External features of ventral surface of midbrain
- 2 cerebral peduncles: crus cerebri, substantia niagra, tegmentum
External features of dorsal surface of midbrain
- called tectum/ corpora quadrigemina
- separated from each other by cruciform sulcus
- vertical limb of sulcus forms depression lodging pineal body above, and frenulum veli below
- sup. brachium connects sup. colliculus to lat. geniculate body, made of optic fibres
- inf. brachium connects inf. colliculus to med. geniculate body, made of auditory fibres
- Trochlear N emerges after decussation at superior medullary velum
Crus cerebri
Middle 3/5: Corticospinal, corticonuclear
Medial 1/5: Frontopontine
Lateral 1/5: Temporopontine, parietopontine, occipitopontine
Substantia niagra
- b/w tegmentum and crus cerebri
- dorsal pars compacta - sends nigrostriatal fibres to caudate nucleus and putamen
- ventral pars reticularis
- cells contain melanin and iron
Grey matter of midbrain at level of inferior colliculus
- Trochlear N nucleus: posterior to MLF
- Mesencephalic N of trigeminal N
- Substantia niagra
- Reticular formation b/w medial lemnisci and central grey matter
White matter of midbrain at level of inferior colliculus
- Decussation of superior cerebellar peduncles
- Medial, trigeminal, spinal, lateral lemniscus - medial to lateral
- MLF
- Tectospinal tracts
- Rubrospinal tracts ventral to cerebellar decussation
Grey matter of midbrain at level of superior colliculus
- Occulomotor nucleus
- Edinger Westphal nucleus supplies sphincter pupillae and ciliary muscles
- Mesencephalic N of trigeminal nerve
- Nucleus of superior colliculus
- Pretectal nucleus
- Red nucleus
White matter of midbrain at level of superior colliculus
- Dorsal tegmental decussation of Meynert
- Ventral tegmental decussation of Forel
- MLF
- All lemnisci except lateral
Connections of superior colliculus
Afferent:
1. Retina through lat. geniculate body, sup. brachium
2. Spinal cord through spinotectal tract
3. Frontal and occipital visual cortex
4. Inferior colliculus
Efferent:
1. Tectospinal and tectobulbar tracts for reflex mvmts of eye, head, neck in response to visual stimuli
Unilateral lesion of superior colliculus
- Neglect of visual stimuli
2. Inability to track moving objects in contra. field
Pretectal nucleus
Aff: from optic tract
Eff: to Edinger Westphal nucleus
Function: part of pupillary and consensual light reflex
Lesion: Argyll Robertson pupil - accommodation reflex intact, light reflex lost
Red nucleus
- ovoid mass of grey matter
- dorsomedial to substantia niagra
- red due to high vascular supply
Connections of red nucleus
Afferents:
1. Cerebellorubral from contra. dentate nucleus
2. Corticorubral from ipsi. motor area
3. Pallidorubral from ipsi. globus pallidus
Efferents:
1. Rubrospinal
2. Rubrobulbar
3. Rubroreticular
* These fibres form ventral decussation of Forel
4. Rubroolivary
Medial Longitudinal Fasiculus
- tract in paramedian plane of brainstem
- extends cranially to interstitial nucleus of Cajal
- caudally contd. with anterior intersegmental fasiculus of SC
- contains fibres from vestibular nuclei
- fibres interconnect nuclei of 3, 4, 5, 6 and spinal nucleus of accessory N
- coordinates mvmts of eyes, head and neck using vestibulocochlear stimulus
Blood supply of midbrain
- Basilar
- Posterior cerebral
- Superior cerebellar
- Anterior choroidal
Weber’s syndrome
- Lesion in cerebral peduncle due to occlusion of posterior cerebral A
- Lesion involves occulomotor N and crus cerebri
1. Ipsi. lateral squint
2. Contra. hemiplegia
3. Contra. paralysis of lower part of face and tongue
4. Ptosis
5. Dilated pupil
Benedikt’s syndrome
- Ischemia of tegmentum
- Involves medial, spinal lemniscus, red nucleus, cerebellar peduncle, occulomotor N
1. Ipsi. lateral squint and ptosis
2. Contra. loss of pain and temp.
3. Contra. loss of tactile, muscle, joint, vibration senses
4. Contra. tremors, involuntary mvmts
Parinaud syndrome
Lesion of superior colliculus
1. Loss of upward gaze
