Download anatomy of brainstem and associated lesions

ANATOMY OF BRAINSTEM AND ASSOCIATED LESIONS - MIDBRAIN:
MIDBRAIN:
At the end of the lecture the student should be able to know:
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External features of midbrain
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Cranial Nerves of the Midbrain
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Internal structure of midbrain
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Lesions of midbrain
MIDBRAIN:
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LANDMARKS
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Cerebral peduncles
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Optic chiasm
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Interpeduncular fossa
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(Superior colliculi)
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(Inferior colliculi)
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(Superior cerebellar peduncle)
MIDBRAIN:
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Cranial Nerves III, IV
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Midbrain is divided at the level of cerebral aqueduct
into:
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Dorsal portion called tectum which largely consists of
inferior and superior colliculi
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Ventral portion, known as tegmentum
EXTERNAL STRUCTURE OF MIDBRAIN:
1. Optic chiasm
2. Interpeduncular fossa
3. Oculomotor nerve (CN III)
4. Trochlear nerve (CN IV)
5. Pons
6. Cerebral peduncles (crus cerebri).
CRANIA NERVES OF THE MDBRAIN:
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Anterior exit
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CN III (1)
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CN VI (5)
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Posterior exit
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CN IV (2)
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MLF - Medial longitudinal fasciculus (7)
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Vestibular nuclei (6)
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Pons (3)
INTERNAL DIVISIONS OF MIDBRAIN:
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Tegmentum is bounded ventrally by the
massive fibre system of the crus cerebri
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The term cerebral peduncle is sometimes used
as a synonym for crus cerebri
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Cerebral peduncle refers to the whole
midbrain on either side excluding the tectum.
INTERNAL DIVISIONS OF MIDBRAIN:
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Ventral to the colliculi the cerebral aqueduct runs the length of the midbrain
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Surrounding the aqueduct is a pear shaped arrangement of grey matter called Periaqueductal
grey matter.
SUBSTANTIA NIGRA:
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These neurons project to the caudate nucleus and putamen of the basal ganglia in the forebrain
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Degeneration of the pars compacta of the substantia nigra is associated with Parkinson’s disease
SUBSTANTIA NIGRA:
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Other non pigmented subdivision of the substantia nigra is called the pars reticulata
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Pars reticulata is considered to be a functional homologue of the medial segment of the globus
pallidus which is also part of the basal ganglia.
INTERNAL STRUCTURE OF MIDBRAIN:
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Cross section at the level of inferior colliculus
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CN IV Trochlear nerve
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MLF
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Dorsal raphe nucleus
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Substantia nigra
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Mesencephalic nucleus of V
LOWER PART OF MIDBRAIN:
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CAUDAL PART OF MIDBRAIN:
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In the caudal part of the midbrain the
inferior colliculus constitutes part of the
ascending acoustic projection
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Ascending auditory fibres run in the lateral
lemniscus which terminates in the inferior
colliculus
CAUDAL PART OF MIDBRAIN:
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Efferent fibres from the
colliculus terminate in the
medial geniculate nucleus of the thalamus
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This nucleus projects to the auditory cortex of the temporal lobe.
INTERNAL STRUCTURE OF MIDBRAIN:
Cross section at the level of superior colliculus:
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Medial geniculate body
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Superior colliculus
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Crus cerebri (cerebral peduncle)
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Red nucleus –Controls arm movement
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Substantia nigra
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Upper midbrain
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Cranial Nerves of Upper Midbrain
ROSTRAL PART OF MIDBRAIN:
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The superior colliculus of the
rostral area of the midbrain is
part of the visual system
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Its main afferents are
corticotectal fibres originating
from the visual cortex of the
occipital lobe and from the
frontal eye field of the frontal
lobe
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These inputs are concerned
with controlling movements of the eyes.
BLOCKAGE OF CEREBRAL AQUEDUCT:
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Cerebral aqueduct is one of the narrowest parts of ventricular system.
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In congenital hydrocephalus, or tumors of midbrain, aqueduct may be blocked which blocks the
flow of CSF.