Mesencephalon (Midbrain) Anatomy PDF

Mesencephalon (Midbrain) Prof. Dr. Selda Önderoğlu Near East University Faculty of medicine Dept. of Anatomy Mesencephalon Shortest part of brain stem About 2 cm RELATIONS: Inf: Pons Post: Cerebellum Sup: Diencephalon External features-Vent...

Mesencephalon (Midbrain) Prof. Dr. Selda Önderoğlu Near East University Faculty of medicine Dept. of Anatomy Mesencephalon Shortest part of brain stem About 2 cm RELATIONS: Inf: Pons Post: Cerebellum Sup: Diencephalon External features-Ventral (ant.) surface Crus cerebri (Cerebral peduncles Interpeduncular fossa (bw.crus cerebri) Oculomotor n. exits from interped. fossa Posterior perforated substance: surface of interpeduncular fossa (post. Cereb. a passes here) Dorsal (post) surface Superior colliculus Inferior colliculus Brachium of superior colliculus Brachium of inferior colliculus Dorsal surface cruciform sulcus Upper limit of sulcus expands into a depression for pineal gland From caudal end of the sulcus; a median frenulum veli is prolonged down over sup medullary velum Lat. to frenulum; trochlear n. emerges Cranial nerves which leave the brain stem at mesencephalon level 1- oculomotor nerve (contains motor and parasympathetic fibers) 2- trochlear nerve (contains motor fibers)  Exit from post. surface of mesencephalon The only nerve Trochlear n. which exit from beain stem’s post surface It Passes ventrally over the lat aspects of cerebral peduncles and Continues its course  Internal structure of mesencephalon Divided into 3 parts Crus cerebri Tegmentum Tectum (lamina tecti) Crus cerebri+ tegmentum: Cerebral peduncle Substantia nigra separates crus cerebri and tegmentum Internal structure of mesencephalon Crus cerebri -2 white matter structures (axons) Formed by fibers emerging from Cerebral Hemispheres Crus cerebri Fibers in crus cerbri From medial to lateral: Frontopontine fibres Corticonuclear fibres Corticospinal fibres Occipitopontine fibres Parietopontine fibres Temporopontine fibres  Tegmentum Between substantia nigra and tectum Cerebral aqueduct (connects 3rd and 4th ventricles) Periaqueductal gray substance (around cerebral aqueduct)  Tectum Posterior to cerebral aqueduct Structures here: Superior colliculus related to auditory pathway Inferior colliculus related to visual pathway Inferior colliculus level Decussation of superior cerebellar peduncle Trochlear nucleus Superior colliculus level Oculomotor nucleus Red nucleus (nucleus ruber) Inferior colliculus Related to Auditory pathway Lateral lemniscus → inferior colliculus → brachium of inferior colliculus → medial geniculate body → auditory cortex Localize the voice Evaluate the frequency of voice Concentrate the attention to a certain voice Motor reflexes related to hearing Substantia nigra Neuron group related Located Bw. crus to basal ganglia cerebri and tegmentum Dark color depend upon to melanin pigment Formed by : Pars compacta (dorsal) Pars reticularis (ventral)  Substantia nigra (connections) Afferents – Caudate nucleus – Putamen – Globus pallidus – Posterior raphe nucl. – Pedunculopontine tegmental nucleus Efferents – Caudate nucleus – Putamen – Thalamus – Superior colliculus – Pedunculopontine tegmental nucleus  Red nucleus (nucleus ruber) Part of reticular formation Dorsomedial to substantia nigra Observed from caudal levels of superior colliculus to caudal levels of diencephalon Parts of red nucleus: Pars parvocellularis (rostral) Pars magnocellularis (caudal)  Connections (red nucleus) Afferents – Cerebellar nuclei – Cerebral cortex (corticorubral fibres) Efferents – Cross mid-line in anterior tegmental decussation – Cerebellum – Brain stem nuclei – Spinal cord (rubrospinal tract); related to flexor muscle tone Interpeduncular nucleus Located at the Interpeduncular fossa (dorsal) At the midline Receive aff fibres from habenular nuclei by fasciculus retroflexus Eff fibers arise as medial forebrain bundle and reach to septal nuclei Superior colliculus (related to visual pathway) Afferents – Retina – Cerebral cortex (corticotectal fibres) – Inferior colliculus – Spinal cord (spinotectal tract) – Substantia nigra Efferents – Brain stem – Spinal cord – Thalamus – Nucleus parabigeminalis – Reticular nuclei – Pretectum – Retina Posterior commissure Contains fibers that cross and course to other cerebral hemisphere ( one of the commissural pathways) Also Has nucleus of post commissure Fibres passing from post comm originate from: pretectal nuclei, nucleus of post com, Cajal’s interstitial nucleus, sup colliculus, dorsal thalamic nuclei  Pretectal area at the level of posterior commissure Contains Pretectal nuclei (related with visual pathways)  Reticular nuclei Nucleus cuneiformis Nucleus subcuneiformis Nucleus tegmenti pedunculopontinus Raphe nuclei: Nucleus raphes dorsalis Cranial n. nuclei Parasympathetic nucleus of oculomotor n. (Edinger- Westphal) Motor nucleus of oculomotor n. Motor nucleus of trochlear n. Mesencephalic nucleus of trigeminal n. (GSA)  Nuclei of oculomotor n. (cran. N. III) at the level of superior colliculus Ventral to periaqueductal grey matter Dorsal to MLF 2 nuclei: 1- P-symp: Edinger-Westphal nucleus: Pregang parasymph fibres from E.W. nucleus → ciliary gang → postgang parasymph fibres from ciliary gang → i,nnervate m. sphincter pupilla, m. Ciliaris 2- Motor nucl.of III: Rectus sup, inf, medialis, obl inf, levator palpebra sup  Motor nucleus of trochlear n. (cran. N. IV) Axons decussate in sup medullary velum motor fibres to Obliquus sup m. (eye)  Mesencephalic nucleus of V Extends from upper levels of pons to sup colliculus level Aff. fibres of this nucleus carry proprioceptive impulses from teeth, periodontium, hard palate, mm. of mastication, joint capsules Cranial nerves and Related to mm. of eye 1-oculomotor (III) 2- trochlear ( IV) 3- abducent (VI) LR6 SO4 REST3  References 1- Clinically Oriented Anatomy, Keith L. Moore 2-Snell’s Anatomy, Richard Snell 3-Atlas of Human Anatomy, Frank H. Netter 4- Snell's Clinical Neuroanatomy,Book by Ryan Splittgerber 5- Gray's Anatomy for Students, Textbook by Adam W. M. Mitchell and Wayne Vogl 6- Gray's Atlas of Anatomy,Textbook by