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Brainstem (I) 李立仁 副教授 解剖學暨細胞生物學科 [email protected] Brainstem General Arrangement Brainstem (I) Three major functions Conduit function : Ascending/descending fibers and numerous relay nuclei are present in the brainstem. Cranial nerve function : All cranial nerves except the olfactory (I) and optic (II) nerves emerge from the brainstem. Integration function : Sensory, motor information and some visceral activities are regulated in the brainstem. #These functions are not mutually exclusive# Brainstem Brainstem (I) General Arrangement Three major components Nuclear groups : Nuclei of cranial nerves Relay nuclei Long fiber tracts: Sensory (ascending) and motor (descending) fibers Reticular formation : Loosely organized clusters of cells #These structures are somewhat interwoven# General Arrangement Brainstem (I) Three major structures Medulla oblongata (myelencephalon) : Caudal limit : the level of foramen magnum Rostral limit : inferior to the bulge of pons Pons (metencephalon) : Broad budge Rostral limit : inferior to the corpora quadrigemina Midbrain (mesencephalon) : Caudal limit : superior to the bulge of pons Rostral limit : inferior to the pineal body (dorsal) and mammillary body (ventral) General Arrangement Brainstem (I) Three major structures Medulla oblongata : consists ascending/descending fibers, relay nuclei to cerebellum, nuclei of cranial nerves VIII – XII and reticular formation. Pons : consists ascending/descending fibers, relay nuclei to cerebellum, nuclei of cranial nerves V – VII and reticular formation. Midbrain : consists ascending/descending fibers, superior and inferior colliculi (visual and auditory reflexes), red nucleus and substantia nigra (motor functions), periaquductal gray (pain control) and nuclei of cranial nerve III and IV. Brainstem (I) General Arrangement Three major areas Tectum (posterior to the ventricular space, midbrain only) consists superior and inferior colliculi (corpora quadrigemina) Tegmentum (anterior to the ventricular space) consists reticular formation, cranial nerve nuclei and tracts, ascending and some descending pathways Appended structures (appended to the anterior surface) consists descending fibers from the cerebral cortex: cerebral peduncles, basal pons and pyramids of the medulla. Brainstem (I) Medulla Oblongata Ventral surface of medulla oblongata Anterior medium sulcus Medullary pyramids - bounded by the anterolateral sulcus - descending fibers from the cerebral cortex to lateral (crossing at pyramidal decussation) and anterior (crossing before teminatation) corticospinal tracts - descending corticobulbar fibers to cranial nerve nuclei Brainstem (I) Medulla Oblongata Ventral surface of medulla oblongata Olive : at level of middle medulla - lateral to anterolateral sulcus - roolets of hypoglossal (XII) nerve exit between pyramids and olives in the anterolateral sulcus - rootlets of accessory (XI), vagus (X), glossopharyngeal (IX) nerves exit lateral to the olives Brainstem (I) Medulla Oblongata Dorsal surface of medulla oblongata Sulci : posterior median sulcus and posterolateral sulcus Fasciculi : fasciculi gracilis and cuneatus Protuberances : Clava (nuclei gracilis), cuneate tubercles (nuclei cuneatus) Tuberculum cinereum (spinal nucleus of trigeminial nerve) Brainstem (I) Medulla Oblongata Fourth ventricle : Floor (rhomboid fossa) : - obex ( ) - posterior median sulcus - hypoglossal trigone - vagal trigone - area postrema ( ) : rostral to the obex, lacking BBB - stria medulares : surface mark of arcuatocerebellar bundle running from the arcuate nucleus to cerebellum Brainstem (I) Medulla Oblongata Fourth ventricle : Roof : - anterior medullary velum - cerebellum - tela choroidea (posterior medullary velum covered by a mesodermal pia meter) anterior medullary velum cerebellum tela choroidea post. medullary velum choroid plexus Brainstem (I) Medulla Oblongata Fourth ventricle : Lateral boundaries : - brachium conjunctivum (sup. cerebellar peduncle) : connects the cerebellum and the midbrain - restiform body (inf. cerebellar peduncle) : connects the cerebellum and medulla - clava and cuneate tubercles Medulla Oblongata Brainstem (I) Fourth ventricle : Openings : - lateral apertures (foramen of Luschka) - median aperture (foramen of Magendie) foramen of Luschka foramen of Magendie Brainstem (I) Medulla Oblongata Internal structures of medulla oblongata Weigert stain for myelin : myelin stained deep blue Brainstem (I) Medulla Oblongata level of pyramidal decussation pyramids pyramidal decussation Brainstem (I) Medulla Oblongata level of pyramidal decussation pyramids and pyramidal decussation (motor) - pyramids contain corticospinal and corticobulbar fibers -- roughly 75-90% of the corticospinal fibers decussate to the opposite side near the caudal border of the medulla form the lateral corticospinal tract --- fibers control the neck and upper extremities cross first (more rostral) --- fibers control the lower extremities cross at lower medulla -- the rest descend ipsilaterlly form the anteral corticospinal tract -- corticobulbar fibers leave the pyramid and terminate on cranial nerve nuclei Brainstem (I) Medulla Oblongata level of pyramidal decussation posterior columns and nuclei spinothalamic tract spinocerebellar tract Brainstem (I) level of pyramidal decussation posterior (dorsal) columns and nuclei - touch and proprioception from the body - afferents from C1 to T6 (upper limb) ascend in the fasciculus cuneatus and project to the nucleus cuneatus - afferents below T6 (lower limb) ascend in the fasciculus gracilis and project to the nucleus gracilis spinothalamic tract (anterolateral fasciculus) - pain and temperature from the body spinocerebellar tract - anterior and posterior - proprioception from the body Medulla Oblongata Brainstem (I) Medulla Oblongata level of pyramidal decussation spinal trigeminal tract and nucleus medial longitudinal fasciculus Brainstem (I) Medulla Oblongata level of pyramidal decussation spinal trigeminal nucleus and tract - caudal part (nucleus caudalis) : pain, temperature from the ipsilateral face - rostral part (nucleus oralis) : tactile from the oral mucosa - intermediate part (nucleus interpolaris) : dental pain medial longitudinal fasciculus - contains ascending/descending fibers derived from various cranial nerve nuclei and reticular formation - displaced laterally as pyramidal fibers decussate Brainstem (I) Medulla Oblongata level of sensory decussation posterior columns and nuclei internal arcuate fibers sensory decussation medial lemniscus Medulla Oblongata Brainstem (I) level of sensory decussation medial lemniscus and lemniscal decussation - primary afferents from C1 to T6 ascend in the fasciculus cuneatus and project to the nucleus cuneatus - primary afferents below T6 ascend in the fasciculus gracilis and project to the nucleus gracilis - axons of 2nd neurons in the posterior column nuclei course ventromedially (as the internal arcuate fibers) and cross to the opposite side (sensory decussation) above the pyramids to form the medial lemniscus. - in the decussation, fibers from nucleus gracilis lie more ventrally C1-T6 Below T6 Brainstem (I) Medulla Oblongata level of sensory decussation accessory (lateral or external) cuneate nucleus Brainstem (I) Medulla Oblongata level of sensory decussation accessory (lateral or external) cuneate nucleus - is part of the spinocerebellar system (not post. column system) -- primary sensory fiber above T1 entering the spinal cord ascend with dorsal column fibers in the fasciculus cuneatus and terminate in the accessory cuneate nucleus -- 2nd neurons send axons as the external arcuate fibers and reach the cerebellum via the restiform body (inferior cerebellar peduncle) - mediates proprioception of neck and upper limb Brainstem (I) Medulla Oblongata level of sensory decussation medial longgitudinal fasciculus arcuate nuclei Brainstem (I) Medulla Oblongata level of sensory decussation arcuate nucleus - anterior to the pyramids - input : controlateral cerebral cortex - output : cerebellum of both sides (via the restiform body) -- ventral external arcuate fibers : along the outer surface of the medulla -- stria medullares : arcuatocerebellar fibers along the midline, cross, and turn laterally course Brainstem (I) Medulla Oblongata level of inferior olive inferior olive complex Brainstem (I) Medulla Oblongata level of inferior olive inferior olive complex - three major groups -- principal olive -- dorsal accessory olive -- medial accessory olive - inputs -- cerebral cortex (via corticospinal tract) -- basal ganglia (via central tegmental tract) -- posterior column nuclei (controlateral side) -- deep cerebellar nuclei (via superior cerebellar peduncle) -- spinal cord - outputs -- controlateral cerebellum (via olivocerebellar tract within inferior cerebellar peduncle) Brainstem (I) Medulla Oblongata level of inferior olive restiform body (inf. cerebellar peduncle) Brainstem (I) level of inferior olive Restiform body (inferior cerebellar peduncle) - ascending fibers : -- olivocerebellar tracts, dorsal spinocerebellar tract, reticulocerebellar tract, cuneocerebellar tract, arcuatocerebellar tract, trigeminocerebellar tract, vestibulocerebellar tract - descending fibers : -- cerebelloolivary tract, cerebelloreticular tract, cerebellovestibular tract, cerebellospinal tracts Medulla Oblongata Brainstem (I) level of inferior olive Medulla Oblongata Pons Brainstem (I) Ventral surface of Pons Pontine protuberance Pontine sulcus : contains basilar artery Cerebellopotine angle : - between pons, medulla and cerebellum - vestibulocochlear (VIII) and facial (VII) nerves Between pons and medulla : abducenes (VI) nerve Rostrolatetral pons : two components of trigeminal (V) nerve (larger sensory and smaller motor) Pons Brainstem (I) Dorsal surface of Pons Floor of the fourth ventricle Midline sulcus Facial colliculi : surface landmark of the genu of the facial nerve and the underlying nucleus of abdecens nerve Pons Brainstem (I) Internal structures of Pons Basilar pons (ventral) - pontine nuclei - fiber tracts Tegmentum (dorsal) - motor nuclei of cranial nerve - sensory nuclei and tracts Pons Brainstem (I) Internal structures of Pons Dorsal tegmentum - medial longitudinal fasciculus - tectospinal tract Basal tegmentum - sensory lemniscus system : medial lemniscus trigeminal tract spinothalamic tract - trapezoid body: transverse fibers from the cochlear nuclei, course through tegmentum and form the lateral lemniscus (specific sensory) - central tegmental tract: fibers from the basal ganglia and midbrain to inferior olive Brainstem (I) level of facial colliculus Pons Brainstem (I) Pons Corticopontocerebellar fibers - relayed in various pontine nuclei on the way to cerebellum (pontocerebellar fibers) via middle cerebellar peduncle - rapid correction of movement inferior and middle cerebellar peduncles Brainstem (I) level of trigeminal nerve Pons Brainstem (I) level of pons-midbrain junction Pons Midbrain Brainstem (I) Dorsal surface of midbrain Corpora quadrigemina - superior colliculus : involved in visual reflex and eye movement - inferior colliculus : relay nucleus in the auditory pathway Trochlear (IV) nerve emerges caudal to inferior colliculi Midbrain Brainstem (I) Ventral surface of midbrain Cerebral peduncles (crus cerebri): - corticofugal fibers (efferents come out of cerebral cortex) to the lower levels - continue into the internal capsule rostrally Interpeduncular fossa : oculomotor (III) nerve emerges Trochlear (IV) nerve appears at the lateral borders of the cerebral peduncles Brainstem (I) Midbrain level of inferior colliculus cerebral aqueduct inferior colliculus superior cerebellar peduncle cerebral peduncle substantia nigra trochlear nucleus Brainstem (I) level of inferior colliculus Nucleus of the inferior colliculus - relay nucleus in the auditory pathway - receives afferents from lateral lemniscus, controlateral inferior colliculus, ispilateral medial geniculate body, primary auditory cortex and cerebellum - send efferents to medial geniculate body, controlateral inferior colliculus and cerebellum - also plays role in sound localization Midbrain Brainstem (I) level of inferior colliculus Brachium conjunctivum (superior cerebellar peduncle) : - fibers form the deep cerebellar nuclei decussate in the midbrain - continue rostrally to the ventrolateral nucleus of the thalamus Cerebral peduncle : corticopotine, corticobulbar and corticospinal (middle 3/5) fibers Midbrain Brainstem (I) level of inferior colliculus Substantia nigra : - pigmented mass between cerebral peduncle and tegmentum -- ventral zona reticulata contains iron compounds (receiving part) -- dorsal zona compacta contains melanin pigment (projecting part) --- cell loss in Parkinson’s disease - dendrites of neurons in the zona compacta arborize in the zona reticulata Midbrain Brainstem (I) Midbrain Substantia nigra : - inputs -- from striatum (GABAergic) : mostly to zona reticulata -- from external part of globus pallidus (GABAergic) : mainly to zona reticulata -- from subthalamic nucleus (Glutamatergic) : mainly to zona reticulata -- from reticular formation : midbrain raphe nuclei (serotonergic) and pedunculopontine nucleus (cholinergic) - outputs -- zona compacta to striatum (caudate and putamen) : nigrostriate fibers (dopaminergic) -- zona compacta to cerebral cortex (limbic system) : nigrocortical tract (dopaminergic) Brainstem (I) Midbrain level of superior colliculus superior colliculus red nucleus Oculomotor nucleus Brainstem (I) Midbrain level of superior colliculus Nucleus of superior colliculus - involved in visual reflex and eye movement - inputs -- from cerebral cortex (visual areas ) : corticocollicular fibers -- from retina -- from spinal cord : ascend with spinothalamic tract -- from inferior colliculus : eye and head are turned toward the source of a sound - outputs : -- to spinal cord -- to cerebellum -- to reticular formation -- to thalamus --- tectothalamic tract to the lateral posterior nucleus, lateral geniculate nucleus and pulvinar of the thalamus, relay stations to the cortex Brainstem (I) Midbrain level of superior colliculus Red nucleus - rich vascularity gives its pinkish hue - involved in motor control - inputs -- from deep cerebellar nuclei -- from motor-related cortical areas (corticorubral fibers) - outputs -- spinal cord (rubrospinal fibers) --- project to the same laminae the corticospinal fibers terminate --- corticorubral fibers and rubrospinal fibers together are the “indirect” or “extrapyramidal” motor system -- cerebellum : via superior cerebellar peduncle -- reticular formation -- inferior olive : via central tegmental tract Brainstem (I) Midbrain level of pretectal nucleus Pretectal nucleus - pupilary light reflex Medial geniculate nucleus (body) - relay in the auditory pathway Lateral geniculate nucleus (body) – relay in the visual pathway Oculomotor nucleus / Edinger-Westphal nucleus Ventral tegmental area – dopaminergic neurons Brainstem (I) level of pretectal nucleus Pretectal nucleus (mesencephalic-diencephalic junction) - pupilary light reflex - input : from retina - output : to E-W nu. Midbrain F E D C B A