Pons Anatomy - SO-NEUMED_PONS_18-19.PPT PDF

PONS (BRIDGE) Prof.Dr. Selda Önderoğlu Faculty of Medicine Department of Anatomy 1- Prosencephalon (Fore Brain) Telencephalon Diencephalon 2- Mesencephalon Mid Brain 3- Rhombencephalon (Hind Brain) -Metencephalon -Pons -Cerebellum - Myelencephalon Medulla Oblongata 4- Spi...

PONS (BRIDGE) Prof.Dr. Selda Önderoğlu Faculty of Medicine Department of Anatomy 1- Prosencephalon (Fore Brain) Telencephalon Diencephalon 2- Mesencephalon Mid Brain 3- Rhombencephalon (Hind Brain) -Metencephalon -Pons -Cerebellum - Myelencephalon Medulla Oblongata 4- Spinal cord Pons- L=about 2.5 cm Relations: Posterior, fourth ventricle, cerebellum Anterior, Clivus (occip. Bone) Clivus pontine cistern Anterior - Transverse Surface- pontine fibers features - Middle - 5th cranial cerebellar nerve peduncle (motor root, 6 sensory root) 7 8 - Pyramidal eminence Basilar sulcus (basilar artery) Basilar artery Coursing in the basilar sulcus  * * * * Pyramidal eminence  Transverse pontine fibres * Posterior Surface -Superior (anterior) medullary vellum, apex - is Hidden by (thin white cerebellum membrane) -Middle -Superior cerebellar cerebellar peduncle (bw pons-cerebel.) peduncle (bw.mesenc.-cerebell.) -Inferior cerebellar peduncle (bw.medulla- Posterior Surface is the upper triangle of rhomboid fossa - Median sulcus -Vestibular area - Medial eminence -Lateral recess - Sulcus limitans -Foramen Luschka (lateral - Facial colliculus foramen) - Auditory tubercle (dorsal cochlear nucleus & a part of cochlear nerve) Sulcus limitans Separates the medially located motor nuclei from the laterally located sensory nuclei. Facial colliculus (formed by abducent nucl+facial n. Fibers coursing around it) ** Vestibular area and nuclei pons medulla Foramen Luschka (lateral foramen) Connects 4th ventricle to the Subarachnoid space (Thus CSF passes from 4th ventricle to the subarachnoid space)  Auditory tubercle and dorsal cochlear nucleus * * Internal Structure 1- Pons proper (ventral pons, basilar portion) 2- Pontine tegmentum (dorsal pons) Two portions are separated by the trapezoid body of the auditory pathway Ventral Pons = (Pons proper, basilar portion) -Has Similar arrangement at all levels -Acts as a relay (synaptic) station for motor fibers from the cerebrum to the cerebellum - Consists: Transverse fibers Longitudinal fibers Pontine nuclei Pontine nuclei Longitudinal fibers: formed by - Corticospinal fibers - Corticobulbar (Corticonuclear) fibers - Corticopontine fibers Corticospinal tract Corticobulbar fibers: (corticonuclear fibers) Some Fibers leave the cortico- spinal tract and synapse at cranial nerve nuclei at pons So:Descends from cortex to the contralateral cranial nerve nuclei Corticopontine fibers (Fronto-temporo-parieto-occipito pontine fibers) Arise from the frontal, temporal, parietal and occipital cortex, descend& without crossing (ipsilateral) and terminate upon the pontine nuclei (*). Pontine nuclei give rise (axons) to transvers fibers of pons which cross the Midline (pass to contralateral Side) and enter cerebellum as the: middle cerebellar peduncle * (=cortico-ponto-cerebellar fibers). Dorsal Part (= pontine tegmentum) -Has differences in its lower and upper portions Tegmentum contains: - Cranial nerve nuclei Pons Upper - Ascending, level descending tracts - Reticular formation Pons Lower level Upper section Lower section Tracts of dorsal portion: -Medial lemniscus ( Continuation of fasciculus gracilis and cuneatus) - Lateral lemniscus (upper pons) - MLF (medial longitudinal fasciculus) - Tectospinal and spinotectal tracts - Anterior and lateral spinothalamic tracts - Anterior spinocerebellar tract - Spinoreticular and reticulospinal fibers - Vestibulospinal tract - Rubrospinal and rubroreticular tracts -Descending autonomic pathways - Central tegmental tract Cranial nerve nuclei in PONS: - 5 (trigeminal n.): -Lower part of mesencephalic nucleus (upper pons) -Upper part of spinal nucleus (lower pons) -Sensory principle nucleus - Motor nucleus (upper pons) -6 (abducens n.): - Motor nucleus (lower pons) - 7 (facial n.): -Superior salivatory nucleus (lower pons) -Motor nucleus (lower pons) - Solitary nucleus (lower pons) -8 (vestibulocochlear n.): -Sup. and lat. vestibular nuclei (lower pons) -Ant.(ventral) and post.(dorsal) cochlear nuclei (lower pons) Upper Tegmentum: Section at the level of the trigeminal nerve 1- The sensory principle nucleus of trigeminal nerve 2- The motor nucleus of trigeminal nerve 3- Nucleus of lateral 5- nucleus of trapezoid lemniscus body 4- Reticulotegmental 6- The mesencephalic nucleus nucleus (pontine reticular formation) of trigeminal nerve Principle Sensory Nucleus of Trigeminal Nerve - Takes the tactile(touch) and pressure sense impulses from head and neck * The Mesencephalic Nucleus of Trigeminal Nerve Begins to appear at uppermost levels of the pons Takes the proprioception sense of head and neck * Nucleus of Lateral Lemniscus Nucl related to auditory pathway Becomes apparent in the uppermost pons Located on the medial aspect of the lateral lemniscus * * Reticular nuclei (pontine reticular formation) 1- Nucleus reticularis pontis caudalis 2- Nucleus reticularis pontis oralis 3- Reticulo-tegmental nucleus 4- Superior central nucleus 5- Raphe nuclei: Scattered through the median parts of medulla and pons 6- Nucleus pigmentosus (locus ceruleus) Reticular nuclei (pontine reticular formation) N. Centralis superior N. Retic. pontis Raphe nuclei oralis N. Retic. pontis caudalis Reticulo tegmental n. LOCUS CAERULEUS -Collection of pigmented cells near the periventricular gray of upper part of fourth ventricule. - Secretes norepinephrine (NA) -Important noradrenergic cell groups of the brain stem. Lower part of the pontine tegmentum: Level of the facial colliculus 1- spinal nucleus of the trigeminal nerve 2- Motor nucleus of abducens nerve 3- motor nucleus of facial nerve 4- Superior salivatory nucleus of facial nerve 5- Solitary tract and nucleus of facial nerve 6- Vestibular nuclei or vestibular nuclear complex 7- Cochlear nucleus Vestibular nuclei (vestibular nuclear complex) - Located deep to the vestibular area Superior - Vestibular nuclear complex: Medial, lateral, superior, inferior vestibular nuclei Lateral - Afferent fibers of these nuclei come by vestibular nerve from inner ear - Efferent fibers from vestibular nuclei course ipsilaterally ( on the same side) to the: cerebellum, Medial Longitudinal fasciculus (MLF), spinal cord, lateral lemniscus Cochlear Nuclei: - Dorsal cochlear nucleus (deep the auditory tubercle) -Ventral cochlear nucleus Nuclei of auditory pathway - Nucleus of trapezoid body (scattered through the fibers of trapezoid body) - Superior olivary nucleus: (lower pons) Motor nucleus of facial nerve: Facial colliculus Superior salivatory nucleus: Parasympathetic nucleus of facial nerve Sends efferent fibers to the salivary and lacrimal glands Solitary tract and nucleus of facial nerve:taste 7 9 10 Motor nucleus of abducens nerve: Lies dorsal to the tegmentum Fibers pass ventral and downwards Leaves the brain stem from the pontabulbar sulcus The spinal nucleus of the trigeminal tract: Continues upwards through the lower part of the pons At higher levels continuous with the principle sensory nucleus of trigeminal nerve Medial longitudinal fasciculus: Retains its place near the midline at all levels of the pontine tegmentum MLF Central tegmental tract: - Includes descending and ascending fibers - Connecting the reticular nuclei in the other parts of the brainstem to each other. Located in the reticular formation MEDIAL INFERIOR PONTINE SYNDROME (MIDDLE ALTERNATING HEMIPLEGIA) Paramedian br. of basilar a. and occlusion of its br. in lower pons - contralateral spastic paralysis--- corticospinal tract - ipsilateral internal strabismus --- (6 th CN)---lateral rectus m. - contralateral positional deficits --- medial lemniscus - ataxic gait --- cerebellar component --- pontine nuclei Normal pain temperature perception Normal 5th cranial components LATERAL INFERIOR PONTINE SYNDROME Area supplied by ant. inf. cerebellar artery - Dizziness (vertigo)/nausea/nystagmus--- vestibular n. and nucleus - Ipsilateral tinnitus/loss of hearing --- cochlear n. and nucleus -Ipsilateral paralysis of upper and lower face mm --- facial nerve - Ipsilateral loss of sensation on face --- trigeminal nucleus - contralateral loss of pain and temperature --- spinothalamic tract - difficulty of walking --- middle cerebellar peduncle