MEDULLA OBLONGATA AND PONS form lower part of brainstem (oblongata, pons, midbrain)

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1 MEDULLA OBLONGATA AND PONS form lower part of brainstem (oblongata, pons, midbrain) Medulla oblongata - is uper continuation of the spinal cord Its caudal part is alike the spinal cord, while - its cranial half is split open to form lower part of the floor of the 4 th ventricle External features of oblongata the sulci and funiculi of spinal cord are continuous on the oblongata - anterior median fissure is crossed by pyramidal decussation - marks the point of transition from the spinal cord to the oblongata - anterior funiculi terminate in pyramids of oblongata (contain corticospinal tracts) - anterolateral sulcus 12 th cranial n. emerges from it - olive (elevated by underlying olivary nucleus) lies behind the anterolateral sulcus - lateral funiculus is continuous into the inferior cerebellar peduncle (joins with the cerebellum) - posterolateral sulcus here the 11 th, 10 th and 9 th cranial nerves emerge from the oblongata - gracile and cuneate fasciculi are continuous from the spinal cord to the oblongata and terminate in : - the gracile tubercle elevated by the gracile nucleus - the cuneate tubercle elevated by the cuneate nucleus - posterior median sulcus is continuous from the spinal cord to the oblongata D o r s a l d i s t r i c t of upper half of oblongata forms lower part of floor of the 4 th ventricle The bulbopontine sulcus separates oblongata and pons ventrally the 6 th, the 7 th and the 8 th cranial nerves arise from the bulbopontine sulcus Pons - v e n t r a l s u r f a c e is prominent convex and marked by sulcus basilaris occupied by basilar artery - laterally pons narrows to form middle cerebellar peduncles terminating in the cerebellum - the 5 th cranial nerves emerge from the anterolateral parts of the pons d o r s a l s u r f a c e of pons forms upper part of the floor of the 4 th ventricle the 4 th ventricle - is upper expanded continuation of the central canal of oblongata - pyramidal in shape - laterally projects into the lateral recesses the floor of the 4 th ventricle is named 6

2 the rhomboid fossa this is formed by dorsal surface of the pons and open upper half of the oblongata rhomboid fossa is marked by: - median sulcus - limitans sulci - median eminences on the median eminence some elevations are found: - hypoglossal triangle - elevated by underlying hypoglossal nerve nucleus - vagal triangle (in lower part) elevated by vagus nerve nucleus - facial coliculus (in upper part of the eminence) overlies abducent nerve nucleus and facial nerve fibres - vestibular area and acoustic tubercle are placed in the lateral recess - striae medullares the strips of white matter running from the lateral recesses towards the median sulcus INTERNAL STRUCTURE OF OBLONGATA AND PONS under the floor of the 4 th ventricle the oblongata and pons contain CRANIAL NERVES NUCLEI arranged in four lines in each half medial and lateral lines of motor nuclei and medial and lateral lines of sensory nuclei MOTOR nuclei medial line of motor nuclei: 1. hypoglossal nucleus is located in the oblongata in lower part of rhomboid fossa 2. abducent nucleus in pontine part of rhomboid fossa lateral line of motor nuclei: 1. 1a: nucleus ambiguus - (placed lateral to the hypoglossal) is a motor nucleus of the 9 th, the 10 th and the 11 th nerves 1b: dorsal (PS) nucleus of vagus n. 1c: inferior salivary nucleus parasymp. ncl. of the 9 th n. 2. 2a: facial nerve nucleus (motor) - its fibres loop around the 6 th n. nucleus to form internal genu facial n. 2b: superior salivary nucleus parasympathetic ncl. of facial n. for the nerve supply of salivary glands submandibular and sublingual 2c: lacrimal nucleus parasympathetic ncl. of facial n. for nerve supply of the lacrimal gland 3. masticatory nucleus - motor ncl. of the trigeminal n. SENSORY nuclei are placed laterally to the motor nuclei 1. nucleus of the tractus solitarius is located lateral to the dorsal nucleus of vagus n. receives: - gustatory fibres via the 7 th, the 9 th and the 10 th cranial nerves and - visceral sensory fibres from the 9 th and the 10 th nerves (gastropulmonary system) 7

3 2. trigeminal nerve nucleus long nucleus traversing all the brainstem, extends from the upper cervical segments of spinal cord to the midbrain trigeminal nucleus is subdivided into: the spinal, pontine and mesencephalic parts the axons of trigeminal n. nucleus ascend in the trigeminothalamic tract (trigeminal lemniscus) to reach special thalamic nuclei 3. vestibular nuclei inferior, medial, superior and lateral are contained in the lateral recesses of rhomboid fossa receive afferents from vestibular apparatus and send efferents to the cerebellum and spinal cord -vestibulocerebellar tract, vestibulospinal tract related to maintaining of equilibrium 4. cochlear nuclei ventral and dorsal (ant. and post.) placed lateral to the vestibular nuclei receive acoustic nerve fibres and send efferents to the diencephalon the tract is named the lateral lemniscus (a part of auditory path) Except the cranial nerves nuclei the grey matter of oblongata and pons includes: 1. gracile nucleus and 2. cuneate nucleus - two nuclei receive nerve fibres from the spinobulbar tract fasciculus gracilis and cuneatus - the axons of gracile and cuneate nuclei cells cross median plane as lemniscal decussation and - ascend upwards to form bulbothalamic tract- medial lemniscus terminating in the special thalamic nuclei 3. olivary nucleus (inferior) is a folded mass of grey matter, open medially as hilum axons cross midline to form olivocerebellar tract interconnecting cerebellum with the spinal cord, red nucleus and reticular formation accessory olivary nuclei are found near the hilum of main olivary nucleus 4. reticular formation is represented by a numerous nerve cells located near the midline receiving afferent fibers from and sending efferent fibers to all parts of CNS 5. arcuate nuclei - are placed under the surface of pyramids represent caudally displaced pontine nuclei - send efferents to the cerebellum 6. pontine nuclei - scattered in the ventral part of pons among the corticospinal tract fibres - are relay stations in the cortico-ponto-cerebellar path 8

4 THE WHITE SUBSTANCE OF THE OBLONGATA AND PONS is composed of ascending and descending tracts ASCENDING TRACTS: are coming from the spinal cord: 1. spinothalamic tract (spinal lemniscus) 2. spinotectal tract 3. spinoreticular tract 4. spinocerebellar tracts starting in the oblongata and pons: 5. medial lemniscus (bulbothalamic tract) contains crossed axons of gracile and cuneate nuclei cells ascending to the thalamic nuclei 6. trigeminothalamic tract (trigeminal lemniscus) 7. solitariothalamic tract begins in the ncl. of the tractus solitarius (gustatory pathway) 8. lateral lemniscus starts in the cochlear nuclei (auditory pathway) DESCENDING TRACTS: 1. corticospinal tract 2. corticonuclear tract terminate on the motor nuclei of cranial nerves 3. tectospinal 4. rubrospinal 5. reticulospinal and 6. vestibulospinal tract 7. medial longitudinal fascicle contains ascending and descending fibres connecting some nuclei of cranial nerves, upper cervical segments and midbrain motor fibres of cranial nerves SM (somatomotor) supply voluntary muscles developed from the somites VM ( visceromotor) supply inner organs Special VM supply voluntary muscles developed from the branchial arches General VM = PS supply involuntary muscles and glands sensory fibres of cranial nerves VS (viscerosensory) - sensations from the inner organs Special VS carry special sensations from the inner organs - taste General VS carry general sensations from the inner organs - mainly pain SS (somatosensory) carry informations from skin, mucous membranes, muscles, General SS convey general sensations (temperature, touch, pain ) Special SS convey auditory 9

5 MESENCEPHALON MIDBRAIN - joins pons with the diencephalon and hemispheres - is connected with cerebellum through the superior cerebellar peduncles - v e n t r a l p a r t - crura cerebri emerge from the hemispheres and enter the pons - anteriorly crura are crossed by optic tracts crura cerebri border interpeduncular fossa - interpeduncular perforate substance marked by minute openings (for passage of central branches of circulus arteriosus) - oculomotor nerves emerge on the medial border of crura d o r s a l s u r f a c e tectum - consists of superior colliculi inferior colliculi colliculi are connected with diencephalon (metathalamus) by brachium of superior colliculus brachium of inferior colliculus - trochlear nerves emerge below the inferior colliculi Internal structure of the midbrain on the cross section midbrain consists of: - tectum - tegmentum - crura cerebri TECTUM contains visual and auditory reflex centres superior colliculi contained grey matter is a centre of visual reflexes receives afferent fibres from: retina and visual cortex spinal cord (spinotectal tract) inferior colliculi sends efferent fibres to: the oblongata, pons (motor nuclei of cranial nerves) - tectonuclear tract the spinal cord (motor nuclei in the anterior horns) tectospinal tract pretectal nucleus lies cranial to the superior colliculi is a centre for the light reflex receives afferent fibres: from the retina - optic tract sends efferent fibres: to the Edinger-Wesphal nucleus (parasympathetic nucl. of oculomotor n.) inferior colliculi grey matter of inf. colliculi represents auditory reflex centres 10

6 afferent fibres: lateral lemniscus (auditory pathway) efferent fibres: to the superior colliculi to thespinal cord tectospinal tract to the nuclei of cranial nerves tectonuclear tracts TEGMENTUM cerebral aquaeduct indicates subdivision of the midbrain on the tectum and tegmentum grey matter of tegmentum: 1. red nucleus is an important part of the extrapyramidal system (belongs to the subcortical motor centres) receives afferents from: cerebellum basal nuclei thalamus sends fibres to: spinal cord reticular formation nuclei of the 3 rd, 4 th, 6 th and 11 th cranial nerves thalamus 2. substantia nigra is a lamina of grey matter (contained cells are pigmented) substantia nigra is also a part of extrapyramidal system connected with: cerebral cortex basal nuclei reticular formation 3. nucleus of oculomotor n. motor nucl. lies in the tegmentum at the level of the superior colliculus accessory nucleus of oculomotor n. Edinger-Westphal nucl. is a parasympathetic nucleus supplying fibres for the sphincter pupillae and ciliaris muscles 4. nucleus of trochlear n. is located in tegmentum at the level of the inf. colliculus trochlear nerves emerge on the dorsal side of midbrain 5. mesencephalic part of trigeminal n. nucleus 6. interstitial nucleus lies near the oculomotor nucl. is an reflex centre sending fibres to the medial longitudinal fascicle 11

7 7. reticular formation groups of nerve cells placed near the midline 8. interpeduncular nucleus mediates autonomic response on the olfactory stimuli white matter of tegmentum: 1. medial lemniscus bulbothalamic tract 2. trigeminal lemniscus trigeminothalamic tract 3. lateral lemniscus auditory path 4. spinal lemniscus spinothalamic tract 5. spinotectal tract 6. tectospinal and tectobulbar tracts 7. tracts to and from the cerebellum 8. medial longitudinal fasciculus contains ascending and descending fibres connecting: - interstitial nucleus main reflex centre - vestibular nuclei - nuclei of the 3 rd, 4 th, 6 th, 7 th, 11 th cranial nerves - motoneurons of the spinal cord med. long. fasciculus coordinates movement of eyes and head in response to the stimulation of the vestibular apparatus CRURA CEREBRI consist of white matter fibres descending from the cortex 1. corticospinal fibres 2. corticonuclear fibres 3. frontopontine fibres parietotemporopontine fibres 12

8 CEREBELLUM 1. takes part in maintenance of the muscular tone 2. co-ordinates the various groups of muscles 3. helps to maintain the balance and equilibrium receives impulses mainly from: muscles and joints vestibular apparatus cortex cerebellum is placed in the posterior cranial fossa connected with oblongata, pons and midbrain by the cerebellar peduncles superior, middle, inferior cerebellum has superior and inferior surfaces separated by horizontal fissure superior surface is separated from the occipital lobes by the tentorium cerebelli cerebellum is subdivided into: vermis - central part hemispheres - lateral parts THE SURFACE OF CEREBELLUM is grooved by sulci separating folia, and fissures which separate lobules and lobes lobules and lobes of cerebellum Vermis (lobules) Hemispheres (lobules) LOBES lingula vinculum lingulae anterior lobe (central) lobule ala of central lobule culmen quadrangular lobule Fissura prima declive simplex lobule posterior lobe folium superior semilunar Horizontal fissure tuber inf. semilunar pyramis biventer lobule uvule tonsil nodule flocculus noduloflocular lobe FYLOGENETICAL AND FUNCTIONAL SUBDIVISION OF THE CEREBELLUM archicerebellum - noduloflocular lobe the oldest part vestibular in connections (receives vestibulocerebellar tracts) paleocerebellum anterior lobe phylogenetically following (next) part spinocerebellar in connections (receives spinocerebellar tracts) 13

9 neocerebellum - posterior lobe the youngest part corticocerebellar in connections (receives cortico-ponto-cerebellar tracts) INTERNAL STRUCTURE OF THE CEREBELLUM grey matter cortex and nuclei white matter central core, laminae arbor vitae cerebellar nuclei: - dentate nucleus is a folded plate of grey matter open medially as the hilum - embolifom nucleus elongated nucleus placed near the hilum - globose nuclei small nuclei also placed near the hilum - fastigial nucleus located in vermis (the oldest of all the nuclei) efferent tracts begin in cerebellar nuclei White matter of the cerebellum 1. fibrea propriae (do not leave cerebellum) - commissural fibres - association fibres 2. projection fibres connect the cerebellum with the other parts of CNS (afferent and efferent fibres) AFFERENT FIBRES - TRACTS 1. vestibulocerebellar tract comes from the vestibular nuclei and vestibular apparatus 2. spinocerebellar tract ant. and post.- carries the impulses from the muscles essential for the muscle tonus 3. bulbocerebellar tract from gracile and cuneate nuclei brings the impulses from the exteroreceptors necessary for the muscular coordination 4. nucleocerebellar tract contains fibres from the nuclei of some cranial nerves mainly trigeminal 5. tectocerebellar tract for passage of auditory and visual impulses 6. rubrocerebellar tract is a part of extrapyramidal connections 7. olivocerebellar tract similar than the preceding 8. reticulocerebellar tract 9. (cortico)pontocerebellar tract EFFERENT FIBRES 1. cerebellothalamic tract 2. cerebellorubral tract 3. cerebellovestibular tract 4. cerebelloreticular tract 5. cerebelloolivary tracts all the tracts serve for performing of crebellar functions maintaining of muscle tonus, equilibrium and muscular coordination 14