Midterm Neuroscience PDF

 EXTERNAL FEATURES OF BRAIN STEM Dr. Ramadan El Gharbawy Professor of Anatomy & Embryology, Beirut Arab University, Lebanon Consultant of General surgery, Egypt Ex-scholar at Emory, USA  OUTLINE & OBJECTIVES Items Objectives 1. External...

 EXTERNAL FEATURES OF BRAIN STEM Dr. Ramadan El Gharbawy Professor of Anatomy & Embryology, Beirut Arab University, Lebanon Consultant of General surgery, Egypt Ex-scholar at Emory, USA  OUTLINE & OBJECTIVES Items Objectives 1. External features of 1. Define the external the anterior surface of features that brain stem distinguish each of the 2. External features of medulla oblongata, the lateral surface of pons and midbrain. brain stem 2. State the cranial 3. External features of nerves attached to the posterior surface each of the medulla of brain stem oblongata, pons and midbrain. Medulla oblongata 1. Anterior median fissure EXTERNAL FEATURES OF 2. Pyramid 3. Pyramidal decussation ATERIOR SURFACE 4. Anterolateral sulcus (preolivary) XII. Hypoglossal nerve 5. Olive 6. Postolivary sulcus IX. Glossopharyngeal nerve X. Vagus nerve Midbrain 10 III XI. Accessory nerve IV Pons 7. Basis pontis V 7 7 V 9 8. Middle cerebellar peduncle VI Pons 9. Basillar sulcus 8 VIII 8 VII V. Trigeminal nerve VI. Abducent nerve IX 5 2 XII X VII. Facial nerve 1 XI VIII. Vestibulo-cochlear nerve Medulla oblongata 4 Midbrain 6 10. Crus cerebri 3 III. Oculomotor nerve IV. Trochlear nerve Brain stem- anterior view  Spinal cord V. Trigeminal 1. Anterolateral sulcus VII. Facial EXTERNAL FEATURES OF VIII. Vestibulo- 2. 3. Anterior motor roots Posterolateral sulcus cochlear LATERAL SURFACE 4. Posterior sensory Midbrain root 14. Lateral lemniscus 5. Spinal tract and IV. Trochlear nerve 23 nucleus of trigeminal 15. Inferior colliculus XI. Spinal accessory 16. Inferior brachium 18 21 22 20 Medulla oblongata 17. Superior colliculus 17 16 6. Olive 18. Superior brachium 7. Inferior cerebellar 19. Superior cerebellar 15 peduncle peduncle IV 8. Tuberculum cinerium Diencephalon 14 19 V IX. Glossopharynge 20. Medial geniculate al nerve body 19 X. Vagus nerve 21. Lateral geniculate 13 XI. Cranial body accessory VIII VII 22. Pineal gland 7 XII. Hypoglossal 23. pulvinar IX nerve X 12 XI 6 XII 9. Fasciculus gracilis 10. Gracile tubercle 10 8 11. Fasciculus cuneatus 11 12. Cuneate tubercle 5 1 9 2 Pons 13. Middle cerebellar 4 XI Posterolateral view 3 peduncle Closed medulla EXTERNAL FEATURES OF POSTERIOR 1. Posterior median sulcus 2. Fasciculus gracilis SURFACE 3. Gracile nucleus 4. Postero-intermediate sulcus 5. Fasciculus cuneatus 6. Cuneate nucleus 7. Posterolateral sulcus Open medulla 18 8. Medullary striae 9. Median sulcus B 19 10. Inferior fovea 20 11. Hypoglossal trigone A 12. Vagal trigone 13. Vestibular trigone 21 Pons 9 15 14. Superior fovea 23 15. Medial eminence 22 16 14 16. Facial colliculus 17 17. Superior vestibular area 8 11 13 Midbrain 9 18. Superior colliculus 12 10 19. Inferior colliculus 6 20. Trochlear nerve 3 Cerebellar peduncles 21. Superior 4 22. Inferior 7 2 23. Middle 5 1 A. Superior medullary velum B. Frenulum of superior medullary velum Posterior view  CRANIAL NERVE SUPERFICIAL ATTACHMENTS Midbrain Medulla oblongata CN III “Oculomotor” CN IX “Glossopharyngeal” CN IV “Trochlear” CN X “Vagus” Pons CN XI “Accessory” CN V “ Trigeminal” CN XII “Hypoglossal” Inferior pontine sulcus CN VI “Abducent” CN VII “ Facial” CN VIII “Vestibulocochlear” THANK YOU  FUNCTIONAL CLASSIFICATION OF CRANIAL NERVE FIBERS AND NUCLEI Dr. Ramadan El Gharbawy Professor of Anatomy and Embryology, Beirut Arab University, Lebanon, Alexandria University (en secondment), Consultant of General surgery, Egypt, Ex-scholar at Emory, USA  OUTLINE & OBJECTIVES Items 1. Mention the functional 1. Functional types of types of the fibers and cranial nerves’ fibers. nuclei of the cranial 2. Functional types of nerves. cranial nerves’ nuclei. 2. List the nuclei of the 3. Cranial nerves’ nuclei in cranial nerves and the brain stem. functional columns in the 4. Functional columns of the brain stem. brain stem. Objectives The student should be able to:  FUNCTIONAL TYPES OF CRANIAL NERVE FIBERS Cranial nerve fibers that supply muscles or exocrine glands are known as motor or Efferent and are designated by the letter “E”. 1. Cranial nerve fibers that supply muscles derived from somites e.g., the extraocular and most of the tongue muscles are called Somatic Efferent and are designated by the letters “SE.” 2. Cranial nerve fibers that supply muscles derived from branchial arches e.g., masticatory and facial experssion muscles are called Special Visceral Efferent and are designated by the letters “SVE”. 3. Cranial nerve fibers that supply smooth muscles or exocrine glands i.e., derivatives of visceral layer of lateral plate mesoderm are called General Visceral and are designated by the letters “GVE”.  FUNCTIONAL TYPES OF CRANIAL NERVE FIBERS Cranial nerve fibers that convey sensations to the brain are known as sensory or Afferent and are designated by the letter “A” 1. Cranial nerve fibers that convey general interoceptive sensation e.g., pain, temperature and mechanical sensation from viscera are called General Visceral Afferent and are designated by the letters “GVA”. 2. Cranial nerve fibers that convey special interoceptive sensation e.g., taste and smell sensations are called Special Visceral Afferent and are designated by the letters “SVA”. 3. Cranial nerve fibers that convey exteroceptive (pain, temperature, pressure, and discriminative tactile sensation)or proprioceptive (position, muscle and joint senses) sensations are called General Somatic Afferent and are designated by the letters “GSA”. 4. Cranial nerve fibers that convey visual, auditory, and equilibrium sensations are called Special Somatic Afferents and are designated by the letters “SSA”.  FUNCTIONAL TYPES OF CRANIAL NERVE NUCLEI Cranial nerve nuclei are – likewise cranial nerve fibers- classified into motor (Efferent) and sensory (Afferent). The Efferent nuclei are either: 1. Somatic Efferent (SE), 2. Special Visceral Efferent (SVE), or 3. General Visceral Efferent (GVE) The afferent nuclei are classified into: 1. General Visceral Afferent (GVA), 2. Special Visceral Afferent (SVA), 3. General Somatic Afferent (GSA), or 4. Special Somatic Afferent (SSA) Oculomotor nerve CRANIAL NERVE NUCLEI IN 1. Oculomotor nucleus (SE) 2. Edinger-westphal nucleus (GVE) THE BRAIN STEM 2 Troclear nerve 1 3. Trochlear nucleus (SE) Trigeminal nerve 4. Motor nucleus of trigeminal (SVE) 3 5. Main sensory nucleus (GSA) 7 6. Spinal nucleus of trigeminal (GSA) 4 12 5 7. Mesencephalic nucleus (GSA) Abducent nerve 8 9 8. Abducent nucleus (SE) 13 14 10 Facial nerve 15 9. Motor nucleus of facial nerve 11 (SVE) 6 16 10. Superior salivatory nucleus (GVE) 17 11. Solitary nucleus (GVA, SVA) 18 6. Spinal nucleus of trigeminal (GSA) Brain stem- posterior phantom view Vestibulocochlear nerve 12. Superior, lateral, inferior and medial CRANIAL NERVE NUCLEI vestibular nuclei (SSA) 13. Ventral and dorsal cochlear nuclei (SSA) IN THE BRAIN STEM Glossopharyngeal nerve 14. Inferior salivatory nucleus (GVE) 2 15. Nucleus ambiguous (SVE) 1 11. Nucleus solitarius (GVA, SVA) 3 8 7 6. Spinal nucleus of trigeminal (GSA) Vagus nerve 45 12 16. Dorsal nucleus of vagus (GVE) 13 15. Nucleus ambiguous (SVE) 9 10 11 11. Nucleus solitarius (GVA, SVA) 6. Spinal nucleus of trigeminal (GSA) 16 14 Accessory nerve 15 15. Nucleus ambiguous for cranial 17 accessory (SVE) 6 18. Accessory nucleus in spinal cord (SE) 15 Hypoglossal nerve 18 17. Hypoglossal nucleus (SE) Medial dissection FUNCTIONAL COLUMNS OF THE BRAIN STEM The motor or Efferent nuclei form three discontinuous columns: 1. SE column includes the oculomotor, trochlear, abducent, and hypoglossal nuclei. 2. SVE column includes the trigeminal motor nucleus, facial nucleus, and nucleus ambiguous. 3. GVE column includes Edinger-westphal nucleus, superior and inferior salivatory nuclei, and dorsal nucleus of vagus. FUNCTIONAL COLUMNS OF THE BRAIN STEM The sensory or Afferent nuclei form four discontinuous columns: 1. GVA column includes nucleus solitarius. 2. SVA column includes nucleus solitarius. 3. GSA column includes the mesencephalic nucleus, main sensory and spinal nuclei of trigeminal. 4. SSA column includes the vestibular and cochlear nuclei  FUNCTIONAL COLUMNS 1. Oculomotor nucleus (SE) 2. Edinger-westphal nucleus (GVE) OF THE BRAIN STEM 3. Trochlear nucleus (SE).1 2 7 4. Motor nucleus of trigeminal (SVE) 5. Main sensory nucleus (GSA) 3 Midbrain 6. Spinal nucleus of trigeminal (GSA) 7. Mesencephalic nucleus (GSA) 4 8. Abducent nucleus (SE) 5 9. Motor nucleus of facial nerve (SVE) 10. Superior salivatory nucleus (GVE) Pons 9 10 11. Solitary nucleus (GVA, SVA) 8 12. Superior, lateral, inferior and medial 12 vestibular nuclei (SSA) 14 11 13. Ventral and dorsal cochlear nuclei 13 (SSA) 14. Inferior salivatory nucleus (GVE) Medulla oblongata 15. Nucleus ambiguous (SVE) 17 15 16 16. Dorsal nucleus of vagus (GVE) 6 17. Hypoglossal nucleus (SE) SE SVE GVE GVA SVAGSA SSA Schema THANK YOU  MEDULLA OBLONGATA Dr. Ramadan El Gharbawy Professor of Anatomy & Embryology, Beirut Arab University, Lebanon Consultant of General Surgery, Egypt Ex-scholar at Emory, USA  OUTLINE AND OBJECTIVES Subtopics Objectives Revisit of the external features of The student should be able to: medulla 1. Describe the external features of Internal structure of medulla: medulla oblongata. 1. A transverse section through the 2. Describe the topography of the medulla oblongata at the level of medulla oblongata in the motor decussation posterior cranial fossa. 2. A transverse section through the 3. Mention the salient feature of the medulla oblongata at the level of transverse section of medulla at the sensory decussation these 3 levels. 3. A transverse section through the medulla at the level of olives  MEDULLA- SHAPE, SITE AND CAVITY The medulla oblongata is conical in shape, its broad extremity being directed superiorly. The medulla oblongata connects the pons superiorly with the spinal cord inferiorly. It joins the pons at the inferior pontine sulcus. The junction of the medulla and spinal cord is at the inferior level of foramen magnum. The central canal continues upward into its lower half; in the upper half of the medulla, it expands as the cavity of the fourth ventricle. Posterior view  MEDULLA- ANTERIOR SURFACE The anterior surface of the medulla shows: 1. The anterior median fissure which is continuous inferiorly with the anterior median fissure of the spinal cord. 2. On each side of the median fissure there Inferior is a pyramid composed of the Pons pontine corticospinal fibers. sulcus 3. Inferiorly, the majority of the descending fibers in the pyramids cross over to the opposite side, forming the decussation Anterior Pyramid of the pyramids. median 4. The few anterior external arcuate fibers fissure Medulla emerge from the anterior median fissure oblongata above the decussation and pass laterally Pyramidal over the surface of the medulla decussation oblongata to enter the cerebellum. Spinal cord MEDULLA- LATERAL SURFACE Posterolateral to the pyramids are the olives, which are oval elevations produced by the underlying inferior olivary nuclei. In the groove between the pyramid and the olive (preolivary sulcus) emerge the Postolivary rootlets of the hypoglossal nerve. sulcus Inferior Posterior to the olives are the inferior cerebellar cerebellar peduncles,which connect the peduncle Preolivary medulla to the cerebellum. Glosso- sulcus In the groove between the olive and the pharyngeal nerve Hypoglossal inferior cerebellar peduncle (postolivary Vagus nerve nerve sulcus) emerge the roots of the Cranial glossopharyngeal and vagus nerves and accessory the cranial roots of the accessory nerve. nerve  MEDULLA- POSTERIOR SURFACE The posterior surface of the superior half of the medulla oblongata forms the Fourth ventricle lower part of the floor of the fourth ventricle. The posterior surface of the inferior half of the medulla is continuous with the posterior aspect of the spinal cord and possesses a posterior median sulcus. Cuneate On each side of the median sulcus, there tubercle is an elongated swelling, the gracile tubercle, produced by the underlying Gracile gracile nucleus. tubercle Lateral to the gracile tubercle is a similar Posterior median sulcus swelling, the cuneate tubercle, produced by the underlying cuneate nucleus. Spinal cord  Anterior median fissure Pyramid MEDULLA Motor Ventral horn OBLONGATA AT THE (pyramidal) decussation (Medial motor cell column) LEVEL OF MOTOR DECUSSATION Nucleus of the Accessory nerve The ventral horns are Ventral spinocerebellar separated from the Lateral Corticospinal tract central grey matter tract Dorsal Spinocerebellar by the corticospinal Spinal nucleus tract fibers, which cross in of trigeminal the motor Spinal tract (pyramidal) of trigeminal Central grey decussation to reach Fasciculus and the contralateral nucleus cuneatus lateral funiculi. Central canal Fasciculus and nucleus gracilis Posterior median sulcus A TS OF THE MEDULLA AT THE Anterior median fissure Pyramid LEVEL OF SENSORY Olivary complex DECUSSATION Anterior external arcuate fibers The pyramids form two large ventral bundles flanking the Medial accessory anterior median fissure. olivary nucleus Decussation of lemnisci The nuclei gracilis and cuneatus are well developed on the dorsal Reticular medullary aspect and retain formation Ventral spinocerebellar tract continuity with the central grey matter. Dorsal spinocerebellar tract Axons of the gracile and cuneate nuclei (internal arcuate fibres) Spinal nucleus of trigeminal pass ventrally in between the central grey matter and the spinal Spinal tract of trigeminal tract of the trigeminal nerve. The fibers then decussate in the Nucleus midline, as the sensory cuneatus decussation, and thereafter form the medial lemniscus, which Fasciculus Internal arcuate fibers ascends to the thalamus. The cuneatus decussation of these internal Central grey matter arcuate fibres is located dorsal to Dorsal intermediate sulcus the pyramids and ventral to the Nucleus gracilis central grey matter. Fasciculus gcilrais Posterior median sulcus  Arcuate nucleus anterior external arcuate fibers A TS OF MEDULLA AT THE Pyramid Preolivary sulcus Principal CAUDAL END OF THE 4TH olivary Fibers of hypoglossal nerve VENTRICLE (AT OLIVE) nucleus Medial accessory olivary The inferior olivary complex nucleus (dorsal accessory, medial Dorsal Olivocerebellar fibers accessory, principal nuclei) is accessory olivary an irregularly crenated mass nucleus of grey matter with a medially directed hilum, through which numerous fibers enter and leave the nucleus. It is separated from the pyramid by the preolivary sulcus and emerging Inferior cere- hypoglossal nerve fibers. Hypoglossal nucleus bellar peduncle  Arcuate nucleus A TS OF MEDULLA AT THE Pyramid Anterior external arcuate fibers CAUDAL END OF THE 4TH Principal olivary Fibers of hypoglossal VENTRICLE (AT OLIVE) nucleus nerve Medial The ventricular floor contains accessory , from medial to lateral, the olivary nucleus hypoglossal nucleus, dorsal Dorsal accessory Olivocerebellar motor nucleus of the vagus, olivary nucleus fibers nucleus solitarius, and the Medial caudal ends of the inferior lemniscus and medial vestibular nuclei. Tectospinal The rostral portion of the tract tractus and nucleus solitarius (the gustatory nucleus) Medial receives taste fibers from longitudinal fasciculus cranial nerves VII, IX and X; its caudal portion (the Solitary cardiorespiratory nucleus) nucleus receives general visceral and tract afferent fibers from these same nerves and subserves Inferior cere- the reflex control of bellar peduncle cardiovascular, respiratory Floor of fourth ventricle Inferior vestibular nucleus and cardiac functions. Hypoglossal nucleus Dorsal vagal Medial vestibular nucleus nucleus  Arcuate nucleus Pyramid Anterior external arcuate fibers A TS OF MEDULLA Principal olivary AT THE CAUDAL nucleus Fibers of hypoglossal nerve Medial END OF THE 4TH accessory olivary VENTRICLE (AT nucleus Reticular OLIVE) Medial lemniscus formation Dorsal accessory Olivocerebellar olivary nucleus fibers Spinal nucleus The medial Anterior spinocerebellar of trigeminal longitudinal Tectospinal nerve Spinal tract fasciculus is near the tract of trigeminal midline ventral to the Medial nerve longitudinal hypoglossal nucleus. fasciculus The reticular Solitary nucleus formation lies and tract centrally in the Dorsal spino- cerebellar tract ventrolateral medulla. Inferior cere- bellar peduncle Inferior vestibular nucleus Floor of fourth ventricle Hypoglossal nucleus Dorsal vagal Medial vestibular nucleus nucleus THANK YOU PONS Dr. Ramadan El Gharbawy Professor of Anatomy & Embryology, Beirut Arab University, Lebanon Consultant of General Surgery, Egypt Ex-scholar at Emory, USA  OUTLINE AND OBJECTIVES Subtopics Objectives Revisit of the external features of The student should be able to: pons 1. Recall the external features of Internal structure of pons: pons. 1. A transverse section of the pons 2. Describe the transverse section of at the level of the facial colliculus pons at these 2 levels. 2. A transverse section of the pons at the level of the principal sensory and motor nuclei of the trigeminal nerve  PONS- SITE AND EXTERNAL Midbrain FEATURES OF ANTERIOR SURFACE The pons is anterior to the cerebellum and Basilar sulcus connects the medulla oblongata to the Basis pontis midbrain. Trigeminal It is about 2.5 cm long. nerve The anterior surface is convex from side to Middle side and shows many transverse fibers that cerebellar converge on each side to form the middle peduncle cerebellar peduncle. Abducent A shallow groove in the midline, the basilar nerve groove, lodges the basilar artery. Vestibulocochlear On the anterolateral surface of the pons, nerve the trigeminal nerve emerges on each side. In the groove between the pons and the medulla oblongata, from medial to lateral, Facial nerve the abducens, facial, and vestibulocochlear nerves emerge. Medulla oblongata  PONS- POSTERIOR SURFACE The posterior surface of pons is triangular in shape and it forms the upper half of the floor Superior of the fourth ventricle. cerebellar Midbrain It is limited laterally by the superior cerebellar peduncle peduncles and is divided into symmetrical Median sulcus Medial Locus halves by a median sulcus. eminence coeruleus Lateral to the median sulcus is an elongated Facial elevation, the medial eminence, which is colliculus bounded laterally by a sulcus, the sulcus limitans (superior fovea). Middle crebellar The inferior end of the medial eminence is slightly expanded to form the facial colliculus. peduncle The floor of the superior part of the sulcus Area limitans is bluish-gray in color and is called the vestibuli substantia ferruginea (locus coeruleus). Lateral to the sulcus limitans is the area vestibuli produced by the underlying vestibular Sulcus limitans nuclei. Medulla oblongata  The basilar part of the pons contains small A TS OF THE PONS AT THE LEVEL OF THE FACIAL COLLICULUS pontine nuclei. The corticopontine fibers Descending tracts Pontine nuclei terminate on the cells of Corticospinal, Transverse fibers of pons these pontine nuclei corticonuclear, corticopontine and their axons- the transverse fibers of pons- cross the midline and intersect the corticospinal and corticonuclear tracts, breaking them up into small bundles. The transverse fibers of Middle pons enter the middle cerebellar cerebellar peduncle and peduncle are distributed to the cerebellar hemisphere. This connection forms the main pathway linking the cerebral cortex to the cerebellum. Fourth ventricle  The medial lemniscus is situated transversely in the most anterior part of the A TS OF THE PONS AT THE LEVEL OF THE FACIAL COLLICULUS tegmentum and is accompanied by the spinal Descending tracts Pontine nuclei Medial lemniscus and lateral lemnisci. Corticospinal, Transverse fibers of pons The facial nucleus lies corticonuclear, posterior to the lateral part corticopontine of the medial lemniscus. Abducent nerve The fibers of the facial nerve wind around the nucleus of the abducens nerve, producing the facial colliculus then pass anteriorly between the facial nucleus and the superior end of the nucleus Facial nerve of the spinal tract of the trigeminal nerve. Facial Middle The medial longitudinal nucleus cerebellar fasciculus- the main peduncle pathway connecting the vestibular and cochlear nuclei with the nuclei of oculomotor, trochlear, and abducens -is situated beneath the floor of the fourth ventricle on either side of the midline. Spinal nucleus and tract Abducent Geniculum of Fourth of trigeminal nerve nucleus facial nerve ventricle Medial longitudinal fasciculus  The medial vestibular nucleus A TS OF THE PONS AT THE LEVEL OF THE FACIAL COLLICULUS is situated lateral Descending tracts Pontine nuclei Medial lemniscus to the abducens Corticospinal, Transverse fibers of pons nucleus and is in corticonuclear, corticopontine close relationship Abducent nerve to the inferior cerebellar Vestibular peduncle. nerve The superior part of the lateral and Facial nerve the inferior part of the superior Facial Middle cerebellar vestibular nucleus nucleus peduncle are found at this Spinal nucleus level. and tract of The posterior and trigeminal nerve anterior cochlear nuclei are also Lateral and superior found at this level. Vestibulocochlear Abducent Geniculum of Fourth vestibular nuclei fibers nucleus facial nerve ventricle Medial longitudinal fasciculus  The spinal nucleus of the A TS OF THE PONS AT THE LEVEL OF THE FACIAL COLLICULUS trigeminal nerve Pontine nuclei Medial lemniscus and its tract lie Descending tracts Corticospinal, Transverse fibers of pons on the corticonuclear, anteromedial corticopontine aspect of the Trapezoid body Abducent nerve inferior Trapezoid nucleus cerebellar Central tegmental Vestibular nerve peduncle. tract The trapezoid Facial nerve body- made up of fibers derived from the Facial nucleus Middle cerebellar cochlear nuclei peduncle and the nuclei of Spinal nucleus the trapezoid and tract of body- runs trigeminal transversely in nerve Inferior the anterior part cerebellar ped. of the Lateral and superior tegmentum. Vestibulocochlear fibers Abducent Geniculum of facial nerve Fourth ventricle vestibular nuclei nucleus Medial longitudinal fasciculus  A TS OF THE PONS AT THE LEVEL OF THE PRINCIPAL SENSORY AND MOTOR NUCLEI OF THE TRIGEMINAL NERVE The basilar part Transverse pontine fibers Trapezoid body Medial lemniscus shows the same internal features Descending fibers of cortical origin Trapezoid nucleus shown at the facial colliculus level. Lateral lemniscus The trapezoid Meddle body and the cerebellar medial lemniscus peduncle are situated in the same position as they were at the level of facial colliculus. The lateral and spinal lemnisci lie at the lateral extremity of the medial lemniscus.  A TS OF THE PONS AT THE LEVEL OF THE PRINCIPAL SENSORY AND MOTOR NUCLEI OF THE TRIGEMINAL NERVE The motor Transverse pontine fibers Trapezoid body Medial lemniscus nucleus of the Descending fibers trigeminal nerve is of cortical origin Trapezoid nucleus situated beneath Lateral lemniscus the lateral part of the fourth Meddle ventricle within cerebellar peduncle Trigeminal nerve the reticular formation. The emerging motor Motor nucleus of trigeminal nerve fibers travel anteriorly through the substance of the pons and exit on its anterior surface. Fourth ventricle  The principal A TS OF THE PONS AT THE LEVEL OF THE PRINCIPAL sensory nucleus of the trigeminal nerve SENSORY AND MOTOR NUCLEI OF THE TRIGEMINAL NERVE is situated on the lateral side of the Transverse pontine fibers Trapezoid body motor nucleus; it is Descending fibers Medial lemniscus continuous inferiorly of cortical origin with the nucleus of Trapezoid nucleus the spinal tract. The entering sensory Lateral lemniscus fibers travel through Superior olivary nucleus the substance of the Meddle pons and lie lateral cerebellar to the motor fibers. Trigeminal nerve peduncle Central The superior tegmental cerebellar peduncle tract is situated Motor nucleus of Medial posterolateral to the trigeminal nerve longitudinal motor nucleus of fasiculus the trigeminal nerve. It is joined by the anterior Principal sensory nucleus spinocerebellar of trigeminal nerve Mesencephalic tract tract. of trigeminal nerve Superior cerebellar peduncle Cerebellar folium Superior medullary velum Fourth ventricle THANK YOU  EXTERNAL FEATURES AND INTERNAL STRUCTURE OF MIDBRAIN Dr. Ramadan El Gharbawy Professor of Anatomy & Embryology, Beirut Arab University, Lebanon Consultant of General Surgery, Egypt Ex-scholar at Emory, USA  OUTLINE AND OBJECTIVES Items Objectives 1. Midbrain- site and length 1. Briefly describe the external features of 2. Revisit of the midbrain external features: the midbrain. o Midbrain-anterior aspect 2. Briefly describe the TS of the midbrain at o Midbrain-posterior and lateral surfaces the levels of the inferior and superior 3. Midbrain- internal structure colliculi. o A TS of the midbrain at the level of the 3. List the fiber bundles in the crus cerebri. inferior colliculi 4. Briefly describe the internal structure of o A TS of the midbrain at the level of the the inferior and superior colliculi and the superior colliculi red nucleus and mention their functions. 4. Crus cerebri 5. Locate the reticular formation in the 5. Inferior colliculus midbrain. 6. Superior colliculus 7. Red nucleus 8. Reticular formation  MIDBRAIN- SITE AND LENGTH The midbrain connects the pons and cerebellum with the forebrain. It ascends through the opening in the tentorium cerebelli, tentorial notch. The midbrain measures about 2 cm in length.  MIDBRAIN-ANTERIOR Posterior ASPECT Crus cerebri Perforated substance On the anterior aspect of the Oculomotor midbrain, a deep depression in the nerve midline, the interpeduncular fossa, is bounded on either side by the crus cerebri. Many small blood vessels perforate the floor of the interpeduncular fossa, and this region is termed the posterior perforated substance. The oculomotor nerve emerges from a groove on the medial side of the crus cerebri and passes forward to the roof of the cavernous sinus.  POSTERIOR AND LATERAL SURFACES On the posterior surface the 4 colliculi (superior and inferior pairs ) are separated by a cruciform Superior colliculus groove. Superior brachium Lateral geniculate The superior colliculi are centers for visual reflexes Inferior colliculus Medial geniculate , and the inferior colliculi are part of the auditory Inferior brachium pathway. Trochlear nerve In the midline below the inferior colliculi, the trochlear nerves emerge, wind around the lateral Lateral aspect of the midbrain to enter the lateral wall of lemniscus the cavernous sinus. On the lateral aspect of the midbrain, the superior and inferior brachia ascend in an anterolateral direction; the lateral lemniscus superomedial. The superior brachium passes from the superior colliculus to the lateral geniculate body and the optic tract; the inferior brachium connects the inferior colliculus to the medial geniculate body.  INTERNAL STRUCTURE Substantia nigra Crus cerebri The tectum is the part of the midbrain Interpeduncular fossa posterior to the cerebral aqueduct. The midbrain comprises two cerebral peduncles each of which is divisible into an anterior part, the crus cerebri, and a posterior part, the tegmentum, by a pigmented band of gray matter, the substantia nigra. The narrow cavity of the midbrain is the cerebral aqueduct, which connects the 3rd and 4th ventricles. Cerebral The cerebral aqueduct is surrounded by peduncle Tegmentum the periaquiductal gray matter. On transverse sections of the midbrain, the interpeduncular fossa can be seen to Cerebral separate the crura cerebri, whereas the Tectum aquiduct tegmentum is continuous across the median plane. Periaquiductal gray  A TS OF THE MIDBRAIN AT THE LEVEL OF THE INFERIOR COLLICULI The inferior colliculus, consisting of a large nucleus of gray matter, lies beneath the corresponding surface elevation. The trochlear nucleus is situated in the central gray matter close to the median plane just posterior to the medial longitudinal fasciculus. The emerging fibers of the trochlear nucleus pass laterally and posteriorly around the central gray matter and leave the midbrain just below the inferior colliculi. The fibers of Medial longitudinal fasciculus the trochlear nerve now decussate completely in the Trochlear nucleus superior medullary velum. Inferior brachium The mesencephalic nuclei of Mesencephalic tract and the trigeminal nerve are lateral Periaqueductal gray matter nucleus of trigeminal to the cerebral aqueduct. Nucleus of inferior colliculus Cerebral aqueduct  A TS OF THE MIDBRAIN AT THE Decussation of superior Interpeduncular fossa cerebellar peduncles Frontopontine fibers LEVEL OF THE INFERIOR Posterior perforated Crus cerebri COLLICULI substance Corticospinal and corticonuclear fibers The decussation of the superior cerebellar peduncles occupies the central part of the tegmentum anterior to the cerebral aqueduct. Substantia The reticular formation is situated nigra lateral to the decussation. The medial lemniscus ascends posterior to the substantia nigra; the spinal and trigeminal lemnisci are Superior situated lateral to the medial cerebellar lemniscus. peduncle Temporopontine The lateral lemniscus is located Reticular formation fibers posterior to the trigeminal lemniscus. Medial longitudinal Medial lemniscus fasciculus The substantia nigra is a large motor Trochlear nucleus Central tegmental tract nucleus situated between the tegmentum, and the crus cerebri and Lateral lemniscus is found throughout the midbrain. The crus cerebri is separated from Periaqueductal gray matter Mesencephalic tract and the tegmentum by the substantia nucleus of trigeminal nigra. Nucleus of inferior colliculus Cerebral aqueduct  The superior colliculus, a A TS OF THE MIDBRAIN AT THE LEVEL OF THE SUPERIOR large nucleus of gray matter that lies beneath the COLLICULI corresponding surface elevation. Crus cerebri Interpeduncular fossa The pretectal nucleus is a Oculomotor nerve small group of neurons situated close to the lateral part of the superior colliculus. The oculomotor nucleus is situated in the central gray Red nucleus matter close to the median Medial plane, just posterior to the longitudinal fasciculus medial longitudinal fasciculus. Oculomotor The fibers of the oculomotor nucleus nerve pass anteriorly through the red nucleus to emerge on the medial side of the crus cerebri in the interpeduncular Periaquiductal gray matter fossa. Superior colliculus Cerebral aqueduct  The medial, spinal, and A TS OF THE MIDBRAIN AT THE LEVEL OF THE SUPERIOR trigeminal lemnisci form a curved band posterior to the COLLICULI substantia nigra, but the Posterior perforated substance lateral lemniscus does not Crus cerebri Interpeduncular fossa Oculomotor nerve extend superiorly to this level. Frontopontine fibers The red nucleus is a rounded mass of gray matter situated Substantia nigra Corticospinal and between the cerebral Corticonuclear fibers aqueduct and the substantia Red nucleus Central nigra. Medial tegmental longitudinal tract The reticular formation is fasciculus Temporo- situated in the tegmentum Pontine lateral and posterior to the Oculomotor fibers nucleus Medial red nucleus. lemniscus Reticular The crus cerebri contains the formation Medial identical important Geniculate body descending tracts fibers that Periaquiductal gray matter are present at the level of the Superior colliculus inferior colliculus. Cerebral aqueduct  The crus cerebri contains important descending tracts and is separated from the tegmentum by the CRUS CEREBRI substantia nigra. The corticospinal and corticonuclear fibers occupy the middle two thirds of the crus. The frontopontine fibers occupy the medial part of the crus. The temporopontine fibers occupy the lateral part of the crus. These descending tracts connect the cerebral cortex to the anterior gray column cells of the spinal cord, the CN nuclei, the pons, and the cerebellum.  INFERIOR COLLICULUS The inferior colliculus, consisting of a large nucleus of gray matter, lies beneath the corresponding surface elevation and forms part of the auditory pathway. It receives many of the terminal fibers of the lateral lemniscus. The pathway then continues through the inferior brachium to the medial geniculate body.  SUPERIOR COLLICULUS The superior colliculus, a large nucleus of gray matter that lies beneath the corresponding surface elevation and forms part of the visual reflexes. It is connected to the lateral geniculate body by the superior brachium. It receives afferent fibers from the optic nerve, the visual cortex, and the spinotectal tract. The efferent fibers form the tectospinal and tectobulbar tracts, which are probably responsible for the reflex movements of the eyes, head, and neck in response to visual stimuli.  PRETECTAL NUCLEUS The afferent pathway for the light reflex ends in the pretectal nucleus. This is a small group of neurons situated close to the lateral part of the superior colliculus. After relaying on the pretectal nucleus’ neurons, their axons pass to and relay on the neurons of the parasympathetic nucleus of the oculomotor nerve (Edinger—Westphal nucleus). The axons of the Edinger-westphal neurons then pass to the oculomotor nerve.  RED NUCLEUS The red nucleus is a rounded mass of gray matter situated between the cerebral aqueduct and the substantia nigra. Its reddish hue, seen in fresh specimens, is due to its vascularity and the presence of an iron-containing pigment in the cytoplasm of many of its neurons. Afferent fibers reach the red nucleus from 1. The cerebral cortex through the corticospinal fibers 2. The cerebellum through the superior cerebellar peduncle 3. The lentiform nucleus, subthalamic and hypothalamic nuclei, substantia nigra, and spinal cord. Efferent fibers leave the red nucleus and pass to 1. The spinal cord through the rubrospinal tract (as this tract descends, it decussates) 2. The reticular formation through the rubroreticular tract 3. The thalamus 4. The substantia nigra  RETICULAR FORMATION The reticular formation is situated in the tegmentum lateral and posterior to the red nucleus. THANK YOU