Done by : Areej Al-Hadidi

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Junior Barnett
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1 Brainstem &diencephalon Done by : Areej Al-Hadidi

2 Brainstem Functions Ascending and descending tracts Reflex centers Cardiovascular and respiratory centers Coughing, sneezing, swallowing Nuclei of the cranial nerves (from III to XII) Motor and sensory Consciousness and arousal **External anatomy of brainstem(ventrally) 1.midbrain: *Optic tracts demonstrate the beginning of the midbrain * It contains cerebral peduncles (basis pedunculi,crus cerebri ),interpeduncular fossa * the descending tracts as corticospinal tract pass anteriorly to the midbrain in cerebral peduncles *cerebral peduncles :continuation of internal capsule *interpeduncular fossa : it is formed by cisterna -It is a deep depression in the midline, which 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 in the lateral wall of the cavernous sinus. *boundaries of interpeduncular fossa -ant:optic chiasm -anteriolateral: optic tract -posteriolateral : cerebral penuncles -post: upper border of the pons Contents: Tuber cinereum,mammilary body, occulomotor nerve & posterior perforated substance

3 2.pons: The anterior surface is convex from side to side and shows many transverse fibers that converge on each side to form the middle cerebellar peduncle.there is a shallow groove in the midline, the basilar groove, which lodges the basilar artery. in the middle Of the anterolateral surface of the pons the trigeminal nerve emerges on each side In the groove between the pons and the medulla oblongata(bulbopontine sulcus), there emerge, from medial to lateral, the abducent, facial, and vestibulocochlear nerves *note: the trochlear nerve is the only nerve exits posteriorly in the midbrain but it winds round cerebral peduncles and runs anteriorly to the orbits,it is also cross over the troculear nerve on the other side 3. medulla oblongata : On the anterior surface of the medulla is the anterior median fissure, which is continuous inferiorly with the anterior median fissure of the spinal cord.on each side of the median fissure, there is a swelling called the pyramid. The pyramids are composed of bundles of nerve fibers, called( corticospinal fibers), which originate in large nerve cells in the precentral gyrus of the cerebral cortex. The pyramids taper inferiorly, and it is here that the majority of the descending fibers cross over to the opposite side, forming the decussation of the pyramids. The anterior external arcuate fibers are a few nerve fibers that emerge from the anterior median fissure above the decussation and pass laterally over the surface of the medulla oblongata to enter the cerebellum. 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 emerge the rootlets of the hypoglossal nerve(pre-olivary sulcus). Posterior to the olives are the inferior cerebellar peduncles,which connect the medulla to the cerebellum. In the groove between the olive and the inferior cerebellar peduncle emerge the roots of the glossopharyngeal and vagus nerves and the cranial roots of the accessory nerve(post-olivary sulcus) *external anatomy of brainstem dorsally: 1.midbrain: On the posterior surface are four colliculi (corpora quadrigemina). These are rounded eminences that are divided into superior and inferior pairs by a vertical and a transverse groove.the superior colliculi are centers for visual reflexes and the inferior colliculi are lower auditory centers. In the midline below the inferior colliculi, the trochlear nerves emerge. These are small-diameter nerves that wind around the lateral aspect of the midbrain to enter the lateral wall of the cavernous sinus.

4 *note: epithalamus is located above the midbrain posteriorly *sup peduncles :btw midbrain and cerebellum 2.medulla oblongata : The posterior surface of the superior half of the medulla oblongata forms the 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. On each side of the median sulcus, there is an elongated swelling, the gracile tubercle, produced by the underlying gracile nucleus Lateral to the gracile tubercle is a similar swelling, the cuneate tubercle, produced by the underlying cuneate nucleus. *Note: cuneate and gracile.second order neurons *rhomboid fossa : pontine part and medullary part 3.rhomboid fossa : *The diamond-shaped floor is formed by the posterior surface of the pons and the cranial half of the medulla oblongata.the floor is divided into symmetrical halves by the median sulcus. On each side of this sulcus, there is an elevation, the medial eminence, which is bounded laterally by another sulcus, the sulcus limitans. Lateral to the sulcus limitans, there is an area known as the vestibular area( lateral point of the fossa) *The facial colliculus is a slight swelling at the inferior end of the medial eminence that is produced by the fibers from the motor nucleus of the facial nerve looping over the abducens nucleus. * Strands of nerve fibers, the stria medullaris, derived from the arcuate nuclei, emerge from the median sulcus and pass laterally over the medial eminence and the vestibular area and enter the inferior cerebellar peduncle to reach the cerebellum *trigon: Vagal trigon (more lateral inferior) Hypoglossal trigon (more medialsuperior) Isthmus superior constriction Obex inferior narrowing Functional Distribution of Brainstem Nuclei *Midline GSE III, IV, VI, XII (most medial,toward skeletal muscles) SVE V, VII, IX, X, XI (branchial arches) GVE III, VII, IX, X (parasympathetic) *Sulcus limitans GVA n. of tractus solitarius SVA n. of tractus solitarius GSA V sensory nuclei SSA vestibular & cochlear

*general somatic efferent: close to the midline,(iii, IV still close to cerebral aqueduct) from sup to inf (III,IV,VI,XII) *GVE: from inf to sup (X,IX,VII,III) IX: inf salivatory nuclei /VII: sup

5 *general somatic efferent: close to the midline,(iii, IV still close to cerebral aqueduct) from sup to inf (III,IV,VI,XII) *GVE: from inf to sup (X,IX,VII,III) IX: inf salivatory nuclei /VII: sup salivatory nuclei /III:EPINGER-WESTPHAL nuclei *The Edinger Westphal nucleus (accessory oculomotor nucleus) is the parasympathetic pre-ganglionic nucleus *Special visceral efferent : deep/ V&VII each has special nuclei whereas IX&X has one nucleus called Nucleus ambiguus *GVA&SVA: nucleus of tractus solitarias taste *nucleus solitaries >> (rostral part, SVA)>> VII, IX, X * nucleus solitaries>> (caudal part, GVA) >> IX, X *lateral to nucleus of tractus solitarias.the longest and largest nucleus (trigeminal nucleus) *trigeminal nucleus: mesencephalic,chief&spinal nuclei Internal Structures of Medulla 1.Level of pyramidal decussation (closed part) /great motor decussation Spinal tract & nucleus of trigeminal nerve Pyramids Decussation of pyramids Nucleus gracilis & cuneatus (part of them) Fasciculus gracilis & cuneatus(mostly)

6 **Note: black color represent fibers while white color represent nuclei 2.Level of internal arcuate fibers (closed part)/great sensory decussation Spinal tract & nucleus of trigeminal nerve Pyramids Fasciculus gracilis &cuneatus Nucleus gracilis & cuneatus Internal arcuate fibers Decussation *The internal arcuate fibers are the axons of second-order sensory neurons that compose the gracile and cuneate nuclei of the medulla oblongata *The internal arcuate fibers first travel anteriorly and laterally around the central gray matter. They then curve medially toward the midline, where they decussate with the corresponding fibers of the opposite side * The decussation takes place anterior to the central gray matter and posterior to the pyramids. *note: The nucleus of the spinal tract of the trigeminal nerve lies lateral to the internal arcuate fibers. The spinal tract of the trigeminal nerve lies lateral to the nucleus Level of olivary nucleus (open part) Hypoglossal nucleus Dorsal vagal nucleus Vestibular nuclei Nucleus of tractus solitarius Spinal tract & nucleus of trigeminal nerve Pyramid Olivary nucleus Inferior cerebellar peduncle Medial lemniscus *The amount of gray matter has increased at this level owing to the presence of the olivary nuclear complex; the nuclei of the vestibulocochlear, glossopharyngeal, vagus, accessory, and hypoglossal nerves; and the arcuate nuclei. *Passing from medial to lateral, (1) the hypoglossal nucleus, (2) the dorsal nucleus of the vagus, (3) the nucleus of the tractus solitarius, and (4) vestibular nuclei

7 *medial lemniscus: large ascending bundle of heavily myelinated axons that decussate in the brainstem, specifically in the medulla oblongata. The medial lemniscus is formed by the crossings of the internal arcuate fibers. Internal Structures of the Pons 1. Caudal part Nucleus of abducent nerve Motor nucleus of facial nerve Medial lemniscus *Facial colliculus:it is produced by the fibers from the motor nucleus of the facial nerve looping over the abducens nucleus 2. Cranial part Motor nucleus of trigeminal nerve Main sensory nucleus of trigeminal is situated on the lateral side of the motor nucleus Middle & superior cerebellar peduncles Pontine nuclei (involve motor activity) Corticospinal fibers Medial lemniscus (pushed posteriorly) **Internal Structures of the Midbrain 1.Level of inferior colliculi Nucleus of trochlear nerve it is situated just posterior to the medial longitudinal fasciculus Mesencephalic nucleus of trigeminal nerve are lateral to the cerebral aqueduct Inferior colliculi Decussation of superior cerebellar peduncles occupies the central part of the tegmentum anterior to the cerebral aqueduct. Substantia nigra a large motor nucleus situated between the tegmentum, and the crus cerebri and is found throughout the midbrain Crus cerebri Medial lemniscus ascends posterior to the substantia nigra *note:from ant to post :crus cerebri,substantia nigra,medial lemniscus

8 2.Level of the superior colliculi Nucleus of oculomotor nerve it is situated just posterior to the medial longitudinal fasciculus Superior colliculi Red nucleus rounded mass of gray matter situated between the cerebral aqueduct and the substantia nigra Substantia nigra Crus cerebri Medial lemniscus * The fibers of the oculomotor nucleus pass anteriorly through the red nucleus to emerge on the medial side of the crus cerebri in the interpeduncular fossa *we can see mammilary bodies anteriorly Good luck

Lecture 4 The BRAINSTEM Medulla Oblongata

Lecture 4 The BRAINSTEM Medulla Oblongata Introduction to brainstem 1- Medulla oblongata 2- Pons 3- Midbrain - - - occupies the posterior cranial fossa of the skull. connects the narrow spinal cord