Brain Stem PDF

# Brain Stem ## Chapter 2 ### Ilos: After this lecture, student should be able to: - Describe the external features and blood supply of pons, medulla and midbrain. - Define the cranial nerves attached to them and the internal location of their nuclei. ### Brain stem - From below upwards it is f...

# Brain Stem ## Chapter 2 ### Ilos: After this lecture, student should be able to: - Describe the external features and blood supply of pons, medulla and midbrain. - Define the cranial nerves attached to them and the internal location of their nuclei. ### Brain stem - From below upwards it is formed of medulla oblongata, pons and midbrain. - Above it is directly continuous with the diencephalon. - Below it is directly continuous with the spinal cord. <br>  <br> ### Medulla Oblongata #### I - External structure - Length: about 3 cm long. - Shape: conical - Extensions: Above, it is continuous with the lower border of the pons, while below it is continuous with the spinal cord. - **Parts:** - a) Open medulla (upper 1/2): forms a part of the floor of the 4th ventricle. - b) Closed medulla (lower 1/2): is traversed by central canal which is continuous with that of the spinal cord. - **External features:** - A) Ventrolateral surface which presents from medial to lateral: - 1) Anterior median fissure: continuous with that of the spinal cord - 2) Pyramid (on each side of anterior median fissure): Is an elongated elevation produced by the cortico-spinal tract (bundle of fibers). - 3) Olive (posterolateral to the pyramid): oval elevation overlying the inferior olivary nucleus, separated from pyramid by an anterolateral sulcus for the exit of hypoglossal nerve(12) (XII) - 4) Inferior cerebellar peduncle (posterior to the olives) Is a bundle of nerve fibers connecting the medulla with the cerebellum, separated from olive by a posterolateral sulcus for the exit of glossopharyngeal, vagus, and cranial root of accessory nerves. <br>  <br> - B) Dorsal surface of the open medulla: - Forms the lower part of the floor of the 4th ventricle. - It is separated from back of pons by a bundle of fibers called medullary stria. - Bounded laterally by the inferior cerebellar peduncles. - It is traversed by a vertical median sulcus, lateral to it an inverted v shaped depression called the inferior fovea, On each side the inferior fovea divides the medullary part into 3 triangular areas, from medial to lateral: - a- Hypoglossal trigone; overlies the nucleus of the hypoglossal nerve. - b- Vagal trigone: overlies the dorsal nucleus of the vagus nerve. - c- Vestibular area: overlies the inferior and medial vestibular nuclei. - Area prostrema (vomiting center): a protuberance at the infero / posterior limit of the 4th ventricle. - C) Dorsal surface of closed medulla presents from medial to lateral - A posterior median sulcus which is continuous with that of the spinal cord. - Gracile tract and tubercle (overlying gracile nucleus) on each side of the sulcus. - Cuneate tract and tubercle (overlying cuneate nucleus). - Tuberculum cinereum: overlies spinal nucleus of trigeminal. - Inferior cerebellar peduncle (ICP) on either side as 2 bundles which extend upwards and laterally along the sides of the 4th ventricle till they reach the lower border of the back of the pons where it bends sharply to enter the cerebellum. <br> ### III. Blood supply of medulla - Anterolateral surface: supplied by anterior spinal and 4th part of vertebral arteries - Postero-lateral surface :supplied by posterior inferior cerebellar artery - Gracile and cuneate tracts and nuclei : supplied by posterior spinal artery ### III. Blood supply of pons - Basis pontis: is supplied by the pontine branches of the basilar artery. - Tegemntum: - a- In lower pons: by the posterior inferior cerebellar artery. - b- In upper pons: by the superior cerebellar artery. ### Midbrain - Length: 0.8 inch (2 cm) connects the pons and cerebellum with the forebrain - Extension: lies between the pons and the diencephalon. <br>  <br> - Ill. Trochlear (IV) nerve: emerges immediately below the inferior colliculus. It is the only cranial nerve that emerges from the dorsal surface of the brain stem <br> ### III. Blood supply of midbrain - 1. Central branches of posterior cerebral artery - 2. Superior cerebellar and posterior communicating ### II. Internal structure