Brain Stem B.U 2025 PDF

Dr. Samia M. Manawy  Learning objectives By the end of this session , the student must be able to:  Identify parts of brain stem  Describe the anatomy of medulla oblongata  Describe the anatomy of pons  Describe the anatomy of midbrain Brain Stem The brainstem is the stru...

Dr. Samia M. Manawy  Learning objectives By the end of this session , the student must be able to:  Identify parts of brain stem  Describe the anatomy of medulla oblongata  Describe the anatomy of pons  Describe the anatomy of midbrain Brain Stem The brainstem is the structure that connects the cerebrum of the brain to the spinal cord and cerebellum The brain stem is composed of the medulla oblongata, pons & midbrain Site: in the posterior cranial fossa. It is related posteriorly to the cerebellum, separated from it by the 4th ventricle. It is stalk like connects narrow spinal cord with expanded forebrain. Functions: Contain ascending and descending tracts connecting spinal cord with higher centers in forebrain. Contain important vital centers of CVS and respiratory system. Contains important cranial nerve nuclei  Different views of the Brain Stem midbrain pons midbrain pons pons cerebellum medulla cerebellum medulla Different views of the Brain Stem midbrain pons 4th v. cerebellum medulla Medulla Oblongata External Features The medulla oblongata constitutes the lower part of the brain stem Superiorly, it is continuous with the pons Inferiorly, it passes through the foramen magnum to become continuous with the spinal cord shape: piriform(conical) in shape, broad superior, about 3 cm in length. pons 4th v. Surfaces: 3 surfaces anterior , posterior and lateral The medulla is differentiated into two halves The lower half OM of the medulla contains a central canal and is called closed medulla (CM) CM The cavity of the upper half is the 4th ventricle and thus the upper half is called the open medulla (OM) Anterolateral surface of medulla (from medial to lateral 1-Anterior median fissure: longitudinal fissure & continuation of that of spinal cord. - Its lower part is obliterated by motor (pyramidal ) decussation. 2-Pyramid: is an elevation on the side of anterior median fissure. Abducent nerve that lies above pyramid 3-Anterolateral sulcus: lateral to pyramid between pyramid and olive. Contain rootlets of hypoglossal nerve(XII) 4- Olive: an elevation lateral to the pyramid, formed by the inferior olivary nucleus , (an extrapyramidal nucleus).It belong to open medulla Notice: Between lower border of pons and olive facial (7th) and auditory nerves(8th) presents.  The antero- lateral view shows: 5- posterolateral sulcus : between olive and inferior cerebellar peduncle, gives attachment to roots of (from above downwards):-to the rootlets of The Glossopharyngeal( IX), vagus (X) & cranial root of accessory nerves (XI) 6- Inferior cerebellar peduncle: connects the medulla oblongata to the cerebellum posterolateral sulcus Inferior cerebellar peduncle Posterior surface the medulla is divided into upper opened part lower closed part Posterior aspect of medulla: The posterior aspect divided into 2 parts: closed medulla and open medulla. The posterior surface of upper half of medulla forms lower part of floor of 4th ventricle (open medulla). The posterior surface of the inferior half of the medulla (closed medulla) is continuous with the posterior aspect of the spinal cord. - Closed medulla: - the lower half, it is the continuation of spinal cord., its cavity is the central canal like spinal cord. - Open medulla: - the upper half in which the central canal is expanded posteriorly and, on the sides, to form the cavity of hindbrain, which is called 4th ventricle. - N.B: Medullary stria is between medulla and pons Lower part (closed medulla from medial to lateral it shows: a. Posterior median sulcus. b. Gracile tract & tubercle: elongated elevation overlying the gracile nucleus. c. Cuneate tract &tubercle: elongated swelling lateral to the gracile tubercle. It C G overlies the cuneate nucleus. d. Inferior cerebellar peduncle. posterior aspect of open medulla oblongata (floor of 4th ventricle) Posterior median sulcus in midline hypoglossal trigone (5)which formed of hypoglossal nerve nucleus lies lateral to the sulcus. inferior fovea lies lateral to hypoglossal trigone. lower vestibular part lateral to inferior fovea. vagal triangle (6 )below inferior fovea. Medullary stria (4):Transverse fibres at pontomedullary junction dividing the floor of 4th ventricle into pontine & (S) medullary parts. Pons (bridge) The middle part of the brain stem Superiorly, continuous with the midbrain Inferiorly, continuous with the medulla oblongata Pons Pons Site: in the posterior cranial fossa anterior to cerebellum. It lies between medulla and midbrain. It is about 1 inch in length. It is bridge connecting right and left cerebellar hemispheres. 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 It has anterior part and posterior part External Features of the Pons Anterior surface: 1. -transverse streaks: the transverse pontine fibers is produced by ponto-cerebellar fibres that collect on either side to form middle cerebellar peduncle. 2. Basilar sulcus: median longitudinal basilar groove for basilar artery. 3. Raised ridge: formed by Pyramidal tract on either side of basilar groove. It is formed by the descending fibers of the pyramidal tract. 4. Trigeminal nerve is attached by 2 roots (smaller medial motor root& larger lateral sensory root) to the lateral part of the anterior surface of pons to the junction between the pons & MCP. 5. Middle cerebellar peduncle (MCP). It turns backwards to sink into the corresponding cerebellar hemisphere. Posterior aspect of pons (tegmental part It is hidden by cerebellum.  It forms the upper half of the floor of the fourth (SCP) ventricle  Continuous below with open medulla  is triangular in shape, is limited laterally by the open medulla superior cerebellar peduncles(SCP)  is divided into symmetrical halves by a median sulcus. Features of Posterior surface of pons 1-Medial eminence by underlying abducent nucleus. 2- Facial colliculus: by nucleus of abducent nerve with fibers of facial nerve curve around it. Upper Vestibular area: It overlies vestibular nuclei. The medullary stria It is transverse nerve fibers which separate the posterior surface of pons from that of medulla Midbrain:  it is the most upper part of brain stem ,2 cm in length, and connects the pons and cerebellum with the forebrain Midbrain  Extent: from upper border of pons to diencephalon.  Site: partly in posterior cranial fossa, passing through tentorial notch.  The midbrain is traversed by a narrow channel, the cerebral aqueduct, which is filled with cerebrospinal fluid.  The cerebral aqueduct( arrow) traverses the midbrain to connect the third ventricle with the fourth ventricle It divides the midbrain into two parts: A. The cerebral peduncles: in front of the aqueduct. The two cerebral peduncles are separated by the interpeduncular fossa. B. The tectum: behind the aqueduct. Anterior aspect of midbrain 1- The cerebral peduncles: The two cerebral peduncles are separated by the interpeduncular fossa 2- Its medial surface shows exit of oculomotor interpeduncular fossa nerve 1 2 Posterior aspect of midbrain On the posterior surface there are four colliculi These are rounded eminences that are divided into superior and inferior colliculi 1-Superior colliculus are centers for visual reflexes 2-Inferior colliculus are lower auditory centers. Emergence of trochlear nerve: attains its exit below inferior colliculi and winds around lateral aspect of midbrain. The nerve appears on anterior aspect Blood supply of the brain stem: 1) Medulla oblongata: It is supplied by the branches of vertebral artery. A-The anterior spinal artery: B-The posterior inferior cerebellar artery (PICA): C-Posterior spinal artery: 2) Pons: It is supplied by branches of basilar artery. 3) mid brain: 1-branches of the posterior cerebral artery (mainly) 2-superior cerebellar artery  optic chiasma Infundibulum of pituitary Mammillary bodies Posterior perforated substance Cerebral peduncle Optic tract Basilar sulcus Middle cerebellar peduncle Anterior median fissure Pyramid. Anterolateral sulcus Olive Posterolateral sulcus  The pineal body superior colliculi inferior colliculi. trochlear nerves. Medial eminence Facial colliculus Vestibular area Middle cerebellar peduncle Hypoglossal triangle Vagal trigone Cuneate tubercle Gracile tubercle Inferior cerebellar peduncle Spinal cord As regard Superior colliculus of midbrain all the following is true except: a. It is on the posterior surface of midbrain b. It is one of four rounded eminences c. It is the center for visual reflexes d. It is the center for auditory reflexes Which of the following is under medial eminence of pons? a. abducent nucleus b. vestibular nuclei c. facial nuclei d. facial nerve fibers