Brain Stem Anatomy PDF

Major Anatomical Divisions of the Brain https://www.youtube.com/watch?v=P7VmluZOVYc 3-D animation Brainstem An overview for a 1 hour lecture Dr. A. Aktar Brainstem • Spinal cord continues rostally into brainstem • 3 Major Subdvisions: Medulla oblongata, pons, mid-brain Brainstem • Brainstem...

Major Anatomical Divisions of the Brain https://www.youtube.com/watch?v=P7VmluZOVYc 3-D animation Brainstem An overview for a 1 hour lecture Dr. A. Aktar Brainstem • Spinal cord continues rostally into brainstem • 3 Major Subdvisions: Medulla oblongata, pons, mid-brain Brainstem • Brainstem has conduit, cranial nerve & integrative functions • These are not mutually exclusive • Contains lower motor neurons for muscles of head • Does initial processing of afferent info from head + additional functions of cranial nerves (attached to brain stem) + distinctive functions • Reticular formation forms central core of brainstem Brain Stem Reticular Formation • Set of of interconnected nuclei located throughout brainstem • Not anatomically well defined because includes neurons located in different parts of brain • Participates in control of movement thru connections w/ spinal cord & cerebellum • Modulates transmission of information in pain pathways • Contains autonomic reflex circuitry • Involved in control of arousal & consciousness • Reticulothalamic projections essential for maintenenace of normal state of consciousness Brainstem . Medulla Oblongata • Where it connects to spinal cord roughly correspons to foramen magnum • Connects higher levels of brain to spinal cord • Responsible for autonomic (involuntary) functions • E.g. vomiting, sneezing, cardiac, respiratory, vasomotor centers, blood pressure Surfaces of Medulla Oblongata Anterior Posterior Medulla Oblongata- External Features Anterior Surface • Anterior median fissure • Medullary pyramid • Pyramidal decussation • Anterolateral groove (sulcus) • Inferior olives Anterior Surface: External Features (from midline laterally) • Anterolateral Sulcus Exits: Hypoglossal N. • Retroolivary Sulcus Exits: - Glossopharyngeal n. (CN IX) - Vagus n. (CN X) - Accessory n. (CN XI) olive Medulla Oblongata- External Features Posterior Surface • Posterior median groove (sulcus) Posterolateral Surface of Medulla Oblongata  Glossopharyngeal N.(CN9)  Vagus N. (CN10)  Accessory N. (CN11)  Inf. cerebellar peduncle Inferior Cerebellar Peduncle Connects medulla to cerebellum Contains fibers of: tracts from cerebellum to medulla oblongata or vice versa Posterior surface of medulla oblongata is the lower triangle of rhomboid fossa (floor of 4th ventricle) 4th Ventricle & Rhomboid Fossa 4th ventricle : • Space btw. medulla & pons-cerebellum • Filled with cerebrospinal fluid Rhomboid fossa:  Floor of 4th ventricle  Shape is quadrangular  Its lower triangle is related to medulla oblongata  Upper triangle is related to pons Pons • Pons – Latin : Bridge • Horseshoe-shaped • Largest part of brainstem, located above medulla & below midbrain • Located in ant. part of posterior cranial fossa • Separated from cerebellum by 4th ventricle • 4th ventricle found btwn dorsal surface of pons & cerebellum • Ventral surface dominated by fibers forming large ventral enlargement: transverse pontocerebellar fibers • Carries fibers from pontine nuclei to cerebellum in the middle cerebellar peduncle • Is the key distinguishing feature of the pons Pons Relations: • Posteriorly: Cerebellum – separated by 4th ventricle • Inferiorly: Medulla oblongata • Superiorly: Mid brain Pons – Posterior Surface • Post surface forms upper half of rhomboid fossa Pons – Anterior Surface • Large bulge formed by transverse pontocerebellar fibers • Basilar groove (sulcus): Midline of ventral surface & location of basilar a. • Pontomedullary junction : Landmark defined by angle btwn lower border of pons & sup. border of medulla Ant aspect of pons Pons – Anterior Surface Several cranial nerves originate from ventral surface • CN V: trigeminal– From lateral aspect of mid pons • CN VI: abducens – From pontomedullary junction, close to midline • CN VII: facial – From cerebellopontine angle - laterally • CN VIII: vestibulocochlear – originates laterally to facial n. Pons – Posterior Surface • Cerebellopontine angle: Angle at junction of pons, medulla & cerebellum • Formed by the cerebellopontine fissure • Fissure is made when cerebellum folds over pons, creating a sharply defined angle between them Pons – Posterior Surface • Connected to cerebellum by middle cerebellar peduncles • Removal of cerebellum reveals underlying 4th ventricle • Floor of 4th ventricle: Formed by dorsal surface of pons & medulla • Facial colliculus: On lower part of medial eminence, bilaterally • Contains abducens n. nuclei & fibers of facial n. that wrap behind the nuclei Pons – Posterior Surface • Connected to cerebellum by middle cerebellar peduncles Midbrain (A.k.a. Mesencephalon) • Shortest part of brain stem • About 2 cm RELATIONS: • Inf: Pons • Post: Cerebellum • Sup: Diencephalon External Features of Midbrain - Ventral (ant.) Surface • Cerebral crus (Cerebral peduncles) • Interpeduncular fossa (btwn. crus cerebri) • Oculomotor n. exits from interpeduncular fossa • Posterior perforated substance: Surface of interpeduncular fossa • Post. cerebral a. passes here Midbrain Dorsal (post) Surface • Superior colliculus • Inferior colliculus Colliculus: Latin- Hill Upper hill, lower hill Sup & Inf. Colliculus Superior Colliculus related to visual pathway • Control of head and eye movements • Conjugate gaze Inferior Colliculus related to auditory pathway • Localize the voice • Evaluate the frequency of voice • Concentrate the attention to a certain voice • Motor reflexes related to hearing Dorsal surface • Cruciform sulcus • Upper limit of sulcus expands into a depression for pineal gland • Trochlear n. emerges Cranial Nerves Which Leave Brain Stem at Mesencephalon Level 1- Oculomotor n. (contains motor & parasympathetic fibers) 2- Trochlear n. (contains motor fibers) Internal Structure of Mesencephalon Divided into 3 parts • Crus cerebri • Tegmentum • Tectum (lamina tecti) • Crus cerebri + tegmentum : Cerebral peduncle • Substantia nigra separates crus cerebri & tegmentum Internal Structure of Mesencephalon Crus Cerebri - 2 white matter structures (axons) - Formed by fibers emerging from cerebral hemispheres - They meet each other at superior border of pons Tegmentum • Latin: Covering • Ventral part of midbrain • Between substantia nigra and tectum Tectum • Latin: Roof Area painted pink • Posterior to cerebral aqueduct Structures here: • Superior colliculus • Inferior colliculus Substantia Nigra Neuron group related to basal ganglia • Located btwn crus cerebri & tegmentum • Dark color due to melanin content • Dopaminergic system involved in initiation of movement • Its disruption instrumental in movement deficits seen in Parkinson’s disease • Also involved in motivation and cognition Red Nucleus (nucleus ruber) • Part of reticular formation • Dorsomedial to substantia nigra • Observed from caudal levels of superior colliculus to caudal levels of diencephalon Posterior Commissure • Contains fibers that cross and course to other cerebral hemisphere ( one of the commissural pathways)