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Brainstem Dr. Sama ul haque Objectives Identify the gross features of the brainstem. Briefly describe the internal structure of the brainstems (ascending and descending pathways, sensory and motor cranial nuclei, substantia nigra, red nucleus, olivary nucleus and reticular formation). Describe the main connections of the sensory cranial nuclei. Objectives Describe the main connections of the motor cranial nuclei. Describe lesions in the brainstem such as medial medullary syndrome and lateral medullary syndrome. Describe the main connections of the substantia nigra and the red nucleus. Brainstem Composed of Medulla Oblongata, Pons and the Midbrain. It lies in the Posterior cranial fossa of the skull. Stalk like in shape. Connects spinal cord with forebrain. Functions: It is a channel for the ascending and descending tracts. It contains important centers associated with respiratory and cardiovascular systems. It contains the nuclei of the cranial nerves. Medulla Oblongata Medulla Oblongata (External features) It connects Pons superiorly with Spinal Cord inferiorly. Begins caudally at foramen magnum. It is conical in shape. Central canal continues to the middle of the medulla and then expand as cavity of 4th ventricle. Medulla Oblongata (External features) Anterior median fissure Pyramids (Pyramidal Tract): Bundles of corticospinal fibers Decussation of pyramids: Inferior part of pyramids Anterior external arcuate fibers: Fibers emerging from anterior median fissure above decussation and run laterally to enter the cerebellum. Olives (Inferior Olivary Nuclei): Posterolateral to Pyramids Roots of hypoglossal nerve: Between Pyramid and Olive Medulla Oblongata (External features) Anterior View Medulla Oblongata (External features) Inferior cerebellar peduncles: Posterior to olives connecting medulla to the cerebellum. Roots of glossopharyngeal, vagus and cranial roots of accessory cranial nerves: Between olive and inferior cerebellar peduncle. Posterior median sulcus Floor of 4th ventricle Hypoglossal triangle Vagal triangle Gracile tubercle Cuneate tubercle Medulla Oblongata (External features) Posterior View Medulla Oblongata (Internal structure) Level of decussation of Pyramids Decussation of corticospinal tracts Gracile fasciculus and nucleus Cuneate fasciculus and nucleus Substantia Gelatinosa of posterior gray column of cord continue as Nucleus of the spinal tract of the trigeminal nerve. Anterior and posterior spinocerebellar tracts Lateral spinothalamic tract Medial accessory olivary nucleus Medulla Oblongata (Internal structure) Level of decussation of Pyramids Medulla Oblongata (Internal structure) Level of decussation of Medial Lemnisci Medial Lemniscus or Sensory Decussation (Internal arcuate fibers from nuclei gracilis and cuneatus). Nucleus of the spinal tract of the trigeminal nerve. Spinal tract of the trigeminal nerve. Anterior and posterior spinocerebellar tracts Lateral and Anterior spinothalamic tracts Medulla Oblongata (Internal structure) Level of decussation of Medial Lemnisci Medulla Oblongata (Internal structure) Level of the Olives Inferior Olivary Nucleus: Gray matter is shaped like a crumpled bag ,facing medially. This nucleus is responsible for the elevation called Olive. Small dorsal and medial Olivary Nuclei. Medial Lemniscus Inferior cerebellar peduncle Medulla Oblongata (Internal structure) Level of the Olives Medial longitudinal fasciculus Tectospinal tract Hypoglossal nucleus Dorsal vagal nucleus Inferior vestibular nucleus Pyramids Medulla Oblongata (Internal structure) Level of the Olives Medulla Oblongata (Internal structure) Level just inferior to the Pons Lateral Vestibular Nucleus Cochlear Nuclei are anterior and posterior to inferior cerebellar peduncle Medulla Oblongata (Internal structure) Level just inferior to the Pons Pons Pons (External features) Lies anterior to the cerebellum. Connects Medulla to Midbrain. Anterior Surface: – Basilar groove – Transverse fibers converging on each side to the Middle Cerebellar peduncle. – Trigeminal nerve (Motor and Sensory Roots). – Between Pons and Medulla Abducent, Facial and Vestibulocochlear arises. – Superficial transverse pontine fibers Pons (External features) Anterior Surface Pons (External features) Posterior Surface: – Forms the upper half of the floor of 4th ventricle – Limited laterally by Superior cerebellar peduncle – Divided by Median sulcus – Lateral to Median sulcus lies Medial eminence – Lateral to Medial eminence lies Sulcus limitans – Lateral to Sulcus limitans lies Vestibular area – The inferior end of Medial eminence is expanded to form Facial colliculus Pons (External features) Pons (Internal structure) Trapezoid body: It is a bundle of fibers and cells in Pons. It is a part of the Auditory Pathway. Pons is divided by transverse fibers of trapezoid body into: The tegmentum posteriorly The basal part anteriorly Pons (Internal structure) Transvers section through caudal part (Passing through Facial Colliculus) Medial Lemniscus Motor nucleus of facial nerve Motor nucleus of Abducent (Facial Colliculus) Cavity of 4th ventricle Medial longitudinal fasciculus Pons (Internal structure) Transvers section through caudal part (Passing through Facial Colliculus) Medial Vestibular Nucleus Superior cerebellar peduncle Middle cerebellar peduncle Transverse pontine fibers Corticospinal and corticonuclear fibers Spinal nucleus of Trigeminal nerve Pons (Internal structure) Transvers section through caudal part (Passing through Facial Colliculus) Pons (Internal structure) Transvers section through cranial part (Passing through Trigeminal Nuclei) Cavity of 4th ventricle Medial longitudinal fasciculus Motor Nucleus of the Trigeminal Nerve Principal Sensory Nucleus of Trigeminal Nerve Pons (Internal structure) Transvers section through cranial part (Passing through Trigeminal Nuclei) Superior cerebellar peduncle Middle cerebellar peduncle Medial Lemniscus Trapezoid body Pons (Internal structure) Transvers section through caudal part (Passing through Trigeminal Nuclei) Thank You