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1. Traversed by: Central Canal. 2. Retains: Some of the Features of the Spinal Cord. 3. Has: Motor Decussation. Ventral Horn Much Attenuated. Dorsal Horn Replaced by Caudal Part of the Trigeminal Sensory Nucleus (Nucleus of the Spinal Tract of the Trigeminal Nerve). It is the Brain Stem continuation of: Substantia Gelatinosa of the dorsal horn of the A large nucleus. Lies: Medial to the Spinal Tract of the Trigeminal Nerve. Extends: Through the whole length of the brain stem. Receives: Pain and Temperature from: Face, Forehead and the Mucous Membrane of the Mouth and Nose. Lies: Superficial to its Nucleus. Between: Cuneate Nucleus and the Spino-cerebellar tract. Formed of: Descending fibers that Terminate in the Trigeminal Nucleus Caudal to the Level of the Pons. It is: Motor Decussation. Formed of: Pyramidal Fibers (75-90%) cross to the opposite side. They descend in the Lateral White Column of the Spinal Cord as the Lateral Corticospinal Tract. Replaced by: Spinocerebellar (Anterior & Posterior) Lateral Spino Thalamic Tracts. Small part appear Deep to the corresponding Gracile and Cuneate Tracts. 1. Traversed by: Central Canal. 2. Has: Sensory Decussation. 3. Pyramids: Prominent Larger in size. Their Axons Form: Internal Arcuate Fibers. Sensory Decussation: Formed by Crossed Internal Arcuate Fibers. Composed Of: Ascending Internal Arcuate Fibers after their crossing. Lies: Adjacent to the middle line. Ventral to the Central Canal. Found in: Medulla, Pons and Midbrain. Terminates in: Thalamus. Lie: Antero lateral to the pyramids. Considered: The Inferior Extension of the Pontine Nuclei. Their Axons Form: External Arcuate Fibers. Connected to: Cerebellum through the Inferior Cerebellar Formed Of: A diffuse mixture of Nerve Fibers and Small Groups of Nerve Cells. Position: Posterolateral to: Pyramids. Ventral to: Spinal Tract and Nucleus of the Trigeminal Nerve. Lateral to the Cuneate nucleus. Receives Unconscious Fibers from the Cervical Region. Connected to: Cerebellum through the Inferior Cerebellar Peduncle. Its Posterior Surface Forms: Lower Part of the Floor of the 4th Ventricle. On Each Side of the Midline. Dorsal to Medial aspect of the Pyramids. Structure: A convoluted mass of gray matter. Has a hilum directed Medially. Lies: Postero lateral to the pyramids. Lateral to the Medial Leminiscus. Receives Fibers From: Motor and Sensory Cerebral Cortices. Red nucleus of the mid brain. Corpus Striatum. Concerned With: (Restiform Body) Lies in: Dorso Lateral part of the Medulla. Connects: Medulla and Cerebellum. Carries: Olivocerebellar. Vestibulocerebellar. Dorsal spinocerebellar. Dorsal and Ventral Nuclei Lie: Dorsal and Lateral to the Inferior Cerebellar Peduncle. Receive Afferents From: Cochlear Nerve. 1. Hypoglossal Nucleus A longitudinal column just lateral to the midline. 2. Dorsal Motor Nucleus of the Vagus Lateral to the hypoglossal nucleus. Contains: Preganglionic Parasympathetic fibers as far as the distal 1/3 of the transverse colon. 3. Vestibular Nuclei (Complex) Consist of Medial, Lateral, Inferior and Superior Nuclei. Lie In the Lateral Part of the Floor of 4th Ventricle. Inferior Vestibular Nucleus is Lateral to the Inferior Fovea. Receive Afferents From Vestibular Nerve. Lie Dorsal to the Inferior Olivary Nucleus. Function Gives Motor Fibers to Constrictors of the Pharynx. Intrinsic Muscles of the Larynx. Lies Close to the midline. Ventromedial to the hypoglossal nucleus. Dorsal to the medial lemniscus. Identified Also in Pons, Midbrain and Upper Levels of the Spinal Cord. Receives Afferents from Vestibular Nerve. Consists of Short Ascending and Descending fibers. They connect Vestibular and Cochlear Nuclei with the Cranial Nuclei (111, 1v and v1) It serves Coordination of Head and Eye Movements in Response to VestibuloCochlear Stimuli. Composed Of the Following Tracts: Spinothalamic (Lateral & Anterior). Trigeminothalamic. Position Deeply Placed. Lateral to the medial leminiscus. Dorsal to the Inferior Olivary Nucleus. Composed of Medial part (well formed in the medulla) . Lateral part (well formed in the pons) . Solitary Tract is in Between. Function Lateral Nucleus Receives Taste Fibers from the Back of the Tongue. Medial Nucleus Receives (GVA) fibers. Position The Most Caudal Point of the Floor of the 4th Ventricle. Function Site of Action of Centrally Acting Emetics. At Its Site Blood Brain Barrier is Lost for Certain Chemicals. Deeply placed. Posterior to the Olivary Nucleus. At this level of the medulla: It represents as a Small part of the system. Descending: Pyramids. Tectospinal. Ascending: Medial leminiscus. Spinal leminiscus. Trigemino thalamic. Ventral spinocerebellar. Thrombosis of branches of the anterior spinal artery. Manifested by : (1) Contralateral hemiplegia of the flaccid type (involvement of the pyramidal fibers only). (2) Contralateral loss of proprioceptive sensation and fine touch (affection of medial lemniscus). (3) Ipsilateral lower motor lesion of the hypoglossal nerve (affection of hypoglossal Thrombosis of the Inferior CerebellarArtery. Manifested by (1) Ipsilateral cerebellar ataxia. (2) Loss of Pain and Temperature From the Ipsilateral half of the Face. (3)Loss of Pain and Temperature from the Contralateral Half of the (4) Ipsilateral paralysis of the muscles of the Palate, Pharynx and Larynx. (5) Ipsilateral loss of Taste from the Posterior Third of the Tongue. (6) Ipsilateral Horner’s syndrome