Lecture 3 Internal Structure of Brain Stem PDF

Anterior view Posterior view  ❑Has three levels. 1-Closed medulla at level of pyramidal decussation.  ❑Has three levels. 1-Closed medulla at level of pyramidal decussation. Tracts: 1. Spinocerebellar tracts. 2. Spinothalamic tracts, 3. Medial longitudinal...

Anterior view Posterior view  ❑Has three levels. 1-Closed medulla at level of pyramidal decussation.  ❑Has three levels. 1-Closed medulla at level of pyramidal decussation. Tracts: 1. Spinocerebellar tracts. 2. Spinothalamic tracts, 3. Medial longitudinal bundle.  2-Closed medulla at level of sensory decussation. Central canal. Gracile and cuneate nuclei, large while their tracts become small. Axons from gracile and cuneate nuclei cross to opposite side forming sensory decussation.  Tracts: 1. Spinocerebellar tracts. 2. Spinothalamic tracts, 3. Medial longitudinal bundle. Reticular formation.  Cortico-spinal fibers: form two masses on the anterior surface of the medulla (pyramids). some cranial nerve nuclei : a) Hypoglossal nucleus. b) Dorsal vagal nucleus. c) lower part of solitary nucleus. d) Spinal trigeminal nucleus  3-Open Medulla: No central canal. Pyramid anterior. Olivary complex, formed mainly by: Inferior olivary nucleus (largest). The arcuate nuclei: anterior to the pyramids. Reticular formation.  Cranial nerve nuclei (9, 10, 11 &12): o Solitary nucleus (sensory nuclei of cranial nerves (IX & X). o Nucleus ambiguus and dorsal nucleus of vagus (motor nuclei of cranial nerves (IX, X and XI). o Hypoglossal nucleus. Trigeminal spinal nucleus and tract Vestibular and cochlear nuclei start to appear. Inferior cerebellar peduncles laterally.  Four cranial nuclei. located at the pons & medulla oblongata, at the floor of the 4th ventricle All nuclei are connected with the cerebellum, spinal cord, thalamus, cranial nuclei of extra ocular-muscles. They are responsible for maintenance of equilibrium and posture, perception of head position and acceleration, as well as general muscle tone. ❑ The pons is divided into posterior part (tegmentum ) and an anterior part (basis pontis ).  A- The Basis Pontis 1. Pontine nuclei: M o t o r n u c l e i receive the corticopontine fibers from the cerebral cortex and give pontocerebellar connections in the corticocerebellar pathway. 2. Transverse pontine fibers: Axons from the pontine nuclei to the cerebellum (M.C.P). 3. Pyramidal tract: they are descending corticopontine, cortico spinal & cortico bulbar fibers. 4. Middle cerebellar peduncles.  B- The Tegmentum: In all levels, contains ascending and descending tracts. Lower pons level (level of facial colliculus): Charactarized by the presence of: 1. Cavity of the 4th ventricle. 2. Spinal trigeminal nucleus (V), abducent nucleus (VI), Facial nerve nucleus (VII) and vestibulo-cochlear nerve nuclei (VIII). NB. Facial nerve fibers loop around abducent nucleus to form facial colliculus. 3. Trapezoid body ( transverse crossing fibers in auditory pathway) between tegmentum and basis pontis. 4. Inferior cerebellar peduncle (I.C.P.). Middle level of pons (at the trigeminal nuclei): It is characterized by the presence of: 1. 4th ventricle is closed. 2. Trigeminal nuclei (motor, main sensory & mesenchephalic nuclei). 3. Trapezoid body. 4. Superior cerebellar peduncle (S. C. P).  Consists of: A-The tectum 1-Inferior colliculi: the center for auditory reflexes. 2-Superior colliculi: center for vision reflexes (correlation of impulses from the retina with the body movements). B- The aqueduct Surrounded with area of grey matter which contains: 1. Trochlear nucleus (IV) at lower midbrain 2. Mesencephalic nucleus of V nerve 3. Occlumotor nucleus of III nerve at upper mid brain 3- Cerebral peduncles: Consists of crus cerebri, substantia nigra, tegmentum. ❑ Substantia nigra separates the tegmentum & the Basis pedunculi (crus cerebri). Its degeneration results in parkinsonism. ❑Basis pedunculi consists of descending fibers; corticobulbar, corticospinal & corticopontine ❑ Tegmentum: ❖ Anterior to grey matter and close to midline. ❖ Continous inferiorly with the tegmentum of the pons and superiorly with the thalamus. ❖ Its constituents vary according to the level of midbrain. ❖ Inferior colliculus level: o Deep origin of trochlear nerve. I- Mid-brain at the level of inferior colliculus : Midbrain at the level of superior colliculus Deep origin of oculomotor nerve.