Descending Tracts - BMS 301 - Galala University - Spring 2023 PDF

BMS 301 Faculty of medicine Spring 2023 Galala University gu.ed u. eg The Descending Tracts By Prof.Dr. Eman Habib Dr.Waleed Nasr  Intended...

BMS 301 Faculty of medicine Spring 2023 Galala University gu.ed u. eg The Descending Tracts By Prof.Dr. Eman Habib Dr.Waleed Nasr  Intended Learning Objectives (ILOs) By the end of this lecture, the students should be able to: By the end of this lecture the student will be able to: 1. Enumerate and Describe the anatomy of descending tracts 2. Explain the effect of injury of these tracts 3. Compare and contrast between these different pathways 3 DESCENDING TRACTS  DESCENDING TRACTS  They are descending fibers concerned with the  VOULANTRY CONTROL OF MOVEMENT,  Muscle Tone And Posture Descending  Descending tractsoriginate pathways from THE CEREBRAL CORTEX primarily  PYRAMIDAL DESCENDING TRACTS From THE TRACT CEREBRAL CORTEX Motor Cells in The Cerebral Cortex CORTICO –SPINAL CORTICO – NUCLEAR TRACT. TRACT = CORTICO – BULBAR SPINAL CORD ANTERIOR CRANIAL NERVE TRACT HORN CELLS NUCLEI in BRAIN STEM MUSCLE OF THE MUSCLE OF THE BODY HEAD  PYRAMIDAL TRACT DESCENDING TRACTS From THE CEREBRAL CORTEX Cerebral Cortex CORTICO – NUCLEAR TRACT =motor CORTICO – BULBAR nuclei of cranial nerves TRACT (Brain Stem) CORTICO –SPINAL TRACT. spinal cord (AHC ; anterior horn cells).  PYRAMIDAL DESCENDING TRACTS From THE TRACT CEREBRAL CORTEX General Rules in Efferent (Motor) Pathway: the Efferent (Motor) Pathway is formed of 2 NEURONS: Upper A) Upper motor neuron: motor neuron Motor Cells in The Cerebral Cortex  Brain stem (cortico nuclear)  spinal cord (cortico-spinal ). B) Lower motor neuron: AHC (spinal cord )  peripheral nerves motor nuclei of cranial nerves (Brain Stem)  cranial lower Cranial nerves motor All these nerves terminate in the striated muscles. neuron  CORTICO –SPINAL TRACT.  Origin: giant pyramidal Pyrami dal neurones CELL or Betz cells S  The majority of fibers arise from  Motor Cerebral Cortex : Motor Cerebral  Motor Area 4 Cortex some Premotor fibers ariseArea 6. from  Sensory cortex  CORTICO –SPINAL TRACT. Laminati  In The Cerebral on: Cortex: the body is represented upside down  the face area lowermost  foot area on the medial surface of the cerebral hemisphere.  Axons of neurons in the cerebral cortex descend & converge in the corona radiata.  In The Internal  CORTICO –SPINAL TRACT. coro na radia ta Inter nal caps ule  Pass in the posterior limb  CORTICO –SPINAL TRACT.  Course:  The Cerebral Cortex  In The Internal Capsule  At the midbrain  At the pons  At the medulla oblongata  spinal cord  CORTICO –SPINAL TRACT.  Course in the brain stem: crus cereb  At the midbrain ri middle 3/5 of the crus cerebri  At the pons Descend as scattered Pyram bundles id  At the medulla oblongata Fibers collect in the medulla form the pyramid  CORTICO –SPINAL TRACT.  at the level of the Medulla  most of the descending fibers cross the midline  (Motor Decussation)  Lateral enter theCortico- lateral white Spinal column Tract  The remaining fibers  of the spinal cord to form DO NOT CROSS the  midline  descend in the spinal Anterior cord Cortico-  In Spinal Tract the Anterior white column   CORTICO –SPINAL TRACT. Lower order neuron (2 nd ): 80% crossed motor anteri nerves end in later or corti al lateral gr. of corti spin co- spin al Anterior horn al co- cells supply muscles of un-crossed 20% limbs motor nerves end in medial gr. of Anterior horn cells of both sides Supply muscles of trunk trunk Ms are Anteri or horn cells Lateral Medial group : group : un-crossed 20% 80% motor nerve end in crossed medial gr. Of both motor n. sides end in this Supply muscles of group trunk trunk supply Ms are CORTICO –SPINAL TRACT. Upper motor neuron lower motor neuron  Upper Motor Neuron Lower Motor Neuron Lesion Lesion Means Lesion of the pyramidal Lesion of AHCs or motor tract cranial nuclei e.g. e.g. capsular hemiplegia. poliomyelitis. Movements Only voluntary All movements are lost movements are lost & the muscle cannot while the involuntary & be moved by any emotional movements means i.e. it is Paralysis are intact of muscle i.e. it is paralysis of movement Muscle tone Clasp knife spasticity Hypotonia [flaccidity] occurs due to occurs. interruption of inhibitory fibers Atrophy Does not occur Disuse atrophy occurs  PYRAMIDAL TRACT DESCENDING TRACTS From THE CEREBRAL CORTEX Cerebral Cortex CORTICO – NUCLEAR TRACT =motor CORTICO – BULBAR nuclei of cranial nerves TRACT (Brain Stem) CORTICO –SPINAL TRACT. spinal cord (AHC ; anterior horn cells).  Cortico-nuclear tract  Part of the descending motor fibers reach the BRAIN STEM (not reach spinal cord )  end on MOTOR NUCLEI of CRANIAL NERVES that lie in the brain stem  which supply muscles of the head.  Each nuclei receive double innervation :  Corticobular tract Medial cortico- Lateral cortico – bulbar bulbar TRACT Nuclei of Nuclei of cranial cranial nerves nerves 3,4,6 5,7,9,10,11,12 Cortico-nuclear  Each tract nuclei receive double innervat ion contralat eral tract Except Two ipsilate ???ral tract  Cortico-nuclear tract Two exceptions : receive Contralateral corticonuclear fibers only 1- lower 1/2 of nucleus of facial nerve CR.N.VII  muscles of the lower part of the face. 2- part of hypoglossal  II. Extrapyramidal Tracts  These are descending tracts  apart from the pyramidal tr.  that influence the AHCs.  named according to their starting point.  either crossed, uncrossed, or a combination.  excitatory or inhibitory to Lecture Quiz  Referencess 1.Richard S. Snell, Clinical Neuroanatomy, from page 137- 166 2- Gray's Anatomy, 40th Edition, 2008 Thank You gu.edu.eg