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Pyramidal tract and extra pyramidal tracts

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Pyramidal tract and extra pyramidal tracts

  1. 1.  Tracts originating from the brain and descending in to spinal cord  These tracts are concerned with various motor activities of body  Two groups › Pyramidal tract › Extra pyramidal tract
  2. 2.  Aka corticospinal tract  Contains axons of cell bodies present in motor cortex of brain.  Pyramidal cells of Betz  Origin :-  30% from primary motor cortex (Area 4)  30% from premotor area and supplementary motor cortex  40% from the somatic sensory area
  3. 3.  The fibers descend as a part of corona radiata  Then pass through the posterior limb of internal capsule  Then downwards through the brainstem  Forming pyramids in the medulla  At the lower part of medulla 90% of the fibers decussate in the midline to reach opposite side  Forming two separate tracts from here
  4. 4.  Constituted by crossed fibers  Descends in the lateral white funiculus of opposite side  These fibers terminate in the internuncial neurons of spinal grey matter.  Internuncial neurons synapse with motor neurons in anterior horn cells  Some fibers end directly on the AH cells  Axons of AH cells supply skeletal muscle through spinal nerve
  5. 5.  Formed by the uncrossed pyramidal fibers  They descend thro ant white funiculi on same side  They reach only till mid thoracic region  On reaching appropriate spinal segment they cross to the opposite side  Terminate in the same way as lateral corticospinal tract
  6. 6.  In brainstem some fibres terminate in motor nuclei of cranial nerve  They cross to opposite side at various levels of brainstem depending upon the nuclei  Which supply muscles of face
  7. 7.  Both the anterior and lateral corticospinal tracts ultimately innevate opposite side of the body  i.e Fibres from the right lobe of cerebral cortex terminate on the left AH cells
  8. 8.  UMN :- neurons giving origin to pyramidal tract  LMN :- AH cells along with their neuron constitutes LMN
  9. 9.  Fibres of CS tract are unmyelinated at birth  Myelination begins at 2nd week after birth and completes at 2years of age  Contains large fibres and small fibres  Large fibres disappear at old age leading to shaky movements
  10. 10.  Cerebral cortex controls voluntary movements of the body thro CS tract  Lesion produce paralysis of concerned muscle group  Sends collateral to other motor control systems like basal ganglia , cerebellum ..
  11. 11.  Descendings tracts other than pyramidal tract are called extra pyramidal tracts › Rubrospinal tract › Vestibulospinal tract › Reticulospinal tract › Tectospinal tract › Olivospinal tract › Medial longitudinal fasciculus
  12. 12.  Origin:- arises from nucleus magnocellularis or red nucleus in midbrain  Course :- fibres cross to the opposite side in the lower part of tegmentum of midbrain  After that follows a course similar to lateral CS tract  Termination :- on the interneurons along with CS tract
  13. 13.  Facilitates flexor muscles and inhibit extensor muscles  Red nucleus receives corticorubral fibres from ipsilateral motor cortex  Cortico-rubro-spinal tract acts as a alternate route of pyramidal tract  Reaches only upper three cervical segments
  14. 14.  Lateral Vestibulospinal Tract:- origin from lateral vestibular nucleus (deiter’s) at lower pons  fibres are somatotopically arranged in this nucleus  Course :- tract is uncrossed and lies in the ant funiculi  They terminate on alpha and gamma motor neuron thro interneuron
  15. 15.  Vestibular nucleus receives afferents from vestibular apparatus mainly from utricle  Adjustment of postural muscles to linear acceleration  Facilitates extensor muscles and inhibits flexor muscle  Maintenance of balance
  16. 16.  Fibres originates from medial vestibular nucleus  Descends thro the anterior funiculi and mostly uncrossed  Fibres ends in AH cells either directly or thro interneuron  Receives inputs from vestibular apparatus mainly from semicircular canals  Controls movements of head with respect to auditory and visual stimuli .
  17. 17.  Two divisions  Medial – pontine Reticulospinal tract  Lateral – medullary Reticulospinal tract  pontine Reticulospinal tract:- arises from medial pontine reticular formation and descends mostly uncrossed and terminates in alpha & gamma motor neurons in spinal cord thro interneurons
  18. 18.  Fibres orginates from medullary reticular formation (gigantocellular) , descends mostly uncrossed in the lateral funiculi and terminates in same way as pontine RS tract
  19. 19.  Reticular formation Receives afferents from cortex  Forming cortico-reticulospinal pathway  Control of movements and muscle tone  Also convey autonomic fibres from higher center to spinal cord
  20. 20.  Pontine and medullary nuclei functions opposite to one another in controlling › Muscle tone › Respiration › Vascular caliber › Antigravity muscles posture
  21. 21.  Fibres originates from superior colliculi  Fibres cross the midline at tegmentum of midbrain (dorsal tegmental decussation)  And descends thro anterior funiculi  Terminates in AH cells of upper cerviccal levels  Functions :- turning head and moving arms in response to visual or other stimuli
  22. 22.  Originates from inferior olivary nucleus  Descends uncrossed and terminates in AH cells  May control reflex muscle activity  Tract is of doubtful existence
  23. 23.  Extends from midbrain downwards  Fibres takes origin from › Vestibular nuclei › Reticular formation › Superior colliculus › Interstitial nucleus of cajal › Posteriior commisure › Has connection Cranial nerves 3, 4, 6, 7 , 8, 12  AH cells of muscles of neck  Function :- harmonius movement of eye and neck
  24. 24.  Upper Motor Neuron paralysis :- paralysis of UM neurons  Lower Motor Neuron Paralysis :- paralysis of LM neurons
  25. 25.  Monoplegia :- paralysis of all muscles of one limb  Hemiplegia :- paralysis of one half of body  Paraplegia :- paralysis of both lower limbs  Quadriplegia :- paralysis of all four limbs

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