![• These nuclei are supplied by nerves from
both sides of the brain, with the exception
of the parts of the facial nerve that control
muscles of the lower face. These muscles
are only innervated by nerves from the
contralateral (opposite) side of the
cortex.[6]](https://image.slidesharecdn.com/23-descendingtracts-231004015542-a47d1b0d/85/23-Descending-tracts-ppt-26-320.jpg)
23-Descending tracts.ppt
- 9. Descending tracts • Pyramidal – corticospinal and corticobulbar • Extrapyramidal
- 12. • In neuroanatomy, the corona radiata is a white matter sheet that continues ventrally as the internal capsule and dorsally as the centrum semiovale. This sheet of both ascending and descending axons carries most of the neural traffic from and to the cerebral cortex. The corona radiata is associated with the corticopontine tract, the corticobulbar tract, and
- 13. • The cerebral crus (crus cerebri) is the anterior portion of the cerebral peduncle which contains the motor tracts, travelling from the cerebral cortex to the pons and spine. The plural of which is cerebral crura
- 19. CORTICOSPINAL TRACTS • Concerned with voluntary discrete & skilled movement, especially of distal parts of limbs • Formed of one neuron • Cells of origin: Large Betz cells in precentral gyrus (primary motor cortex)
- 20. CORTICOSPINAL TRACTS LATERAL CORTICOSPINAL TRACT • Formed of 75 – 90% of fibers • Fibers decussate in the medulla (motor decussation) • Fibers descends in lateral white column of spinal cord • Fibers terminate in contralateral ventral horn cells of spinal cord
- 21. CORTICOSPINAL TRACTS VENTRAL CORTICOSPINAL TRACT • Formed of 10 – 25% of fibers • Fibers descend uncrossed in medulla • Fibers descends in ventral white column of spinal cord • Fibers decussate near to their termination in the spinal cord • Fibers terminate in contralateral ventral horn cells of spinal cord
- 26. • These nuclei are supplied by nerves from both sides of the brain, with the exception of the parts of the facial nerve that control muscles of the lower face. These muscles are only innervated by nerves from the contralateral (opposite) side of the cortex.[6]
- 28. RUBROSPINAL TRACTS • Cells of origin: red nucleus in midbrain • Receives afferents from motor cortex & cerebellum • Represents a route through which cerebral cortex & cerebellum can influence motor activity • Axons cross in ventral tegmental decussation
- 29. RUBROSPINAL TRACTS • Axons descend in lateral white column of spinal cord (Tract is ventrolateral & partly mixed with lateral corticospinal tract) • Axons terminate in contralateral ventral horn cells of spinal cord • The tract carries excitatory fibers to motor neurones of limb flexor muscles
- 31. TECTOSPINAL TRACT • Cells of origin: superior colliculus in midbrain • Axons cross in dorsal tegmental decussation • Axons descend in ventral white column of spinal cord • Axons terminate in contralateral ventral horn cells of spinal cord • The tract mediates reflex movement in response to visual stimuli
- 32. VESTIBULOSPINAL TRACTS LATERAL VESTIBULOSPINAL TRACT • Cells of origin: lateral vestibular nucleus • Axons desend in ventral white column of spinal cord • Axons terminate in ipsilateral ventral horn cells of spinal cord • The tract mediates excitatory influences upon extensor motor neurones to maintain posture
- 33. VESTIBULOSPINAL TRACTS MEDIAL VESTIBULOSPINAL TRACT • Cells of origin: medial vestibular nucleus • Axons desend in ventral white column of spinal cord (as a part of medial longitudinal fasciculus) • Axons terminate in ipsilateral ventral horn cells of spinal cord • The medial longitudinal fasciculus consists of both ascending & descending fibers that link vestibular nuclei to nuclei supplying the extraocular muscles for coordination of head and eye movements
- 35. RETICULOSPINAL TRACTS MEDIAL RETICULOSPINAL TRACT • Cells of origin: pontine reticular formation • Axons descend in ventral white column of spinal cord • Axons terminate in ipsilateral ventral horn cells of spinal cord
- 36. RETICULOSPINAL TRACTS LATERAL RETICULOSPINAL TRACT • Cells of origin: medullary reticular formation • Axons descend in ventral white column of spinal cord on both sides (both crossed & uncrossed) • Axons terminate in ipsilateral & contralateral ventral horn cells of spinal cord
- 37. RETICULOSPINAL TRACTS • Concerned with control of reflex activity & muscle tone
- 38. • Thank u ..
- 39. CORTICOSPINAL TRACTS PATHWAY • Axons descend in : 1. Corona radiata 2. Posterior limb of internal capsule 3. Crus cerebri (middle 3/5) 4. Basis pontis 5. Pyramid of medulla