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About tracts

1. Descending Tracts

2. Corticospinal (Pyramidal) Tract most important output pathway from the motor cortex originates about 30 per cent from the primary motor cortex 30 per cent from the premotor and supplementary motor areas 40 per cent from the somatosensory areas

3. Pathway of the Corticospinal Tracts After leaving the cortex, it passes through the posterior limb of the internal capsule and then downward through the brain stem, forming the pyramids of the medulla. The majority of the pyramidal fibers then cross in the lower medulla to the opposite side and descend into the lateral corticospinal tracts of the cord finally terminating principally on the interneurons in the intermediate regions of the cord gray matter a few terminate on sensory relay neurons in the dorsal horn and a very few terminate directly on the anterior motor neurons that cause muscle contraction.

4. A few of the fibers do not cross to the opposite side in the medulla but pass ipsilaterally down the cord in the ventral corticospinal tracts. Many if not most of these fibers eventually cross to the opposite side of the cord either in the neck or in the upper thoracic region. These fibers may be concerned with control of bilateral postural movements by the supplementary motor cortex.

5. Betz Cells found only in the primary motor cortex. are a population of large myelinated fibers with a mean diameter of 16 micrometers, They are most impressive fibers in the pyramidal tract. about 60 micrometers in diameter their fibers transmit nerve impulses to the spinal cord at a velocity of about 70 m/sec, the most rapid rate of transmission of any signals from the brain to the cord about 34,000 of these large Betz cell fibers in each corticospinal tract (3%) The total number of fibers in each corticospinal tract is more than 1 million,

6. 2.Anterior Vestibulospinal Tract • Originate from the medial vestibular nuclei in the medulla oblangata . • Most fibers uncrossed • In the anterior white column along the periphery, lateral to tectospinal tract • Run upto the thoracic segments of the cord • Terminate at Anterior Motor neurons either directly or via interneurons

7. 3.Lateral Vestibulospinal Tract • Origin from lateral Vestibular Nucleus in the Medulla ( Deiter Neucleus ) • Present throughout the cord • Anterior Part of the lateral white column • Very few fibers cross to the opposite side before descending • Terminate at Anterior Motor neurons directly or via Inter neurons • Impulses concerned with Tone and posture from vestibular apparatus and cerebellum.

8. 5.Tectospinal Tract • Arises from Sup Colliculus in the Mid Brain • Extend upto lower cervical • Cross the midline in dorsal tegmental decussation and descend in the Ant. White Column • Terminate at Ant. Motor neurons directly or via Inter neurons • Movemenat of hand in response to visual and auditory stimuli

9. 6.Rubrospinal Tract Arise from the Red Nucleus Lateral White Column Fibers descend to the spinal cord where they lie ventrolateral to and intertwined with the corticospinal tract  Excitation of the motor neurons controlling tone of limb flexor muscles and inhibitory to extension during gait Facilitatory of flexion and inhibitory to extension in cervical and lumbar spine and distal extremity muscles Red nucleus is related to force, velocity and direction of movement