Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Thursday Neuroanatomy 3-3-2011 Lecture 4 Descending tracts Tracts of spinal cord Ascending tracts descending tracts 1- Ascending tracts : bundles of ascending nerve fibers (sensory nerve fibers) that ascend from the spinal cord to higher centers to connect the spinal cord with the brain . The ascending tracts carry afferent information that's divided into 2 main groups: - Exteroceptive information: originates from outside the body such as pain, touch and temperature. - proprioceptive information: originates from inside the body such as muscles and skin. 2- Descending tracts : bundles of descending nerve fibers (motor nerve fibers) that descend in the white matter from different supraspinal nerve centers in the brain. The descending tracts carry efferent information . Simple form of descending motor pathway from the cerebral cortex to the skeletal muscle, note the 3 neurons involved (1) (2) (3) . Simple form of the ascending sensory pathway from the sensory nerve ending to the cerebral cortex, note the 3 neurons involved. 1 The motor neurons Upper motor neurons lower motor neurons 1- Lower motor neurons: the motor neurons situated in the anterior gray columns of the spinal cord (alpha and gamma motor neurons) that send axons to innervate skeletal muscles through the anterior root of the spinal nerves and they constitute the final common pathway to the muscles . Lower motor neurons affected by nervous impulses that descend from the medulla, pons, midbrain and cerebral cortex . 2- Upper motor neurons : the neurons above lower motor neurons as the supraspinal neurons and their tracts. Descending tracts From brain stem and pass through from cerebral cortex Lateral part of white column anterior or medial part Rubrospinal tract 1- tectospinal tract 2- Vestibulospinal tract 3- Reticulospinal tract Pontine medullary 2 Corticospinal tract 1- Corticospinal tract **Origin : cerebral cortex (in common) 1/3 of the fibers originate from primary motor cortex (area 4) 1/3 originate from secondary motor cortex (area 6) 1/3 originate from parietal lobe (area 3,1, and 2 ) **termination :anterior gray horn (alpha and gamma motor neurons) ** function : carry motor information from cerebral cortex to alpha and gamma motor neurons that innervates muscles through the anterior root of spinal cord . **path : 1- The Corticospinal tract pass from cerebral cortex without crossing until the lower part of medulla oblongata where the bundles become grouped together along the anterior portion of the medulla oblongata to form a swelling known as pyramid and that's why corticospinal tract is called pyramidal tract . 2- At the junction of the medulla oblongata and the spinal cord: ** most of the fibers cross the midline at the decussation of the pyramids and enter the lateral white column of the spinal cord to form the lateral corticospinal tract . ** the remaining fibers don't cross in decussation but descend in the anterior white column of spinal cord as the anterior spinal corticospinal tract. 3- These fibers terminate eventually in the anterior gray column of the spinal cord . 4- Alpha and gamma motor neurons send axons to innervate skeletal muscle through the anterior root of spinal nerves . Note : motor decussation is crossing of the right and left parts of lateral corticospinal tract at the lower border of medulla oblongata . 3 2- Rubrospinal tract : **origin : red nucleus in midbrain **termination : anterior gray column ** function : facilitates the activity of flexor muscles and inhibits the activity of extensor muscles . ** Contralateral (there's crossing in this tract) 3-Vestibulospinal tract : **origin : vestibular nuclei ** termination : the anterior gray column **function: the inner ear and the cerebellum by this tract facilitate the activity of extensor muscles and inhibit the activity of the flexor muscle in association with the maintenance of balance. **ipsilateral (this tract descends without crossing) 4-Tectospinal tract : **origin : Superior colliculus of midbrain **termination : the anterior gray column of the upper cervical segments of the spinal cord (don't forget that just the upper cervical segments). **function : coordination of movement of head, neck and eyes in response to auditory or visual stimulus . **Contralateral (there's crossing ) -notice that tectospinal tract and Rubrospinal tract originate from midbrain. 5- Reticulospinal tract : **origin : reticular formation that is (group of nerve cells and nerve fibers exist throughout the brain stem = midbrain+pons+medulla oblongata. **termination: anterior gray column **function : influence voluntary movement and reflex activity . 4 (Dr said that its function isn't that important to memorize ) **parts : 1- Pontine reticulospinal tract : formed by neurons in pons that send axons (pontine reticulospinal tract) which are mostly uncrossed down into the spinal cord. 2- Medullary reticulospinal tract : formed by similar neurons in medulla that send axons(medullary reticulospinal tract) which are crossed and uncrossed and mostly crossed. - I put pictures of all the tracts in the last page so that u can compare between them .. - you can visit this website(http://neuroscience.uth.tmc.edu/s3/iii2-3.html) that show the path of each tract when u press (play) beside the picture of each one .. DONE BY : Do7a n3erat Dedicated to : *my Brother Seif (wish u the best in the world ) * my Loyal sisters & friends : Lara abu 7ammour & Hind mihyar *my sweet friends : Samar 3abid – Lara mazahreh - Maryam Bader – Zein Abu zeitoon 5 6