THE SPINAL CORD PART II ASCENDING TRACTS The spinal cord is divided into an "H" shaped central area of gray matter and surrounding white matter (myelinated fiber tracts). The white matter is divided into a dorsal, lateral and ventral funiculus. The dorsal funiculus (dorsal columns) are made up of thickly myelinated fibers whose cell bodies (like all sensory fibers) are in the dorsal root ganglia which lies near the intervertebral foramen. The fibers enter the dorsal horn and pass to the posterior funiculus where they ascend. 1. What area of the posterior funiculus do the fibers from the sacral area lie medial lateral dorsal ventral Right! No, the answer is A. The fibers layer on the lateral part of the posterior funiculus as they enter from more rostral parts of the body. At the level of the 6th thoracic segment the fibers form a more lateral group of fibers called the tractus cuneatus. 2. Fibers that ascend in the dorsal funiculus synapse in nuclei in the dorsal column at the level of the cervical spinal cord medulla pons mesencephalon Right! No, the answer is B. The fibers in the tractus gracilis synapse in the nucleus gracilis and the fibers in the more medial tractus cuneatus. On the dorsal surface of the medulla, these nuclei form two bumps called the clava and cuneate tubercles. The axons from these nuclei cross in the midline and ascend to the thalamus and from there to the sensory cortex. 3. The ascending dorsal spinocerebellar tract carries ______ impulses. pain and touch proprioceptive motor efferent vibratory Right! No, the answer is B. Proprioceptive impulses come from receptors in muscles,tendons and joints. The central processes of these neurons in the dorsal root ganglia enter the spinal cord and synapse in the nucleus dorsalis (column of Clark, lamina VII of Rexed). These second order neurons pass laterally and form the dorsal spinocerebellar tract. 4. The fibers in the dorsal spinocerebellar tract reach the cerebellum via the superior cerebellar peduncle (brachium conjunctivum) inferior cerebellar peduncle (restiform body) middle cerebellar peduncle none of the above Right! No, the answer is B. These fibers terminate in the rostral and caudal portion of the vermis. The actual information the cerebellum receives by way of the dorsal spinocerebellar tract involves strength and character of muscle contraction. 5. The fibers in the ventral spinocerebellar tract convey impulses largely from Ruffini corpuscles neuromuscular spindles Golgi tendon organs Pacinian corpuscles Right! No, the answer is C. The dorsal root fibers carrying these impulses ascend or descend a few segments in the dorsal funiculus and then synapse in laminae V to VII of Rexed. The second order neurons then cross the cord and ascend in the ventral spinocerebellar tract. 6. The second order neurons in the ventral spinocerebellar tract enter the cerebellum via the superior cerebellar peduncle (brachium conjunctivum) middle cerebellar peduncle inferior cerebellar peduncle (restiform body) none of the above Right! No, the answer is A. The fibers cross as they enter the cerebellum thus they undergo a double crossing - in spinal cord and cerebellum. 7. In addition to the dorsal funiculus, discriminative touch impulses may be carried by the ______ tract in the lateral funiculus. spinothalamic dorsal spinocerebellar ventral spinocerebellar spinocervical thalamic Right! No, the answer is D. The persistence of sensations carried by dorsal funiculus after total lesions of the dorsal funiculus indicate another tract carries these sensations. Spinocervical thalamic tract is believed to be this pathway. 8. The ascending lateral spinothalamic tract is concerned with proprioception touch pain and temperature pressure Right! No, the answer is C. As with the other sensory fibers the cell bodies for pain fibers are in the dorsal root ganglia. 9. The incoming fibers carrying pain impulses synapse the dorsal horn in laminae II to VI of Rexed. True False Right! No, the answer is true. The axons from cells in laminae II to VI in turn synapse in laminae V to VII and these axons cross in the ventral white commissure to the lateral funiculus (within a few segments above fiber entry level) to form the lateral spinothalamic tract. 10. In the spinothalamic tract sacral fibers are most lateral pain sensing fibers are located ventrally fibers conveying thermal sense are located dorsally fibers ascend to the thalamus Right! No, All the foils are correct! 11. Lesions involving the lateral spinothalamic tract cause loss of pain in contralateral half of body below the lesion thermal sense below the lesion, on contralateral side touch ipsilateral to lesion pain and thermal sense below the lesion in ipsilateral half of the body Right! No, the first two foils are correct! The fibers in the spinothalamic tract carry pain and temperature impulses from the contralateral side of the body. 12. Lesions of dorsal root ganglia cause loss of pain and temperature. ipsilateral to the lesion contralateral to the lesion bilaterally none of the above Right! No, the answer is A. A lesion of the dorsal root ganglia would block the impulses of the nerve before they reach the spinal cord, thus the sensory loss would be ipsilateral. In practice, the deficit from one dorsal root ganglion lesion probably could not be detected because of the overlap in skin from the spinal nerves above and below it. 13. A lesion in the white anterior commissure would cause loss of pain and temperature. ipsilateral to the lesion bilateral to the lesion contralateral to the lesion none of the above Right! No, the answer is B. In a condition called syringomyelia, the enlarged central canal damages the anterior white commissure of the spinal cord. If this occurs in the cervical area, some fingers may not perceive pain, a smoker could burn his fingers on a short cigarette and not feel it. 14. In the Gate Control theory of pain, the Gate is opened by small fibers with a continuous flow of impulses large, thickly myelinated fibers, which fire in response to impulse Right! No, the answer is A. 15. The anterior spinothalamic tract is concerned with pain temperature light touch proprioception Right! No, the answer is C. As with other sensory fibers from the periphery, the cell bodies of the anterior ventral spinothalamic tract are in the dorsal root ganglia. The proximal ends of the fibers synapse in dorsal horn laminae VI to VII and the second order neurons then cross to the opposite side in the anterior white commissure and ascend as the anterior spinothalamic tract. Some authors do not recognize a distinction between the anterior (ventral) and lateral spinothalamic tracts, and indicate that they have overlapping functions. The descending tracts in the spinal cord include the corticospinal, rubrospinal, vestibulospinal, reticulospinal and tectospinal tracts. 16. The cells of origin of the corticospinal tract are located in the dorsal root ganglia ventral horn of the cord cerebral cortex nucleus gracilis none of the above Right! No, the answer is C. The axons of the corticospinal tract descend through the brain, brain stem and much of the cord. 17. The axons of cortical motor neurons cross to the opposite side in the midbrain pons medulla cervical spinal cord Right! No, the answer is C. Most of the descending corticospinal fibers cross in the lower medulla (pyramidal decussation) and pass laterally to form the corticospinal tract. Those fibers that do not cross descend as the anterior corticospinal tract. 18. The caliber of the majority of the fibers in the corticospinal tract are small (1 to 4 micron) medium (5 to 10 micron) large (greater than 10 micron) Right! No, the answer is A. Only a few per cent of the fibers in the corticospinal tract are greater than 10 micron and these come from the large Betz cells in the cerebral cortex.