Lecture# 10 SC pathways+dermatomes.p.ptx

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1. Function of spinal cord & ascending tracts + dermatomes

2. SPINAL CORD FUCNTIONS OF SPINAL CORD AND ASCENDING TRACTS 2

3. Spinal Cord A thin column of nerve tissue that extends downward from the brain through the vertebral column to the level of the second lumbar vertebra. Transmits pain signals and other nerve impulses to and from the brain and controls reflexes actions. About 18 inches (45 cm) long Located in the vertebral canal Ends between vertebrae L 1 and L 2 31 pairs of spinal nerves 3

4. Spinal Cord Regions Cervical Thoracic Lumbar Sacral 4

5. Three main components 1. Spinal nerves 2. Nerve Tissue 3. Meninges 5

6. Figure 13-2 6

7. Conus medullaris thin, conical end of the spinal cord Cauda equina nerve roots extending below conus medullaris Filum terminale thin thread of fibrous tissue at end of conus medullaris attaches to coccygeal ligament 7

8. Functions of spinal cord To propagate sensory stimuli from organs to the brain To carry commands from the brain towards the organs Reflex action 8

9. TRACT It is a bundle of fibers carrying one or a group of motor or sensory impulses in CNS having a similar origin, course, termination and function. 9

10. Ascending tracts Carry afferent impulses from spinal cord to brain. Pathway for each sensation is formed by two or three groups of neurons, which are: 1. First order neurons 2. Second order neurons 3. Third order neurons 10

11. First order neuron First order neurons receive sensory impulses from the receptors and send them to sensory neurons present in the posterior gray horn of spinal cord through their fibers

12. dorsal root dorsal root ganglion spinal nerve dorsal horn 12 CNS FIRST ORDER NEURON

13. Second order neuron Second order neurons are the sensory neurons present in the posterior gray horn. Fibers from these neurons form the ascending tracts of spinal cord. These fibers carry sensory impulses from spinal cord to different brain areas below cerebral cortex ( subcortical areas) such as thalamus . All the ascending tracts are formed by fibers of second order neurons of the sensory pathways except the ascending tracts in the posterior white funiculus , which are formed by the fibers of first order neurons.

14. SECOND ORDER NEURON cross the mid line in front of central canal VPL 1 st 2 nd 14

15. Third order neuron Third order neurons are in the subcortical areas. Fibers of these neurons carry the sensory impulses from subcortical areas to cerebral cortex.

16. Ascending tracts Carry afferent impulses from spinal cord to brain Tracts in posterior column 1. Fasciculus gracilis carries proprioception and fine touch from lower half of body 2. Fasciculus cuneatus carries proprioception and fine touch from upper half of body 19

17. Tracts in anterior column 3. Anterior or ventral spinothalamic tract carries simple touch from all body below head Itch, Tickle, Pressure, Crude touch sensations 4. Anterior or Ventral spinocerebellar tract proprioceptors 20

18. Tracts in lateral column 5. Lateral or dorsal spinothalamic tract: carries pain and temperature from all body below head 6. Lateral or dorsal spinocerebellar tract: carries unconscious kinesthetic sense ( muscle memory) 21

19. 7. Spino tectal tract: Provide afferent information for spino visual reflexes and brings movements of the eyes and head toward the source of the stimulation 8. Spino olivary tract Provides an indirect pathway for further afferent information to reach the cerebellum 9. Spino vestibular tract balance by facilitating the activity of the extensor muscles 10. Spinopontine tract They allow modification of actions, or error correction, and are hence important in learning motor skills 11. Spinoreticular tract The tract is from spinal cord---to  reticular formation to  thalamus . It is responsible for automatic responses to pain, such as in the case of injury. 22

20. Table no 143.2 Ascending tract of spinal cord Page no 808.. (v. imp )

21. Figure 13–8 Dermatome Area of skin supplied by single spinal nerve. 24

22. Significance of dermatomes Dermatomes have clinical significance, especially in the diagnosis of certain diseases. Symptoms that follow a dermatome, such as pain or a rash, may indicate a pathology that involves the related nerve root. Examples include dysfunction of the spine or a viral  infection .

23. Example Viruses that lie dormant in nerve ganglia (e.g.  varicella zoster virus, which causes both chickenpox  and   herpes zoster commonly  shingles), often cause either pain, rash or both in a pattern defined by a dermatome. However, the symptoms may not appear across the entire dermatome

24. Thanksss ..