25. Describe at least two characteristics for each region of the spinal cord whe

Question

25. Describe at least two characteristics for each region of the spinal cord when looking at a histological, horizontal cut. Remember WWGG 26. Name the three plexuses. Identify one spinal nerve from each plexus and describe its function (i.e. what group of muscles does it innervate?) What would loss of function in that nerve constitute? 27. Draw and label the components of the polysynaptic reflex arc. How do these components work to improve reaction time? 28. What nerves give rise to general senses? What are the two types of general sensory pathways? How do they differ? What are examples of general senses? 29. What nerves give rise to special senses? What are the five special senses? Identify the cranial nerve involved with each

Explanation / Answer

25. The histological horizontal cut of a spinal cord shows that it is bilaterally symmetrical. The spinal cord is separated into two halves by ventral median fissure on the ventral side. For the dorsal side, they are demarcated by dorsan median sulcus. A dorsan median spetum further separates the two halves dorsally. The entry of dorsal rootlets are marked by dorsolateral sulcus.

The center of the section shows the central canal which is lined by ependymal cells. The central canal is surrounded by the gray matter which is shaped like a butterfly. The white matter further surrounds the gray matter and fills up the remaining space of the section.

The white matter gradually ceases towards the end of spinal cord and the gray matter blends into a single mass. The differential distribution of myelin in the central nervous system accounts for the differences in white matter and gray matter. White matter appears white in colour while gray matter appears to be grayish. White matter contain myelinated axons and myelin producing oligodendrocytes. Moreover, white matter also do not contain neuronal cell bodies. Gray matter contains somata, neuronal cell bodies and unmyelinated axons.

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