What are dermatomes and how are they related to spinal nerves?

[sameeralord]

wiki-A dermatome is an area of skin that is mainly supplied by a single spinal nerve. There are eight cervical nerves, twelve thoracic nerves, five lumbar nerves and five sacral nerves. Each of these nerves relays sensation (including pain) from a particular region of skin to the brain.

My understanding is that one spinal nerve contains bothe afferent and efferent fibers. So shouldn't a dermatome have an efferent compartment as well. Do dermatomes only have afferent fibres or is it simply that we consider only the afferent part as the dermatome of that spinal nerve.

Thanks!

 

[Monique]

I have no idea what you just said What kind of classes are you taking?

 

[Moonbear]

I have no idea what you just said What kind of classes are you taking?

Anatomy.


Dermatomes refer to the sensory components of the spinal nerves. But it is correct that spinal nerves convey both efferent and afferent fibers. Only a portion of each spinal nerve gives off the cutaneous branches that supply the skin, the rest goes elsewhere, such as the muscles (myotomes get even more confusing than dermatomes!).

Also, keep in mind that the definition you've given for dermatomes is what you see in the simplest examples, such as along the thorax and abdomen. The limbs are a bit more complicated, because the spinal nerves supplying them form plexuses first before they give off branches providing cutaneous innervation. You can roughly map out dermatomes in the limbs, but there's also overlap, which is why you'll see different dermatome maps in different textbooks...not everyone agrees on them. It also means that you won't necessarily see anesthesia of a region unless two or more spinal levels are damaged, because of that overlap. (This is of course WHY you need to learn dermatomes, because testing for loss of sensation can help assess the level and extent of a spinal cord or spinal nerve injury.)

 

[sameeralord]

Thanks! Good stuff!

 

[Monique]

Anatomy.

Ah, I know how to distinguish a hand from a foot and what the general layout of the organs in the body is, but that's generally how far my knowledge of gross anatomy goes I guess those courses were only offered to med students, it's an interesting subject though.

 

[Moonbear]

Ah, I know how to distinguish a hand from a foot and what the general layout of the organs in the body is, but that's generally how far my knowledge of gross anatomy goes I guess those courses were only offered to med students, it's an interesting subject though.

I'm curious if sameeralord is in med school or some other major. We do offer some undergrad anatomy courses for specific health-related majors, and other schools do offer more general anatomy courses for undergrad bio majors, but they usually don't bother getting much into things like dermatomes. Usually we only torture the med students with those, and give a really basic explanation to the dental students. It's really only the ER docs and neurologists who end up needing to use them in practice, the rest just need it to pass their board exams and have some general sense that an area of numbness on the skin is a good reason for referral to one of those other two types of doc.