1. What is an alpha motor neuron and where is it located?
2. What is an axon and what is used for myelination of an axon?
3. What are the terminal nerve branches and what is the significance of the innervation ratio?
4. What is the difference between Type I and Type II motor neurons? Which is tested in electrodiagnosis?
5. What is the Henneman Size Principle?
Answers:
1. An alpha motor neuron is the cell body of the motor nerve and is located in the anterior horn of the spinal cord.
2. An axon is the branch of the cell body that propagates current. It is myelinated by Schwann cells. (Or may be unmyelinated.)
3. Terminal nerve branches extend from the distal axon and innervate individual muscle fibers. The innervation ratio (IR) refers to the number of fibers innervated by one axon. A higher IR implies more force is generated while a lower IR is associated with muscles for fine movement.
4. Type I has smaller cell body, thinner axons, lower IR, and are slow twitch. Type II has larger cell body, thicker axons, higher IR, and are fast twitch. Only Type I fibers are tested in electrodiagnosis.
5. The Henneman Size Principle says that smaller alpha motor neurons (Type I) are recruited first.
3 comments:
In your book on page 297 you state that electrodiagnostics only eval Ia fibers. These axons are listed in table 5-2 as the largest diameter. Yet, on this post and on page 296 table 5-1 it states that Type I motor neurons (tested in electrodiagnosis) have thinner axonal diameter. please clarify this. I get that the "test answer" is Ia and that alpha's are the ones tested but I can't rectify the "thin" Type I motor neuron's with the "large diameter" Ia fibers.
Yeah, I don't 100% understand table 5-2.
And by the way, I am NOT Cuccurullo. I'm just outlining the book for my own study purposes.
great job!
i'm pm&r specialist in turkey and i studied this book last year and thinking of making a blog like this.
but there is no need any more :)
i ll advise to all friends.
in turkey we are also so busy with rheumatology as pm&r specialist, even we have fellowship program in rheumatology. do you a website as good as yours:) in rheumatology?
thank you again.
ozgur
Post a Comment