What are reflexes mediated by spinal nerves reffered to ?

Question

What are reflexes mediated by spinal nerves reffered to ?

and

What are reflexes mediated by cranial nerves reffered to ?

Answer 1

This is actually a pretty complicated question, but I'll try and give you a relatively simple answer.

By definition, a reflex is an involuntary, stereotyped response to a sensory input.  That's a fancy way of saying that it's something you can't help doing when the proper stimulus is applied, and that it looks pretty much the same in everyone.  

All reflexes have some kind of receptor structure and an associated afferent (going towards something with a cell body to synapse or fire on) neuron and efferent (coming back to the  site) neuron.  Most reflexes have another neuron in between as well, which is, logically enough, called an 'interneuron.'  The stimulus comes from the end organ you are testing (usually a tendon, for spinal reflexes).

As a general rule, reflexes mediated by spinal nerves generally have afferents with cell bodies in a dorsal root ganglion (a structure just outside the spinal cord) and going to alpha motor neurons in the anterior horn of the spinal cord.  At least, that's the case for the commonly known reflexes like the patellar (knee-jerk) reflex and the biceps and brachioradialis reflexes (which are NOT mediated by cranial nerves, but rather by cervical nerves C5 and C6).  So I think that is the answer you are looking for to your first question, although this is a vast oversimplification.  There is also some input from the cortex of the brain and in some cases from segments of the spine higher than the one being tested (which is the 'suprasegmental' aspect referred to above).

Cranial nerves are much more complicated to explain.  Probably the best explanation I can give you in a brief format is that cranial nerves synapse in structures within the brain called 'nuclei,' which are basically clusters of cell bodies within the brainstem that are homologous to the areas in the spinal cord where spinal nerve bodies are.  Cranial nerve reflexes include things like the gag reflex (which tests CN X or the vagus nerve, along with CN IX or the glossopharyngeal) and the corneal reflex (CN V or the trigeminal nerve as well as CN VII or the facial nerve).

Hope that helps!

Answer 2

As the spinals nerves are originated from spinal cord, the reflexes mediated by them are reffered to as spinal reflexes. Depending upon the segments involved, the spinal reflexes are divided into 3 groups:

segmental;intra segmental & suprasegmental spinal reflexes.



Reflexes mediated by cranial nerves are reffered to as cranial nerve reflexes.There are 12pairs of cranial nerves,each with a name that refers to its function or appearance.Cranial nerve reflexes have specific names according to there function. eg:gag reflex,biceps reflex,brachioradialis reflex etc.