Bio111Guides

University of Alaska Southeast

Lab 13 Spinal Nerves

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Activity 1: Initiating stretch reflexes

Striking my subject’s knee with the reflex hammer resulted in a sudden upward jerk of the leg and foot. This happened with each knee tested. Striking the patellar ligament below the patella triggered an afferent (sensory) impulse in the femoral nerve to the spinal cord. At the spinal cord,  a motor neuron receives the impulse and then conducts an efferent (motor) impulse back to the quadriceps femoris muscle triggering contraction which causes the lower leg to jerk.

Trying the test again while my subject was distracted seemed to result in a slightly more vigorous response than the first time around. Mental distraction seems to results in a stronger reaction.  Doning the test again while my subject clasped the counter he sat on, again resulted in a knee jerk reflex, but the jerk seemed more tensed or tighter, not quite as sudden. We did not have my subject jog in place because he said he could jog “forever” before becoming fatigued. But I do think that muscle condition (being fatigued) would play an important part in the type of stretch reflex exhibited. I would think if the muscle was fatigued, the reflex would not be quite as strong or sudden. It would probably be a weaker, lesser jerk.

I did not get a good reflex ankle jerk with my subject. Maybe I didn’t strike the right area. I was a bit nervous of causing pain!

Activity 2: Initiating the crossed extensor reflex

On pricking my subject’s index finger with a pencil, I saw a strong reaction of the index finger flexing. The extensor part of this reflex seemed to occur more slowly than the previous reflexes tested. I didn’t see the contralateral effect of a response on the other side of the body (I didn’t know to look for that).

Activity 3: Initiating the plantar reflex

Testing the plantar reflex, my subject’s toes seemed to curl slightly while the foot straightened out from the ankle. Babinski’s sign (a normal reaction in newborns where the toes flair or spread out was absent.

Activity 4: Initiating the corneal reflex

I did not test the Corneal Reflex as I would not want to damage or hurt my subject’s eye (I was at work). But I conjecture that he would have blinked or quickly closed his eye had I touched the cornea with a cotton swab as directed. This reflexive action of the eyelid serves to protect the eye from damage by foreign objects.

Activity 6: Initiating pupillary reflexes

The efferent pathway results in the consensual response because the oculomotor nerves generate impulses from the same area to both eyes. (A consensual response is any reflex observed on one side of the body when the other side has been stimulated.) Both the sympathetic and the parasympathetic division of the ANS were active during testing of the pupillary reflexes. The purpose of the pupillary response would be to protect the eye from too much sunlight and to aid vision in very light or dark situations.

Activity 9: Testing reaction time for basic and acquired reflexes

(I still have to do Activity 9)

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