× Didn't find what you were looking for? Ask a question
Top Posters
Since Sunday
a
5
k
5
c
5
B
5
l
5
C
4
s
4
a
4
t
4
i
4
r
4
r
4
This topic contains 1 attachment.
Home Q & A Board Biology-Related Homework Help Anatomy and Physiology
New Topic  
TheForumLord TheForumLord
wrote...
Posts: 2
Rep: 0 0
9 years ago
Dear experts,

I need to complete the laboratory experiments of "NERVE" from the University of Chicago and I am having several misunderstandings I will be glad to receive help with:

1.  As far as I understand, if we consider a single axon (as the one this lab focuses on), every action potential should look exactly the same, and have the same amplitude. If so, how is it possible that in our case (see attached picture), we have a decrease in the action potential amplitude when we decrease the stimulus intensity ? (see the red line I added on the picture)

2.Will someone please help me understand why does the progressive reduction of the stimulus intensity cause the onset of the action potential to occur at progressively longer times after the cessation of the stimulus? (I.e- we have an increase in the latent period?)

I will probably have some more questions regarding this lab experiments, and will be help to gain some more insights on.

Thanks a lot in advance !
 Attached file 
Thumbnail(s):
You must login or register to gain access to this attachment.
Read 1573 times
2 Replies

Related Topics

Replies
rsb
wrote...
#1
9 years ago
Once the depolarization caused by the stimulus is above threshold, the resulting neuronal action potential is a complete action potential (i.e., it is all-or-nothing). If the stimulus strength is increased, the size of the action potential does not get larger (see figure). If the size (i.e., amplitude) of the action potential is always the same and independent of the size of the stimulus, how then does the nervous system code the intensity of the stimulus? The trick that the nervous system uses is that the strength of the stimulus is coded into the frequency of the action potentials that are generated. Thus, the stronger the stimulus, the higher the frequency at which action potentials are generated. Therefore, we say that our nervous system is frequency-modulated and not amplitude-modulated. The frequency of action potentials is directly related to the intensity of the stimulus.



If a threshold stimulus is applied to a neuron and maintained (top, red trace), action potentials occur at a maximum frequency that is limited by the sum of the absolute and relative refractory periods (bottom, blue trace). Here, a threshold stimulus refers to that which is just strong enough to bring a resting neuron to threshold. Thus, with maintained threshold stimulus, subsequent action potentials occur only at the end of the relative refractory period of the preceding action potential. The top and bottom traces are on the same time scale. The dashed line represents the threshold voltage (Vthreshold) of approximately −50 mV. ARP, absolute refractory period; RRP, relative refractory period.
TheForumLord Author
wrote...
#2
9 years ago
Dear rsb,


Thanks for your reply.
I agree with all of your thoughts, but the thing is that (please check the attached figure I put in the first message) in this case if seems like the action potentials are "graded", and increasing the stimulus intensity cause an increase in the action potential amplitude.
Your explanation is exactly why I can't understand the reasoning behind this "graded action potential".

In addition, will you please help me with my second question?

Thanks again!
New Topic      
Quick Reply
Explore
Post your homework questions and get free online help from our incredible volunteers
  968 People Browsing
Start New Topic Take the Tour CoursesNew Study Tools Topics Trending Browse by Textbook
Live Chat
Related Images
  
 421
  
 143
  
 326