Type Ia Sensory Fibers

[ecoli]

How do they sense the velocity of the muscle stretch, and how does that produce action potentials?

 

I'm trying to figure out how the patellar reflex works in detail for this lab report. I'm not sure if I need that in my report, but I'm very curious about it, and wikipedia sort of glosses over it.

 

"This change in length of the spindle is transduced (transformed into electric membrane potentials) by two types of sensory afferents,"

 

- How does this happen?

[Glider]

The membranes of the afferent terminals are sensitive to deformation. These afferent terminals are 'wound around' the spindles in a spiral. Mechanical deformation of the afferent terminal membrane causes ion channels to open resulting volleys of action potentials (APs).

 

Afferent AP volleys signal two components of an event; duration (length of volley) and intensity (frequency of volley; i.e. number of APs in the volley).

 

So, a slow deformation of a muscle spindle (e.g. raising a glass to your mouth) provides a volley of longer duration and lower frequency than a fast deformation (e.g. ballistic motion like throwing a ball) that will produce shorter duration volleys of higher frequency.

 

It's pretty much the same for all sensory (afferent) fibres. As all APs are the same, regardless of the stimulus type, afferent fibres use length and frequency of AP volleys to signal duration and intensity of the stimulus.

[ecoli]

So mechanical deformation is linked to some sort of physically-gated ion channel in the afferent sensory neurons?

[Glider]

Yep. I'm a bit hazy on the precise detail though. It's either that mechanical deformation of the membrane causes a locallised change in membrane potential that triggers voltage gated sodium channels, or that mechanical defomation directly causes ion channels to open (which causes a localised change in membrane potential...blah, blah).

 

I think it's the latter, as I can't think of another way of inducing localised depolarisation.

[ecoli]

ok, thanks.

[CharonY]

Just wanted to add that they are indeed stretch sensitive ion channels. AFAIK the precise mechanism of the way these channels react to the stretch is still unknown. There was something else involved by my memory is failing me now.

[blike]

I have these notes from my neuroscience class which covers this process in detail -- but my school "portal" is down and I have no idea where I put the actual hard copies. I'll get them to you as soon as the portal is back up

[Glider]

Thanks CharonY, I thought they were, but time takes it toll.

 

That'd be useful Blike, thanks

[Revenged]

I'm trying to figure out how the patellar reflex works in detail for this lab report. I'm not sure if I need that in my report, but I'm very curious about it, and wikipedia sort of glosses over it.

 

One point that might help you... Quadracept contraction is caused by a monosynaptic reflex but the antagonistic relaxation of hamstrings is caused by a 3 neural pathway... The extra neurone is an interneurone ('relay') neurone in the CNS...

[ecoli]

One point that might help you... Quadracept contraction is caused by a monosynaptic reflex but the antagonistic relaxation of hamstrings is caused by a 3 neural pathway... The extra neurone is an interneurone ('relay') neurone in the CNS...

 

Yep, I knew that