PHYS20008 membrane potential question

[Starlight]

What do you define as good quality? Is it like 2-3 sentences or a full paragraph etc?

You'll kind of get an indication from each blog i.e what is required. Just say what you want to say in each post, each post can be of different lengths. I think you can imagine if you were a moderator of the blog posts that 2 sentences is not really going to be a good indication of what you have learnt from the course/blog topic.

[Belgarion]

Hi guys,
in the attached screenshot, I'm kind of confused about one thing. 
If you look at the yellow area (the active area where the Na channels are open) you can see that the polarity across the membrane is reversed (negative outside, positive inside).
Is this really accurate? 
So, I understand that the -90mV charge that holds K+ inside the cell at RMP is due to negatively charged proteins and stuff like that (I actually wish they didn't gloss over it so much, because its pretty confusing to just say "the cell has a negative charge". Like, what?).
But at the peak of a action potential, is it REALLY a negative charge on the outside of the membrane?  Or did they just draw it like that for illustrative purposes?  I don't really understand how the polarity totally swaps - I understand that the concentration gradient across the membrane gets reduced, but to have it switch polarity completely?
Does anyone know what I'm on about? I'm confused.

Also dont forget that it just involves the ions at the very surface of the membrane. There are still millions of of ions on either side of the membrane that do not move

[ss12345]

Hey guys,

Just going the Week 4 Concept Check quiz and having some confusion over one question....

Which of the following could potentially inhibit an alpha motor neuron?? Select all that apply

The golgi tendon organ reflex
The muscle spindle reflex
Inputs from the brain motor cortex
Inputs from the cerebellum
Local spinal cord interneurons

What do you think? I know GTO reflex will definitely inhibit AM neurons. I thought no to muscle spindle reflex at first but then I realised while this results in excitation of some AM neurons, it will cause inhibition in the antagonistic muscle... therefore it also applies. Local spinal cord interneurons I suspect is correct but really not sure about the brain motor cortex and the cerebellum!! Any ideas??

[MelonBar]

hey mate i defo think local cord interneurons is one, but dunno about muscle spindle/motor cortex/cerebellum. i know the motor cortex can defo activate alpha MNs, and the cerebellum is involved in muscle memory and balance according to charles. there might be more info in the pre-reading textbook refs or modules.

[MelonBar]

carn fellas motor cortex?? cerebellum?

[Starlight]

carn fellas motor cortex?? cerebellum?

I think all of these are correct:
The golgi tendon organ reflex
The muscle spindle reflex
Inputs from the brain motor cortex
Inputs from the cerebellum
Local spinal cord interneurons

The reasoning for GTO, muscle spindle & interneurons has already been mentioned.
According to my neuroscience notes: Motor cortex contains upper motor neurons that control the excitability of lower motor neurons (alpha motor neurons).
Cerebellum outputs are to the motor cortex (so for example it could inhibit the upper motor neurons to in turn inhibit the LMNs for tasks e.g. controlling balance).

So i'd say all 5 are correct (keeping in mind that the cerebellum indirectly inhibits lower motor neurons via the upper motor neurons)

[ss12345]

Thanks heaps for the help!!!
I just submitted the test and yep you were correct, all five of those options were correct.

[ChickenCh0wM1en]

Thanks heaps for the help!!!
I just submitted the test and yep you were correct, all five of those options were correct.

Hey dude, with the muscle spindle, with the alpha motor neuron that is stimulated (reflex excitation), is another alpha motor neuron inhibited?

Also, with the end plate potential at the NMJ, is that also counted as a graded potential? (I think it is but not 100% sure).

[Starlight]

^^

Excitation pathway:
1) Increased muscle stretch--> Detection by muscle spindles--> Muscle spindles fire afferent APs to muscle spindle cell bodies in the dorsal root ganglia -> Cell bodies make direct synaptc connections with alpha motor neurons --> Alpha motor neurons are excited -> a-M neurons excite the agonist/synergist muscle (that was stretched & which contains the muscle spindle receptors) -> Muscle contracts to promote the reflex (opposite) response

Inhibition pathway:

2) Increased muscle stretch--> Detection by muscle spindles--> Muscle spindles fire afferent APs to muscle spindle cell bodies in the dorsal root ganglia -> Cell bodies make direct synaptc connections with inhibitory interneurons -> Alpha motor neurons are inhibited -> a-M neurons inhibit the antagonist muscle (that does not contain the muscle spindle receptors that detected the stretch in the synergist muscle) -> Antagonist muscle is relaxed/inhibited from contracting to prevent it from opposing the contractile response of the agonist muscle

Also, the end plate potential is just one huge graded potential event that always results in a contraction of the connected muscle. (for reasons that outlined in the textbook/ charles from lectures)

[hobbitle]

El, you're insane. In the best way.

[MelonBar]

el2012 is my hero

[Starlight]

Thanks El you da best!

El, you're insane. In the best way.

el2012 is my hero

Happy to help folks!

[MelonBar]

Thanks heaps for the help!!!
I just submitted the test and yep you were correct, all five of those options were correct.

I ticked all 5 as well and got 10/10. apparently if you unticked muscle spindles you still got marks for the question, hmm.

[hobbitle]

Yeah I lost one mark because I didn't check spindles

[hobbitle]

Can anyone help explain something to me?

So far I've been imagining all neurons how motoneurons look, with the cell body at one end, then the axon, and the terminals at the other end.  Heaps of other terminals synapsing onto that cell body, triggering graded potentials.  But I've just been revising a bit and have started thinking about neurons where the cell body is in the middle of the length of the neuron, like in sensory neurons. 

So how does this work when it comes to generating a strong enough graded potential in the cell body to then trigger an AP along the axon? Eg say there is a specialised receptor cell like a rod or a cone that receives stimulus... the diagram we have shows that that cell synapses onto a sensory neurone but the cell body of the neurone is half way down the axon. Where is the location of the axon hillock in this situation i.e. the area in which an AP is triggered if threshold is reached?  If the axon hillock is in the cell body, which is far away from the special sense receptor, how does the information from the sense receptor get there, in order to propagate down the axon?