NERVE IMPULSES - AQA A LEVEL BIOLOGY + EXAM QUESTIONS RUN THROUGH

In this video, I explain ALL of the content required for the "Nerve Impulses" section for AQA A Level Biology. This includes: structure of a myelinated neuron, resting potential, action potentials, the all-or-nothing principle, the refractory period, transmission of action potentials in myelinated & non-myelinated neurons and factors affecting speed of conductance. Time stamps to each of these sections are in the comments. The content in this video also crosses over with other exam boards.
I also go through a few exam questions and explain their mark schemes.
Please leave a comment if you have any questions, I'll be more than happy to answer them!!! :)

[@AlevelBiologyHelp]

00:54 = Structure of a myelinated neuron
02:51 = Resting potential and how it's maintained (sodium-potassium pump)
05:34 = Formation of an action potential
10:39 = The all-or-nothing principle
11:12 = The refractory period
12:01 = Transmission of action potentials in myelinated and non-myelinated neurons
13:51 = Factors that affect the speed of conductance
14:40 = Exam questions and mark schemes

[@reddevildifford7619]

I have a test in 2 days. I haven't done a proper written exam since pre-covid times. These videos are extremely helpful for the subjects that I've had most trouble on. You're awesome and thank you!

[@yasamannamazi9654]

Your channel has helped me LOADS!!!! Thank you so much ☺️

[@AlevelBiologyHelp]

You're very welcome!

[@raphaelking1378]

Actually an amazing video, wish my teachers were half as good as u, ty for the help

[@legendlegend4459]

you are amazing thank you

[@mariaali1827]

You have the best bio vids🥰

[@LeeroyPaul]

❤ thank you 😊 helps a lot

[@nazish47]

Thank you so much! When revising over this topic using different resources, I have noticed that the figures of charges are slightly different. For example in the CGP textbook it says the threshold is around -55mv, which is close to -50mv as mentioned in the video. In the exam do we write 'around' then?

[@AlevelBiologyHelp]

So threshold potential can be anywhere between -55 and -50 mv, so it doesn't really matter which one you write in the exam, so you could write "around", but I used to just put -50 but it doesn't really matter.

[@O_-dq3oq]

this is great, thanks

[@sam-wu2ff]

Hi,
Just a quick question, in a neurones cell membrane (at resting state) the outside is positively charged and the inside is negatively charged and in order to maintain the resting state sodium-potassium pumps and potassium ion channels pump Na + and K + in and out the membrane, but why are there opposite charges when both Sodium and Potassium ions are positively charged? How did the inside become negative when positive ions are being transported ?

[@cameronhewitt6849]

3 sodium’s leave for every 2 potassium’s entering, this means it’s less positive inside than our as a loss of 1+ occurs every time this transaction occurs. There are also potassium channels which potassium leaves via diffusion due to the concentration being larger inside over time, this also decreases the positive charge inside. So overall the charge is LESS positive inside than out. Hope this helped.

[@sam-wu2ff]

@@cameronhewitt6849 it did help thanks :)
I was just thinking about the inside of the neurone cell membrane and why it’s negatively charged, but it does make sense that it just gets less negative through the process of potassium ions being pumped in thorough the sodium and potassium pump and out through the potassium ion channel

[@AlevelBiologyHelp]

@@sam-wu2ff Hi! The inside of the membrane isn't necessarily negatively charged, it's just the voltage becomes more negative for the reason that Cameron explained above!

[@takudzwamundondo5371]

Thanks very much now l get it

[@safandsound]

How does myelination increase the speed of an action potential? Is it enough to say that it acts as an electrical insulator?

[@AlevelBiologyHelp]

Hi, myelination increases speed because action potentials occur at the Nodes of Ranvier (the gaps between the Schwann cells that make up myelin) , meaning that action potentials "jump" from node to node, which is much quicker, and is also called "saltatory conduction". :)

[@simonmasters3295]

@@AlevelBiologyHelp Hi Chemistry teacher here. I appreciate your thrust is passing an exam.
But more seriously How does the action potential jump?
One minute you are talking about ions moving across membranes and the all-or-nothing signal moving along the axon, next you say it moves faster in myelin sheathed axons. It may do, but it is no way an explanation. Do you think the myelin sheath is active in propagating the impulse?
One of the stumbling points in A Level Biology's treatment of nerve impulses, was for me, and still is as far as I can see a failure to explain how the moving signal comprises "information" or forms "memories".
If I ask you to imagine the way nerves work and signals propagate, the isolated nerve cell diagram is standard reference but you cannot say how it works without reference to other nerves and synapses. Here is Jeff Hawkins - he knows a lot about this stuff and I suggest has some ideas we should definitely teach at A Level
th-cam.com/video/5KnFrf3UDQY/w-d-xo.html

[@AlevelBiologyHelp]

@@simonmasters3295 Thanks for the feedback Simon! I agree with the point that the myelin sheath is active in propagating the impulse. And yes, A Level Biology can be a bit rubbish in explaining stuff, it's all quite dumbed down. :)

[@shivparmar5759]

Is this everything we need to know about nerve impulses

[@AlevelBiologyHelp]

Yes :)

[@simonmasters3295]

@@AlevelBiologyHelp See my comment above

[@safandsound]

Why are too many action potentials occurring at once a bad thing, and what would be the harm if they travelled in both directions? Also, thank you so much for all of these videos, they're so helpful!

[@AlevelBiologyHelp]

Hi! So there are many reasons why too many action potentials would be bad. One reason is that a build up of calcium ions would occur (due to overactivity of voltage gated calcium channels), which would trigger apoptosis of the neuron (cell suicide). Action potentials cannot travel in both directions due to what occurs in the refractory period, but if they did travel in both directions, reflexes would be very slow and this maybe could trigger apoptosis again possibly (not certain!) :)