neurons are cells within the nervous system that carry electrical impulses

it is the basic cells that compose the nervous system

dendrites - short branched fibres tha convert chemical infomration from other nuerons or receptors cells into electircal signals

axons - an elongated fibre that transmits electical signals to terminal regfions for communication with other neurons or effectors

soma - a cell body containing the nucleus cytoplasm and organelles, where essential metabolic processes occur to mantain cell survival

in some nuerons, the axons may be surrounded by an insulating layer known as the myelin sheath

the myelin sheath improves the conduction speed of electrical impulses along the axon but it requires additional spance and energy myelin sheath

all cells have a resting potential. tbhis is the voltage (ions— electic signals) difference between the inside and outside of a cell

in a human nerve cell the typical resting potential is approx -70 mV, inside is more negative relative to the outside. needs to be mantained at all times except for when the signal is being sent through the nerve (when it changes)

mantaining the resting potential by 3 main factors

sodium-pottassium pumps move sodium ions out of the neuron and the at the same time trasnfer pottasium ions in. this is conducted by atp and can carry 2 types of ions. for every 3 sodium ions pumped out, 2 pottasiums are pumped in

the pumped ions will leak back via membrain via diffusion and slightly more permeable to pottasium than sodium (adding into the conc gradient and charge imbalance ) and the proteins (neg charges)

amoeba sister video

NaK pump help mantain a resting membrain potential . initially open in the intracellular part of the cells

positive charges hard to go pass the membrane so they need a pump or a channel.

resting potential is changed by some type of stimulus.

electrochemical gradient — diff type of ions and charges

you need to have na and k so you can mantain the resting potential, u can mantain the resting potential so you can create an action potential which is the signal that can get set to the next neuron. in order for those actional potential to be generated, you need to depolarise the cell.

a nerve impulse is an action potential that starts at the dendrites of a neuron and is then propagayed along the axon to the synapse/axon terminal of the neuron

action potential - rapid change in membrane potential and itt has 2 phases

depolarisation -

change from - to + inside the neuron

it continues along the axon

repolarisation -

bringing it back to the resting phase before, that -70

refractoring period is just when it’s trying to go back to -70 but no signals are sent unless its already 70 mv

depolarisation (positive feedback because we’re continuing the positive change throughout the neuron)

a change from negative to positive

sodium channels in our membrane is passive transport so sodium ions flood into our neuron and fuse inside and it causes our inside to be more positive than negative

re-polarisation (negative feedback because it wants to get it back to -70mv)

changing back from positive to negative

sodium channels close and the pottasium channel open up and pottasiums now leave so it causes the inside of the neuron to be negative again

this is all how signals get sent through

our potassium pump stays open until it falls back again to -80 mV and thats when the body is trying to bring it back up

refractory period

sodium and potasium pumps are working to restore resting potential because the concentration gradient of sodium and potasium ion have not been re-established again

if u cant get the threshold, than the process of depolarisation wont open up so sodium channels will fail to open. so it’s either complete depolarisation or no depolarisation. “ an all for nothing “ process

steps of a nerve impulse

1. resting potential is -70mv

2. sodium potasium pumps maintain the resting potential when more sodium ions are outside and more potassium ion are inside

3. when a neuron is stimulated, sodium ion channels open

4. sodium ions diffuse in causing depolarisation (thats the signal)

5. a nerve impulse is sent as a wave of depolarisation along the membrane

6. potassium ion channels open

7. potassium ions diffuse out causing repolarisation

8. sodium potassium pumps re-establish the resting potential

Variation in the speed of nerve impulses

in humans the diameter is usually 1 micrometer with a speed of approximated 1 meter per second

in squid the diameter is typically 500 micrometer and has a speed of 25 meters per second

and the reasons why they have giant axons is so there’s a rapid response to danger but the downside is that they take more space and resources

myelination - a form of insulation of axons

• made of the phospholid bilayer (fatty acid) and acts as an insulator

• if u insulate a wire, it makes the electrical signal faster

• Schwann cells lay down the layers of phospholipids

  its really important because they speeed up and can increase up to 100 meters per second

• myelin and insulation can be generated much much faster, improves reaction time

• disadvantage is that it does take up a lot of space