B15 Nervous Coordination and Muscles Flashcards
How do we maintain resting potential of a neurone
Using sodium-potassium ion pumps.
They actively transport 3 Na+ out the neurone
They actively transport 2 K+ into the neurone.
Ensures more positive ions outside the neurone than inside
What is the resting potential of neurones
-70mV
4 steps in order of how an Action Potential is formed
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Restoring of the resting potential via Na-K ion pump
When a neurone is stimulated, the membrane becomes
depolarised
What is the threshold potential
-55mV
Depolarisation process
If the threshold potential of -55mV is met:
Na+ channels open
K+ channels closed
So Na+ diffuse into the neurone via facilitated diffusion.
This decreases the potential difference across the membrane until it reaches a voltage of around +30mV
Repolarisation process
Na+ channels close
K+ channels open
K+ ions diffuse down their concentration gradients out of the neurone which reestablishes the charge difference in the membrane.
Hyperpolarisation
Few too many K+ ions diffuse out as the K+ channels are too slow to close.
So the charge difference exceeds the resting potential
Restoring of RP
The action of the sodium-potassium ion pump restores the balance of Na and K on either side of the membrane
Diagram of an action potential. Time against voltage
Search it up
How is an AP stimulated across the neuronea
A wave of depolarisation occurs along the neurone because sodium ions diffuse into the neurone sideways
What is the refractory period
Time immediately after an action potential has been stimulated where a neurone cannot be stimulated so an AP cant occur.
This is because ion channels are recovering
Why is a refractory period good
Ensures AP’s don’t overlap/ prevents neurones from being overstimulated
Ensures that AP’s are unidirectionals
Different sized stimuli result in …
Different frequencies of action potentials
Factors affecting the speed of an action potential
Myelination
Axon diameter
Temperature
How does myelination affect the conduction velocity of an AP
Myelin Sheath acts as an electrical insulator which prevents ion movement across the membrane
Depolarisation can only occur at the nodes of Ranvier where the voltage-gated sodium ion channels are concentrated
So action potentials ‘jump’ from node to node - saltatory conduction
What is saltatory conduction
When action potentials jump from node to node in myelinated neurones
Why does axon diameter affect the speed of an AP on a neurone
A bigger axon, AP travels quicker because there is less resistance to the flow of ions in the neurone
How does temperature affect the conduction velocity of an action potential
ions have a greater kinetic energy so diffuse faster and depolarisation can occur at a faster rate
ofc till optimum temp where channel proteins will denature and stuff
Synaptic Transmission process
- Action potential reaches the end of the presynaptic neurone.
- This triggers the opening of voltage-gated Calcium ion channels so Ca2+ enter the presynaptic neurone via facilitated diffusion
- Influx of calcium ions triggers the movement of vesicles towards the presynaptic membrane
- Vesicles fuse with membrane and release neurotransmitters via exocytosis
- NTs diffuse across the synaptic cleft and are detected by receptors on the postsynaptic neurone
- This triggers the opening of Na+ ion channels so sodium ions move into the postsynaptic neurone which stimulates depolarisation and therefore an AP is stimulated on the postsynaptic neurone.
What 2 things allow APs to travel unidirectionally
- refractory period
- receptors are found on the postsynaptic neurone
What are cholinergic synapses
Synapses that use acetylcholine as the neurotransmitter
What is acetylcholine broken down by
acetylcholinesterase
How does acetylcholinesterase break down acetylcholine
into acetate and choline
products are reabsorbed into the presynaptic neurone to synthesise the neurotransmitter
