Topic 6: Nervous Coordination Flashcards
What is a neurone’s resting state?
The resting potential, when its not being stimulated so the outside of the membrane is more positively charged then the inside
What is the voltage at resting state or a neurone?
-70mV
What is voltage the measure of?
Difference in charge between the inside and outside of a membrane
What is a resting potential created and maintained by?
Sodium-Potassium pumps, potassium ion channels in a neurones membrane
What form of transport does sodium-potassium pump using?
Active transport
What do the sodium potassium pump use active transport to do?
Move 3 sodium ions out for every 2 potassium ions moving in (ATP needed)
What do potassium ion channels allow?
Facilitated diffusion of potassium ions out of the neurone, down their concentration gradient
Explain the 3 steps of creating and maintaining a resting potential?
1) Sodium-potassium pumps move sodium ions out of the neurone but the membrane isn’t permeable to sodium ions so they can’t diffuse back in. Creating electrochemical gradient more positive na+ outside than in
2) The sodium-potassium pump also moves potassium ions into the neurone
3) When the cell is at rest, more potassium ion channels are open. Meaning that the membrane is permeable to K+ ions so some diffuse back out through potassium ion channels
When does an action potential occur?
When a neurone is stimulated and other ion channels e.g Na+ open, if the stimulus is big enough it’ll trigger a rapid change in potential difference
When the neurone is stimulated what doe this cause the cell membrane to do?
Become depolarised
In terms of an action potential what does the stimulus do?
This excites the neurone cell membrane, causing sodium ion channels to open.
The membrane becomes more permeable to sodium so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient making the neurone less negative
In terms of an action potential what happens at depolarisation?
If the potential difference reaches the threshold more sodium ion channels open, so more sodium ion diffuses into the neurone
In terms of an action potential what happens at repolarisation?
At a potential difference of -30mV the sodium ion channels close and potassium ion channels open
The membrane is more permeable to potassium so potassium ions diffuse out of the neurone
Starting to get the membrane back to its resting potential
In terms of an action potential, what happens at hyperpolarisation?
Potassium ion channels are slow to close so there’s a slight ‘overshoot’ where too many K+ ions diffuse out of the neurone
The potential difference becomes more negative than the resting potential
After the action potential what happens at the resting potential?
The ions reset, the Na-K pump returns the membrane to its resting potential by pmping sodium ions out and potassium in maintaining the resting potential until the membrane’s exited by another stimulus
After an action potential why can’t the neurone be stimulated again straight away?
As the ion channels are recovering and they can’t be made to open
When does the refractory period occur?
For Na+: during repolarisation when they are closed
For K+: during hyperpolarisation
What does the refractory process act as?
Time delay between one AT and the next, making sure they don’t over lap
How is a wave of depolarisation along a neurone caused?
When an AP happens, some of the sodium ions that enter the neurone diffuses sideways
Causing sodium ions channels in the next region of the neurone to open and Na+ diffuse into that part
When a wave of depolarisation occurs what happens?
The wave moves away from the parts of the membrane in the refractory period because these parts can’t fire an AP
What is the All-or-northing principle?
Once the threshold is reached, an AP will always fire with the same change in voltage, no matter how big the stimulus is
If the threshold isn’t reached, an AP won’t fire
In terms of action potentials, what does a bigger stimulus happen?
It won’t cause a bigger action potential but it will cause them to fire more frequently
What are the 3 factors that affect the speed of conduction?
Myelination (saltatory conduction), axon diameter and temprature
What is myelin sheath?
It is an electrical insulator
In the peripheral NS, what is the sheath made from?
Schwann cell
Between the Schwann cels what are the tiny patches of bare membrane called?
Nodes of Ranvier
What is concentrated at the Nodes of Ranvier?
Sodium ions
What is saltatory conduction?
In a myelinated neurone, the neurone cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse ‘jumps’ from node to node it happens really fast
How does conduction occur in non-myelinated neurones?
The impulse travels as a wave along the whole length of axon membrane, so you get depolarisation along the whole length of the membrane, this is slower than saltatory conduction
How does axon diameter affect speed of conduction?
AP’s are conducted quicker along axons with bigger diameters because there’s less resistance to the flow of ions than in the cytoplasm of a smaller axon
With less resistance, depolarisation reaches other parts of the neurone cell membrane quicker
How does temperature affect speed of conduction?
The speed of conduction increases as the temperature increases too, because ions diffuse faster
The speed only increases up to around 40 degrees though after that the protein begin to denature and the speed decreases
What is a synapse?
Junction between 2 neurone’s or between a neurone and an effector cell
Whats a synaptic cleft?
The tiny gap between cells at the synaptic cleft
What does the presynaptic cleft have that the postsynaptic neurone doesn’t?
A swelling called synaptic knob
