Neurones Flashcards
When the membrane is at it’s resting potential, is the inside of the membrane positively or negative charged?
Inside is negatively charged in comparison to the outside of the membrane as there are more positive ions on the outside of the membrane
What does polarised mean?
There is a difference in charge across the membrane
What is the voltage across the membrane when its at its resting potential?
-70mV
What two mechanisms is the resting potential of the membrane controlled by?
Sodium-potassium pump
Potassium ion channels
How does the sodium-potassium pump maintain the resting potential of the membrane?
Use active transport to move three sodium ions (Na+) out of the neurone for every two potassium ions (K+) moved in
What is required for the active transport of K+ and Na+ ions?
ATP
How do potassium ion channels (leak channels) maintain the resting membrane potential?
Allow facilitated diffusion of potassium ions (K+) out of the neurone, down their concentration gradient
What is the membrane not permeable to? What does this create?
Sodium ions - they can’t diffuse back in
An electrochemical gradient
What happens to the sodium ion channels (leak channels) when the neurone is stimulated?
They open
What causes the membrane to become depolarised (No longer polarised)?
If the stimulus is big enough to cause a rapid change in potential difference
What type of sodium ion channels are involved?
Voltage gated
What is the threshold level?
-55mV
What happens when a stimulus excites the neurone cell membrane?
Sodium ion channels open
Membrane becomes more permeable to sodium
Sodium ions diffuse into the neurone down the sodium ion electrochemical gradient created by the sodium potassium pump
- Makes the inside of the neurone less negative
What is depolarisation?
If the potential difference reaches the threshold level, more sodium ion channels open causing more sodium ions to diffuse into the neurone
What is re-polarisation?
- The sodium ion channels close and the potassium ion channels open
- Potassium ions diffuse out of the neurone down the potassium ion concentration gradient which starts to get it back to its resting potential
Which ion is the membrane more permeable to?
Potassium
What mV does re-polarisation occur?
+30mV
What is hyper polarisation?
Too many potassium ions diffuse out of the neurone so there is a slight overshoot where the potential difference becomes slightly more negative than the resting potential
Why does hyper polarisation occur?
The potassium ion channels are slow to close
What is the resting potential?
The potential difference when the membrane isn’t being stimulated
What is the order of events when an action potential arrives?
- Stimulus
- Depolarisation
- Re-polarisation
- Hyperpolarisation
- Resting potential
What is the refractory period?
Period of recovery for the ion channels and acts as a time delay between one action potential and the next
Why is the refractory period important?
Makes sure that action potentials don’t overlap but pass along as separate impulses
Limits the frequency at which the nerve impulses can be transmitted and that action potentials are unidirectional
What is a wave of depolarisation?
Some of the sodium ions that enter the neurone diffuse sideways
Sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part
What is the all or nothing principle?
The threshold level has to be reached for an action potential to be fired
What will a bigger stimulus cause?
Action potentials to be fired more frequently
It wont cause a bigger action potential as they are all the same size
What three factors affect the speed of conduction?
- Myelination
- Axon diameter
- Temperature
What is myelination?
The neurone having a myelin sheath
What is a myelin sheath?
Electrical insulator
What is myelin sheath made out of?
Schwann cells
What are nodes of Ranvier?
Gaps in between the Schwann cells
What is saltatory conduction?
The electrical impulse jumps from node to node
Why is saltatory conduction good?
It is really fast
How does axon diameter affect the speed of conduction?
Action potentials conducted quicker along axons with bigger diameters because theres less resistance to the flow of ions than in the cytoplasm of a smaller axon
How does temperature affect the speed of conduction?
Ions diffuse faster as the temperature increases
What temperature does the speed of conduction start to slow instead of increase and why?
Around 40 degrees C
The proteins begin to denature
