Action potentials Flashcards
What is a nerve impulse (physically)
Movement of ions into and out of the axon membrane
Which ions are involved in nerve impulses
Na+ and K+ in and out of the membrane axon
Types of transport proteins in the axon membrane
Na+/K+ pump requiring ATP
Voltage gated Na+ channels (can be open or closed)
Voltage gated K+ channels (can be open or colsed)
K+ channels (always open)
What is the purpose of K+ channels
To make the axon membrane more permeable to K+ than Na+
Resting potential of axon?
The p.d between the inside and outside of the axon membrane, when a nerve impulse is NOT being conducted
Inside axon is more negatively charged than outside
What is found inside the axon 3
Cytoplasm
Negatively charged proteins and organic phosphates
Value for typical resting potential generated?
-70 milli Volts (mV)
How is the membrane described when at resting potential
Polarised
What is the sodium potassium pump continuously doing?
Actively transporting 3 Na+ ions out of the axon and 2 K+ into the axon
What is the affect of the activity of the sodium potassium pump, why?
3 positive ions out and only 2 in so:
The cytoplasm becomes more negatively charged than the surrounding tissue fluid
Concentration grads of K+ and Na+ ions are created
Where on the axon are the ion channels and pumps found
Nodes of Ranvier
Describe the movement of K+ through the perm. open K+ channels in response to the conc grad created by the Na+/K+ pumps, and affect.
Diffuse out of the axon down conc grad but against charge grad.
Makes inside axon even more negative
3 Factors contributing to the negative resting p.d of the axon membrane
3 Na+ pumped out, only 2 K+ pumped in
K+ ions diffuse out down conc grad
Presence of negatively charged proteins and organic phosphates in axon
Electrochemical gradient?
Based on charge (electro) and concentration (chemical)
What causes the ion channels to open and close
Voltage
What affect will a stimulus have on a voltage-gated Na+ channel, and after 3
Opens it
Some Na+ diffuse RAPIDLY into axon down electrochemical grad
p.d increases
Threshold value of p.d to open all voltage gated Na+ channels
-55mV
Action potential?
Rapid, fleeting change in p.d across a membrane
What will allow for the p.d to reach the threshold
If enough Na+ diffuse into the axon upon the opening of the singular channel
When all Na+ channels open?
Na+ diffuses in RAPIDLY
p.d will always increase to around +40mV (max p.d possible)
The axon membrane has depolarised
When -55mV is surpassed how can the permeability of the axon membrane be described
It has become permeable to Na+
What does the membrane being depolarised mean?
It has become less negative than its resting potential
Affect of K+ channels opening
K+ rapidly diffuses out of the axon down the electrochemical gradient
p.d briefly becomes more negative than resting potential: -90mV
Polarised membrane meaning? 3
There is a difference in charge across the membrane
The p.d is at a rest
Inside the membrane is more negative than outside
What happens to the ion chanel gates at +40mV
Na+ channels close
K+ channels open
Name for p.d dropping dramatically, past the resting potential (overshoot)
Hyperpolarisation
What happens after hyperpolarisation, at -90mV
3
K+ channels close
Sodium potassium pump restarts and restores resting potential
The membrane re polarises
What characterises of cells allows them to generate action potentials? And which cells can? 2
Excitability
Muscle cells and neurones
What must occur for action potential to be generated by a stimulus
Depolarisation of the axon must exceed -55mV
Threshold stimulus?
Stimulus great enough to cause depolarisation of the axon membrane > -55mV and induce an action potential in the neurone
All or nothing law? 2
Idea that action potential generated is always the same size and strength, does not vary with the size or strength of the stimulus above the threshold
If stimulus is below threshold, there is no action potential
Action potential compared to impulse
Action potential is a single event, nerve impulse is the spreading of the AP across the neurone is a wave of APs
