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Title: Action Potential
Description: A level standard and beyond notes on action potentials
Description: A level standard and beyond notes on action potentials
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Monday, 13 November 2017
Action Potentials
Learning Objectives
- Summarise, with an example of each, the features which distinguish the
neural, endocrine, and paracrine intercellular communication systems
- Given the intracellular and extracellular concentrations of Na+, K+ and Cl-,
describe how these concentrations are maintained
- Explain how the resting membrane potential is a consequence of the
concetration gradients of ions across the plasma membrane and of the
relative ion permeabilities of the membrane
- Describe how ion channels can respond to voltage, with particular reference
to the action potential
- Draw a typical action potential, and describe the changes in ionic
permeability that occur at each stage
Cell communication
Paracrine - act locally
Includes neural communication where neurotransmitters released from nerves
...
Paracrine signalling can also occur where there are directly coupled cells, via a gap
junction (electrical and chemical coupling in cardiac and smooth muscle)
...
The pump makes Na+
concentration high in extracellular space and low in intracellular
...
There are also more K+ passive
leak channels than Na+ leak channels
...
This results in the intracellular space having a net negative voltage
(-70mV)
...
5
...
Excitable cells
These are nerve cells and
muscles that have electrical
activity
...
Voltage gated ion channels are
found on the axon, especially
at the hillock
...
There are
Na+ and K+ voltage gated
channels
...
The inactivation gate opens when the cell is in the resting
2
Monday, 13 November 2017
state
...
K+ channels
These open in after depolarisation so that the cell repolarises
Properties of action potential
All or nothing principle
If depolarisation does not reach the threshold, there is no action potential
generated
...
If it reaches or exceeds the threshold, the action
potential generated is always the same
...
Refractory period
The absolute refractory period is during the peak of the action potential
...
The relative refractory period is before the closure of K+ channels (repolarisation
and hyperpolarisation)
...
An action
potential is still possible if the stimulus is large enough
...
The supra threshold graded potential can produce a higher
number of action potentials within a given period
...
This
prevents them from returning to a ‘resting state’, so prevents the voltage gated Na+
channels from reopening and stimulating subsequent action potentials
Title: Action Potential
Description: A level standard and beyond notes on action potentials
Description: A level standard and beyond notes on action potentials