Action Potential Flashcards
What is an action potential?
Action potential is the spread of electrical potential travelling as an impulse across a neuron.
Which cells generate action potentials?
Neurons, endocrine cells and muscle cells.
Why do action potentials occur?
For cell-cell communication (neurons) release of hormones (endocrine) and for muscle contraction (muscle)
What is a pyramidal cell?
Neuron in the cerebral cortex.
What is the role of a neuron?
Generate action potentials for cell-cell communication
What is the all or nothing response?
Electrical potential received from post-synaptic neuron and summated at the axon hillock must exceed -70mV to generate another action potential.
What are the stages of an action potential?
Action impulses received from pre-synaptic neuron via the dendritic tree which travels as positive and negative electrical impulses towards the soma where it is integrated and the sum of this generates an impulse at the axon hillock if it exceeds -70mV travels along the axon to be distributed as an action potential at the axon terminal.
What is decremental spread?
The decreased speed of conduction of electrical impulses which occurs at the axon hillock where negative and positive electrical charges are summated
What is non-decremental spread?
Maintained velocity of conduction of electrical impulse along the axon.
What is a membrane potential?
The difference in charge between the intracellular and extracellular environment, measured in mV.
What is the resting potential?
-70mV, maintained by th Na+/K+ potassium pump which creates a slightly negative internal environment.
How are electric charges separated across a membrane?
Membrane is semi-permeable, repellant against polar charges
What is an ion channel?
Composed of protein subunits which create a central pore in the membrane
What are the types of ion channels?
Leak and Gated channels.
What are leak channels?
Constantly open and allow ions to pass through
What are voltage gated channels?
Type of gated channel which only opens in response to a certain threshold of membrane potential.
What are ligand gated channels?
Type of gated channel which only opens in response to a certain ligand.
What is the Na+/K+ pump?
Ion pump which determines resting potential. Inside the cell, 3Na+ and ADP bind and ATP is hydrolysed which causes pump to change shape and by active transport release 3na+ externally. This exposes the pump for 2K+ to bind and release of Pi group from ATP hydrolysis enables pump to revert back and take K+ into the internal cell environment.
What features determine the resting potential?
Low protein permeability, Active transport of Na+/K+ and passive transport /high permeability to K+.
Where is Na+ found in the cell environment?
Externally,
Where is K+ found in the cell environment?
Internally
What is the extracellular charge?
Positive
What is the intracellular charge?
Negative
What is equibrium potential?
The balance between chemical gradient and electrical gradient across the cell.
The balance between chemical gradient and electrical gradient across the cell.
How do we determine the equilibrium potential for an ion?
Using the Narnst equation.
What is the valency of Na+?
+1
What is the valency of K+?
+1
How does equilibrium potential change with a greater conc outside the cell?
Increases which interferes with generating an action potential
What does the Nerst equation rely on?
Valency and ion concentration in and outside the cell of a single ion type. Does not account for permeability.
What is the difference between Nerst and Goldman equation?
Goldmann considers the valency, permeability and ion concentration of multiple ion types.
Which neuron has the biggest influence on resting membrane potential?
K+ due to its passive transport which makes it highly permeable inside neurons
How does action potential affect membrane potential?
Causes membrane potential to increase. Leaky K+ channels allow K+ to enter the cell passively. When it reaches the threshold of -55mV, voltage gated Na+ channels open and Na+ enters which causes rapid depolarisation and membrane potential reaches +40mV. Here, voltage gated K+ channels open and Voltage gated Na+ channels begin to inactivate. Voltage Gated K+ along with leaky K+ channels cause the hyperrefractory period and voltage gated K+ channels close and leaky K+ restores it back to -70mv
What is the subthreshold?
Magnitude (size) of action potentials
What is the suprathreshold?
Frequency of action potentials. A greater action potential will increase the suprathreshold.
How does conduction occur in an unmyelinated neuron?
Na+ causes localised depolarisation at the axon hillock which leads to activation of voltage gated Na+ channels to generate action potential to next channel and immediately inactivate, creating a one way impulse.
How does conduction occur in an myelinated neuron?
Na+ causes localised depolarisation at the axon hillock which causes activation of the Nodes of ranvier, concentrated Na+ channels that create a saltatory jumping impulse with a greater velocity
How does myelination affect conductivity?
Increases conductivity and found in neurons with a larger diameter
What are the features of unmyelinated neurons?
Lower conductivity and found in neurons with a smaller diameter.
How does diameter affect conductivity?
Larger diameter reduces resistance so greater conductivity
What is EEG used for?
To test for brain death, for brain surgery, hearing and vision issues and sleep disorders.
What is transcranial direct current stimulation?
Use of electrodes to generate a current for cortical excitability to areas of the brain which treats stroke and depression
What is multiple sclerosis?
Autoimmune disease where T cells attack the myelin sheath of the neurons of the brain, spinal cord or peripheral nerve that leads to impaired transmission
What is tetradotoxin?
Voltage gated Na+ channel blocker
What are local anaesthetics?
Voltage gated Na+ channel blocker at a localised region which prevents depolarisation. Effects can be prolonged with a vasodilator such as adrenaline
What are the types of local anaesthetics?
Esters like cocaine (one i) which are less stable and have a higher likelihood of an allergic reaction. Amides like lidococaine (two i’s) which are more stable and used
What is carbamazepine?
Epileptic drug which is used as an anticonvulsant that increases the inactivated state of Na+ channels and refractory period.
