Action potentials Flashcards
which ions do the ECF mainly contain
Na+ and Cl-
which ions do the ICF mainly contain
K+ and other larger negative molecules(like phosphate)
hyperpolarisation
When the membrane potential becomes more negative than the resting potential, it is referred to as hyperpolarization. This makes the cell less excitable because a stronger stimulus is required to reach the threshold for generating an action potential
depolarisation
If the stimulus is strong enough and causes an influx of positive ions (such as sodium ions) into the cell, the membrane potential becomes less negative. If this depolarization reaches a certain threshold, it triggers an action potential.
resting membrane potential
Charge across the membrane at rest, i.e. ion channels not open
at resting membrane potential, what is the voltage of the axon
-70mv
repolarisation
the membrane potential returns to its resting state. This involves the closing of sodium channels and the opening of potassium channels, allowing potassium ions to leave the cell.
how does the Na+/K- ATPase pump function
Cytoplasmic Na+ binds to the sodium-potassium pump
Na+ binding stimulates phosphorylation of the pump by ATP
Phosphorylation causes the protein to change its conformation expelling Na+ to the outside
Extracellular K+ binds to the protein triggering release of the phosphate
Loss of the phosphate returns the protein to its original conformation
K+ is released and Na+ sites are free to bind again – cycle repeats
movement of ions in and out of the cell stops at which point
at the point where the concentrations of ions in and out of the cell equilibrate
action potentials
a rapid and transient change in the membrane potential of a cell, particularly in excitable cells such as neurons and muscle cells
briefly describe the process by which an action potential is generated
Neurons at rest have a resting membrane potential, typically around -70 millivolts. This is maintained by the unequal distribution of ions across the cell membrane, with more sodium (Na+) outside and more potassium (K+) inside.
An action potential is triggered by a stimulus that brings the membrane potential to a critical level called the threshold. This stimulus could be a neurotransmitter binding to receptors on the cell membrane or a sensory input reaching a certain intensity
Once the threshold is reached, voltage-gated sodium channels in the membrane open, allowing sodium ions to rush into the cell. This influx of positive charge depolarizes the cell, making the inside more positive
The rapid influx of sodium ions leads to a sharp increase in membrane potential, known as the rising phase of the action potential. The membrane potential approaches the sodium equilibrium potential
As the membrane potential becomes more positive, the voltage-gated sodium channels undergo inactivation, preventing further sodium influx
Repolarisation
Hyperpolarization
Refractory Period
the threshold for an action potential is typically around……
-50 to -55mv
propagation/conduction
this is when the action potential travels down the length of the neuron, initiating another action potential in the adjacent region of the membrane.
how are the action potential and the speed of conduction affected in unmyelinated neurons
AP generated all along the axon
there is continuous conduction
Amplitude of action potential does not change
what is the rate of conduction dependent on in unmyelinated neurons
the diameter of the neuron
