Ligand Gated Ion Channels Flashcards
What are the four fundamental types of ion channels are?
o Voltage Gated Ion Channels
o Ligand Gated Ion Channels
o Signal gated ion Channels
o Resting channels (also called “leak” channels)
- Explain how changes in permeability of an ion alter the membrane potential of a cell.
The Goldman Katz equation shown below predicts that a change in permeability of an ion will change the membrane potential.
The simplest way to remember the effects of ion channel opening is to remember that, if only one ion permeability increases, the membrane potential will tend to move towards the Nernst potential for that ion.
See chart to refer to the Nernst potential
Read
From the table in objective 3 above, the potassium Nernst potential is -94.8. Thus, if a cell is at -60mV potential, the membrane potential will become more negative in response to opening of a potassium channel. When a cell becomes more negative, we say it is “hyperpolarized” Like potassium, opening chloride channels also makes the cell more hyperpolarized since chloride also has a very negative Nernst potential. In the case of sodium, the -60mV cell will move to the sodium Nernst potential of +66.6 mV, thus more positive or “depolarized”. In the nervous system, depolarization makes neurons fire while hyperpolarization makes them resistant to firing. Thus opening potassium or chloride channels would be inhibitory and opening sodium channels is excitatory
Read and know
It is also of note that closing channels has the opposite effect of opening them. When a channel is closed, the cell moves away from the Nernst potential for that ion. Thus closing potassium or chloride channels will depolarize while closing sodium channels will hyperpolarize.
Read
The AP has three primary phases. In the first phase, the axon depolarizes. This depolarization phase is driven by opening of voltage gated sodium channels (positive Nernst potential). Near the peak of the action potential, voltage gated potassium channels open and Na channels close. Since potassium has a large negative Nernst potential, increasing permeability to potassium tends to produce a hyperpolarizing effect that re-polarizes the membrane (repolarizing phase). The effect is robust and slightly “undershooting” the resting membrane potential. At this point, the potassium channels close and the membrane slightly depolarizes back to baseline.
Read
An EPSP is a passive _______________ of a post-synaptic membrane in response to opening of a Na+ or Na+/K+ channels.
Depolarization
The opening of the sodium channel increases sodium permeability, drives the cell toward the sodium Nernst potential. Both sodium and potassium may be conducted but the sodium effect dominates. Each channel that opens moves the potential at the dendrite and cell body more positive. Since there are no voltage gated sodium channels in this part of the cell, no active action potential is generated until the depolarizing effect reaches the axon.
An IPSP is similar to an EPSP except the ion channel that opens is a chloride channel. Increasing the permeability of chloride will hyperpolarize the cell. This makes the cell less excitable.
Read
Read 6 for explanation on cys loop, glutamate receptors and ATP gated K channels.
Read
See objective 7 and read
Read
