Introduction to NAS Flashcards
what makes the bilayer impermeable to charged molecules?
it is hydrophobic
what do ion pumps in the membrane do to membrane potential?
maintain concentration gradients
They don’t set the membrane potential of the cell – they providing the starting point for the ability of the cell to generate electrical signals.
what 2 ions are in the PM and what are their concentrations?
The 2 important ions are K+ and Na+
K+ concentration is high inside the cell, low outside
Na+ concentration is low inside the cell, high outside
what are the basic electrical processes of the PM?
The inside of all cells contains an excess of anions leading to a negative voltage within the cell.
The size of the negative voltage inside different cells differs due to a difference of anions.
This negative voltage is known as the Membrane Potential (Em)
In neurones, this may be −65 mV
Balance of charges determines value of Em
why is the term “chemically heterogenous” used when referring to ion channels?
the exposed ends of a channel proteins are hydrophilic and their middle surfaces (embedded in the membrane) are hydrophobic.
what are the 3 different classifications for ion channels?
non-gated (leak)
voltage- gated
ligand
what is the gating mechanism for ion channels?
A stimulus will cause this gate to open and cause a conformational change to allow an ion through
what are non-gated (leak) channels?
set resting membrane potential, they don’t have gates and are open all the time
what are voltage gated channels?
generate Action Potentials
what are ligand channels?
generate Em changes at synapse, where the ligand is a neurotransmitter which binds to the channel, acting as a stimulus to open the gate.
what is the resting membrane potential and what does it mean?
Resting Membrane Potential (Em) = -60 to -70 mV
This means:
There is an excess of negative charge inside the cell
The voltage is stable – so there is an equal movement of ions inside and outside the cell
how is resting membrane potential achieved?
The plasma membrane contains Non-gated (leak): K+ channels and Na+ channels
Therefore, the membrane has a permeability to each ion (PK , PNa)
Chemical gradient: There is an unequal ion distribution so ions will flow down their concentration gradient
K+ concentration is higher inside 🡪 driven to leave cell through ion channels (efflux)
Na+ concentration is higher outside 🡪 driven to enter cell through ion channels (influx)
Electrical force: Ions are charged (Na+/K+) thus are attracted by voltage inside cell (Em)
At negative Em, drive for K+ and Na+ to move into the cell (influx)
what determines the permeability of a ion in a PM?
The number of the leak channels for each different ion is the factor which sets the permeability for that ion.
what does driving an ion across the membrane electrically require?
the membrane possesses channels permeable to that ion to provide conductance
There is an electrical potential difference across the membrane
how is a chemical gradient generated in a PM?
There is a higher concentration of K+ inside the cell than outside so K+ efflux
This results in a loss of positive charge from inside cell
This creates negative Em which sets up an Electrical Force