1 - Intro to CNS Pharmacology Flashcards
What protein families have evolved to allow ionic passage across the phospholipid membrane?
Ion channels: ion movement follows concentration gradient
Transporters, ATPase driven pumps.
Ion channels have a _______ channel in the center. What is their function? What do they have on each side?
Hydrophilic center.
Glycosylated on extracellular side, kinase consensus on intracellular side.
Highly evolved to be selective for ions and to be regulated by changes in the environment.
What are characteristics of passive ion channels?
Non-gated
Always open
What are characteristics of active ion channels?
Mechanism exists for regulation of open/closed state.
Gating mechanisms:
- Voltage-gated
- Small extracellular molecules (nts)
- Other membrane proteins
- Intracellular molecules (ions, ATP).
What are characteristics of leak ion channels?
Channel that’s open at resting membrane potential.
Can be either active or passive.
(all passive channels are leak channels but not all leak channels are passive).
What causes a resting membrane potential to occur?
- Most intracellular proteins are anions trapped in the cell.
- Leak channels in the membrane allow for the movement of potassium and chloride across the membrane.
- Conductance of K+ is 100x greater than the conductance of Na+ due to many more K+ leak channels than Na+ leak channels.
What ions are at a higher concentration extracellularly? What about intracellularly?
Extracellular: Na+ and Cl-
Intracellular: Proteins (anions), K+, and a small amount of Cl-
What is electrochemical potential?
The chemical difference, along with the potential difference, across a membrane causes an electrochemical potential.
What is the nernst potential? What are the approximate nernst potentials for K+, Na+, and Cl-?
The membrane potential at which an ion is in electrochemical equilibrium across the membrane. (the electrical potential needed to maintain the E:I ration).
K+: -90 mV
Na+: +50 mV
Cl-: -70 mV
Why is the equilibrium potential sometimes referred to as the reversal potential?
Because the movement of ions (such as Na+ into the cell) with their concentration gradient, go beyond the
What do neurons with an Na+/K+ ATPase pump do?
Move Na+ out of the cell and K+ into the cell.
This is not enough to set the gradients but opposes leak channels.
What is an action potential?
All or none electric impulse transmitted across the plasma membrane.
~100 mV in amplitude and 1-10 ms in duration.
Propagated down the axon potential through cycles of depolarization and repolarization.
Propagation of action potentials involve what two channels?
- Voltage-gated sodium channels
2. Voltage-gated potassium channels
How do voltage-gated sodium channels contribute to action potentials?
Depolarization causes voltage-gated Na channels to open, this causes an increase in intracellular Na and thus causes depolarization.
(in the slide its listed in a circle)
How do voltage gated potassium channels contribute to the AP?
More gradual openings and slower inactivation than voltage gated sodium channels.
What are synaptic potentials?
Mechanism by which the initial chance in membrane potential occurs to begin an AP.
Describe the changes in membrane potential caused by synaptic potentials?
Graded, small, and short (only a few mV and a few msec in duration)
Local (no propagation)
Able to summate: spatial and temporal
What are the two types of synaptic potentials?
Excitatory postsynaptic potential (EPSP)
Inhibitory postsynaptic potential (IPSP)
What is an excitatory postsynaptic potential (EPSP)?
Membrane potential that moves to more positive values.
Can be spatial and temporally summated.
What is an inhibitory postsynaptic potential (IPSP)?
Membrane potential that moves to more negative values.
Impacts a summating EPSP.
What are the two mechanisms by which an EPSP can occur?
- Increased conductance: open a ligand gated ion channel for sodium or calcium
- nicotinic receptor or some glu receptors - Decreased conductance: closing a channel that is open at resting membrane potential (leak channel), these are slower onset changes that last longer.
What are the two ways by which decreased conductance can cause an EPSP?
- Potassium channels
- Initiated by G protein coupled receptors: phosphorylation of K channel by protein kinase A resulting in its closure (Gs is invovled)
What are three ways in which increasing conductance can cause an IPSP?
- Ligand gated chloride channels (GABA-A receptor)
- Opening of K+ channels via direct interaction with G protein and K channel.
- Opening of K channels via changes in phosphorylation state of K+ channels that are closed.
What makes up the resting potential?
Non-gated (leak) potassium and chloride channels.
Some non-gated (leak) sodium channels.
Usually steady from -35 to -70 mV
