Lecture Set 21

Question 1

Describe how the membrane potential is created, and how ions move across the membrane

Answer 1

Membrane potential due to ion concentrations. Done through the Na-K pump, as well as K leak channels, leads to net movement of + charges outside. - charges are stuck in the cytosol as macromolecules.

Ions can move through channels, either non-gated (leak), voltage-gated, or ligand-gated. They move down their electrochemical gradient. In passive diffusion, always moves down gradient, speed of movement depends on voltage.

Question 2

what are the two equations to know?

Answer 2

Nernst = determines membrane potential if membrane was permeable ONLY to that ion
Goldman-Hodgkin-Katz (GHK) equation takes into account permeabilities of Na, K, and Cl. Na in/out, K in/out, Cl out/in

Question 3

Describe how action potentials are propagated and created

Answer 3

ligand-gated channels are activated by neurotransmitters binding, causes graded potential through ion influx, if potential is strong enough, spreads to axon hillock and activates voltage-gated Na channels that create action potential. It then depolarizes the next set of Na channels (if saltatory conduction, insulation due to myelin sheath created by Schwann cells or oligodendrocytes increases distance between channels located at the Nodes of Ranvier) to spread the action potential down the axon

Question 4

Describe the shape and numbers and ion channels in the action potential

Answer 4

goes from -60 to + 40 then -75 during repolarization. Na channels have 3 conformations, open, activation gate closed (absolute refractory), and inactivation gate closed (relative refractory period), K channels open during repolarization and hyperpolarization

Question 5

Describe the synaptic junction

Answer 5

depolarization reaches the end of the axon, opens voltage gated Ca channels, allows influx of Ca and exocytosis of neurotransmitter that crosses the junction to the ligand gated receptors to set up another gated potential. NTs can either create a new action potential, inhibit an action potential, or create a signal transduction cascade. neurotransmitter can be removed via enzyme degradation, reuptake, or diffusion