Family Weekend Dr. Davis in Office or Lab 10-11:30 am Concerning Test # 1 Types of questions Recall information Apply to situations Chapter questions Refugee physiology Check Moodle site for 1QQ grades 28 September Topics Graded potentials Action Potentials Properties of V-gated ion channels AP conduction

1QQ # 10 for 8:30 class At resting membrane potential The concentration gradient favors the entry of Na+ The electrostatic driving force favors the entry of Na+ The concentration gradient favors the exit of K+ The electrostatic driving force favors the exit of K+ The membrane is more permeable to Na+ than to K+. Suppose you have a cell with the normal concentrations of Na+ and K+ on either side of the membrane, and you were able to make the membrane absolutely and completely impermeable to Na+. A) What would the membrane potential be? (include the units.) B) What equation would you use to calculate the membrane potential?

1QQ # 10 for 9:30 class At the equilibrium potential for Na+ The concentration gradient favors the entry of Na+ The electrostatic driving force favors the entry of Na+ The concentration gradient favors the exit of K+ The electrostatic driving force favors the exit of K+ The membrane is more permeable to Na+ than to K+. Suppose you have a cell with the normal concentrations of Na+ and K+ on either side of the membrane, and you were able to make the membrane absolutely and completely impermeable to K+. A) What would the membrane potential be. (include the units.) B) What equation would you use to calculate the membrane potential?

S 1

S 2 Excitable membranes & special structures make Neurons good Electrical Communicators Ligand-gated ion channels in membranes of dendrites and soma…. Graded potential conducted decrementally }receiving Axon hillock “integrates” and produces an “all-or-nothing” Action Potential conducted non-decrementally and unidirectionally. Synapse on other neurons, skeletal muscle, smooth muscle, cardiac muscle, glands }sending Voltage-gated ion channels in membrane of axon hillock and axon….. Action potentials = “all or nothing!”

….. Ligand-gated ….. Mechanically-gated ….. Voltage-gated S 3 Types and locations of Ion Channels Sensory neuron Leak Channels Gated Channels ….. Ligand-gated ….. Mechanically-gated ….. Voltage-gated w/ LGCs and MGCs Intracellular Recording Electrode or Stimulating Electrode Interneurons & Motoneurons w/ LGCs w/ VGCs

S 4 Expanded on next slide What happens when the membrane is depolarized by more than about 15 mV? Action potentials are all or nothing. Analogy of shutter release pressure on a camera, either trips shutter or not. How is the intensity of a stimulus encoded by action potential if all action potentials have the same size (amplitude)?

S 5 Relevance of the GHK equation

S 6 To reset from inactivated state to closed state, membrane must repolarize. Open at -55 mV Membrane must repolarize to “reset” Na+ Channels to be capable of opening again. Compare and contrast voltage-gated Na and K channels based on time to open and duration of open time.

Voltage-gated Na+ channel S 7 Voltage-gated Na+ channel Tetrodotoxin from ovary of Puffer fish, used in Japanese sushi (fugu) scienceblogs.com/.../upload/2006/03/channel.jpg

What types of ion-channels are labeled in this neuron in red? TTX with red fluorescent marker

Relative permeabilities Duration of AP Refractory periods absolute RP relative RP Rising Phase Falling Phase Why does the peak of the action potential not reach ENa? Properties of V-gated Na+ and K+ channels account for the shape of the action potential and the refractory periods.

S 10

Natural ways to Initate an Action Potential Graded depolarization in cell body reach threshold at axon hillock Unstable membrane potential cycles: pacemaker potentials in pacemaker cells of heart, smooth muscles of gut, and medullary neurons for respiratory rhythm. Graded depolarization in in receptive membranes of sensory neurons reach threshold for AP. i.e. nociceptors and stretch receptors.

S 12 Who Cares? Novacaine, lydocaine, xylocaine, All block voltage-gated Na+ channels Prevent action potentials, so stimulus does not result in an action potential in sensory neurons which would convey that information to the brain where person would be conscious of the stimulus!

S 13 Questions About Action Potential Conduction: How does an action potential move along the axon? Why doesn’t the amplitude get smaller with distance? Why is the conduction of an action potential unidirectional? What is the absolute refractory period and what is going on with voltage gated sodium channels that accounts for the absolute refractory period? What is the relative refractory period and what is going on with voltage gated sodium channels that accounts for the relative refractory period? Axon Hillock Axon

S 14 In unmyelinated axons, action potential must be generated at each point along the membrane, a relatively slow process that involves influx of Na+ which sets up positive feedback cycle. In myelinated axons, action potential must be generated only at the nodes of Ranvier, which allows AP to be conducted much faster and with fewer ions moving, and thus less energetically expensive.