Vertebrates 14 - Phys. of Nervous system Flashcards
Galvani
Discovered electrical signals needed to contract frog legs. Also created battery (Zn/Cu)
Early 1900’s nerve studies
use oscilloscopes, amplifiers, probes. Discovered membrane potential. Negative in (proteins), positive out (Na+ pumped out): -70mV)
Resting membrane potential factors
Depends on permeability of membrane to ions. Leak channels (G L) always open. RMP closest to E ion that is most permeable. Na/K pump maintains gradient.
Passive Electrical properties of membranes
Steady state of ion movement through channels. Nernst equation and Ohm’s law.
Ohm’s law
V=IR. Channels like resistors (or rather conductor**), membrane like capacitor. Conductance G = 1/R. Rearrange = I (Amps) = G (Siemens) x V
How does V affect ion movement?
Positive charge won’t flow out as much if other positive charge there. Only affects ion movements when it is NOT at equilibrium potential
Nernst equation
Eion = (58mv/Z) log([ion]out/[ion]in). Calculate equilibrium potential when ion won’t flow.
Electromotive force
Driving force, electrical gradient, difference b/w voltage of membrane and equilibrium potential (Em - Eion). I = G x emf (volts)
What does conductance (G) tell you?
Can tell you the number of channels available to move the ion in question
Research on action potentials
Cole and Curtis (USA) and Hodgkin and Huxley (UK). Studied the giant axons of squid about 50 years ago.
Giant axons in squid
Line the mantel, cause the mantel to contract rapidly and move via jet propulsion
Study of current in action potentials
Used voltage clamp and amplifier to affect potential, then changed variables to see what was causing the current flow (eliminate K, see difference in current)
Steps in action potential
Threshold, Na channels open and Na goes in. K channels open and flow out. Na/K pump not involved in the depolarization but is important to reestablish gradient.
Patch clamp
Measure voltage across one channel. Help to study
Molecular biology and action potentials
Many genes isolated, can close and study them. Also, there are many different types for each kind (ie many Na channels).
Toxins and ion channels
Many toxins affect ion channels. Used to study ion channels and in drug design to help pain.
Tetrodotoxin
From bacteria in pufferfish. Blocks Na channels, so many action potentials are blocked.
Saxitoxin
From shellfish. Causes paralyzation. Blocks Na channels
Conotoxin
From exotic snail which eats fish. Toxin paralyzes fish. Different types block Na channels, Ca channels, K channels, Ach receptors, or block inactivation of Na channels
Charybdotoxin
In scorpions. Block K channels.
Agatoxins
From the funnel-web spider. Also paralyzes. Block Na channels, voltage dependent Ca channels
Apamin
In bee stings. Not paralyzing, but affects ion channels. Block calcium gated K channels
Dendrotoxins
From black mamba snake. Paralysis. Block K channels
Voltage gated sodium channel. States.
Close, open, inactivated. Opens when membrane is depolarized. Then shifts to inactivated, happens automatically. Goes back to close when membrane repolarizes.
