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.
Voltage gated sodium channel details.
Some sensitive to tetrodotoxin and saxitoxin. Isolated from electroplaques of electric eel. Multisubunit. Many genes cloned.
Voltage gated potassium channel
Open or close. Opens because of depolarization. Some sensitive to apamin, charybdotoxin, dendrotoxin. Multisubunit, many genes.
Voltage gated calcium channel.
Roles: electrical excitability, Ca entry, NT release, excitation/Contraction couple (DHPR). Some sensitive to conotoxins, agatoxins, drugs (ie for blood pressure). Many genes cloned.
Reading: Why do vertebrates need ability to sense heat?
So they don’t die!
Reading: How do vertebrates sense heat?
Specialized nerve ending in skin. Two types: cold or warm. Usually only really activate at noxious temp. Also neurons in hypothalamus to measure core temp
Reading: Pit vipers
Pits on snout have infrared receptors. innervated by trigeminal nerve. They have overlapping fields which helps them focus. Very senesitive, even .02˚C.
Reading: Trigeminal nerve
Major nerve in the face, innervates many sensory organs, some motor.
Reading: Trigeminal nerve in Vampire bats
Innervates heat sensors in upper lip and nose flaps
Reading: IR ion channel in vampires
TRPV1. It is truncated, so shorter than other animals’, more sensitive to lower temperatures (30˚C and up), helps find warm spot on animals.
Reading: TRPV1 channel in other animals.
Longer than vampire’s. Also sensitive to heat, but hotter temp (42˚C). Also activated by capsasin, a protein in hot peppers.
Reading: How does the TRPV1 gene differ?
In bats TRVP1 is alternatively spliced, but only in trigeminal nerve
