Vertebrates 14 - Phys. of Nervous system

Question 1

Galvani

Answer 1

Discovered electrical signals needed to contract frog legs. Also created battery (Zn/Cu)

Question 2

Early 1900’s nerve studies

Answer 2

use oscilloscopes, amplifiers, probes. Discovered membrane potential. Negative in (proteins), positive out (Na+ pumped out): -70mV)

Question 3

Resting membrane potential factors

Answer 3

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.

Question 4

Passive Electrical properties of membranes

Answer 4

Steady state of ion movement through channels. Nernst equation and Ohm’s law.

Question 5

Ohm’s law

Answer 5

V=IR. Channels like resistors (or rather conductor**), membrane like capacitor. Conductance G = 1/R. Rearrange = I (Amps) = G (Siemens) x V

Question 6

How does V affect ion movement?

Answer 6

Positive charge won’t flow out as much if other positive charge there. Only affects ion movements when it is NOT at equilibrium potential

Question 7

Nernst equation

Answer 7

Eion = (58mv/Z) log([ion]out/[ion]in). Calculate equilibrium potential when ion won’t flow.

Question 8

Electromotive force

Answer 8

Driving force, electrical gradient, difference b/w voltage of membrane and equilibrium potential (Em - Eion). I = G x emf (volts)

Question 9

What does conductance (G) tell you?

Answer 9

Can tell you the number of channels available to move the ion in question

Question 10

Research on action potentials

Answer 10

Cole and Curtis (USA) and Hodgkin and Huxley (UK). Studied the giant axons of squid about 50 years ago.

Question 11

Giant axons in squid

Answer 11

Line the mantel, cause the mantel to contract rapidly and move via jet propulsion

Question 12

Study of current in action potentials

Answer 12

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)

Question 13

Steps in action potential

Answer 13

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.

Question 14

Patch clamp

Answer 14

Measure voltage across one channel. Help to study

Question 15

Molecular biology and action potentials

Answer 15

Many genes isolated, can close and study them. Also, there are many different types for each kind (ie many Na channels).

Question 16

Toxins and ion channels

Answer 16

Many toxins affect ion channels. Used to study ion channels and in drug design to help pain.

Question 17

Tetrodotoxin

Answer 17

From bacteria in pufferfish. Blocks Na channels, so many action potentials are blocked.

Question 18

Saxitoxin

Answer 18

From shellfish. Causes paralyzation. Blocks Na channels

Question 19

Conotoxin

Answer 19

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

Question 20

Charybdotoxin

Answer 20

In scorpions. Block K channels.

Question 21

Agatoxins

Answer 21

From the funnel-web spider. Also paralyzes. Block Na channels, voltage dependent Ca channels

Question 22

Apamin

Answer 22

In bee stings. Not paralyzing, but affects ion channels. Block calcium gated K channels

Question 23

Dendrotoxins

Answer 23

From black mamba snake. Paralysis. Block K channels

Question 24

Voltage gated sodium channel. States.

Answer 24

Close, open, inactivated. Opens when membrane is depolarized. Then shifts to inactivated, happens automatically. Goes back to close when membrane repolarizes.

Question 25

Voltage gated sodium channel details.

Answer 25

Some sensitive to tetrodotoxin and saxitoxin. Isolated from electroplaques of electric eel. Multisubunit. Many genes cloned.

Question 26

Voltage gated potassium channel

Answer 26

Open or close. Opens because of depolarization. Some sensitive to apamin, charybdotoxin, dendrotoxin. Multisubunit, many genes.

Question 27

Voltage gated calcium channel.

Answer 27

Roles: electrical excitability, Ca entry, NT release, excitation/Contraction couple (DHPR). Some sensitive to conotoxins, agatoxins, drugs (ie for blood pressure). Many genes cloned.

Question 28

Reading: Why do vertebrates need ability to sense heat?

Answer 28

So they don’t die!

Question 29

Reading: How do vertebrates sense heat?

Answer 29

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

Question 30

Reading: Pit vipers

Answer 30

Pits on snout have infrared receptors. innervated by trigeminal nerve. They have overlapping fields which helps them focus. Very senesitive, even .02˚C.

Question 31

Reading: Trigeminal nerve

Answer 31

Major nerve in the face, innervates many sensory organs, some motor.

Question 32

Reading: Trigeminal nerve in Vampire bats

Answer 32

Innervates heat sensors in upper lip and nose flaps

Question 33

Reading: IR ion channel in vampires

Answer 33

TRPV1. It is truncated, so shorter than other animals’, more sensitive to lower temperatures (30˚C and up), helps find warm spot on animals.

Question 34

Reading: TRPV1 channel in other animals.

Answer 34

Longer than vampire’s. Also sensitive to heat, but hotter temp (42˚C). Also activated by capsasin, a protein in hot peppers.

Question 35

Reading: How does the TRPV1 gene differ?

Answer 35

In bats TRVP1 is alternatively spliced, but only in trigeminal nerve