Lecture 9

Question 1

What was Descartes Theory for movement?

Answer 1

Movement is like hydraulics

Question 2

What did Fritsch and Hitzig do?

Answer 2

Put electrodes into the cortex of dogs and ran a current

Question 3

How does electricity flow?

Answer 3

From the negative pole (source of electrons) to the positive pole (lower charge).

Question 4

What is electrical potential and how is it measured?

Answer 4

The ability to do work through the use of stored potential electrical energy. Difference in charge=electrical potential. Measured in volts.

Question 5

How do we measure an electrical potential in neuroscience?

Answer 5

Measure them in an axon, run a current to see what happens at different spots. Measuring point is static but current passes through.

Question 6

What did Alan Hodgkin and Andrew Huxley discover?

Answer 6

Tested a squid axon. Described the electrical activity of a neuron. Nerve impulses result as a change in ion concentration across the axon membrane (1963 nobel prize)

Question 7

How do substances move along a concentration gradient?

Answer 7

Moves from an area of high concentration to low concentration-spreads out evenly.

Question 8

What is a voltage gradient?

Answer 8

Same as a concentration gradient, but instead spreads out the charge evenly.

Question 9

What are cations and anions?

Answer 9

Cations-Positively charged ions

Anions-Negatively charged ions

Question 10

What happens if you put a semi-permeable membrane in a solution?

Answer 10

Ex) if only chloride can pass, it will go from the area of high concentration to low concentration. However! The voltage gradient works in the opposite direction and tries to pull the ions back. This causes a difference in charge that is greatest at the barrier.

Question 11

Concentration gradient=voltage gradient…. what does this mean?

Answer 11

The two are in equilibrium (semi-permeable membrane), BUT there is a difference in ion concentration.

Question 12

What is resting potential?

Answer 12

An electrical charge across the cell membrane in the absence of stimulation (for most neurons it is around -70 mv). More negative in the intercellular side.

Question 13

Which particles produce the resting potential?

Answer 13

Sodium and Chloride (more concentrated OUTSIDE). Potassium and A- (more concentrated INSIDE).

Question 14

Why is the resting potential maintained?

Answer 14

Because of the location of the ions

1) Large A- molecules cannot leave the cell, making the INSIDE more negative
2) Ungated potassium channels allow it to move in and out of the cell freely, but gated Na+ channels keep sodium out.
3) Sodium potassium pumps extrude sodium from intracellular fluid and inject potassium (2 K+ for 3 Na+), makes outside more positive.

Question 15

Where do large, negatively charged proteins come from?

Answer 15

Cells and protein synthesis.

Question 16

How does potassium move into the cell during rest?

Answer 16

To balance the negative charge created by large proteins, potassium rushes into the cell (opposites attract), rush is limited by the concentration of potassium inside the cell, a few remain outside. There aren’t enough potassium ions to balance he A- ions which keeps charge negative.

Question 17

What are graded potentials?

Answer 17

Small voltage fluctuation in cell membrane, restricted to vicinity on the axon where ion concentrations change. Can result in hyperpolarization or depolarization.

Question 18

What is hyperpolarization?

Answer 18

Increase in electrical charge across membrane-inside becomes more negative. Inward flow of Chloride, outward of Potassium (inhibition).

Question 19

What is depolarization?

Answer 19

Decrease in electrical charge across membrane, associated with inward flow of sodium. (excitation)

Question 20

What is Fugu?

Answer 20

Really toxic Japanese pufferfish containing Tetrodotoxin (TTX)

Question 21

What is TTX and what does it do?

Answer 21

It blocks sodium channels, impending electrical activity (prevents depolarization from occuring), It acts in the periphery but not the brain due to the blood-brain barrier, so you are fully conscious while your entire body is paralyzed.

Question 22

What is an action potential?

Answer 22

When the depolarizing graded potentl is strong enough there is a brief reverse in polarity of an axon (1ms). Is a local phenomenon.

Question 23

What is threshold potential?

Answer 23

Voltage at which an action potential is triggered (-50mv). Opens doors of Na+ and K+ voltage sensitive channels

Question 24

What are voltage-sensitive ion channels?

Answer 24

Gated protein channels that open or close at specific membrane voltages.

Question 25

Which channel opens sooner?

Answer 25

Na+ as it is more sensitive.

Question 26

How do the ions flow in the action potential?

Answer 26

Sodium channels open first, allowing it to rush in, inside of cell becomes more positive (depolarized). Potassium channels open next, allowing potassium out, the cell becomes more negative (repolarized).

Question 27

What is the absolute refractory period?

Answer 27

The state of an axon in the repolarizing period during which a new action potential cannot be elicited. Gate 2 of sodium channels, which is not voltage sensitive, is closed.

Question 28

What is the relative refractory period (hyperpol)?

Answer 28

Increased electrical current is required to produce another action potential, potassium channels are still open.

Question 29

What do the refractory periods do?

Answer 29

Limit the firing rate of neurons.

Question 30

What is a nerve impulse?

Answer 30

The propogation of an action potential along an axon.

Question 31

What does it mean when we say the action potential is actively propogated?

Answer 31

It’s size and shape remain constant along the axon.