2.2 The Nerve Impulse

Question 0

Potassium (kalium)

Answer 0

[K]
An mineral that functions in nerve signal transmission, muscle contraction, blood pressure regulation, and maintenance of pH balance

Sammen med natrium (sodium) regulerer det sammensetningen av kroppsvæskene

Question 1

Sodium (natrium)

Answer 1

[Na]
A mineral that functions in nerve signal transmission, bloodpressure regulation, cell function, and maintenance of pH balance

Sammen med kalium (potassium) regulerer det sammensetningen av kroppsvæskene

Question 2

Electrical gradient, aka polarization

Answer 2

A difference in electrical charge between the inside and outside of the cell. The neuron inside the membrane has a slightly negative electrical potential with respect to the outside, mainly because of negatively charged proteins inside the cell.

En potensialforskjell mellom to elektroder av samme materiale.

Question 3

Resting potential

Answer 3

The difference in voltage in a resting neuron

Question 4

The membrane is selectively permeable

Answer 4

Some chemicals pass through the membrane more freely than others, like

• oxygen
• carbon dioxide
• uera
• water

Question 5

Sodium-potassium pump

Answer 5

Is an active transport that requires energy. The protein complex repeatedly transports three sodium ions out of the cell while drawing two potassium ions into it.

Question 6

Concentration gradient

Answer 6

The difference in distibution of ions across the neuron’s membrane.

Sodium is more concentrated outside than inside, so just by the laws of probability, sodium is more likely to enter the cell than to leave it.

Analogy: imagine two rooms connected by a door. There are 100 cats in room A and only 10 in room B. Cats are more likely to move from A to B than from B to A

Question 7

Action potential

Answer 7

Messages sendt by axons.

Transmits without loss of intensity over distance. The cost is a deley between the stimulus and ist arrival in the brain

Question 8

Hyperpolarization

Answer 8

Inhibitory

Increased the neurons polarization

Is an exaggeration of the usual negative charge within a cell (to be more negative level than usual)

Question 9

Depolarization

Answer 9

Reduce the neurons polarization toward zero

Is a decrease in the amount of negative charge within a cell

Question 10

Threshold of excitation

Answer 10

Minimum amount of membrane depolarization necessary to trigger an action potential.

When the potential reaches the threshold, the membrane opens its sodium channels and premits sodium ions to flow into the cell.

Question 11

Voltage-gated channels

Answer 11

Membrane channel whose permeability to sodium (or some other ion) depends on the voltage difference across the membrane

Question 12

Local anesthetic

Answer 12

Drugs attach to the sodium channels of the membrane, preventing sodium ions from entering, and thereby stopping action potentials.

So, when your reseptors are screaming, “pain, pain, pain!” but the axons can’t transmit the message to your brain, and so you don’t feel it

Question 13

The All-or-none Law

Answer 13

Puts constraints on how an axon can send a message. To signal the difference between a weak stimulus and a strong stimulus, the axon can’t send bigger og faster action potentials (just like flushing a toilet).
All it can change is the timing;

Analogy: you exchange coded messages with someone who can see your window when you flick the lights on and off. The two of you might agree, e.g, to indicate some kind of danger by the frequency of flashes. Much of the brain’s signaling follows the same principle.

Question 14

Refractory period

Answer 14

After an action potential, the cell resists the production of futher action potentials.

Has two mechanisms:

1. The sodium channels are closed
2. Potassium is flowing out of the cell at a faster than usual rate

Question 15

Absolute refractory period

Answer 15

Is the first part of the refractory period, where the membrane cannot produse an action potential, regardless of the stimulation

Anology: There is a short time right after you flush a toilet when you cannot make it flush again

Question 16

Relative refractory period

Answer 16

The second part of the refractory period is stronger than usual stimulus is necessary to initiate an action potential.

Question 17

Axon hillock

Answer 17

A swelling where the axon exists the soma (body cell).

Question 18

Propagation of the action potential

Answer 18

Describes the transmission of an action potential down an axon

Question 19

Myelin sheaths

Answer 19

An insulating material composed of fats and proteins that covers vertebrate axon to increase the speed of the impulse

Anology: suppose your job is to take written messages over a long distance without using any mechanical device. Taking each message and running with it would be reliable but slow. If you tied each message to a ball and threw it, you could increase the speed, but your throws would not travel far enough. The best solution is to station people at a moderate distances along the route and throw the message-bearing ball from person to person until it reaches its destination.

Question 20

Myelinated axons

Answer 20

The axons coverd with a myelin sheath, and is only found in vertebrates

Question 21

Saltatory conduction

Answer 21

The jumping of action potentials from node (node of Ranvier) to node.
Providing rapid conduction of impulses and conserves energy.

Question 22

Local neurons

Answer 22

Small neurons without axon.
These neurons exchange information with only their closest neighbors.
Do not follow the all-or-none law

Question 23

Graded potentials

Answer 23

When a local neuron recives information from other neurons.

A membrane potential that varies in magnitude in porpotion to the intensity of the stimulus