Stimulus And Excitability Of Nerve

Question 1

Excitability

Answer 1

Property of the living cell to respond to change in the environment

Question 2

Stimulus

Answer 2

A change in the environment that evokes a response from the cell

Question 3

Characteristics of stimuli

Answer 3

1. All living cells are excitable
2. Evoke a response in the cell
3. Produces a biological response
4. Then electrical response
5. potential in the cell membrane changes
6. Stimulus extremely variable : physical, chemical and electrical

Question 4

What causes change in membrane potential

Answer 4

Any factor that causes sodium ions to begin to diffuse inward through the membrane of the nerve in sufficient number can set off automatic regenerative opening of sodium channels results in a change of membrane potential.

Question 5

Automatic regenerative opening all sodium channels can result from

Answer 5

1. Mechanical disturbance of the membrane
2. chemical effects on the the membrane
3. passage of electricity through the membrane

Question 6

Example of mechanical disturbance to cause action potential

Answer 6

Mechanical pressure to excite sensory nerve endings in the skin

Question 7

Example of chemical disturbance to cause action potential

Answer 7

Chemical neurotransmitters to transmit signals someone one neuron to the next in the brain

Question 8

Example of electricity disturbance to cause action potential

Answer 8

Electrical current to transmit signals began successive muscle cells of the heart and intestines

Question 9

How is the nerve excited my negatively charged

Answer 9

electrode two small electrodes which are negatively charged and positively charged separately place on the electrode. The negative current from the electrode decreases the three voltage on the outside of the membrane to a negative value nearer to the voltage of the negative potential inside the fiber. This decreases the electrical voltage across the membrane and allow Sodium channels to open resulting in action potential. A

Question 10

What causes Hyperpolarization

Answer 10

The positive electrode injects positive charges outside the membrane, heighten the voltage difference across the membrane. This causes a state of hyperpolarization, which decreases the excitable

Question 11

Acute local potential

Answer 11

Disturbance of the membrane potential for as long as 1ms or more

Question 12

Acute subthershold potential

Answer 12

When Acute local Potential fail to elicit an action potential

Question 13

Threshold level

Answer 13

When local potential barely reached the level required to elicit an action potential that occurs after a short “latent period”

Question 14

When Acute local Potential is greater than threshold

Answer 14

Action potential occurs after less of the latent period

Question 15

How is Excitability inhibited

Answer 15

1. +ve electrode injecting +ve charge on the outside
2. High extracellular calcium ion conc.
3. Local anesthetics

Question 16

High calcium level effect on Excitability

Answer 16

High extracellular calcium ion conc decreases membrane permeability to Sodium ions and reduce Excitability

Question 17

Local anesthetics

Answer 17

Procaine, tetracain

Question 18

How do local anesthetics work

Answer 18

Directly act on the activation gates of sodium channels making it difficult for these gates to open reducing membrane Excitability. When excusable has been reduced so low that the ratio of action potential strength to Excitability threshold (safety factor) is reduced below 1.0 nerve impulse Falls to pass along anesthetized nerve