nerve impulse + action potential

Question 1

define nerve impulse

Answer 1

the electrical message that is transmitted down the axon of a neuron

Question 2

define resting potential

Answer 2

state of the neuron prior to the sending of a nerve impulse

Question 3

define electrical gradient

Answer 3

the difference in electrical charge inside and out of cell > membrane maintains

Question 4

define electrical polarization

Answer 4

the difference in electrical charge of two locations

Question 5

describe the membrane and what it allows to pass-through

Answer 5

selectively permeable = allowing some chemicals to pass more freely than others

• sodium, potassium calcium, and chloride pass-through
• sodium channels = closed
• potassium channels = partially closed

Question 6

define sodium-potassium pump

Answer 6

a protein complex that continually pumps three sodium ions out of cells while drawing two potassium ions into the cells
- helps maintain the electrical gradient

Question 7

what is action potential?

Answer 7

rapid depolarization of the neuron

- stimulation of the neuron past the threshold of excitation triggers it

Question 8

list the steps of action potential

Answer 8

1. depolarisation
2. repolarization
3. refractory period

Question 9

describe the first step of action potential

Answer 9

depolarisation = sudden increase in membrane potential

• when a neuron is stimulated, some sodium channels are opened
• sodium ions move in and intracellular fluid becomes less negative which increases the potential difference
• if the potential difference increases to -55mV, voltage-gated sodium channels open, and sodium ions rush in
• the inward movement of sodium is too great to be balanced by outward movement of potassium, making inside more positive
• orignal polarity increases to +40mv = depolarised membrane

Question 10

describe the second step of action potential

Answer 10

repolarisation

• sodium channels close which stops the influx of sodium ions
• simultaneously, potassium channels open, increasing K flow out of the cell
• this makes the inside more negative and decreases membrane potential and the membrane is repolarised

Question 11

describe the third step of action potential

Answer 11

refractory period
- once sodium channels have opened they quickly become inactivated - unresponsive to stimulus
f- or a brief period, the membrane won’t undergo another action potential
- lasts form -55mV to -70mV

Question 12

define hyperpolarization

Answer 12

increase the polariazation

Question 13

define depolarization

Answer 13

refers to decreasing the polarization to zero

Question 14

define the threshold of excitement

Answer 14

any stimulation beyond a certain level and results in massive depolarisation, reaches -55V

Question 15

what are voltage-activated channels

Answer 15

membrane channels whore permeability depends upon the voltage difference across the membrane
- sodium channels

Question 16

what is the all or none law?

Answer 16

states that the amplitude & velocity of an action potential are independent of the intensity of the stimulus

Question 17

define the refractory period

Answer 17

after action potential where the neuron resists another action potential

Question 18

define the absolute refractory period

Answer 18

first part

- membrane cannot produce an action potential

Question 19

define the relative refractory period

Answer 19

2nd part

- needs stronger stimulus to trigger an action potential

Question 20

what is the state of sodium and potassium channels when the membrane is at rest

Answer 20

sodium channels are closed

potassium channels are partially closed allowing slow passage of sodium

Question 21

how does action potential work to carry a message

Answer 21

occurs in one section of membrane and triggers an AP in adjacent membrane and continues along length of neuron

Question 22

how does conduction of nerve impulse occur along unmyelinated fibres

Answer 22

• AP travels along the whole length of the membrane, moving away from the stimulation point
• impulse is prevented from going back by a refractory period

Question 23

how does conduction of a nerve impulse occur along myelinated fibres

Answer 23

• ions cannot flow between inside and outside of the membrane
• AP jumps from one node of Ranvier to the next via saltatory conduction
• allows nerve impulse to travel much faster