neural transmission

Question 1

what are nervous signals?

Answer 1

nervous signals are a change in resting potential

Question 2

what is depolarisation?

Answer 2

the neuron becomes less negative

Question 3

what is hyper polarisation?

Answer 3

the neuron becomes more negative

Question 4

what is the theoretical experiment to explain action potential when you inject hyper polarisation current?

Answer 4

1. inject a hyper polarisation current into electrode 1 and record the voltage from electrode 2 and 3
2. however much negative current you inject the voltage for electrode 2 is the same as electrode 1
3. electrode 3 will not change its voltage
4. this suggests that the inside of the neuron (axoplasm) has high resistance to current spread

Question 5

what is the theoretical experiment to explain action potential when you inject current above -15mV?

Answer 5

1. inject current above -15mV in electrode 1
2. electrode 2 goes positive then negative (much bigger response)
3. this is action potential
4. action potential is regenerated as it moves along the axon
5. electrode 3 also gets a response

Question 6

what is the threshold to trigger action potential?

Answer 6

15-20 mV is threshold , threshold triggers action potential

Question 7

how do you trigger action potential?

Answer 7

to trigger action potential you have to depolarise inside of neuron by about 15mV

Question 8

explain action potential steps?

Answer 8

1. inside of neuron is negative during resting potential
2. threshold depolarisation opens Na channels
3. Na rushes into the neuron until it reaches equilibrium potential is reached at 50 mv
4. neuron suddenly becomes negative
5. inside of neuron becomes negative due to K channels opening both electrical and chemical force push k out neuron
6. K will continue to move outside the neuron till equilibrium is reached
7. sodium/potassium pumps 2 K back into neuron and remove 3 Na out

Question 9

what is the effect of Na on action potential?

Answer 9

less sodium=less action potential

Question 10

what forces act on potassium when the neuron is depolarised during action potential?

Answer 10

both the electrical and chemical force are acting to push potassium out of the neuron

Question 11

what is the function of protein when you depolarise a neuron?

Answer 11

.the plasma membrane of the cell contains proteins which act as ion channels
.proteins change shape when you depolarise a neuron
.proteins change shape to let Na through / stop Na in

Question 12

explain the hypothetical mechanism for the mode of action of an ion channel?

Answer 12

1. in a resting neuron positive in protein attracts negative in neuron , the channel is shut
2. to trigger action potential inside of neuron becomes positive
3. the positive charge inside neuron repels the positive part inside the protein
4. this causes the molecule to flip and open up the channel and Na will move

Question 13

why is action potential regenerated along the neuron?

Answer 13

.action potentials dont diminish in size as they travel along a neuron
. they therefore must be regenerated as they go along

Question 14

explain action potential transmission?

Answer 14

1. resting neuron is negative on inside and positive on the outside
2. to trigger action potential depolarise neuron this opens Na channel
3. Na rushes inside neuron
4. inside neuron becomes positive
5. Na ions get attracted to the forward part of neuron that has not been stimulated and where action potential isnt present
6. local circuit is set up where opposites attract
7. action potential triggers next bit of axon to make action potential this is called a local circuit

Question 15

what is a local circuit?

Answer 15

action potential triggers the next bit of axon to make action potential

Question 16

how can the speed of impulse propagation be increased?

Answer 16

1. increasing the diameter of the axon
bigger axon=faster speed of conduction
2. myelinisation
myelin sheet is good insulator
myelinisation  saves a lot of space

Question 17

what is saltatory conduction?

Answer 17

action potential are only regenerated at the nodes of ranvier
they leak from one node to another

Question 18

what is refractory period?

Answer 18

.the interval after an action potential during which a second action potential absolutely cannot be initiated no matter how intense the stimulus
. this is caused by the Na/K pump

Question 19

explain the dependence of threshold on axon diameter?

Answer 19

bigger axon = lower threshold = easier to stimulate
bigger axon need less voltage to stimulate action potential
bigger neurons are most sensitive so conduct faster

Question 20

what are the types of neural transmission?

Answer 20

. action potential

.electronic current spread (most common in short neurons)