signals of of the nervous system

Question 1

What are nervous signals?

Answer 1

change in resting potential

Question 2

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

Answer 2

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 3

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

Answer 3

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 4

What are the steps of the experiment?

Answer 4

• Inject small hyper- polarising currents through electrode 1 of 10mv
• Check what recorded at electrode 2 and 3
• While electrode 2 - record a small hyper polarisation of 10mv
• At electrode 3 don’t record anything
• Then can carry on recording -15mV to electrode 1 and 2 and not at 3 etc etc.
• Shows hyperolarisation can’t get along axon between electrode 2 and 3- shows axon is a poor conductor of electricity

Question 5

What is action potential said to be?

Answer 5

• All or nothing event
• If depolarise neuron by 15mV or more it reaches a threshold which triggers a.p.
• You don’t Geta. bigger a.p however much you depolarise greater.

Question 6

What is depolarisation?

Answer 6

the neuron becomes less negative

Question 7

What is hyper polarisation?

Answer 7

the neuron becomes more negative

Question 8

what is the threshold to trigger action potential?

Answer 8

15-20 mV is threshold , threshold triggers action potential
how do you trigger action potential?
to trigger action potential you have to depolarise inside of neuron by about 15mV

Question 9

What are the steps to an action potential?

Answer 9

1. inside of neuron is negative during resting potential
2. threshold depolarisation opens Na channels
3. Na rushes down its electrochemical gradient into the neuron until it reaches equilibrium potential is reached at 50 mv- Na ion channels shut
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
   - Resting state of neuron is restored

Question 10

what is the effect of Na on action potential?

Answer 10

less sodium=less action potential

Question 11

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

Answer 11

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

Question 12

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

Answer 12

.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 13

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

Answer 13

.the plasma membrane of the cell contains proteins which act as ion channels
.proteins change shape when you depolarise a neuron- to trigger the a.p you need a threshold depolarisation so you put a positive charge within the neuron
.proteins change shape to let Na through / stop Na in

Question 14

why is action potential regenerated along the neuron?

Answer 14

.action potentials dont diminish in size as they travel along a neuron
. they therefore must be regenerated as they go along
-they are regenerated along the nodes of ranvier- a.p leaps from node to node- saltaotory conduction.

Question 15

explain action potential transmission?

Answer 15

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 16

what is a local circuit?

Answer 16

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

Question 17

how can the speed of impulse propagation be increased?

Answer 17

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 18

what is saltatory conduction?

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)

Question 21

What are gates/channels that ions go through ?

Answer 21

• Plasma membrnae-phospoholipid bilayer- which have proteins in this layer-
• these proteins form these ion channels

Question 22

What is the molecular structure for ion channels?

Answer 22

• Proteins made up of amino acid chains
• Have complicated 3D structures
• Na and K Ion channels- Long chain of a.a. that go though membrane several times and every time they go through membrane they form a helix- form a cluster within plasma membrane- ions can get through these complicated clusters.
• proteins change shape to open and close.

Question 23

What is the protein structure of a Na channel in a resting neuron?

Answer 23

• the pore in the centre of protein is shut and won’t let Na through.

Question 24

What is the protein structure on a threshold depolarisation ?

Answer 24

-You can trigger action potential by making inside of neuron positive - this positive charge will change shape of protein, the pore opens up and now Na ions can enter the neuron.

Question 25

What are the types of ion channels?

Answer 25

• Voltage gated channel- change in charge would change the shape of protein to let ions through
• Ligand gated- chemical binding to protein can cause protein to change shape and open up ionic channel
• Mechanically gated channel- mechanical forces opening up the ionic channels for e.g touch or hearing- a.p go through sensory neuron.- mechanical stimuli

Question 26

What are local (electronic) potentials ?

Answer 26

• Properties of neuron has a higher resistant to current spread
• a small current depolarisation at one end of the neuron will get smaller as it is conducting along the neuron
• therefore show diminish in size and not be propagated along (longer) neurons.

Question 27

What is the advantage of myelin?

Answer 27

• Saves a lot of space

- each axon conducts at the same velocity- loads of axon myelinated .

Question 28

What is a refractory period?

Answer 28

the interval after an action potential during which a second action potential absolutely cannot be initiated no matter how intense the stimulus