Signalling

Question 1

what is electrical signalling?

Answer 1

ion movement, i.e. movement of electrical charge

Question 2

what is the axon of a neutron?

Answer 2

can be very long, where the nerve impulse travels along

Question 3

what is a nerve impulse?

Answer 3

a wave of altered charge across tercel cell membranes that sweeps along axon. also known as depolarisation, action potential

Question 4

what is a membrane potential?

Answer 4

voltage difference between the inside and the outside of the cell. it is maintained by ion pumps in plasma membrane.

Question 5

what is the electrical potential difference across neutron plasma membrane?

Answer 5

approx -79mV. K+ ions higher inside the cell, Na+ and Cl- higher outside the cell.

Question 6

what happens when a nerve impulse is stimulated?

Answer 6

Na+ ion channels open and they flow into cell, increasing membrane potential. this causes the opening of voltage gated K+ to flow out of the cell

Question 7

what ensures the signal only travels in one direction?

Answer 7

the refractory period. the time immediately following AP when new AP cannot be initiated in the same area of membrane

Question 8

what are the multiple inputs from the multiple different dendrites?

Answer 8

(EPSP’s) - excitatory Pre-synaptic potentials
(IPSP’s) inhibitory pre- synaptic potentials
(graded) very in magnitude

Question 9

what is the summation of changes in membrane potential?

Answer 9

EPSP increases chance of AP initiation ; IPSP decreases chances

Question 10

what is the threshold voltage in most human nerve cells and what happens If this is reached?

Answer 10

-55mV, if overall membrane potential reaches this then the Na+ channels open and AP is initiated

Question 11

what is spatial summation?

Answer 11

summation of inputs from different areas of cell, eg from different dendrites

Question 12

what is temporal summation?

Answer 12

-input occurs multiple times from the same area/ dendrite
-repeated inputs in short Time period - summation
-summation -> AP’s generated more or less frequently

Question 13

how is the AP frequency increased?

Answer 13

the greater the stimulus then the greater the frequency, the magnitude always stays the same

Question 14

what happens when the AP reaches the end of the neuron?

Answer 14

it must cross the synapse and then the AP can be set up in the next neutron

Question 15

what are excitatory chemical signals?

Answer 15

promote formation of AP in receiving neutron

Question 16

what are inhibitory chemical signals?

Answer 16

inhibit formation of AP in receiving neuron

Question 17

amino acid and derivatives NT examples?

Answer 17

glutamine - main excitatory neurotransmitters in CNS
GABA - main inhibitory neurotransmitters in CNS

Question 18

catecholamines (monoamines)?

Answer 18

derived from Tyr
eg dopamine, serotonin

Question 19

acetylcholine?

Answer 19

derived drom choline
neuromuscular junction

Question 20

peptides?

Answer 20

substance P, endorphins

Question 21

How does GABA-A (ion channel receptor) work ?

Answer 21

binding of the ligand GABA to receptor causes conformational change that opens the ion channel (ligand- gated). Cl- move into cell and hyper polarisation makes it harder to reach the threshold voltage for AP formation in post synaptic cell.

Question 22

how does the acetylcholine channel work?

Answer 22

-nAChR is a sodium ion channel receptor
-ACh binding allows Na+ entry
-Na+ influx - depolarisation of muscle cell membrane
-depolarisation initiates contraction
-acetylcholinesterase in cleft removes EACh

Question 23

what are gap junctions?

Answer 23

small pores in adjacent cells which are formed by connexions. pre is very small and ions can diffuse between cells according to concentration gradients.

Question 24

what are some examples of electrical signalling between gap junctions?

Answer 24

electrical synapses between neurons (most are chemical) and cardiac myocytes

Question 25

how does the heartbeat?

Answer 25

electrical impulses travelling across heart tissue causes contraction of cardiac muscle. specialised cells with neuron like properties spread charge throughout heart. atria first then ventricles. Ion flow between adjacent muscle cells (myocytes)

Question 26

where and when is adrenaline produced?

Answer 26

produced by adrenal glands in situations of acute stress. vital for sympathetic fight to flight response

Question 27

why is adrenaline released?

Answer 27

sympathetic NS causes the adrenal medulla to produce adrenaline.

Question 27

what are adrenal glands?

Answer 27

small triangular shaped glands located on top of both kidneys. produce hormones that help regulate metabolism, immune system, blood pressure and respond to stress.

Question 28

what are some of the effects of adrenaline?

Answer 28

increased HR
increased respiration
mobilising glucose stores
(all help body to fight or flight)

Question 29

what is GTP?

Answer 29

it is similar to ATP and can act as an energy source. they can be hydrolysed to release energy which produces GDP

Question 30

what happens when G-proteins are bound to GTP?

Answer 30

they are active, they have evergy which they can use by hydrolysing the GTP. this leaves them in an inactive GDP-bound state. activates downstream effector proteins.

Question 31

what are GPCR’s?

Answer 31

they use large hererotrimeric G proteins, not small monomeric G-proteins like Ras.

Question 32

what does GAP/GRS protein do?

Answer 32

acts as the off switch, returns the system back to inactive state.