How nerves work 3

Question 1

what is an action potential?

Answer 1

used to transmit big signals along an axon and they’re needed as axons are poor conductors

Question 2

what does muscle need in order to contract?

Answer 2

an action potential

Question 3

process of action potential production

Answer 3

• a local graded potential depolarises cell to threshold
  and fires action potential
• at synapse in CNS another graded potential is needed to depolarise next cell and fire another action potential. This time a neurotransmitter is released by the pre-synaptic terminal and this binds to the receptors on the post-synaptic cell causing gated- ion channels to open (usually) and ions to flow through. This depolarises the next cell to threshold and another action potential is fired.

Question 4

what happens at sensory terminal?

Answer 4

ion channels open and respond directly to a stimulus and depolarise the cell
if this depolarisation reaches threshold an action potential is sent to CNS to synapse there and this is called a generator potential or synaptic potential

Question 5

what happens at the neuromuscular junction?

Answer 5

here acetylcholine is released at presynaptic terminal and binds to receptors on the post synaptic terminal.
An end plate potential is produced- always reaches threshold.

Question 6

what is a pacemaker potential?

Answer 6

some neurons in the brain spontaneously depolarise so they have their own pacemaker potential to determine when they reach threshold and when to fire an action potential
-it is another example of a graded potential

Question 7

what is meant by graded potentials being ‘decremental’?

Answer 7

potentials that don’t travel very well down neurons
- a lot of charge leaks out of the membrane as it isn’t well insulated so further down the axon less current will be flowing through

Question 8

what other names are there for graded potentials?

Answer 8

decremental
electrotonic
local
non-propogated

Question 9

the bigger the stimulus the bigger the….

Answer 9

graded potential produced

which in turn opens more channels by releasing more neurotransmitters

Question 10

what is an inhibitory post- synaptic potential

Answer 10

a kind of synaptic potential that makes a post- synaptic neuron less likely to generate an action potential.

Question 11

example of an inhibitory neurotransmitter?

Answer 11

GABA

Question 12

how does GABA work?

Answer 12

• GABA receptors typically open channels that are selectively permeable to Cl-
• When these channels open, Cl- can flow across the membrane and into the cell hyperpolarising it
• this takes the cell away from threshold (more negative)

Question 13

what is an excitatory post- synaptic potential

Answer 13

makes a cell more likely to fire an action potential

occurs by opening Na+ or Ca2+ channels to depolarise the cell

Question 14

what is the main excitatory neurotransmitter in the CNS? give examples of others too

Answer 14

glutamate - main
acetylcholine
catecholamines
serotonin 
histamine

Question 15

what happens to a graded potential the further it is from the axon hillock?

Answer 15

the potential decays more as it takes longer to get to the axon hillock
information coming in does so through dendrites and then travels through cell body to the axon hillock which is the last point of summation until potential is fired down axon so the further it has to travel more it will decay

Question 16

what is summation?

Answer 16

the sum of all excitations and inhibitions in area near neuron
all PSPs gather at axon hillock and are added together to see whether an action potential will be fired

Question 17

what is temporal summation?

Answer 17

PSPs reach the axon hillock in quick succession and are added together
but they MUST arrive one after another in a very short space of time in order to be summated
they may be weak individually but once added together they reach the threshold

Question 18

what is spatial summation?

Answer 18

Various PSPs that arrive at the same time are added together

once added again they can then reach threshold and an A.P is produced

Question 19

what happens if an EPSP and IPSP arrive at the same time

Answer 19

they can knock each other out

Question 20

if multiple EPSPs and IPSPs join what can happen to the excitatory signal?

Answer 20

it can be inhibited slightly but won’t be completely cancelled out

Question 21

Depending on which neurotransmitter is released at NMJ what can happen?

Answer 21

different channels could open and so could be IPSP or EPSP

Question 22

why are there folds at the NMJ

Answer 22

Allows more voltage gated Na+ channels to be closer to the ligand gated acetylcholine receptor so the graded potential doesn’t have far to go