synaptic signalling

Question 1

outline the structure of the synapse

Question 2

what are the different synaptic arrangements in CNS

Answer 2

1. axodendritic - axon to dendrite
2. axosomatic - bind onto the soma (body)
3. axoaxonic - bind onto another axon (neurone 2) before it then passes onto neurone 3)

Question 3

TRUE or FALSE the closer to the axon hillock the contact then the less influence it has on AP generation

Answer 3

FALSE - closer to axon hillock = greater influence of AP generation

Question 4

what are the types of receptor signalling mechanisms

Answer 4

Ionotropic (receptors and ligand-gated channels)

metabotropic (G-protein coupled)

Question 5

how do ionotropic receptor signalling mechanisms work

Answer 5

1. transmitter binds
2. conformational change
3. opens channels within the protein allowing for ion movement = AP

Question 6

how does metabotropic receptor signalling mechanism work

Answer 6

1. transmitter binds
2. conformational change
3. activates G-porteins
4. activates effector systems
5. indirect effect on channel’s excitability (open/closing)

Question 7

compare ionotropic and metabotropic receptor signalling pathways

Answer 7

ionotropic
- fast transmission
- shorter lasting
- direct impact on channels

metabotropic
- slower transmission
- longer lasting effects
- indirect effect on channels

Question 8

how do neurones communicate the output signal

Answer 8

1. receives messages from connecting neurones
2. integrates all inputs
3. sends a frequency-encoded message

Question 9

how is strength of signal sent through neurones if action potential is an all-or-nothing

Answer 9

strength relayed through
FREQUENCY ENCODED MESSAGES
- bigger signals are sent with the firing of more action potentials after each other (quick succession)

Question 10

when channels open on post-synaptic membrane what happens to allow spread of impulse

Answer 10

channels open = influx of Na+ (down conc and electrochemical)
this is EPSP
(small excitatory post synaptic potential) if threshold is reached =
DEPOLARISTION

Question 11

what ways do axons ensure that they achieve AP if one EPSP alone isn’t enough

Answer 11

1. spatial summation
2. temporal summation

Question 12

how does spatial summation work to generate action potential

Answer 12

spatial = summing of post synaptic potentials from several synapses
- multiple synptic inputs = all releasing EPSP
increases change of threshold reached

Question 13

how does temporal summation work to generate an action potential

Answer 13

temporal = summing of post synaptic potentials generated at same synapse, in rapid succession

increase EPSE from one synapse by firing them at high frequency

Question 14

show the effects of spatial summation and temporal summation of a graph

Answer 14

spatial = similar to normal action potential

temporal = like a stair case up to threshold and then normal action potential

Question 15

how do inhibitory synapses work to prevent action potential being reached

Answer 15

• binding causes movement of Cl- into the cell = hyperpolairsation
  similar process of EPSP but IPSP (inhibitory post synaptic potential)
  -> small bump below resting potential

Question 16

what happens if a axon has both an EPSP and IPSP acting upon them

Answer 16

equal but opposite post synaptic membrane potential = no impact on the mV (remains resting)

Question 17

what is a sustained threshold stimulus

Answer 17

this is a stimulus that keeps triggering an action potential as soon as threshold is reached (during repolarisation)

it is only limited by
ARP + RRP (absolute refractory period and relative refractory period)

Question 18

if there is a supra-threshold stimulus what does that do

Answer 18

action potentials are send during the RRP (just after VGNaC have reset)