Paper 1:

Question 1

What is a rapidly adapting stretch receptor neuron?

Answer 1

if you depolarize/stretch the neuron (stop firing of APs) and hold this stimulus, it will fire AP as soon as it is stimulated, but will adapt rapidly and slow firing of APs

Question 2

What is a slowly adapting stretch receptor neuron?

Answer 2

if you depolarize/stretch the neuron (stop firing of APs) and hold this stimulus, it will continue to fire APs

Question 3

What are accessory neurons in the crustaceans?

Answer 3

neuron hypothesized to be the source of inhibition to those dendrites – has axon terminals near the dendrites of both sensory receptor cells

Question 4

What is a receptor potential?

Answer 4

transmembrane potential difference produced by activation of sensory receptor

Question 5

What can extracellular recordings record?

Answer 5

APs only

image shows horizontal line with vertical lines corresponding to the number of APs in the correct places

Question 6

Figure 2

What happens when the body wall of a crayfish is stretched?

Answer 6

1. sensory cell generates receptor potential
2. cell depolarizes and fires steady APs

• slowly adapting receptor cell, therefore stays depolarized and continues to fire APs as long as you keep it stretched

Question 7

Figure 3

What can be seen at a lower frequency of inhibitory axon stimulation?

Answer 7

individual IPSPs that briefly make the membrane more negative

Question 8

Figure 3

What can be seen at a higher frequency of inhibitory axon stimulation?

Answer 8

no individual IPSPs – trace remains at the most hyperpolarized values throughout stimulation

Question 9

What does an IPSP do?

Answer 9

• inhibits the neuron

- hyperpolarizes the cell

Question 10

Figure 3

What happens do APs if you increase inhibitory stimulation?

Answer 10

no change

Question 11

Figure 3D

When might an IPSP flip signs?

Answer 11

when inhibitory pulse is timed for the trough at the end of the AP

Question 12

Figure 4

What did the authors do to change the level of Vm in this fast receptor cell?

Answer 12

bigger stretch = larger receptor potential (more depolarization from RMP)

Question 13

Figure 4

What happens to the IPSP train when the cell is depolarized less than ~5mV from RMP?

Answer 13

IPSP train polarity has changed – are now depolarizations (pointing slightly upward)

Question 14

Figure 5

What is stretch depolarization

Answer 14

distance away from RMP (driving force for inhibitory conductance)

Question 15

What is a main conclusion of the paper so far?

Answer 15

membrane effect of inhibition depends on the state of the sensory receptor cell

Question 16

Figure 7

What is seen when two IPSPs co-occur in time?

Answer 16

almost no temporal summation occurs

Question 17

Figure 7

Why do the authors report time to half decay, instead of full decay?

Answer 17

• baselines (at the holding potential) are often messy

- where a PSP joins the baseline is also very noisy to measure

Question 18

Figure 8A

What happens to the membrane potential after high frequency inhibitory stimulation? How does this differ from the ‘typical’ effect of inhibitory stimulation?

Answer 18

after the end of high frequency stimulation of the inhibitory neuron (second arrow), there is ’post-inhibitory polarization’ that continues for a several ms after

Question 19

When the inhibitory neuron is stimulated, two processes with distinct properties can occur and overlap in the same stretch receptor neuron (two different forms of inhibition). What are they?

Answer 19

• rapid, ‘low threshold’ polarization events are triggered which reverse their polarity at Vm of ~ -60 mV (ie. ERev = -60 mV)
• delayed, longer-lasting, ‘high threshold’ polarization events are triggered with strong stimulation and are always outward currents (hyperpolarizing) at all membrane potentials tested (RMP and above) (ie. ERev < -65 mV)

Question 20

Why are there two different types of inhibition?

Answer 20

• we know that synaptic inhibition occurs through chemical neurotransmission
• for most neurotransmitters found in crustacean nervous system (or in vertebrate nervous system), there is more than one type of receptor molecule that can be bound activated by a neurotransmitter
• different receptors (encoded by different genes) have different properties, and cause different effects in postsynaptic cell
• this can include changing opening different kinds of ion channel – ie. causing changes in membrane permeability to different ions