Insect motor control 2

Question 1

What are the different neurons involved in motor control in insects?

(4 marks)

Answer 1

• Sensory neurons
• Local interneurons
• Intersegmental interneurons
• Motor neurons

Question 2

What do sensory neurons in insect motor control do?

(1 mark)

Answer 2

Some hairs measure wind currents, and strain detectors measure distortion of cuticle

Question 3

What do local interneurons do in more complex systems?

(3 marks)

Answer 3

• Have spiking and non-spiking interneurons
• Spiking interneurons suport action potentials
• Non-spiking interneurons don’t fire an action potential

Question 4

What is a key feature of intersegmental interneurons?

(1 mark)

Answer 4

Dendrites are in one ganglion and axon runs to one or more other ganglia

Question 5

What does the chordotonal organ do?

(1 mark)

Answer 5

Monitor position and speed of joint movement

Question 6

What is the chordotonal and what does it do?

(3 marks)

Answer 6

• A tissue with 50-60 cell bodies of sensory neurons suspended in hollow space in limbs
• Connected to tibia & when tibia moves, there’s a difference in strain that’s put on nerve cells of the sensory neurons attatched to tibia
• Has a population of neurons that respond to different states of movement

Question 7

Where are sensory neurons in the ear cell bodies scattered around?

Answer 7

The hearing organ and immediately under the coritcal. Axons from these nerves end in ‘grey matter’ equivalent

Question 8

What is in a sensory neuropile?

(1 mark)

Answer 8

Rich in endings from sensory neurons

Question 9

How is the inflow of information controlled by inhibitory synapses?

(3 marks)

Answer 9

• On axon terminals sensory neurons = cholinergic and motor neurons = glutamatergic
• Can control the release of glutamate with GABA by synapse of inhibitory neurons on such terminals
• aka Presynaptic inhibition
  
  • ​a way of condensing neurons to produce movements that are controlled subtly

Question 10

Where are dendrites and axons of spiking interneurons located in the neuropile(s)?

(2 marks)

Answer 10

• Dendrites and short axons in the ventral sesnory neuropile
• Axon terminals are in the dorsal motor neuropile

Question 11

What method would you adopt to record the action potential of one neuron?

(4 marks)

Answer 11

• Put electrode in cell body
• Can narrow down glass tube electrode by heat - at tip you can put a metal electrode
• When recording action potential actuall comparing action potential against the earth
• ‘Bumps’ seen are the results of the dendrites

Question 12

Why are you unable to get an extracellualr recording from just one neuron with the use of hooks?

(1 mark)

Answer 12

The method means you receive action potentials from many neurons

Question 13

How do you do an extracellular recording?

(1 mark)

Answer 13

• Recorded by hooks and electrodes on a nerve

Question 14

How do you interpret an electrophysiological trace?

Answer 14

• spikes on top of the line represent the intracellular recordings (upper trace)
• spikes on the bottom of the line represent the extracellular recordings
• each spike is an action potential (lower trace)
• an epsp is an excitatory action potential seen as the spike goes UP
• an ipsp is an inhibitory action potential seen when there is a drop
  *

Question 15

What do the upper and lower trace show on an electrophysiological graph?

(2 marks)

Answer 15

Upper trace: neurone is excited, though the individual epsps responsible can’t be sensed - result = increase in sqpike frequency

Lower trace: neuron is inhibited and the (individual ipsps cannot be seen) preventing spiking

A

Question 16

How can interneurons excite motor neurons?

(2 marks)

Answer 16

• An interneuron that’s depolarised will inhibit a motor neuron so the motor neuron is hyperpolarised
• When interneuron is hyperpolarised, motor neuron is released from inhibition and causes an action potential (also due to other inputs)
• Affect can be viewd by manipulating pre-synaptic membrane

Question 17

Why do spiking local interneurons get direct sensory input?

(1 mark)

Answer 17

• Touch sensory hairs get burst of action potential which leads to the depolarisation of interneurons

Question 18

What response does the interneuron give when touching the leg and knee?

Answer 18

Excitatory

Question 19

What response is given by the interneuron when the upper femur is touched?

Answer 19

Inhibition (through inhibitory interneuron)

Question 20

Is the process of inhibition in an interneuron direct or indirect?

Answer 20

Indirect

Question 21

What does the synaptic bouton do?

Answer 21

• It’s a swelling on an axon terminal - with lots of synaptic vesicles
• Makes outputs onto small dendrites

Question 22

What are the conslusions we can draw about spiking local interneurons?

(4 marks)

Answer 22

• Receive indirect and direct input from sensory neurons
  
  • can activate have one part of leg activated and the other inhibited
• Dendrites make output synapses (get more circuitory for number of neurons involved)
• Few input synapses - likely involved in presynaptic inhibition

Question 23

What conclusions can be made about non-spiking local interneurons?

(4 marks)

Answer 23

• Don’t fire action potentials and has no absolute threshold
• Whether NT released dependent on how depolarised the membrane is but still no ^^
• Has graded NT release - as membrane potential changes so does NT released
• Doesn’t have resting potential

Question 24

What happens to non spiking interneurons if a neuron contains an excitatory transmitter?

(2 marks)

Answer 24

• Post-stynaptic neuron excited as non spiking interneuron is depolarised
• But if non spiking interneuron hyperpolarised get less excitation

Question 25

What happens if a non-spiking neuron contains an inhibitory transmitter?

Answer 25

Post synaptic neuron is depolarised and excited as non spiking interneuron is hyperpolarised

Question 26

Where does a non-spiking interneuron mainly receive input from?

(2 marks)

Answer 26

Spiking interneurons but NO direct sensory input

It contacts groups of motor neurons so orchestrating MN in different muscles to produce co-ordinated activity: regarded as pre-intermotor neurons

Question 27

This is here for you to learn the comparisons between the effects of spiking and non spiking neurons onto motor neuron synapses.

Don’t put 5 till thoroughly memorised xoxo

Answer 27

Question 28

How do non-spiking neurons release a neuorotransmitter at their normal ‘resting potential’?

(2 marks)

Answer 28

• Inject depolarising cufrent into inhibitory non-spiking interneuron to increase the release of GABA as it hyperpolarises the MN
  
  • Then inject a current to hyperpolarise the interneuron and reduce excitablity and release of GABA in MN and get epsps and action potential