Insect motor control 1

Question 1

What are the 3 main ganglia in the insect head?

(3 marks)

Answer 1

• Protocereburm
• Deutocerebrum
• Tritocerebrum

Fuse to form the head

Question 2

What is the thorax made up of?

(2 marks)

Answer 2

• 3 thoracic ganglia - each one controls one pair of legs (3 pairs)
• Meso and metathoracic ganglia control a pair of wings each

Question 3

What is the abdomen made up of?

(2 marks)

Answer 3

• Terminal abdominal ganglia (4 fused ganglia)
• No appendages or limbs involved in respiration - only controlled using body wall ganglia

Question 4

What does each ganglion in an insect receive innervation from and what neurons does it contain?

(2 marks)

Answer 4

• Innervated by sensory nerve endings
• Contains motor neurons and interneurons to mediate complex limb reflexes

Question 5

How many abdominal ganglia are there?

Answer 5

8

Question 6

What kind of neuronal tracts do ganglia contain?

(2 marks)

Answer 6

• Ascending and descending axon tracts - unmyelinated, same role as white matter
• Cell bodies of neurons that are on the periphary of the ventral surface

Question 7

Where are the synaptic regions in invertebrae?

Answer 7

Neuropile

Question 8

What neurotransmitters do motor and sensory neurons use?

(2 marks)

Answer 8

• Motor neurons: glutamate
• Sensory neurons: ACh

Both excitatory

Question 9

What is the difference between a large motor neuron and a small one?

(3 marks)

Answer 9

Large motor neuron - contacts many muscle fibres

Small motor neuron - may contact only 10

Difference is important to optimise fine contol of muscle

Question 10

How many motor neurons contact one muscle fibres?

Answer 10

1

Question 11

What happens when a motor neuron fires an action potential?

(2 marks)

Answer 11

• Releases NT ACh
• Releases Ca²⁺ into muscle and contracts

Question 12

What are association neurons?

Answer 12

Neurons that carry impulses from motor neuron to CNS - linked by other parts of the NS

Question 13

What is the ‘size principle of recruitment (muslce activation)’?

(6 marks)

Answer 13

• Increasing strength of contraction with more muscle fibres
• Activate small MN which only runs to a few muscle fibres
• Increase it by adding more small MN
• As more force generated, brinf in bigger units
• Want to increase large contraction of muscle - recriot large motor neurons
• As contraction reaches a maximum, largest motor neurons recruited

Question 14

How many motor neurons rougly supply each muscle?

Answer 14

2-10 motor neurons

Question 15

What is the difference between fast and slow motor neurons?

(2 marks)

Answer 15

• Fast: release a lot of neurotransmitter at action potential get large muscle contraction
• Slow: release a little neurotransmitter in action potential and get small muscle contraction

Question 16

What is the difference between the epsps produce by fast and slow motor neurons?

(3 marks)

Answer 16

• Fast excitatory neurons induce large epsps
• Slow excitatory neurons induce small epsps
  
  • so get small contraction epsps can summate together to become larger

Question 17

What neurotransmitter do inhibitory motor neurons use?

Answer 17

GABA - supply multiple muscles via several nerves to end contraction rapidly (produces inhibitory post synaptic potential in muscle fibres)

Question 18

Study the image on the next slide - inhibitory mn

Answer 18

Question 19

What are the muscles implicatged in the jumping muscle of the locus hind leg?

(4 marks)

Answer 19

• Fast extensor tibia - fast epsp
• Slow extensory tibia - slow epsp
• Common inhibitor - ipsp

Muscle membrane gives graded level of control as it integrates the excitatoy and inhibitory inputs

Question 20

Label what muscles are in this image and attach to the correct epsp/ipsp’s.

(6 marks)

Answer 20

Question 21

What are modulatory motor neurons (DUM)?

(3 marks)

Answer 21

• Dorsal unpaired median neurons
• Send axons to many muscles on both side of body
• Uses neurotransmitter octopamine - not found in vertebrate but same as noradrenaline and dopamine

Question 22

What do DUM neurons do?

(6 marks)

Answer 22

• Modify actions of other neurons and response of muscle fibres
• Don’t cause muscle contraction
• Octopmaine increases amount of glutamate released at synapse ⇒increasing muscle twitch by up to 5%
  
  • Increases how fast muscle relaxes - causes muscle force to not decrease because of rapid relaxation of muscle
  • Increases amount of ATP inside muscle from carbohydrates
  • Mobilises lipid for energy production

Question 23

What is each motorneuron in invertebrae used for?

(4 marks)

Answer 23

1. Slow extensor tibia (SETi) mainly for walking - increase spike frequency gradually - increase force generated in muscle fibres
2. Common Inhibitor (CI) ensure each contraction ends quickly
3. Fast extensor (FETi) - used in jumping and kicking and activates all muscle fibres
4. Modulator (DUMETi) - increase effect of excitors and optimises energy availability

Question 24

What can motor neurons also work as?

Answer 24

• Interneurons - some excitatory insect motor neurons make output synapses from their dendrites i.e. act as interneurons as well as motorneurons