Insect motor control 1 Flashcards
What are the 3 main ganglia in the insect head?
(3 marks)
- Protocereburm
- Deutocerebrum
- Tritocerebrum
Fuse to form the head
What is the thorax made up of?
(2 marks)
- 3 thoracic ganglia - each one controls one pair of legs (3 pairs)
- Meso and metathoracic ganglia control a pair of wings each
What is the abdomen made up of?
(2 marks)
- Terminal abdominal ganglia (4 fused ganglia)
- No appendages or limbs involved in respiration - only controlled using body wall ganglia
What does each ganglion in an insect receive innervation from and what neurons does it contain?
(2 marks)
- Innervated by sensory nerve endings
- Contains motor neurons and interneurons to mediate complex limb reflexes
How many abdominal ganglia are there?
8
What kind of neuronal tracts do ganglia contain?
(2 marks)
- Ascending and descending axon tracts - unmyelinated, same role as white matter
- Cell bodies of neurons that are on the periphary of the ventral surface
Where are the synaptic regions in invertebrae?
Neuropile
What neurotransmitters do motor and sensory neurons use?
(2 marks)
- Motor neurons: glutamate
- Sensory neurons: ACh
Both excitatory
What is the difference between a large motor neuron and a small one?
(3 marks)
Large motor neuron - contacts many muscle fibres
Small motor neuron - may contact only 10
Difference is important to optimise fine contol of muscle
How many motor neurons contact one muscle fibres?
1
What happens when a motor neuron fires an action potential?
(2 marks)
- Releases NT ACh
- Releases Ca2+ into muscle and contracts
What are association neurons?
Neurons that carry impulses from motor neuron to CNS - linked by other parts of the NS
What is the ‘size principle of recruitment (muslce activation)’?
(6 marks)
- 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
How many motor neurons rougly supply each muscle?
2-10 motor neurons
What is the difference between fast and slow motor neurons?
(2 marks)
- 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
What is the difference between the epsps produce by fast and slow motor neurons?
(3 marks)
- Fast excitatory neurons induce large epsps
- Slow excitatory neurons induce small epsps
- so get small contraction epsps can summate together to become larger
What neurotransmitter do inhibitory motor neurons use?
GABA - supply multiple muscles via several nerves to end contraction rapidly (produces inhibitory post synaptic potential in muscle fibres)
Study the image on the next slide - inhibitory mn
What are the muscles implicatged in the jumping muscle of the locus hind leg?
(4 marks)
- 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
Label what muscles are in this image and attach to the correct epsp/ipsp’s.
(6 marks)
What are modulatory motor neurons (DUM)?
(3 marks)
- 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
What do DUM neurons do?
(6 marks)
- 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
What is each motorneuron in invertebrae used for?
(4 marks)
- Slow extensor tibia (SETi) mainly for walking - increase spike frequency gradually - increase force generated in muscle fibres
- Common Inhibitor (CI) ensure each contraction ends quickly
- Fast extensor (FETi) - used in jumping and kicking and activates all muscle fibres
- Modulator (DUMETi) - increase effect of excitors and optimises energy availability
What can motor neurons also work as?
- Interneurons - some excitatory insect motor neurons make output synapses from their dendrites i.e. act as interneurons as well as motorneurons
