B&B Invertebrate motor control

Question 1

How many neurons do the following have:
1mm3 mouse cortex
Entire nervous system of fly Musca
Entire nervous system of bee Apis

Answer 1

100,000
350,000
850,000

Question 2

Describe how the nervous system of an insect is organised

Answer 2

Composed of a system of ganglia
Segmental NS
Each ganglion control one segment
Each ganglion linked to the other by connectors
Carry the axons of long interneurons
Large structures eg brain are created by the fusion ganglia

Question 3

Describe how the ganglia of an insect are organised

Answer 3

Have tracts (ascending and descending axons). Connectives running between them. Axons are not myelinated (so do not look like white matter but have the same role)
Cell bodies of motor and interneurons are on the outside of the ganglia (mainly ventral and lateral surface)
The synaptic regions (neuropile) lie in the centre (equivalent of grey matter in vertebrates)

Question 4

Vertebrate motor neurones use WHAT

Vertebrate sensory neurones use WHAT

Answer 4

acetyl choline

glutamate

Question 5

Invertebrate motor neurones use WHAT

Invertebrate sensory neurones use WHAT

Answer 5

glutamate

acetyl choline

Question 6

In vertebrates, dendrites emerge from the cell body. Where do they emerge from in invertebrates?

Answer 6

A process comes off the cell body and they emerge from this - sometimes called a neurite

Question 7

What is a motor pool? vertebrates

Answer 7

Each muscle is supplied by hundreds or thousands of motor neurones - this is a motor pool (the group of hundreds of motor neurons that control a single muscle)

Question 8

What is a motor unit? vertebrates

Answer 8

Each motor neurone contacts many muscle fibres

Question 9

True or false vertebrates

Large motor neurons contact many muscle fibres while small motor neurons contact only a few

Answer 9

True

Question 10

Each muscle fibre is innervated by how many motorneurones? vertebrates

Answer 10

1

Question 11

Because vertebrate muscle fibres respond with AP when they are stimulated, we call their contractions what?

Answer 11

All or nothing

Question 12

What is the size principle of muscle activation?

Answer 12

Movements that use small forces - small motor neurones are recruited
Movements that use large forces - large motor neurones recruited
Contraction reaches maximum - largest motor units recruited

Question 13

Invertebrate motor neurons can be described as fast or slow. What does this mean in terms of transmitter?

Answer 13

Fast neurons release a lot of transmitter with each AP and small neurons release little transmitter

Question 14

In invertebrates, each motor neurone supplies most of the muscle fibres within the muscle.
True or false?

Answer 14

True

Question 15

In invertebrates, when glutamate is released, they don’t generate an AP in the muscle membrane but a what?

Answer 15

excitatory post synaptic potential (epsp)
This allows summation between epsps and other potentials
Fast excitatory motor neurons induce large epsps

Question 16

If epsps come close together what happens?

Answer 16

They will summate to become larger

Question 17

Describe inhibitory motor neurons in invertebrates

Answer 17

Neurotransmitter is GABA
Produces an inhibitory post synaptic potential in muscle fibres
Each inhibitory neurone has an axon that branches axons into several nerves and contacts many muscles
Their main role is to end the contraction rapidly to prevent overlap with the contraction of antagonist muscles

Question 18

The extensor tibia muscle lies within the femur and does what?

Answer 18

extends the tibia during walking and jumping

Fast extensor tibia, slow extensor tibia and common inhibitor

Question 19

what is an epsp and an ipsp

Answer 19

epsp = excitatory post synaptic potential
ipsp = inhibitory post synaptic potential

Question 20

DUM neurones are modulatory motor neurones. They send axons to many muscles on both sides of the body. What does DUM stand for?

Answer 20

Dorsal unpaired median neurones

Question 21

What neurotransmitter do DUM neurones contain?

Answer 21

Octopamine
Not found in vertebrates
Structurally related to noradrenaline and dopamine

Question 22

DUM neurons do not generate epsps or ipsps. What does this mean?

Answer 22

This means they do not cause contraction

Instead, octopamine acts on the cellular components within the muscles and on the motor neurone axons

Question 23

Describe what happens when octopamine is released.

Answer 23

Released from DUM neurones
Increases the amount of glutamate released at the synapse
This increases muscle twitch by 5%
It increases how fast the muscle is relaxed
This is important in rhythmic activity eg locomotion
Increases muscle ATP production from carbohydrates
Mobilises lipid for energy production

Question 24

Vertebrate muscles require hundreds or thousands of motor neurones to allow precise control of the force generated
The locust extensor tibiae muscle requires how many motorneurones?

Answer 24

4
SETi
FETi
CI
DUMETi

Question 25

Describe SETi

Answer 25

The slow extensor Used mainly for walking Increasing spike frequency gradually increases the force generated in many muscle fibres

Question 26

Describe FETi

Answer 26

The fast extensor Used in kicking or jumping Activates all muscle fibres

Question 27

Describe CI

Answer 27

The common inhibitor | Ensures that each contraction ends quickly

Question 28

Describe DUMETi

Answer 28

The modulator | Increases the effect of the excitors and optimises energy availability

Question 29

True or false | Insect motor neurones can act as interneurones

Answer 29

True Some excitatory insect motor neurones make output synapses from their dendrites not true of inhibitory or dum

Question 30

What are the 2 types of local interneurones?

Answer 30

Spiking localinterneurones | Non-spiking local interneurones (don't fire AP)

Question 31

What are intersegmental interneurones?

Answer 31

Projecting | Their dendrites are in one ganglion and their axon runs to one or more other ganglia

Question 32

What are some sensory structures on an insect's body?

Answer 32

Touch sensitive and chemosensory hairs | Cuticular strain detectors

Question 33

What is a chordotonal organ?

Answer 33

Monitor joint angle and speed of movement Lie in parallel to muscles Have their own tendon Which stretches the dendrites of the sensory cells as the joint moves

Question 34

What is the sensory neuropile rich in?

Answer 34

The ends of the axons of sensory neurones

Question 35

The inflow of sensory information can be controlled by what?

Answer 35

Inhibitory synapses Contain neurotransmitter GABA Blocks glutamate release from the sensory axons

Question 36

What is presynaptic inhibition?

Answer 36

The inflow of sensory info being controlled by inhibitory synapses Found on all vertebrate and invertebrate sensory axons

Question 37

Sensory neurones synapse onto what (whose branches are entirely contained within one ganglion)

Answer 37

Spiking local interneurones These have 2 fields of branches One in the sensory neuropile and one in the motor neuropile linked by a short axon

Question 38

How are extracellular recordings made?

Answer 38

Using 2 hook electrodes on a nerve APs go above and below the line as they move past first one electrode then the other 1st positive then negative

Question 39

How are intracellular recordings made?

Answer 39

Put electrode (hollow glass capillary) inside neurone In the cell body Close to dendrites so large psps, far from axon so small spikes Small upwards and downwards peaks are excitatory and inhibitory synapse potentials APs (spikes) are very sharp upward deflections

Question 40

True or false | Excitation is direct and inhibition is indirect

Answer 40

False - other way around | Inhibition (inhibitory interneurone between the sensory neurone and the spiking local interneurone)

Question 41

Choose correct word Spiking local interneurons The dendrites receive direct/indirect excitatory input synapses from sensory neurones The dendrites also receive direct/indirect inhibitory inputs from sensory neurones They are therefore primarily sensory/motor interneurones The dendrites also make input/output synapses which is almost never seen in the vertebrate CNA

Answer 41

Direct Indirect Sensory Output

Question 42

What is graded transmitter release?

Answer 42

As the membrane potential changes, so does the amount of transmitter released So cannot be said to have a true resting potential

Question 43

If the neurons contain an excitatory transmitter, the postsynaptic neurones are what as the non spiking neurones are what?

Answer 43

Excited | Depolarised but also may be inhibited as the non spiking neurones are hyperpolarised

Question 44

If the non spiking neurons contain an inhibitory transmitter, their postsynaptic neurones are what as the non spiking neurones are what?

Answer 44

Inhibited | Depolarised but also may be excited as the non spiking neurones are depolarised

Question 45

Non spiking interneurones contain groups of motor neurones. They are therefore what?

Answer 45

Premotor interneurones

Question 46

True or false Depolarising one non spiking neuron that drives flexor muscles can lead to the inhibition of another non spiking neuron that drives extensor muscles

Answer 46

True

Question 47

What does the cuticular spring do?

Answer 47

Stores energy

Question 48

A locusts jump is not just powered by direct muscle action but also by energy stored where?

Answer 48

Cuticular spring | Adds power and speed

Question 49

In vertebrates, body energy is not stored in the cuticular spring but where?

Answer 49

Tendons

Question 50

What are descending contralateral movement detectors? DCMD

Answer 50

Detects movement across visual field

Question 51

What do DCMDs activate and what does it do?

Answer 51

Activated the cocking neurone | Initiates jump motor sequence

Question 52

What does the cocking neurone activate?

Answer 52

Via the mesothoracic ganglion it activates the fast extensor tibae mn and the flexor mn

Question 53

The fast extensor MN has a synapse directly onto the flexor mn. why?

Answer 53

Coactivate muscles to disort the cuticular spring

Question 54

Sat on the surface of the cuticle are campaniform sensillae. What do they do?

Answer 54

Buckle when the cuticle is put under strain Dendrites beneath which will send info to ganglia Go directly to fast extensor mn and flexor mn

Question 55

What neurone inhibits the flexor neurone, thus triggering the jump?

Answer 55

M neurone

Question 56

What does the common inhibitor mn do?

Answer 56

Inhibits flexor muscle directly

Question 57

Strong connections between the DCMD and the what often trigger an AP?

Answer 57

M neurone

Question 58

How does a mantis shrimp use its claw?

Answer 58

Same principle as locust jump | The extensor and flexor muscle contract together to deform the cuticle of the saddle which is part of the exoskeleton

Question 59

In the mantis shrimp, the co-contraction of the flexor and extensor muscles disorts the saddle and especially the what?

Answer 59

The merus bar | To store energy for the strike