B&B Invertebrate motor control Flashcards
How many neurons do the following have:
1mm3 mouse cortex
Entire nervous system of fly Musca
Entire nervous system of bee Apis
100,000
350,000
850,000
Describe how the nervous system of an insect is organised
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
Describe how the ganglia of an insect are organised
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)
Vertebrate motor neurones use WHAT
Vertebrate sensory neurones use WHAT
acetyl choline
glutamate
Invertebrate motor neurones use WHAT
Invertebrate sensory neurones use WHAT
glutamate
acetyl choline
In vertebrates, dendrites emerge from the cell body. Where do they emerge from in invertebrates?
A process comes off the cell body and they emerge from this - sometimes called a neurite
What is a motor pool? vertebrates
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)
What is a motor unit? vertebrates
Each motor neurone contacts many muscle fibres
True or false vertebrates
Large motor neurons contact many muscle fibres while small motor neurons contact only a few
True
Each muscle fibre is innervated by how many motorneurones? vertebrates
1
Because vertebrate muscle fibres respond with AP when they are stimulated, we call their contractions what?
All or nothing
What is the size principle of muscle activation?
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
Invertebrate motor neurons can be described as fast or slow. What does this mean in terms of transmitter?
Fast neurons release a lot of transmitter with each AP and small neurons release little transmitter
In invertebrates, each motor neurone supplies most of the muscle fibres within the muscle.
True or false?
True
In invertebrates, when glutamate is released, they don’t generate an AP in the muscle membrane but a what?
excitatory post synaptic potential (epsp)
This allows summation between epsps and other potentials
Fast excitatory motor neurons induce large epsps
If epsps come close together what happens?
They will summate to become larger
Describe inhibitory motor neurons in invertebrates
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
The extensor tibia muscle lies within the femur and does what?
extends the tibia during walking and jumping
Fast extensor tibia, slow extensor tibia and common inhibitor
what is an epsp and an ipsp
epsp = excitatory post synaptic potential ipsp = inhibitory post synaptic potential
DUM neurones are modulatory motor neurones. They send axons to many muscles on both sides of the body. What does DUM stand for?
Dorsal unpaired median neurones
What neurotransmitter do DUM neurones contain?
Octopamine
Not found in vertebrates
Structurally related to noradrenaline and dopamine
DUM neurons do not generate epsps or ipsps. What does this mean?
This means they do not cause contraction
Instead, octopamine acts on the cellular components within the muscles and on the motor neurone axons
Describe what happens when octopamine is released.
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
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?
4 SETi FETi CI DUMETi
Describe SETi
The slow extensor
Used mainly for walking
Increasing spike frequency gradually increases the force generated in many muscle fibres
Describe FETi
The fast extensor
Used in kicking or jumping
Activates all muscle fibres
Describe CI
The common inhibitor
Ensures that each contraction ends quickly
Describe DUMETi
The modulator
Increases the effect of the excitors and optimises energy availability
True or false
Insect motor neurones can act as interneurones
True
Some excitatory insect motor neurones make output synapses from their dendrites
not true of inhibitory or dum
What are the 2 types of local interneurones?
Spiking localinterneurones
Non-spiking local interneurones (don’t fire AP)
What are intersegmental interneurones?
Projecting
Their dendrites are in one ganglion and their axon runs to one or more other ganglia
What are some sensory structures on an insect’s body?
Touch sensitive and chemosensory hairs
Cuticular strain detectors
What is a chordotonal organ?
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
What is the sensory neuropile rich in?
The ends of the axons of sensory neurones
The inflow of sensory information can be controlled by what?
Inhibitory synapses
Contain neurotransmitter GABA
Blocks glutamate release from the sensory axons
What is presynaptic inhibition?
The inflow of sensory info being controlled by inhibitory synapses
Found on all vertebrate and invertebrate sensory axons
Sensory neurones synapse onto what (whose branches are entirely contained within one ganglion)
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
How are extracellular recordings made?
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
How are intracellular recordings made?
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
True or false
Excitation is direct and inhibition is indirect
False - other way around
Inhibition (inhibitory interneurone between the sensory neurone and the spiking local interneurone)
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
Direct
Indirect
Sensory
Output
What is graded transmitter release?
As the membrane potential changes, so does the amount of transmitter released
So cannot be said to have a true resting potential
If the neurons contain an excitatory transmitter, the postsynaptic neurones are what as the non spiking neurones are what?
Excited
Depolarised but also may be inhibited as the non spiking neurones are hyperpolarised
If the non spiking neurons contain an inhibitory transmitter, their postsynaptic neurones are what as the non spiking neurones are what?
Inhibited
Depolarised but also may be excited as the non spiking neurones are depolarised
Non spiking interneurones contain groups of motor neurones. They are therefore what?
Premotor interneurones
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
True
What does the cuticular spring do?
Stores energy
A locusts jump is not just powered by direct muscle action but also by energy stored where?
Cuticular spring
Adds power and speed
In vertebrates, body energy is not stored in the cuticular spring but where?
Tendons
What are descending contralateral movement detectors? DCMD
Detects movement across visual field
What do DCMDs activate and what does it do?
Activated the cocking neurone
Initiates jump motor sequence
What does the cocking neurone activate?
Via the mesothoracic ganglion it activates the fast extensor tibae mn and the flexor mn
The fast extensor MN has a synapse directly onto the flexor mn. why?
Coactivate muscles to disort the cuticular spring
Sat on the surface of the cuticle are campaniform sensillae. What do they do?
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
What neurone inhibits the flexor neurone, thus triggering the jump?
M neurone
What does the common inhibitor mn do?
Inhibits flexor muscle directly
Strong connections between the DCMD and the what often trigger an AP?
M neurone
How does a mantis shrimp use its claw?
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
In the mantis shrimp, the co-contraction of the flexor and extensor muscles disorts the saddle and especially the what?
The merus bar
To store energy for the strike
