Reeasing Mechanism: Command Nuerons

Question 1

What is a command nuerons?

Answer 1

A single nueron that completes single behaviour patterns

Question 2

What is a internueron?

Answer 2

A nueron that is part of the central nervous system

Question 3

Are command nuerons necessary for a given behaviour?

Answer 3

Yes they are, the behaviour does not occur without the nueron

Question 4

Are command nuerons sufficient?

Answer 4

Yes, they have to be sufficient enough to make the behaviour on its own

Question 5

How can we test if a command nueron is sufficient?

Answer 5

We can make the nueron excited through an electrode,inject it with a current and force it to create an action potential

Question 6

CASE STUDY 1: what is the cray fish tail flip

Answer 6

1. It occurs in red swamp cray fish
   2.it is a stereotypical tail slip response
2. It is an escape behaviour that requires the cray fish to bend their tail and spin it to propel them backwards

Question 7

CASE STUDY 1: is the cray fish tail bend a stereotypical behaviour?

Answer 7

Yes it is, because. It looks the exact same every time it is triggered

Question 8

What is the fish tail flip controlled by?

Answer 8

The lateral giant and medial giant internuerons

Question 9

What is required to cause the tail flip circuit?

Answer 9

A single spike - this can be caused by a single touch

Question 10

What is the cray fish?

Answer 10

They cray fish is an arthropod segmented animal
Each segment is connected by a ventral nerve which contains the lateral and medial giant nuerons
There are 4 axons
They are bilaterallysymmetrical
They are uniquely identifiable

Question 11

What is the medial giant flip?

Answer 11

Medial giant has a coil body cranial to its axon and end its caudal to the animal
It is excited by tactile stimulation
An action potential travels down the nerve cord exciting the muscles at each segment, the whole abdomen curved and propels the animal backwards away from the cranial end

Question 12

What is the lateral giant flip?

Answer 12

Sensory hairs on the cray fish tail stimulates
Only males output a synapse at the front end of the abdomen so the caudal end remains still
The animal is then somersaulted forward

Question 13

What are non-giant tail flips?

Answer 13

Over 18% of attacks on crayfish are fatal
Giant nueron-elicited tail flips are much faster and give a greater escape probability

Question 14

What are the reliable output connections of the lateral giant nueron

Answer 14

The lateral giant is a sequence of nuerons connected by synapses.
The synapses on the muscle are always excitory chemical synapses
Flat-line synapses are electrical synapses = very fast
In the output there are fast reliable connections through the synapses
However there is always a backup pathway known as the redundant pathway

Question 15

Why si the lateral giant internueron hard to excite?

Answer 15

The reason why is because it sensory filters through hair cells - physical touch or water movement will activate the LGI.
This means that the response will only occur when they are stimulated in a rapid way - unexpected
But if water movements are subtle and slow - no excitement will happen

Question 16

How does the signalling work in the lateral giant internueorn?

Answer 16

Each hair cell sends a a message through a chemical synapse
If the hair cell is constantly activated the synapse will habituate
However is the stimulus is closely associated in space and time are more effective. So if a cluster of hair cells is excited, each signal reinforces the signal around it to make it stronger

Question 17

Is the LGI necessary and sufficient?

Answer 17

Sufficient? Yes if the tail flip always occurs
Necessary? -yes if hyperpolarised - tail taps do not cause a flip. This is why non-giant tail flips exist

Question 18

How do you know if the LGI is reliable?

Answer 18

It has electrical chemical synapses-it occurs really fast
Has two pathways - main pathway and redundant pathway
Causes an electrical summation of two potentials
It has one quick immediate electrical signal - one is larger which is the chemical signal

Question 19

Does the LGI carry out executive functions?

Answer 19

The LGI inhibits extensors while the flexors inhibit MRO, extensor MN
LGI then inhibits flexor system via indirect (delayed) connections which inhibits MoG and flexor muscles plus Gis and sensory inputs
Subsequent escape swimming is by a different pathway

Question 20

CASE STUDY 2: what is the telost C-start?

Answer 20

C-starts occur due to a startling stimulus - touch/vibration

Question 21

CASE STUDY 2: what occurs during the C-start?

Answer 21

1. Fish bends trunk into a C,drawn in eyes, close mouth and extends its fins
   2.the body straightens which propels the fish away
   3.swimming will then follows

Question 22

CASE STUDY 2: which animal does C-start occur in?

Answer 22

It only occurs in vertebrate animal and it specifically occurs in teleost fish

Question 23

Case study 2: what happens if you tap on a glass full of fish?

Answer 23

When you tap on a fish tank the fish swim away frantically - this is the C-start
1.the tap on the tank creates a vibration
2. The fish will go into a C-shape and swi away

Question 24

How is the C-start different to a lateral giant internueron escape?

Answer 24

The C-start is different to the lateral giant escape because it depends on where the stimulus occurs to where the tail bends and gets the fish away. This can happen in any direction

Question 25

What is the mauthner nueron?

Answer 25

The mauthner nueron is made up of 2 nuerons
It is located in the hindbrain and sends signals down the axon into the spinal cord
It mostly excites the contralateral musculature

Question 26

What happens when the mauthner nueron receives an action potential?

Answer 26

The mauthner nueron will recieve the spike and a C-start will occur after it

Question 27

Is the C-start variable?

Answer 27

Yes because its respons relies on where the stimulus occurs.
It will not take the same form every time

Question 28

How does the C-start differ from the they crayfish tail flip?

Answer 28

The crayfish is stereotypical- looks the same
The C-start varies so it is not sterotypical

Question 29

How does sensory filtering and decision making occur in the mauthner nueron?

Answer 29

Spike inputs into the mauthner nueron
The R pathway attatches to the dendrites - there are 2 pathways which is an electrical synapse (Fast pathway) and chemical synapse
The synapse will then cause an EPSP

Question 30

What is the executive function of the mauthner nueron

Answer 30

It excites ipsilateral inhibits contralateral muscles - excited nueron on same side -so if left side excited it stays on left side
Excites cranial relay nuerons activating MNs that draw in eyes and close mouth
There are two pathways for reliablility
It excites the crossed inhibitory nueron which inhibits the muscle on the opposing side to contract

Question 31

What is the criterion for a mauthner nueron?

Answer 31

You will always get a C-start - the mauthnew nueron is sufficient enough for a c-start but its not for a natural behaviour
Electrical stimulation ofmauthnew nueron will always cause a C-start - but real C-starts are always variable
They are not sufficient enough for natural behaviour - unless when stimuli appear from the rear

Question 32

What if the MID2CM is activated, what happens to C-starts

Answer 32

The mauthner only activate if stimulus is coming from behaving
MIDS will produce trains of spikes which will go down a lot of nuerons which may change how C-starts occur

Question 33

Is the C-start necessary?

Answer 33

A c-start can occur
However, recent results in zebra ish shows that complete direction of M-cell significantly disrupts the C-starts
Also a functional axon initial segment is key for the fast behaviour

Question 34

Do,fast reliable stereotypes escape reesponses have any limitations?

Answer 34

Non-directional - can out the a stimulation worse than the original one
Some predators can exploit. Involuntary response - sea snakes use aC-starts to their advantages

Question 35

How do snakes use C-starts to their advantage?

Answer 35

Snakes move the body to make the fish C start causes the snake to eat prey
So the vibrations in the water from prey causes the fish to change position which the snake can locate