Reeasing Mechanism: Command Nuerons Flashcards
What is a command nuerons?
A single nueron that completes single behaviour patterns
What is a internueron?
A nueron that is part of the central nervous system
Are command nuerons necessary for a given behaviour?
Yes they are, the behaviour does not occur without the nueron
Are command nuerons sufficient?
Yes, they have to be sufficient enough to make the behaviour on its own
How can we test if a command nueron is sufficient?
We can make the nueron excited through an electrode,inject it with a current and force it to create an action potential
CASE STUDY 1: what is the cray fish tail flip
- It occurs in red swamp cray fish
2.it is a stereotypical tail slip response - It is an escape behaviour that requires the cray fish to bend their tail and spin it to propel them backwards
CASE STUDY 1: is the cray fish tail bend a stereotypical behaviour?
Yes it is, because. It looks the exact same every time it is triggered
What is the fish tail flip controlled by?
The lateral giant and medial giant internuerons
What is required to cause the tail flip circuit?
A single spike - this can be caused by a single touch
What is the cray fish?
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
What is the medial giant flip?
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
What is the lateral giant flip?
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
What are non-giant tail flips?
Over 18% of attacks on crayfish are fatal
Giant nueron-elicited tail flips are much faster and give a greater escape probability
What are the reliable output connections of the lateral giant nueron
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
Why si the lateral giant internueron hard to excite?
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
How does the signalling work in the lateral giant internueorn?
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
Is the LGI necessary and sufficient?
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
How do you know if the LGI is reliable?
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
Does the LGI carry out executive functions?
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
CASE STUDY 2: what is the telost C-start?
C-starts occur due to a startling stimulus - touch/vibration
CASE STUDY 2: what occurs during the C-start?
- 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
CASE STUDY 2: which animal does C-start occur in?
It only occurs in vertebrate animal and it specifically occurs in teleost fish
Case study 2: what happens if you tap on a glass full of fish?
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
How is the C-start different to a lateral giant internueron escape?
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
