Fish startle behaviour

Question 1

startle behaviour

Answer 1

fast bend of body to a c shape (a c start)
tail straightens
fish may swim

Question 2

Mauthner neuron

Answer 2

colossal fibres in spinal cord of fishes- 1 each side
a uniquely identifiable neuron in vertebrate
cell body and 2 primary dendrites in hind brain
axon crosses over and descends nerve cord to contact trunk motor neurons
most studied in goldfish and zebra fish
in most teleosts and some amphibia
cell bosy and dendrites sum EPSPs from sensory neurons and interneurons
both electrical and chemical synapses involved
spike travels at 85m per s so motor neurons along body excites almost simultaneously

Question 3

Executive functions- Inhibiting other side

Answer 3

each M neuron excites trunk and tail muscles on same side as its axon and inhibits those on opposite side
LR M neurons inhibit each other via interneurons (rare electrical inhibition)
interneurons send axons that wrap tightly around hillock of M neuron so when they spike they almost strangle the M and inhibit it

Question 4

Executive functions- Inhibiting sensory inputs

Answer 4

through interneurons in the brain, also suppresses sensory inputs, using both postsynaptic and presynaptic inhibition

Question 5

Command Neuron

Answer 5

a single neuron that triggers a specific, naturally occuring behaviour pattern in response to a natural stimuli

Question 6

Is Mauthner a command neuron?

Answer 6

Not so strictly
In 1980s, found that if M neuron removed, fish can still make rapid escapes
free-swimming fish make less stereotyped startle responses than restrained fish in which M neuron is stimulated

Question 7

Other hind brain neurons similar to M neuron

Answer 7

M neurons start startle but augmented by others
MiD3CM etc are also responsive to loud sounds but have different receptive field- they can make trains of spikes
stimuli from front activate other hind brain neurons in addition to M neuron
steering may require several neurons acting together
also requires lateral line

Question 8

Eaton et al (1990)- Mauthner not a command neuron

Answer 8

reflexes trigger by electrical stimulation of single M cells were significantly weaker and less variable
must be two primary groups of reticulospinal neurons in escape triggering network
first includes M cell and determines LR direction and second determines onset time and direction of stage 2 of the response
coupling of 2 primary groups results in propulsive force and turning flexibility