Lecture 6: Giant Axons and Escape mechanisms

Question 1

Why are giant axons important for escape behavior? (4)

Answer 1

because an escape mechanism is:

-Rapid
-All or none
-Complex
-Dominant

Question 2

Examples of escape behavior

Answer 2

-in squid, jet propulsion to escape predators. Humboldt squid can go from 0-40mph in 2 seconds thanks to their response

-In fish, the c-start response causes them to bend into a c shape to rapidly change direction. All the muscles on one side of their body contract, while all the muscles on the other side of their body are prevented fom contracting

Question 3

squid escape mechanism (4)

Answer 3

-visual or sensory information activates. First order giant neurons. These are two neurons on the ventral magnocellular lobe with giant axons attached

-The first order axons make electrical synapses on the second order neurons found on the dorsal magnocellular lobe

• Second order axons make a chemical synapse with the 3rd order neurons in the stellate ganglion

-3rd order axons make synapses on the muscle to control the contraction of the circular mantle, ejecting water and propelling the squid

Question 4

Stellate nerves in squid (3)

Answer 4

-Have one giant axon and many smaller axons

-Giant axons is responsible for the contraction of the circular mantle during jetting

-smaller axons are responsible for chromatophores, contracting muscle to move water over gills, tail muscles, and mantle refilling muscle

Question 5

Mauthner neurons (5)

Answer 5

-allow for the c-start response in fish
-have myelinated giant axons that are much smaller than squid ones
-have a faster conduction velocity than squid axons
-have electrical, chemical, and mixed synapses
-have much more complex whirring compared to squid