Quiz 1

animals have solved conduction velocity problem in 2 ways:

1. By increasing the diameter of axons, thereby increasing their conduction velocities.

2. By evolving interrupted myelination of axons, which gives rise to saltatory conduction.

spikes in the LGFs trigger rapid ______________

tail withdrawal

How does MGF and LGF spikes cause withdrawal of the worm?

giant fibers activate excitatory motor neurons whose axons extend into segmental nerves and synapse with longitudinal muscle fibers in the body wall. Contraction of these fibers shortens the body.

LGFs are excited by touch to ____________, which are within the LGF sensory field

posterior segments

MGF spikes are excited by touch to______________, which are within the MGF sensory field

anterior segments

Giant fibers are excited by ______________

sensory neurons in the worm's skin

Spikes in the MGF trigger rapid ___________

head withdrawal

the lateral fibers respond to stimuli at the ___________________

posterior (tail) end

sensory connections are such that the median fiber responds to stimulation at the _______________

anterior (head) end of the worm

The earthworm has _____

myelinated giant axons running the length of the nerve cord, one __________, and two lateral fibers

three, median fiber and two lateral fibers

conduction through myelinated zone is

passive an fat

spikes are actively regenerated only at

gaps in the myelin sheath

The other strategy to increase conduction velocity is to

_--------------

decrease membrane capacitance

as the cross-sectional area of the axoplasm is increased, its resistance __

per unit length decreases

one strategy that can be used to maximize conduction velocity is to

------------, which can be done by

decrease internal resistance, increasing axon diameter

The conduction velocity of an action potential depends on the _

__ at which the membrane capacitance (stored charge) in front of the propagating active region is discharged to threshold by the spread of positive charge

rate