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30 Mar 2018

A stressor is:

A) a stimulus with the potential for triggering the flight-or-fight response

B) a symbolic event that triggers a psychological reaction

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Reid Wolff
Reid WolffLv2
1 Apr 2018

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Related questions

The sympathetic nervous system is responsible for _______functions and uses _______ as its neurotransmitter(s).

Select one:

a. energy conservation; acetylcholine

b. energy conservation; acetylcholine and norepinephrine

c. fight or flight; acetylcholine

d. fight or flight; acetylcholine and norepinephrine

With regard to glial cells, _______ form the myelin sheath inthe CNS, while _______ help maintain the ionic and chemicalenvironment.

Select one:

a. Schwann cells; astrocytes

b. oligodendroglia; astrocytes

c. oligodendroglia; microglia

d. Schwann cells; microglia

How does spacing apart sodium and potassium channels allow theaction potential to travel faster down the axon? This is the reasonalways cited for saltatory conduction and myelination, but mymental model of conduction tells me that the density of ion gatesalong the axon should not affect the speed of the AP.

To illustrate, consider a myelinated axon. A wave of Na+ fromaction potential site 1, a node of Ranvier, rushes into and quicklydiffuses down the axon. (It travels in both directions, butbackwards is still in the refractory period.) It diffuses throughthe myelinated region, its concentration always diminishing. Beforeit attenuates too much, however, it happens upon node of Ranvier 2,where it triggers another action potential. A new wave of Na+rushes in and the cycle repeats. This should be plain so far.

Now imagine that there is actually a node of Ranvier halfwaybetween node 1 and 2, called node 1.5. The wave of Na+, on its wayto node 2, happens to trigger an action potential at node 1.5, fromwhich a wave of Na+ pours in and either boosts the original wave orreplaces it by taking its momentum. Now the reinforced waveproceeds to node 2 and triggers it just as soon as, perhaps evensooner than, if node 1.5 had not existed. Repeatedly insert nodesat higher densities until the situation is simply lack ofmyelination, and we conclude that unmyelinated axons can transmitan action-potential-triggering wave of Na+ as fast as or fasterthan a myelinated one.

In short, my point of confusion is this: I cannot seehow a higher density of gated channels can possibly slow down thewavefront of Na+ that triggers action potentials. Ifanything, the additional influxes of Na+ should speed up theall-important wavefront, assuming that new waves really "eitherboost the original wave or replace it by taking its momentum", andalso assuming that the wavefront of Na+ is really all-important forsignal transmission, and also assuming that the mere presence of(voltage?) gated ion channels in the membrane does notsignificantly retard the wavefront.

But the usual explanation for why saltatory conduction is fasterthan continuous conduction (a fact I hope is empirically andunambiguously established) relies on the putativeslowing effect of ion channels on the signal fore. Please explainthis effect in more detail, if it is not amisconception.

Question 5

*The specific molecule in the eye that has to absorb photons for the perception of vision to occur is:

A. G-protein

B. Opsin

C. Retinal

D. cGMP

Question 6

*Transduction is a conversion of

A. Stimulus energy into energy of a graded potential

B. Presynaptic nerve impulses into postsynaptic nerve impulses

C. Receptor energy into stimulus energy

D. Electrical energy into mechanical energy

Question 7

What is a Drosophila ‘ERG’?

A. The signal is the combined signal of may action potentials

B. The signal is the response of only one specific photoreceptor class

C. It is a combined response signal of many photoreceptors and secondary order neurons

D. The signal is the combined signal of many graded potentials

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