Physiology 3120 Lecture Notes - Afferent Nerve Fiber, Receptive Field, Myelin

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26 Nov 2011

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Wednesday, october 21, 2009: all rapidly adapting receptors are associated with connective tissue. 6 different touch receptors (therefore touch is a hugely important sensation/stimulus) Some slowly adapting (free nerve ending, merkel"s, ruffini) Can detect vibrations of stimuli (fast adapting receptors) very accurately: free nerve endings part of the sensation of many modalities; different sensation mechanisms between. Touch receptors have axons that conduct signals at about 80m/s; pain receptors (at the fastest) have axons that conduct signals at about 20m/s. May reflect an increased need for tactile sensation in mammals compared with lower-order modalities: touch faster than pain organisms, pain: two types. Slow pain/ache: goes through the c pathway. Fast/sharp pain: goes through alpha-delta pathway: clusters of axons in a nerve: classification by conduction velocity. Alpha conduct signals faster than beta axons; different diameters produce different conduction velocities; larger diameter = faster conduction; all of these fibres are a fibres.

Related Questions

It is not possible to see very small objects, such as viruses,using an ordinary light microscope. An electron microscope can viewsuch objects using an electron beam instead of a light beam.Electron microscopy has proved invaluable for investigations ofviruses, cell membranes and subcellular structures, bacterialsurfaces, visual receptors, chloroplasts, and the contractileproperties of muscles. The "lenses" of an electron microscopeconsist of electric and magnetic fields that control the electronbeam.

As an example of the manipulation of an electron beam, consider anelectron traveling away from the origin along the x axis in the xyplane with initial velocity v = vi. As it passes through the regionx = 0 to x = d, the electron experiences acceleration a = ax + ay,where ax and ay are constants. For the case vi = 1.77 107 m/s, ax =7.35 1014 m/s2, and ay = 1.45 1015 m/s2, determine the following,at x = d = 0.0100 m.
(a) the position of the electron
yf =__________ m
(b) the velocity of the electron
vf =________ m/s +__________ m/s
(c) the speed of the electron
|vf| =___________ m/s
(d) the direction of travel of the electron (i.e. the angle betweenits velocity and the x axis)
=________ Â°

It is not possible to see very small objects, such as viruses, using an ordinary light microscope. An electron microscope, however, can view such objects using an electron beam instead of a light beam. Electron microscopy has proved invaluable for investigations of viruses, cell membranes, and subcellular structures, bacterial surfaces, visual receptors, chloroplasts, and the contractile properties of muscles. The “lenses” of an electron microscope consist of electric and magnetic fields that control the electron beam. As an example of the manipulation of an electron beam, consider an electron traveling away from the origin along the x-axis in the XY plane with an initial velocity . As it passes through the region x = 0 to x = d, the electron experiences acceleration where a_x and a_y are constants. For the case v_i = 1.80 × 10⁷ m/s, a_x = 8.00 × 10¹⁴ m/s², and a_y = 1.60 × 10¹⁵ m/s² determine at x = d = 0.010 0 m (a) the position of the electron, (b) the velocity of the electron, (c) the speed of the electron, and (d) the direction of travel of the electron (i.e., the angle between its velocity and the x-axis).

yellowbeetle239

1. The Jeans instability occurs when
Athe pressure in a gascloud is less than its gravitationalforce.
Bthe pressure in a gascloud is greater than its gravitationalforce.
Cthe temperature in acollapsing cloud is hot enough to fuseHydrogen.
Dthe temperature in acollapsing cloud is hot enough to fuse Helium.

2. At what stage in its life does a star pass through theprotostarphase?
AAfter condensationbut before nuclear reactions begin in itscore.
BWhile it is convertinghydrogen into helium in its core.
CAfter nuclear reactionsend in its core, but before the red giantphase.
DWhen it is expanding insize as a red giant or supergiant.

3. The characteristics of an open cluster of stars are
Aa few hundredmembers, often very young and still embedded in thegas and dustfrom which they were formed.
Bmany thousand members, ofdifferent ages.
Ca few dozen members, theremnant of a globular cluster of starsfrom which most of themembers have escaped.
Dhundreds of thousands ofmembers, all very old, and no or verylittle interstellar gas anddust.

4. What is a protostar?
AA star near the endof its life, before it explodes as asupernova.
BA sphere of gas aftercollapse from an interstellar cloud butbefore nuclear reactionshave begun.
CA small interstellarcloud, before it collapses to become astar.
DA shell of gas left behindfrom the explosion of a star as asupernova.

5. What is an H II region?
AA region of hot,ionized hydrogen around one or more O and Bstars.
BA region of molecularhydrogen inside a giant molecularcloud.
CA region of neutral,atomic hydrogen in interstellar space.
DA region of gas and dustformed by the explosion of a massive star.

6. The total time that the Sun will spend as a main sequencestaris
Aabout 4.5 millionyears.
Bat least 200 billion yearsyears.
Cabout 1 millionyears.
Dabout 10 billionyears.

7. How is a star's lifetime related to its mass?
AThe lifetimes ofstars are too long to measure, so it is not knownhow (or if) theirlifetimes depend on mass.
BA star's lifetime does notdepend on its mass.
CLower-mass stars runthrough their lives faster and have shorterlifetimes.
DHigher-mass stars runthrough their lives faster and have shorterlifetimes.

8. In the Hertzsprung-Russell diagram, how does the position ofatypical star change while it is at the main sequence phase ofitsevolution?
AA star's position onthe main sequence is determined only by itsmass and not its age,and so, stars do not move along the mainsequence duringevolution.
BMassive stars (4 solarmasses) move toward the upper left as theirluminosity increases,while lower-mass stars move toward the lowerright as theirtemperature decreases.
CStars move from upperright to lower left while they are on themain sequence.
DStars move from upper leftto lower right while they are on themain sequence.

9. Why does the core of the Sun contain more helium andlesshydrogen than does the surface of the Sun?
AHelium condenses moreeasily so, when the Sun was forming the corebecame helium-rich;vast quantities of hydrogen were added onlyafter the core becamemassive enough.
BThe hydrogen has beenlifted out of the core by the Sun's magneticfield.
CHelium is heavier thanhydrogen, and has sunk toward the center ina process of chemicaldifferentiation.
DThermonuclear reactionshave converted much of the originalhydrogen in the core intohelium.

10. In terms of nuclear reactions, what is the next stage ofastar's life after the end of hydrogen burning in thecore?
AHydrogen burning ina thin shell around the core.
BHelium burning in thecore.
CCarbon burning.
DDeath (it becomes eithera supernova or a white dwarf).

Physiology 3120 Lecture Notes - Afferent Nerve Fiber, Receptive Field, Myelin

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