What is adaptation of a sensory receptor? At what stages does it occur? What are

Question

What is adaptation of a sensory receptor? At what stages does it occur? What are its functions? 1) Where is rhodopsin localized in the vertebrate retinal rod? Where is the receptor potential generated? How does the transduction mechanism of the rod increase light sensitivity? 2) 3) How are time and intensity linked to localization of sound? 4) How are different frequencies of sound detected by the inner ear? 5) In 2014, researchers reported that the number of odors that can be detected by humans is in the trillions. This is up from the previous estimate of 10,000. Explain how this is possible? 6) Using the following scenario, describe the role of the following sensory receptors: Ils of th Also be sure to list the where each receptor is located and whether it is ionotropic or metabotropic You are up late studying vertebrate physiology and you suddenly feel hungry so you decide to walk towards the vending machine and after eyeing the snacks you opt for a candy bar. You place the money in the machine, press the button for you selection, then take a bite of your snack. Part 2 Acetylcholinesterase Lab: Which fraction of heart acetyl cholinesterase had the highest rate of AchEesterase activity? Why do you think this was? 7) How did increasing the concentration of tacrine affect the change in absorbance in your experiment? 8)

Explanation / Answer

ANSWER:

1.ADAPTATION OF SENSORY RECEPTORS:The sensory receptors respond to a constant stimulus not with a single discharge,but with a repetitive burst of nerve impulses,adaptation is not immediate.When a receptor is continuously stimulated with the same strength of stimulus,after some time the receptor stops sending impulses through afferent nerve.

Adaptation of the sensory receptors occurs when there is change in the position of the body parts that is proprioceptive changes.

Adaptation receptors are of 2 types:

1.Phasic receptors:these get adapted rapidly.Touch and pressure receptors are phasic receptors.

2.Tonic receptors:these adapt slowly.Pain and Cold and Muscle spindle are the tonic receptors.

In Touch receptors adaptation is rapid,thus if a hair is bent,impulses are set up only at that movement,but not after it has ceased, although the hair is kept in the abnormal position..

The rate of adaptation in the temperature receptors is intermediate between that of the muscular and tactile receptors.

Pain receptors show little adaptation.

ANSWER:

2.RHODOPSIN:The rods of the eye contain a purplish red protein called RHODOPSIN or VISUAL PURPLE,which is bleached by the light.Rods are composed of a pile of discs normal to the rod axis.Rhodopsin molecules lie with their resonating axes in the planes of these discs and can move freely in these planes but not out of them.

If rods are activated by light absorbed by rhodopsin and if every quantum so absorbed is equivalent in its contribution of vision,then the rhodopsin absorption spectrum should coincide with the scotopic or twilight sesitivity function.

Rhodopsin consists of a protein ,opsin, combined with retinene,which is aldehyde of vitamin A.

Rhodopsin absorbs some of the light rays entering the pupil,the black melanin pigmented layer behind the retina absorbs a great deal of it, whereas the rhodopsin absorbs some of it during the passage through the retina going in and out.

Strong light bleaches rhodopsin,but doesnot not bleach melanin.The change in reflected light intensity on the bleaching is due to visual pigments and in the peripheral part of the retina and this is ascribable only to rhodopsin.

ANSWER:

3.LOCALIZATION OF SOUND:The ability to detect the source from where the sound is produced or the direction through which the sound wave is coming is called sound localization.

The cerebral cortex and also the medial geniculate body play an important role in localization of sound.

INTENSITY:The intensity or the loudness of the sound correlates with the rate of discharge from individual fibers of auditory nerve and with the total number of nerve fibers discharging.The threshold intensity of sound wave is not constant,it varies in accordance to the frequency of the sound.

TIME:If a person is exposed to a louder noise for a particular frequency for longer duration , he becomes deaf to the sound of that frequency,as the organ of corti is destroyed in specific portions.

Hence time and intensity are directly linked to the localization of sound.

ANSWER:4.

ROLE OF INNER EAR IN DETECTING DIFFERENT FREQUENIES OF SOUND:The movement of the foot plate of stapes against oval window causes movement of perilymph in scala vestibuli.The fluid will not move all the way from the oval window toward round window through the helicotrema.

So the immediate effect is on the basilar membrane near the oval window.The movement of the fluid in the scala vestibuli causes displacement of fluid in the scala media,as the vestibular membrane is flexible,and this causes bulging of the basal portion of the basilar membrane towards round window.This in turn moves the scala tympani towards round window and the bulging of the round window in the middle ear.

The elastic tension developed in the basilar fibers in the bulged portion of the basilar membrane initiates a wave which travels along the basilar membrane towards the helicotrema and this is callec a travelling wave.

While travelling through the basilar membrane from base to apex ,the wave becomes stronger and stronger and at one portion it becomes very strong and immediately vibrates back and forth.The wave ceases here and doesnot move further and this point is called resonance point.

ANSER:6.SNACKING UPON A CANDY BAR AND ROLE OF THE FOLLOWING RECEPTORS:

MERKEL'S DISCS:These are the touch receptors situated in the skin and respond to the mechanical stimulation of TOUCH.The role of the Merkel's disc is very important in the given above situation because touching the vending machine sensation is carried by these receptors ,though they donot create the action potential but are similar to excitatory postsynaptic potential.When a receptor is stimulated ,a non-propagated depolarization occurs and this is called receptor potential or generator potential.

HAIRCELLS OF THE MACULA:The stereocelia and kinocelium of each haircell are embedded in the otolith membrane of the macula.And the role of these haircells is excitatory reception when the person hears the sound of the vending machine ,the haircells get activated.

GUSTATORY RECEPTORS:These are the sense organs for taste or gustatory sensation.The chemoreceptors for taste are stimulated by substances dissolved in mouth by saliva.The dissolved substances act on the microvilli of taste receptors exposed to taste pores and this causes development of receptor potential in the receptor cells.This in turn is responsible for the generation of action potential in the sensory neurons.

In the above situation the candy bar is sweet in taste and in the receptors of sweet taste ,cyclic AMP causes depolarizaion.

CONE PHOTORECEPTORS:These have the threshold for the light stimulus , hence they are sensitive only to bright light,and the cones are also responsible for acuity of vision and colour vision.

When the person see the candy bar machine his cone receptors are stimulated or activated highly due to the bright light of the machine.

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