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17 Cards in this Set
- Front
- Back
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describe the pacinian corpuscle |
-respond to changes in mechanical pressure -it is a sensory receptor -it is specific to a single type of stimulus -produces a generator potential by acting as a transducer |
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describe the pacinian corpuscle as a transducer to generatea generator potential |
-all stimuli involve a change in some form of energy -it is the ole of the transducer to convert the change in dorm of energy by the stimulus into a form that can be understood by the body -the stimulus always involves a change in ome form of energy -the nerve impulse is also a form of energy -receptors therefore transduce one form of energy into another -receptors in the nervous system convert energy of a stimulus into a nervous impulse known as a generator potential |
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what is the structure and function of a pacinian corpuscle |
-they respond to mechanical stimuli such as pressure -they occur deep in the skin and are most abundant on the fingers,joints and soles of the feet or external genitalia -they enable the organisms to know which joints are cjhangeing direction -the single senory neurone of a paacinian corpuscle is at the centre of layers of tissue each separated by gel |
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describe the stretch mediated sodium channel |
-a type of sodium channel found at the centre of a pacinian corpusle at the end of a sensory neurone -there permability to sodium changes when they are deformed -for example by stretching |
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describe how the stretch meditated sodium channel works |
-in its normal resting state the stretch mediated channels are too narrow to allow sodium ions to pass along them.in this state the neurone of the pacinian corpuscle has a resting potential -when pressure is applied to the pacinian corpusle it is deformed and the membrane around its neurones becomes stretched -this stretching widens the sodium channels in the membrane and sodium iond diffuse into the neurone -the influxof sodium ions changes the potential of the membrane thereby producing a generator potential -the generator potential in turn producers the action potential that passes along the neurone and then ia other neurones to the central nervous system |
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describe how receptors work together in the eye |
-the light receptor cells of the eye are found on its intermost layer called the retina -the millions of light receptor cellsfound are of two types -rods and cones -both rods and cones act as transducers by conserving light energy in to the electrical energy of a nerv impulse |
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describe rod cells |
-mainly in the peripheral parts of the retina -rods have rhodopsin and are sensitive to different wavlengths of light -they only see in black and white as they cant distinguish between different wave lengths of light |
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what happens when ligh eneters the eye |
-hits photoreceptor and is absorbe by light sensitive optical pigments -light bleaches the pigments causing a chemical change and altering the membrane permeability to sodium ions -a genertore potential is established and if it reaches the threshold an impulse is sent along a bipolar neurone -bipolar neuroenss connect photoreceptors to the optic nerve which takes impulses to the brain |
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how do rod cells produce impulses |
-the rhodopsin pigment is broken down in a process called bleaching -at low intensites light is sufficuent to cause this breakdown -opsin causes a vhange in the permeability of the rod cell to sodium which initiates a generator potential -moving form light to dark allows ight-bleached pigment to be restored ro its unbleached form rhodopsin -this is called dark adptation |
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what is sensitivity and acuity |
sensitivity-rfers to the level of light nedded for the cells to function acuity-refers to their ability to perceive detail |
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desribe the sensitivity of rods |
-higher than cones -several rods are connected to each bipolar cell so they all contribute to the generator potential -so many weak generator potentials combine to reach the threshold making it more likely that the threshold is reached and an action poential is triggered -there is an addictive effect of a smal amount of light striking several rod cells |
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descrieb the visual acuity of rods |
-because many rods join to the saame neurone it means light from two points close together cant be told apart -only a single impulse traveling to the brain regardless of how many neurones are stimulted |
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describe cones |
-packed togethe rin the fovea -have idopsin -3 colour pigments so when stimulated in different propotions you see different colours. -pigments are red blue and green |
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how do cones produce an impulse |
-sensitve to high light intensities due to the presence of iodopsin -in bright light iodopsin is broken down into its constituent parts -generating an action potential in the ganglion cell -there are three different types of cone cell each containg a differet form of iodopsin -each form of iodopsin absorbs a different wavelength of light -the clour seen depends on the relative degree of stimulation of the three different types of cone cell |
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desribe the sensitivity of cones |
-they work best in bright light -so are less sensitive than rods -this is because one cone joins to one neurone so more light is required to reach the threshold and trigger an action potential |
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describe the acuity of cones |
-greater acuity than rods -each cone is connected to an individual neurone that are close together -any impluses generated by an individual cone are transmitted to the brain -light hitting 2 cones and reacing the threshols means that two action potential reach the brain -greatest concentration of ones is in the fovea so only a small area of the retinais stimulated so very accurate vision |
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what happens if you stare at a brightly coloured purple picture for a minute then turn away and look at something else |
when staring at purple the red and blue cones ae stimulated and they then become overstimulated and sop working so when you look at something else it will appear green for a few minutes |
