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21 Cards in this Set
- Front
- Back
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what is a potential difference |
the difference in voltage across a membrane |
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what is a resting potential |
the potential difference when at rest |
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what is a generator potential |
the change in potential difference due to a stimulus - generator potential. |
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what is an action potential |
an electrical impulse along a neurone |
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how do receptor cell communicate information via the nervous system |
-when a nervous system is in its resting state there's a difference in charge between the inside and outside of the cell- this is generated by ion pumps and ion channels = there is a potential difference. -when a stimulus is detected the cell membrane is excited and becomes more permeable - allowing more ions to move in and out of the cell = altering the potentital difference. the change in potenial difference due to a stimulus = the generator potential - a bigger stimulus excites the membrane more, causing a bigger movement of ions and a bigger change in potential difference = a bigger generator potential is produced - if the generator potential is big enough it'l trigger an action potential - which causes an electrical impulse to be sent down a neurone |
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what is needed for the action potential to be triggered |
an action potential is only triggered if the generator potential reaches a threshold level |
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how is the stength of the stimulus measured |
by the frequency of the action potentials |
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what are pacinian corpuscles and what do they do |
they are mechanoreceptosrs - they detect mechanical stimuli e.g pressure and vibration |
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how do pacinian corpuscles detect pressure |
pacinian corpuscles contain the ending of a sensory neurone = sensory nerve ending -the sensory nerveending is wrapped in loads of layers of connective tissue = lamellae -when a paciniam corpuscle is stimulated the lamelllae are deformed and press on the sensory nerve ending - this causes a deformation of stretch mediated sodium channels in the sensory neurone's cell membrane -the sodium ion channels open and sodium ions diffuse intto the cell creating a generator potential. -if the generator potential reaches a threshold it generates an action potential |
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what do photoreceptors in the eye do |
they detect light |
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what is the optic nerve |
a bundle of neurones |
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describe the process of light entering the eye so that information is sent to the brain |
light enters the eye, hits the photoreceptors and is absorbed by light sensitive pigments. -light bleaches the pigments, causing a chemical change and altering the membrane permeability to sodium - a generator potential is created and when it reaches a threshold a nerve impulse is sent along a bipolar neurone -a bipolar neurone connect photoreceptors to the optic nerve, which take impulses to the brain |
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what are the two types of photoreceptors |
rods and cones |
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where are rods mainly found |
in the peripheral parts of the retina |
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where are cones usually found |
cones are found packed together in the fovea |
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what are the 3 types of cones |
red sensitive , blue sensitive and green sensitive |
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why are rods more sensitive to light |
thy fire action potentials in dim light - this is because many rods join one neurone -so many weak generator potentials combine to reach the threshold and trigger an action potential |
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why are cones less sensitive |
because they only fire action potentials n bright light = only one cone joins one neurone =takes more light to reach the threshold and trigger an action potential. |
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what is visual acuity |
the ability to tell apart points that are close together |
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why do rods give low visual acuity |
because many rods join the same neurone which means light from two objects close together cant be told apart |
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why do cones give high visual acuity |
because cones are close together and 1 cone joines 1 neurone. when light from 2 points hits 2 cones, 2 action potentials one from each cone, go to the brain - so you can distinguish two points that are close together as 2 separate points |
