3.6.1.2 Receptors(A-level only) Flashcards
Examples of sensory receptors and their specific stimuli
Mechanoreceptor: pressure and movement └ e.g Pacinian corpuscle, skin Chemoreceptor: chemicals └ e.g. olfactory receptor, nose Thermoreceptor: heat └ e.g. end-bulbs of Krause, tongue Photoreceptors: light └ e.g. cone cell, eye
Function of sensory receptors
└act as transducers converting the stimulus into electrical energy and producing a generator potential. When the generator potential gets big enough, and the threshold is reached it is converts into an action potential.
Transducer role definition
└detects stimulus and converts into a nerve impulse called a generator potential
Generator potential definition
└change in potential difference
Action potential definition
└a change in the membrane potential that produces a nerve impulse
Threshold definition
└ the minimum amount of stimulus a neuron needs to respond
Location of Pacinian corpuscle
Skin
└mainly fingers, genitals, hands, feet
└also ligaments, tendons, joints
Structure of pacinian corpuscle
└an end of a sensory neurone/sensory nerve ending
└wrapped in/surrounded by connective tissue (lamellae) which is separated by a gel
How a generator potential is created by a pacinian corpuscle
No pressure/resting state
└stretch mediated sodium channels are closed/ too narrow for sodium ions (Na+) to pass through
└found in membrane of sensory nerve endings in the pacinian corpuscle
└maintains resting potential difference in Na+ across membrane
└more Na+ outside than inside
Pressure
└deforms/ changes pacinian corpuscles shape
└stretches the surrounding membrane
└widens stretch mediated Na+ channels
└causes Na+ influx as they diffuse into neurone/cell down the concentration gradient
└the positive charge on the Na+ changes the membrane potential
└causes depolarisation to occur
└more Na+ inside than outside
└depolarisation creates a generator potential
└if the generator potential gets large enough, the threshold is reached and an action potential occurs (wave of depolarisation) along the sensory neuron
└aka electrical impulse
└transmitted along neurone to CNS
Stretch mediated sodium channels
…
Resting potential definition
└potential difference between the inside of the non-stimulated neuron and the surrounding interstitial fluid (humans: -70 mV)
Depolarisation definition
└sodium ions rushing into the cell down their concentration gradient, changing the electric charge of the interior
Generator potential definition
└change in potential difference
Threshold definition
└ the minimum amount of stimulus a neuron needs to respond
Action potential definition
└a change in the membrane potential that produces a nerve impulse
Lots of pressure
Pacinian corpuscle
└increase pressure
└more sodium ion channels open
└more Na+ diffuse into cell/neurone
└bigger generator potential
└threshold is more likely to be reached so action potential is met more often
└increases the frequency of impulses sent along sensory neurone
Slight pressure
Pacinian corpuscle
└slight pressure- may go unnoticed
└fewer sodium ion channels open
└less Na+ diffuse into cell/neurone
└lower generator potential
└threshold is less likely to be reached so no action potentials
└decreases the frequency of impulses sent along sensory neurone/ no impulses
Adaptation
Pacinian corpuscle
└continuous stimulation of a sensory neurone
└ decreased frequency of impulses/ stop them-
└useful as it prevents overloading the nervous system with insignificant information
└e.g. the pressure from clothing
Light receptor cell/ photoreceptor definition
A specialized structure or cell that is sensitive to light
e.g. rod and cone cells in the eyes retina
Light receptor cell location
The retina
Light receptor cell/ photoreceptor types
rod cells
cone cells
Light receptor cell- transducers
They convert light energy into an electrical impulse.
Rod cell location
On the retina.
Rod cells most abundant at the peripheries of the retina
Rod cell distribution
Periphery of retina = mostly rod cells
