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level: 14.4 Receptors

Questions and Answers List

level questions: 14.4 Receptors

QuestionAnswer
Pacinian corpuscles- Responds to changes in mechanical pressure - Occur deep in skin, most abundant on fingers, feet + genitalia - Also occur in joints, ligaments + tendons, to enable organism to know which joints are changing direction
Features of the pacinian corpuscles- Specific to single type of stimulus - Produces a generator potential by acting as a transducer
Specific to single type of stimulus- Responds only to mechanical pressure - It will not respond to other stimuli like heat
Produces a generator potential by acting as a transducer- All stimuli involve a change in some form of energy - The transducer converts the change in form of energy by the stimulus into a form, like nerve impulses, that can be understood by the body
Generator potential (further info)- The nerve impulse is also a form of energy - Receptors therefore convert 1 form of energy into another - Receptors in the nervous system convert energy of the stimulus into a nervous impulse known as generator potential
Structure of the Pacinian corpuscle- Single sensory neuron is at the center of layers of tissue - Each separated by a gel, looks like an onion - Sensory neuron has special type of sodium channel in its plasma membrane, stretch-mediated sodium channel
The stretch-mediated sodium channel- Their permeability to sodium changes when they are deformed, e.g. by stretching
Function of the Pacinian corpuscle (1)- In its normal state, the stretch-mediated sodium channels of the membrane around the neuron are too narrow to allow sodium ions to pass along them - In this state, the neuron has resting potential
Function of the Pacinian corpuscle (2)- When pressure is applied to the PC, it is deformed + the membrane around its neuron becomes stretched
Function of the Pacinian corpuscle (3)- Influx of sodium ions changes potential of the membrane (i.e. becomes depolarised) - Producing a generator potential
Function of the Pacinian corpuscle (4)- The generator potential creates an action potential (nerve impulse) that passes along the neuron - Then via other neurons, to the CNS
Receptors working together in the eye- Light receptor cells of the mammalian eye are found on its innermost layer, the retina - Either rod cells or cone cells - Both act as transducers by conserving light energy into electrical energy of a nerve impulse
Rod cells- Cannot distinguish different wavelengths of light, images seen only in black + white - Many connected to single sensory neuron in optic nerve - Used to detect light of low intensity
Why rod cells respond to low-intensity light- A certain threshold value has to be exceeded before generator potential is created in bipolar cells (to which rod cells are connected) - As a no. of rod cells are connected to a single bipolar cell (=retinal convergence), there is much greater chance that the threshold value will be exceeded than if only a single rod rod cell were connected to each bipolar cell - This is due to summation - In order to create a generator potential, the pigment in the rd cells (rhodopsin) must be broken down - There is enough energy from low-intensity light to cause this breakdown
Why rod cell give low visual acuity- Many rods are joined to a single bipolar cell - Which means light from 2 points close together cant be told apart
Cone cells- 3 different types, each responding to a different range of wavelengths of light - Depending on the proportion of each type that is stimulated, we can perceive images in full colour
Why do cone cells respond to high-intensity light- Each joined to specific separate bipolar cells connected to a sensory neuron in optic nerve - So it takes more light to reach the threshold + trigger an action potential
Why do cone cells sensitive to different wavelengths- CC contain iodopsin (pigment) needs higher light intensity for its breakdown + create a generator potential - 3 different types of CC, has specific type of iodopsin - So each CC sensitive to a different specific range of wavelengths
Why do cone cells have good visual acuity- Each connected to single bipolar cell, they are close together - When light from 2 points hits 2 cones, 2 action potentials (1 from each cone) go to the brain - So you can distinguish 2 points that are close together apart
Where are cone cells and rod cells found exactly- Fovea, lens on the retina opposite the pupil where light is focused - The fovea receives the highest intensity of light - So CC, are found at the fovea - RC found at the peripheries of the retina, where LI is lowest
Differences between rod cells and cone cells (ROD)- Rod-shaped - Greater no. than cone cells - Peripheries of the retina - Give poor visual acuity - Sensitive to low-intensity light - One type only
Differences between rod cells and cone cells (CONE)- Cone-shaped - Fewer no. than rod cells - At fovea - Give good visual acuity - Not sensitive to low-intensity light - 3 types each responding to different wavelengths of light