Receptors, Flashcards
Two key facts of a receptor
(From spec)
receptors respond only to specific stimuli
stimulation of a receptor leads to the establishment of a generator potential.
How does a pacinian corpuscle demonstrate that a receptor is specific to a single type of stimulus
It responds only to mechanical pressure
Will not respond to other stimuli like heat, light, sound
How does the pacinian corpuscle demonstrate that the stimulation of a receptor leads to the establishment of a generator potential.
All stimuli involve a change in some sort of energy (heat, light, sound, mechanical)
Nerve impulses are also a form of energy
Receptors act as a transducer (convert mechanical energy into nerve impulses)
Nerve impulses are known as a generator potential
Basic structure of pacinian corpuscle
Example of a mechanical stimuli
Pressure change
Where are pacinian corpuscles found
Deep in the skin
Most abundant on fingers, soles of feet, external genitalia
Joints, ligaments, tendons (enable organisms to know which joints are changing direction)
Stretch mediated sodium channel
The sensory neurone ending at the centre of the PC has a special type of sodium channel in its plasma membrane.
Their permeability to sodium changes when they are deformed (eg by stretching)
Function of PC
Resting state: stretch mediated sodium channels are too narrow to allow sodium ions to pass along them, so PC has a resting potential
Pressure applied to PC: deformation, membrane stretches. Widens the sodium channels so sodium ions diffuse into the neurone
This influx of sodium ions changes the potential of the membrane (depolarises). Produces a generator potential
The generator potential creates an action potential (nerve impulse) that passes along the neurone and to others then to CNS
Taxis
Simple response
Direction determines by direction of stimulus
Motile organism responses to a change in environment by moving its whole body either towards or away from the stimulus
Receptors in the eye
Light receptors found in the retina
Two types: rod and cone cells
Act as transducers by converting light energy into a nerve impulse
How receptors in the eye work
Light hits photo receptors in the eye
Absorbed by optical pigments which are bleached
Causes a chemical change that alters permeability of membrane to sodium ions
Generator potential created
Nerve impulse travels along bipolar neurone to the optic nerve
Rods
Peripheral parts of retina
Structure of CNS
Brain and spinal cord
peripheral nervous system
Nerves that branch out from the brain and spinal cord
Somatic nervous system
Controls conscious activities
Autonomic nervous system
Controls unconscious activities
Split into sympathetic and parasympathetic nervous systems which have opposite effects on the body
Sympathetic nervous system
Fight or flight response
Parasympathetic nervous system
Control of heart rate
Rest state
How light enters the eye
Light enters the eye through the pupil, and the amount of light that enters is controlled by the muscles of the iris. Light rays are focused by the lens onto the retina
Bipolar neurone
Connects photoreceptors to optic nerve
Cones
Packed together in fovea
Rods vs cones in terms of colours
Rods and cones contain different optical pigments making them sensitive to different wavelengths
of light. Rods only give information in black and white (monochromatic vision), but cones give
information in colour
(trichromatic vision).
Types of cones
contain
a different optical
pigment
red-sensitive,
green-sensitive
blue-sensitive.
When they’re stimulated in different proportions you see different colours.
Visual acuity
the ability to tell apart points that are close together
Visual acuity of rods vs cones
Rods give low visual acuity because many rods join the same bipolar neurone, which means light from two points close together can’t be told apart.
Cones give high visual acuity because cones are close together and one cone joins one bipolar neurone. When light from two points hits two cones, two action potentials (one from each cone) go to the brain — so you can distinguish two points that are close together as two separate points.
