A4. Receptors Flashcards
How receptors work
Receptors are _________- they only detect one particular __________, eg, light or glucose concentration or pressure (e.g. Pacinian corpuscles). There are many different types of receptor that each detect a different type of stimulus. Some receptors are cells, eg, photoreceptors are receptor cells that connect to the nervous system. Some receptors are proteins on cell surface membranes, eg, _________receptors are proteins found in the cell membranes of some ____________cells.
Receptors are specific - they only detect one particular stimulus, eg, light or glucose concentration or pressure (e.g. Pacinian corpuscles). There are many different types of receptor that each detect a different type of stimulus. Some receptors are cells, eg, photoreceptors are receptor cells that connect to the nervous system. Some receptors are proteins on cell surface membranes, eg, glucose receptors are proteins found in the cell membranes of some pancreatic cells.
The resting potential
When a nervous system receptor is in its resting state (not being stimulated), there’s a difference in charge between the inside and the outside of the cell - the _________ is _______________charged relative to the ___________. This means there’s a voltage across the membrane. Voltage is also known as potential difference. The potential difference when a cell is at rest is called its resting potential. The resting potential is generated by ____ _______and ___ ________
When a nervous system receptor is in its resting state (not being stimulated), there’s a difference in charge between the inside and the outside of the cell - the inside is negatively charged relative to the outside. This means there’s a voltage across the membrane. Voltage is also known as potential difference. The potential difference when a cell is at rest is called its resting potential. The resting potential is generated by ion pumps and ion channels
Figure 1: Relative charges either side of a receptor cell membrane at rest.
The generator potential
When a ____________is detected, the cell membrane is _________and becomes ______ ___________, allowing more ______to move __ and____ of the ____- altering the ____________ difference. The change in potential difference due to a stimulus is called the ___________potential. A bigger stimulus excites the membrane more, causing a bigger movement of ions and a bigger change in potential difference - so a _________ _______________ ___________ is produced
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 potential difference. The change in potential difference due to a stimulus is called the generator potential. A bigger stimulus excites the membrane more, causing a bigger movement of ions and a bigger change in potential difference - so a bigger generator potential is produced
Figure 2: The bigger stimulus produces the bigger generator potential.
The action potential
If the generator potential is big enough it’ll trigger an _______potential - an _________ impulse along a neurone. An action potential is only triggered if the _____________potential reaches a certain level called the _____________ level. Action potentials are all ____ _____, so the strength of the stimulus is measured by the __________of ________ __________(the __________of ___________ ___________triggered during a _________ ______ ________). If the stimulus is too weak the generator potential won’t reach the ____________, so there’s no ________ potential
If the generator potential is big enough it’ll trigger an action potential - an electrical impulse along a neurone. An action potential is only triggered if the generator potential reaches a certain level called the threshold level. Action potentials are all one size, so the strength of the stimulus is measured by the frequency of action potentials (the number of action potentials triggered during a certain time period). If the stimulus is too weak the generator potential won’t reach the threshold, so there’s no action potential
Figure 3: Generator potential not reaching the threshold (A) and reaching the threshold (B).
Pacinian corpuscles
Pacinian corpuscles are ________________- they detect __________stimuli, e.g. ____________and __________. They’re found in your _____. Pacinian corpuscles contain the ____of a ___________neurone, imaginatively called a __________ ________ _________. This is wrapped in loads of layers of connective tissue called __________
Pacinian corpuscles are mechanoreceptors - they detect mechanical stimuli, e.g. pressure and vibrations. They’re found in your skin. Pacinian corpuscles contain the end of a sensory neurone, imaginatively called a sensory nerve ending. This is wrapped in loads of layers of connective tissue called lamellae
Pacinian corpuscles
When a Pacinian corpuscle is ____________, e.g. by a tap on the arm, the ___________are ____________and __________on the _____________ ________ _________. This causes the ___________ _____________’s _____ ____________to _________, _______________the _________-_____________ ___________ ____ ___________. The _____________ _____and ____________ ____ ________into the cell, creating a ____________potential. If the _____________potential reaches the ____________, it triggers an _________potential.
When a Pacinian corpuscle is stimulated, e.g. by a tap on the arm, the lamellae are deformed and press on the sensory nerve ending. This causes the sensory neurone’s cell membrane to stretch, deforming the stretch-mediated sodium ion channels. The channels open and sodium ions diffuse into the cell, creating a generator potential. If the generator potential reaches the threshold, it triggers an action potential.
Figure 4: A Pacinian corpuscle at rest (top) and during stimulation (bottom).
Tip: The bigger the stimulus (i.e. the more pressure that’s applied), the more ___________ __________ open. This creates a bigger _____________-potential, which is more likely to reach the ____________and cause an ________potential.
Tip: The bigger the stimulus (i.e. the more pressure that’s applied), the more sodium channels open. This creates a bigger generator potential, which is more likely to reach the threshold and cause an action potential.
Photoreceptors
Photoreceptors are receptors in your eye that detect ______. Light enters the eye through the ________, and the amount of light that enters is controlled by the _______of the ____. Light rays are focused by the ______ onto the ________, which lines the __________of the eye. The retina contains the _______________ ____. The _______is an ______of the _________where there are lots of _________________. Nerve impulses from the photoreceptor cells are carried from the _________to the brain by the ______nerve, which is a __________of neurones. Where the _______ _____leaves the eye is called the ________ _____-there aren’t any _______________cells, so it’s _____sensitive to light.
Photoreceptors are receptors in your eye that detect light. 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, which lines the inside of the eye. The retina contains the photoreceptor cells. The fovea is an area of the retina where there are lots of photoreceptors. Nerve impulses from the photoreceptor cells are carried from the retina to the brain by the optic nerve, which is a bundle of neurones. Where the optic nerve leaves the eye is called the blind spot-there aren’t any photoreceptor cells, so it’s not sensitive to light.
Figure 6: Cross-section of an eye.
How photoreceptors work
Light enters the eye, hits the _________________and is absorbed by light-sensitive optical pigments. Light __________the _________, causing a __________change and altering the ____________ _____________ to _________ _____. A _____________ potential is created and if it reaches the _____________, a nerve impulse is sent along a ___________neurone. Bipolar neurones connect photoreceptors to the _______nerve, which takes impulses to the ________
Light enters the eye, hits the photoreceptors and is absorbed by light-sensitive optical pigments. Light bleaches the pigments, causing a chemical change and altering the membrane permeability to sodium ions. A generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone. Bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain
Figure 8: Nervous communication in the eye.
Figure 9: Diagram showing the location of rods and cones.
Sensitivity - rods
Rods cells are very ___________to ______ (they work well in ____ light). This is because many rods join one __________ neurone, so ________ ______ ______________ _______ combine to reach the ___________ and trigger an ________ potential.
Rods cells are very sensitive to light (they work well in dim light). This is because many rods join one bipolar neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential.
Sensitivity - cones
Cones are ____ __________than rods (they work best in _______light). This is because ____cone joins one _________ neurone, so it takes ______light to reach the __________and trigger an ________potential.
Cones are less sensitive than rods (they work best in bright light). This is because one cone joins one bipolar neurone, so it takes more light to reach the threshold and trigger an action potential.
Visual acuity - rods
Visual acuity is the ability to tell apart points that are close together. Rods give ____visual acuity because _____ ____join the _____ _________neurone, which means _______from ___ points _______together can’t be told apart.
Visual acuity is the ability to tell apart points that are close together. 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.
Visual acuity - cones
Cones give _____ visual acuity because cones are _______ together and ____ _____joins ____ ________ . When ______from ____points hits ______ cones, two action potentials (one from each cone) go to the brain - so you can __________two points that are close together as two separate points.
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.
Summary table of rods and cones - 5 things
