Mammalian sensory receptors
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Explainer Video
Summary
Mammalian sensory receptors
In a nutshell
Receptors detect stimuli. Pacinian corpuscles are receptors that detect stimuli, such as pressure, in your skin and photoreceptors are receptors that detect light in your eye. Stimuli can be detected by baroreceptors and chemoreceptors, which causes a change in heart rate.
Receptors
Definition
Receptors are cells or proteins on cell surface membranes that detect a stimulus and pass on information about it. Each receptor is specific to a different type of stimulus.
Pacinian corpuscles
Pacinian corpuscles are pressure receptors found deep in your skin, they respond to mechanical stimuli such as pressure and vibrations which is why they are known as mechanoreceptors.
The centre of a Pacinian corpuscle contains a sensory nerve ending which a sodium ion channel known as a stretch-mediated sodium ion channel. When these ion channels are deformed by stretching or another mechanical stimulus, they open and sodium ions are able to diffuse into the cell.
Pacinian corpuscle mechanism
| 1. | In its resting state, the stretch mediated sodium ion channels are too narrow to allow sodium ions through. The Pacinian corpuscle neurone has a resting potential. |
| 2. | If pressure is applied to the Pacinian corpuscle, it becomes deformed and the membrane surrounding its neurone is stretched. This causes the stretch-mediated sodium ion channels to widen and allows sodium ions to diffuse into the membrane. |
| 3. | The influx of sodium ions causes the membrane to become depolarised as the potential of the membrane has changed and a generator potential is produced. The generator potential creates an action potential which passes along the neurone to other neurones to the central nervous system. |
Photoreceptors
Definition
Photoreceptors are light receptors that are found in the eye.
| 1. | Iris | The muscles of the iris control the amount of light that enters the eye. |
2. | Pupil | This is where light enters the eye. |
| 3. | Lens | Light rays are focused by the lens. |
| 4. | Retina | Light rays are focused onto the retina which contains photoreceptor cells. |
| 5. | Fovea | This is an area of the retina that contains lots of photoreceptors. |
| 6. | Optic nerve | This is a bundle of neurones that carries nerve impulses from photoreceptor cells to the brain. |
| 7. | Blind spot | This is where the optic nerve leaves the eye, there are no photoreceptor cells and it is therefore insensitive to light. |
Rod and cone cells
There are two main types of photoreceptor, these are rod and cone cells.
Rod cells | Cone cells |
 |  |
| Rod-shaped. | Cone-shaped. |
| Much more abundant than cone cells. | Fewer numbers than rod cells. |
| Found in the peripheral parts of the retina, they are absent in the fovea. | Less are found in the periphery, they are more concentrated in the fovea. |
| Low visual acuity because many rods join the same neurone so light from two points close together cannot be differentiated. | High visual acuity because cones are close together and one cone is attached to one neurone. |
| Sensitive to light so work well in dim light because many rods join one neurone, meaning many weak generator potentials combine to reach the threshold and trigger an action potential. | Less sensitive to light so work better in bright light as one cone is attached to one neurone so more light is required to reach the threshold and trigger an action potential. |
| Contains the pigment rhodopsin. | Contains the pigment iodopsin. |
| One type; only give information in black and white. | Three types; each contain a different optical pigment: red-sensitive, green-sensitive and blue-sensitive. They are stimulated in different colours which is what allows you to see in different colours. |
Structure of the retina
Heart rate
Stimuli that are detected by receptors can cause heart rate to speed up or slow down.
Stimulus | Receptor | Neurone and transmitter | Effector | Response |
| High blood oxygen, low carbon dioxide or high pH. | Chemoreceptors | This sends impulses to the medulla, which in turn, sends impulses along parasympathetic neurones. They secrete acetylcholine which binds to receptors on the sinoatrial node. | Cardiac muscles | Heart rate decreases to return oxygen, carbon dioxide and pH levels back to normal. |
| Low blood oxygen, high carbon dioxide or low pH. | Chemoreceptors | This sends impulses to the medulla, which in turn, sends impulses along sympathetic neurones. They secrete noradrenaline which binds to receptors on the sinoatrial node. | Cardiac muscles | Heart rate increases to return oxygen, carbon dioxide and pH levels back to normal. |
| High blood pressure. | Baroreceptors | This sends impulses to the medulla, which in turn, sends impulses along parasympathetic neurones. They secrete acetylcholine which binds to receptors on the sinoatrial node. | Cardiac muscles | Heart rate decreases to reduce blood pressure back to normal. |
| Low blood pressure. | Baroreceptors | This sends impulses to the medulla, which in turn, sends impulses along sympathetic neurones. They secrete noradrenaline which binds to receptors on the sinoatrial node. | Cardiac muscles | Heart rate increases to increase blood pressure back to normal. |
FAQs - Frequently Asked Questions
What are photoreceptors?
Photoreceptors are light receptors that are found in the eye.
What are Pacinian corpuscles?
Pacinian corpuscles are pressure receptors found deep in your skin, they respond to mechanical stimuli such as pressure and vibrations which is why they are known as mechanoreceptors.
What are receptors?
Receptors are cells or proteins on cell surface membranes that detect a stimulus and pass on information about it. Each receptor is specific to a different type of stimulus.