Receptors

Receptors

1. These are cells which detect a stimulus and are usually found on the surface of cells.

2. They are very specific and detect only one form of a stimulus, e.g. photoreceptors only detect light intensity.

3. Resting potential

   • During this, the inside of the receptor cell is positive and the outside is negative, creating a voltage in the cell membrane.
     • Voltage is also known is also known as potential difference, hence why this is called resting potential.
       • Also, since nothing is happening yet, the resting potential has to be maintained by the movement of Na+ through ion pumps and channels.
         • As Sodium ions are positively charged, if they move out into the receptor cell, the inside would become more positive.
           • For every 2 K+ in, 3Na out.

4. generator potential

   • This comes after resting potential and is created by the detection of a stimulus
     • This detection causes the receptor cell membrane to become more permeable, opening more ion channels, so Na+ ions diffuse in and out of a cell, resulting in a larger potential difference of the cell membrane.
       • The stronger the stimulus, the higher the generator potential.

5. Action potential

   • The potential differences are measured in milivolts (mV).
   • If the generator potential reaches a particular level, an action potential is triggered which causes a nerve impulse to travel through a sensory neuron. This level is known as the threshold.
     • After this, the impulse travels to your brain to send the information really fast.

6. The Pacinian corpuscle

   • It is found on the surface of your skin.
   • It is a mechanoreceptor so only detects, movement and vibrations.
     • After it detects a stimulus e.g. a tap on your arm, its layers deform.
       • This means the membrane of your sensory nerve ending also deform e.g. the stretch-mediated Na+ channels.
         • The movement of Na+ by active transport creates a generator potential. If it reaches the threshold, an impulse is released.
           • This allows you to feel certain objects

7. Rods and cones.

   • These are found on the retina in your eye
   • These are photoreceptors so detect light intensity
     • The light shines through the lens in your eye, onto your rods and cones (the optical pigments).
       • The rods only detect black and white light. However, they have a low visual acuity (the detail of your image).
         • This is because many rods are joined to just one bipolar nerve, which joins onto the optic nerve.
           • Therefore, the message your brain receives is more so it cannot distinguish between two points..
         • These are found in the peripheral part of the retina.
       • The cones detect 3 colors, green, red and blue.
         • They have a larger visual acuity as each cone is joined t only one bipolar neuron.
           • They also absorbs low light intensities compared to rods.