Receptors

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

1. This comes after resting potential and is created by the detection of a stimulus
   1. 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.
      1. The stronger the stimulus, the higher the generator potential.

Annotations:

• The potential differences are measured in milivolts (mV).

1. 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.
   1. After this, the impulse travels to your brain to send the information really fast.

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

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