Receptors Flashcards
What are receptors?
Cells which detect stimulus (change in environment)
How can a response be shown in a flow chart?
Stimulus -> Receptor -> Sensory neurone -> Coordinator -> Motor neuron -> Effector -> Response
Why do organisms respond to different stimuli
To increase their chances of survival
Describe what the nervous system is made up of
Peripheral nervous system - includes receptors, sensory and motor neruones
CNS - includes coordination centres such as the brain and spinal cord
What stimulus does the Pacinian corpuscle respond to?
Large pressure changes and vibrations
Where are Pacinian corpuscles found?
Deep into the skin mainly in hands and feet.
What is the structure of a Pacinian corpuscle?
Consists of a single sensory neurone wrapped up with layers of connective tissue called lamellae which are separated by gel in each layer. They also contain an axon. The sensory neurone also has a plasma membrane
Describe the plasma membrane in the Pacinian corpuscle
Contain stretch-mediated sodium ion channels which remain closed unless they are deformed and stretched. Pressure must be applied to allow Na+ to move into sensory neurone of Pacinian corpuscle
Describe how a Pacinian corpuscle produces a generator potential when stimulated
Increase in pressure deforms the membrane allowing the stretch-mediated sodium ion channels to open. Na+ can flow in which causes depolarisation which results in generator potential.
Which 2 types of photoreceptors are in the retina?
Rods and cones
Describe rod cells
- Found in peripheral of retina
- They are monochromatic meaning they only give information in black and white because they cannot distinguish between different wavelengths.
- They are very sensitive to light meaning they can fire action potentials in dim light
- They have low visual acuity (vision is not very accurate) because many rods are joined to one neurone.
- Contains pigment rhodopsin
How is a generator potential established in rod cells
- Rhodopsin is broken down by dim light energy, not much is needed, low-intensity light is enough
- Enough pigment has to be broken down in order for the threshold to be reached in the bipolar cell
- This threshold can be reached in low light because of summation, many rod cells connecting to one neurone.
Describe cone cells
- There are three types of cone cells that contain different iodopsin pigment (red, green and blue) which all absorb different wavelengths of light
- They produce trichromatic vision meaning that images are seen in colour
- They are packed together in the fovea
- They are less sensitive to light meaning they only fire action potentials when in bright light.
Why is iodopsin only broken down in high intensity/bright light and why is this an advantage?
There is no spatial summation since only 1 cone cells connects to 1 bipolar cell which is why we can’t see colour in the dark.
Advantage - high visual acuity since the brain can distinguish between separate light sources hence clearer vision.
Why are more cone cells located in the fovea and more rod cells further away
Fovea receives the highest intensity of light and cone cells only respond to high light intensities to trigger action potentials. Rods are found further back because they can trigger action potentials in dim light.
