AQA Biol 5 Receptors

• Increase in physical activity
• CO2 increases due to more respiration
• Blood pH is lowered
• Chemoreceptors in the carotid artery walls increase frequency of impulses to the medulla oblongata
• The centre in the medulla oblongata that controls heart rate increases the frequency of impulses to the SAN via the sympathetic pathway
• SAN increases the heart rate
• Increased blood flow removes excess CO2 faster, breathing increases, CO2 expired
• Carbon dioxide levels return to normal
• pH rises to normal levels

• Blood pressure is higher than normal
• Pressure receptors transmit an impulse to the centre in the medulla oblongata that decreases heart rate
• the medulla oblongata sends impulses via the parasympathetic pathway to the SAN
• Heart rate decreases
• Blood pressure decreases

• Blood pressure is lower than normal
• Pressure receptors transmit an impulse to the centre in the medulla oblongata that increases heart rate
• the medulla oblongata sends impulses via the sympathetic pathway to the SAN
• Heart rate increases
• Blood pressure increases

• In Rod Cells, light causes the breakdown of the pigment Rhodopsin, that results in the generation of an action potential.  
• Many rod cells are connected to the same bipolar cell.  Since the threshold must be reached in the bipolar cells and they can all contribute to reaching this threshold (spatial summation) they will function at low light intensities.  
• This means that rod cells have a high sensitivity to light.  
• However, since many rods are attached to the same neurone, only one impulse will be generated and it is impossible for the brain to determine which rod cell was stimulated to begin with.  This results in rod cells having a poor visual acuity (they can't distinguish between two points of light close together) 
• More frequent at the periphery of retina
• Noneat the fovea

The Pacinian Corpuscle responds to pressure.  It consists of the end of a sensory neurone in the centre of layers of tissue, each seperated by a viscous gel.  The sensory neurone of a pacinian corpuscle has stretch-mediated sodium channels in the membrane.

• During its resting state, strech-mediated sodium channels are closed so that sodium ions cannot move through.  The corpuscle therfore maintains a resting potential.
• When pressure is applied, the membrane of the neurone is stretched by the layers of tissue causing sodium channels to open, allowing sodium ions to diffuse in.
• The inflix of sodium ions cause a change in the polarity of the neurone, creating a generator potential.
• The stronger the pressure, the greater the generator potential, until it reaches a threshold, when an action potential is triggered. 

• There are three types of cone cells, which are each respond to a different colour.
• The colour interpreted depends on the proportion of each type that is stimulated.
• Cone cells break down the pigment Iodopsin to create an action potential.
  
• Cone cells are each connected to one bipolar cell, meaning that a high light intensity is required to reach the threshold potential (temporal summation)
• This means that cone cells have a low light sensitivity.
• However because each cone cell is attached to one bipolar cell, when two adjacent cone cells are stimulated, two seperate nervous impulses will be sent to your brain so you can distinguish between two points.  This results in cone cells having a high visual acuity.