receptors

• stimulus 


  detectable change in the environment which is detected by receptors
• the reflex arc with a stimulus

  -receptor

  -sensory neurone

  -coordinator

  -motor neurone

  -effector

  -response
• importance of reflex arc

  rapid-short pathway

  autonomic-no thought involved

  protect you-harmful stimuli
• phototropism


  response to light
• response to gravity


  gravitropism
• response to water


  hydroptropism
• IAA


  controls cell elongation in shoots

  made in tips
• phototropism in shoots


  shoot tip produces IAA, IAA accumulates on the shaded side. stimulates cell elongation, plant bends towards the light
• phototropism in roots


  root tip produces IAA

  IAA inhibits cell elongation

  root bends away from light

  negative phototropism
• negative gravitropism 


  shoot tip produces IAA. IAA diffuses from upder side to lower sisde. stimulating cell elongation so plant grows upwards
• positive gravitropism 


  root tip produces IAA accumulates on lower side of root IAA inhibits cell elongation.

  bends down towards gravity
• taxis 


  directional response of an organism either towards or away from the stimulus
• kinesis


  change in speed and rate of change of direction in response to a stimulus
• receptors


  response to a specific stimuli which leads to a generator potential
• pacinian corpsucle 


  responds to pressure changes
• how does the Pacinian corpuscle detects pressure

  stretch mediated sodium ion channels are deformed,sodium ions diffuse into sensory neurone
• myogenic meaning


  cardiac muscle can contract and relax without receiving signals from nerves.
• sinoatrial node


  located in the right atrium and is known as the pacemaker, releases a wave of depolarization across the atria causing the muscles to contract.
• bundle of his - runs through the septum.

  • passes the wave of depolarisation down the septum and Purkinje fibres in the ventricle
• purkyne fibres


  walls of ventricles spread wave of depolarisation from AVN across the bottom of the heart. The muscular walls of ventricles contract from the bottom up
• non-conductive 


  located between atria and ventricles prevents wave of depolarisation travelling dwon to ventricles. causes slight delay in ventricles filling up
• Receptors responds to a specific stimulus and this leads to the establishment of a generator potential which causes a response
• 3 types of receptor

  pacinian corpuscle

  rods

  cones
• pacinian corpuscle


  is a pressure receptor which is located in the skin
• structure of Pacinian corpuscle

  sensory neurone which has special channel proteins
• what type of channel protein does pacinian corpuscle have?

  stretch mediated sodium channels
• pressure applied to the stretch mediated sodium channels mean

  they will open and Na+ enters the sensory neurone generating a generator potential
• Human retina contains what two photo receptors

  rods and cones
• rod cells only generate images in

  black and white
• How do rod cells create a generator potential

  pigment in rod cells rhodopsin must be broken down by light energy
• Many rod cells are connected to one sensory neurone which means


  they can detect light at a very low intensity
• negative of rod cell

  low visual acuity
• cone cells process images

  in colour
• three types of cone cell pigments

  red green and blue
• the different pigmented cone cells produce absorb different wavelengths of light
• iodopsin in cone cells is only broken down if 


  there is a high light intensity
• one cone cell connects to a bipolar cell and has high visual acuity
• the distribution of rod and cone cells

  is uneven
• light is focused by

  fovea
• most cone cells are located near

  fovea