Topic 5 - Response and Regulation

• The nervous system

  • There are 5 sense organs which contain receptor cells
  • Receptor cells detect external stimuli and send an electrical signal across neurones to the central nervous system which consists of the brain and the spinal cord to coordinate a response
• Sense Organs and Stimulus

  • Eye - light
  • Ear - sound
  • Nose - chemical smells
  • Tongue - chemical tastes
  • Skin - pain, pressure, and temperature
• • A reflex action is a fast and automatic response to a stimulus
  • Some reflex actions are also protective
• Examples of reflex actions

  • Blinking - for protection of eye
  • Sneezing - for removal of substance from nose
  • Withdrawal of hand - to prevent harm to body
• The reflex arc

  • In the reflex arc, there is a path taken by an electrical impulse from the stimulus to get a response by an effector (muscle/gland)

  Process:

  Stimulus detected by receptor -> sensory neurone -> synapse -> relay neurone -> synapse -> motor neurone -> effector -> response
• A response is the contraction of a muscle to prevent something that could be harmful - for example: hot pan - withdrawal of hand
• The eye

  • Iris - muscles that alter size of pupil to control amount of light entering
  • Sclera - protective, tough, white outer coat
  • Choroid - pigmented layer which absorbs light to prevent reflection, contains blood vessels
  • Retina - light sensitive layer, where image is formed, impulses sent to optic nerve
  • Optic nerve - carries impulses from retina to brain
  • Cornea - clear part of sclera that allows light to enter and refracts light entering pupil
  • Blindspot - where optic nerves leave the eye, no light sensitive cells
  • Lens - changes shape to focus light onto retina
• The hole in the centre of the iris allows light to enter
• A tropism is a growth response in a plant to a one directional stimulus and is caused by the release of the hormone auxin
• Positive phototropism

  • Growth towards light
• Positive gravitropism

  • Root growth down into the ground with gravity
• Regulating glucose -

  Glucose levels too high

  Glucose levels too high:

  • Eating (carbohydrates) increases glucose in blood
  • Pancreas detects increase and releases hormone insulin into the blood
  • Insulin travels through blood to liver
  • Insulin instructs liver to convert glucose into insoluble glycogen for storage
  • Glucose levels decrease to normal levels
• Regulating glucose -

  Glucose levels too low

  Glucose levels too low:

  • Exercising decreases glucose in the blood
  • Pancreas detects decrease and releases hormone glucagon into blood
  • Glucagon travels through blood and instructs liver to convert stored glycogen back into glucose and release into blood
  • Glucose levels increase to normal levels
• Homeostasis

  Maintaining a constant internal environment
• Negative feedback

  A mechanism that maintains optimum conditions in the body
• Temperature regulation -

  When the body is too hot

  When the body is too hot:

  • Hairs lie flat and less air is trapped so more heat is radiated from the body
  • More sweat is produced by the sweat glands
  • This sweat travels up through the sweat duct and is released through the sweat pore onto the skin and then evaporates carrying heat away from the body
  • Vasodilations occurs - blood vessels get wider -> increases blood flow -> more heat from the blood is lost to the environment
• Temperature regulation -

  When the body is too cold

  When the body is too cold:

  • Hairs stand up trapping a layer of insulating air which reduces heat loss
  • Shivering occurs which is the involuntary contraction of muscles which increases respiration rate and hence releases heat
  • Vasoconstrictions occur -> blood vessels get narrower -> restricts blood flow -> less heat lost from blood to environment
• The body must be kept at 37 degrees celsius for optimum conditions for enzyme processes
• Glands produce hormones
• Diabetes 


  A condition where you're unable to control glucose levels
• Glucose levels can be detected by collecting a urine sample and using the benedict's solution to determine the level of glucose

  Result colour -

  blue (least amount of glucose) -> green -> yellow -> orange -> brick red (most amount of glucose)
• Type 1 diabetes


  • A condition where the body doesn't produce enough insulin

  Cause: potentially due to an overreaction of the body to a certain virus -> destruction of insulin cells by immune system

  Treatment: injecting insulin
• Type 2 diabetes 


  • A condition where the body doesn't respond to the insulin produced

  Cause: high sugar intake (carbohydrates)

  Treatment: low sugar diet, lifestyle changes
• Lifestyle factors

  Diet -

  • A diet high in sugars and carbohydrates can lead to obesity or type 2 diabetes

  Drug and alcohol abuse -

  • Leads to dependence and addiction where people suffer withdrawal symptoms
  • Alcohol causes slowing of reaction times and in the long term can cause heart, liver or circulatory disease
• The eye 


  Diagram -

  
• The reflex arc 


  Diagram -