Tropic responses

• Homeostasis


  Maintaining a constant internal environment
• Things that need to be kept constant in the body

  • Temperature around 37 degrees Celsius
  • Levels of sugar in the blood
  • Levels of ions and water
  • Blood pressure
  • Amounts of waste in the blood such as carbon dioxide and urea
• Negative feedback


  1. Brain uses hormone or nervous system to send a signal to the part of the body that can rectify the problem

  2. Detects the stimulus

  3. Reacts by responding accordingly

  4. Brings the body back to the normal levels
• Blood sugar level increases after a meal

  Pancreas releases insulin that causes the sugar to be stored in the liver, returning blood sugar level to normal
• Homeostasis is important because our metabolism, controlled by enzymes, only works in very specific conditions
• If conditions change, enzymes could stop working and we could die
• Homeostasis happens without you having to think about it
• Nervous system


  Consists of the central nervous system (brain and spinal cord) and the peripheral nervous system (all other nerves)
• Neurons


  • Carry electrical impulses at rapid speeds (up to 100 meters per second) to transmit information in and out of the nervous system
• Types of neurons


  • Sensory neurons
  • Relay neurons
  • Motor neurons
• Sensory neurons


  Pick up information from receptors and carry the signal into the central nervous system
• Relay neurons


  Coordinate information within the central nervous system, passing signals between different connections
• Motor neurons


  Send signals from the central nervous system to effectors (muscles or glands) to cause a response
• Synapse


  Tiny gaps between neurons where electrical impulses are converted to chemical signals to pass information between neurons
• Voluntary response


  Coordinated by the brain (e.g. picking up a cup of tea)
• Reflex


  Automatic, rapid response to a stimulus that does not involve the brain (e.g. iris reflex, withdrawing hand from heat)
• Reflex arc


  1. Stimulus

  2. Receptor

  3. Sensory neuron

  4. Relay neuron

  5. Motor neuron

  6. Effector response
• Stimuli


  Changes in the environment that organisms need to detect and respond to
• Organisms


  • Need to be able to detect stimuli
  • Need to be able to respond to stimuli
  • Need to stay alive
  • Need to be able to reproduce
• Receptors


  Specialized cells that detect stimuli
• Effectors


  Cells that carry out the response to stimuli, often muscle cells or glands
• Internal environment


  • Needs to be kept constant for metabolic reactions and enzymes to work properly
  • Includes things like water, carbon dioxide, glucose, pH, salt, temperature
• Homeostasis


  Maintaining a constant internal environment
• Detecting and responding to stimuli

  1. Detect stimuli using receptors

  2. Nervous system and endocrine system connect receptors to effectors

  3. Effectors carry out response
• Nervous system


  • Rapid communication via electrical impulses
  • Short-lived responses
  • Acts on small areas
• Endocrine system


  • Slower response via hormones in the blood
  • Long-lasting effects
  • Can have widespread effects on organs and many cells
• Nervous system and endocrine system


  Complement each other, body can choose which to use depending on the stimulus