B10: human nervous system

• Homeostasis


  The control of internal environment in response to external change
• Things that need to be controlled in the body to stay safe

  • Temperature
  • Blood glucose levels
  • Water content
• Negative feedback system

  Detects a change, combats that change, continuously moving
• If you are too cold


  You will start to shiver and your veins will leave the surface of your skin to warm up
• If you become too warm

  You will start to sweat and your veins will return to the surface of your skin to lose heat
• Stimulus

  Change in the environment
• Receptors

  Detect changes in the environment
• Coordination centre


  Issues a response carried out by effectors
• Central nervous system


  A coordination centre that detects changes, coordinates a response
• Neurons


  Carry electrical signals through the body
• Types of neurons

  • Sensory neurons
  • Motor neurons
• Synapse


  Gap between two neurons where electrical signal is turned into a chemical signal before being turned back into an electrical signal
• Reflex

  Bypasses the central nervous system to provide a quick response
• It took until around the 1860s for scientists to start thinking the brain is split into different parts
• In the early 18th century, scientists had electrified different parts of the brain and it showed muscles would contract
• Phineas Gage survived having an iron rod go through his brain, which made scientists think the brain must be divided into different sections
• Cerebral cortex


  Controls all our conscious thoughts
• Medulla


  Controls all our unconscious thoughts like heartbeat and breathing
• MRI scans


  • Can be used to stimulate parts of the brain and see which parts are active
  • Can be used to see which part of the brain is affected by a stroke and the resulting symptoms
• Key parts of the eye

  • Cornea
  • Iris
  • Lens
  • Retina
  • Optic nerve
  • Sclera
• Pupil size


  Controlled by muscles in the iris as a reflex reaction to light intensity
• Lens shape


  Changes to focus on near or far objects