The human nervous system

• Brain


  A mass of nerve tissue consisting of billions of interconnected neurones that acts as the main control centre of the nervous system

  
• Brain mapping


  A set of neuroscience techniques used to create a map of the various brain areas and their functions

  
• Neuroscientist


  A scientist who studies the brain and nervous system
• Magnetic resonance imaging (MRI)


  Can be used to look at which parts of the brain are most active during certain activities

  
• MRI scanner


  A type of scanner that uses strong magnetic fields and radio waves to produce images of inside of the body

  
• Electrical stimulation


  Can be used to look at behaviour in response to stimulation and narrow down specific brain regions to their functions

  
• Electroencephalogram (EEG)


  A test that detects and records electrical activity in the brain

  
• Examine brain damage


  To look at areas of damage and link these areas to their function by seeing what effects the damage causes

  
• Brain damage


  Injury to a particular part or parts of the brain
• Brain surgery


  Needed to remove tumours or excess fluid such as blood

  
• Complex structures


  It can be difficult to work out which parts carry out what function
• Delicate and easy to damage


  Brain examination should ideally be non-invasive to prevent injury and brain surgery should be carefully carried out
• Difficult to access the brain

  A complication of brain investigation that can be overcome using techniques such as EEG or MRI scanners

  
• Consequences of brain surgery


  There is a possibility of damaging the brain further or side effects can be created which can affect quality of life
• Brain disease


  Damage to the brain caused by illness or trauma
• Pupil


  Centre of the iris, it varies in size to regulate the amount of light that reaches the retina

  
• Iris


  Made up of muscles called circular and radial muscles that work antagonistically to regulate the size of the pupil

  
• Reflex response to dim light


  Circular muscles relax, radial muscles contract, pupil dilates so that more light can enter the eye

  
• Reflex response to bright light


  Circular muscles contract, radial muscles relax, pupil constricts so that less light can enter the eye

  
• Cornea


  Focuses the entry of light into the eye but is fixed and unable to adjust its focus

  
• Lens


  Focuses light rays to the back of the eye and can change shape to adjust focus for distant and near objects

  
• Retina


  The light-sensitive surface at the back of the eye containing receptor cells that detect light

  
• Accommodation


  The process by which the eye lens changes shape to focus on near or distant objects

  
• Ciliary muscles


  Works with the suspensory ligaments and can contract or relax to adjust the shape of the lens

  
• Suspensory ligaments


  Works with the ciliary muscles and can loosen or be pulled tight to adjust the shape of the lens

  
• Focusing on a near object

  Ciliary muscles contract, suspensory ligaments loosen, lens is thicker and refracts light rays strongly

  
• Focusing on a distant object

  Ciliary muscles relax, suspensory ligaments pull tight, lens is pulled thin and only slightly refracts light rays

  
• Hyperopia (long-sightedness)


  Where a person has difficulty focusing on nearby objects because the light rays focus behind the retina

  
• Causes of hyperopia


  When the lens is too weak or the eyeball is too short

  
• Myopia (short-sightedness)


  Where a person has difficulty focusing on distant objects because the light rays focus in front of the retina

  
• Causes of myopia


  When the lens is too strong or eyeball is too long

  
• Convex lenses


  Used for correcting hyperopia by moving an image forward and focusing it on the retina

  
• Concave lenses


  Used for correcting myopia by moving an image further back and focusing it on the retina

  
• Modern sight treatments

  Hard and soft contact lenses, laser surgery and lens replacement

  
• Homeostasis


  The regulation of conditions in a cell or organism in order to optimally respond to internal and external changes

  
• Body temperature


  The amount of heat in the body which is controlled by homeostasis to ensure cells and enzymes function properly
• Enzymes and colder temperatures


  Enzymes work best at their optimum temperature, if it becomes too cold the enzymes will not have enough energy for successful reactions

  
• Enzymes and hotter temperatures


  Enzymes work best at their optimum temperature, if it becomes too hot the enzymes will denature and be unable to function

  
• Blood temperature


  Temperature of the blood is normally around 37 degrees celsius, which is the optimal temperature for human enzyme activity
• Thermoregulatory centre


  The area of the brain that is sensitive to the temperature of the blood