homeostasis

• what is homeostasis?

   all of the processes that happen in a cell or organism to maintain optimal conditions. This is needed to respond to changes in the internal and external environment.
• What can happen if the body stops operating in optimal internal conditions?

  slower metabolic reactions, enzymes denature
• Conditions in the body that need to be regulated are:

  temperature, urea, water, glucose concentration and carbon dioxide
• what do receptors do?

  detect changes in the environment
• what are effectors?


  muscles or glands which carry out responses to stimuli
• what are coordination centres?

  brain or spinal cord - receive and process information arriving from receptor cells
• what are neurotransmitters?

  Neurotransmitters are chemicals that diffuse across synapses and bind to receptors on the next neurone.
• what is a reflex action?

  A reflex action is an unconscious response that allows a person to respond to a dangerous situation automatically and rapidly via a reflex arc.
• what are the components of a reflex arc?

  stimulus, receptor , neurones, effector, response
• What triggers the release of neurotransmitters at a synapse in the brain?

  an electrical impulse
• When the electrical impulse reaches the end of the neurone, chemicals called neurotransmitters are released. The chemicals diffuse across the synapse and bind to receptors on the next neurone.
• what does the sensory neurone do?

  carries the signal in the form of an electrical impulse to the CNS
• what does the relay neurone do?

  relays the electrical impulse from the sensory neurone to the appropriate motor neurone.
• what does the motor neurone do?

  carries the electrical impulse from the CNS to an effector.
• Reflex arc

  A sequence of events that occurs in response to a stimulus
• Reflex arc

  1. Stimulus detected by receptor

  2. Sensory neurone carries electrical impulse to CNS

  3. Motor neurone carries electrical impulse from CNS to effector

  4. Effector (muscle or gland) brings about action in response to change in internal or external environment
• The stimulus is detected by a receptor
• The sensory neurone carries the signal, in the form of an electrical impulse, to the central nervous system (CNS)
• The motor neurone carries the electrical impulse from the CNS to an effector
• An effector (a muscle or gland) brings about an action in response to the change in the internal or external environment
• what is a stimulus?


  a change in the environment to which the body needs to respond which is detected by a receptor
• what is the function of the cerebral cortex?

  memory , intelligence , senses , language , conscious thought
• what is the function of the cerebellum?

  balance and muscle coordination
• what is the function of the hypothalamus

  regulates body temperature and sends signals to the pituitary gland
• what is the function of the medulla?

  unconscious activities: breathing and heart rate
• how do scientists study the brain?

  study people with brain damage , electrically stimulate different parts of the brain , scanning the brain: MRI scan, PET scan, CT scan
• why is treating the brain difficult?


  wide range of things can go wrong e.g. tumours , trauma , infection , mental health problems , infection

  its physically difficult to fix anything since the surrounding brain tissue is fragile

  Its complex so we dont fully understand it and it is difficult to fix with drugs
• where in the brain is the medulla found?

  in the brain stem
• what is the cornea and what does it do?

  Transparent outer layer of the eye that refracts light and helps focus light onto the retina.
• what is the iris and what does it do?

  The iris is the colored part of the eye that controls the size of the pupil to regulate the amount of light entering the eye.
• what is the pupil and what does it do?

  gap in the middle of the iris which allows light to pass through the lens
• what is the role of the lens ?

  to refract light and it can change its shape to control how strongly it refracts the light to focus it onto the retina
• what is the retina?

  The innermost layer of the eye, responsible for converting light into electrical signals for transmission to the brain. It contains two types of receptor cells
• what are rod cells?

  receptor cells located in the retina which are more sensitive to light than cone cells but only allow you to see in black and white
• what are cone cells?

  Photoreceptor cells in the retina responsible for color vision.
• what is the fovea?


  an area in the retina which contains only cone cells : is where light is focused
• what is the function of the optic nerve?

  transmits impulses generated by receptor cells to the brain
• what happens to the iris when there is low light?

  it dilates
• what happens to the circular and radial muscles when the pupil constricts?

  the circular muscle contracts and the radial muscle relaxes
• what is the role of the ciliary muscles?

  control the thickness of the lens