homeostasis

• Homeostasis


  The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
• Enzymes and cells require very stable conditions in order to work
• The body has systems in place to keep the internal conditions optimum for the cells to function
• Internal conditions maintained by homeostasis

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Automatic control systems


  • Involve the nervous system or hormones
  • Detect changes in the environment (internal or external) through receptor cells
  • Pass information to a Coordination Center (brain, spinal cord, pancreas)
  • Coordination Center sends instructions to an effector (muscle or gland) to carry out a response
• Stimulus


  A change to the environment detected by receptor cells
• Nervous system


  Consists of two parts: central nervous system (brain and spinal cord) and other nerves running to and from the central nervous system
• Homeostasis


  1. Stimulus

  2. Receptor

  3. Coordination Center

  4. Effector

  5. Response
• Neuron


  Another way of saying nerve cell
• Reflex arc


  1. Stimulus detected by receptor

  2. Electrical impulse passed along sensory neuron to central nervous system

  3. Electrical impulse passed along relay neuron in central nervous system

  4. Electrical impulse passed along motor neuron to effector

  5. Effector (muscle) contracts, response occurs
• Reflexes are automatic and rapid, with no decision-making by the conscious part of the brain
• Reflexes help to protect us from danger
• Measuring a person's reaction time


  1. Person 1 sits on stool with good posture

  2. Person 1 places dominant arm across table with hand overhanging

  3. Person 2 holds ruler vertically with 0 cm mark between Person 1's thumb and first finger

  4. Person 2 tells Person 1 to prepare to catch ruler

  5. Person 2 drops ruler at random time

  6. Person 1 catches ruler with thumb and first finger

  7. Person 2 records measurement at top of Person 1's thumb

  8. Repeat test several times and calculate mean

  9. Switch roles, Person 1 tests Person 2's reaction time
• Independent variable


  The variable that is changed (the person having reaction time tested)
• Dependent variable


  The variable that is measured (the reaction time)
• Control variables


  • Constant stick working distance between thumb and first finger
  • Measure ruler at top of thumb
  • Keep conditions in room the same (lighting, background noise)
• Changing control variables could affect the dependent variable (reaction time)
• Other independent variables that could be investigated:
• Investigating effect of practice

  One person catches ruler many times, see if reaction time changes
• Investigating effect of hand used

  Test with dominant hand, then non-dominant hand of same person
• Investigating effect of caffeine

  1. Test subject drinks measured amount of cola 30 mins before, compare to normal reaction time

  2. Also test with caffeine-free cola
• Need to check test subjects have no medical issues affected by caffeine
• Tests should be carried out in lab where hazardous chemicals are not normally used
• Homeostasis is the process of maintaining a stable internal environment, despite changing conditions.
• Why is it important to maintain a stable internal environment within the body?So that our cells and enzymes can function optimally, and not get damaged.
• Name 3 internal conditions that homeostasis regulates.1Blood glucose concentration.

  2Body temperature.

  3Water levels. 

  (there are many more, such as blood pH and ion levels)
• What is the difference between internal conditions and external conditions?Internal conditions refer to the conditions inside the body, such as body temperature.

  External conditions refer to the conditions outside the body, such as room temperature. 
• A receptor detects stimuli (a change in the internal or external environment).
• A coordination centre interprets changes and organises a response.
• Where are the coordination centres located in the body?

  1. Brain.
  2. Spinal cord.
  3. Pancreas.
• An effector brings about a response to restore optimum conditions.
• What are the 2 types of effectors, and what do they do when stimulated?

  1. Muscles - contract.
  2. Glands - release hormones.
• The nervous system is a complex network of nerves that carry messages from the brain and spinal cord to and from various parts of the body. 
• The endocrine system is made up of glands that release hormones.

  These hormones act as chemical messengers that allow communication throughout the body.
• Negative feedback is when a change in a system causes an action that reverses the change.

  For example, a rise in temperature will cause a fall in temperature.
• What is the central nervous system (CNS) composed of?The brain and spinal cord.
• What passes along nerve cells?Electrical impulses.
• How does a synapse transmit an electrical signal?When an electrical impulse reaches the end of a neurone, it causes the release of chemicals(neurotransmitters).

  These chemicals then diffuse across the synapse and stimulate the next neurone to carry another electrical impulse. 
• What is the role of the cerebral cortex?The cerebral cortex is responsible for the higher-level processes of the human brain, including: language, memory, reasoning, thought, learning, decision-making, emotion, intelligence, and personality.

  (You don't have to remember all of these examples)
• he cerebellum is responsible for maintaining your balance and posture.