Homeostasis

• Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.
• The automatic control systems in the human body can involve the nervous system or hormones.
• The features of an automatic control system are: receptor cells, co-ordination centre and effector.
• Receptor cells detect stimuli in the environment. Internal conditions may mean blood glucose concentration. External conditions may mean temperature of the skin. Receptor cells now pass information to a coordination centre, for example the brain, the spinal cord or the pancreas.
• The coordination centre recieves and processes the information from the receptor cells. The coordination centre now sends instructions to the effector.
• An effector is a muscle or a gland which restores the optimum level.
• The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions.
• Measuring a person's reaction time

  1. Person 1 sits on a stool with good upright posture

  2. Person 1 places the forearm of their dominant arm across the table with hand overhanging the edge

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

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

  5. Person 2 drops the ruler at a random time

  6. Person 1 catches the ruler with thumb and first finger as quickly as possible

  7. Person 2 records the measurement on the ruler level with Person 1's thumb

  8. Repeat the test several times and calculate the mean
• Reaction time


  Time taken for a person to respond to a stimulus
• Control variables


  • Variables that are kept constant to avoid affecting the dependent variable
  • Examples: distance between thumb and first finger, measuring at top of thumb, room conditions
• Other independent variables that could be investigated: effect of practice, dominant vs non-dominant hand, effect of chemicals like caffeine
• The cerebellum is the part of the brain that controls balance, coordination of movement and muscular activity. The cerebellum (“little brain”) is a fist-sized portion of the brain located at the back of the head.
• The cerebrum is the highly folded part of the brain that controls personality, conscious thought, language and memory. It’s split into the left and right hemisphere.
• The medulla oblongata controls unconscious activities, such as heart rate and breathing rate. Your medulla is the bottom-most part of your brain.
• The hypothalamus is the regulating centre for temperature and water balance within the body.
• Non-invasive brain procedures include:

  Electrical stimulation

  Scientists have stimulated different parts of the brain with a weak electrical current and asked patients to describe what they experienced. If the motor area is stimulated, the patient makes an involuntary movement. If the visual area is stimulated, they may see a flash of colour. EEGs (Electroencephalograms) can be created and studied, to observe the electrical activity in the brain.
• MRI brain scans

  Modern imaging methods such as MRI (Magnetic Resonance Imaging) scans, use strong magnetic fields and radio waves to show details of brain structure and function. Patients are asked to perform various tasks and, by looking at the scan, scientists can see which parts of the brain are active when the task is carried out.
• Risks

  Brain surgery may be needed to remove a tumour or excess fluid, such as blood. All surgery carries a level of risk, but due to the complexity and delicacy of the brain, investigating and treating brain disorders can be very difficult. If surgery is undergone more damage or side-effects may be created, which could affect the patients' quality of life. Serious considerations about the risks involved against the benefits need to be undertaken first.
• Neuroscientists have been able to map the regions of the brain to particular functions by studying patients with brain damage, electrically stimulating different parts of the brain and using MRI scanning techniques. The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult
• Accommodation is the process of changing the shape of the lens to focus on near or distant objects.

  To focus on a near object:

  • the ciliary muscles contract

  • the suspensory ligaments loosen

  • the lens is then thicker and refracts light rays strongly.

  To focus on a distant object:

  • the ciliary muscles relax

  • the suspensory ligaments are pulled tight

  • the lens is then pulled thin and only slightly refracts light rays
• Body temperature


  Monitored and controlled by the thermoregulatory centre in the brain
• Thermoregulatory centre


  • Contains receptors sensitive to the temperature of the blood
  • Receives nervous impulses from temperature receptors in the skin
• When body temperature is too high

  1. Blood vessels dilate (vasodilation)

  2. Sweat is produced from the sweat glands
• Vasodilation and sweating


  Cause a transfer of energy from the skin to the environment
• When body temperature is too low


  1. Blood vessels constrict (vasoconstriction)

  2. Sweating stops

  3. Skeletal muscles contract (shiver)
• The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream. The blood carries the hormone to a target organ where it produces an effect. Compared to the nervous system the effects are slower but act for longer
• The pituitary gland in the brain is a ‘master gland’ which secretes several hormones into the blood in response to body conditions. These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects
• The thyroid gland produces thyroxine.  

  The pancreas produces insulin.  

  The adrenal glands produce adrenaline. 

  The testes produce testosterone.  

  The ovaries produce oestrogen.   
• Blood glucose concentration is monitored and controlled by the pancreas. If the blood glucose concentration is too high, the pancreas produces the hormone insulin that causes glucose to move from the blood into the cells. In liver and muscle cells excess glucose is converted to glycogen for storage.