homeostasis

• Our cells need the right conditions to function properly. Homeostasis is the regulation of these conditions inside us to maintain a stable environment in response to internal and external changes.
• The 3 main automatic control systems

  • maintaining body temperature
  • blood glucose levels
  • water content
• 3 main components of control systems

  • receptors
  • coordination centres
  • effectors
• Negative feedback 


  A process that counteracts something to return to normal conditions.

  • receptor detects a stimulus level as too high
  • the coordination centre receives this info and organises a response
  • effector produces the response that counteracts the change and restores optimum level
• The nervous system


  CNS (central nervous system) consists of the brain and spinal cord in mammals. The CNS is connected to the body by sensory and motor neurones.
• Sensory neurones


  The neurones that carry info as electrical impulses from the receptors to the CNS.
• Motor neurones


  The neurones that carry info as electrical impulses from the CNS to the effectors.
• Effectors


  Muscles and glands that respond to nervous impulses. They bring about change.
• Receptors


  Cells that can detect stimuli
• Order of response

  • stimulus
  • receptor
  • sensory neurone
  • CNS
  • motor neurone
  • effector
  • response
• Synapses are the connection between two neurones. The nerve signal is transferred by chemicals called neurotransmitters, which diffuse across the gap. These chemicals set off a new electrical signal to the next neurone.
• Reflexes are rapid, automatic responses to stimuli that do not involve the conscious part of the brain. They can reduce the chance of injury. The passage of info in a reflex is called a reflex arc.
• Sensory neurone - relay neurone - motor neurone
• Reflex reactions are much faster because you don't have to think about it.
• The brain is in charge of all the complex behaviours, and controls what we do.

  • cerebral cortex - responsible for things such as consciousness, intelligence, language and memory
  • cerebellum - muscle coordination
  • medulla - unconscious activities such as breathing and heart rate

  A) cerebral cortex

  B) medulla

  C) cerebellum

  D) spinal cord

  
• If a small part of the brain has been damaged, the effect this has on the patient can tell us what that part of the brain does.
• The brain can be electrically stimulated by pushing electrodes into the tissue. By observing what happens, we can infer what the brain is doing.
• MRI (magnetic resonance imaging) is a technique that uses magnetic fields and radio waves to produce detailed images of the brain. Scientists use it to find which areas of the brain are active when people are doing things such as listening to music.
• Knowledge of the brain has led to the development of new treatments for disorders. However, it carries risks of physical damage.
• Parts of the eye

  A) suspensory ligaments

  B) retina

  C) optic nerve

  D) sclera

  E) ciliary muscle

  F) lens

  G) pupil

  H) cornea

  I) iris

  
• • the sclera is the tough outer supporting wall of the eye
  • the cornea is a transparent outer layer in front of the eye, and it refracts light
  • the iris contains muscles that control the diameter of the pupil (the hole) and controls how much light gets in
• • the lens focuses the light onto the retina (receptors cells are sensitive to light)
  • the shape of the lens is controlled by the ciliary muscles and suspensory ligaments
  • the optic nerve carries impulses from receptors to brain
• The iris reflex


  When light receptors detect very bright light, a reflex is triggered to make the pupils smaller. The circular muscles contract and the radial muscles relax, reducing the amount of light entering the eye.

  
• In dim light, the radial muscles contract and the circular muscles relax, allowing more light to enter the eye and making the pupil wider.

  
• Accommodation 


  The eye focuses light on the retina by changing the shape of the lens.
• To look at near objects

  The ciliary muscles contract and the suspensory muscles relax, making the lens fatter. This increases the amount of light refracting.
• To look at distant objects

  The ciliary muscles relax and the suspensory ligaments contract, making the lens thinner. This means less light is refracting.
• Long-sightedness (hyperopia)


  This occurs when the eyeball is too short. The images of near objects are focussed behind the retina. You can use a convex lens to fix this.
• Short-sightedness (myopia) 


  This occurs when the eyeball is too long. The images of distant objects are focussed in front of the retina. You can use a concave lens to fix this.
• Treatments for vision defects

  • contact lenses - they are popular because they are almost invisible, but they carry a risk of eye infections
  • laser eye surgery - lasers can vaporise tissue to change the shape of the cornea. Risks include infections or reactions
  • lens replacement surgery - lens is replaced with artificial ones (pig's or plastic). Carries higher risks such as possible damage to the retina
• There is a thermoregulatory centre in the brain which contains receptors sensitive to the temperature of the blood. It also receives impulses from temperature receptors in the skin.
• When you're too hot:

  • hairs lie flat
  • sweat is produced by the sweat glands and evaporates, transferring energy to the surroundings
  • vasodilation - blood vessels dilate so more blood flows close to the surface, transferring energy to surroundings
• When you're too cold:

  • hairs stand up to trap an insulating layer of air
  • no sweat
  • vasoconstriction - blood vessels constrict to close of the blood supply
  • shivering - muscles contracting automatically - which requires respiration, transferring energy to warm the body
• The endocrine system


  Hormones are produced in various glands called the endocrine glands.
• Pituitary glands


  This gland produces many hormones, which is a reason why it is called the master gland. These hormones act on other glands to release hormones that bring about change.
• Thyroid


  Produces thyroxine, which is involved in the rate of metabolism, heart rate and temperature.
• Adrenal gland


  This produces adrenaline, which is used for a fight or flight response.
• Ovaries produce oestrogen and progesterone, which are hormones that regulate the menstrual cycle. Testes produce testosterone, which is a male hormone that controls puberty and sperm production.
• The pancreas produces insulin and glucagon to regulate blood glucose levels.
• Nerves take action very fast, act for a short time, and act on a very precise area. Hormones however take slower action, act for a longer time, and act in a more general area.