PAPER TOPIC

• what is homeostasis?

  the regulation of the conditions inside your body to maintain a stable internal environment, in response to changes in both internal and external conditions
• you have lots of control systems in your body to regulate your internal environment - these include bother nervous and hormonal communication systems

  the control systems are made up of receptors, coordination centres and effectors
• A negative feedback loop:

  • optimum level
  • level changes
  • receptors detect change
  • coordination centre receives and processes the information, organises the response
  • effectors respond
  • level brought back to optimum
• cerebral cortex -

  the outer wrinkly layer of the brain

  it's responsible for things like consciousness, intelligence, momory and language
• medulla -

  at the base of the brain, at the top of the spinal cord. it controls unconscious activates like breathing and your heartbeat
• cerebellum -

  at the back of the brain

  it's responsible for muscle coordination
• studying patients with brain damage -

  if a small part of the brain had been damaged, the effect this has on the patient can tell you a lot about what the damaged part of the brain does.
• electrically stimulating the brain -

  done by pushing a tiny electrode into the tissue and giving it a small zap of electricity

  by observing what stimulating different parts of the brain does, it's possible to get an idea of what those parts do
• MRI scans -

  a magnetic resonance imaging scanner is a big fancy tube-like machine that can produce a very detailed picture of the brain's structures. scientists use it to find out what areas of the brain are active when people are doing things like listening to music or trying to recall a memory
• • electrical stimulation of the brain can help reduce muscle tremors caused by nervous system disorders such as Parkinson's disease.
  • surgery to remove a part of the brain that's causing seizures can be an option to treat epilepsy if it can't be controlled by medication
• Sclera

  The tough, supporting wall of the eye
• Cornea

  The transparent outer layer found at the front of the eye, it refracts light into the eye
• Pupil

  The hole in the centre of the eye, through which light enters
• Iris

  Contains muscle that allow it to control the diameter of the pupil and therefore how much light enters the eye
• Retina

  The layer at the back of the eye that contains two types of light receptor cells. One type is sensitive to light intensity and the other is sensitive to colour
• Lens

  Focuses the light onto the retina
• Ciliary muscle and suspensory ligaments

  Control the shape of the lens
• Optic nerve

  Carries impulses from the receptors on the retina to the brain
• the iris reflex -

  • when light receptors detect very bright light, a reflex it triggered that makes the pupil smaller. the circular muscles in the iris contract and the radial muscles relax. this reduces the amount of light that can enter the eye.
  • in dim light the radial muscles contract and the circular muscles relax making the pupil wider.
• accommodation -

  the ability to look at near and distant objects is an example of a reflex - it's an automatic reaction, not controlled by the conscious brain.

  accommodation is when the eye focuses light on the retina by changing the shape of the nerve
• looking at near objects -

  1. the ciliary muscle contracts, which slackens the suspensory ligaments.
  2. the lens becomes fat (more curved)
  3. this increases the amount by which it refracts light
• looking at distant objects -

  1. the ciliary muscle relaxes, which allows the suspensory ligaments to pull tight.
  2. this makes the lens go thin (less curved)
  3. so it refracts light by a smaller amount
• short-sightedness (myopia)

  • unable to focus on distant objects
  • this occurs when the lens is the wrong shape and refracts the light too much or the eyeball is too long
  • the images of distant objects are brought into focus in front of the retina
  • glasses with a concave lens so that light rays focus on the retina
• long-sightedness (hyperopia)

  • unable to focus on near objects.
  • this occurs when the lens is the wrong shape and doesn't refract the light enough or the eyeball is too short.
  • the images of near objects are brought into focus behind the retina
  • glasses with a convex lens to refract the light rays to focus on the retina
• contact lenses -

  • lightweight, more convenient and almost invisible
  • hard lenses and soft lenses
  • soft lenses are more comfortable but carry a higher risk of eye infections than hard lenses
• laser eye surgery -

  • a laser can be used to vaporise tissue, changing the shape of the cornea
  • slimming it down makes it less powerful and can improve short sight
  • changing the shape so that it's more powerful will improve long sight
  • risk of complications like infection or the eye reacting in a way that makes your vision worse
• replacement lens surgery -

  • the natural lens is removed and replaced by an artificial lens made of clear plastic
  • higher risks than laser surgery
  • possible damage to the retina
• thermoregulatory centre -

  • acts as your own personal thermostat

  1. receptors in the thermoregulatory centre that are sensitive to the temperature of the blood flowing through the brain
  2. receptors in the skin that send information about skin temperature via nervous impulses
• responding to a rise in body temp -

  • receptors detect that the core body temp is too high and send impulses to the thermoregulatory centre
  • the thermoregulatory centre processes the information and triggers the effectors automatically
• responses that reduce core body temp -

  1. hairs on the skin lie flat. less air is trapped acting as an insulating layer so heat can transfer to surroundings
  2. sweat id produced. sweat evaporates transferring energy to environment
  3. blood vessels dilate do blood flows closer to the surface of the skin. vasodilation help transfer energy to surroundings
• responding to a fall in body temp -

  • fall in body temp
  • receptors detect change
  • thermoregulatory centre receives the processes the information, then sends impulses to effectors
  • effectors respond
  • body temp rises
• responses that increase core body temp -

  1. hairs stand up. traps an insulating layer reducing energy transferred
  2. no sweat is produced
  3. vasoconstriction reduces blood flow to skins surface reducing energy transferred to surroundings
  4. shiver, this needs respiration which transfers some energy to warm the body
• the menstrual cycle -

  • stage 1 - day 1 is when the bleeding starts. the uterus lining breaks down for about four days
  • stage 2 - the lining of the uterus builds up again from day 4 to day 14 into a thick spongy layer full of blood vessels ready for a fertilised egg
  • stage 3 - an egg is released from the ovary at day 14 (ovulation)
  • stage 4 - the wall is then maintained for about 14 days until day 28. if no fertilised egg had landed on the uterus wall by day 28 the spongy lining starts to break down again and the whole cycle starts again
• follicle stimulating hormone (FSH)

  FSH causes an egg to mature in one of the ovaries, in a structure called a follicle
• luteinising hormone - (LH)

  LH stimulates the release of an egg at day 14 (ovulation)
• oestrogen and progesterone -

  these hormones are involved in the growth and maintenance of the uterus lining
• hormonal interaction -

  1. FSH is produced in the pituitary gland and causes and egg to mature in an ovary. it also stimulates the ovaries to produce oestrogen.
  2. oestrogen is produced in the ovaries and causes the lining of the uterus to grow. it also stimulates the release of LH and inhibits the release of FSH.
• hormonal interaction -

  3. LH is produced by the pituitary gland and stimulates the release of an egg at day 14

  4. progesterone is produced in the ovaries by the remains of the follicle after ovulation. it maintains the lining of the uterus during the second half of the cycle. when the level of progesterone falls the lining breaks down. progesterone inhibits the release of LH and FSH.
• reducing fertility -

  oestrogen can be used to prevent egg release. if levels remain high for a long time it inhibits FSH production so egg release stops and stays stopped.

  progesterone inhibits egg maturation and the release of an egg. it also stimulate production of a thick cervical mucus which prevents any sperm getting through and reaching the egg.
• oral contraceptives - oestrogen and progesterone pill and just progesterone pill


  benefits with the combined pill -

  • over 99% effective
  • reduces the risk of getting some types of cancer

  problems -

  • isn't 100% effective
  • side effects like nausea, headache
  • doesn't protect against STDs