homeostasis

• What is homeostasis?


  The regulation of conditions inside the body to maintain a stable internal environment in response to changes in both internal and external conditions
• What things do automatic control systems regulate?

  Body temperature, blood glucose level and water content
• What are the three main components that work together in automatic control systems?

  Receptors, coordination centres and effectors
• What does negative feedback do?

  When the level of something in the body is too high or low, the body uses negative feedback to bring it back to normal
• How does negative feedback work?

  Receptor detects a stimulus - level is too high or low. Coordination centre receives and processes the information, then organises a response. Effector produces a response and restores the optimum level.

  The effectors will continue to produce this response for as long as they are being stimulated by a coordination centre. This sometimes leads to the opposite problem occuring, in which case the negative feedback process starts again
• What makes up the nervous system?

  The central nervous system, sensory neurones, motor neurones and effectors
• What is the central nervous system?


  The brain and the spinal chord, connected to the body by sensory neurones and motor neurones
• What are sensory neurones?


  The neurones that carry information as electrical impulses from the receptors to the CNS
• What are motor neurones?

  The neurones that carry electrical impulses from the CNS to effectors
• What are effectors?


  Muscles and glands which respond to nervous impulses
• What are synapses and what do they do?


  They are the connections between two neurones. The nerve signal is transferred by chemicals (neurotransmitters) which diffuse across the gap and set off a new electrical signal in the next neurone
• What are reflexes?


  Rapid, automatic responses to stimuli that don't involve the conscious part of the brain
• How does a reflex arc work?

  Stimulus is detected by receptors, causing impulses to be sent along a sensory neurone to a relay neurone in the CNS. Impulses reach a synapse between sensory neurone and relay neurone, causing neurotransmitters to be released, which diffuse across the gap and cause an impulse to be sent down the relay neurone. The same thing happens when the impulses reach a synapse between the relay neurone and the motor neurone. The impulses travel down the motor neurone to the effector, which produces a response
• How would you investigate reaction times?

  Ruler drop test or computer test
• What is the cerebral cortex?

  The outer layer of the brain which is responsible for conciousness, intelligence, memory and language
• What is the medulla?

  It controls unconscious activities such as breathing and is at the point where the spinal cord meets the brain
• What is the cerebellum?


  At the back of the brain, it is responsible for muscle coordination
• How do scientists study the brain?

  Studying patients with brain damage, electrically stimulating the brain and MRI scans
• How has research into the brain helped people?

  Developed treatment of disorders of the nervous system. For example, electrical stimulation can reduce muscle tremors caused by Parkinson's
• What are the risks of researching the brain?

  Physical damage to the brain or increased problems with brain function
• What are the different parts of the eye?

  Sclera - tough supporting wall of the eye;

  Cornea - transparent outer layer at the front of the eye which refracts light into the eye;

  Iris - muscles that control the diameter of the pupil and therefore how much light enters the eye;

  Lens - focuses light onto the retina;

  Retina - contains receptor cells sensitive to light intensity and colour;

  Ciliary muscles and suspensory ligaments - control shape of the lens;

  Optic nerve - carries impulses from the receptors on the retina to the brain
• How does the eye respond to light intensity?

  In bright light, reflex is triggered that causes the circular muscles in the iris to contract and the radial muscles to relax, making the pupil smaller.

  The opposite happens in low light
• How does the eye focus on near objects?

  The ciliary muscles contract, which slackens the suspensory ligaments, making the lens fatter and more curved, increasing the amount by which it refracts light
• How does the eye focus on distant objects?

  The ciliary muscles relax, allowing the suspensory ligaments to pull tight, making the lens thinner and less curved, decreasing the amount by which it refracts light
• What is hyperopia?


  Long-sightedness
• What causes hyperopia and how can it be corrected?

  It occurs when the eyeball is too short or the lens doesn't refract light enough, causing images of near objects to focus behind the retina.

  It can be corrected by glasses with convex lenses to refract the light more so that images form behind the retina
• What is myopia?


  Short-sightedness
• What causes myopia and how can it be corrected?

  It occurs when the lens is the wrong shape so that it refracts light too much or when the eyeball is too long, which causes the images of distant objects to be focused in front of the retina.

  It can be corrected by glasses with concave lenses
• How can vision defects be treated?

  Glasses, contact lenses, laser eye surgery, replacement lens surgery
• What are contact lenses?

  Thin lenses that sit on the surface of the eye and are shaped to compensate for the fault in focusing. They are lightweight and almost invisible. They are more convenient than glasses for sports. There are hard lenses and soft lenses - soft lenses are more comfortable, but carry a higher risk of eye infections than hard lenses
• What is laser eye surgery?

  A laser vaporises tissue, changing the shape of the cornea and how strongly it refracts light into the eye. It can treat both long-sightedness and short-sightedness. Like all surgical procedures, there are risks of complications, such as infection or the eye reaction in a way that makes vision worse
• What is replacement lens surgery?

  Removing the natural lens and replacing it with an artificial plastic lens. It involves work inside the eye, so has more risks that laser eye surgery, including possible damage to the retina (which could lead to sight loss)
• How does the body detect extreme temperature and react to it?

  Temperature receptors in the skin and in the thermoregulatory centre detect that the core body temperature is too high or low. The thermoregulatory centre acts as a coordination centre - it receives information from temperature receptors and triggers effectors automatically. Effectors produce a response to counteract the change
• What is meant by effectors working antagonistically?

  In some cases, one effector heats and another cools at the same time to achieve a very precise temperature. This mechanism allows a more sensitive response
• What do effectors do in response to the core body temperature being too high?

  Sweat is produced by sweat glands and evaporates from the skin, transferring thermal energy to the environment.

  Vasodilation - Blood vessels supplying the skin dilate so more blood flows close to the surface of the skin, transferring thermal energy from the skin to the environment
• What do effectors do in response to the core body temperature being too low?

  Hairs stand up to trap an insulating layer of air. No sweat is produced.

  Vasoconstriction - Blood vessels supplying the skin capillaries constrict to close of the blood supply to the skin, meaning less thermal energy is lost from the skin into the environment.

  Shivering (automatic muscle contractions) needs respiration which transfers some energy to warm the body
• What are hormones?


  Chemical messengers sent in the blood to target organs to affect and control them. They control things in organs and cells that need constant adjustment. They have relatively long-lasting effects
• What makes up the endocrine system?

  The pituitary gland, the thyroid, the adrenal gland, the pancreas and the ovaries in females and the testes in males
• What does the pituitary gland do?

  It produces many hormones that regulate body conditions. Called "the master gland" because the hormones it produces act on other glands, directing them to release hormones that bring about change
• What does the thyroid do?

  Produces thyroxine, which is involved in regulating things like the rate of metabolism, heart rate and temperature