homeostasis and response

• homeostasis


  maintaining a stable internal environment
• The nervous system


  detects and reacts to stimuli
• central nervous system (CNS)

  consists of the brain and spinal cord, CNS is connected to the body by sensory neurones and motor neurones, coordinates a response
• sensory neurone


  carries information as electrical impulses from the receptors to the CNS
• motor neurone


  carries electrical impulses from the CNS to the effectors
• effector


  all your muscles and glands which respond to nervous impulses
• the nervous system process

  1. receptors detect a stimuli 2. effectors respond to nervous impulses and bring about a change
• synapses(connect neurones)


  connection between the two neurones; the nerve signal is transferred by chemicals which diffuse across the gap; these chemicals then set off a new electrical signal in the neurone
• reflexes (prevent injury)


  rapid, automatic responses to certain stimuli that don't involve the conscious part of the brain
• Reflex arc: The passage of information from receptor to effector involves neurons that go through the spinal cord or an unconscious part of the brain.
• When a stimulus is detected by receptors, impulses are sent along a sensory neurone to a relay neurone in the Central Nervous System (CNS).
• When impulses reach a synapse between the sensory neurone and the relay neurone, they trigger chemicals to be released- these chemicals cause impulses to be sent along the relay neurone.
• When the impulses reach a synapse between the relay neurone and a motor neurone, chemicals are released and cause impulses to be sent along the motor neurone.
• The impulses then travel along the motor neurone to the effector.
• The muscle contracts, making you move.
• reaction time

  the time it takes to respond to a stimulus
• measuring reaction time

  1. person being tested should sit with their arm resting on the edge of the table. 2. hold a ruler vertically between thumb and forefinger where 0 is level. 3. drop the ruler without warning and try to catch it. 4. reaction time is measured by the number where the ruler is caught. 5. repeat this several times and calculate mean
• hormones

  chemical molecules released directly into the blood
• When blood glucose level is too high

  Insulin is secreted by the pancreas; glucose moves from the blood into liver and muscles cells; insulin makes liver turn glucose into glycogen; blood glucose reduced
• When blood glucose level is too low

  Glucagon is secreted by the pancreas; glucagon makes liver turn glycogen into glucose; glucose is released into blood by liver; blood glucose increased
• four hormones: 1. FSH


  produced in the pituitary gland, causes egg to mature, stimulates the release of oestrogen
• four hormones: 2. Oestrogen


  produced in the ovaries, causes the lining of the uterus to grow, stimulates the release of LH and inhibits release of FSH
• four hormones: 3. LH


  produced by the pituitary gland, stimulates the release of an egg at day 14 (ovulation)
• four hormones: 4. Progesterone


  produced in the ovaries by the remains of the follicle after ovulation, maintains the lining of the uterus during the second half of the cycle, when progesterone levels fall the lining breaks down, inhibits the release of LH and FSH
• IVF treatment

  Involves collecting eggs from a women's ovaries and fertilising them in a lab using a man's sperm. The sperm is injected directly into the egg. The fertilised eggs are then grown into embryos and once they are tiny balls of cells, one or two are transferred to the woman's uterus to improve chance of pregnancy. FSH and LH are given before egg collection to stimulate several eggs to mature
• Adrenaline - prepares you for "fight or flight"


  hormone released by the adrenal glands in response to stressful or scary situations- triggers mechanisms that increase the supply of oxygen and glucose to cells in the brain and muscles
• Thyroxine- regulates metabolism


  hormone released by the thyroid gland, important for many processes such as stimulating protein synthesis for growth and development, released in response to thyroid stimulating hormone which is released from the pituitary gland
• basal metabolic rate


  the speed at which chemical reactions in the body occur while the body is at rest