Coordination and Response

• Receptors detect stimuli. They are a group of cells that detect external stimuli (eg. rod and cone cells in the eye detect the changes in light)
• Effectors are cells that bring about a response to a stimuli. Muscle cells contract whereas glands secrete hormones.
• Receptors communicate with effectors via the nervous system, the hormonal system or sometime both.
• The nervous system is made up of neurones in your body. There are 3 types of neurones: sensory neurones, relay neurones and motor neurones
• The central nervous system consists of the brain and spinal cord only. When receptors in a sense organ detect a stimulus, they send electrical impulses along sensory neurones to the CNS.
• The CNS after sends electrical impulses to an effector along the motor neurone. The effector then responds accordingly.
• The job of the CNS is to coordinate the response. A response always need a stimulus, receptor and an effector. Neurones transmit information using high electrical impulses so a rapid response can be brought about.
• The connection between two neurones are called synapses. The nerve signal is transferred by chemicals called neurotransmitters which diffuse across the gap. These chemicals then set off a new electrical signal in the next neurone.
• Reflexes are automatic responses to certain stimuli, the route taken by the information in a reflex called a reflex arc.
• 1. When a stimulus is detected by receptors, an impulse sent along a sensory neurone to the Central Nervous System.
  2. In the Central Nervous System the sensory neurone passes on the message to the relay neurone.
• 3. Relay neurone relays the impulses to a motor neurone.

  4. The impulse then travels along the motor neurone to the effector.

  5. The muscle then contracts and moves your hand away from the stimulus.
• This happens really fast because the neurones in reflex arc go through the spinal cord or through an unconscious part of the brain.
• Some - stimulus

  Really - receptor

  Sexy - sensory neurone

  Russians - relay neurone

  Make - motor neurone

  Elephant - effector

  Rugs - response
• • conjunctiva - lubricates and protects the surface of the eye
  • sclera - the tough outer layer that protects the eye
  • cornea - refracts light into the eye shape. its transparent and has no blood vessels to supply it with oxygen so oxygen diffuses in from the outer surfaces.
• • iris - controls the diameter of the pupil therefore how much light enters the eye.
  • lens - focuses light onto the retina.
  • retina - light sensitive part which is covered in rods and cones. Rods are more sensitive in dim light and can't sense colour + cones are sensitive to colour but aren't so good in dim light. There are loads of cones at the fovea.
  • the optic nerve - carries impulses from the receptors to the brain
• Very bright light can damage the retina so humans have a reflex to protect it.

  1. very bright light triggers a reflex making the pupils smaller allowing less light in. circular muscles contract and radial muscles relax
  2. in dim light, the radial muscles contract which makes pupils bigger , circular muscles relax.
• To look at distant objects:

  1. the ciliary muscles relax which allows the suspensory ligaments to pull light. This makes the lens go thin so it refracts light by a smaller amount.
• To look at near objects: CCC

  1. the ciliary muscles contract which slackens the suspensory ligaments, the lens become more curved which increases the amount it reflects light.
• short sighted people are unable to focus on distant objects which occurs when the cornea or lens bends the light too much or the eyeball is too long.
• long sighted people are unable to focus on near objects as the cornea or lens doesn't bend enough light or the eyeball is too short. The images are brought into focus behind the retina.
• Hormones are chemicals released directly into the blood. they only;y affect particular cells in particular place. They are produced in glands and travel quite slowly which tend to have long lasting effects.
• Adrenaline comes from an adrenal glands(on top of the kidneys)
• Adrenaline readies the body for a "fight or flight" response. it increases heart rate, blood flow to the muscles and blood sugar level.
• Insulin is produced in the pancreas. Its role is to help control the blood sugar level. Its effect is that it stimulates the liver to turn glucose into glycogen for storage.
• Testosterone is produced in the testes and its the main male sex hormone. It promotes male secondary sexual characteristic e.g. facial hair
• Progesterone is produced in the ovaries and its role is to support pregnancy. It does this by maintaining the lining of the uterus.
• Oestrogen is produced in the ovaries. This is the main female sex hormone. It controls the menstrual cycle and promotes female secondary characteristics e.g widening of the hips
• ADH is produced in the pituitary gland (in the brain), it controls water content. It increases the permeability of the collecting ducts in the kidneys.
• FSH is produced in.the pituitary gland. It's a female sex hormone that causes an egg to mature in an ovary. stimulates the ovaries to produce oestrogen.
• LH is produced in the pituitary gland and stimulates the release of an egg from the ovaries. It's a female sex hormone.
• Nerves; very fast message, acts for a very short time , act on a very precise area
• Hormones: slower message, act for a long time, act in a more general way
• If a response lasts for a long time, it's probably hormonal.
• Homeostasis os the maintenance of a constant internal environmental.
• Water is taken into the body as food and drink and is lost from the body by sweat, urine and breathing.
• The enzymes in the human body work best at 37 degrees and so this is the temperature your body tries to maintain. A part of your brain acts as your own personal thermostat. It's sensitive to the blood temperature in the skin that provides information about skin temperature.
• 1. When you're too hot, lots of sweat is produced, when its evaporates it transfers energy from your skin to the environment, cooling you down.
• 2. When you're too hot, vasodilation is when your blood vessels close to the surface of the skin widen. It allows more blood to flow near the surface so it can transfer more energy into the surroundings which cools you down.
• 3. When your too hot, hairs lie flat on the skin.
• 1. When your too cold, very little sweat is produced
  2. Vasoconstriction (blood vessels near the surface constrict) so less blood flows near the surface so less energy is transferred to the surroundings.
  3. you can shiver, increases your rate of respiration, transfers more energy to warm the body. Exercise does the same
  4. Hairs stand on end to trap an insulating layer of air which helps keep you warm.