Unit 3 - Organism Level Systems

• Central nervous system


  Part of the nervous system made up of the brain and spinal cord
• Nervous system


  • Made up of neurones
  • Goes to all parts of the body
• Sensory receptors


  • Detect a change in the environment
  • Different receptors detect different stimuli
• Detecting a stimulus

  1. Receptors detect stimulus

  2. Information sent as nervous impulses along sensory neurones

  3. Impulses travel to the CNS
• CNS


  Coordinates the response
• Responding to a stimulus

  1. Impulses travel through the CNS along relay neurones

  2. CNS sends information to an effector along a motor neurone

  3. Effector responds accordingly
• Neurones

  • Electrical impulses are passed along the axon of a neurone.
  • The structure of sensory and motor neurones are slightly different. However, both types of neurones have branched ending, so they can connect with low of other neurones.
  • Some atoms are also surrounded by a fatty (myelin) sheath. This acts as an electrical insulator, speeding up the electrical impulse.
  • Neurones are long, which also speeds up the impulse. Connecting with another neurone slows the impulse down, so one long neurone is much quicker than lots of short ones joined together.
• Synapse's

  The connection between two neurons is called a synapse. It's basically just a very tiny gap.

  • The electrical impulse trigger the release of transmitter chemicals, which diffuse across the gap.
  • These chemicals bind to receptor molecules in the membrane of the next neurone. This sets off a new electrical impulse.
• Sensory neurone

  A) receptor cell

  B) Myelin sheath

  C) long dendron

  D) cell body

  E) short axon

  F) axon

  
• Relay neurone

  A) Dendrite

  B) Cell body

  C) Axon

  
• Motor neurone

  A) Dendrite

  B) Cell body

  C) long axon

  D) myelin sheath

  E) effector cells

  F) ---> direction of impulse

  
• Reflex actions

  • Reflex actions are automatic, so they're even quicker than normal responses. The passage of information in a reflex is called a reflex arc.
  • The conscious brain isn't involved in a reflex arc. The sensory neurone connects to a relay neurone in the spinal cord. This links directly to the right motor neurone, so no time is wasted thinking about a response.
• Hormones

  • Hormones are chemical produced in various glands called endocrine glands. These glands make up your endocrine system.
  • Hormones are released directly into the blood. The blood then carries them to other parts of the body.
  • They travel all over the body, but they only affect particular cells in particular places.
  • The affected cells are called target cells - they have the right receptors to respond to that hormone.
• Adrenaline

  A hormone released by the adrenal gland that prepares the body for 'flight or fight'
• Adrenaline

  • Increases the supply of oxygen and glucose to cells
• How adrenaline prepares the body for 'flight or fight'


  1. Adrenaline binds to receptors in the heart

  2. Increases heart rate and blood pressure

  3. Increases blood flow to muscles

  4. Increases oxygen and glucose supply to muscle cells

  5. Adrenaline binds to receptors in the liver

  6. Causes liver to release glucose into the bloodstream

  7. Increases blood glucose level
• Effects of adrenaline

  • Increases heart rate and blood pressure
  • Increases blood flow to muscles
  • Increases blood glucose level
• Negative feedback

  • Your body can control the levels of hormones in the blood using negative feedback systems. When the body detects that the level of a substance has gone above or below the normal level, it triggers a response to bring the level back to normal.
• Thyroxine

  • Thyroxine is a hormone released by the thyroid gland.
  • It controls your metabolism. It also helps growth and protein synthesis.
  • Thyroxine is released in response to thyroid stimulating hormone (TSH), which is released from the pituitary gland.
• Sex hormones

  • Testosterone - this is the main male sex hormone. It's produced in the testes.
  • Oestrogen - this is the main female sex hormone. It's produced in the ovaries and involved in the menstrual cycle.
  • Progesterone - this is produced in the ovaries. It helps to support pregnancy and is involved in the menstrual cycle.
  • FSH and LH - these hormones are released from the pituitary gland in the brain. They help control the menstrual cycle.
• The menstrual cycle

  The menstrual cycle is the monthly sequence of events. This is what happens at each stage:

  • Day 1 is when menstruation starts. The uterus lining is released.
  • 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.
  • The lining is then maintained for about 14 days, until day 28. If no fertilised egg has implanted into the uterus wall by day 28, the spongy lining starts to break down again and the whole cycle starts over.
• The 4 hormones in the menstrual cycle

  • FSH - causes an egg to mature in one of the ovaries - stimulates the ovaries to produce oestrogen.
  • Oestrogen - causes the lining of the uterus to thicken and grow - stimulates the production of LH - inhibits the production of FSH so only one egg is released.
  • LH - stimulates the release of an egg at day 14 - indirectly stimulates progesterone production.
  • Progesterone - maintains the lining of the uterus. When the level of progesterone falls and there's a low oestrogen level, the lining breaks down - inhibits the production of FSH and LH.
• Contraceptives

  Method - injection, implant, mini-pill, intrauterine system.

  Hormones included - progesterone

  How it works - Stimulates the production of thick cervical mucus making it less likely that any sperm will get through. Thins lining of the uterus to reduce the chance of pregnancy. Prevents ovulation by stopping the production of FSH and LH.

  Method - combined pill, patch.

  Hormones included - progesterone and oestrogen

  How it works - all the effects above, plus oestrogen also prevents ovulation.
• Non-hormonal contraceptive

  • Barrier methods - these try to stop the egg and sperm meeting.
  • Intrauterine devices - T-shaped devices that contain copper. They're inserted into the uterus and prevent sperm from surviving.
  • Sterilisation - involves a surgical procedure to cut or tie tubes in the reproductive system.
• Blood sugar levels

  • Conditions in your body need to be kept steady - this is so all the metabolic reactions vital for keeping you alive can continue.
  • To maintain a constant internal environment, your body needs to respond to both internal and external changes.
  • For example, the level of glucose in the blood must be kept steady:
  • Eating foods containing carbohydrates puts glucose into the blood from the small intestine. The normal metabolism of cells remove glucose from the blood.
  • Excess glucose can be stored as glycogen in the liver and muscles.
• Type 1 diabetes

  This is where the pancreas produces little to no insulin. The result is that a person's blood glucose level can kill them, People with type 1 diabetes need insulin therapy. This usually involves injecting insulin several times a day. This makes sure that glucose is removed from the blood and stops glucose levels from getting to high. The amount of insulin needed depends on the person's diet and how active they are.
• Type 2 diabetes

  This is where a person becomes resistant to insulin. Being overweight can increase your chance of developing type 2 diabetes.