B3 - Organism Level Systems

• What does your CNS do?

  Co-ordinates a response (decides what to do about the stimulus).
• What is your nervous system made up of?

  Neurons (nerve cells) which go to all parts of the body.
• Your body has lots of sensory receptors. What are these?

  Things that detect a change in your environment (a stimulus). Different sensory receptors detect different stimuli.

  E.g. receptors in your eye detect light

  receptors in your skin detect touch (pressure) and temp. change
• What happens when a stimulus is detected by a receptor?

  The information is sent as nervous (electrical) impulses along sensory neurons to the central nervous system (CNS).
• What does the CNS consist of?

  The brain and the spinal cord.
• What happens after the information is sent to the CNS?

  It coordinates a response and sends the information to an effector (muslce/gland) along a motor neurone. The effector then responds accordingly (e.g. a muscle may contract or a gland may secrete a hormone).
• What's the difference between the sensory neurons and motor neurons?

  Sensory neurons connect the receptors and the CNS, motor neurons connect the CNS and the effectors.
• How do neurons transmit information?

  As electrical impulses.
• Electrical impulses are passed along what?

  The axon of the neuron

  
• What allows neurons to connect with lots of other neurons?

  Their dendrites (branched endings)
• Some axons are surrounded by what?

  Fatty (myelin) sheath.

  This acts as an electrical insulator, speeding up the electrical impulse.

  
• How are neurons designed to speed up the impulse?

  They are long; connecting with another neuron slows down the impulse, so one long one is much quicker than many short ones.
• What is a synapse?

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

  
• How are electrical impulses transferred between neurones?

  The electrical impulse triggers 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.
• What are reflex actions and how are they useful?

  Reflex actions are automatic (done without thinking) so they're even quicker than normal responses.

  Reflex actions stop you injuring yourself.
• What is a reflex arc?


  The passage of information in a reflex.
• What isn't involved in a reflex arc?

  The conscious brain. The sensory neurone connects to a relay neurone in the spinal cord or an unconscious part of the brain - which links directly to the right motor neurone, so no time's wasted when thinking about the right response.

  
• What do relay neurons do?

  Connect sensory neurons to motor neurons.
• What is the role of reflex actions?

  They have a protective role.

  E.g. snatching back hand when touching hot plate
• Give an example of a reflex arc after a bee sting?

  1) Bee stings finger

  2) Stimulation of pain receptor

  3) Message travels along sensory neurons

  4) Message is passed along a relay neurone.

  5) Message travels along a motor neurone.

  6) When message reaches muscle, it contracts to move arm away from bee.
• Label the eye with the cornea, iris, lens, pupil, ciliary body, suspensory ligaments, optic nerve and retina.

  
• What does the cornea do?

  Refracts (bends) light into the eye.

  
• What does the iris do?

  Controls how much light enters the pupil (hole in middle).

  
• What does the lens do?

  Refracts light, focusing it onto the retina.

  
• What do the ciliary body and suspensory ligaments do?

  The ciliary body, which has ciliary muscles, which are attached to suspensory ligaments - they work together to alter the shape of the lens.

  
• What is the retina?

  The light sensitive part of the eye. It's covered in receptors called rods and cones, which detect light.

  
• What do rods and cones do?

  Detect light.
• Describe rods?

  Rods are more sensitive in dim light but can't sense colour.
• Describe cones?


  Cones are sensitive to different colours but are not so good in dim light.
• What does the optic nerve do?

  Carries impulses from the receptors to the brain.

  
• Why is the lens elastic?

  So the eye can focus light by changing the shape of the lens.
• What happens when we look at distant objects?

  The ciliary muscle relaxes, which allows the suspensory ligaments to pull tight.

  This pulls the lens into a less rounded shape, so light is refracted less.
• What happens when we look at close objects?

  The ciliary muscle contracts, which slackens the suspensory ligaments.

  The lens becomes a more rounded shape, so light is refracted more.
• What is long sightedness?

  Long sighted people are unable to focus on near objects.
• When does long sightedness occur?

  This occurs when the lens is the wrong shape, and doesn't bend the light enough, or the eyeball is too short. When you're long sighted, the images of near objects are brought into focus behind the retina
• How can long sightedness be corrected?

  You can use glasses or contact lenses with a convex lens to correct it.
• What is short-sightedness?


  Short sighted people are unable to focus on distant objects.
• When does short-sightedness occur?

  This occurs when the lens is the wrong shape, and bends the light too much or the eyeball is too long. The images of distant objects are brought into focus in front of the retina.
• How can short sightedness be corrected?

  You can use glasses or contact lenses with a concave lens to correct it, or an alternative is corneal laser surgery.
• What is colour blindness?

  Colour blind people can't tell the difference between certain colours. The most common form of the disorder is red-green colour blindness. It is caused when red or green cones (photoreceptor cells) in the retina are not working properly.