Topic 9

• Define homeostasis


  The maintenance of a constant internal environment
• Examples of homeostasis control

  - temperature

  - water levels

  - glucose levels
• Stimulus and response


  stimulus - receptor - coordinator - effector - response
• What does the nervous system control

  nerve impulses
• What does the endocrine system control

  - hormone production and transportation
• What are the 3 neurons

  Sensory, relay and motor
• Define synapse


  junction between two neurons
• Define stimulus


  A change in the environment that produces a response
• Define reflex arc


  the nerve pathway involved in a reflex action including at its simplest a sensory nerve and a motor nerve with a synapse between.
• CNS


  brain and spinal cord
• What happens at the synapse

  When a nerve impulse reaches the synapse at the end of a neuron, it cannot pass directly to the next one. Instead, it triggers the neuron to release a chemical neurotransmitter. The neurotransmitter drifts across the gap between the two neurons.
• Cornea


  Transparent cover at the front of the eye that does most of the refraction of light rays.
• Pupil


  Hole in the iris that allows light to enter the eye.
• Iris


  Coloured muscle that controls the size of the pupil and therefore how much light enters the eye.
• Lens


  Changes shape to focus on the retina.
• Ciliary Muscles


  Contract or relax to change the shape of the lens.
• Suspensory Muscles


  Hold the lens in position.
• Retina


  A layer of light sensitive receptors. There are two types of light receptors: cones that can detect colour and rods that work in dim light to produce only black and white vision.
• Optic Nerve


  A bundle of sensory neurons that carry nerve impulses to the brain.
• Sclera


  Tough, white, protective outer layer of the eye.
• Fovea


  The most sensitive function of the retina.
• What happens to the pupils in dim light

  - they dilate because the radial muscles contract
• What happens to the pupils in bright light

  - they constrict because the circular muscles contract
• Focus on distant objects

  - ciliary muscles relax

  - suspensory ligaments tighten

  - lens thins
• Focus on close objects

  - ciliary muscles contract

  - suspensory ligaments relax

  - lens becomes rounder for more light refraction
• Fat layer


  insulation
• Sensory cells


  can detect heat/pressure
• Blood vessel near skin surface

  can dilate/contract to constrict the blood flow
• Erector muscle


  contacts to move the hair
• Sweat pore


  releases sweat onto our skin
• Hair


  traps a layer of air to insulate us
• Epidermis

  outer layer of dead cells
• Dermis


  Living layer of the skin
• Sweat gland


  makes sweat
• What happens in vasoconstriction

  blood flow in the skin decreases, lowering heat loss
• What happens in vasodilation

  blood flow in the skin increases, facilitating heat loss
• Why is thermoregulation important

  - because it keeps the internal temperature at the correct temperature so that everything in our bodies stay at the correct temperature to function
• Maintenance of blood glucose levels

  - glucose enters the digestive system and then blood

  - blood has a high blood glucose concentration

  - the pancreas monitors blood glucose levels and releases insulin

  - the blood then has insulin and glucose in it

  - the insulin then triggers the liver to remove the glucose from the blood

  - the blood then has a normal amount of glucose in it
• What is phototropism


  Growth in response to light
• What is positive phototropism

  When a plant grows towards the light