Unit 6 bio

• Stimulus


  A detectable change in the environment
• Receptors


  Cells that can detect changes in the environment
• Tropisms


  • Plant responses to their surroundings via growth
  • Can be positive (grow towards stimulus) or negative (grow away from stimulus)
  • Stimuli are light and gravity
• Auxin (IAA)


  Growth factor that controls cell elongation in shoots and inhibits growth in roots
• Phototropism


  1. Shoot tip cells produce IAA

  2. IAA diffuses to shady side

  3. Cells on shady side elongate

  4. Shoot bends towards light
• Gravitropism


  1. IAA diffuses to lower side of shoot

  2. Lower cells elongate

  3. Shoot bends upwards against gravity
• Gravitropism in roots


  1. IAA moves to lower side

  2. Upper cells elongate

  3. Root bends downwards towards gravity
• Reflex


  Rapid automatic response to protect from danger
• Reflex arc


  Made up of 3 neurons: sensory, intermediate, motor
• Taxis


  Organism moves its entire body towards or away from a stimulus
• Kinesis


  Organism changes speed of movement and rate of direction changes in response to stimuli
• Pacinian corpuscles


  • Pressure receptors in deep skin
  • Contain stretch-activated sodium channels
  • Detect pressure changes
• Rods


  • Photoreceptors in retina
  • Detect light at low intensities
  • Provide black and white vision with low acuity
• Cones


  • Photoreceptors in retina
  • Detect colour at high light intensities
  • Provide high visual acuity
• Cardiac muscle is myogenic - it contracts and relaxes on its own
• Structures controlling heart rate

  • Sinoatrial (SA) node (pacemaker)
  • Atrioventricular (AV) node
  • Bundle of His
  • Purkinje fibres
• Cardiac cycle control


  1. SA node depolarization spreads to atria

  2. AV node delays depolarization

  3. Depolarization travels down Bundle of His and Purkinje fibres to ventricles
• Wave of depolarization


  Electrical impulse that travels through the heart
• Non-conductive layer of tissue

  • Separates the atria and ventricles
  • Prevents the wave of depolarization traveling straight down to the ventricles
• Wave of depolarization travels

  1. Released by the AV node

  2. Travels down the bundle of His

  3. Travels up through the Purkinje fibers
• Delay


  Time it takes for the apex of the heart and the ventricle walls to contract
• Advantage of delay


  • Allows the atria to contract and force blood into the ventricles before the ventricles contract
  • Ventricles contract from the apex first and then move upwards, forcing all the blood out
• Cardiac muscle contraction and relaxation cycle

  1. Cells depolarize

  2. Cells repolarize and relax
• Autonomic nervous system


  Controls the heart rate automatically, without conscious control
• Parts of the autonomic nervous system


  • Sympathetic nervous system
  • Parasympathetic nervous system
• Sympathetic nervous system


  Increases heart rate by causing the SA node to release depolarization waves more frequently
• Parasympathetic nervous system


  Decreases heart rate by causing the SA node to release depolarization waves less frequently
• Stimuli that change heart rate

  • pH
  • Blood pressure
• Chemoreceptors


  Detect changes in pH
• Pressure receptors


  Detect changes in blood pressure
• Location of chemoreceptors and pressure receptors

  Walls of the aorta and carotid artery
• High respiratory rate


  Decreases blood pH due to excess CO2 and lactic acid
• Decreased blood pH


  Increases heart rate to remove excess CO2
• High blood pressure


  Increases impulses through the parasympathetic nervous system to decrease heart rate
• Low blood pressure


  Increases impulses through the sympathetic nervous system to increase heart rate
• Myelinated motor neuron structure

  • Cell body with organelles
  • Dendrites carrying action potentials
  • Axon conducting nerve impulses
  • Schwann cells forming myelin sheath
  • Nodes of Ranvier where axon is not insulated
• Resting potential


  Difference in electrical charge inside and outside the axon when no stimulus is present (-70 mV)
• Establishment and maintenance of resting potential

  1. Sodium-potassium pump actively transports 2 K+ ions in and 3 Na+ ions out

  2. Creates electrochemical gradient

  3. More K+ ions diffuse out than Na+ ions diffuse in, resulting in net negative charge inside
• Action potential


  Increase in voltage beyond the threshold (-55 mV) that generates a nervous impulse
• Generation of action potential

  1. Stimulus opens voltage-gated Na+ channels

  2. Na+ ions diffuse in, causing depolarization

  3. More Na+ channels open, further depolarizing

  4. Voltage-gated Na+ channels close, K+ channels open, repolarization occurs