cordination

• How an action potential is transmitted along a sensory neurone in a mammal

  1. Action potential stimulates neighbouring area of membrane

  2. Na+ moves sideways/attracted to areas at resting potential

  3. Local circuit causes Na+ ion channels to open/2nd depolarisation

  4. Transmission in one direction due to hyperpolarisation/refractory period

  5. Myelin sheath/Schwann cell insulates axon/dendron/neurone

  6. Depolarisation/action potential only at nodes of Ranvier/unmyelinated part

  7. Saltatory conduction/action potential 'jumps' from node to node
• Roles of synapse

  • Ensure one-way transmission
  • Filter out infrequent impulses/temporal summation
  • Allow interconnection/integration of nerve (cell) pathways/many neurones
  • Spatial summation/convergence of impulses/divergence of impulses
  • Role of memory/learning
  • Inhibitory effect
• How myelin sheath increases speed

  1. Myelin insulates axon

  2. Action potentials/depolarisation only at nodes (of Ranvier)

  3. Local circuits set up between nodes

  4. Action potentials/impulses 'jump' from node to node or saltatory conduction
• Tropomyosin


  Covers/uncovers myosin binding sites on actin
• Myosin


  • ATP hydrolysis causes head to pivot/rotate/tilt/stand up
  • Binds to actin to form cross-bridges
  • ADP and Pi detach
  • Head swings back/returns to previous position
  • New ATP binds
  • Detaches from actin/cross-bridges break
• Sensory receptor cells in mammalian nervous system

  • Detect/respond to change in stimulus
  • Examples: light/heat/sound/touch/pressure/pain/chemicals/taste/smell/tension
  • Act as transducers/convert stimulus energy to electrical energy
  • Produce generator/receptor/action potential
  • Passes impulse to/along sensory neurone
• ATP in contraction of striated muscle

  • Myosin binding site exposed
  • Myosin head binds to actin/forms cross bridge
  • ADP released causes motion of myosin head
  • Actin moved
  • Power stroke
  • ATP binds to myosin head
  • Myosin head detaches from actin
  • Myosin head/ATPase causes hydrolysis of ATP
  • Myosin head moves back to original position
  • ATP needed to pump Ca2 back into sarcoplasmic reticulum
• How gibberellin is involved in activating genes for stem elongation

  1. DELLA proteins prevent activation of genes

  2. Gibberellin binds to receptors (on cell surface membrane)

  3. Causes breakdown of DELLA proteins

  4. Transcription/gene expression/gene activation/mRNA synthesis can occur
• Role played by gibberellin in germination

  1. Seed absorbs water

  2. Embryo produces gibberellin

  3. Gibberellin moves to/acts on/stimulates aleurone layer

  4. Production of amylase occurs

  5. Amylase hydrolyses/breaks down starch in endosperm

  6. Embryo uses sugars for respiration/growth
• Acetylcholinesterase


  • Breaks down acetylcholine
  • So acetylcholine leaves binding site/receptor
  • Depolarisation stops in post-synaptic membrane
  • Stops continuous action potentials (in post-synaptic membrane)
  • Recycles ACh
• Venus fly trap

  1. Action potential/depolarisation reaches lobe (of leaf)

  2. H+ pumped out of cells/pumped into cell walls

  3. Cell wall loosens / cross-links broken

  4. Calcium pectate dissolves/breaks down (in middle lamella)

  5. Ca2+ (ions) enter cells

  6. Water enters, by osmosis/ down water potential gradient

  7. Hinge/midrib cells expand/become turgid

  8. Leaves/lobes become concave
• Negative Feedback


  1. Change in a parameter detected by receptor

  2. Coordination/described

  3. Corrective action taken by effector

  4. Return to set point/norm/optimum
• How dip sticks function to test for glucose in a sample of urine


  1. Dip stick has immobilised enzymes

  2. Dipped in urine

  3. Glucose oxidase and peroxidase

  4. Glucose reacts to give hydrogen peroxide

  5. Hydrogen peroxide reacts with colourless substance/chromogen to give colour change

  6. Compare with colour chart

  7. More glucose gives darker colour/colour intensity gives glucose quantity
• Ultrastructure of striated muscle

  • Fibres are multinucleate
  • Cell surface membrane is sarcolemma
  • Sarcoplasm has many mitochondria
  • Sarcoplasmic reticulum membranes have protein pumps
  • Transverse system tubules/T-system
  • Thick filament/myosin, attached to M line
  • Thin filament/actin, attached to Z line
  • Interdigitation of filaments causes striated appearance
  • Description of A/H/I bands
  • Sarcomere is the distance between M lines
  • Myosin is a fibrous protein with globular protein head
  • Actin is a chain of globular protein molecules
  • Tropomyosin/troponin, attached to actin