Action Potentials

• The graph above shows the voltage changes which occur across a nerve cell membrane during an action potential.

  Which point corresponds to membrane depolarisation?

  B

  
• Which point on the above graph represents membrane hyperpolarisation?

  D

  
• At which point are the gated potassium channels fully open?

  C

  
• What is the approximate value of the membrane potential at point X?

  -70mV

  
• What is the approximate value of the membrane potential at point Y?

  30mV

  
• On average, how long do the voltage changes occurring during an action potential take to occur in atypical nerve cell?

  1 millisecond
• An action potential is only generated when a stimulus exceeds a certain threshold level, and the size of the action potential remains constant no matter how much greater than threshold the stimulus is. This is known as:

  The all-or-none law
• Place the following events in the correct order of occurrence during an action potential:

  1. Gated Na+ channels open and allow Na+ ions to rush into the nerve cell
  2. The nerve cell returns to its resting state
  3. A stimulus of threshold strength or above is applied to the nerve cell
  4. The membrane polarisation changes from negative to positive
  5. Gated K+ channels open, and K+ ions flow out of the nerve cell

  3 1 4 5 2
• The speed of propagation of an action potential (conduction velocity) is increased by which one of the following?

  Myelination
• The Relative Refractory Period in nerve cells is caused by:

  1. slow opening of gated sodium channel
  2. slow closure of gated potassium channels
  3. temporary lack of available sodium ions for adequate depolarisation
  4. accumulation of excess sodium ions inside the cell
  5. complete closure of all gated ion channels in the membrane

  2
• Myelin is synthesised by:

  1. Schwann cells
  2. the nodes of ranvier
  3. secretions from nerve axons
  4. fibroblasts in the connective tissue surrounding cells
  5. the nerve cell bodies

  1
• Which of the following are examples of neurotransmitters released from nerve cell terminals?

  I. acetylcholine;

  II dopamine;

  III. 5-hydroxytryptamine;

  IV. noradrenaline;

  V. glutamine

  All of the above
• At an inhibitory synapse;

  1. Release of the neurotransmitter from the pre-synaptic neurone increases the likelihood of generating an action potential in the post-synaptic neurone
  2. Neurotransmitter release is inhibited at the synaptic terminal
  3. Post-synaptic receptor sites are blocked
  4. Release of the neurotransmitter from the pre-synaptic neurone decreases the likelihood of generating an action potential in the post-synaptic neurone
  5. Synaptic vesicles are destroyed

  4
• A rapid change in membrane potential that propagates along a neuron's axon


  Action potential
• What is required for signal transmission along a neuron

  Multiple action potentials in sequence
• What is the direction of propagation?

  From one end of the axon to the other
• A fatty insulating sheath surround axons

  Myelin
• What cells produce myelin

  Schwann cells
• How it myelin arranged around the axon

  In concentric layers
• Gaps in themeylin sheath along an axon

  Node of Ranvier