5.1.3 Neuronal Communication

• What type of neurone is shown below

  Sensory

  A) dendron

  B) cell body

  C) axon

  
• Which neurone?

  Motor

  A) nodes of ranvier

  B) Schwann cells

  C) axon

  
• Pacinian Corpuscle

  1. when pressure is applied, the layers of connective tissue are distorted - stretch mediated Na+ channels open and the Na+ enter
  2. generator potential reached - action potential
  3. Depolarisation
• How is a resting potential established

  1. Na+/K+ pump
  2. 3 Na+ out and 2 K+ in
  3. Inside the cell is more negative than outside
  4. electrochemical gradient
• 3 processes of the Schwann cells

  1. Electrical insualtion
  2. Phagocytosis
  3. nerve regeneration
• Myelinated Axons

  1. Conduct faster impulses
  2. Saltatory Conduction - impulse jumps from one node of Ranvier to another
  3. impulse does not have to travel whole length of axon
• Depolarisation

  1. Stimulus cases facilitated diffusion of Na+ into cell
  2. Potential difference in cell is more postivie
  3. reaches threshold potential (-50mV), voltage-gated Na+ channels open
• Repolarisation

  1. Voltage-gated Na+ close and the voltage-gated K+ open
  2. potential difference in the cell becomes more negative
• Hyperpolarisation

  1. Potential difference becomes more negative than the resting potential
  2. Enters the refractory period - no stimulus is large enough to raise the potential above the threshold
  3. Voltage-gated K+ close and the Na+/K+ re-establishes resting potential
• Importance of refractory period

  1. no action potential can be generated
  2. ensures impulse travels in one direction
  3. limits the frequency of the impulse transmission - larger stimuli have higher frequency
• Local Current

  • Na+ diffuses sideways along the neurone
  • causes slight depolarisation opens the voltage-gated Na+ channels
  • this causes full depolarisation
  • action potential moved along the neurone
• Presynaptic --> postsynaptic neurones

  1. Action potenial opens the voltage-gated Ca2+ channels in the bulb
  2. Ca2+ fuses with the presynaptic membrane and are released via exocytosis
  3. Acetylcholine diffuses across the cleft and binds to receptor sites on the Na+ channels on the postsynaptic membrane
  4. generator potential created by the opening of Na+.
• Inhibitory synapse

  1. Neurotransmitter binds to and opens Cl- channels on the post synaptic membrane triggering K+ channels to open
  2. Cl- move in and K+ diffuses out
  3. potential difference becomes more negative - hyperpolarisation
  4. No action potential
• Temporal summation

  One presynaptic neurone releases neurotransmitter to many postsynaptic neurone
• Spatial Summation

  multiple presynaptic neurone releasing neurotransmitter to one postsynaptic
• Acetylcholinesterase

  1. hydrolyses acetylcholine into acetyl and choline
  2. diffuses back into the presynaptic membrane
  3. ATP reforms acetylcholine
• Features common to all neurones

  1. cell body; organelles and high proportion of RER
  2. Dendrons - branch into dendrites and carry impulse towards the cell body
  3. Axon - long, unbranched, carries impulse away from the cell body
• Transducers

  Convert one form of energy into another
• Significance of frequency of impulse transmission

  Larger the stimuli, the more frequent the impulse. the amplitude is the same.
• Inhibitory and Excitatory Neurotransmitter

  1. Inhibitory - prevent generation of action potential by opening K+ channels causing hyperpolarisation
  2. Excitatory - stimulate generation of action potentials by opening Na+ channels.