Neurons and synaptic transmission AO1

• There are 100 billion neurons (nerve cells) in the human nervous system, 80% of which are located in the brain
• Neurons


  Nerve cells that process and transmit messages through electrical and chemical signals
• Types of neurons


  • Motor neurons
  • Sensory neurons
  • Relay neurons
• Neurons


  • Vary in size from less than a millimetre to up to a metre long
  • All share the same basic structure
• Cell body (soma)


  Includes a nucleus, which contains the genetic material of the cell
• Dendrites


  Branch-like structures that protrude from the cell body and carry nerve impulses from neighbouring neurons towards the cell body
• Axon


  Carries the impulses away from the cell body down the length of the neuron
• Myelin sheath


  Fatty layer that protects the axon and speeds up electrical transmission of the impulses
• Nodes of Ranvier


  Speed up the transmission of the impulse by forcing it to 'jump' across the gaps along the axon
• Terminal buttons


  Communicate with the next neuron in the chain across a gap known as the synapse
• Resting state


  Inside of the cell is negatively charged compared to the outside
• Activated state


  Inside of the cell becomes positively charged for a split second causing an action potential toward the end of the neuron
• Neural networks


  Groups of neurons that communicate with each other
• Synapse


  Space between neurons, includes the presynaptic terminal and postsynaptic receptor site
• Synaptic transmission


  1. Electrical impulse reaches presynaptic terminal

  2. Triggers release of neurotransmitters from synaptic vesicles

  3. Neurotransmitters diffuse across synapse

  4. Taken up by postsynaptic receptor sites

  5. Chemical message converted back into electrical impulse
• Neurotransmitters


  • Acetylcholine (ACh)
  • Serotonin
  • Adrenaline
• Neurotransmitters


  Have either an excitatory or inhibitory effect on the neighbouring neuron
• Summation


  1. Excitatory and inhibitory influences are summed

  2. If net effect is inhibitory, postsynaptic neuron is less likely to fire

  3. If net effect is excitatory, postsynaptic neuron is more likely to fire
• Increased understanding of neurotransmitters has led to development of psychoactive drugs to treat mental disorders
• SSRIs (selective serotonin reuptake inhibitor)


  Drugs that down the reuptake of serotonin after it has crossed the synapse, ensuring it stays active for longer in the brain