neurons & synaptic transmission

• neuron


  - Basic building blocks of the nervous system.

  - Nerve cells that process and transmit messages through electrical & chemical signals
• how many neurons are in the body?

  100 billion and 80% are in the brain
• function and structure of the sensory neuron

  Function = carry message from the PNS to CNS

  
  

  Structure = long dendrites & short axons
• function and structure of the relay neuron

  Function = connect sensory neurons to motor neurons or other relay neurons

  
  

  Structure = short dendrites
• function and structure of the motor neuron

  Function = connect the CNS to effectors

  
  

  Structure = short dendrites & long axons
• axon


  carries impulses away from the cell body

  - covered in the fatty layer of the myelin sheath which protects it and speeds up the electrical transmission
• dendrites


  branch-like structures which carry nerve impulses from neighbouring neurons towards the cell body
• myelin sheath


  nodes of ranvier
• electrical transmission (firing of a neuron)

  - When in the resting state the inside of the cell is negatively charged compared to the outside

  - When it is activated by a stimulus, the inside becomes positively charged for a split-second causing an action potential

  Action potential = creates an electrical impose that travels down the axon to the end of the neuron
• synaptic transmission


  Process in which neighbouring neurons communicate with each other by sending chemical messages across the gap that separates them
• neurotransmitter


  - Chemicals that diffuse across the synapse to the next neuron

  - Taken up by the postsynaptic receptors (dendrites)

  - Then transferred back to an electrical message
• excitation


  When a neurotransmitter increases the positive charge of the postsynaptic neuron, it increases the likelihood that the neuron will fire up and pass on the electrical impulse
• example of excitation


  Adrenaline is both a hormone and a neurotransmitter.
• inhibition


  When a neurotransmitter increases the negative charge of the postsynaptic neuron,it decreases the likelihood that the neuron will fire up and pass on the electrical impulse
• example of inhibition


  Serotonin
• summation


  Whether a post-synaptic neuron fires is decided by summation.

  That means how the excitatory and inhibitory influences are summed

  - if the net effect on the post-synaptic neuron is inhibitory, it is less likely to fire.

  -If the net effect on the post-synaptic neuron is excitatory, it is likely to fire as it will become positively charged and travel down the neuron.
• synaptic transmission (steps)


  1. electrical impulse reaches a presynaptic neuron (end)

  2. triggers release of neurotransmitters via synaptic vesicles

  3. neurotransmitter is taken up by postsynaptic receptor site

  4. transferred back to an electrical transmission