neurons and synaptic transmission

• neuron


  the basic building blocks of the neurons system, neurons are nerve cells that process and transmit messages through electrical and chemical signals
• sensory neurons 


  carry messages from the PNS to the CNS

  have long dendrites and short axons
• relay neurons 


  these connect the sensory neurons to the motor or other relay neurons

  short dendrites and short axons
• motor neurons


  connect the CNS to effectors such as muscles and glands

  short dendrites and long axons
• neuron sizes


  less than a millimetre to up to a metre long
• cell body

  • includes nucleus (contains genetic material)
  • branch- like structures (dendrites, protrude from cell body- carry nerve impulses from neighbouring neurons towards the cell body)
  • axon- carries the impulses away from cell body- covered in fatty layer of myelin sheath that protects axon
  • myelin sheath- segmented by gaps called nodes of Ranvier
  • nodes of Ranvier- speed up transmission of the impulse by forcing it to jump
  • terminal buttons- at end of axon- communicate with the next neuron
• electric transmission- the firing of a neuron

  • neuron is in a resting state, inside cell is negatively charged compared to outside
  • neuron is activated by stimulus, inside of the cell becomes positively charged for a split second causing an action potential to occur
  • creates and electrical impulse that travels down the axon towards the end of neuron
• chemical transmission

  • neurons communicate with each other within groups known as neural networks
  • neurons are separated by the next synapse
  • synapse includes the space between them- synaptic cleft
  • signals within neurons are transmitted electrically- signals between neurons are transmitted chemically
  • electrical impulse reaches the end of neuron it triggers release of neurotransmitters
• neurotransmitter 


  brain chemicals released from synaptic vesicles that relay signals across the synapse from one neuron to another

  they can be broadly divided into those that perform an excitatory function
• excitation


  when a neurotransmitter, like adrenaline, increases the positive charge of the postsynaptic neuron increases the likelihood that it will fire
• inhabitation 


  when a neurotransmitter, like serotonin, makes the change of the postsynaptic neuron more negative when a neurotransmitter, like serotonin, makes the change of the postsynaptic neuron more negative

  decreases the likelihood it will fire
• summation 


  • whether the postsynaptic neuron will fire or not= decided by summation
  • excitatory and inhibitory influences are summed
  • if net effect on the postsynaptic neuron is inhibitory then postsynaptic neuron is less likely to fire
  • once electrical impulse is created, it travels down the neuron