Neurons and synaptic transmision

• Neurons


  Nerve cells that process and transmit messages through electrical and chemical signals
• There are over 100 billion neurons in the human nervous system and 80 percent of those are located in the brain</b>
• Electrical transmission of information in neurons

  When a neuron is in a resting state the inside of the cell is negatively charged compared to the outside, when a neuron is activated by a stimulus the inside of the cell becomes positively charged for a split second which causes an action potential that travels down the length of the neuron
• Types of neurons


  • Sensory neurons
  • Relay neurons
  • Motor neurons
• Sensory neurons


  • Carry information from the peripheral nervous system to the central nervous system, found in receptors like eyes, ears, tongue, skin, carry impulses to the spinal cord and brain
• Motor neurons


  • Found in the central nervous system, connect the central nervous system to effectors like muscles and glands to control muscle movement, release neurotransmitters that bind to receptors on muscles to trigger a response
• Relay neurons


  • Found in the brain and spinal cord, allow sensory and motor neurons to communicate with each other
• Stimulus to response example

  1. Pain receptors in hand stimulated

  2. Sensory neuron carries information

  3. Relay neuron passes information

  4. Motor neuron triggers muscle movement to pull hand away
• Neuron structure


  • Dendrites
  • Cell body
  • Axon
  • Axon terminals
• Dendrites


  Branch-like structures that receive nerve impulses from neighbouring neurons or sensory receptors and carry information towards the cell body
• Cell body


  Includes the nucleus which contains the genetic material
• Axon


  Carries impulses in the form of an action potential away from the cell body down the length of the neuron to the axon terminals, insulated by the myelin sheath which speeds up transmission
• Axon terminals


  Responsible for communicating with the next neuron across the synapse
• Synaptic transmission


  The chemical transmission of information between neurons across the synapse
• Synaptic transmission


  1. Impulse arrives at presynaptic neuron

  2. Neurotransmitters released from vesicles into synapse

  3. Neurotransmitters diffuse across synapse

  4. Bind to postsynaptic receptor sites

  5. Converted back to electrical impulse in new neuron
• Neurotransmitters can only be released from the presynaptic neuron and bind to receptors on the postsynaptic neuron, not the other way around
• Examples of neurotransmitters


  • Serotonin
  • Dopamine
  • Acetylcholine
  • Adrenaline
• Excitation


  Neurotransmitters like adrenaline increase the positive charge of the postsynaptic neuron, making it more likely to fire an action potential
• Inhibition


  Neurotransmitters like serotonin decrease the positive charge of the postsynaptic neuron, making it less likely to fire an action potential
• Summation


  The net effect of excitatory and inhibitory signals determines whether the postsynaptic neuron reaches the threshold to fire an action potential
• Exam questions on neurons and synaptic transmission

  • 6 mark question applying knowledge
  • 3 mark labelling question
  • 4 mark question on neurotransmitter release
  • 4 mark question on excitation and inhibition
  • 6 mark question describing synaptic transmission
  • Open-ended question on how drug therapies work