Neurons

• What is a Neuron?

  A neuron is a specialised cell that transmits information through electrical and chemical signals
• Around how many neurons are found in the nervous system?

  100 billion
• What is a sensory neuron?

  Transmits sensory information from the body to the CNS
• What is a motor neuron?

  Carries nerve impulses from the CNS to effectors (muscles and glands)
• What is a relay neuron?


  Found in the brain and spinal cord. They carry nerve impulses between neurons connecting sensory and motor neurons
• Sensory neuron


  labelled

  
• Motor neuron


  labelled

  
• Relay neuron


  labelled

  
• Structure of a neuron

  labelled

  
• What are Dendrites?


  Branch like structures of a neuron that receive signals from other neurons and send nerve impulses towards the cell body
• What is the Nucleus?

  Contains genetic information
• What is the Cell Body?

  Includes a nucleus where there is genetic information
• What is the Axon?


  Carries nerve impulses away from the cell body
• What is the Myelin Sheath?

  Insulates and protects the axon and helps to speed up the electrical transmission along the axon
• What are the Nodes of Ranvier?

  Gaps in the Myelin Sheath that force the impulse to 'jump' across gaps along the axon. This increases the speed of the electrical impulse
• What are the Terminal Buttons?

  Send impulses to the next neuron across the synapse through the release of neurotransmitters
• Neurons in action: Touching a hot pan

  1. Stimulus - you touch something hot
  2. Receptors in the skin detect a stimulus
  3. Sensory neuron sends electrical impulse to the relay in the spinal cord
  4. Relay neuron receives impulse and sends to the motor neuron
  5. Motor neuron sends impulse to an effector
  6. Effector produces a response which is moving your hand away
• Synaptic Transmission

  1. When the impulse reaches the end of the axon, it arrives at the pre synaptic terminal
  2. Are made of small structures called vesicles (contain neurotransmitters e.g serotonin)
  3. The electrical impulse that had travelled down the axon triggers the release of the neurotransmitter which diffuses down the synapse
  4. Then attach to the dendrites of the next neuron and the neurotransmitter is converted back into an electrical impulse
  5. Some go through a process of reuptake where excess neurotransmitters are reabsorbed back into the pre synaptic terminal
• What is Excitation?


  When a neurotransmitter increases the positive charge of the post synaptic neuron. This increases the likelihood the neuron will fire and pass on the electrical impulse
• What is Inhibition?


  When a neurotransmitter increases the negative charge of the post synaptic neuron. This decreases the likelihood the neuron will fire and pass on the electrical impulse
• Summation

  • Whether a post synaptic neuron fires is decided by summation
  • The action potential of the post synaptic neuron is only triggered if the sum of the excitatory and inhibitory signals at any one time meet the threshold
• Jeremy digs in the garden and feels the spade hit a rock and stops digging. Explain how sensory, relay and motor neurons would function in this situation

  • Sensory neurons send information from the senses to the brain
  • Receptors in Jeremy’s hand would sense the spade hitting the rock and send information to his CNS
  • Relay neurons act between sensory and relay neuron and decide how to respond to the situation
  • Motor neurons send messages to the muscles or effectors
  • The message from the brain instructs Jeremy’s arm muscles to stop working and stop the digging action