Renshaw Cell

• Renshaw Cell:

  • the Renshaw cell is another type of interneuron - it is an inhibitory interneuron
  • it is found in the ventral horn of the grey matter, located where the alpha motor neurones are located

  
• Renshaw Cell & AHC pt1:

  • alpha motor neurone (AHC) sends its axon out through ventral root to muscles
  • but AHC also almost immediately send lateral branch to an inhibitory interneuron called the Renshaw cell to from an excitatory synapse as AHC releases acetylcholine
  • this causes depolarisation of Renshaw cell, producing action potentials travelling down its axon to the same AHC
  • the synapse from the Renshaw cell to the AHC is inhibitory as the neurotransmitter is glycine, causing hyperpolarisation, causing the alpha motor neurone to reduce/stop frequency of action potentials

  
• Renshaw Cell & AHC pt2:

  • blue circle above represents a neurone from one of the descending tracts coming down to synapse to the alpha motor neurone (AHC) which is already constantly receiving excitatory input, if not the AHC would constantly generate action potentials, causing muscles to constantly contract - Renshaw cell prevents this as its a mechanism by which alpha motor neuron is switched off and reset, allowing burst of activity (what muscles require for contraction) instead of nonstop
  • so without Renshaw cell, output of AHC would just be constant action potentials generated

  
• Renshaw Cell & AHC pt3:

  • Renshaw cell helps prevent nonstop contraction and instead provide fractionated movements to produce discrete, time limited movements, important for dextrous activity
  • some pts have clostridium poisoning, where glycine is affected, so the Renshaw cells are "knocked out of action", causing pts to go into tetanus (spasms)

  
• Renshaw Cell & AHC pt4:

  • in reality theres inputs into the renshaw cell from the descending tracts, altering the level of activity of the renshaw cell
  • so the negative feedback loop can be ramped up or down in terms of its effect, so depending on the task and the motor behaviour, this negative feedback loop can be set accordingly ensuring the feedback loop is perfectly tuned with your activity to fractionate your movement