10. Motor System

• Motor system


  Refers to the nerve cells that are used to control our body whose two key roles are planning and executing voluntary action, and controlling involuntary movements like digesting food
• The motor system is like a series of nested loops, the main one being motor command descending from the brain to the muscle and sensory feedback ascending from muscle to brain
• Prefrontal cortex(PFC)


  Responsible for planning of voluntary movements. Not necessarily the movements themselves, but they decide what is appropriate in what situation and weigh the consequences
• Wisconsin card sorting task


  Where test subjects have to sort cards and are told if they are right or wrong, but the categories change without them being told. Relies on the PFC to update the new rules to determine the body's movement of the cards
• Posterior parietal cortex


  Major associative cortex for motor function, largely concerned with integrating visual and somatosensory info to determine appropriate action (like how to walk through a cluttered room)
• Main structures of the motor cortex, all in posterior part of frontal lobe:

  • Premotor area (PM)
  • Supplemental motor area (SMA)
  • Primary motor cortex (M1)
• Broca's area


  Motor cortex structure that contributes to motor processes related to language
• Premotor area (PM)


  Modulates motor output and generally acts before motor activity. Activity also increases when imagining performing complex finger patterns like playing the violin
• Mirror neurons


  Cells whose existence are debated who activate during a movement, but also when we see another person performing that same movement, but it's so complex it probably can't be done on the level of individual neurons
• Supplemental motor area (SMA)


  Upstream of motor cortex but also sends projections down the spinal chord. Seems to be responsible for coordinating motor tasks that require both hemispheres to communicate
• Primary motor cortex (M1)


  Major control center for movements in response to a "command" which influences motor neurons
• Upper motor neurons communicate down the spinal chord and into glands or muscles (influenced by M1 cells). Lower motor neurons are found in the brain stem or down the spinal chord and fire whenever the upper motor neurons tell them to
• Penfield 's goals were to figure out which parts of the motor cortex did what by stimulating them with electrodes, while ensuring that hand movement and speech were left untouched in epilepsy patients
• Penfield made 2 major discoveries:

  • Stimulation caused contralateral activity
  • Different populations of neurons are responsible for different muscle groups
• Motor homunculus


  Like the sensory one but instead shows what parts of the motor cortex controls what muscle groups
• Brain-machine interface

  Decoding efferent neuron signals to help amputees control their prosthetic limbs
• Electrocorticogram (eCoG)


  Procedure where a surgeon puts in a high-density electrode array capable of sensing cortical activity on the surface of M1 with crazy spatial and temporal resolution required for realistic movements.