THE RETURN OF HOMOUNCULUS: The Somatopically Organized Motor Cortex

The Motor Cortex in the brain is somatotopically organized. This means that your brain has arranged the functions of your voluntary muscle as if it was a Homunculus lying down all snuggled up in your cranium.

Pretty cool right?

The Motor Cortex and Homounculus


The Motor Cortex


Your motor cortex is anterior to the central sulcus, with Area 6 in control of planning movement, well Area 4 being responsible for the execution of that movement. The motor cortex talks to motor neurons in the spinal cord via two major descending pathways: the lateral and the ventromedial.

In the Lateral Pathway, the signals travel through the red nucleus, the corticospinal tract, and the rubrospinal tract. It controls the voluntary movement of distal musculature, or your buns and thighs. (You know, the muscles you work out the most when you go to the gym…if you try to.) This group of muscles are under direct cortical control. Ie. you think you do.

The second descending pathway in the motor cortex is the Ventromedial Pathway. It controls posture and locomotion and is mostly involuntary. It begins and stops a “basic” process. It involves the tectospinal tract, the vestibulospinal tracts,, and the pontine reticulospinal tract.

The Basal Ganglia


The Around the Ear Shaped Basal Ganglia.


The Basal Ganglia seems to be responsible for the bulk of voluntary movement and initiation of new movements. It is apart of the motor loop: the communication

Anatomy of the basal ganglia

  • Caudate nucleus
  • Globus pallidus (GPi/GPe)
  • Putamen

    Write it out!
  • Subthalamic nucleus
  • Interacts with the Midbrain: substantia nigra

Direct Pathway

Cortex->Stritum->GPi/SNr->Thalamus->Cortex->Brain Stem


Indirect Pathway

Cortex->Striatium->GPe->STN->Thalamus->Cortex->Brain Stem

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