The supplementary motor area (SMA) is a part of the
back frontal lobe (an area of tissue in the front part of
the brain) that helps plan motor movements. The SMA is
believed to be responsible for muscle posture
(particularly during stance and walking), muscle tone
(tension), coordination of both sides of the body
(especially the hands), motor sequencing control, and
initiation of movements created from within (i.e.,
thoughts) as opposed to those stimulated by
SMA location in the brain
Damage to this part of the brain cause involuntary grasping. However, the functions of
the SMA in humans are still an area of ongoing research as this is a topic that has been
studied mostly in monkeys. The SMA has connections to the spinal cord, the premotor
cortex below it (another part of the frontal lobe that helps with motor planning), and the
prefrontal cortex. The prefrontal cortex is an area in the front part of the brain that
mediates personality expression and executive functioning (higher level thinking skills).
The SMA has been divided into six subregions.
Like the premotor cortex, the SMA corresponds to where Brodmann's area 6 is located.
Brodmann's areas are 47 different brain regions located on a map of the brain created by
the German anatomist, Korbinian Brodmann. Brodmann’s area expands over the middle
part of the cerebral hemisphere and is represented on both sides of the brain. The
supplemental motor area is also known as the supplemental motor cortex.
Supplementary motor area comes from the Latin word “supplementum” meaning “something added to
supply a deficiency,” the Latin word “motor” meaning “to move,” and the Latin word “area” meaning “open
space.” Put the words together and you literally have “something added to an open space to supply a
motor deficiency” but a better translation to convey the intended meaning would be “something added to
an area to supply motor movements.”