Describe the arrangement of neurons in the primary motor cortex Solution The primary motor cortex or M1 is found to be located in the dorsal portion of the frontal lobe in the brain. This is the region which is involved in coding force and direction of movement and M1 works along with posterior parietal cortex, premotor cortex, the supplementary motor area etc to execute its actions. In M1 region we can find Betz cells (large neurons) along with other cortical neurons, these will send long axons till the end of the spinal cord, so that they can synapse onto the interneuron circuitry of the spinal cord. They also send neurons on the alpha motor neurons located in the spinal cord to have connection with the muscles. Using Golgi method, the morphology and the spatial arrangement of neurons in the primary motor cortex has been studies, which revealed the presence of great variety of pyramidal and non-pyramidal cells in M1 region and main difference between these cells is due to their difference in shape, size and also with respect to dimensions and distribution of dendritic trees. It has been reported that columnar aggregation formed were observed in sub-layers III b and c, formed by the somata and dendritic trees of pyramidal and non-pyramidal cells, these are 100- 300 micron wide and are found to be separated by cell-sparse spaces of 50-100 micron width. In these aggregations, we can find several bundles formed by apical dendrites of pyramidal cells. The columnar width was not surpassed by most non-pyramidal cells of dendrites. In layers III and V, the dendrites and somata of pyramidal cells were found to be showing a preferential orientation in the same direction and they will run parallel to the main axis of the gyrus. But in layers II, IV, and V, what aggregations we found in layer III were not found but in layer V, around the giant Betz cells, there was a loose assemblage of neurons of all sizes group were found to be located. The radii of myelinated fibers entering and leaving the white matter were found to be forming radial appearance in Layer VI. The vertical, columnar organization and the asymmetry of somata and dendritic trees were found to be more pronounced when it comes to the boundary of the central sulcus and boundary of precentral gyrus..

1. Describe the arrangement of neurons in the primary motor cortex
Solution
The primary motor cortex or M1 is found to be located in the dorsal portion of the frontal lobe in
the brain.
This is the region which is involved in coding force and direction of movement and M1 works
along with posterior parietal cortex, premotor cortex, the supplementary motor area etc to
execute its actions.
In M1 region we can find Betz cells (large neurons) along with other cortical neurons, these will
send long axons till the end of the spinal cord, so that they can synapse onto the interneuron
circuitry of the spinal cord. They also send neurons on the alpha motor neurons located in the
spinal cord to have connection with the muscles.
Using Golgi method, the morphology and the spatial arrangement of neurons in the primary
motor cortex has been studies, which revealed the presence of great variety of pyramidal and
non-pyramidal cells in M1 region and main difference between these cells is due to their
difference in shape, size and also with respect to dimensions and distribution of dendritic trees.
It has been reported that columnar aggregation formed were observed in sub-layers III b and c,
formed by the somata and dendritic trees of pyramidal and non-pyramidal cells, these are 100-
300 micron wide and are found to be separated by cell-sparse spaces of 50-100 micron width.
In these aggregations, we can find several bundles formed by apical dendrites of pyramidal cells.
The columnar width was not surpassed by most non-pyramidal cells of dendrites.
In layers III and V, the dendrites and somata of pyramidal cells were found to be showing a
preferential orientation in the same direction and they will run parallel to the main axis of the
gyrus.
But in layers II, IV, and V, what aggregations we found in layer III were not found but in layer
V, around the giant Betz cells, there was a loose assemblage of neurons of all sizes group were
found to be located.
The radii of myelinated fibers entering and leaving the white matter were found to be forming
radial appearance in Layer VI.
The vertical, columnar organization and the asymmetry of somata and dendritic trees were found
to be more pronounced when it comes to the boundary of the central sulcus and boundary of
precentral gyrus.