Motor cortex. Area 4. (DOUBLET)

Motor cortex. Area 4.

Primary motor cortex, , Primary somato-motor cortex, Motor cortex, SM I, Betz giant cells, BA 4

The bark area is located on the anterior central cortex, mainly on the outside of the hemisphere and has many names: motor cortex, motor cortex, primary locomotor cortex, primary somato-motor cortex, SM I. From here the pyramidal system (tractus cortico-nuclearis to the motor neuron of various cranial nerves and tractus cortico-spinalis i.e. Pyramidal path, to the motor neurons of the spinal cord).

Brodmannarea 4 (+ a strip of area 6) is the area from which the volitional control of our movements originates. This is especially true of the complex movements one can perform with the tongue and lips and with the extremities, especially with the hands and fingers.
Area 4's cytoatectonic is very special. Here you will find in layer five (lamina V), the largest nerve cells of the cerebral cortex, the so-called Betz giant cells.
Area 4 is the starting point for the main part of the so-called pyramidal system, a much talked about pathway system, which more or less directly connects the cerebrum cortex, area 4 (and parts of area 6), to the motor neurons in the brainstem and spinal cord on the opposite half of the body.
The part of the pyramidal pathway system that ends in the brainstem and affects the motor neurons of the cranial nerves (blinking, mimicry, chewing, tongue movements, swallowing, vocal cord movements) is called the cortico-nuclear pathway. The part of the pyramidal pathway that ends in the spinal cord is called the cortico-spinal pathway or "pyramidal pathway".

Electric stimulus of SM I causes muscle twitching on the opposite half of the body. It can be said that different parts of the SMI cortex control different muscles/muscle groups on the opposite half of the body and that SM I contains a map of the muscles of the opposite body half.
If we draw this map on the surface of the anterior central winding and then take into account how large the area of bark is "connected" to a certain muscle or muscle bump (on the opposite body half), we get the map image of what is called "the motor homunculus" (homunculus = small human).
This map shows that the muscles of the larynx, pharynx and tongue are controlled from the part of area 4 that covers the insula.
If we then move upwards along the anterior central winding, we first pass through the right-facing opposite half of the face equipped with a grotesquely large mouth (i.e. a comparatively large area of bark controls the movements of the lips, speech), then the rest of the opposite half of the body follows lying upside down with a giant hand that turns into a spindly arm attached to a spindly torso that, on the inside of the anterior central winding, the lower limb passes with a rather large foot.

The primary motor cortex appears to be of particular importance for the control of muscles responsible for our ability to express speech sounds (phonem) and our skill in performing conscious and intricate hand and finger movements.