Corpus: Primary motor cortex

The primary motor cortex is a cortex area of the lobus frontalis that is functionally part of the motor cortex. The processes of the pyramidal cells located here mainly descend into the spinal cord and control the motor neurones there directly or indirectly. The primary motor cortex thus serves to execute the motor programme that has been designed in the superordinate cortical fields in interaction with other areas of the brain and therefore forms an important part of the motor system's final pathway.

Localisation[Bearbeiten]

The primary motor cortex lies rostral to the central sulcus in the precentral gyrus, extends over the medial and superolateral facies and largely corresponds to Brodmann's area 4.

Arrangement of the neurones and course of the processes[Bearbeiten]

The first (central, upper) motor neurones localised in the primary motor cortex are arranged somatotopically according to the motor homunculus. They are Betz cells (approx. 5 %) and other pyramidal cells (approx. 95 %). Their axons extend peripherally in the capsula interna as somatotopically organised corticonuclear and corticospinal tracts with the processes of neurons from other areas of the cortex (secondary motor cortex, sensory cortex).

While some processes leave the capsula interna towards the thalamic nuclei or the corpus striatum, the remaining processes descend into the brain stem or the spinal cord. In the brain stem, they form synapses with neurones of motor nucleus areas, e.g. the nucleus ruber, the nucleus olivaris, the pons nuclei and the formatio reticularis. In the spinal cord, they form synaptic connections with the second (peripheral, lower) motor neurones located there or with interneurones that control the second motor neurones. The first motor neurones thus directly or indirectly regulate the activity of certain motor units.

Histological features[Bearbeiten]

The primary motor cortex has a very prominent lamina V, whereas the lamina IV is only very small (or barely present).