Final answer:
Neurons in the primary motor cortex connect to lower motor neurons in the brain stem and spinal cord via the corticobulbar and corticospinal tracts, allowing for control over voluntary muscle movements.
Step-by-step explanation:
The neurons in the primary motor cortex primarily connect to lower motor neurons in the brain stem and spinal cord. Specific neurons known as Betz cells within the primary motor cortex send their axons down two main pathways, which are the corticobulbar tract and the corticospinal tract. The corticobulbar tract controls muscles of the head and neck via connections with motor neurons in the brain stem, while the corticospinal tract predominantly controls muscles throughout the body by crossing midline in the medulla oblongata and synapsing on motor neurons in the ventral horn of the spinal cord.
This organization allows for precise control over skeletal muscle movements, from complex, agile actions, such as those of the fingers, to more gross movements, such as those of the buttock and back muscles. The primary motor cortex is characterized by a somatotopic map, referred to as a motor homunculus, where different body parts are mapped onto the precentral gyrus in an orderly fashion.