Final answer:
Muscle relaxants affect the brain's motor cortex, basal ganglia, cerebellum, and brain stem nuclei, with the motor cortex's precentral gyrus and the spinal cord's ventral horn being specifically involved in the initiation and control of muscular movement.
Step-by-step explanation:
The regions of the brain that can be affected by muscle relaxants include the motor cortex, basal ganglia, cerebellum, and brain stem nuclei. Specifically, the motor cortex, located in the precentral gyrus of the frontal lobe, is crucial for initiating voluntary movement and contains the upper motor neurons that project to the spinal cord. The basal ganglia play a significant role in modulating movements and are involved with the effects of certain muscle relaxants that act on neurotransmitter activity, such as dopaminergic systems. The cerebellum assists in coordination and precision of movements, while brain stem nuclei govern involuntary muscle functions.
Within the spinal cord, motor neurons are found in the ventral (anterior) horn of the spinal gray matter, and these neurons are responsible for directly innervating skeletal muscles, thus controlling their contraction.