The corticospinal tract serves as the primary pathway for motor function in the human brain, transmitting signals from upper motoneurons to lower motoneurons to ultimately produce muscle contractions. Motoneurons generate firing patterns in response to synaptic input, with the voltage-sensitive conductance determining the cell's output based on thresholds and firing. However, neuromodulators in the central nervous system (CNS), including those in the brainstem, intricately regulate activity in corticospinal motor pathways by regulating the gain of motoneuron output. The purpose of this PhD Thesis is to examine the neuromodulatory role that muscarinic acetylcholine receptors (mAChRs) have on human corticospinal corticospinal motor pathways. To achieve this, three studies were performed using a human, double-blinded, placebo-controlled and crossover design. Each study assessed the effects of a muscarinic blockade (Phenergan 25 mg) on the motor system using TMS, peripheral nerve stimulation and somatosensory recordings. [...]