As mentioned earlier, Quadriplegia affects both arms and legs (it is Paralysis of all four limbs) and it is deeply connected to the complex network of the human nervous system. Each of our muscle movements is controlled by our nervous system through voluntary and involuntary signals.
When there is any damage to a critical component/s of this network (like the brain or the spinal cord), signals to the muscles can be disrupted. This interruption can contribute to movement and sensation impairment in both upper and lower body parts, and thus, quadriplegia paralysis.