Final answer:
The autonomic nervous system is responsible for controlling involuntary functions in the body, including reflex actions like the knee response, without the direct involvement of the brain. It includes the sympathetic and parasympathetic systems which work to maintain homeostasis.
Step-by-step explanation:
The nerves that come out of the spinal cord and go to organs, which are controlled automatically, are part of the autonomic nervous system.
This system manages involuntary functions such as heart rate, breathing, digestion, and other internal organ activities. The autonomic nervous system can be further subdivided into the sympathetic and parasympathetic nervous systems, which often have opposing effects to maintain homeostasis.
Reflexes like the knee reaction or withdrawing a hand from a hot object are controlled by motor reflexes, mediated by the spinal cord, and can occur without direct brain involvement.
These reflexes involve rapid synaptic connections and can be part of both the somatic and autonomic nervous systems.