Final answer:
The true statement among the options provided is that a first-order neuron extends from the sensory receptor to the central nervous system. The primary motor cortex is located in the precentral gyrus of the frontal lobe and is responsible for muscle movement stimulation. The optic nerve is solely a sensory nerve, and nuclei refer to nerve cell collections within the CNS.
Step-by-step explanation:
The true statement in question is: "c. a first-order neuron extends from the sensory receptor to the central nervous system." The primary motor area, or primary motor cortex, is not located on the post-central gyrus but in fact, it is located in the precentral gyrus of the frontal lobe, according to the neurosurgeon Walter Penfield's research, which included stimulating the cerebral cortex and observing muscle movements. The optic cranial nerve is not a mixed nerve; it is strictly a sensory nerve responsible for visual sensation. The term 'nuclei' in the nervous system context refers to collections of nerve cells inside the CNS, not outside. Lastly, the canal that connects the third and fourth ventricles and runs through the midbrain is known as the cerebral aqueduct (aqueduct of Sylvius), not the foramen of Monro. In the central nervous system (CNS), neurons that carry sensory information from the periphery to the CNS are part of a pathway system. The first-order neurons begin at sensory receptors and then project into the CNS through spinal nerves or cranial nerves, such as in the case of somatosensory information coming from different parts of the body.