Final answer:
The gray rami communicantes from the middle cervical ganglion of the sympathetic trunk are received by the corresponding cervical spinal nerves, which innervate various neck and shoulder effector organs.
Step-by-step explanation:
The nerves that receive the gray rami communicantes from the middle cervical ganglion of the sympathetic trunk are typically the spinal nerves that correspond to the levels at which the ganglia are found. The gray rami communicantes are unmyelinated structures that provide a short connection from a sympathetic chain ganglion to the spinal nerve, containing the postganglionic sympathetic fibers. On the other hand, the white rami communicantes are myelinated and connect the central neurons in the spinal cord to the sympathetic chain ganglia, containing the preganglionic sympathetic fibers. The middle cervical ganglion often sends gray rami communicantes to the cervical spinal nerves, which may participate in the innervation of various effector organs in the neck and shoulder regions.