Final answer:
The spinal cord is organized into segments each connected to the body through spinal nerves, which have two roots for motor and sensory functions. Nerve plexuses reorganize axons from these nerves to innervate specific areas effectively. The peripheral nervous system's two divisions are somatic and autonomic systems.
Step-by-step explanation:
The spinal cord is functionally organized into 30 segments that correspond with the vertebrae. Each segment is associated with peripheral nerves that branch out and are connected to specific parts of the body. The spinal nerves are responsible for sending sensory and motor information to and from different regions of the body. These nerves comprise combined sensory and motor axons that separate into two roots: the sensory axons enter the spinal cord through the dorsal nerve root, and the motor fibers emerge through the ventral nerve root.
Sensory nerves carry messages into the spinal cord, while motor nerves transmit instructions out to muscles and organs. The spinal nerves enable communication between the brain and the body, although some sensory inputs are processed directly by the spinal cord without brain involvement.
Along the spinal cord, there are four major nerve plexuses formed by the spinal nerves: cervical, brachial, lumbar, and sacral plexuses. These plexuses represent networks of nerve fibers that reorganize axons from different spinal nerves to innervate specific body areas effectively.
The peripheral nervous system includes all the nerves outside the brain and spinal cord and has two main divisions: the somatic nervous system, which controls voluntary movements, and the autonomic nervous system, which regulates involuntary functions.
The spinal cord varies in length across the regions of the vertebral column, with spinal nerves emerging at different levels. In the lumbar and sacral regions, the nerves form the cauda equina due to the growth of the vertebral column beyond the length of the spinal cord. The dorsal root ganglion at each level is an enlargement responsible for processing sensory information.