The rami communications
The branch of the spinal nerve that contains only autonomic fibers is the rami communicantes. These are divided into the white rami communicantes, which carry preganglionic sympathetic fibers to the sympathetic ganglia, and the gray rami communicantes, which carry postganglionic sympathetic fibers back to the spinal nerve. These branches are essential for the autonomic nervous system's regulation of involuntary functions.
The autonomic fibers are contained within the ventral (anterior) root of the spinal nerve. These fibers are responsible for carrying signals to and from the autonomic nervous system, which controls involuntary bodily functions.
The ventral roots contain motor fibers.
The preganglionic fibers that connect a spinal nerve with an autonomic ganglion in the thoracic and lumbar regions of the spinal cord are part of the sympathetic nervous system. These fibers originate from the lateral horns of the spinal cord and are myelinated, allowing for rapid signal transmission. They typically travel through the ventral roots and enter the sympathetic chain or prevertebral ganglia to synapse with postganglionic neurons.
Brain
The preganglionic fibers of the autonomic nervous system travel through the cranial nerves (in the head) and the spinal nerves (in the rest of the body). They synapse with postganglionic neurons in autonomic ganglia before reaching their target organs.
Spinal nerves are called mixed nerves because they all carry motor, sensory, and autonomic signals between the spinal cord and the body.
They are referred to as thoracolumbar outflow and run parallel to the spinal cord in a series on connected ganglion.
Postganglionic fibers innervate glands in the body primarily through the autonomic nervous system, specifically the sympathetic and parasympathetic divisions. These fibers originate from autonomic ganglia and connect to target tissues, including glands, often by traveling alongside spinal nerves. In the case of sympathetic innervation, postganglionic fibers may follow blood vessels or directly innervate glands like the adrenal medulla. In contrast, parasympathetic fibers arise from cranial nerves and sacral spinal nerves, directly influencing glands such as salivary and lacrimal glands.
axons of sensory neurons
The brachial plexus contains fibers from the ventral rami of the cervical spinal nerves (C5-C8) and the first thoracic spinal nerve (T1). These fibers combine to form the nerves that innervate the upper limb.
The 3 major contents of the brain are the cerebrum, cerebellum, and the Autonomic nervous system.