Thoracic nerves (12) (T-1 through T-12).
Lumbar nerves (5) (L-1 through L-5).
Sacral nerves (5) (S-1 through S-5).
Coccygeal nerve (1).
b. In the human body, every spinal nerve has essentially the same structure and
components. By learning the anatomy of one spinal nerve, you can understand the
anatomy of all spinal nerves. Like a tree, a typical spinal nerve has roots, a trunk, and
branches (rami) (figure 2-4).
(1) Coming off of the posterior and anterior sides of the spinal cord are the
posterior (sensory) and anterior (motor) roots of the spinal nerve. An enlargement on
the posterior root is the posterior root ganglion. (A ganglion is a collection of neuron cell
bodies, together, outside the CNS.)
(2) Laterally, the posterior and anterior roots of the spinal nerve join to form
the spinal nerve trunk. The spinal nerve trunk of each spinal nerve is located in the
appropriate intervertebral foramen of the vertebral column. (An intervertebral foramen
is a passage found on both sides of a vertebrae. It is formed by the columnar alignment
of the vertebrae.)
(3) Where the spinal nerve trunk emerges laterally from the intervertebral
foramen, the trunk divides into two major branches. These branches are called the
anterior (ventral) and posterior (dorsal) primary rami (ramus, singular). The posterior
primary rami go to the back. The anterior primary rami go the sides and front of the
body and also to the upper and lower extremities.
c. A nerve has been defined as a collection of neuron processes. These
processes may belong to different types of neurons--afferent (sensory), efferent (motor),
or the visceral motor neurons of the autonomic nervous system. (The ANS will be
An afferent neuron carries sensory information from the periphery to the
(2) An efferent neuron carries motor commands from the CNS to the
periphery of the body.