Sacral part of spinal cord

The sacral part of spinal cord lies below the lumbar region and above the coccygeal segments.

Like other parts of the spinal cord, the sacral part of spinal cord, contains a centrally located, butterfly-shaped gray matter that is organized into anterior (motor) and posterior (sensory) gray columns or horns. However, in contrast to the cervical and lumbosacral regions, the gray matter in the sacral part of spinal cord is relatively small, with smaller anterior and posterior horns. This is because most of the expanded gray matter required to innervate the lower limb musculature resides in the lumbar region.

The anterior gray horn of the sacral spinal cord contains motor neurons that innervate perineal muscles and some structures of the lower limbs.

The posterior gray horns, which are primarily sensory, house nuclei such as the substantia gelatinosa and the nucleus proprius, which extend throughout the entire spinal cord. The substantia gelatinosa processes and relays sensory input related to pain and temperature, while the nucleus proprius is involved in transmitting proprioceptive, vibration, and two-point discrimination information. Clarke’s column, a nucleus involved in proprioception, is not found in the sacral region because it terminates around the L3/L4 levels.

Unlike the thoracic and upper lumbar regions (T1–L2), which contain preganglionic sympathetic neurons in their lateral gray horns, the sacral region houses preganglionic parasympathetic cell bodies in the S2–S4 segments. These neurons are part of the sacral component of the parasympathetic outflow, contributing to the autonomic control of pelvic organs such as the bladder, rectum, and reproductive structures.

The two sides of the gray matter are connected by a gray commissure that surrounds the central canal.

The gray matter is surrounded by bundles of white matter fibers or tracts (or funiculi). These include the anterior, posterior and lateral white columns.

Surrounding the gray matter are the white matter tracts or funiculi, which are divided into anterior, posterior, and lateral columns. The anterior and lateral white columns in the sacral cord are similar to other spinal regions, transmitting both ascending and descending information. However, a significant feature of the posterior white column is the absence of the fasciculus cuneatus, a tract that transmits (vibration, proprioception, and two-point discrimination) sensations from the upper limbs. The fasciculus gracilis, on the other hand, which transmits similar information from the lower limbs, remains present throughout the entire length of the spinal cord and hence, can be seen in the sacral part of spinal cord.