Dorsal ramus of spinal nerve

Dorsal ramus of spinal nerve refers to a branch of a spinal nerve that innervates muscles, joints, and skin of the back. The spinal nerves are part of the peripheral nervous system and emerge from the spinal cord. Each spinal nerve divides into a dorsal (posterior) and ventral (anterior) ramus. The dorsal ramus contains motor and sensory fibers and is responsible for the innervation of the posterior parts of the trunk.

Anatomy

The spinal nerves are numbered according to the vertebrae from which they emerge. There are 31 pairs of spinal nerves: 8 cervical (C1-C8), 12 thoracic (T1-T12), 5 lumbar (L1-L5), 5 sacral (S1-S5), and 1 coccygeal (Co1). Each spinal nerve exits the spinal column through an intervertebral foramen and then divides into the dorsal and ventral rami shortly after.

The dorsal ramus of each spinal nerve innervates a specific segment of the skin and muscles of the back. In terms of muscles, it primarily innervates the intrinsic muscles of the back, which are responsible for the movements and posture of the vertebral column. These muscles are divided into three groups: superficial, intermediate, and deep. The dorsal ramus also provides sensory innervation to the skin overlying these muscles.

Function

The primary function of the dorsal ramus is to supply motor innervation to the muscles of the back and sensory innervation to the skin. This includes control over movements such as extension, lateral flexion, and rotation of the vertebral column. Additionally, the sensory fibers carry information regarding touch, temperature, and pain from the skin to the central nervous system.

Clinical Significance

Damage or irritation to the dorsal ramus can lead to back pain and muscle weakness. One common condition associated with the dorsal ramus is facet syndrome, which is a disorder of the zygapophysial joints innervated by the medial branch of the dorsal ramus. Another condition is the dorsal ramus syndrome, characterized by pain and sensory disturbances in the area innervated by the affected nerve.

See Also

• Spinal nerve
• Ventral ramus of spinal nerve
• Intervertebral foramen
• Facet syndrome
• Peripheral nervous system