Nerve
Spinal nerve
Short nerve trunk joining sensory and motor root fibers
High-yield
There are eight cervical nerve pairs but seven cervical vertebrae. C1–C7 emerge above their corresponding vertebrae, C8 between C7 and T1, and subsequent nerves below their like-numbered vertebrae.
Overview
A spinal nerve forms when ventral motor and dorsal sensory roots join. Its branches then distribute fibers to the body: dorsal rami serve intrinsic back muscles and skin, while ventral rami serve the limbs and anterolateral trunk. Both rami usually contain sensory and motor fibers.
Reference facts
- Origin
- Joining of the ventral and dorsal roots associated with one spinal cord segment, with variable dorsal-root development at C1
- Root value
- 31 paired segmental nerves: C1–C8, T1–T12, L1–L5, S1–S5 and Co1
- Course
- Roots usually unite near an intervertebral foramen, then divide into dorsal and ventral rami; upper cervical and sacral exits have different local bony relationships
- Motor
- Somatic motor fibers to skeletal muscle, together with autonomic fibers; thoracolumbar roots carry sympathetic output and S2–S4 roots carry sacral parasympathetic output
- Sensory
- Sensory fibers from skin, muscles, joints and visceral structures, with primary neuron cell bodies in dorsal root ganglia
Clinical correlation
Sympathetic fibers reach spinal nerves through communicating branches. Gray rami distribute postganglionic fibers at all spinal levels; white rami carrying preganglionic fibers are concentrated at T1–L2. Fibers can travel within the sympathetic trunk to reach higher or lower levels.
Frequently asked questions
What are the roots of the spinal nerve?
31 paired segmental nerves: C1–C8, T1–T12, L1–L5, S1–S5 and Co1.
What muscles does the spinal nerve supply?
Somatic motor fibers to skeletal muscle, together with autonomic fibers; thoracolumbar roots carry sympathetic output and S2–S4 roots carry sacral parasympathetic output.
What is the sensory distribution of the spinal nerve?
Sensory fibers from skin, muscles, joints and visceral structures, with primary neuron cell bodies in dorsal root ganglia.
What is the course of the spinal nerve?
Roots usually unite near an intervertebral foramen, then divide into dorsal and ventral rami; upper cervical and sacral exits have different local bony relationships.