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Category: Medical

Topic: Nervous System A&P

Level: Paramedic

Next Unit: The Cranial Nerves

7 minute read

Peripheral Spinal Nerves

The spinal nerves are considered mixed nerves, meaning that they carry motor, sensory, and autonomic information between the spinal cord and brain and the body.The CNS is heavily segregated based on function. Although sensory and motor nerve tracts may run close to one another in the spine and brain stem, they are still distinct tracts. They exit the spine via the dorsal root ganglia (sensory, pain) and anterior root ganglia (motor), coalescing into single bundles that cannot be separated based on function on their journeys to the areas they innervate.  


Nerve Plexuses

Nerve plexuses are located near the cervical, lumbar, and sacral vertebrae bilaterally. These areas are "intermixings" of spinal nerve roots that have combined from the root ganglia (ventral = motor; dorsal = sensory), where the neurons mix and rearrange before traveling down the respective limb(s) or area(s). 

There are 31 pairs of spinal nerves, one on each side of the vertebral column. separated into nerve plexuses that innervate the skin and skeletal muscles of the area that they are located within. The mixed nerves that form from them have both sensory and motor functions, including muscle contraction, body coordination and control, and reaction to extreme temperatures, pain, and pressure. 

  • The CERVICAL PLEXUS consists of the ventral rami (anterior division of the spinal nerve, as opposed to the dorsal rami or posterior division of the spinal nerve) of spinal nerves C1-C5 and innervates the neck and extends into the thoracic cavity controlling the diaphragm. (C3-5 contribute to the phrenic nerve.)

  • The BRACHIAL PLEXUS consists of the ventral rami of spinal nerves C4, C5, and T1 and innervates the pectoral girdle and upper limbs.
  • The LUMBAR PLEXUS consists of the ventral rami of spinal nerves T12 and L1-L4 and innervates the pelvic girdle. (Contains the femoral and obturator nerves.) 
  • The SACRAL PLEXUS consists of the ventral rami of spinal nerves L4, L5, and S1-S4 and innervates the lower limbs and bladder functions. The dorsal rami serve the same local functions as their ventral counterparts, but affect the posterior portion of the body. (Most of the sacral plexus will coalesce into the sciatic nerve.) 

Sustained posturing in certain positions can cause a temporary cessation of transmission as the nerves are stretched. This most commonly happens in surgery or while intoxicated.


Spinal Nerves

The central nervous system includes the brain and the spinal cord. The spinal cord functions as a transmission pathway for motor information from the brain to the body, a sensory pathway for information from the body to the brain, and also functions as a center for coordinating certain reflexes.

The spinal nerves are grouped and labeled by the region of the body they are located in: