3.3. Plexuses

What is a Plexus?

Both spinal and cranial nerves form plexuses in the peripheral nervous system. A plexus is simply a network of somatic or autonomic nerves. Within this network, neurons are redistributed to create new peripheral nerves. Note that there are no synapses in peripheral plexuses. Plexuses are normally classified based on the type of neurons they contain, i.e. they are either somatic or autonomic. There a number of important plexuses in the different anatomical regions of the body; these are described below and shown in Figure 3.3.1.

Important Somatic Plexuses

Note: these plexuses are present on both sides of the body.

Cervical plexus

Originates from the anterior rami of C1 - C4. It is located in the lateral parts of the upper and middle neck and supplies the skin and muscles there.

Brachial Plexus

Originates from the anterior rami of C5 - T1. It is located in the root of the neck, shoulder and upper arm. This will be the source of all the nerves in the upper limb. The brachial plexus and its major terminal nerve branches are displayed in the diagram above.

Lumbar plexus

Originates from the anterior rami of L1 - L4. It is located in the lower posterior abdominal region, at the lumbar level.

Sacral plexus

Originates from the anterior rami of S1 - S4. It is located in the lower posterior pelvic region. The lumbar and sacral plexuses supply nerves to the pelvis and lower limbs.

Important Autonomic Plexuses

Cardiac plexus

The cardiac plexus has superficial and deep parts. The superficial part is located on the aortic arch, while the deep part is located on the trachea. These parts contain the sympathetic and parasympathetic fibres of the autonomic nervous system that influence the heart rate.

Oesophageal plexus

The oesophageal plexus is located on the oesophagus before it passes through the diaphragm and into the abdomen.

Prevertebral plexus

The prevertebral plexus is located on the abdominal aorta in the lumbar region of the torso. This plexus is actually made up of a number of small plexuses that supply the stomach, kidneys and intestines.

Hypogastric plexuses

These plexuses lie within the pelvis and supply sympathetic and parasympathetic nerves to the pelvic organs, such as the rectum and bladder.

Clinical Top Tip:

Plexus Injuries

Damage to the brachial plexus can occur in a number of ways, e.g. stretching of, and pressure on, the nerves that make up the brachial plexus. Stretching injuries may be experienced during whiplash in a car crash. Pressure injuries may occur after a fall – the clavicle can fracture after falling on outstretched arms; it then presses down on the nerves. Symptoms can include varying degrees of loss of sensation and movement in the affected arm, and they will depend on the nerves that are affected(C5, C6, C7, C8 and/ or T1) and where exactly the nerves are damaged(the closer to the spinal cord the injury is, the more likely the symptoms will be wide spread).

The Goofy Anatomist