Mediastinum and Nerves

Question 1

What is the brachial plexus?

Answer 1

Bilateral networks in the thoracic cavity. Formed by ventral rami, C6-8 and T1-2.

Question 2

What are the phrenic nerves?

Answer 2

Bilateral nerves that branch at diaphragm to supply whole structure. Ventral rami, C5-7.

Question 3

What are the intercostal nerves?

Answer 3

Run down caudal surfaces of ribs in costal groove to supply intercostal muscles. Have superficial branches to supply lateral and ventral walls and overlying skin.

Question 4

Describe thoracic sympathetic innervation.

Answer 4

Preganglionic fibre exits via ventral root and communicating ramus to reach the sympathetic chain. Synapses at any paravertebral ganglia , including cervico-thoracic and middle cervical ganglia (which are linked by the ansa subclavia). Exits via sympathetic nerves to supply cardiac or pulmonary plexuses.

Question 5

Describe thoracic parasympathetic innervation.

Answer 5

Vagus nerve is bilateral and mixed. Enters the thorax via the vagosympathetic trunks and supplies preganglionic fibres going to cardiac and pulmonary plexuses, as well as the recurrent laryngeal nerve.

Question 6

Describe sympathetic innervation of the head.

Answer 6

Preganglionic fibre exits via a ventral root at T1-2 and communicating ramus to reach the sympathetic chain. Reach vagosympathetic trunks and synapses with paravertebral ganglia called cranial cervical sympathetic ganglia at the base of the skull. Postganglionic fibre leaves CCSG to supply the head and neck.

Question 7

Describe sympathetic innervation of the pelvis and abdomen.

Answer 7

Preganglionic fibre exits via ventral root and communicating ramus to reach sympathetic chain. Form splanchnic nerves and pass to abdomen and synapse at a prevertebral ganglia, such as coeliacomesenteric ganglion. Postganglionic fibres supply GI tract, bladder and travel via hypogastric nerve to reproductive organs.

Question 8

Describe parasympathetic innervation to extra-thoracic structures.

Answer 8

• Parasympathetic fibres found in several cranial nerves supplying the head and neck.
• Dorsal and ventral vagal trunks enter abdomen with oesophagus via diaphragm to supply abdomen.
• At S2-4, pelvic nerves supply distal colon, rectum, bladder and reproductive organs.