Nerves

Question 1

What is the course of the phrenic nerves?

Answer 1

Travel vertically down the neck and through the superior thoracic aperture through the mediastinum, anterior to the root of the lungs

Left: crosses over aortic arch
Right: runs lateral to SVC

Question 2

Where can diaphragmatic pain be referred to?

Answer 2

Diaphragmatic pain can be referred to the shoulder tip (C3,4,5 dermatome). The pain is referred because the same spinal levels supplying the phrenic nerve (C3-5) also supply cutaneous regions of the skin at the shoulder (dermatomal distribution)

Question 3

Describe the distribution and function of the sympathetic chains and thoracic splanchnic nerves.

Answer 3

At levels between T1 and L2 there is an additional bulge in the grey matter known as the lateral horn

Nerves from lateral horn go to sympathetic ganglion (trunk)The sympathetic nerve can synapse straight away to post ganglionic neurone (to blood vessels, sweat glands, arrector pili etc.)

• Or can go to prevertebral ganglion where they synapse to innervate viscera
• Or they can go up or down the trunk to synapse at a different ganglion (e.g sympathetic innervation to the head at T1)

White ramus communicans contains myelinated preganglionic sympathetic fibres
Grey ramus communicans contains unmyelinated postganglionic sympathetic fibres

Question 4

What are the fibres in the lower sympathetic trunk called and which vertebral levels do they branch off at?

Answer 4

Splanchnic Nerves - T5-T12

Question 5

What is the course of the right phrenic nerve?

Answer 5

• Enter superior mediastinum lateral to right vagus and posterior to beginning of right brachiocephalic vein
• Continues infeirorly on right side of brahciocephalic vein and vena cava
• When enters middle mediastinum, descends along right side of pericardial sac (in fibrours pericaridum) anteiror to right lung root
• Leaves thorax by passing through diaphragm

Question 6

What is the course of the left phrenic nerve?

Answer 6

• Enters supeiror mediastinum lateral to left vagus and posterior to left brachiocephalic vein
• Descneds across left lteral surfsce of aortic arch (pass superficially to left bagus and left superior intercostal vein)
• When enters middle mediastinum, follows left side of pericardial sac (in fibrous pericardium) anteiror to left lung root
• Leaves thorax by piercing diagphragm near heart apex

Question 7

What is the course of the right vagus nerve?

Answer 7

• Enters superior mediastinum etween right brachiocephalic vein and brachiocephalic trunk
• Desends posteriorly towards trachea
• Crosses trachea laterally
• Passes posteriroly to root of right lung to reach oesphagus
• Before oespahgus corssed by arch of azygous vein

Question 8

What is the course of the left vagus nerve?

Answer 8

• Enter superior mediastinum posterior to left brachiocephalic vein between left common carotid and left subclvaian
• Lies just deep of mediastinal part of parietal pleura
• Crosses left side of arch of aorta
• Descedns posteriorly
• Passes posteiror to root of left lung
• Reaches osephagus