L7. Nerves of the Diaphragm and Thorax

Question 1

What the attachments/ boundaries of the diaphragm

Answer 1

The inferior costal margin anteriorly, laterally the free ribs and then to the vertebral column is the 2 crura.
The right dome is higher than the left, reaching up to Rib 5

Question 2

What are the ligaments, of the diaphragm and structures that pass through them

Answer 2

Arcuate ligaments:
-Median made from L&R crura - aka aortic hiatus

• Medial made from the Crura to the transverse process of L1 - thickening of psoas fascia. Passing behind = symp tunk
• Lateral made from L1 TP to rib 12 -thickening of quad lumborum fascia.

Question 3

What are the openings of the diaphragm and structures that pass through them

Answer 3

• Caval opening at T8 - central tendon for IVC and Right phrenic nerve
• Oesophageal hiatus at T10 for oesophagus and 2 Vagal trunks of CNX
• Aortic hiatus at T12, Aorta, azygos and hemiazygos vein, thoracic duct

Question 4

What structures go piercing through the diaphragm

Answer 4

Left phrenic nerve through the muscular portion due to heart position.
Greater, less and least splanchnic nerves are formed from their roots, travel medially then pierces the cruca into the abdomen
Also the Superior epigastric artery.

Question 5

What is the arterial and nerve supply to the diaphragm and the course of this nerve from neck to abdomen

Answer 5

Inferior phrenic arteries - the first major branch of the abdominal aorta.
Phrenic nerve:
1. Anterior rami C3-5. containing motor, sensory and symp fibres.
2. It runs obliquely over anterior surface of Ant. Scalene muscle, passing between subclavian artery and vein into the throrax.
3. It passes anterior to hila of lung
4. Gives off pericardial, mediastinal and diaphragmatic ParietalP branches
5. RHS through Cava opening, LHS courses further out from midline, piercing muscular diaphragm

Question 6

For somatic nerves what is difference between dorsal and ventral ramus, root ganglion and root

Answer 6

The ramus are the last in the points that direct the fully formed spinal nerve to the dorsal or ventral anatomical position in the body.
The root ganglions are where the cell bodies of neurons belonging to the dorsal - sensory and ventral - motor somatic neurons.
Afferent sensory neurons travel back to the spinal cord by the dorsal root. Efferent motor neurons travel out of the spinal cord via ventral root.

Question 7

What synapse makes a somatic reflex arc. 2 different

Answer 7

A sensory neuron synapses with motor neuron at the same level. Or it synapses with a chain of interneurons which can ascend or descend before synpasing with efferent motor neuron.

Question 8

Explain how the structure of the sympathetic chain and why it can supply the whole body despite output from a certain section

Answer 8

Sympathetic nerves come from T1-L1/2 levels. At these levels, efferent sympathetic nerves exit and afferent sympathetic nerves come back. These levels have white rami (myelinated) which allows the fibres to enter the Sympathetic chain. This chain lies paravertebrally and extends to all levels with a joining called Ganglion impar at the bottom.
Fibres exit out of the chain at different levels through grey (unmyelinated) rami.

Question 9

Explain the steps for efferent sympathetic nerve transmission

Answer 9

Firstly the fibres in T1-L1/2 come from the lateral horn->ventral horn, exits through the ventral root-> white ramus communicans.
From here it can
1. Form a synapse with post ganglionic neuron and exit out through gray ramus at the same level
2. Ascend or descend in the chain before synapsing with post ganglionic neuron and exiting out gray ramus at that level.
For these two, the fibres will then join up with the spinal nerve fibres and exit out of the Ventral or Dorsal ramus for the anatomical position

3. Exit on their own path separate from spinal nerves to either synapse later at peripheral ganglia or plexuses before going to viscera. This is a splanchnic nerve.

Question 10

What are the 4 Thoracic splanchnic nerves, roots, plexus and region associated with - top to bottom

Answer 10

1. Cardiopulmonary sn (T1-4) for Cardiac and pulmonary plexuses. This is for Heart and lungs
2. Greater Sn (T5-9) for Coeliac plexus. This is for Foregut and adrenals
3. Lesser Sn (T10-11) for Superior mesenteric plexus. This is for midgut.
4. Least Sn (T12) for aorticorenal plexus. This is for kidneys and adrenals.

Question 11

Explain how the afferent sympathetic flow and how it is interpreted

Answer 11

1. Pain eg. stretch in the gut, chemical insult, ischaemia - is carried by the visceral afferent back to the level of the sympathetic chain its efferent originated from.
2. It goes through the white ramus to join the somatic afferent fibres
3. They both go into the dorsal root ganglion and into the dorsal root of the spinal cord.
4. Therefore brain interprets pain as coming from the somatic spinal segment- ie intercostals- not the viscera. This is called Referred pain and usually corresponds to dermatomes.

Question 12

How is pain referred from a heart attack

Answer 12

Sympathetic nerves from mostly
T1- arm pain
T2-4 - chest pain
which its supply, however it can also get
C3-5 - pericardium - shoulder and back pain possible via the link to the sympathetic chain in the neck.

Question 13

What are the 3 signs of Horners syndrome and what causes it

Answer 13

1. Miosis: constriction of pupil- losing natural dilatation of symp
2. Ptosis: drooping of upper eyelids. lose innervation of levator palpabae sup.
3. Anhidrosis: decreased sweating.
   All on side of sympathetic trunk that was damaged due to compression? in upper chest/neck region.

Question 14

What would happen to the phrenic nerve damage on one side

Answer 14

The diaphragm on that side would relax -> raise higher