Vagus and sympathetic system of the thorax

Question 1

Learning outcomes

Answer 1

After this lecture, time spent in the dissecting room, and further private study you should be able to:

1. Describe the course and distribution of the right and left vagus nerves
2. Describe (again) the clinical importance of the anatomy of the left recurrent laryngeal nerve
3. Describe the position and extent of the sympathetic trunks and ganglia
4. Describe the pre- and post-ganglionic neural connections of the sympathetic trunks
5. Describe the functions of the sympathetic trunks and their branches
6. State the signs of Horner’s syndrome
7. Describe the pre- and post-ganglionic neural connections of the parasympathetic system
8. Compare and contrast the functional anatomy of the sympathetic and parasympathetic systems

Question 2

What is the afferent nervous system?

Answer 2

The sensory (somatic and visceral) system of the PNS

Question 3

Discuss the autonomic nervous system

Answer 3

Under the control of the hypothalamus.
Dual innervation: Sympathetics and parasympathetics exert opposite effects in a particular organ/tissue but they functionally complement each other to keep the body functioning normally.
Certain blood vessels, errector pili muscle and sweat glands are supplied by sympathetics only

STABLE INTERNAL ENVIRONMENT
Regulates the visceral activity (Circulation, respiration, digestion, excretion, reproduction)
• Supplies smooth muscles (walls of the blood vessels, bronchi, intestines)
• Supplies the cardiac muscle
• Supplies the glands
Regulates body temperature
Autonomic fibres “accompany” the general visceral afferent fibres

Question 4

Describe an autonomic nerve

Answer 4

Reach the end organ with two neurons

Cell body of the 1st neuron (preganglionic neuron) is at grey matter of the spinal cord or brain stem
− axon is myelinated

Cell body of the 2nd neuron (postganglionic neuron) is at an autonomic ganglion
− axon is unmyelinated

Question 5

Describe the actions of the parasympathetic system

Answer 5

 Rest & digest or Rest & repose - conserves energy
 Slows breathing and heart rate, reducing cardiac output and BP
 Stimulates digestion (secretion of digestive enzymes)
 Opens sphincters
 Secretomotor to glands (salivary, lacrimal)
 Constricts pupils (accommodation for close focus)

Question 6

Describe the vagus nerve

Answer 6

 The parasympathetic innervation of the thoracic viscera is by the 10th cranial nerve, vagus
 Vagus leaves cranial cavity through jugular foramen, descends between internal jugular vein and internal (then common) carotid artery

 Right vagus enters the thoracic cavity between the right subclavian artery and Brachiocephalic vein
Subclavian artery

 Left vagus enters the thoracic cavity posterior to the left Brachiocephalic vein, between the subclavian and common carotid arteries
 The right vagus gives off recurrent laryngeal nerve, which winds around right subclavian artery

 The left vagus gives off recurrent laryngeal nerve, which winds around the aortic arch (aortopulmonary window), just posterolateral to the ligamentum arteriosum
 Recurrent laryngeal nerves supply
− Intrinsic laryngeal muscles (Except 1)
− Middle and inferior pharyngeal constrictor muscles
− sensory to the laryngeal cavity below the level of the vocal folds

Question 7

Describe the action of the sympathetic system

Answer 7

 It prepares the body to “Fight or flight” situations  body uses energy
 Increases heart rate and strength of heart beat
 Dilates coronary arteries (indirectly, by local metabolic factors)
 Constricts peripheral arteries
 Relaxes bronchial smooth muscles (Increases respiratory efficiency)
 Closes sphincters
 Controls body temperature (blood vessels, sweat glands)

Question 8

Describe the structure of the sympathetic system

Answer 8

(THORACOLUMBAR OUTFLOW)

 Preganglionic cell bodies lie in the intermediolateral horn of T1-L2 spinal cord segments

 Postganglionic cell bodies lie either in paravertebral sympathetic ganglia
− Anterior to the neck of the ribs -> lateral aspect of the vertebral bodies
− Covered by the parietal pleura
− Interconnected -> sympathetic chain (sympathetic trunk)

 Postganglionic cell bodies lie in prevertebral sympathetic ganglia
− around the origins of branches of abdominal aorta

 Each sympathetic trunk extends between the atlas and coccyx

 Trunks fuse with each other in the single ganglion impar, opposite the coccyx

 Number of paravertebral sympathetic ganglia Stellate Ganglion (cervicothoracic ganglion) (C7-T1)

Question 9

Look at the paths bit of lecture

Answer 9

.4 pathways for cell bodies of sympathetic system (T1 -L2)

Lateral horn of spinal cord holds sympathetic neurons. Presynaptic mylenatied neuron leaves spinal cord via anterior root via spinal nerve anterior branch and passes into sympathetic chain. (Link between anterior spinal nerve and sympathetic chain is called white ramus communicantes) When it enters the sympathetic chain it may:

1. Synapse with the post synaptic neuron at the same level, post synaptic axon (unmylenated) may join anterior or posterior branch on leaving through the grey ramus communicantes. - Will travel to lower thorax/abdomen/thigh + organs like heart (roughly)
2. It may synapse only after ascending to cervical ganglia by passing up the chain. Post synaptic ganglion will join cervical spinal nerves to supply upper thorax, limbs and head+neck as well as the heart (No white ramus communicantes as no entry at cervical level
3. It may pass down the sympathetic chain to lumbar or sacral ganglia and synapse w post synaptic neuron which will leave via grey (unmylenated) ramus communicantes and supply lower thigh and lower structures from there. No white ramus communicantes below L2
4. Sympathetic axons enter ganglion at their level, but pass through without synapsing and go straight to internal organs. Synapse w post synaptic neuron closer to organs. These nerves are called splanchnic nerves. (pre synaptic sympathetic neurons that don’t synapse in sympathetic paravertebral chain)
   (5) The adrenal medulla is supplied directly (it is itself like a ganglion)

Question 10

What are the splanchnic nerves?

Answer 10

Thoracic splanchnic nerves
• Greater splanchnic nerve: T5-9
Sympathetic Trunk
• Lesser splanchnic nerve: T10-11
• Least splanchnic nerve: T12

Lumbar splanchnic nerves

Pelvic splanchnic nerves

Thoracic splanchnic nerves

• Greater splanchnic nerve: T5-9
• Lesser splanchnic nerve: T10-11
• Least splanchnic nerve: T12

Lumbar splanchnic nerves

Pelvic splanchnic nerves - parasympathetic, unlike others

Question 11

Where do the different parts of the sympathetic system of the thorax come from?

Answer 11

 Sympathetics of the head from T1 - T3 segments
 Sympathetics of the upper limb from T4 - T6 segments
 Sympathetics of the thoracic and abdominal walls from T1 - T12 segments
 Sympathetics of the lower limb from T12 to L2 segments
 Remember the referred pain from visceral structures to the matching dermatome

Question 12

Discuss the visceral plexuses

Answer 12

VISCERAL PLEXUSES
 Sympathetic and parasympathetic fibres mix and form autonomic or visceral plexuses in the thorax, abdomen or pelvis
 Visceral plexuses in the thorax
• Cardiac plexus: Anterior to the bifurcation of the trachea and
posterior to the ascending aorta
• Pulmonary plexus: Anterior and (mainly) posterior to the roots of the lungs
• Oesophageal plexus: Around the oesophagus

Question 13

Discuss the cardiac plexus

Answer 13

 Sympathetics from T1-5 -> T1-5 ganglia + inferior and middle cervical ganglia
− Visceral afferent fibres travel alongside the sympathetic nerves
− Referred pain from heart to T1 /T2 dermatomes (medial aspect of left arm) +T3-5

 Parasympathetics from vagus

Question 14

Discuss the pulmonary plexus

Answer 14

 Sympathetics from T2-4 -> T2-4 ganglia

 Parasympathetics from vagus

Question 15

Discuss the phrenic nerve

Answer 15

Sole motor supply to the diaphragm
Also supplies sensory fibres to 
    the mediastinal parietal pleura
    parietal pericardium
    peritoneum and pleura related to the central tendon of the diaphragm

Question 16

Discuss the intercostal nerves

Answer 16

 Anterior rami of the thoracic spinal nerves

 Mixed nerves
– Motor branches to intercostal and abdominal wall muscles
– Visceromotor branches to vessels
– Lateral cutaneous branch
– Anterior cutaneous branch

Question 17

Discuss Pancoast’s tumour

Answer 17

Tumour at the apex of the lung may affect the sympathetic trunk or stellate ganglion, compromising sympathetic supply to the head and neck on the same side
Horner’s syndrome
• Ptosis (drooping) of the upper eyelid 
• Pupillary constriction (miosis)
• Anhydrosis (lack of sweating)
• Flushing of the face