Nerves of the Thorax Flashcards
What controls the autonomic nervous system?
The hypothalamus
Name some examples of structures only supplied by sympathetic nerves
Certain blood vessels, errector pili muscles and sweat glands
Describe the course and myelination status
The cell body of the preganglionic neuron comes out from the lateral horn of grey matter and is myelinated so appears white. The postganglionic neuron arises from autonomic ganglia and is unmyelinated.
Briefly describe the function of the parasympathetic system
- Conserves energy.
- Slows breathing and HR by reducing CO and BP.
- Stimulates digestion.
- Open sphincters.
- Constricts pupils.
- Secretomotor to glands (salivary and lacrimal)
What is the parasympathetic innervation via? Where does this nerve arise from?
The vagus nerve which is the 10th cranial nerve. It leaves cranial cavity via jugular foramen and descends between internal jugular vein and internal carotid artery.
Where does the right vagus enter the thoracic cavity?
Between right subclavian artery and brachiocephalic trunk
Where does the left vagus nerve enter the thoracic cavity?
Posterior to the left brachiocephalic vein, between the subclavian and common carotid artery.
What does the right vagus nerve give off and where does it travel?
Gives off recurrent laryngeal nerve which winds around the subclavian artery
What does the left vagus nerve give off and where does it travel?
Gives off recurrent laryngeal nerve which winds around aortic arch just posterolateral to ligamentum anteriosum.
What is the function of the recurrent laryngeal nerves?
They supply:
- Intrinsic laryngeal muscles,
- Middle inferior pharyngeal constrictor muscles and,
- Sensory to laryngeal cavity below the level of vocal folds.
Briefly describe the sympathetic system (thoracolumbar outflow)
Body uses energy;
- Increases HR and strength of beat.
- Dilates coronary arteries,
- Constricts peripheral arteries.
- Relaxes bronchial smooth muscle,
- Closes sphincters,
- Controls body temp via BV and sweat glands.
Where are the preganglionic call bodies of the sympathetic system found?
In the intermediolateral (lateral) horn of grey matter in spinal segments T1-L2
Where are the postganglionic cell bodies of the sympathetic NS found?
Lie in either paravertebral sympathetic ganglia (lateral to vertebral bodies and anterior to neck or ribs, covered by parietal pleura) or in the prevertebral sympathetic ganglia, (lie around origins of branches of abdominal aorta).
Describe the ganglia of the cervical region
Superior ganglia, formed by the fusion of sympathetic nerves from C1-4, Middle ganglion by fusion of C5-6 and Inferior cervical ganglia by C7-8
What is the stellate ganglion?
It is the inferior cervical ganglia and T1. So fusion of C7-T1, it occurs occasionally
What allows for the fusion of the left and right sympathetic trunk?
The ganglion impar which sits just opposite the coccyx
Describe the different ways synapse in the sympathetic ganglia
- Synapse at its level
- Travel up the change and synapse in a cervical ganglia,
- Travel down and synapse in a lumbar/sacral ganglion
- pass through the sympathetic trunk without synapsing
Describe the direction of travel of neurons that synapse at its level in the sympathetic ganglia. Where does it supply?
Preganglionic fibres entre at its spinal level via white ramus communicantes and synapses onto postganglionic fibres which leave the ganglion via grey ramus communicantes and then join the spinal nerve at its level (either T1 to L2). These will supply the heart and dermatomes of T1 to L2
Describe the travel of sympathetic neurons that synapse at a higher level and what to they supply?
They enter the ganglia via white ramus communicantes at the levels of T1-L2 and then travel up to synapse in cervical ganglion. The post ganglionic axons pass into the grey ramus communicantes and join cervical spinal nerves. They will sipply heart, eyes and cervical dermatomes
Describe the travel of sympathetic neurons that synapse in lumbar/sacral regions. Where do these supply?
Enters the ganglia via WRC and then travels down to a ganglion either in the lumbar or sacral region, synapses and exits as postganglionic fibre via the GRC and joins the lumbar/sacral spinal nerves. They send sensory supply the lower limbs (lumbar and sacral dermatomes)
Describe the travel of the sympathetic neurons that do not synapse in the ganglion? What do they supply?
The preganglionic fibres pass through the trunk without synapsing and travel in splanchnic nerves to abdomen and synapse in the prevertebral ganglia to supply the abdominal viscera
What are the different splanchic nevres?
Thoracic splanchnic nerves (greater (T5-9), lesser (T10-11) and least splanchnic nerve (T12)), then lumber splanchnic nerves and pelvic splanchnic nerves
What is the unique 5th pathway the sympathetic fibres can travel?
Sympathetic fibres pass through the trunk without synapsing and instead synapse on the adrenal medulla directly. (it acts like a ganglion itself)
Describe what segments supply the sympathetics of the;
- Head,
- UL,
- Thoracic and abdo walls,
- LL
H - T1-T3,
UL - T4-T6,
TAW - T1 -T12,
LL - T12 to L2
What are the visceral plexuses?
A mix of sympathetic and parasympathetic fibres that mix to form visceral plexuses such as the cardiac plexus, pulmonary plexus and oesophageal plexus.
Describe features of the cardiac plexus
Sympathetics from T1-5 ganglia, middle and inferior cervical ganglia, parasympathetics from the vagus nerve
Describe features of the pulmonary plexus
Sympathetic from T2-4 ganglia and parasympathetics from vagus. Forms plexus around main bronchus.
Describe features of phrenic nerve
Sole motor supply to diaphragm. Sensory supply to mediastinum parietal pleura, parietal pericardium, peritoneum and pleura relating to central tendon of diaphragm
What is horner’s syndrome?
Cause by pancoast’s tumour which compromises the sympathetic supply to the head and neck on the same side as tumour. It causes ptosis of upper eyelid, pupillary constriction, anhydrosis and flushing of the face.
