The thoracic inlet Flashcards
What is the thoracic inlet formed from?
The first thoracic vertebrae, the first ribs and their costal cartilages and the manubrium
What does the first rib articulate with?
The head articulates with its own first thoracic vertebra
The neck articulates with the transverse process of T1
In what direction do the bodies of the ribs travel?
Downwards and forwards towards their costal cartilages
What does a chrondrosternal joint connect?
The lateral border of the sternum and the costal cartilages
What is the classification of a chondrosternal joint?
A primary cartilaginous, immobile joint
In what direction does the thoracic inlet slope?
Downwards and forwards
What is the mediastinum?
The space between the pleural cavities which occupies the centre of the thoracic cavity
What are the borders of the superior mediastinum?
It is limited superiorly by the thoracic inlet and inferiorly by a transverse plane that passes backwards from the manubriosternal joint to the T4/5 intervertebral disc.
How are the brachiocephalic veins formed?
The union of the internal jugular vein with the subclavian vein, posterior to the sternoclavicular joint
What are the subclavian veins?
The continuations of the axillary veins and arch over the first rib, anterior to scalenus anterior
What path is taken by the internal jugular veins and what do they supply?
They start in the jugular foramina in the skull, from the sigmoid sinuses.
They descend in the neck lateral to the internal and common carotid arteries, and receive much of the deep venous drainage from the head and neck
What happens to the brachiocephalic veins?
They unite to form the superior vena cava behind the lower border of the first right costal cartilage
What are the major veins in the thoracic inlet?
Brachiocephalic
Subclavian
Internal jugular
Where does the arch of the aorta travel after leaving the heart?
Passes mainly anteroposteriorly from the manubrium, beginning and ending at the T4/5 level. It runs beside the trachea and arches over the left main bronchus
What are the 3 main branches from the aorta?
- Brachiocephalic
- Left common carotid
- Left subclavian
Where is the brachiocephalic artery and what does it divide into?
Lies to the right of the trachea and ascends to divide into the right subclavian and right common carotid arteries
Where does the subclavian artery lie?
Behind scalenus anterior and is described as having three parts in relation to that muscle
What are the main branches of the subclavian artery?
- Internal thoracic artery
- Vertebral artery
- Thyrocervical trunk
- Costocervical trunk
Where does the internal thoracic artery run and what does it supply?
Down the inner aspect of the thoracic wall behind the costal cartilages just lateral to the sternum, sending anterior intercostal branches into the appropriate spaces and perforating branches to supply the breast.
Its terminal branches are the musculophrenic and superior epigastric arteries
What is the path of the vertebral artery?
Ascends and enters the transverse foramen of C6, where it ascends in these foramina, finally entering the foramen magnum. It unites with its partner to form the basilar artery, supplying cerebellum and occipital lobe. During its course it also sends spinal branches to the vertebrae and spinal cord.
What arteries are given off by the thyrocervical trunk and what do they supply?
Gives the inferior thyroid artery supplying the lower poles of the thyroid gland, and the ascending cervical, suprascapular, and transverse cervical arteries. These arteries lie in the posterior triangle of neck, supplying adjacent muscles.
The suprascapular artery provides important branches to the scapular anastomosis which is completed by branches from the axillary artery in the upper limb
What does the costocervical trunk supply?
Posterior intercostal arteries to the upper intercostal spaces, and the deep cervical artery to deep structures in the neck
What is the path taken by the common carotid artery on both sides?
Ascends in the carotid sheath on scalenus anterior, dividing into internal and external carotid arteries at the upper border of the thyroid cartilage, which is around the C4 level
What is the path taken by the internal carotid artery on both sides?
Ascends to enter the carotid canal in the skull to supply the orbit and brain
What branches are given by the external carotid artery?
Ascending pharyngeal, superior thyroid, lingual, facial, occipital, posterior auricular, with its terminal branches being the superficial temporal and maxillary arteries
Where is the thoracic duct located?
Enters the junction of the left subclavian and left internal jugular veins behind the sternoclavicular joint
How is lymph from the thorax drained into the vascular system?
Via the thoracic and lymphatic trunk
What type of organ is the thymus gland?
Primary lymphoid organ
Where is the thymus gland?
It lies in the superior mediastinum and the anterior part of the inferior mediastinum.
How does the size of the thymus gland change with age?
Larger in childhood
After puberty, it atrophies and undergoes fibrofatty degeneration
Where is the left phrenic nerve in the thorax?
Above the aortic arch and anterior to the apex of the lung
It descends to the fibrous pericardium overlying the left ventricle
Where is the right phrenic nerve in the thorax?
Runs behind the right brachiocephalic vein and then onto the right side of the superior vena cava and right atrium
What nerve roots are the phrenic nerves from?
C3, 4, 5
What is the role of the phrenic nerves?
Supply motor and sensory fibres to the diaphragm and sensory fibres to the pericardium, mediastinal pleura, and subdiaphragmatic peritoneum
Where is the left vagus nerve in the thorax?
Descends in the carotid sheath lateral to the common carotid artery. At the aortic arch, it is crossed anteriorly by the phrenic nerve. It then descends behind the left bronchus to form the pulmonary plexus
What branch is given off by the left vagus nerve?
Where is this nerve located?
The left recurrent laryngeal nerve
Winds around (lateral to) the ligamentum arteriosum and ascends medial to the aortic arch
Where is the right vagus nerve in the thorax?
Runs with the common carotid artery and the brachiocephalic trunk. It runs beside the trachea before descending behind the right main bronchus
What branch is given off by the right vagus nerve?
Where is this branch given off?
The right recurrent laryngeal nerve
As it passes anteriorly over the subclavian artery
Where to the recurrent laryngeal nerves travel to?
Ascend in the tracheo-oesophageal groove to reach the larynx
What is the anterior vagal trunk composed of?
Predominantly of parasympathetic fibres from the left vagus
What is the posterior vagal trunk composed of?
Predominantly of parasympathetic fibres from the right vagus
Where do the vagal trunks travel?
What do they innervate?
Through the diaphragm to the stomach
They provide parasympathetic supply to the intestinal tract as far as two-thirds of the way along the transverse colon
What plexuses are formed by the vagus nerves?
Both vagi contribute parasympathetic fibres to the pulmonary plexus, then reform as an oesophageal plexus which gives of the anterior and posterior trunks
Where does sympathetic outflow emerge from the spinal cord?
T1 - L1 only
How is the sympathetic chain formed?
Preganglionic fibres leave the anterior rami of the spinal nerves and constitute the white rami communicantes
What ganglia are formed by the sympathetic chain?
- Inferior cervical ganglion
- Middle cervical ganglion
- Superior cervical ganglion
Where is the sympathetic chain?
Lateral to the vertebral column, extends from the thorax to the neck
Describe the inferior cervical ganglion
Often fuses with the upper thoracic ganglion to become the stellate ganglion. It lies on the neck of the first rib and forms a plexus on the subclavian artery to be distributed with its branches
Describe the middle cervical ganglion
Closely related to the inferior thyroid artery and sends branches with it
Describe the superior cervical ganglion
Lies opposite the atlas and axis, and sends branches to form plexuses on the external and internal carotid arteries to be distributed with their branches.
What is given off by all 3 cervical ganglia?
All three ganglia give branches to the cardiac plexuses, and also grey rami communicantes to the cervical somatic nerves
How many grey rami communicantes are sent to cervical somatic nerves by the INFERIOR cervical ganglion?
2
How many grey rami communicantes are sent to cervical somatic nerves by the MIDDLE cervical ganglion?
2
How many grey rami communicantes are sent to cervical somatic nerves by the SUPERIOR cervical ganglion?
4
What the effect of vagal innervation in the heart, lungs and GI tract?
Heart: decreases heart rate and cardiac output
Lungs: mediates bronchoconstriction
GI tract: relaxes sphincters and stimulates general peristalsis
What is controlled by sympathetic innervation?
Arrector pili muscles (pilomotor)
Vascular constriction (vasomotor)
Sweat glands (sudomotor)
In the head and neck, sympathetic innervation also causes pupillary dilatation (counteracting the parasympathetic) and raises the eyelid involuntarily through supplying part of levator palpebrae superioris
