superior & posterior mediastinum & diaphragm

Question 1

what is the mediastinum?

Answer 1

the central component of the thoracic cavity located between the 2 pleural sacs
-contains most of the thoracic organs (not lungs!)

Question 2

how is the mediastinum divided?

Answer 2

• divided into 2 parts by an imaginary line that runs from the sternal angle to the T4 vertebrae
  -superior mediastinum - extends upwards
  -inferior mediastinum - extends downwards and is further subdivided into the anterior, middle and posterior mediastinum

Question 3

what are the anatomical borders of the superior mediastinum?

Answer 3

-superior - thoracic inlet (important anatomical passageway between neck and thorax - formed by 1st rib)
-inferior - level of sternal angle
-anterior - manubrium of sternum
-posterior - T1-T4
-lateral - pleurae of lungs

Question 4

what important arteries does the superior mediastinum contain?

Answer 4

-arch of aorta
-the 3 main branches of the arch of aorta arise in the SM - brachiocephalic, left common carotid & left subclavian

Question 5

what important veins are located in the superior mediastinum?

Answer 5

• brachiocephalic veins (draining blood from upper bod)
  -superior intercostal vein - collects blood from left 2nd & 3rd intercostal vein
  -azygos vein

Question 6

Describe the nerves that the superior mediastinum contains

Answer 6

-vagus nerve - 2 distinctive paths
- right vagus nerve - runs parallel to trachea and passes posteriorly to superior VC
-left vagus nerve - enters SM between left common carotid & left subclavian arteries
-left recurrent laryngeal nerve arises from left vagus nerve
-phrenic nerve

Question 7

other than vessels and nerves, what other structures are contained within the superior mediastinum?

Answer 7

-thymus
-trachea
-oesophagus
-thoracic duct

Question 8

what is the anterior mediastinum?

Answer 8

a division of the inferior mediastinum

Question 9

what does the anterior mediastinum contain?

Answer 9

no major structures

Question 10

what is the middle mediastinum?

Answer 10

the largest subdivision of the inferior mediastinum

Question 11

what does the middle mediastinum contain?

Answer 11

• heart and its protective pericardium
  -tracheal bifurcation
  -left and right main bronchi
  -ascending aorta
  -pulmonary trunk - right and left pulmonary arteries
  -superior vena cava
  -phrenic nerves (L +R)
  -cardiac plexus

Question 12

what is the cardiac plexus?

Answer 12

a network of nerves located at the base of the heart, containing sympathetic and parasympathetic fibres

Question 13

what is the posterior mediastinum?

Answer 13

a subdivision of the inferior mediastinum

Question 14

what major structures does the posterior mediastinum contain?

Answer 14

-oesophagus & its nerve plexus
-descending thoracic aorta & branches
-azygos system of veins
-thoracic duct and associated lymph nodes

Question 15

what is the descending thoracic aorta?

Answer 15

-continuation of the arch of the aorta, . -It descends through the posterior mediastinum to the left of the vertebrae
- thoracic aorta becomes the abdominal aorta later on

Question 16

what is the thoracic duct?

Answer 16

-largest lymphatic vessel in the body, allowing return of lymph from most of the body into the venous system.
- thoracic duct receives lymphatic drainage from the intercostal spaces and neighbouring anatomical structures through a number of branches.

Question 17

what are the 2 main functions of the diaphragm?

Answer 17

• separates the thoracic cavity from the abdominal cavity
  -contracts and relaxes - aiding in inspiration & expiration

Question 18

what are the 3 peripheral attachments of the diaphragm?

Answer 18

-lumbar vertebrae and arcuate ligaments
-costal cartilages of ribs 7-10
-xiphoid process of the sternum

Question 19

what are arcuate ligaments and name the 3 of them in the diaphragm

Answer 19

-fibrous bands found around the diaphragm and the abdominal aorta
-median arcuate ligament, lateral arcuate ligament & the medial arcuate ligament

Question 20

what do the muscle fibres of the diaphragm combine to form and what does this structure ascend to?

Answer 20

• a central tendon
  -this tendon ascends to fuse with the inferior surface of the fibrous pericardium

Question 21

what are the 2 sides of the diaphragm called?

Answer 21

-right and left dome

Question 22

what are the 3 hiatus’ in the diaphragm?

Answer 22

-caval hiatus
-oesophageal hiatus
-aortic hiatus

Question 23

what happens to the diaphragm and the oesophagus during inspiration?

Answer 23

-diaphragm pulls down to allow the expansion of the thoracic cavity
-the oesophagus narrows during inspiration to prevent reflux

Question 23

what nerve gives a motor supply to the diaphragm?

Answer 23

the phrenic nerve

Question 24

why can diaphragm pain be referred to the shoulder?

Answer 24

due to the shared innervation of the phrenic nerve. The phrenic nerve originates from the cervical spinal nerves C3-C5
-phrenic nerve also provides some sensory innervation to shoulder