4. Thorax IV Flashcards
What is the cardiac skeleton?
- Collection of dense, fibrous tissue in the form of four rings
- These four rings interconnect in a plane between the atria and ventricles
- The cardiac skeleton surrounds the AV origices, aortic orifice and the opening of the pulmonary trunk
- Helps maintain integrity of openings and acts as attachment point for cusps
- Separates muscular wall of atria from ventricles as well as electronically isolating the ventricles (the AV bundle is the single connection between these two groups of myocardium)
Why is it important for the walls of the atria to be electronically isolated from ventricles?
So that atria contract first and then action potential travels to ventricles to cause contraction (in order for blood to empty into the ventricles and then be forced out of ventrices. If both atria and ventricles received electronic impulses simultaneously then there would be no proper flow of blood)
Label this image
How many papillary muscles are there in the right ventricle?
- There are three cusps with corresponding papillary muscles attached to them (via chordae tendinae)
- Anterior, posterior and septal
- The septal papillary muscle is not always obvious hence chordae tendinae appears to be attached directly to trabeculae carnae
- Largest cusp is the anterior cusp
- Posterior may consist of 1-3 structures
- Septal is small/inconsistent
What is the septomarginal trabeula?
- bridge between the lower interventricular septum to the base of anterior papillary muscle
- septomarginal trabecula is aka the moderator band
- the septomarginal trabecula carries a portion of cardiac conduction system to anterior wall of the right ventricle
- hence whole of right ventricle contracts in a coordinated way
How many cusps are there in the left atrioventricular valve?
- Two
- Anterior and posterior forming the mitral valve (bicuspid valve)
- The anterior papillary muscles are more prominent than the posterior
- As there is no third cusp there is no septal papillary muscle on left ventricle
Where is the ascending aorta located?
Inside the pericardial sac
Where is the arch of the aorta located?
Superior mediastinum, behind manubrium sterni (manubrium of the sternum)
Becomes continuous with the descending aorta at the level of the sternal angle
What are the branches of the aortic arch?
Right: brachiocephalic trunk (which divides to right common carotid artery and right subclavian artery)
Left: left common carotid artery and left subclavian artery
Is there variation from person to person regarding branches from the aortic arch?
yes, can get vertebral arteries branching from aorta instead of subclavian, or brachiocephalic trunk on left instead of right, or no brachiocephalic trunk etc.
Where does descending aorta begin?
Level of sternal angle (T4-T5)
descends in the posterior mediastinum and passes through aortic hiatus of diaphragm at T12
passes posterior to the left main bronchus
which intercostal arteries are branches of the musculophrenic artery?
Anterior intercostal arteries T7-T12
Which intercostal arteries are branches of the superior intercostal artery?
Posterior intercostal arteries T1-T2
What fuses to form the right/left brachiocephalic veins?
The internal jugular veins and subclavian veins fuse to become the brachiocephalic veins
How is SVC formed?
Fusion of right and left brachiocephalic veins
How is IVC formed?
Fusion of right and left common iliac veins
Where must lymph pass through before returning to the bloodstream?
At least one lymph node as this filters lymph and contains a congregation of immune cells
lymph goes through afferent vessel to lymph nodes, gets exposed to immune cells, then leaves via efferent vessels (which contain cleaner lymph to be returned to the bloodstream)
Where do the lymph vessels of the anterior thoracic wall drain into?
Parasternal lymph nodes
Diaphragmatic lymph nodes
Where do lymph vessels of the posterior thoracic wall drain into?
Intercostal lymph nodes located at head and neck of ribs
Where do the lymph vessels of the lungs drain into?
Tracheobronchial lymph nodes
What is the major lymphatic vessel of the body?
The thoracic duct
Where does the thoracic duct start?
Cisterna chyli (a dilated sac at the inferior porteion of the thoracic duct)
Which vein does the thoracic duct drain into?
Left brachiocephalic vein (passes behind the arch of the aorta to enter the left brachiocephalic vein)
Which parts of the body does the thoracic duct drain?
- All parts below level of diaphragm
- left side of body above level of diaphragm
What lymph vessel drains the right side of the body above the level of the diaphragm?
Right lymphatic duct (drains upper right quadrant of the body)
Where does the right lymphatic duct drain into?
Right subclavian vein
What is the outflow of the sympathetic system?
Thoracolumbar outflow
From which horn of grey matter does the sympathetic outflow originate?
Lateral horn of grey matter
Where do some neurons of sympathetic nervous system synapse?
some preganglionic fibres synapse at the sympathetic chain (paravertebral ganglia on either side of the vertebral column)
Which areas of the spinal cord contain a lateral horn in its grey matter?
Only the thoracic and the lumbar (sacral and cervical do not have any lateral horns)
Hence, if we see a cross-section of spinal cord containing a lateral horn we know it is either from the thoracic or lumbar region.
Where does sympathetic outflow run from and to?
T1-L2
Why do some sympathetic neurons pass up or down the sympathetic chain without synapsing at the paravertebral ganglia?
In order to โsupplyโ sympathetic innervation to their target areas, hence move up or down chain to get closer to their targets and then synapse at the ganglia
Where does the sympathetic neuron pass through to enter the paravertebral ganglia?
white ramus communicans
Describe the course of the sympathetic neuron from when it leaves lateral horn of grey matter
- Travel along with spinal nerve
- Travels through white matter communicans
- Enters paravertebral ganglion, may or may not synapse here
- if it does synapse, it runs along with the spinal nerve through the grey matter communicans
Which communicating matter does a pre-ganglionic sympathetic nerve pass through and which does a post-ganglionic sympathetic nerve pass through?
White ramus communicans (pre-ganglionic)
Grey ramus communicans (post-ganglionic)
What is the benefits of having (mostly) short pre-ganglionic sympathetic nerve fibres and many long post-ganglionic nerve fibres?
Widespread and divergent response
Important for fight or flight repsonse because want to get innervation to msucles, limbs, increase cardiac output etc.
What are the lower 8 ganglia of the sympathetic nervous system called?
Thoracic Splanchnic nerves
They do not synapse at the paravertebral ganglia, hence have long pre-ganglionic fibres passing through the sympathetic chain
Instead, they synapse at pre-vertebral ganglia (mostly located around the blood vessels of the aorta) which are much closer to the target organ
The much shorter post-ganglionic fibres โinnervateโ visceral tissues and organs within abdominopelvic cavity
What are the benefits of the post-ganglionic fibres of the splanchnic nerves being so short?
More controlled, limited and direct response to particular organ or strucutre.
Which sympathetic nerves make up part of the greater splanchnic nerves?
T5-T9/10
Where do the pre-ganglionic fibres of the greater splanchnic nerves synapse?
The coeliac ganglion
What do the post-ganglionic fibres of the greater splanchnic nerves innvervate?
The foregut viscera
What level are the pre-ganglionic fibres of the lesser splanchnic nerves coming from?
T9-T10 OR T10-T11
Where do the pre-ganglionic fibres of the lesser splanchnic nerves synapse?
aorticorenal ganglion/ superior mesenteric ganglion
What do the post-synaptic fibres of the lesser splanchnic nerves innvervate?
Midgut viscera
What is the level at which the pre-ganglionic fibre of the least splanchnic nerves are located?
T12
Where does the pre-glanglionic fibre of the least splanchnic nerve synapse?
Renal ganglion
What do the post-synaptic ganglia of the least splanchnic nerves innervate?
Kidneys and upper ureter
What is the level of the pre-ganglionic fibres of the lumbar splanchnic nerves?
L1-L2
what do the the post-ganglionic fibres of the lumbar splanchnic nerves innvervate?
Hindgut viscera
Where do the pre-glanglionic fibres of the lumbar splanchnic nerves synapse?
inferior mesenteric ganglion
Where do phrenic nerves originate from?
C3, 4, 5 which then fuse to become the right and left phrenic nerves
What kind of fibres do the phrenic nerves contain?
Sensory, motor and sympathetic nerve fibres
What structures do the phrenic nerves innervate?
Only source of motor supply for the diaphragm
Sensation to the central tendon of the diaphragm
sensation to mediastinal and diaphragmatic pleura and the pericardium
Describe course of C3, 4 and 5
Sympathetic fibres originated in the thoracic region and moved up or down sympathetic chain
Synapsed at the cervical region and then run with spinal nerve to the diaphragm
What is location of the phrenic nerves?
Enter superior mediastinum lateral to vagus nerve and posterior to brachiocephalic vein
Passes nteriorly to hilum of the lung (lung root) and over the pericardium of heart, sending small pericardial branches to it
what is vagus nerve?
CN X (10)
passes posterior to the lung route
part of the parasympathetic nervous system
involved in autonomic control of the heart and digestive tract etc.
travels in the carotid sheath alongside the carotid artery and internal jugular vein
โsuppliesโ motor parasympathetic fibres to all organs except adrenal glands, from neck down to the second segment of the transverse colon (this is innervated by the pelvic splanchnic nerves)
Controls few skeletal muscles like superior, middle and inferior pharyngeal constrictors and muscles of the larynx (recurrent laryngeal)
parasympathetic innervation to the sino-atrial and atrio-ventricular nodes of the heart
What trunks do the vagus nerves form in the thorax?
- Right vagus nerve forms the posterior vagal trunk
- Left vagus nerve forms the anterior vagal trunk
What is the signigicance of the vagal trunks?
Branches from the vagal trunks contribure to the oesophageal plexus which innervates smooth muscle of the oesophagus
Two other branches arise in thorax
- left recurrent larungeal nerve - hooks under arch of aorta, ascending to invervate intrinsic msucles of the larynx
- cardaic branches - innervate to regulate heart rate and โprovideโ visceral sensation to the organ
