How many sections is the mediastinum divided into?
4 areas - the heart contained within a fibrous sac
What is the route of the phrenic nerves?
C3, 4, 5 keep the diaphragm alive
They descend across the lateral border of the pericardium and into the diaphragm.
The phrenic nerve lies on top of the pericardial sac
How can you tell the difference between the phrenic and vagus nerve?
Identify the hilum, if the nerve sits anterior (phrenic) and if it sits posterior to the hilum (vagus)
What are the layers of the pericardium?
3 layers - fibrous, serous (parietal) and epicardium (serous visceral)
Between the two layers of serous pericaridum is the pericardial sac filled with pericardial fluid
What is a haemopericardium?
When the pericardial cavity fills with blood and the pressure around the heart prevents cardiac contraction (cardiac tamponade)
What is a pericardiocentesis?
The drainage of fluid from the pericardial cavity - the needle is inserted via the inrfasternal angle and directed superoposteriorly aspirating continously
What is the transverse pericardial sinus?
A space within the pericardial cavity that lies posterosuperioly. It lies posterior to the ascending aorta and pulmonary trunk, and anterior to the SVC
What are the great vessels in the pericardial cavity?
4 holes for the pulmonary veins Pulmonary artery Aorta SVC IVC
What are the clinically important surfaces on the heart?
Anterior (sternocostal) surface
Base (posterior) surface
Inferior (diaphragmatic) surface
What are the clinically important borders of the heart?
Right border
Left (lateral) border
Inferior border
Superior border
Where do you palpate the apex beat?
5th intercostal space in the midclavicular line (mitral area) Cardiac enlargement (cardiomegaly) often shifts the apex beat to the left
What is the most lateral nerve of the heart?
Phrenic nerve
What is the most medial nerve of the heart?
Vagus nerve
What makes up the SVC?
Brachiocephalic, internal jugular and subclavian vein
What drains into the internal jugular vein?
The head and neck
What drains into the subclavian?
Upper arm
What makes up the brachiocephalic vein?
The joining of the internal jugula and subclavian vein
What are the 3 parts to the aorta?
The ascending aorta then becomes the arch of the aorta and then comes the descending aorta that passes posteriorly to the heart
What are the 3 branches of the arch of the aorta?
Brachiocephalic trunk
Left common carotid (head and neck on left)
Left subclavian (left upper limb)
What is the purpose of the auricle?
The auricles are extensions of the atria which allow the atrial to fill with more blood
What is contained within the coronary groove?
Right coronary artery
It marks the tricuspid valve (boundary between the right atrium and right ventricle
What does the anterior interventricular groove hold?
A branch of the lelft coronary artery (LAD - left anterior descending artery)
What makes up the majority of the base of the heart?
Left atrium
What is the coronary sinus?
The main venous drainage of the heart - it is a short venous conduit (in the atrioventricular groove posteriorly) which receives deoxygenated blood from most of the cardiac veins and drains into the right atrium
The coronary sinus is the inferior surface and anything about it is the base
Where is the interventricualr groove?
Indicates the boudary between the two ventricles on the diaphragmatic surface of teh heart. The posterior interventricualr artery sits in it
What is the purpose of the azygous vein?
Drainage for the intercostal arteries, it will drain into the SVC
What is the first branch of the aorta?
The coronary arteries (NOT the braciocephalic trunk)
Why can you not usually see the coronary arteries?
They are covered with fat
Where does the right coronary artery run?
The right atrioventricular groove - retracts to the right auricle to locate the origin of the vessel
What will the circumflex artery anastomse with?
The circumflex artery will anastomose with the posterior interventricular artery, and therefore the left and right coronary arteries are connected via anastomoses
What is the purpose of grooves in the heart?
The grooves on the heart surface indicate the positions of the cardiac septum which divides the heart into a left and right side. Use the grooves to enable identification from the surface of the heart of the 4 internal chambers in dissection
What is a septum?
A muscular wall that separates the right and left heart
What are the two parts to the septum?
The part between the two atria is called the inter-atrial septum (indicated by the inter-atrial groove)
The part between the two ventricles is called the inter-ventricular septum (indicated by the anterior inter-ventricular groove)
What can occur with a septal defect?
The mixing of atrial and venous blood in the heart - can be a life threatening problem. This can cause hypoxaemia
What are the two surfaces of the right atrium?
Muscular and smooth
The crista terminalis differentiates smooth and muscular area
What is the oval fossa?
Embryological remnant that was that was a connection between the left and right atria which closes at birth
What shape are the AV vales?
Leaflet
What are the shapes of the pulmonary and aortic valves?
Semilunar
What are papillary muscles?
Muscles attached to the valves and onto the ventricular walls. The papillary muscle is attaches to the valves via the tendinous chord - their function is to prevent regurgitation during ventricular contraction
What is the fibrous skeleton?
A skeleton of connective tissue that gives the valves structural integrity and also assists electrical conduction within the heart
What is a moderator band?
A shortcut of electrical activity to the anterior cusp of the tricuspid valve allowing contraction at the same time as the other 2 cusps
What are the 3 supplies of nerves to the heart?
Autonomic innervations (sympathetic and parasympathetic)
Visceral afferent nerves (pain fibers, reflex afferents)
Conduction system of heart and arrhythmia
How does the autonomic innervation and visceral afferent nerves reach the heart?
Via the cardiac plexus
Where do the pain fibers travel?
They travel to the spinal chord alongside the sympathetic nerves in the cardiopulmonary splanchnic nerves and cardiopulmonary plexus
How do the visceral afferents travel from the baroreceptors to the brain?
In the vagus nerve (some in accessory spinal nerve)
How do the sympathetic nerves get from the CNS to the organs?
Via presynaptic and postsynaptic fibers
They synapse in the sympathetic chain ganglion
What is a ganglion?
The synapse between an axon of a presynaptic neurone and the cell body of the postsynaptic fiber
What are the neurotransmitters present in the sympathetic chain?
Acetylcholine (presynaptic to ganglion
Noradrenaline (ganglion and organ)
What is the course of the sympathetic fibers leaving the CNS?
They travel inferiorly within the spinal cord tracts and then exit the spinal cord in one of T1-L2/3 spinal nerves (thoracolumbar)
What are the 5 options that the sympathetic nerves can do once they leave the spinal cord?
Go into the ganglion of that level and synapse
Travel superiorly in the sympathetic chain to another ganglion and synapse
Travel inferiorly in the sympathetic chain to another ganglion and synapse
Pass straight through the sympathetic chain ganglion without synapsing (abdominopelvic splanchinic nerves )
Pass straight through to the adrenal medulla without synapsing as an abdominopelvic splanchinc nerve (directly stimulating adrenaline release)
What nerves run through the cardiopulmonary splanchnic nerves?
Sympathetic nerves to the heart and lungs
Postsynaptic fibers from cervical and upper thoracic sympathetic chains
Found behind the great vessels
What is contained within the cardiac plexus?
Sympathetic fibers (cardiopulmonary splanchinic nerve) Parasympathetic fibers (vagus) Visceral afferent fibers (pain fibers are relayed in the sympathetics, baroreceptors are relayed in the vagus) It is an intertwining of nerves that runs behind the heart and sits on-top of the trachea
What is the neuotransmitter present in parasymathetic signals?
Acetylcholine
What is the supply to the organs of the lower abdomen, pelvis and perineum?
Pelvic splanchnic nerves are PARAsympathetic
Where can somatic pain be felt?
Muscular Joint Bony Intervertebral disc Fibrous (pericardial) Nerve
What does somatic pain feel like?
Sharp, stabbing, well localised
Where can you feel visceral (organ) pain?
Heart and great vessels
Trachea
Oesophagus
Abdominal viscerae
What does visceral pain feel like?
Dull, aching, nauseating, poorly localised
What is radiating pain?
Pain felt in the centre of the chest AND felt spreading from there (upper limbs, back, neck)
What is referred pain?
Pain only felt at a site remote from the area of tissue damage in the chest (upper limbs, back, neck)
What is acute/chronic pain?
Repeated acute episodes vs chronic pain
Why is somatic pain sharp?
It is well locaised due to precisely (somatotopically) organised pathways from periphery and projections to cortex
What is the action of the nerve if you get prodded in the chest?
The impulse will travel along the anterior ramus, then through the spinal nerve of the dermatome where you were prodded, through the posterior root and rootlets and into the spinal chord.
The impulse then crosses the spinal cord where it will enter the cerebral cortex
What is the function of the postcentral gyrus of the parietal lobe (somatosensory)?
AP’s arriving here will bring body wall (somatic) sensations into conscioussness
What is the function of the precentral gyrus of the frontal lobe (somatomotor)?
AP’s originating here will bring about contraction of the body wall (somatic) skeletal muscle
What is the sensory homunculus?
The areas of the cerebral neocortex where sensations from different body wall structures reach conscioussness
What are teh three somatic central chest pain sources?
Herpes zoster
Muscle, joint or bone
Parietal pleura and fibrous pericardium
How can herpes zoster cause central chest pain?
Reactivation of dormant virus in posterior root ganglion, pain can be felt anywhere in that dermatome
The pain preceds with blisters - patient with shingles developing in T4/5 dermatome may present with central chest pain
How can muslce/joint/bones cause central chest pain?
Pectoralis major/intercostal muscle strain
Disolcated costochondral joint
Costoertebral joint inflammation
Slipped thoracic intervetebral disc
How can the parietal pleura and fibrous pericadium cause central chest pain?
Pleurisy
Pereicarditis
What are dull central chest pain sources?
Trachea (tracheitis)
Aorta (ruptured aneurysm of aortic arch)
Oesophagus (oesophagitis)
Heart (angina, MI)
Abdominal viscarae (gastritis, cholecystitis, pancreatitis, hepatitis)
What separates the cerebrum into the parietal and frontal lobe?
Central sulcus
What does the sternal angle separate in the mediastinum?
Anything above is superior mediastinum (great vessels in superior mediastinum)
What are some significant features of the right mediastinum?
Vagus nerve found on trachea, passes posteriorly to the root of the lung and willl follow the oesophagus into the abdomen
The azygous vein crosses over the top of the root of the lung to drain into the SVC
“Venous side”
What are the bulges in the intercostal spaces?
Sympathetic ganglia
What are some significant features of the left mediastinum?
“Arterial side”
Only on the left can you identify the aorta
The vagus nerve crosses the aorta - it will branch to give the recurrent laryngeal nerve
What is the ligamentum arteriosum?
Remnant of ductus arteriosus that connects the PT to the arch of the aorta
How does referred/radial pain occur?
Due to the close proximity of where the somatic and visceral afferents synapse in the spinal cord. The route visceral afferents take from heart via neck & upper thoracic regions of trunk/cord leads to radiating and referred pain from the heart – due to lack of precision in route taken by visceral afferents to the spinal cord
How can radiating pain be explained?
If the pain if originating in a somatic structure then the radiation is along the affected dermatome
If the pain is from the heart then the radiation is to the dermatomes supplied by the spinal cord levels at which the cardiac visceral afferents enter the sympathetic chain/spinal cord
Why does referred pain occur?
Due to afferent (sensory) fibres from soma and afferent (sensory) fibres from viscera (visceral afferents) entering the spinal cord at the same levels
The brain chooses to believe that the pain signals coming from the organ, are actually coming from the soma
in CARDIAC referred pain the brain chooses to believe the pain signals are coming from the upper limbs (especially the left upper limb) or from the back, neck (or jaw).
What are the different types of MI?
Classified due to which surface of the heart has been affected:
Anterior MI
Inferior MI
Anterolateral MI
What do the coronary arteries arise from?
The right and left aortic sinuses of the ascending aorta
Where does the right coronary artery sit?
In the right atrioventricular groove - retract right auricle to locate origin of vessel
What are the two branches of the RCA?
Marginal artery (moves horizontally at the inferior aspect of heart) Posterior interventricular artery (back of heart)
Where does the LCA sit?
In the left atrioventricular groove between the pulmonary trunk and left auricle
What are the branches of the LCA?
Marginal artery (runs along lateral aspect of left side of heart) Circumflex artery (runs along the back of the heart) Left anterior descending - runs down from the left atria to the left ventricle Lateral (diagonal) branch - branches off the LAD
What supplies the AV and SA node?
The branches of the RCA - if blood supply becomes compromised arrhythmia’s can arise
What supplies the inter-ventricular septum?
Dual blood supply from RCA and LCA
What are the 4 commonest sites for coronary atherosclerosis?
LAD
RCA
Circumflex
Left (main stem) coronary artery
How can coronary atherosclerosis be treated?
CABG (coronary artery bypass grafting)
What is the thoracic outlet?
The area of the superior mediastinum that is bounded by ribs 1, T1 vertebra and the jugular notch
What is located in the anterior mediastinum during childhood and what happens during puberty?
The thymus but after puberty it involutes and is converted to adipose (fatty) tissue
What is located within the middle mediastinum?
Pericardium
Heart
The parts of the great vessels that connect with the heart: inferior part of the SVC, superior part of the IVC, pulmonary trunk and pulmonary arteries, pulmonary veins and ascending aorta
What parts of the great vessels are located within the middle mediastinum?
The initial parts of the great vessels are contained within the middle mediastinum
What is located within the posterior mediastinum?
The azygous vein (conveys blood from the intercostal veins to the SVC)
Sympathetic chains/trunks
Thoracic duct
Vagus nerves - contained within a plexus
2 main bronchi
Thoracic aorta
The oesophagus
How do the vagus nerves and the oesophagus leave the posterior mediastinum?
The nerve plexus along with the oesophagus leaves the posterior mediastinum via 2 vagal trunks
What is the route of the azygous vein?
It arches anteriorly, superior to the right lung root to drain into the SVC. The structure sitting immediately superior and posterior to the root of the lung is the azygous vein
What is the other name for the descending aorta?
The thoracic aorta
What branches off the ascending aorta?
The coronary arteries
What branches off the aortic arch?
Braciocephalic trunk, left common cartoid and the left subclavian
What do the common carotid arteries supply?
The head and neck
What do the subclavian arteries supply?
The upper limbs
What do the bilateral branches of the descending aorta supply?
The posterior intercostal arteries
What supplies the anterior intercostal arteries?
They internal thoracic arteries
What do the unilateral branches coming off the descending aorta supply?
Branches from the thoracic aorta’s anterior surface:
Bronchial arteries (arterial blood for lung tissue)
Oesophageal arteries
Mediastinal arteries
Pericardial arteries
Phrenic arteries (for diaphragm)
Where does the aorta pass through the diaphragm?
Aortic hiatus
What are the two subdivisions of lymphatics?
Superficial and deep
The superficial lymph vessels accompany superficial veins and deep lymph vessels will accompany deep veins
What is the largest lymphatic structure in the body?
The thoracic duct
What drains into the left venous angle?
The thoracic duct - left subclavian and internal jugular vein
What drains into thoracic duct?
All of the lower limbs, abdomen, left arm and left half of head and neck
Where does the lymph from the right arm an right half of head and neck drain into?
The right lymphatic duct at the right venous angle
What veins at are the venous angles?
The subclavian and internal jugular veins which join together to form the braciocephalic veins
Where are the bronchopulmonary veins located?
The hilar nodes are around the main bronchus at the lung root
Where will lymph that arrives at hilar nodes travel to?
It will travel to the trachea-bronchial lymph nodes around the bifurcation of the trachea (posterior mediastinum)
Where can the left inferior lobe sometimes drain into?
The right lymphatic duct
Where can the thoracic duct be located?
It is a tiny structure but can be located between the azygous vein and the oesophagus. Looking at the posterior mediastinum and if something is pinned between the azygous vein and the oesophagus then it will be the thoracic duct
What it a trick to finding the vagus and phrenic nerve?
Find the root of the lung - anterior is phrenic and posterior is the vagus nerve
What is underneath the liamentum arteriosum?
The recurrent laryngeal branch of the left vagus nerve
Why is the laryngeal nerve recurrent?
It heads back up towards the larynx
What are the big visceral structures in the superior mediastinum from anterior to posterior?
Veins are most anterior structure, then the arteries (arch of aorta), behind that is the oesophagus.
The most posterior part of the superior mediastinum is the thoracic duct
What are the nerves in the superior mediastinum from lateral to medial?
Most laterally is the phrenic nerve
The middle nerve is the vagus nerve
The most medial nerve is the recurrent laryngeal nerve
What are the central veins?
IJV Subclavian Brachiocephalic SVC Right atrium IVC Iliac veins Femoral
What is the most common access point in central venous cannulation?
Internal jugular vein
Femoral veins
Where does the right recurrent laryngeal nerve hook under?
It hooks under the right subclavian artery and so it does NOT enter the chest
What do the phrenic nerves supply?
The anterior rami of cervical spinal nerves 3,4 and 5 Somatic motor to the diaphragm Somatic sensory to: Mediastinal parietal pleura Fibrous pericardium Diaphragmatic parietal pleura Diaphragmatic parietal peritoneum
Where will diaphragmatic pain refer to?
The shoulder tip
What does the vagus nerve supply?
Cranial nerves X
Contain:
Somatic sensory nerves for the palate, laryngopharynx and larynx
Somatic motor nerves for the pharynx and larynx
Autonomic parasympathetic nerves for the thoracic and abdominal organs
Recurrent laryngeal nerve - branches of the vagus nerve that supply the pharynx and larynx
What does the cephalic vein supply?
The superficial vein of the upper limb
What do the anterior intercostal arteries drain into?
The internal thoracic vein