5. Heart and nerves of the thorax Flashcards
Pericardium
Fibro-serous sac surrounding heart and its great vessels Consists of 2 layers: Fibrous and Serous Serous has 2 parts: Parietal: lines fibrous Visceral: adheres to heart
How many pericardial sinuses are there? Describe each
2
Transverse pericardial sinus: separates arteries from veins
Oblique pericardial sinus: is formed by reflection onto the pulmonary veins of heart
Where would you palpate to feel the apex beat of the heart?
5th intercostal space
Describe the outflow of chambers of the heart
Right atrium: Blood returns via SVC and IVC (body) and coronary sinus (heart)
Left atrium: Blood returns via pulmonary veins
Right ventricle: Outflow to the pulmonary trunk
Left ventricle: Outflow to the ascending aorta
Coronary sinus
Point at which main drainage veins of heart (Coronary veins) empty into right atrium
What does the foramen oval provide?
1st opportunity for blood to bypass lungs in foetal circulation
Blood can flow from the right atrium to the left atrium
What happens to the foramen oval after birth?
Closes after birth
Becomes the fossa ovale
What happens to the ductus arteriosus after birth?
Becomes the Ligamentum arteriosum connects PT to aortic arch
Chordae tendonae in the right ventricle
Chordae tendonae stop inversion of tricuspid valve.
How are chordae tendonae arranged in the ventricles
Embedded in the wall of the ventricle by projections (papillary muscles)
Pair of semilunar valves
Pulmonary valve
Aortic valve
Pair of atrioventricular valves
Mitral
Tricuspid
Left ventricle structure
Much thicker left ventricle wall
Trabecular carnae: net like structure
Papillary muscles tether chordae tendonae, preventing eversion of mitral valve
What are the “bowl” like structures forming the aortic valve are called?
Aortic sinuses
Describe the aortic sinuses
In the walls of 2 aortic sinuses there is a hole for the coronary arteries (2 have holes as we have 2 coronary arteries). These with holes are called coronary aortic sinsues.
The 1 aortic sinus with no hole is called a non-coronary aortic sinus
Myocardial Infarction
Lack of blood to the heart muscle causes it to die
Ischaemic event
Blood supply issue
Cardiac arrest
Arrest of beat of heart
Electrical issue
Interventricular branches
Branches that go down between ventricles
Marginal branches
Branches that run across margins
Circumflex branches
Branches that turn back on themselves
Right dominant coronary artery
More common variation
Posterior interventricular branch arises from the right coronary artery
Left dominant coronary artery
Less common variation
Posterior interventricular branch arises from the left coronary artery
Where do coronary veins drain?
All Coronary veins drain into coronary sinus
(vessel that sits between left atrium and left ventricle).
Collects deoxygenated blood from heart muscle and returns it to the right atrium
Describe the conducting system of the heart
Excitation begins in SAN
Spreads wave of depolarization across atria causing contraction
Concurrently wave stimulates AVN
Travels through the bundle of His
Then along bundle branches, through Purkinje fibres, causing ventricular contraction
What does the somatic nervous system innervate? (voluntary)
Skin
Skeletal muscles
What does the autonomic nervous system innervate?
Organs and parts of organs such as smooth muscle and glands
Describe the somatic spinal nerves
Motor to skeletal muscle only (cannot function without them)
Sensory to body wall but not to viscera
Composition of dorsal and ventral root and rami
Dorsal root has only sensory fibres
Dorsal ramus has motor and sensory fibres
Ventral root has only motor fibres
Ventral ramus has motor and sensory fibres
What may happen to somatic spinal nerves that are segmental?
Segmental nerves may combine to form plexi supplying specialised areas (cervical, brachial, lumbosacral)
Ramus
Division of already mixed spinal nerve:
motor and sensory neurones
Dermatome
An area of skin which is supplied by a single spinal nerve on one side or from a single spinal cord segment
Myotome
Part of a skeletal muscle supplied by a single spinal nerve on one side or from a single spinal cord segment
How many pairs of intercostal nerves are there?
11 intercostal + 1 subcostal
Composition of intercostal nerves
Mixed:
Motor and sensory
What are the branches of the intercostal nerves?
Lateral cutaneous branch (anterior and posterior branches)
Anterior cutaneous branch (medial and lateral branches)
What structures do the phrenic nerves provide sensory and motor innervation to?
Motor: diaphragm Sensory: Central diaphragm Mediastinal pleura Pericardium Peritoneum of central diaphragm
Where are the phrenic nerves derived from?
Anterior rami of spinal nerves C3, C4 and C5
Location of phrenic nerves (with relation to lung root)
In front of the lung root
Parasympathetic pathway
Craniosacral: as the nuclei it comes from and goes back to are in the brain or sacral part of spinal cord
Sympathetic pathway
Thoracolumbar: as it only emerges from the thoracic and lumbar parts of the spinal cord
Which nervous system do phrenic and vagus nerves belong to?
Autonomic nervous system
Phrenic nerve supplies skeletal muscle of diaphragm. Although its automatic, it is under voluntary control (can hold breath)
Where do sympathetic preganglionic neurones to the body wall synapse?
In the ganglia of the sympathetic trunk
What runs either side of the vertebral column? Describe this
A “chain” runs on each side of the vertebral column which has enlargements (sympathetic ganglia).
At sympathetic ganglia, the sympathetic nerves can get out and go to their destination
Where does sympathetic outflow from the spinal cord occur?
T1 to L2
Describe the grey matter from T1-L2
There is an extra horn (the intermediate/ intermediolateral horn) between dorsal and ventral horn
Cell bodies giving rise to sympathetic nerve are located here
Where do sympathetic preganglionic neurons to the viscera synapse?
In unpaired ganglia
Difference between white and grey ramus communicans
White ramus communicans contains myelinated fibres
Grey ramus communicans contains unmyelinated fibres
The sympathetic trunk receive which spinal nerves?
Branches from spinal nerves T1 to L2
Function of sympathetic trunks
Distribute sympathetic nerves to smooth muscle and glands throughout body
Also bring pain fibres back to CNS from viscera
What is the significance of sympathetic fibres in spinal nerves T5-T12?
=Thoracic splanchnic nerves that carry sympathetic fibres to the abdomen.
What are the 5 sets of nerves that contain parasympathetic fibres?
Occulomotor (III) c. nerves Facial (VII) c. nerves Glossopharyngeal (IX) c. nerves Vagus (X) c. nerves Sacral spinal nerves (S2-S4)
Which spinal nerves do sympathetic fibres to the heart and lungs come from?
T2-T4 passing through cervical and upper thoracic ganglia of sympathetic trunk
Where do many of the sympathetic fibres to the heart and lungs synapse?
In micro-ganglia of the pulmonary and cardiac plexuses rather than in the trunk ganglia
What effect do sympathetic and parasympathetic nerves have on bronchioles?
Sympathetic: bronchodilation
Parasympathetic (vagus): bronchoconstriction
What are the effect of sympathetic and parasympathetic efferents to the heart?
Sympathetic: increase HR and force of contraction
Parasympathetic (vagus): decrease HR and vasoconstrict coronary arteries
What are the roles of sympathetic and parasympathetic afferents from the heart?
Sympathetic: relay pain sensations from the heart
Parasympathetic (vagus): relay BP and chemical information from the heart
Where does the vagus nerve arise and where does it leave the skull?
Vagus nerves arise in the medulla and it leaves the skull via the jugular foramina
Describe the path of descent of the vagus nerve.
The 2 vagus nerves pass postero-laterally to the common carotid arteries.
Right vagus passes posterior to the right lung root
Left vagus nerve crosses over anterior to the aortic arch and then posterior to the left lung root
Both vagi form a plexus round the oesophagus
Separate to form anterior and posterior oesophageal/gastric nerves
What are roles of sympathetic and parasympathetic afferents from the oesophageal plexus?
Sympathetic: relays pain sensation from the oesophagus
Parasympathetic: senses normal physiological information from the oesophagus
Branches of the vagus provide sensory content from…?
Gut and lungs
Branches of the vagus provide NO AUTONOMIC SUPPLY to the body wall.
Describe the vagus nerves and their branches
Branches to chest and abdomen are parasympathetic (control smooth and cardiac muscle + glands of gut and airways)
Also have large sensory fibres (enteroceptor) from gut and lungs
Unlike sympathetic they provide no autonomic supply to the body wall (eg arterioles and sweat glands)
Describe the recurrent laryngeal branch of vagus nerve
Not parasympathetic: runs back up neck to supply most skeletal muscles of larynx
Intrinsic nerves of the oesophagus
This plexus of ganglia and axons within the oesophageal wall coordinates its activity.
Can be up- or down-regulated by autonomic nerves.
Part of the enteric nervous system.
