Chapter 3 - Walls of Thorax Flashcards
Name the intercostal muscles
- External intercostal
- Internal intercostal
- Transversus thoracis - subcostalis + intercostalis intimi + sternocostalis
Extent of external intercostal muscles
- From tubercle of rib posteriorly to costochondral junction anteriorly
- Between costochondral junction to sternum replaced by external intercostal membrane
- Posterior part continuous with superior costotransverse ligament
- Fibres run downwards, forwards and medially
Extent of the internal intercostal muscles
- From lateral border of sternum to angle of rib
- Continues as internal intercostal membrane which is continuous with superior costotransverse ligament
- Fibres run downwards, backwards and laterally
Extent of transversus thoracis muscle
Subcostalis - Posterior part of lower intercostal spaces
Intercostalis intimi - Middle 2/3rds of all spaces
Sternocostalis - Anterior parts of upper spaces
Intercostal nerves distribution
- They are ventral primary rami of T1-T11 spinal N
- All supply intercostal spaces
- Upper 2 also supply upper limb
- Lower 5 also supply abdominal wall
- 3-6 Typical intercostal N
Intercostal N relations
- Passes below neck of rib and enters costal groove
- Posterior part: between pleura and internal intercostal membrane
- Anterior part: between intercostalis intimi and internal intercostal muscle
- In the front, pierces intercostal muscles and forms ANTERIOR CUTANEOUS N
Muscular branches of intercostal N
- Supply intercostal muscles, serratus posterior superior
2. Collateral branch arises near angle of rib and supplies neurovascular space
Sensory branches of intercostal N
- Main and collateral branch supply pleura and periosteum
- Lateral cutaneous branch near angle of rib supplies skin
- Anterior cutaneous branch near sternum supplies skin
Intercostobrachial N
- It is the lateral cutaneous branch of 2nd intercostal N.
- Supplies skin of floor of axilla and upper medial part of arm
Boundaries of typical intercostal space
Superior: Costal groove of rib above
Inferior: Upper border of rib below
Anterior: Sternum
Posterior: Thoracic vertebra
Contents of typical intercostal space
- Intercostal muscles
- 2 anterior intercostal A and V
- Posterior intercostal A and V
- Intercostal N and collateral branch
Origin of posterior intercostal A
1-2: superior intercostal A -> costocervical trunk -> subclavian A
3-11: descending thoracic aorta
Course of posterior intercostal A
- Right A pass behind esophagus, thoracic duct, azygos vein and sympathetic chain
- Left A pass behind hemiazygos vein and sympathetic chain
- In intercostal space, intercostal V and N are present above and below resp.
- Ends at costochondral unction by anastamosing with upper anterior intercostal A
Branches of intercostal A
- Dorsal: to skin of back and vertebrae
- Collateral: anastamoses with lower anterior intercostal A
- Muscular: to intercostal muscles, pectoral, serratus anterior
- Lateral cutaneous: accompanies LCN
- Mammary: from 2,3,4 to mammary gland
- Right bronchial: from 3rd right PIA
Anterior intercostal A
- 2 in each space: upper and lower
- 1-6 from internal thoracic A
- 7-9: from musculophrenic A
- End at costochondral junction
Anterior intercostal V
- 1-3 drain into internal thoracic V
- 4-6 into vena comitantes of internal thoracic A
- 7-9 into vena comitantes of muculophrenic A
Posterior intercostal V on left side
1- Left brachiocephalic
2,3,4- Superior intercostal -> left brachiocephalic
5-8 - Accessory hemiazygos
9-11 - Hemiazygos
Posterior intercostal V on right side
1- Right brachiocephalic
2,3,4 - Superior intercostal -> azygos
5-11 - Azygos
Relations of internal thoracic A
ABOVE 1ST RIB It runs behind 1. Sternal end of clavicle 2. Internal jugular V 3. Brachiocephalic V 4. 1st costal cartilage 5. Phrenic N
BELOW FIRST RIB Anteriorly: 1. Pectoralis major 2. 1-6 costal cartilages 3. External intercostal membranes 4. Internal intercostal muscles 5. 1-6 intercostal N
Posteriorly:
- Endothoracic fascia
- Pleura
- Sternocostalis
Branches of internal thoracic A
- Pericardiacophrenic: to pericardium and pleura
- Mediastinal: to thymus, mediastinum fat
- 2 anterior intercostal A at each space
- Superior epigastric A: enters rectus sheath
- Musculophrenic A: runs behind 7,8,9 costal cartilages and gives 2 intercostal branches at each space. Perforates diaphragm near 9th CC
Formation of azygos V
- Union of:
- Lumbar azygos
- Right subcostal
- Ascending lumbar
- Occupies posterior medistinum and joins superior vena cava
- Enters thorax by passing through aortic opening
Relations of azygos V
Anteriorly: Oesophagus
Posteriorly: Thoracic vertebrae, Right posterior intercostal V
Right: Right lung, pleura
Left: Thoracic duct, Aorta, Trachea, Vagus
Tributaries of azygos V
- Right superior intercostal V
- 5-11 right posterior intercostal V
- Hemiazygos V
- Accessory hemiazygos V
- Right bronchial V
Hemiazygos V
- Formed by union of:
- Left lumbar azygos
- Left ascending lumbar
- Left subcostal
- Pierces crus of diaphragm, ascends on left side of vertebra, overlapped by aorta, joins azygos
- Gives 9-12 left posterior intercostal V
Accessory hemiazygos V
- Begins in 4/5th intercostal space
- At level of 8th space, turns right, passes behind aorta and thoracic duct and joins azygos
- Gives 5-8 left posterior intercostal V
Branches of thoracic sympathetic trunk
LATERAL
-Grey rami communicans supply skin
MEDIAL
- Upper 5-pulmonary, cardiac, aortic an doesophageal branches
- Lower 7-Greater, Lesser and least splanchnic N
Greater splanchnic N
- 5-9
- ends in coelic ganglio, aorticorenal ganglion, suprarenal gland
Lesser splanchnic N
- 10,11
- Coeliac ganglion
