LECTURE 22 - THORACIC WALLS AND DIAPHRAM Function – protection and breathing Ribcage – bony framework of the thorax supporting the thoracic cage covered by tissues like muscles and skin. The breast is also part of the thoracic wall The ribcage is composed of the following bones– • Sternum – made of three parts, o Manubrium – the top section of the sternum where sternoclavicular joints are found o The body o Xiphoid process – the bottom • 12 thoracic vertebrae and intervertebral discs • 12 pairs of ribs and costal cartilages o true ribs – ribs 1 – 7 have their own cartilage that directly articulates to the sternum o false ribs – ribs 8 – 10 have cartilage that articulate with the cartilage of the above rib, hence they indirectly articulate with the sternum o floating ribs – ribs 11 and 12 do not have cartilage and do not articulate with the sternum The structure of typical ribs - Ribs 3 – 9 are typical ribs, and 1,2, 10 – 12 are atypical ribs Typical ribs – • vertebral end – the head of the rib is at the posterior and articulates with the transverse processes of the spine, • the vertebral end has two smooth impressions called facets, then the vertebral end narrows into a neck • articular facet - tubercle that is smooth for articulation • the tubercle lateral to the articular facet is for muscle attachment • the body of the rib is curved • the top of the body is called the superior border, the bottom is the inferior border. • The costal groove runs along the inferior border and it is for neurovascular supply to muscles between ribs • sternal end – anterior, smooth Thoracic vertebra – Typically have 3 facets on each side. There are 2 on the body of the vertebrae (superior and inferior costal facets) that articulate with the vertebral head of the rib. This is the costovertebral joint – 1 rib articulates with two vertebra, eg the 7th rib will articulate with T6 and T7 vertebra. There is one on the transverse processes called the transverse costal facet which articulates with the tubercle. The costotransverse joint is the joint between the smooth tubercle of the rib and the transverse process of the above vertebrae Thoracic apertures – the ribcage has 2 openings, the superior aperture and the inferior aperture. The superior aperture is at T1. It is partially closed by the suprapleural membrane, but is centrally open The inferior aperture is at T12 posteriorly and at the xiphoid process anteriorly. It is completely closed off by the diaphragm The diaphragm – muscle with a central tendon / insertion and a circular origin around the inferior aperture. The diaphragm has two domes that attach to lumbar vertebrae via crus. The right dome is higher because it is pushed up by the liver, and the right crus is longer than the left crus for a firmer attachment. When the diaphragm contracts it increases the volume in the rib cage, decreases the pressure in the rib cage and leads to inspiration (breathe in) There are three holes in the diaphragm and they have the following functions • Allows the vena cava to pass through • Allows the esophagus to pass trhough • Allows the aorta to pass through The aorta doesn’t really create a hole but it passes through the space between the two crus – allowing the aortas blood pressure to remain the same during contractions of the diaphragm Nerve supply of the diaphragm comes from phrenic nerves (Cervical supply) Intercostal space The space between ribs is called the intercostal space. It contains intercostal muscles, intercostal nerves, intercostal arteries and intercostal veins. Intercostal muscles are organized in three layers • External – replaced by intercostal membrane anteriorly, contraction of these muscles pulls ribs up and out to increase volume during inspiration • Internal – fibres in opposite direction of external muscles, at the posterior of the ribcage replaced by intercostal membrane, in theory contraction should lead to expiration but expiration is actually passive. • Innermost – discontinuous patchy layer Nerve and vascular supply from the costal groove. The groove is organized as vein, artery, then nerve (top to bottom). The intercostal nerve comes from posterior rami of T1 – T11 spinal nerves, runs between internal and innermost muscles, and supplies the intercostal space and the thoracic wall. Two types of intercostal arteries • Posterior intercostal arteries – originate from the aorta • Anterior intercostal arteries – originate from internal thoracic arteries The intercostal arteries supply to the intercostal space and the cutaneous of the wall Movements of the thoracic wall The thorax can be changed at the vertical axis via the diaphragm, contract longer, relax shorter Anterposterior movements by movement of the upper ribs The lateral dimension by movements of the lower ribs .