What are the ribs and intercostal muscles formed by?
What are the sternum and costal cartilages formed by?
Like the vertebral column, the ribs and intercostal muscles are formed by somite-derived mesenchymal cells.
The sternum and costal cartilages are derivatives of mesenchymal cells in the parietal mesoderm.
Name the structures that articulate with the:
a) superolateral border of the sternal manubrium
b) lateral borders of the sternal manubrium, body, and xiphoid process
Articulating structures of the sternum:
a) superolateral border of the sternal manubrium - clavicles (sternoclavicular joints)
b) lateral borders of the sternal manubrium - costal cartilages (the hyaline cartilaginous anterior ends of ribs 1-7)
What is landmark for the articulation of the 2nd ribs?
What forms the costal margin of the ribs?
What is unique about the 11-12th ribs?
The sternal angle serves as a landmark for articulation of the 2nd ribs.
The costal cartilages of ribs 8-10 attach to the cartilage of the rib above to form the costal margin.
Ribs 11-12 are floating ribs which lack costal cartilages and end posterior to the costal margin.
What structures serve as the posterior articular sites for the ribs?
What covers the intercostal spaces of the ribs?
The costal facets on the thoracic vertebral bodies and transverse processes provide posterior articular sites for the ribs.
The intercostal spaces are covered by the external and internal intercostal muscles.
Where is the subcostal space and which spinal nerve constitutes the subcostal nerve?
The subcostal space is located below the 12th rib and does not lie between ribs. The anterior ramus (branch) of spinal nerve T12 is the subcostal nerve.
Why does rib counting during physical exams start at the second rib?
The 1st rib is not palpable.
Define the boundaries of the superior thoracic aperture and list the structures that pass through it.
Boundaries of the superior thoracic aperture:
a) posteriorly - vertebra T1 (its body protrudes anteriorly into the opening)
b) laterally - 1st pair of ribs and their costal cartilages
c) anteriorly - the superior border of the manubrium
Why do a diminished pulse, cutaneous pallor, and coldness of the upper limb indicate a supernumerary cervical rib?
A supernumerary cervical rib means that there is an extra rib in the cervical region that may be obstructing vital vessels meant for the upper limb.
Identify the vertical lines of the thoracic wall, A through J in the image below.
Next to what vertical thoracic line are the nipples in men and young nulliparous women located?
The nipples in men and young nulliparous women are located adjacent to the midclavicular lines at the 4th intercostal space (ICS).
What structures push the diaphragm superiorly and which of these structures can reach the 4th intercostal space?
The liver, stomach, and spleen (abdominal organs) create the superior projection of the diaphragm and the superior surface of the liver can reach the 4th ICS.
What physical changes occur in the diaphragm during inspiration and what nerves innervates this action?
During inspiration, the diaphragm contracts and flattens its right and left domes (created by the abdominal organs) and draws air into the lungs.
This action is innervated by the phrenic nerves.
What is the normal adult respiratory rate?
The normal adult respiratory rate is 12-20 breaths/minute.
Why after ipsilateral paralysis of the diaphragm, does the paralyzed dome ascend during inspiration and descend during expiration?
Ipsilateral paralysis of the diaphragm occurs often because the right and left domes are innervated by separate branches of the phrenic nerve.
The paralyzed dome will not contract during inspiration, therefore while the unparalyzed dome pushes the inferior abdominal organs down, the paralyzed dome has no strength and is instead pushed superiorly by the abdominal organs beneath it.
The paralyzed dome descends during expiration because of the positive pressure in the thoracic cavity created by normal expirative actions.
Besides the actions of the diaphragm, what occurs during fored inspiration?
During forced inspiration, the external intercostal muscles contract to elevate the ribs and expand the anterior/posterior and transverse dimensions of the thoracic cavity.
The scalene muscles contract to keep the first two ribs in place, thus assisting elevation of ribs 3-12.
Besides the actions of the diaphragm, what occurs during forced expiration?
During forced expiration, contraction of the internal intercostal muscles lowers the elevated ribs to their resting position.
Why do patients experiencing dyspnea lean on their knees to assist respiration?
The reason people experiencing dyspnea lean on their knees is because in this position, their pectoral girdle is fixed and their accessory muscles are better able to act on their rib attachments to expand the thorax.
Which spinal nerves innervate the intercostal muscles and from where do they arise?
The intercostal nerves which arise from the anterior rami of the thoracic spinal nerves innervate the intercostal muscles.
The dermatomes of the medial sides of the arms are innervated by what nerve?
The lateral cutaneous branches of the spinal nerve T2 (2nd intercostal nerve) innervate the dermatomes of the medial sides of the arm.
What is the posterior rami of the intercostal nerves responsible for innervating?
The posterior rami of the intercostal nerves are responsible for innervating the intrinsic muscles of the back and provide cutaneous branches to the posterior thoracic wall.
Through what route do visceral motor nerve fibers take to innervate smooth muscle and sweat glands in the body wall?
Visceral motor nerve fibers innervate smooth muscle and sweat glands in the body wall by traveling through white and gray communicating rami to and from from the paravertebral ganglia of the sympathetic trunk.
What gives rise to the posterior and anterior intercostal arteries, respectively?
Where do these sects of arteries ultimately anastomose?
The posterior intercostal arteries arise from the thoracic aorta.
The anterior intercostal arteries arise from the internal thoracic arteries, which arise from the subclavian arteries.
The posterior and anterior intercostal arteries anastomose in the intercostal space.