Logan Steele
The human body is a complex structure with many muscles and bones working in tandem to enable movement. One such set of bones that are integral to the skeletal structure is the ribs. The ribs play a critical role in breathing, as they protect the contents of the thoracic cavity and increase/decrease the size of the thoracic cavity, assisting the lungs in respiration. The second rib, in particular, is thinner and longer than the first rib and has a tuberosity on its superior surface for the attachment of the serratus anterior muscle. This muscle, along with the diaphragm, is responsible for inspiration. Additionally, the intercostal muscles, which get their name from the Latin words meaning between ribs, link each rib to its neighbours, allowing for the expansion and contraction of the rib cage during breathing.
| Characteristics | Values |
|---|---|
| Muscles attached to the second rib | Posterior scalene, serratus posterior superior, levator costae, iliocostalis cervicis, iliocostalis thoracis, serratus anterior, internal and external intercostal muscles |
| Function | Serves as an anchor for the pleura of the lungs |
| Nerves | Second thoracic nerve (with the anterior/intercostal branch and the posterior branch), second thoracic sympathetic ganglion (with pulmonary, cardia) |
| Conditions | Bronchitis, broncho-pneumonia, pleurisy, and tuberculosis |
| Intercostal Muscles | Link each rib to its neighbour, change the size of the ribcage, and are part of the thoracic wall |
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What You'll Learn
Posterior scalene, serratus posterior superior, levator costae, iliocostalis cervicis, and iliocostalis thoracis
The second rib is larger than the first rib, and several muscles are attached to it. These include the posterior scalene, serratus posterior superior, levator costae, iliocostalis cervicis, and iliocostalis thoracis. The serratus posterior superior is a muscle that crosses over two muscles of the erector spinae group: the longissimus thoracis and iliocostalis thoracis. It raises the ribs and expands the chest, aiding in respiration. Trigger points in the serratus posterior superior muscles can be caused by illness, coughing, certain movements and postures, and paradoxical breathing.
The iliocostalis cervicis arises from the angles of the third, fourth, fifth, and sixth ribs, and is inserted into the posterior tubercles of the transverse processes of the fourth, fifth, and sixth cervical vertebrae. The iliocostalis thoracis arises from the upper borders of the angles of the lower six ribs medial to the tendons of insertion of the iliocostalis lumborum.
The levator costae muscle works synergistically with the serratus posterior superior. The internal and external intercostal muscles are also attached to the second rib. The intercostal muscles are part of the rib cage and link each rib to its neighbours. They work in sets to expand and shrink the space inside the rib cage, which is how breathing is possible.
The second rib is associated with the lungs and their function. A lesion of the second rib can cause issues in the lungs, bronchi, and pleura. It can also cause issues in the head, neck, and heart through the sympathetic nervous system.
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Serratus anterior muscle
The serratus anterior is a fan-shaped muscle that originates on the superolateral surfaces of the first to eighth or ninth ribs at the lateral wall of the thorax. Its main part lies deep under the scapula and the pectoral muscles. It is easily palpable between the pectoralis major and latissimus dorsi muscles. In athletic bodies, the muscle may even be visible to the naked eye along the ribs underneath the axilla.
The serratus anterior muscle is divided into three parts: the superior part, the middle part, and the inferior part. The superior part originates from the first to second rib and inserts at the superior angle of the scapula. The middle part originates from the second to third rib and inserts at the medial border of the scapula. The inferior part originates from the fourth to eighth or ninth rib and inserts at the medial border and inferior angle of the scapula. The lowest attachment may extend to the tenth rib in approximately 10% of the population. The inferior part of the muscle is the most prominent and powerful.
The serratus anterior acts on the scapula and is the prime mover in both scapular protraction and scapular upward rotation. It is a key scapular stabiliser, keeping the shoulder blades against the ribcage when at rest and during movement. When the shoulder blade is in a fixed position, the serratus anterior lifts the ribcage and supports breathing. It is also known as the "'boxer's muscle'" as it is largely responsible for the protraction of the scapula, a movement that occurs when throwing a punch.
The innervation of the serratus anterior is supplied by the long thoracic nerve, a branch of the brachial plexus. The vascular supply to the muscle comes from the superior and lateral thoracic arteries, as well as branches from the thoracodorsal artery.
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Internal and external intercostal muscles
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces, or the gaps between the 12 ribs. They are divided into three groups: external intercostal muscles, internal intercostal muscles, and innermost intercostal muscles. The internal intercostal muscles form the middle layer of the intercostal musculature, with the external intercostals being the most superficial and the innermost intercostals being the deepest.
The external intercostal muscles are situated at the front, the internal intercostal muscles are in the middle, and the innermost intercostal muscles are at the back. The internal and external intercostal muscles work in sync to expand and contract the rib cage, which is how breathing is possible. The external intercostal muscles contribute primarily to inhaling, while the internal intercostal muscles contribute to exhaling. The innermost intercostal muscles support the internal intercostal muscles during exhalation.
The internal intercostal muscles originate from the costal groove of one rib, extending inferolaterally, and insert onto the superior border of the rib below. They are innervated by the intercostal nerves and receive a blood supply from the anterior and posterior intercostal arteries, the costocervical trunk, internal thoracic arteries, and musculophrenic arteries.
The external intercostal muscles originate at the lower border of each rib, inserting onto the superior border of the rib below. They are also innervated by the intercostal nerves (T1-T11) and receive their blood supply from the anterior and posterior intercostal arteries.
The internal and external intercostal muscles are attached to the second rib.
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The second rib's relationship with lung function
The ribs are the skeletal protection for the lungs and the chest cavity. They act as a bony framework for the thoracic cavity, shielding the lungs from damage. The lungs are covered by double-layered pleural membranes, and the internal surface of the second rib acts as an anchor for the pleura of the lungs.
The intercostal muscles are part of the rib cage and link each rib to its neighbours. They are so-called because they are situated in the intercostal spaces, or the gaps between the ribs. The flexing action of the intercostal muscles makes the rib cage expand and contract, changing the size of the space inside the rib cage, which is how breathing is possible. The internal and external intercostal muscles work in sync, like rowing teams. When you inhale, the external intercostal muscles pull together to expand your rib cage, creating suction that pulls air into the lungs. When you exhale, the internal intercostal muscles work in a similar way, pushing air out of the lungs.
The second rib is attached to the posterior scalene, serratus posterior superior, levator costae, iliocostalis cervicis, iliocostalis thoracis, and serratus anterior muscles. There are also attachments of the internal and external intercostal muscles to the second rib. The second rib is also associated with the second thoracic nerve and the second thoracic sympathetic ganglion.
A lesion of the second rib can be either causative or reflexive in conditions such as bronchitis, broncho-pneumonia, pleurisy, and tuberculosis. This is due to the nervous transmission to the lung and pleura being highly sympathetic, as well as the mechanical strain placed on the pleura, which alters the pressure dynamics inside the thorax.
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The second rib's nervous connections
The second rib is associated with the following nerves: the second thoracic nerve (with the anterior/intercostal branch and the posterior branch), and the second thoracic sympathetic ganglion (with pulmonary, cardia).
A lesion of the second rib will generally express through the pleura, the lungs, the bronchi, and the second intercostal nerve. Conditions associated with a lesion of the second rib include bronchitis, broncho-pneumonia, pleurisy, and tuberculosis. A lesion of the second rib can be either causative or reflexive in the aforementioned conditions.
The term 'intercostal' refers to the course of nerves in the intercostal space, where they run alongside intercostal vessels. Intercostal nerves carry motor and sensory fibres, providing segmental supply to the structures of the thoracic and abdominal walls. They carry sensory afferents from the skin of the thoracic and abdominal walls, ribs, pleura, and peritoneum.
Intercostal nerves also carry sympathetic innervation to structures such as sweat glands and blood vessels of the thoracic and abdominal walls. The sympathetic nervous system can go into overdrive in the head, neck, heart, and lungs, allowing opportunistic pathogens to thrive.
The intercostal muscles are part of the rib cage, linking each rib to its neighbours. They work in sets, with their flexing action expanding or shrinking the rib cage, aiding in the process of breathing.
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Frequently asked questions
The serratus anterior, serratus posterior superior, and subcostalis muscles attach to the second rib.
The serratus anterior is a muscle that originates anterolaterally from the first to eighth ribs.
The serratus posterior superior is a thin muscle located deep to other muscles, which makes it difficult to palpate and discern.
The subcostalis muscles are located within the same plane as the innermost intercostals. They may span one or multiple ribs and are more numerous within the inferior regions of the posterior thoracic wall.
