Intercostal muscles

Examples of Intercostal muscles in the following topics:

• Anterior Muscles

  • Lying below the pectoral muscles, the intercostal muscles form the chest wall and play a key role in respiration.
  • External Intercostals – The external intercostals are the most superficial of the intercostal muscles.
  • Internal Intercostals- Lying below the external intercostals, the internal intercostals are continuous with the internal oblique muscle of the abdomen.
  • Innermost Intercostals – The deepest lying of the intercostals, these muscles are similar in structure to the internal intercostals.
  • The intercostals are muscles between the ribs that form the chest cavity wall.

• Expiration

  • There are two groups of muscles that are involved in forced exhalation.
  • Internal Intercostal Muscles: Muscles of the ribcage that help lower the ribcage, which pushes down on the thoracic cavity, causing forced exhalation.
  • Note that these are not the same as the external intercostal muscles involved in inspiration.
  • Abdominal Muscles: Any number of muscles in the abdomen that exert pressure on the diaphragm from below to expand it, which in turn contracts the thoracic cavity, causing forced exhalation.
  • This happens due to elastic properties of the lungs, as well as the internal intercostal muscles that lower the rib cage and decrease thoracic volume.

• Neural Mechanisms (Cortex)

  • The processes that drive its functions aren't fully understood, but it works by sending signals to the spinal cord, which sends signals to the muscles it controls, such as the diaphragm and the accessory muscles for respiration.
  • Initiation of the voluntary contraction and relaxation of the internal and external intercostal muscles takes place in the superior portion of the primary motor cortex.
  • This is most likely due to the focus and mental preparation of the voluntary muscular movement that occurs when one decides to initiate that muscle movement.
  • The posterior thoracic nerves: These nerves stimulate the intercostal muscles located around the pleura.
  • They are considered to be part of a larger group of intercostal nerves that stimulate regions across the thorax and abdomen.

• Functional Anatomy of the Respiratory System

  • The respiratory system include lungs, airways and respiratory muscles.
  • Inhalation is initiated by the activity of the diaphragm and supported by the external intercostal muscles.
  • Pectoral muscles and latissimus dorsi are also accessory muscles for the activity of the lungs.
  • Active or forced exhalation is achieved by the abdominal and the internal intercostal muscles.
  • During forced exhalation, as when blowing out a candle, the expiratory muscles, including the abdominal muscles and internal intercostal muscles, generate abdominal and thoracic pressure that force air out of the lungs.

• Inspiration

  • The diaphragm is the primary muscle involved in breathing, however several other muscles play a role in certain circumstances.
  • These muscles are referred to as accessory muscles of inhalation.
  • External intercostal muscles: muscles located in between the ribs that help the thoracic cavity (and thus pleural cavity) to expand during quiet and forced inspiration.
  • Sternocleidomastoid muscle: muscles that connect the sternum to the neck and allow for rotation and turning of the head.
  • Trapezius muscle: muscles in the shoulders, which retracts the scapula and expands the upper part of the thoracic cavity.

• Aging and the Respiratory System

  • In mammals, breathing (inhaling) occurs during the contraction and flattening of the diaphragm, a domed muscle separating the thorax and abdomen.
  • When requirements increase, the abdominal muscles resist expansion.
  • Expiration follows relaxation of diaphragm and abdominal muscles, but can be increased by the downward action of abdominal muscles on the rib cage.
  • Auxiliary intercostal muscles stiffen and shape the rib cage.
  • Age also contributes to loss of strength and mass in the chest muscles—these weaken, bones and cartilage start to deteriorate, and posture changes.

• Intercostal Nerves

  • The anterior divisions of the thoracic spinal nerves (T1–T11) are called the intercostal nerves.
  • The other smaller branch, the first intercostal nerve, runs along the first intercostal space and ends on the front of the chest as the first anterior cutaneous branch of the thorax.
  • Near the sternum, they cross in front of the internal mammary artery and transversus thoracis muscle, pierce the intercostales interni, the anterior intercostal membranes, and pectoralis major, and supply the integument of the front of the thorax and over the mamma, forming the anterior cutaneous branches of the thorax.
  • The anterior divisions of the seventh, eighth, ninth, tenth, and eleventh thoracic intercostal nerves are continued anteriorly from the intercostal spaces into the abdominal wall; hence they are named thoraco-abdominal nerves or thoracicoabdominal intercostal nerves.
  • This enables them to control the contraction of muscles, as well as provide specific sensory information regarding the skin and parietal pleura.

• Amyotrophic Lateral Sclerosis

  • Unable to function, the muscles weaken and atrophy.
  • The earliest symptoms of ALS are typically obvious weakness and/or muscle atrophy.
  • Other presenting symptoms include muscle fasciculation (twitching), cramping, or stiffness of affected muscles; muscle weakness affecting an arm or a leg; and/or slurred and nasal speech.
  • Symptoms of lower motor neuron degeneration include muscle weakness and atrophy, muscle cramps, and fleeting twitches of muscles that can be seen under the skin (fasciculations).
  • As the diaphragm and intercostal muscles (rib cage) that support breathing weaken, measures of lung function such as forced vital capacity and inspiratory pressure diminish.

• Overview of the Spinal Nerves

  • The dorsal ramus contains nerves that serve the dorsal portions of the trunk; it carries visceral motor, somatic motor, and somatic sensory information to and from the skin and muscles of the back (epaxial muscles).
  • The muscles innervated by the cervical nerves are the sternohyoid, sternothyroid, and omohyoid muscles.
  • The intercostal nerves come from thoracic nerves T1–T11, and run between the ribs.
  • They then pierce the rhomboid and trapezius muscles, and reach the skin by the sides of the spinous processes.
  • The lateral branches supply the erector spinae muscles.

• How Skeletal Muscles Are Named

  • Parallel muscles are characterized by fascicles that run parallel to one another, and contraction of these muscle groups acts as an extension of the contraction of a single muscle fiber.
  • Convergent muscles have a common point of attachment, from which the muscle fascicles extend outward, not necessarily in a specific spatial pattern, allowing the muscle to cover a broad surface.
  • In Pennate muscles, the tendon runs through the length of the muscle.
  • However, these muscles tend to have relatively more muscle fibers than similarly sized parallel muscles, and thus carry more tension.
  • If the central tendon branches within a pennate muscle, the muscle is called multipennate.