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Longitudinal muscles are those that run lengthwise along the body, as opposed to circular muscles, which encircle it. They are found in the esophagus, distal stomach, and small and large intestines, and play a key role in peristalsis, a propulsive activity that helps move food through the gastrointestinal (GI) tract. During peristalsis, longitudinal muscles contract and relax in coordination with circular muscles, causing the esophagus to shorten and widen, which reduces resistance to propulsion and facilitates the movement of food.
| Characteristics | Values |
|---|---|
| Structure | Longitudinal muscle fibres run lengthwise along the body |
| In transverse section, fibres are arranged in radiating plates | |
| In nematodes, the bands are composed of a single layer of cells | |
| Function | Contraction promotes propulsion |
| Contraction causes esophageal shortening | |
| Contraction of the longitudinal muscle on the aborad side of the bolus causes the segment to shorten and widen | |
| Contraction of the longitudinal muscle relaxes orad to the bolus | |
| Contraction of the longitudinal muscle in the distal oesophagus induces LES relaxation |
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What You'll Learn
Longitudinal muscle contraction causes esophageal shortening
Longitudinal muscles are muscle fibres that run lengthwise along the body. They are present in the esophagus, where they work in conjunction with circular muscles to facilitate peristalsis, the process of pushing food down the digestive tract.
Peristalsis in the esophagus involves the contraction of both circular and longitudinal muscle layers. The circular muscles contract behind a food bolus (on the orad side) and relax in front of it (on the aborad side). Simultaneously, the longitudinal muscles relax in front of the bolus and contract behind it. This coordinated movement propels the bolus towards the stomach.
The contraction of longitudinal muscles leads to the shortening of the muscle segment. This shortening enlarges and widens the lumen, reducing resistance to propulsion and facilitating the passage of food. The relationship between longitudinal muscle contraction and esophageal shortening has been studied using radio-opaque markers implanted on the esophageal wall, strain gauge recordings, ultrasound imaging, and manometry studies.
The longitudinal muscle contraction of the distal esophagus is believed to play a crucial role in inducing lower esophageal sphincter (LES) relaxation. This relaxation is mediated by the activation of stretch-sensitive motor neurons in the LES. The coordination between the longitudinal and circular muscle layers ensures the efficient propulsion of food through the esophagus during the process of swallowing.
In summary, longitudinal muscle contraction causes esophageal shortening, which is a fundamental aspect of peristalsis in the esophagus. This shortening reduces resistance to propulsion, allowing for the smooth passage of food. The understanding of this process has been enhanced by various studies and imaging techniques, providing valuable insights into the motor function of the esophagus.
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The longitudinal muscle is composed of a single layer of cells
Longitudinal muscles are those that run lengthwise along the body. They are found in the esophagus, distal stomach, and small and large intestines. They also exist in the tongue, where they allow for delicate and fast movements.
In the esophagus, longitudinal muscles contract prior to and outlast circular muscle contraction by 2-4 seconds. The two layers contract in a precisely coordinated way, with the onset, peak, and termination of contraction occurring together. The contraction of longitudinal muscles in the esophagus causes it to shorten.
The mass of the esophageal muscularis propria is split evenly between circular and longitudinal muscle fibres. The longitudinal muscle in the upper esophagus contracts during the initial period after a swallow, generating the active tension necessary to shorten the upper esophagus.
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Longitudinal muscle fibres run lengthwise along the body
In the trunk, the longitudinal muscles work in conjunction with the circular muscles. When both types of muscles contract, fluid flows out of the body's internal cavity through the mouth if it is slightly open.
In the oesophagus, longitudinal muscles contract and relax in coordination with the circular muscles to facilitate peristalsis, the process of moving food or drink through the oesophagus to the stomach. During peristalsis, the longitudinal muscles shorten the oesophagus, which enlarges the lumen and reduces resistance to propulsion, allowing food or drink to pass through more easily.
In the tongue, the superior longitudinal muscle contains a mix of slow and fast fibres. The blade of the tongue contains more fast fibres, allowing it to perform delicate and rapid movements by changing its shape.
In other organisms, longitudinal muscle fibres have different roles. For example, in sea cucumbers, the longitudinal muscle bands are composed of a single layer of cells, and their contraction or extension affects the shape of the tube feet.
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Longitudinal muscle contraction promotes propulsion
Longitudinal muscles are muscle fibres that run lengthwise along the body. They are found in the esophagus, stomach, and intestines, and play an important role in peristalsis, a propulsive activity that involves the coordination of circular and longitudinal muscle layers.
During peristalsis, the circular and longitudinal muscles contract and relax in a specific sequence to propel food or fluids through the digestive system. The circular muscle contracts behind a food bolus (on the orad side) and relaxes in front of it (on the aborad side). Simultaneously, the longitudinal muscle relaxes in front of the bolus and contracts behind it. This coordinated movement creates a wave-like motion that pushes the food bolus towards the anus.
The contraction of longitudinal muscles is particularly important for propulsion. When the longitudinal muscle contracts, the segment shortens, and this shortening enlarges and widens the lumen. The reduced resistance in the lumen facilitates propulsion, allowing the contents to move more easily through the digestive tract.
The complex interaction between circular and longitudinal muscles in the esophagus has been studied using various methods, including intraluminal pressure measurements, radio-opaque markers, cineradiography, ultrasound imaging, and manometry. These studies have revealed that longitudinal muscle contraction causes esophageal shortening and that the two layers of muscles contract in a precisely coordinated manner.
In summary, longitudinal muscle contraction plays a crucial role in propulsion by reducing resistance and facilitating the movement of food or fluids through the digestive system. Understanding this complex process is essential for comprehending the overall functioning of the human body's digestive and propulsive systems.
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The longitudinal muscle relaxes orad to the bolus
The longitudinal muscle is a type of muscle fibre that runs lengthwise along the body. It works in conjunction with circular muscle fibres, which encircle the body, to produce contrasting movements. The contraction of longitudinal muscles can lead to the shortening of the body, which then widens.
The term 'orad' is used to describe the direction towards the mouth or oral region.
A 'bolus' is a medical term used to describe the administration of a single, relatively large dose of a substance. This can be done in a variety of ways, including intravenous (IV) injection, intramuscular injection, subcutaneous injection, and more.
Therefore, the statement "The longitudinal muscle relaxes orad to the bolus" can be understood to mean that the longitudinal muscle relaxes towards the mouth in response to the administration of a large dose of a substance. This could be related to the process of swallowing, where the longitudinal muscle of the oesophagus relaxes to allow for the passage of food or liquid towards the stomach. This process is known as peristalsis, which involves the coordinated contraction and relaxation of both longitudinal and circular muscle layers in the oesophagus.
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Frequently asked questions
Longitudinal muscle fibres run lengthwise along the body. They are arranged in radiating plates, with fewer than 50 plates and spaces between them.
When longitudinal muscles contract, the body shortens and widens. This is known as peristalsis, a propulsive activity that involves both circular and longitudinal muscle layers of the esophagus, distal stomach, and small and large intestines.
The circular and longitudinal muscle layers contract together during peristalsis. However, the longitudinal muscle can contract independently of the circular muscle during transient LES relaxation.
