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Intrinsic muscles are smaller muscles that are wholly contained within a larger muscle group. They are found in the tongue, hands, feet, and core. For example, the intrinsic core muscles include the transverse abdominals, internal, multifidus, diaphragm, and pelvic floor. The function of these muscles is to support the lumbar spine and create intra-abdominal pressure. Similarly, the intrinsic muscles of the tongue help to change its shape. The intrinsic muscles of the hand and foot are responsible for various functions such as grip strength and stabilization.
| Characteristics | Values |
|---|---|
| Definition | A group of muscles located within or situated deeper in a structure, in contrast to extrinsic muscles which are located superficially |
| Examples | Intrinsic hand muscles, intrinsic foot muscles, intrinsic back muscles, intrinsic muscles of the tongue |
| Function | Fine motor functions, pinch strength, support, stability, posture, movement of vertebral column |
| Innervation | Ulnar nerve, median nerve, hypoglossal nerve, spinal nerves |
| Blood supply | Ulnar and radial arteries |
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What You'll Learn
- Intrinsic back muscles include the erector spinae, which is made up of three intermediate muscles
- Intrinsic tongue muscles include the superior longitudinal muscle, which curls the tip of the tongue
- Intrinsic hand muscles include the adductor pollicis, which is involved in pinch strength
- Intrinsic foot muscles are core muscles that provide support and stability to the arches of the foot
- Intrinsic muscles are located deeper in a structure, closer to the skeleton, than extrinsic muscles
Intrinsic back muscles include the erector spinae, which is made up of three intermediate muscles
Intrinsic muscles are those that develop embryologically within a body part. In the context of the back, the intrinsic muscles are the deep muscles that develop within the back and are associated with the movements of the vertebral column and the control of posture.
The intrinsic back muscles can be divided into three layers: superficial, intermediate, and deep. The superficial muscles are associated with the movements of the shoulder and neck. The intermediate muscles are associated with the movement of the thoracic cage. The deep muscles are associated with the movements of the vertebral column and are considered the "true back muscles".
The erector spinae is an intermediate intrinsic back muscle. It is formed by three intermediate muscles: the iliocostalis, longissimus, and spinalis. Together, these muscles form a column situated posterolaterally to the spinal column, between the vertebral spinous processes and the costal angle of the ribs. All three muscles can be further subdivided by their superior attachments into lumborum, thoracic, cervicis, and capitis. They all share a common tendinous origin, arising from the posterior aspect of the iliac crest, sacroiliac, and supraspinous ligaments.
The iliocostalis muscle is located laterally within the erector spinae and is associated with the ribs. It can be divided into three parts: lumborum, thoracis, and cervicis. The longissimus muscle forms the central column of the erector spinae and is the longest and thickest of the group. Like the iliocostalis, it is divided into three regions based on its attachments: longissimus thoracis, which is further subdivided into thoracic and lumbar parts; longissimus capitis; and longissimus cervicis. The spinalis muscle is the smallest of the three muscle columns and is located medially within the erector spinae. It can be divided into thoracic, cervicis, and capitis, although the cervicis part is absent in some individuals.
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Intrinsic tongue muscles include the superior longitudinal muscle, which curls the tip of the tongue
Intrinsic muscles are those that develop within a specific body part and act to change its shape. For example, the deep muscles of the back are intrinsic muscles as they develop embryologically in the back. Similarly, the intrinsic muscles of the tongue are contained completely within the tongue and act to change its shape.
The tongue has four paired intrinsic muscles: the superior longitudinal, inferior longitudinal, transverse, and vertical muscles. These muscles affect the shape and size of the tongue, facilitating speech, eating, and swallowing. The superior longitudinal muscle runs from the distal and a septum in the centre of the tongue, called the median septum, and inserts into the outer portion of the tongue. This muscle acts to curl the tip of the tongue and lateral surfaces superiorly, and shorten the tongue when used in conjunction with the inferior longitudinal muscle. The superior longitudinal muscle is located immediately underneath the mucosa of the dorsal surface of the tongue and is superior to the transverse and vertical muscles.
The superior longitudinal muscle is made up of a thin layer of muscle fibres travelling in a mixture of oblique and longitudinal axes just deep to the superior mucosal surface of the organ. These fibres arise from the median fibrous septum, as well as the fibrous layer of submucosa from the level of the epiglottis. They eventually insert along the lateral and apical margins of the organ. The net effect of these muscles is the shortening of the organ.
The transverse muscle proceeds from an origin along the median septum out to the lateral borders of the tongue. The vertical muscle fibres intertwine in the intermediate muscle layer of the tongue with the fibres of the transverse muscle. They run vertically within the tongue and, when contracted, will flatten and widen the tongue. The inferior longitudinal muscle runs parallel to the superior longitudinal intrinsic muscle from the base of the tongue to the tip.
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Intrinsic hand muscles include the adductor pollicis, which is involved in pinch strength
Intrinsic muscles are those that develop embryologically in a particular body part, and are thus described as being contained within that body part. For example, the intrinsic muscles of the tongue are contained completely within the tongue and act to change its shape. Similarly, the intrinsic muscles of the back are those that develop in the back and are associated with the movements of the vertebral column and the control of posture.
The adductor pollicis is an intrinsic muscle of the hand. It is triangular in shape and has two heads: the oblique head and the transverse head. This muscle extends from the third metacarpal and capitate bones to the base of the first proximal phalanx. The adductor pollicis is the most powerful of the intrinsic muscles of the hand. Its main function is the adduction of the thumb, which is the movement of the thumb towards the index finger from an abducted position. This action is critical for hand dexterity and is essential for functions that require pinching and gripping. Pinch strength is obtained through the action of the first DI and adductor pollicis muscle, which both receive innervation from the ulnar nerve.
The adductor pollicis is the sole muscle of the adductor compartment of the hand and does not form part of the thenar muscle group, which includes the abductor pollicis, flexor pollicis brevis, and opponens pollicis. The adductor pollicis aids the later stages of opposition of the thumb, which is a combination of adduction, medial rotation, flexion, and adduction of the thumb so that it can touch each fingertip of the same hand. The strength of the adductor pollicis can be tested by pushing the thumb against the index finger while attempting to pull them apart.
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Intrinsic foot muscles are core muscles that provide support and stability to the arches of the foot
Intrinsic muscles are those that develop within a specific body part and are responsible for its movement. For example, the intrinsic muscles of the tongue are contained completely within the tongue and act to change its shape.
The intrinsic foot muscles are a group of muscles that originate and insert within the foot. They are also referred to as the core muscles of the foot. These muscles are arranged in four layers on the plantar (bottom) aspect of the foot. The plantar group consists of all the other intrinsic muscles of the foot and can be further divided into two groups: the dorsal and plantar muscles. The dorsal group consists of two muscles, the extensor digitorum brevis and extensor hallucis brevis, which act to extend the toes. The plantar group consists of four muscle layers, going from superficial (plantar) to deep (dorsal) within the foot.
The intrinsic foot muscles have two main functions. Firstly, they stabilise the foot and support the arches, thus maintaining foot structure. The plantar aponeurosis, for example, is a thickening of the deep fascia that runs along the sole of the foot and acts to support the longitudinal arch of the foot. Secondly, they aid the actions of the muscles of the lower leg to produce fine movements of the toes.
The intrinsic foot muscles are vital for good foot function and play a crucial role in the proper function of the foot during sports activities. Improving the strength and function of these muscles can promote positive biomechanical changes in the longitudinal arch of the foot and contribute to reducing the risk of falls in older adults. Additionally, these muscles are important in the non-operative treatment of various pathologic conditions, such as hammer toe, claw toe deformities, and plantar fasciitis.
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Intrinsic muscles are located deeper in a structure, closer to the skeleton, than extrinsic muscles
Intrinsic muscles are those located within or deeper in a structure, closer to the skeleton, than extrinsic muscles. They are situated underneath the erector spinae, a column formed by the iliocostalis, longissimus, and spinalis muscles. The deep intrinsic muscles of the back, for instance, are associated with the movements of the vertebral column and the control of posture. These muscles are covered by deep fascia, which plays a crucial role in their organisation.
The intrinsic muscles of the hand are responsible for fine motor functions and include muscles such as the adductor pollicis and hypothenar muscles. Similarly, the intrinsic muscles of the tongue, including the superior and inferior longitudinal muscles, the transverse muscle, and the verticalis muscle, are responsible for changing the shape of the tongue.
In the foot, the intrinsic muscles are vital for proper foot function and stability, similar to the abdominal and paraspinal muscles that maintain posture and stability during movement. Weakness in these muscles can lead to issues such as curling toes and foot pain. Strengthening these muscles through exercises, stretching, and massage can improve foot strength, flexibility, and coordination.
Intrinsic muscles can also be found in other parts of the body, such as the head and neck, where they have specific functions related to the structures they are associated with. Overall, intrinsic muscles play a crucial role in various bodily functions and movements, and their health and strength are essential for maintaining stability and proper function in different parts of the body.
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Frequently asked questions
Intrinsic muscles are a group of muscles located within or situated deeper in a structure, in contrast to extrinsic muscles, which are located superficially.
Examples of intrinsic muscles include the hand, back, foot, and tongue muscles.
Intrinsic muscles have various functions depending on their location. For example, the intrinsic muscles of the hand are responsible for fine motor functions, while the intrinsic muscles of the back are associated with movements of the vertebral column and control of posture.
There are specific exercises and therapies that can help strengthen intrinsic muscles. For example, to strengthen the intrinsic foot muscles, one can perform toe extension exercises, the "dance step to nowhere" exercise, or marble pickup.
