Dominic Stone
Intrinsic muscles are those located within or deeper in a structure, as opposed to extrinsic muscles, which are located more superficially. The intrinsic muscles refer to the muscles closest to the axial and appendicular skeleton. For example, the intrinsic muscles of the hand are those lying deeper in the hand, such as the interossei and lumbrical muscles. The intrinsic muscles of the back are well-developed and extend from the sacrum to the base of the skull, playing a role in the movement of the vertebral column and control of posture. The intrinsic muscles of the tongue are contained completely within the tongue and act to change its shape.
| Characteristics | Values |
|---|---|
| Definition | A group of muscles located within or situated deeper in a structure, in contrast to extrinsic muscles located rather superficially |
| Examples | Intrinsic muscles of the hand, tongue, back, foot |
| Function | The intrinsic muscles of the hand are important for various hand functions, such as pinch and grip strength. The intrinsic muscles of the tongue act to change the shape of the tongue. The intrinsic muscles of the back are associated with the movements of the vertebral column and the control of posture. |
| Innervation | The intrinsic muscles of the hand are innervated by the radial, median, and ulnar nerves. The intrinsic muscles of the tongue are innervated by the hypoglossal nerve. |
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What You'll Learn
Intrinsic muscles of the hand
Intrinsic muscles are located within the hand itself and are responsible for the fine motor functions of the hand. The muscles of the hand are innervated by the radial, median, and ulnar nerves. The median nerve innervates the flexors of the wrist and digits, the abductors and opponens of the thumb, and the first and second lumbricals. The lateral two lumbricals (of the index and middle fingers) are innervated by the median nerve, while the medial two lumbricals (of the little and ring fingers) are innervated by the ulnar nerve. The ulnar nerve innervates the remaining intrinsic muscles of the hand, including the hypothenar eminence muscles. The hypothenar eminence is a muscular protrusion on the medial side of the palm, at the base of the little finger. The opponens digit minimi is one of the hypothenar muscles and lies deep to the others. It originates from the hook of the hamate and associated flexor retinaculum, inserting into the medial margin of the fifth metacarpal.
The thenar muscles are three short muscles located at the base of the thumb, producing a bulge known as the thenar eminence. These muscles are responsible for the fine movements of the thumb. The median nerve innervates all the thenar muscles, including the opponens pollicis, the largest of the thenar muscles, which lies underneath the other two. The opponens pollicis originates from the tubercle of the trapezium and the associated flexor retinaculum and inserts onto the lateral margin of the first metacarpal. The thumb has one long flexor and a short flexor in the thenar muscle group, which allows for the thumb to move in opposition, making grasping possible.
The fingers have two long flexors, located on the underside of the forearm, which insert by tendons into the phalanges of the fingers. The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx. The flexors allow for the actual bending of the fingers. The extensors are located on the back of the forearm and are connected in a more complex way to the dorsum of the fingers. The tendons of the extensors unite with the interosseous and lumbrical muscles to form the extensor hood mechanism.
The interosseous muscles are located between the metacarpal bones of the hand and can be divided into two groups: dorsal and palmar. The dorsal interossei are responsible for the abduction of the fingers, while the palmar interossei are responsible for the adduction of the fingers. The interossei also assist the lumbricals in flexion at the metacarpophalangeal (MCP) joints and extension at the interphalangeal (IP) joints. The intrinsic muscles of the hand play a crucial role in creating a functional grasp, as they balance finger movement and create a broad sweeping movement during flexion.
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Intrinsic muscles of the tongue
The intrinsic muscles of the tongue are a group of four muscular bands that are entirely within the tongue with no external attachments. They are also known as the tongue's core muscles. Their primary function is to alter the shape of the tongue, which is essential for speaking. They also help the tongue move food around the mouth, mix it with saliva, and separate undesired particles.
The four intrinsic muscles are:
- Superior longitudinal muscle
- Inferior longitudinal muscle
- Transverse muscle
- Vertical muscle
The tongue is a muscular organ situated in the oral cavity, and it is an accessory digestive organ. Its main functions include the sensation of taste, mastication (chewing), deglutition (swallowing), speech, and clearing the oral cavity. The tongue is formed by eight paired muscles, four intrinsic and four extrinsic. The extrinsic muscles, in contrast to the intrinsic muscles, are outside the tongue but are functionally associated with it and help it perform its functions. They are the genioglossus, hyoglossus, styloglossus, and palatoglossus muscles.
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Intrinsic muscles of the foot
Intrinsic muscles are those located within a structure, situated deeper in a structure, as opposed to extrinsic muscles, which are located more superficially. The intrinsic muscles of the foot are responsible for the fine motor actions of the foot, such as the movement of individual digits and toes. They also provide support by maintaining and stabilising the arches of the foot.
There are 19 intrinsic foot muscles, with 10 located in the plantar aspect (sole) of the foot and two located within the dorsum of the foot. The plantar muscles act collectively to stabilise the arches of the foot and individually to control the movement of the digits. They are innervated by the medial or lateral plantar nerves, which are branches of the tibial nerve. The four layers of the plantar muscles (from superficial to deep) are made up of the following:
- The first layer contains three muscles and is located underneath the plantar fascia.
- The second layer contains two muscles: the quadratus plantae and the lumbricals.
- The third layer contains three muscles: the flexor hallucis brevis, adductor hallucis, and flexor digiti minimi brevis.
- The fourth layer contains one muscle: the abductor hallucis, located on the medial side of the sole.
The two intrinsic muscles located within the dorsum of the foot are the extensor digitorum brevis and extensor hallucis brevis.
The intrinsic muscles of the foot are small and often tight from frequent use, especially in activities like ballet. They benefit from regular stretching, massage, and specific exercises to improve their flexibility, coordination, and overall function. Strengthening these muscles can improve foot posture, balance, strength, and running mechanics, as well as reduce the risk of falls, especially in older adults.
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Intrinsic back muscles
Intrinsic muscles refer to muscles that are located within or situated deeper in a structure. They are the muscles closest to the axial and appendicular skeleton. For example, the intrinsic muscles of the hand are those lying deeper in the hand, such as the interossei and lumbrical muscles. Similarly, the intrinsic muscles of the back, or the deep back muscles, are those that fuse with the vertebral column. They are well-developed and extend from the skull base to the sacrum. They are associated with the movements of the vertebral column and the control of posture. The intrinsic back muscles are covered by deep fascia, which plays a key role in their organisation.
The deep back muscles can be divided into four layers: superficial, intermediate, deep, and deepest. The superficial layer is composed of the splenius muscles (spinotransversales muscles), which include the splenius capitis and splenius cervicis. These muscles are located on the posterolateral aspect of the neck and the posterior upper thorax, overlying the deep muscles of the neck. The intermediate layer contains the large erector spinae muscles, which are sometimes referred to as the long muscles of the back. The erector spinae is composed of three vertical columns of muscle that lie side by side: the iliocostalis, longissimus, and spinalis muscles.
The deep intrinsic muscles are located underneath the erector spinae and are known as the transversospinales. They are a group of short muscles associated with the transverse and spinous processes of the vertebral column. The semispinalis is the most superficial of the deep intrinsic muscles. The multifidus is located underneath the semispinalis muscle and is most developed in the lumbar area.
The deepest layer of the intrinsic back muscles includes the rotatores muscles. These muscles, along with the semispinalis and multifidus, are innervated by the segmental branches of the posterior rami of spinal nerves. They receive their blood supply from the deep cervical, posterior intercostal, subcostal, or lumbar arteries, which can vary from person to person.
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Intermediate intrinsic back muscles
Intrinsic muscles refer to muscles that are located within or deeper in a structure. The intrinsic muscles are those closest to the axial and appendicular skeleton. The intrinsic back muscles can be divided into three layers: superficial, intermediate, and deep. The intermediate intrinsic back muscles are associated with movements of the thoracic cage.
There are three intermediate intrinsic back muscles: the iliocostalis, longissimus, and spinalis. Together, these muscles form a column known as the erector spinae. The erector spinae is situated posterolaterally to the spinal column, between the vertebral spinous processes and the costal angle of the ribs. The erector spinae is the largest of the deep back muscles and lies on either side of the vertebral column.
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 lumborum and thoracis arise from the common tendinous origin and attach to the costal angle of the ribs and the transverse processes of the thoracic vertebrae. The cervicis attaches to the cervical transverse processes.
The spinalis muscle is located medially within the erector spinae and is the smallest of the three muscle columns. It can be divided into the thoracic, cervicis, and capitis, although the cervicis is absent in some individuals. The spinalis muscle arises from the common tendinous origin and attaches to the spinous processes of the cervical and thoracic vertebrae and the occipital bone of the skull.
The multifidus is another muscle that belongs to the intermediate layer of the transversospinalis muscle group. It is composed of many short, triangular muscles that span the entire length of the vertebral column but are thickest and most developed in the lumbar region. The multifidus cervicis arises from the superior articular processes of vertebrae C4-C7, while the multifidus thoracis originates from the transverse process of the thoracic vertebra. The multifidus lumborum arises from the mammillary processes of lumbar vertebrae, the posterior aspect of the sacrum, and the posterior iliac spine. The main function of the multifidus is to stabilize the vertebrae during movements of the spine.
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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.
The intrinsic muscles of the hand are located within the various hand osseofascial compartments within the anatomic confines of the wrist (proximally) and phalanges (distally).
The intrinsic muscles of the back extend from the sacrum to the base of the skull. They are associated with the movements of the vertebral column and the control of posture.
