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Intrinsic muscles are those located within or situated deeper in a structure, as opposed to extrinsic muscles, which are located more superficially. 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. The intrinsic muscles of the tongue include the superior longitudinal muscle, the inferior longitudinal muscle, the transverse muscle, and the verticalis muscle. These muscles are contained completely within the tongue and act to change its shape. The intrinsic muscles of the back are associated with the movements of the vertebral column and the control of posture. They extend from the sacrum to the base of the skull. The intrinsic muscles of the foot are small but play a mighty role in foot and ankle function, contributing to stability and balance.
| Characteristics | Values |
|---|---|
| Definition | A group of muscles located within or situated deeper in a structure, in contrast to extrinsic muscles located rather superficially |
| Location | Intrinsic muscles refer to the muscles closest to the axial and appendicular skeleton, e.g., hand, tongue, foot, back |
| Function | Movement of the hand and fingers, change the shape of the tongue, foot and ankle stability, vertebral column movement, posture control |
| Size | Varies from the abductor hallucis (largest) to the lumbricals (smallest) |
| Functionality | May not be specific to high force production or high excursion |
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What You'll Learn
Intrinsic muscles of the tongue
Intrinsic muscles are those that develop embryologically in the back and are thus described as intrinsic muscles. They are associated with the movements of the vertebral column and the control of posture.
The intrinsic muscles of the tongue are contained completely within the tongue and act to change its shape. The tongue is a muscular organ situated in the oral cavity and 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 also involved in breathing.
There are four intrinsic muscles of the tongue, found in relatively distinct layers: the superior longitudinal, inferior longitudinal, transverse, and vertical muscles. 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. It curls the tip of the tongue and lateral surfaces superiorly and shortens the tongue when used with the inferior longitudinal muscle. The transverse muscle proceeds from an origin along the median septum out to the lateral borders of the tongue. The vertical muscle fibres intertwine with the transverse muscle fibres in the intermediate muscle layer of the tongue. They run vertically within the tongue and, when contracted, flatten and widen it. The inferior longitudinal muscle runs parallel to the superior longitudinal muscle from the base of the tongue to its tip.
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Intrinsic muscles of the hand
Intrinsic muscles are those located within the hand itself. They are responsible for the fine motor functions of the hand. The embryological development of the hand's intrinsic muscles begins in week 4 of pregnancy, with muscles developing in weeks 5 and 6. The blood supply to these muscles comes from the ulnar and radial arteries.
The thenar muscles are three short muscles located at the base of the thumb. They are responsible for the thumb's fine movements and produce a bulge known as the thenar eminence. The median nerve innervates all the thenar muscles. The opponens pollicis, the largest of the thenar muscles, originates from the tubercle of the trapezium and the associated flexor retinaculum and inserts onto the lateral margin of the first metacarpal.
The hypothenar muscles, on the other hand, form the hypothenar eminence, a protrusion on the medial side of the palm at the base of the little finger. The ulnar nerve innervates these muscles. The abductor digiti minimi, the most superficial of the hypothenar muscle group, originates from the pisiform and the tendon of the flexor carpi ulnaris and attaches to the base of the proximal phalanx of the little finger. It abducts the little finger.
The lumbricals are crucial to finger movement, linking the extensor tendons to the flexor tendons. There are four lumbricals in the hand, each associated with a finger. The lateral two lumbricals (index and middle fingers) are innervated by the median nerve, while the medial two lumbricals (ring and little fingers) are innervated by the ulnar nerve.
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Intrinsic muscles of the foot
The muscles of the foot are divided into two groups: extrinsic and intrinsic. The extrinsic muscles are found in the lower leg and are responsible for actions such as eversion, inversion, plantarflexion, and dorsiflexion of the foot. The intrinsic muscles, on the other hand, are located entirely within the foot and are responsible for the fine motor actions of the toes.
The intrinsic foot muscles can be further divided into two main groups: the dorsal and plantar muscles. The dorsal group consists of two muscles: the extensor digitorum brevis and the extensor hallucis brevis. These muscles act to extend the toes and are innervated by the deep fibular nerve. The plantar group, on the other hand, consists of four layers of muscles, going from superficial to deep within the foot. The first layer is the most superficial and consists of the abductor hallucis, flexor digitorum brevis, and abductor digiti minimi muscles. These muscles lie immediately deep to the plantar aponeurosis in the sole of the foot. The abductor hallucis muscle, in particular, contributes to a small soft tissue bulge on the medial side of the sole.
The second plantar layer contains two muscles: the quadratus plantae and the lumbricals. The quadratus plantae is a flat, square-shaped muscle with two heads of origin. It originates from the medial and lateral plantar surfaces of the calcaneus. The lumbricals, on the other hand, consist of four muscles that are each located medial to their respective tendon of the flexor digitorum longus. These muscles are responsible for flexion at the metatarsophalangeal joints and extension at the interphalangeal joints.
The third and fourth layers of the plantar muscles contain a total of five muscles, including the flexor hallucis brevis, adductor hallucis, and flexor digiti minimi brevis. These muscles are associated with movements of the great toe and the little toe.
Overall, the intrinsic muscles of the foot play an important role in stabilising the foot, supporting the arches, and producing fine movements of the toes. Weakness in these muscles can lead to issues such as foot pain and impaired balance, while strengthening them can improve foot function and reduce the risk of falls, especially in older adults.
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Intrinsic back muscles
The intrinsic back muscles, also known as deep back muscles, are a group of muscles that develop embryologically in the back. They are well-developed and extend from the sacrum to the base of the skull. These muscles are associated with the movements of the vertebral column and play a crucial role in maintaining posture and producing movements of the head, neck, and trunk.
The deep back muscles consist of four layers: superficial, intermediate, deep, and deepest. The superficial layer comprises the splenius 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. The intermediate layer contains the erector spinae muscles, which are composed of three vertical columns of muscle: the iliocostalis, longissimus, and spinalis. These muscles form a column known as the erector spinae, which is situated posterolaterally to the spinal column.
The deep layer of intrinsic back muscles, known as the transversospinales, consists of three major muscles: the semispinalis, multifidus, and rotatores. These muscles are associated with the transverse and spinous processes of the vertebral column. The semispinalis is the most superficial of the deep intrinsic muscles and can be divided into thoracic, cervicis, and capitis sections. The multifidus is located underneath the semispinalis and is most prominent in the lumbar region.
The deepest layer of intrinsic back muscles includes the short, deep intrinsic muscles that lie underneath the erector spinae. These muscles play a crucial role in the movement and stability of the vertebral column. The intrinsic back muscles work together with other muscle groups to produce complex movements and maintain the body's posture. They receive their nervous supply primarily from the dorsal rami of the spinal nerves, providing sensation to the skin of the back and the deep muscles.
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Innervation of intrinsic muscles
The intrinsic muscles of the hand are located within the hand itself and are responsible for fine motor functions. The nerves of the hand and wrist originate from the brachial plexus, which is located proximally in the root of the neck and axillary region. The important nerves from the brachial plexus that innervate the hand and wrist are the median, ulnar, and radial nerves.
The median nerve passes through the carpal tunnel under the flexor retinaculum of the hand and divides into recurrent and common palmar digital branches. The recurrent branch provides motor supply for the three thenar muscles, while the first and second lumbrical muscles are innervated by the palmar digital branches. The lateral two lumbricals (of the index and middle fingers) are also innervated by the median nerve.
The ulnar nerve innervates all the intrinsic muscles of the hand except four muscles, which are supplied by the median nerve. These four muscles are the lateral two lumbricals, opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis. The ulnar nerve supplies the hypothenar, interossei, and medial two lumbricals muscles. It also innervates the opponens digit minimi, abductor digiti minimi, and flexor digiti minimi brevis muscles of the hypothenar eminence.
The radial nerve innervates the finger extensors and the thumb abductor. It is completely sensory in the hand and provides palmar and dorsal cutaneous innervation to the little finger and medial half of the ring finger.
The intrinsic back muscles can be divided into three layers: superficial, intermediate, and deep. The superficial muscles are the spinotransversales, which include the splenius capitis and splenius cervicis. These muscles are innervated by the posterior rami of the lower cervical spinal nerves and are responsible for rotating and extending the head and neck. The intermediate intrinsic back muscles are the iliocostalis, longissimus, and spinalis, which form the erector spinae. The deep intrinsic muscles are the transversospinales, which include the semispinalis, multifidus, and rotatores. These muscles are innervated by the posterior rami of the spinal nerves.
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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.
Intrinsic muscles are found in the back, tongue, hand, and foot.
The deep intrinsic muscles of the back are associated with the movements of the vertebral column and the control of posture.
The intrinsic muscles in the foot provide stability and optimal function. They also contribute to the neuromotor aspect of foot and ankle stability.
