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Intrinsic muscles are those that are located within or deeper in a structure, unlike extrinsic muscles, which are located superficially. 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 tongue are contained completely within the tongue and act to change its shape. These include the superior longitudinal muscle, the inferior longitudinal muscle, the transverse muscle, and the verticalis muscle. Intrinsic muscles are important for stability and balance, and their stimulation is essential for the growth of extrinsic muscles.
| Characteristics | Values |
|---|---|
| Intrinsic muscles of the tongue | Change the shape of the tongue |
| Superficial muscles | Associated with movements of the shoulder |
| Intermediate muscles | Associated with movements of the thoracic cage |
| Deep muscles | Associated with movements of the vertebral column |
| Intrinsic back muscles | Located underneath the erector spinae |
| Can be divided into transversospinales and splenius muscles | |
| Associated with the control of posture | |
| Intrinsic foot muscles | Abductor hallucis, flexor digitorum brevis, and quadratus plantae |
| Associated with balance control | |
| Intrinsic hand muscles | Important for various hand functions, such as pinch and grip strength |
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What You'll Learn
Intrinsic muscles of the tongue
The tongue is a muscular organ situated in the oral cavity, with eight paired muscles: four intrinsic and four extrinsic. The intrinsic muscles of the tongue are contained completely within the tongue and act to change its shape. The extrinsic muscles, on the other hand, are in charge of moving the tongue in different directions.
The four intrinsic muscles of the tongue are:
- Superior longitudinal muscle: This 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 its lateral surfaces, and shortens the tongue when used with the inferior longitudinal muscle.
- Inferior longitudinal muscle: This muscle runs parallel to the superior longitudinal muscle, from the base of the tongue to its tip.
- Transverse muscle: This muscle proceeds from an origin along the median septum out to the lateral borders of the tongue.
- Vertical muscle: The fibres of this muscle intertwine with the transverse muscle in the intermediate muscle layer of the tongue. They run vertically within the tongue and, when contracted, flatten and widen it.
The tongue is involved in several functions, including digestion, taste perception, and speech. It helps move food around the mouth, mixes it with saliva, and separates unwanted particles. It also enables the formation of the food bolus in the oral preparatory phase of swallowing and takes part in the oral phase of swallowing by elevating and sweeping posteriorly to propel the food bolus past the anterior tonsillar pillar, triggering the swallowing reflex.
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Intrinsic muscles of the foot
Intrinsic muscles are those smaller muscles that exist entirely within the confines of the muscle and occur deep within the structure. The intrinsic muscles of the foot are, therefore, contained within the foot itself and act to stabilise the foot, support the arches, and produce fine movements of the toes.
The intrinsic foot muscles can be divided into two main groups: the plantar and the dorsal. The plantar muscles are located in the sole of the foot, while the dorsal muscles are located in the dorsum of the foot. There are ten intrinsic muscles in the plantar aspect (sole) of the foot, which act collectively to stabilise the arches of the foot and individually to control the movement of the digits. The plantar group can be further divided into four layers, going from superficial (plantar) to deep (dorsal) within the foot. The first layer is the most superficial and consists of abductor hallucis, flexor digitorum brevis, and abductor digiti minimi. The second plantar layer contains two muscles: the quadratus plantae and the lumbricals. There are four lumbrical muscles in the foot, each located medial to their respective tendon of the flexor digitorum longus. The third layer contains three muscles: the flexor hallucis brevis, adductor hallucis, and flexor digiti minimi brevis.
The dorsal group consists of two muscles: the extensor digitorum brevis and the extensor hallucis brevis. Both muscles act to extend the toes and are innervated by the deep fibular nerve. The extensor digitorum brevis originates on the superolateral surface of the calcaneus, while the extensor hallucis brevis originates on the same surface and runs along the centre of the dorsal surface of the foot before inserting onto the base of the proximal phalanx of the big toe.
The intrinsic foot muscles are similar in function to the abdominal and paraspinal muscles of the lumbopelvic-hip core muscles, which are responsible for maintaining posture and stability during gait. Improving the strength and function of weak intrinsic muscles is important for many reasons, such as improving foot morphology and function, balance, strength, and running mechanics. Specific exercises targeting the strengthening of these muscles include the "dance step to nowhere" exercise, marble pickup, and proprioceptive training (balance and stability exercises).
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Intrinsic muscles of the hand
Intrinsic muscles are those smaller muscles that exist entirely within the confines of the muscle and occur deep within the structure. They are responsible for stabilising the extrinsic muscles. The intrinsic muscles of the hand are those lying deeper in the hand, such as the interossei and lumbrical muscles. The interossei muscles are located between the metacarpal bones of the hand and can be divided into two groups: dorsal and palmar. The lumbricals are crucial to finger movement, linking the extensor tendons to the flexor tendons. They originate from a tendon of the flexor digitorum profundus and pass dorsally and laterally around each finger, inserting into the extensor hood. 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 hypothenar muscles form a muscular protrusion on the medial side of the palm, at the base of the little finger. The abductor digiti minimi is the most superficial of the hypothenar muscle group. It 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. The flexor digiti minimi brevis lies laterally to the abductor digiti minimi in the hand. It originates from the hook of hamate and adjacent flexor retinaculum and inserts into the base of the proximal phalanx of the little finger. The opponens digit minimi lies deep to the other hypothenar muscles. It originates from the hook of hamate and associated flexor retinaculum and inserts into the medial margin of metacarpal V.
The thenar muscles are three short muscles located at the base of the thumb and are responsible for the fine movements of the thumb. The median nerve innervates all the thenar muscles. The opponens pollicis is the largest of the thenar muscles and lies underneath the other two. It originates from the tubercle of the trapezium and the associated flexor retinaculum and inserts onto the lateral margin of the first metacarpal.
Blood supply to the intrinsic hand muscles comes from the ulnar and radial arteries and their anostomotic branches and collateral circulation. The ulnar and radial arteries cross the wrist to enter the hand and send vessels deep and superficially, forming two anastomoses called the superficial and deep palmar arches. The ulnar artery contributes to the majority of the blood supply of the superficial palmar arch, while the radial artery contributes to the majority of the deep palmar arch. The nerves of the intrinsic hand arise from the brachial plexus, a network of nerves from ventral rami between the C5 to T1 nerve roots. The nerves of the brachial plexus that supply muscles of the intrinsic hand include the median and ulnar nerve.
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Intrinsic back muscles
Intrinsic muscles are those smaller muscles that exist entirely within the confines of the muscle and occur deep within the 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.
The muscles of the back can be divided into three groups: superficial, intermediate, and intrinsic. The deep muscles develop embryologically in the back and are thus described as intrinsic muscles. The superficial and intermediate muscles do not develop in the back and are classified as extrinsic muscles.
The deep back muscles, also called intrinsic or true back muscles, consist of four layers of muscles: superficial, intermediate, deep, and deepest layers. These muscles lie on each side of the vertebral column, deep to the thoracolumbar fascia. They span the entire length of the vertebral column, extending from the cranium to the pelvis. The deep back muscles act together to provide support and maintain the body's posture, as well as to produce movements of the head, neck, and trunk. The main functions of these muscles are flexion, extension, lateral flexion, and axial rotation of the vertebral column.
The superficial muscle layer is composed of the splenius muscles (spinotransversales muscles), which are the splenius capitis and splenius cervicis. These flat muscles are located on the posterolateral aspect of the neck and the posterior upper thorax, overlying the deep muscles of the neck. The splenius muscles originate from the spinous processes of cervical and thoracic vertebrae.
The intermediate layer contains the large erector spinae muscles, which are sometimes called the long muscles of the back. This muscle group is the largest of the deep back muscles and lies on either side of the vertebral column between the spinous processes of the vertebrae and the angles of the ribs. The muscles are composed of three vertical columns of muscle that lie side by side. From lateral to medial, these are the iliocostalis, longissimus, and spinalis muscles. Each muscle column is subdivided into regions (lumborum, thoracic, cervicis, capitis) based on which region of the axial skeleton it attaches to superiorly.
The deep intrinsic muscles are located underneath the erector spinae, and are known collectively as the transversospinales. They are a group of short muscles, associated with the transverse and spinous processes of the vertebral column. There are three major muscles in this group: the semispinalis, multifidus, and rotatores.
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Superficial, intermediate, and intrinsic muscles
The muscles of the back can be divided into three groups: superficial, intermediate, and intrinsic (deep) muscles.
The superficial muscles are associated with movements of the shoulder. These include the splenius muscles, which are 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. They originate from the spinous processes of cervical and thoracic vertebrae and are innervated by the posterior rami of the middle and lower cervical spinal nerves.
The intermediate 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, which is situated posterolaterally to the spinal column. The erector spinae is the smallest of the three muscle columns and can be subdivided into the thoracic, cervicis, and capitis.
The intrinsic (deep) muscles are associated with movements of the vertebral column and the control of posture. They develop embryologically in the back and are thus described as intrinsic muscles. These muscles extend from the sacrum to the base of the skull and are covered by deep fascia, which is important for their organisation. There are three major muscles in this group: the semispinalis, multifidus, and rotatores. The semispinalis is the most superficial of the deep intrinsic muscles and can be divided into the thoracic, cervicis, and capitis.
Additionally, the intrinsic muscles of the tongue are contained completely within it and act to change its shape. There are four muscles found in distinct layers, including the superior longitudinal muscle and the transverse muscle.
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Frequently asked questions
Intrinsic muscles are those that develop within a body part, as opposed to extrinsic muscles, which develop elsewhere and course a pathway to their insertion.
Intrinsic muscles can be found in the back, tongue, foot, and hand.
Intrinsic muscles are important for various functions, including posture, balance, and hand functions such as grip strength.
