Muscles Flashcards
Muscles of the Back
The muscles of the back can be divided into three groups – superficial, intermediate and intrinsic:
- Superficial – associated with movements of the shoulder.
- Intermediate – associated with movements of the thoracic cage.
- Deep – associated with movements of the vertebral column.
Superficial Back Muscles
The superficial back muscles are situated underneath the skin and superficial fascia. They originate from the vertebral column and attach to the bones of the shoulder – the clavicle, scapula and humerus. All these muscles are therefore associated with movements of the upper limb.
The muscles in this group are the trapezius, latissimus dorsi, levator scapulae and the rhomboids. The trapezius and the latissimus dorsi lie the most superficially, with the trapezius covering the rhomboids and levator scapulae.
Trapezius
Trapezius
The trapezius is a broad, flat and triangular muscle. The muscles on each side form a trapezoid shape. It is the most superficial of all the back muscles.
Attachments: Originates the skull, spinous processes of C7-T12 and the ligamentum nuchae. The fibres attach to the clavicle, acromion and the scapula spine.
Innervation: Motor innervation is from the accessory nerve. It also receives proprioceptor fibres from C3 and C4 spinal nerves.
Actions: The upper fibres of the trapezius elevates the scapula and rotates it during abduction of the arm. The middle fibres retract the scapula and the lower fibres pull the scapula inferiorly.
Lattissimus Dorsi
The latissimus dorsi originates from the lower part of the back, where it covers a wide area.
Attachments: Has a broad origin – arising from the spinous processes of T6-T12, iliac crest, thoracolumbar fascia and the inferior three ribs. The fibres converge into a tendon that attaches to the intertubecular sulcus of the humerus.
Innervation: Thoracodorsal nerve.
Actions: Extends, adducts and medially rotates the upper limb.
Levator Scapulae
The levator scapulae is a small strap-like muscle. It begins in the neck, and descends to attach to the scapula.
Attachments: Originates from the transverse processes of the C1-C4 vertebrae and attaches to the medial border of the scapula.
Innervation: Dorsal scapular nerve.
Actions: Elevates the scapula
Rhomboids
There are two rhomboid muscles – major and minor. The rhomboid minor is situated superiorly to the major.
Rhomboid Major
Attachments: Originates from the spinous processes of T2-T5 vertebrae. Attaches to the medial border of the scapula, between the scapula spine and inferior angle.
Innervation: Dorsal scapula nerve.
Actions: Retracts and rotates the scapula.
Rhomboid Minor
Attachments: Originates from the spinous processes of C7-T1 vertebrae. Attaches to the medial border of the scapula, at the level of the spine of scapula.
Innervation: Dorsal scapula nerve.
Actions: Retracts and rotates the scapula.
Intermediate Back Muscles
The intermediate group contains two muscles – the serratus posterior superior andserratus posterior inferior. These muscles run from the vertebral column to the ribcage, and assist with elevating and depressing the ribs. They are thought to have a slight respiratory function.
Serratus Posterior Superior
The serratus posterior superior is a thin, rectangular shaped muscle. It lies deep to the rhomboid muscles on the upper back.
Attachments: Originates from the lower part of the ligamentum nuchae, and the cervical and thoracic spines (usually C7 – T3). The fibres pass in an inferolateral direction, attaching to ribs 2-5.
Innervation: Intercostal nerves.
Actions: Elevates ribs 2-5
Serratus Posterior Inferior
The serratus posterior inferior is broad and strong. It lies underneath the latissimus dorsi.
Attachments: Originates from the thoracic and lumbar spines (usually T11 – L3). The fibres pass in an superolateral direction, attaching to ribs 9-12.
Innervation: Intercostal nerves.
Actions: Elevates ribs 9-12.
Intrinsic (Deep) Back Muscles
The deep muscles of the back are well developed, and collectively 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.
The muscles themselves are covered by deep fascia, which plays a key role in their organisation.
Anatomically, the deep back muscles can be divided into three layers; superficial, intermediate and deep
Superficial Intrinsic Back Muscles
The superficial muscles are also known as the spinotransversales. There are two muscles in this group – splenius capitis and splenius cervicis. They are both associated with movements of the head and neck.
They are located on the posterolateral aspect of the neck, covering the deeper neck muscles.
Splenius Capitis
Attachments: Originates from the lower aspect of the ligamentum nuchae, and the spinous processes of C7 – T3/4 vertebrae. The fibres ascend, attaching to the mastoid process and the occipital bone of the skull.
Innervation: Posterior rami of spinal nerves C3 and C4.
Actions: Rotate head to the same side
Splenius Cervicis
- *Attachments**: Originates from the spinous processes of T3-T6 vertebae. The fibres ascend, attaching to the transverse processes of C1-3/4.
- *Innervation**: Posterior rami of the lower cervical spinal nerves.
- *Actions**: Rotate head to the same side.
Intermediate Intrinsic Back Muscles
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 spinal column, between the vertebral spinous processes and the costal angle of the ribs.
All three muscles can be subdivided by their superior attachments (into lumborum, thoracic, cervicis and capitis). They also all have a common tendinous origin, which arises from:
Lumbar and lower thoracic vertebrae.
Sacrum.
Posterior aspect of iliac crest.
Sacroiliac and supraspinous ligaments.
Iliocostalis
The iliocostalis muscle is located laterally within the erector spinae. It is associated with the ribs, and can be divided into three parts – lumborum, thoracis, and cervicis.
Attachments: Arises from the common tendinous origin, and attaches to the costal angle of the ribs and the cervical transverse processes.
Innervation: Posterior rami of the spinal nerves.
Actions: Acts unilaterally to laterally flex the vertebral column. Acts bilaterally to extend the vertebral column and head.
Longissimus
The longissimus muscle is situated between the iliocostalis and spinalis. It is the largest of the three columns. It can be divided into three parts – thoracic, cervicis and capitis.
Attachments: Arises from the common tendinous origin, and attaches to the lower ribs, the transverse processes of C2 – T12, and the mastoid process of the skull.
Innervation: Posterior rami of the spinal nerves.
Actions: Acts unilaterally to laterally flex the vertebral column. Acts bilaterally to extend the vertebral column and head.
Spinalis
The spinalis muscle is located medially within the erector spinae. It is the smallest of the three muscle columns. It can be divided into the thoracic, cervicis and capitis (although the cervicis part is absent in some individuals).
Attachments: Arises from the common tendinous origin, and attaches to the spinous processes of C2, T1-T8 and the occipital bone of the skull.
Innervation: Posterior rami of the spinal nerves.
Actions: Acts unilaterally to laterally flex the vertebral column. Acts bilaterally to extend the vertebral column and head.
Deep Intrinsic Back Muscles
The deep intrinsic muscles are located underneath the erector spinae. 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.
Semispinalis
The semispinalis is the most superficial of the deep intrinsic muscles. Much like the intermediate muscles, it can be divided by its superior attachments into thoracic, cervicis and capitis.
Attachments: Originates from the transverse processes of C4-T10. The fibres ascend 4-6 vertebral segments, attaching to the spinous processes of C2-T4, and to the occipital bone of the skull.
Innervation: Posterior rami of the spinal nerves.
Actions: Extends and contralaterally rotates the head and vertebral column.
Multifidus
The multifidus is located underneath the semispinalis muscle. It is best developed in the lumbar area.
Attachments: Has a broad origin – arises from the sacrum, posterior iliac spine, common tendinous origin of the erector spinae, mamillary processes of lumbar vertebrae, transverse processes of T1-T3 and articular processes of C4-C7. The fibres ascend 2-4 vertebral segments, attaching the spinous processes of the vertebrae.
Innervation: Posterior rami of the spinal nerves.
Actions: Stablises the vertebral column
Rotatores
The rotatores are most prominant in the thoracic region
Attachments: Originates from the vertebral transverse processes. The fibres ascend, and attach to the lamina and spinous processes of the immediately superior vertebrae.
Innervation: Posterior rami of the spinal nerves.
Actions: Stablises the vertebral column, and has a proprioceptive function.
Minor Deep Intrinsic Muscles
Interspinales: Spans between adjacent spinous processes. Acts to stablise the vertebral column.
Intertranversari – Spans between adjacent transverse processes. Acts to stablise the vertebral column.
Levatores costarum – Originates from the transverse processes of C7-T11, and attaches to the rib immediately below. Acts to elevate the ribs.
Muscles of the Foot
The muscles acting on the foot can be divided into two distinct groups; extrinsic and intrinsicmuscles.
The extrinsic muscles arise from the anterior, posterior and lateral compartments of the leg. They are mainly responsible for actions such as eversion, inversion, plantarflexion and dorsiflexion of the foot.
The intrinsic muscles are located within the foot and are responsible for the more fine motor actions of the foot, for example movement of individual digits.
Dorsal Aspect
Whilst many of the extrinsic muscles attach to the dorsum of the foot, there are only two intrinsic muscles located in this compartment – the extensor digitorum brevis, and the extensor hallucis brevis.
They are mainly responsible for assisting some of the extrinsic muscles in their actions. Both muscles are innervated by the deep fibular nerve.
Extensor Digitorum Brevis
The extensor digitorum brevis muscle lies deep to the tendon of the extensor digitorum longus.
- *Attachments**: Originates from the calcaneus, the interosseus talocalcaneal ligament and the inferior extensor retinaculum. It attaches to the long extensor tendons of the four medial digits.
- *Actions**: Aids the extensor digitorum longus in extending the medial four toes at the metatarsophalangeal and interphalangeal joints.
- *Innervation**: Deep fibular nerve
Extensor Hallucis Brevis
The extensor hallucis brevis muscle is medial to extensor digitorum longus and lateral to extensor hallucis longus.
- *Attachments**: Originates from the calcaneus, the interosseus talocalcaneal ligament and the inferior extensor retinaculum. It attaches to the base of the proximal phalanx of the great toe.
- *Actions**: Aids the extensor hallucis longus in extending the great toe at the metatarsophalangeal joint.
- *Innervation**: Deep fibular nerve.
Plantar Aspect
There are 10 intrinsic muscles located in the sole of the foot. They act collectively to stablise the arches of the foot, and individually to control movement of the digits. All the muscles are innervated either by the medial plantar nerve or the lateral plantar nerve, which are both branches of the tibial nerve.
The muscle of the plantar aspect are described in four layers (superficial to deep).
First Layer
The first layer of muscles is the most superficial to the sole, and is located immediately underneath the plantar fascia. There are three muscles in this layer.
Abductor Hallucis
The abductor hallucis muscle is located on the medial side of the sole, where it contributes to a small soft tissue bulge.
- *Attachments**: Originates from the medial tubercle of the calcaneus, the flexor retinaculum and the plantar aponeurosis. It attaches to the medial base of the proximal phalanx of the great toe.
- *Actions**: Abducts and flexes the great toe.
- *Innervation**: Medial plantar nerve.
Flexor Digitorum Brevis
The flexor digitorum brevis muscle is located laterally to the abductor hallucis. It sits in the center of the sole, sandwiched between the plantar aponeurosis and the tendons of flexor digitorum longus.
Attachments: Originates from the medial tubercle of the calcaneus and the plantar aponeurosis. It attaches to the middle phalanges of the lateral four digits.
Actions: Flexes the lateral four digits at the proximal interphalangeal joints.
Innervation: Medial plantar nerve.
Abductor Digiti Minimi
The abductor digiti minimi muscle is located on the lateral side of the foot. It is homologous with the abductor digiti minimi of the hand.
- *Attachments**: Originates from the medial and lateral tubercles of the calcaneus and the plantar aponeurosis. It attaches to the lateral base of the proximal phalanx of the 5th digit.
- *Actions**: Abducts and flexes the 5th digit.
- *Innervation**: Lateral plantar nerve.
Second Layer
The second layer contains two muscles – the quadratus plantae, and the lumbricals. In addition, the tendons of the flexor digitorum longus (an extrinsic muscle of the foot) pass through this layer.
Quadratus Plantae
The quadratus plantae muscle is located superior to the flexor digitorum longus tendons. It is separated from the first layer of muscles by the lateral plantar vessels and nerve.
- *Attachments**: Originates from the medial and lateral plantar surface of the calcaneus. It attaches to the tendons of flexor digitorum longus.
- *Actions**: Assists flexor digitorum longus in flexing the lateral four digits.
- *Innervation**: Lateral plantar nerve.
Lumbricals
There are four lumbrical muscles in the foot. They are each located medial to their respective tendon of the flexor digitorum longus.
- *Attachments**: Originates from the tendons of flexor digitorum longus. Attaches to the extensor hoods of the lateral four digits.
- *Actions**: Flexes at the metatarsophalangeal joints, while extending the interphalangeal joints.
- *Innervation**: The most medial lumbrical is innervated by the medial plantar nerve. The remaining three are innervated by the lateral plantar nerve.
Third Layer
The third layer contains three muscles. The flexor hallucis brevis and adductor hallucis are associated with movements of the great toe. The remaining muscle, the flexor digiti minimi brevis, moves the little toe
Flexor Hallucis Brevis
The flexor hallucis brevis muscle is located on the medial side of the foot. It originates from two places on the sole of the foot.
- *Attachments**: Originates from the plantar surfaces of the cuboid and lateral cuneiforms, and from the tendon of the posterior tibialis tendon. Attaches to the base of the proximal phalanx of the great toe.
- *Actions**: Flexes the proximal phalanx of the great toe at the metatarsophalangeal joint.
- *Innervation**: Medial plantar nerve.
Adductor Hallucis
The adductor hallucis muscle is located laterally to the flexor hallucis brevis. It consists of an oblique and transverse head.
- *Attachments**: The oblique head originates from the bases of the first four metatarsals. The transverse head originates from the plantar ligaments of the metatarsophalangeal joints. Both heads attach to the lateral base of the proximal phalanx of the great toe.
- *Actions**: Adduct the great toe. Assists in forming the transverse arch of the foot.
- *Innervation**: Deep branch of lateral plantar nerve.
Flexor Digiti Minimi Brevis
The flexor digiti minimi brevis muscle is located on the lateral side of the foot, underneath the metatarsal of the little toe. It resembles the interossei in structure.
- *Attachments**: Originates from the base of the fifth metatarsal. Attaches to the base of the proximal phalanx of the fifth digit.
- *Actions**: Flexes the proximal phalanx of the fifth digit.
- *Innervation**: Superficial branch of lateral plantar nerve.
Fourth Layer
The plantar and dorsal interossei comprise the fourth and final plantar muscle layer. The plantar interossei have a unipennate morphology, while the dorsal interossei are bipennate.
Plantar Interossei
There are three plantar interossei, which are located between the metatarsals. Each arises from a single metatarsal.
- *Attachments**: Originates from the medial side of metatarsals three to five. Attaches to the medial sides of the phalanges of digits three to five.
- *Actions**: Adduct digits three to five and flex the metatarsophalangeal joints.
- *Innervation**: Lateral plantar nerve
Dorsal Interossei
There are four dorsal interossei, which are located between the metatarsals. Each arises from two metatarsals.
- *Attachments**: Originates from the sides of metatarsals one to five. The first muscle attaches to the medial side of the proximal phalanx of the second digit. The second to fourth interossei attach to the lateral sides of the proximal phalanxes of digits two to four.
- *Actions**: Abduct digits two to four and flex the metatarsophalangeal joints.
- *Innervation**: Lateral plantar nerve.
Gluteal Region Muscles
The gluteal region is an anatomical area located posteriorly to the pelvic girdle, at the proximal end of the femur. The muscles in this region move the lower limb at the hip joint.
The muscles of the gluteal region can be broadly divided into two groups:
Superficial abductors and extenders – A group of large muscles that abduct and extend the femur. It includes the gluteus maximus, gluteus medius and gluteus minimus.
Deep lateral rotators – A group of smaller muscles, that mainly act to laterally rotate the femur. It includes the quadratus femoris, piriformis, gemellus superior, gemellus inferior and obturator internus.
Superficial Gluteal Muscles
The superficial muscles in the gluteal region consist of the three glutei. They act mainly act to abduct and extend the lower limb at the hip joint.
Gluteus Maximus
The gluteus maximus is the largest of the gluteal muscles. It is also the most the most superficial, producing the shape of the buttocks.
Attachments: Originates from the gluteal (posterior) surface of the ilium, sacrum and coccyx. It slopes across the buttock at a 45 degree angle, then inserts into the iliotibial tract and greater trochanter of the femur.
Actions: It is the main extensor of the thigh, and assists with lateral rotation. However, it is only used when force is required, such as running or climbing.
Innervation: Inferior gluteal nerve.
Gluteus Medius
The gluteus medius muscle is fan shaped and lies between to the gluteus maximus and the mnimus. It is similar is shape and function to the gluteus minimus.
- *Attachments**: Originates from the gluteal surface of the ilium and inserts into the lateral surface of the greater trochanter.
- *Actions**: Abducts and medially rotates the lower limb. During locomotion, it secures the pelvis, preventing pelvic drop of the opposite limb.
- *Innervation**: Superior gluteal nerve.
Gluteus Minimus
The gluteus minimus is the deepest and smallest of the superficial gluteal muscles. It is similar is shape and function to the gluteus medius.
- *Attachments**: Originates from the ilium and converges to form a tendon, inserting to the anterior side of the greater trochanter.
- *Actions**: Abducts and medially rotates the lower limb. During locomotion, it secures the pelvis, preventing pelvic drop of the opposite limb.
- *Innervation**: Superior gluteal nerve.
Deep Gluteal Muscles
The deep gluteal muscles are a set of smaller muscles, located underneath the gluteus minimus. The general action of these muscles is to laterally rotate the lower limb. They also stablise the hip joint by ‘pulling’ the femoral head into the acetabulum of the pelvis.
Piriformis
The piriformis muscle is a key landmark in the gluteal region (see ‘clinical relevance’ below). It is the most superior of the deep muscles.
- *Attachments**: Originates from the anterior surface of the sacrum. It then travels infero-laterally, through the greater sciatic foramen, to insert into the greater trochanter of the femur.
- *Actions**: Lateral rotation and abduction.
- *Innervation**: Nerve to piriformis.
Obturator Internus
The obturator internus forms the lateral walls of the pelvic cavity. In some texts, the obturator internus and the gemelli muscles are considered as one muscle – the triceps coxae.
- *Attachments**: Originates from the pubis and ischium at the obturator foramen. It travels through the lesser sciatic foramen, and attaches to the greater trochanter of the femur.
- *Actions**: Lateral rotation and abduction.
- *Innervation**: Nerve to obturator internus.
The Gemelli – Superior and Inferior
The gemelli are two narrow and triangular muscles. They are separated by the obturator internus tendon.
- *Attachments**: The superior gemellus muscle originates from the ischial spine, the inferior from the ischial tuberosity. They both attach to the greater trochanter of the femur.
- *Actions**: Lateral rotation and abduction.
- *Innervation**: The superior gemellus muscle is innervated by the nerve to obturator internus, the inferior gemellus is innervated by the nerve to quadratus femoris.
Quadratus Femoris
The quadratus femoris is a flat square shaped muscle. It is the most inferior of the deep gluteal muscles, located below the gemelli and obturator internus.
- *Attachments**: It originates from the lateral side of the ischial tuberosity, and attaches to the quadrate tuberosity on the intertrochanteric crest.
- *Actions**: Lateral rotation.
- *Innervation**: Nerve to quadratus femoris.
Muscles of the AnteriorThigh
The musculature of the thigh can be split into three sections; anterior, medial and posterior. Each compartment has a distinct innervation and function.
The muscles in the anterior compartment of the thigh are innervated by the femoral nerve(L2-L4), and as a general rule, act to extend the leg at the knee joint.
There are three major muscles in the anterior thigh – the pectineus, sartorius andquadriceps femoris. In addition to these, the end of the iliopsoas muscle passes into the anterior compartment.
Iliopsoas
The iliopsoas is actually two muscles, thepsoas major and the iliacus. They originate in different areas, but come together to form a tendon, hence why they are commonly referred to as one muscle.
Unlike many of the anterior thigh muscles, the iliopsoas does not extend the leg at the knee joint.
Attachments: The psoas major originates from the lumbar vertebrae, and the iliacus originates from the iliac fossa of the pelvis. They insert together onto the lesser trochanter of the femur.
Actions: The iliopsoas flexes the lower limb at the hip joint and assists in lateral rotation at the hip joint.
Innervation: The psoas major is innervated by anterior rami of L1-3, while the iliacus is innervated by the femoral nerve.
Quadriceps Femoris
The quadriceps femoris consists of four individual muscles; three vastus muscles and the rectus femoris. They form the main bulk of the thigh, and collectively are one of the most powerful muscles in the body.
The quadriceps femoris attaches to the patella via a tendon. The patella attaches to the tibia by the patella tendon. The quadriceps femoris is the main extensor of the knee.
Vastus Muscles
There are three vastus muscles – vastus medialis, vastus intermedius and vastus lateralis.
They are located exactly where their names suggest; the medialis lies on the medial side of the anterior thigh, and the lateralis lies on the lateral side. The intermedius is found deep to the other muscles.
Collectively, the vastus muscles extend at the knee joint, and are innervated by the femoral nerve.
Rectus Femoris
- *Attachments**: Originates from the ilium, just superior to the acetabulum. It runs straight down the leg (the latin for straight is rectus), and attaches to the patella by the quadriceps femoris tendon.
- *Actions**: This is the only muscle of the quadriceps to cross both the hip and knee joints. It flexes the leg at the hip joint, and extends at the knee joint.
- *Innervation**: Femoral nerve.
Sartorius
The sartorius muscle in the longest muscle in the body. It is long and thin, running across the thigh in a inferomedial direction. It is found more superficially to the other muscles in the leg.
- *Attachments**: Originates from the anterior superior iliac spine, and attaches to the superior, medial surface of the tibia.
- *Actions**: At the hip joint, it is a flexor, abductor and lateral rotator. At the knee joint, it is also a flexor.
- *Innervation**: Femoral nerve.
Pectineus
This muscle can be classified into either the anterior or medial compartments or the thigh. It is innervated by the femoral nerve, a characteristic of the anterior compartment, but its actions are typical of a muscle from the medial compartment. It forms part of the base of the femoral triangle.
- *Attachments**: It originates from the pectineal line on the anterior surface of the pelvis, and attaches to the pectineal line on the posterior side of the femur, just inferior to the lesser trochanter.
- *Actions**: Adduction and flexion at the hip joint.
- *Innervation**: Femoral nerve and Obturator
Muscles of the Medial Thigh
The muscles in the medial compartment of the thigh are collectively known as the hip adductors. There are five muscles in this group; gracilis, obturator externus, adductor brevis, adductor longus and adductor magnus.
All the medial thigh muscles are innervated by the obturator nerve, which arises from the lumbar plexus. Arterial supply is via the obturator artery.
Adductor Magnus
The adductor magnus is the largest muscle in the medial compartment. It lies posteriorly to the other muscles.
Functionally, the muscle can be divided into two parts; the adductor part, and the hamstring part.
Attachments: The adductor part originates from the inferior rami of pubis and the rami of ischium, attaching to the linea aspera of the femur. The hamstring portion originates from the ischial tuberosity and attaches to the adductor tubercle on the distal and medial side of the femur.
Actions: They both adduct the thigh. The adductor component also flexes the thigh, with the hamstring portion extending the thigh.
Innervation: Adductor part is innervated by the obturator nerve (L2-L4), the hamstring part is innervated by the tibial nerve (L4-S3)
Adductor Longus
The adductor longus is a large, flat muscle. It partially covers the adductor brevis and magnus. The muscle forms the medial border of the femoral triangle.
- *Attachments**: Originates from the pubis, and expands into a fan shape, attaching broadly to the linea aspera of the femur
- *Actions**: Adduction and medial rotation of the thigh.
- *Innervation**: Obturator nerve (L2-L4).
Adductor Brevis
The adductor brevis is a short muscle, lying underneath the adductor longus.
It lies in between the anterior and posterior divisions of the obturator nerve. Therefore, it can be used as an anatomical landmark to identify the aforementioned branches.
- *Attachments**: Originates from the body of pubis and inferior pubic rami. It attaches to the linea aspera on the posterior surface of the femur, proximal to the adductor longus.
- *Actions**: Adduction of the thigh.
- *Innervation**: Obturator nerve (L2-L4).
Obturator Externus
This is one of the smaller muscles of the medial thigh, and it is located most superiorly.
- *Attachments**: It originates from the membrane of the obturator foramen, and adjacent bone. It passes under the neck of femur, attaching to the posterior aspect of the greater trochanter.
- *Actions**: Laterally rotates the thigh.
- *Innervation**: Obturator nerve (L2-L4).
Gracilis
The gracilis is the most superficial and medial of the muscles in this compartment. It crosses at both the hip and knee joints. It is sometimes transplanted into the hand or forearm to replace a damaged muscle.
- *Attachments**: It originates from the inferior rami of the pubis, and the body of the pubis. Descending almost vertically down the leg, it attaches to the medial surface of the tibia, inbetween the tendons of the sartorius (anteriorly) and the semitendinosus (posteriorly).
- *Actions**: Adduction of the thigh at the hip, and flexion of the leg at the knee.
- *Innervation**: Obturator nerve (L2-L4).
Muscles in the Posterior Thigh
The muscles in the posterior compartment of the thigh are collectively known as the hamstrings. They consist of the biceps femoris, semitendinosus and semimembranosus – as a group they act to extend at the hip, and flex at the knee. They are innervated by the sciatic nerve (L4-S3) as it descends through the thigh.
The hamstrings form prominent tendons medially and laterally at the back of the knee. This explains the phrase ‘hamstringing the enemy’ – whereby these tendons are cut.
Biceps Femoris
Like the biceps brachii in the arm, the biceps femoris muscle has two heads – a long head and a short head.
It is the most lateral of the muscles in the posterior thigh – the common tendon of the two heads can be felt laterally at the posterior knee.
Attachments: The long head originates from the ischial tuberosity of the pelvis. The short head originates from the linea aspera on posterior surface of the femur. Together, the heads form a tendon, which inserts into the head of the fibula.
Actions: Main action is flexion at the knee. It also extends the leg at the hip, and laterally rotates at the hip and knee.
Innervation: Long head innervated by the tibial part of the sciatic nerve, whereas the short head is innervated by the common fibular part of the sciatic nerve.
Semitendinosus
The semitendinosus is a largely tendinous muscle. It lies medially to the biceps femoris, and covers the majority of the semimembranosus.
- *Attachments**: It originates from the ischial tuberosity of the pelvis, and attaches to the medial surface of the tibia.
- *Actions**: Flexion of the leg at the knee joint. Extension of thigh at the hip. Medially rotates the thigh at the hip joint and the leg at the knee joint.
- *Innervation**: Tibial part of the sciatic nerve.
Semimembranosus
The semimembranosus muscle is flattened and broad. It is located underneath the the semitendinosus.
- *Attachments**: It originates from the ischial tuberosity, but does so more superiorly than the semitendinosus and biceps femoris. It attaches to the medial tibial condyle.
- *Actions**: Flexion of the leg at the knee joint. Extension of thigh at the hip. Medially rotates the thigh at the hip joint and the leg at the knee joint.
- *Innervation**: Tibial part of the sciatic nerve.
Fascia Lata
The fascia lata is a deep fascial investment of the whole thigh musculature and is analogous to a strong, extensible and elasticated stocking. It begins most proximally around the iliac crest and inguinal ligament and ends most distally to the bony prominences of the tibia; where it continues to become the deep fascia of the leg (the crural fascia).
The width of the fascia lata varies considerably at different regions of the thigh. It is thickest along the superolateral aspect of the thigh, originating from the fascial condensations from gluteus maximusand medius, and also from around the knee where the fascia receives reinforcing fibres from tendons. The fascial investment is thinnest where it covers the adductor muscles of the medial thigh.
The deepest aspect of fascia lata gives rise to three intermuscular septa that attach centrally to the femur. This divides the thigh musculature into three compartments; anterior, medial and lateral. The lateral intermuscular septum is the strongest of the three due to reinforcement from the iliotibial tract (see later), whereas the other two septa are proportionately weaker.
An ovoid hiatus is present in the fascia lata just inferior to the inguinal ligament known as the saphenous opening. This gap serves as an entry point for efferent lymphatic vessels and the great saphenous vein, draining into superficial inguinal lymph nodes and the femoral vein respectively. A covering of membranous tissue (the cribriform fascia) covers the hiatus which develops inferomedially from a sharp margin of the gap (the falciform margin).
IlioTibial Tract
The iliotibial tract is a longitudinal thickening of the fascia lata, which is strengthened posteriorly by fibres from the gluteus maximus. It is located laterally in the thigh, extending from the iliac tubercle to the lateral tibial condyle. The ITT has three main functions:
Movement: acts as an extensor, abductor and lateral rotator of the hip, with an additional role in providing lateral stabilisation to the knee joint.
Compartmentalisation: The deepest aspect of ITT extends centrally to form the lateral intermuscular septum of the thigh and attaches to the femur.
Muscular sheath – forms a sheath for the tensor fascia lata muscle.
Tensor Fascia Lata
The tensor fascia lata is a gluteal muscle that acts as a flexor, abductor and internal rotator of the hip. Its nomenclature however, is devised from its additional role in tensing the fascia lata.
The muscle originates from the iliac crest, and descends down the superolateral thigh. At the junction of the middle and upper thirds of the thigh, it inserts into the anterior aspect of the iliotibial tract. When stimulated, the tensor fasciae lata tautens the iliotibial band and braces the knee, especially when the opposite foot is lifted.
The property of TFL tightening the fascia lata is analogous to hoisting an elastic stocking up the thigh. When the fascia lata is pulled taut, it forces muscle groups closer together within their intermuscular septa towards the femur. This action centralises muscle weight and limits outward expansion, which in turn reduces the overall force required for movement at the hip joint.
An additional property of tensing the fascia lata is that it makes muscle contraction more efficient in compressing deep veins. This ensures adequate venous return to the heart from the lower limbs.
Muscles in the Anterior Leg
There are four muscles in the anterior compartment of the leg; tibialis anterior, extensor digitorun longus, extensor hallucis longus and fibularis tertius.
Collectively, they act to dorsiflex and invert the foot at the ankle joint. The extensor digitorum longus and extensor hallucis longus also extend the toes. The muscles in this compartment are innervated by the deep fibular nerve (L4-L5), and blood is supplied via theanterior tibial artery.
Extensor Hallucis Longus
The extensor hallucis longus is located deep to the EDL and TA.
- *Attachments**: Originates from the medial surface of the fibular shaft. The tendon crosses anterior to the ankle joint and attaches to the base of the distal phalanx of the great toe.
- *Action**: Extension of the great toe and dorsiflexion of the foot.
- *Innervation**: Deep fibular nerve.
Muscles in the Lateral Leg
There are two muscles in the lateral compartment of the leg; the fibularis longus and brevis. In older texts, they are referred to as the peroneal longus and brevis. As the fibularis longus and brevis are in the same muscular compartment, they have the same function and innervation.
The common anatomical function of the muscles is eversion – turning the sole of the foot outwards. You’ll notice that from the anatomical position, only a few degrees of eversion is possible. In reality, the job of these muscles is to fix the medial margin of the foot during running, and preventing excessive inversion.
Superficial Posterior Leg Muscles
The superficial muscles form the characteristic ‘calf’ shape of the posterior leg. They all insert into the calcaneus of the foot (the heel bone), via the calcaneal tendon. The calcaneal reflex tests spinal roots S1-S2.
To minimise friction during movement, there are two bursae (fluid filled sacs) associated with the calcaneal tendon:
Subcutaneous calcaneal bursa – lies between the skin and the calcaneal tendon.
Deep bursa of the calcaneal tendon – lies between the tendon and the calcaneus.
Deep Posterior Leg Muscles
There are four muscles in the deep compartment of the posterior leg. One muscle, the popliteus, acts only on the knee joint. The remaining three muscles (tibialis posterior, flexor hallucis longus and flexor digitorum longus) act on the ankle and foot.
Flexor Hallucis Longus
The flexor hallucis longus muscle is found on the lateral side of leg. This is slightly counter-intuitive, as it is opposite the great toe, which it acts on.
- *Attachments**: Originates from the posterior surface of the fibula, attaches to the plantar surface of the phalanx of the great toe.
- *Actions**: Flexes the great toe.
- *Innervation**: Tibial nerve.
Infrahyoid Muscles
There are four infrahyoid muscles, located underneath the hyoid bone in the neck. They can be divided into those in the superficial plane (sternohyoid and omohyoid), and those in the deep plane (sternothyroid and thyrohyoid).
Thyrohyoid
The thryrohyoid muscle is a short band of muscle, located underneath the posterior portions of the omohyoid and sternohyoid muscles. It is a continuation of the sternothyroid muscle.
Attachments: It arises from the thyroid cartilage of the larynx, and ascends to attach to the hyoid bone.
Actions: It depresses the hyoid. However, if the hyoid is fixed, it can raise the larynx.
Innervation: Anterior ramus of C1, carried within the hypoglossal nerve.
Ansa Cervicalis
The ansa cervicalis (or ansa hypoglossi in older literature) is a loop of nerves that are part of the cervical plexus. It lies superficial to the internal jugular vein in the carotid triangle. Its name means “handle of the neck” in Latin.
Branches from the ansa cervicalis innervate most of the infrahyoid muscles, including the sternothyroid muscle, sternohyoid muscle, and the omohyoid muscle. Note that the thyrohyoid muscle, which is also an infrahyoid muscle, is innervated by cervical spinal nerve 1 via the hypoglossal nerve. In addition, the ansa cervicalis does not innervate the stylohyoid muscle, which is innervated by the facial nerve.
Suprahyoid Muscles
There are four suprahyoid muscles. As the name suggests, all the muscles are locatedsuperiorly to the hyoid bone of the neck. In addition, they all act to elevate the hyoid bone, an action that initiates swallowing.
All the muscles are paired structures, appearing in the left and right sides of the neck.
Digastric
This muscle is comprised of two muscular bellies, connected by a tendon. In some cadavers this tendon can perforate the stylohyoid.
Attachments: The anterior belly arises from the digastric fossa of the mandible. The posterior belly arises from the mastoid process of the temporal bone. The two bellies are connected by an intermediate tendon, which is attached to the hyoid bone via a fibrous sling.
Actions: Depresses the mandible and elevates the hyoid bone.
Innervation: The two parts of the digastric muscles have different innervations. The anterior belly is innervated by the trigeminal nerve, the posterior by the facial nerve.
Thoracic Cage Muscles
There are five muscles that make up the thoracic cage; the intercostals (external, internal and innermost), subcostals, and transversus thoracis. These muscles act to change the volume of the thoracic cavity during respiration.
There are some other muscles that do not comprise the thoracic wall, but do attach to it. These include the pectoralis major, minor, serratus anterior and the scalene muscles.
Transversus Thoracis
These muscles originate from the lower part of the manubrium and xiphoid process, attaching to the costal cartilages of ribs 2-6. They are continuous with the transversus abdominus inferiorly.
They are innervated by the intercostal nerves and act to pull the ribs downwards, providing a weak expiratory function
Levator Ani Muscles
Innervated by branches of the pudendal nerve, roots S2, S3 and S4.
The levator ani is a broad sheet of muscle. It is composed of three separate paired muscles, called the pubococcygeus, puborectalis and iliococcygeus.
These muscles have attachments to the pelvis as follows:
Anterior – The pubic bodies of the hip bone.
Laterally – Thickened fascia of the obturator internus muscle, known as the tendinous arch.
Posteriorly – The ischial spines of the hip bone.
Coccygeus
Innervated by the anterior rami of S4 and S5.
The coccygeus is the smaller, and most posterior, pelvic floor component. The levator ani muscles situated anteriorly. It originates from the ischial spines and travels to the lateral aspect of the sacrum and coccyx, along the sacrospinous ligament.
AnteroLateral Abdominal Wall
The layers of the abdominal wall consist of (external to internal):
Skin.
Superficial fascia (or subcutaneous tissue).
Muscles and associated fascia.
Parietal peritoneum.
Vertical Abdominal Muscles
- rectus abdominis
- pyramidalis
Posterior Abdominal Muscles
There are five muscles in the posterior abdominal wall: the iliacus, psoas major, psoas minor, quadratus lumborum and the diaphragm.
Quadratus Lumborum
The quadratus lumborum muscle is located laterally in the posterior abdominal wall. It is a thick muscular sheet which is quadrilateral in shape. The muscle is positioned superficially to the psoas major.
Attachments: It originates from the iliac crest and liolumbar ligament. The fibres travel superomedially, inserting onto the transverse processes of L1 – L4 and the inferior border of the 12th rib.
Actions: Extension and lateral flexion of the vertebral column, It also fixes the 12th rib during inspiration, so that the contraction of diaphragm is not wasted.
Innervation: Anterior rami of T12- L4 nerves.
Extrinisic Tongue Muscles
Stylo– is anything from the styloid process, a thin extension of the bottom of the cranium, just near where the jawbone joins.
Genio– indicates a position just behind and under the front teeth in the lower jaw (mandible).
Hyo– indicates the hyoid bone, a semi-circular bone located on top of the voice box.
Glosso– indicates an insertion into the tongue, and palato- indicates the soft palate.
Two longitudinal muscles are present –geniohyoideus to form the base of the tongue, and styloglossus to draw the tongue back in the mouth. Vertical movement is controlled from the hyoglossus posteriorly, and genioglossus anteriorly. Palatoglossus is a little unusual – it extends from the soft palate, around the edge of the mouth, and into the tongue. It is involved in controlling swallowing.
Masseter
The masseter muscle is the most powerful muscle of mastication. It is quadrangular in shape, and can be split into two parts; deep and superficial.
The entirety of the muscle lies superficially to the pterygoids and temporalis, covering them.
Attachments: The superficial part originates from maxillary process of the zygomatic bone. The deep part originates from the zygomatic arch of thetemporal bone. Both parts attach to the ramus of the mandible.
Actions: Elevates the mandible, closing the mouth.
Innervation: Mandibular nerve (V3).
Temporalis
The temporalis muscle originates from the temporal fossa – a shallow depression on the lateral aspect of the skull. The muscle is covered by tough fascia, this can harvested surgically, and used to repair a perforated tympanic membrane (an operation known as a myringoplasty).
Attachments: Originates from the temporal fossa. It condenses into a tendon, which inserts onto the coronoid process of the mandible.
Actions: Elevates the mandible, closing the mouth. Also retracts the mandible, pulling the jaw posteriorly.
Innervation: Mandibular nerve (V3).
Lateral Pterygoid
The lateral pterygoid muscle has a triangular shape, with two heads; superior and inferior. It has horizontally orientated muscle fibres, and thus is the major protractor of the mandible.
- *Attachments**: The superior head originates from the greater wing of the sphenoid. The inferior head originates from the lateral pterygoid plate of the sphenoid. The two heads converge into a tendon, which attaches to the neck of the mandible.
- *Actions**: Acting bilaterally, the lateral pterygoids protract the mandible, pushing the jaw forwards. Unilateral action produces the ‘side to side’ movement of the jaw.
- *Innervation**: Mandibular nerve (V3).
Orbital Group
The orbital group of facial muscles contains two muscles associated with the eye socket. These muscles control the movements of the eyelids, important in protecting the cornea from damage. They are both innervated by the facial nerve.
Oral Group
These are the most important group of the facial expressors – the are responsible for movements of the mouth and lips. Such movements are required in singing and whistling, and add emphasis to vocal communication. The oral group of muscles consists of the orbicularis oris, buccinator, and various smaller muscles.
Levator Palpebrae Superioris
The levator palpebrae superioris (LPS) is the only muscle involved in raising the superior eyelid. A small portion of this muscle contains a collection of smooth muscle fibres – known as the superior tarsal muscle. In contrast to the LPS, the superior tarsal muscle is innervated by the sympathetic nervous system.
Attachments: Originates from the lesser wing of the sphenoid bone, immediately above the optic foramen. It attaches to the superior tarsal plate of the upper eyelid (a thick plate of connective tissue).
Actions: Elevates the upper eyelid.
Innervation: The levator palpebrae superioris is innervated by the oculomotor nerve (CN III). The superior tarsal muscle (located within the LPS) is innervated by the sympathetic nervous system.
Lateral Rectus
- *Attachments**: Originates from the lateral part of the common tendinous ring, and attaches to the anterio-lateral aspect of the sclera.
- *Actions**: Abducts the eyeball.
- *Innervation**: Abducens nerve (CN VI).
Pathways through the Diaphragm
The diaphragm divides the thoracic and abdominal cavities. Thus, any vessels that pass between the two cavities will pierce the diaphragm. There are three openings that act as conduit for these structures:
Oesophagal opening (T10 level): Transmits the oesophagus, vagus nerves, and oesophageal branches of the left gastric vessels.
Aortic opening (T12 level): Transmits the aorta, thoracic duct (a large lymphatic vessel) and azygous vein.
Caval opening (T8 level): Transmits the inferior vena cava.
Pectoralis Major
This a large, fan shaped muscle, and is the most superficial muscle in the pectoral region. It also makes up most of the anterior wall of the axilla
The muscle has two heads – a clavicular head (attaches to the clavicle), and a sternocostal head (attaches to the sternum and ribs). Fibres from both heads attach to the edge of the intertubecular groove of the humerus.
The two heads can work independently or synergistically. Together, they act to adduct and medially rotate the humerus at the shoulder. The clavicular head also performsflexion.
The pectoralis major is innervated by the medial and lateral pectoral nerves, which are derived from the brachial plexus.
Pectoralis Minor
The pectoralis minor muscle is much smaller than the pectoralis major, and lies posterior (underneath) to it. With the pectoralis major, it forms part of the anterior wall of the axilla.
The muscle has a triangular shape, originating from the anterior surfaces of ribs 3 – 5. The fibres then converge to attach to the corocoid process of the scapula. Attaching to the scapula forms a ‘bridge’, which vessels passing into the upper limb must travel underneath
Contraction of the pectoralis minor depresses the shoulder(an inferior motion), and it is innervated by the medial pectoral nerve.
Serratus Anterior
The serratus anterior is found more laterally in the chest and, forms the medial wall of the axilla.
The muscle consists of several strips, which originate from ribs 2-8. They attach to the costal (rib facing) surface of the medial border of the scapula.
The main action of the serratus anterior is to rotate the scapula, allowing the arm to be raised over 90 degrees. It also holds the scapula against the ribcage – this is particularly useful when upper limb reaches anteriorly (e.g punching).
It is innervated by the long thoracic nerve
Deltoid
The deltoid muscle is shaped like the Greek letter delta – Δ. It can be divided into a anterior, middle and posterior part.
Attachments: Originates from the scapula and clavicle, and attaches to the deltoid tuberosity on the lateral surface of the humerus.
Innervation: Axillary nerve.
Actions: The anterior fibres flex the arm at the shoulder, the posterior fibres extend the arm at the shoulder. The middle fibres are the major abductor of the arm – it takes over from the supraspinatus, which abducts the first 15 degrees.
Rotator Cuff Muscles
The rotator cuff muscles are a group of four muscles that originate from the scapula and attach to the humeral head. Collectively, the resting tone of these muscles acts to ‘pull’ the humeral head into the glenoid fossa. This gives the glenohumeral joint a lot of additional stability.
In addition to their collective function, the rotator cuff muscles also have their own individual actions.
Biceps Brachii
The biceps is a two headed muscle. Although nearly all of the muscle mass is locatedanterior to the humerus, it has no attachment to the humerus.
The long head originates from the supraglenoid tubercle of the scapula
The short head originates from the coracoid process of the scapula.
The tendon of the long head passes through the shoulder joint and intertubecular groove of the humerus to meet the short head. At the level of the humeral shaft, the two heads combine to form the muscle belly. Distally, the biceps attaches to the radial tuberosity.
The main action of the biceps brachii is supination of the forearm. It also flexes the arm at the elbow and at the shoulder.
Innervation is from the musculocutaneous nerve (C5,C6, mainly C6). A tap on the biceps tendon tests spinal cord segment C6.
As the tendon enters the forearm, a connective tissue sheet is given off, called the bicipital aponeurosis. This forms the roof of the cubital fossa and blends with the deep fascia of the anterior forearm.
Coracobrachialis
The coracobrachialis muscle lies deep to the biceps brachii in the arm.
It originates from the coracoid process of the scapula. The muscle passes through the axilla, and attaches the medial side of the humeral shaft, at the level of the deltoid tubercle.
The coracobrachialis is a flexor of the arm at the shoulder, and is innervated by themusculocutaneous nerve (C5,C6,C7, mainly C6).
Brachialis
The brachialis muscle lies deep to the biceps brachii, and is found more distally than the other muscles of the arm. It forms the base of the cubital fossa.
It originates from the medial and lateral surfaces of the humeral shaft, and inserts into the tuberosity of ulna just distal to the elbow joint.
The brachialis muscle is the main flexor at the elbow. Nervous supply is by the musculocutaneous nerve (C5,C6, mainly C6), although a small lateral portion is innervated by the radial nerve.
Posterior Compartment of Arm
Triceps Brachii
This is a muscle with three heads, and the only muscle in the posterior compartment. The medial head of the triceps lies deeper than the other two, which cover it. The medial head is therefore not visible unless the other two heads are dissected away.
The three heads:
Long head – Originates from the infraglenoid tubercle
Lateral head – Originates from the humerus, superior to the radial grove
Medial head – Originates from the humerus, inferior to the radial groove
The three heads combine to make one muscle, they converge to a tendon, which then attach to the olecranon of the ulna.
The triceps brachii performs extension of the arm at the elbow. It is innervated by the radial nerve (C6, C7, C8, mainly C7). A tap on the triceps tendon tests spinal segment C7.
Superfical Compartment of Anterior Forearm
The superficial muscles in the anterior compartment are the flexor carpi ulnaris, palmaris longus, flexor carpi radialis and pronator teres. They all originate from a common tendon, which arises from the medial epicondyle of the humerus.
