Muscles Flashcards

Question

Extensor Digitorum Brevis

Answer 1

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

Answer 2

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.

Answer 3

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).

Answer 4

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.

Answer 5

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.

Answer 6

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.

Answer 7

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.

Answer 8

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.

Answer 9

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.

Answer 10

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.

Answer 11

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

Answer 12

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.

Answer 13

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.

Answer 14

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.

Answer 15

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.

Answer 16

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

Answer 17

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.

Answer 18

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.

Answer 19

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.

Answer 20

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.

Answer 21

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.

Answer 22

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.

Answer 23

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.

Answer 24

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.

Answer 25

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.

Answer 26

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.

Answer 27

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.

Answer 28

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.

Answer 29

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.

Answer 30

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.

Answer 31

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.

Answer 32

* *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.

Answer 33

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.

Answer 34

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

Answer 35

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.

Answer 36

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)

Answer 37

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).

Answer 38

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).

Answer 39

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).

Answer 40

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).

Answer 41

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.

Answer 42

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.

Answer 43

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.

Answer 44

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.

Answer 45

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).

Answer 46

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.

Answer 47

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.

Answer 48

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.

Answer 49

The tibialis anterior muscle is located alongside the lateral surface of the tibia. It is the strongest dorsiflexor of the foot. To test the power of the tibialis anterior, the patient can be asked to stand on their heels. **Attachments**: Originates from the lateral surface of the tibia, attaches to the medial cuneiform and the base of metatarsal I. **Actions**: Dorsiflexion and inversion of the foot. **Innervation**: Deep fibular nerve.

Answer 50

The extensor digitorum longus lies lateral and deep to the tibialis anterior. The tendons of the EDL can be palpated on the dorsal surface of the foot. * *Attachments**: Originates from the lateral condyle of the tibia and the medial surface of the fibula. The fibres converge into a tendon, which travels to the dorsal surface of the foot. The tendon splits into four, each inserting onto a toe. * *Actions**: Extension of the lateral four toes, and dorsiflexion of the foot. * *Innervation**: Deep fibular nerve.

Answer 51

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.

Answer 52

The fibularis tertius muscles arises from the most inferior part of the EDL. It is not present in all individuals, and is considered by some texts as a part of the extensor digitorum longus. * *Attachments**: Originates with the extensor digitorum longus from the medial surface of the fibula. The tendon descends with the EDL, until they reach the dorsal surface of the foot. The fibularis tertius tendon then diverges and attaches to metatarsal V. * *Actions**: Eversion and dorsiflexion of the foot. * *Innervation**: Deep fibular nerve.

Answer 53

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.

Answer 54

This is the longer and more superficial muscle of the two. **Attachments**: The tendon of the fibularis longus has a slightly odd anatomical course: The fibularis longus originates from the superior and lateral surface of the fibula and the lateral tibial condyle. The fibres converge into a tendon, which the descends into the foot, posterior to the lateral malleolus. The tendon then crosses under the foot, and attaches to the bones on the medial side, namely the medial cuneiform and base of metatarsal I. **Actions**: Eversion and plantarflexion of the foot. Also supports the lateral and tranverse arches of the foot. **Innervation**: Superficial fibular (peroneal) nerve, L4-S1.

Answer 55

The fibularis brevis muscles is deeper and shorter than the fibularis longus. ## Footnote **Attachments**: It originates from the inferior and lateral surface of the fibular shaft. The muscle belly forms a tendon, which descends with the fibularis longus tendon. It travels into the foot, posterior to the lateral malleolus, passing over the calcaneus and the cuboidal bones. The tendon of the fibularis brevis attaches to a tubercle on metatarsal V. **Actions**: Eversion of the foot. **Innervation**: Superficial fibular (peroneal) nerve, L4-S1.

Answer 56

The posterior compartment of the leg contains seven muscles, organised into two layers –superficial and deep. The two layers are separated by a band of fascia. The posterior leg is the largest of the three compartments. Collectively, the muscles in this area plantarflex and invert the foot. They are innervated by the tibial nerve, a terminal branch of the sciatic nerve.

Answer 57

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.

Answer 58

The gastrocnemius is the most superficial of all the muscles in the posterior leg. It has two heads – medial and lateral, which converge to form a single muscle belly. The muscle is comprise of mainly fast twitch muscle fibres, which produce forceful movements such as running and jumping. **Attachments**: The lateral head originates from the lateral femoral condyle, and medial from the medial condyle. The fibres converge, and form a single muscle belly. In the lower part of the leg, the muscle belly combines with the soleus to from the calcaneal tendon, with inserts onto the calcaneus (the heel bone). **Actions**: It plantarflexes at the ankle joint, and because it crosses the knee, it is a flexor there. **Innervation**: Tibial nerve.

Answer 59

The plantaris is a small muscle with a long tendon, which can be mistaken for a nerve as it descends down the leg. It is absent in 10% of people. * *Attachments**: Originates from the lateral supracondylar line of the femur. The muscle descends medially, condensing into a tendon that runs down the leg, between the gastrocnemius and soleus. The tendon blends with the calcaneal tendon. * *Actions**: It plantarflexes at the ankle joint, and because it crosses the knee, it is a flexor there. It is not a vital muscle for these movements. * *Innervation**: Tibial nerve.

Answer 60

The soleus is located deep to the gastrocnemius. It is large and flat, named soleus due to its resemblance of a sole – a flat fish. * *Attachments**: Originates from the soleal line of the tibia and proximal fibular area. The muscle narrows in the lower part of the leg, and joins the calcaneal tendon. * *Actions**: Plantarflexes the foot at the ankle joint. * *Innervation**: Tibial Nerve.

Answer 61

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.

Answer 62

The popliteus is located superiorly in the leg. It lies behind the knee joint, forming the base of the popliteal fossa. There is a bursa (fluid filled sac) that lies between the popliteal tendon and the posterior surface of the knee joint. It is called the popliteus bursa. **Attachments**: Originates from the posterior surface of the tibia, attaches to the lateral condyle of the femur. **Actions**: Laterally rotates the femur on the tibia – ‘unlocking’ the joint so that flexion at the knee joint can occur. **Innervation**: Tibial nerve.

Answer 63

The tibialis posterior is the deepest out of the four muscles. It lies between the flexor digitorum longus and the flexor hallucis longus. * *Attachments**: Originates from the interosseous membrane between the tibia and fibula, and posterior surfaces of the two bones. The tendon enters the foot posterior to the medial malleolus, and attaches to the plantar surfaces of the medial tarsal bones. * *Actions**: Inverts and plantarflexes the foot, maintains the medial arch of the foot. * *Innervation**: Tibial nerve.

Answer 64

The FDL is (surprisingly) a smaller muscle than the flexor hallucis longus. It is located medially in the posterior leg. * *Attachments**: Originates from the medial surface of the tibia, attaches to the plantar surfaces of the lateral four digits. * *Actions**: Flexes the lateral four toes. * *Innervation**: Tibial nerve.

Answer 65

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.

Answer 66

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).

Answer 67

Along with the omohyoid, the sternohyoid lies superficially in the neck. **Attachments**: The sternohyoid muscle originates from the sternum and sternoclavicular joint. It ascends to insert onto the hyoid bone. **Actions**: Depresses the hyoid bone. **Innervation**: Anterior rami of C1-C3, carried by a branch of the ansa cervicalis.

Answer 68

The muscle, like the suprahyoid digastric, is split into two bellies, connected by a muscular tendon. It is located slightly laterally to the sternohyoid. **Attachments**: The inferior belly of the omohyoid arises from the scapula. It runs superiomedially, moving underneath the sternocleidomastoid. Here, it is attached to the the superior belly by an intermediate tendon. This tendon is attached to the clavicle by the deep cervical fascia. The superior belly ascends to attach to the hyoid bone. **Actions**: Depresses the hyoid bone. **Innervation**: Anterior rami of C1-C3, carried by a branch of the ansa cervicalis.

Answer 69

This muscle is wider and deeper than the sternohyoid. **Attachments**: The sternothryoid runs from the manubrium of the sternum to the thyroid cartilage. **Actions**: Depresses the thyroid cartilage. **Innervation**: Anterior rami of C1-C3, carried by a branch of the ansa cervicalis.

Answer 70

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.

Answer 71

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.

Answer 72

1. rami colli of facial nerve 2. transversus colli

Answer 73

The nerve loop is assisted by an upper root ( Radix superior ) from the nerve fibers of the segments C1 and C2 and by a lower root (Radix inferior ) from C2 and C3 formed.

Answer 74

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.

Answer 75

The stylohyoid is a thin muscular strip, which is located superiorly to the digastric muscle. **Attachments**: Arises from the styloid process of the temporal bone, and attaches to the lateral side of the hyoid bone. **Actions**: Initiates a swallowing actions by pulling the hyoid bone in an posterior and superior direction. **Innervation**: Facial Nerve (VII).

Answer 76

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.

Answer 77

The mylohyoid muscle is a broad, triangular shaped muscle. It forms the floor of the oral cavity, thus supporting the floor of the mouth. **Attachments**: It originates from the mylohyoid line of the mandible, and attaches onto the hyoid bone. **Actions**: Elevates the floor of the mouth and the hyoid bone. **Innervation**: Trigeminal nerve.

Answer 78

Located deep to the mylohyoid muscle, the geniohyoid lies close to the midline of the neck. **Attachments**: Arises from the inferior mental spine of the mandible. It then travels inferiorly and posteriorly to attach to the hyoid bone. **Actions**: Depresses the mandible and elevates the hyoid bone. **Innervation**: By C1 roots that run within hypoglossal nerve.

Answer 79

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.

Answer 80

There are 11 pairs of external intercostal muscles. They run inferoanteriorly from the rib above to the rib below, and are continuous with the external oblique of the abdomen. They are innervated by the intercostal nerves, and act to increase the volume of the thoracic cage during forced inspiration.

Answer 81

These flat muscles lie deep to the external intercostals. Like the external intercostals, they run from the rib above to the one below, but in an opposite direction (inferoposteriorly). They are continuous with the internal oblique muscle of the abdominal wall. They are innervated by the intercostal nerve, and act to decrease the volume of the thoracic cage during forced expiration.

Answer 82

These muscles are the deepest of the intercostal muscles, and are similar in structure to the internal intercostals. They are separated from the internal intercostals by the intercostal neurovascular bundle and are found in the most lateral portion of the intercostal spaces. Their innervation and action is the same as the internal intercostals.

Answer 83

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

Answer 84

The subcostal muscles are found in the inferior portion of the thoracic wall. They comprise of thin slips of muscle, which run from the internal surface of one rib, to second and third ribs below. The direction of the fibres parallels that of the innermost intercostal.

Answer 85

There are three components of the pelvic floor: Levator ani muscles (largest component). Coccygeus muscle. Fascia coverings of the muscles.

Answer 86

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.

Answer 87

The puborectalis muscle is a U-shaped sling, extending from the bodies of the pubic bones, past the urogenital hiatus, around the anal canal. Its tonic contraction bends the canal anteriorly, creating the anorectal angle (90degrees) at the anorectal junction (where the rectum meets the anus). The main function of this thick muscle is to maintain faecal continence – during defecation this muscle relaxes.

Answer 88

The muscle fibres of the pubococcygeus are the main constituent of the levator ani. They arise from the body of the pubic bone and the anterior aspect of the tendinous arch. The fibres travel around the margin of the urogenital hiatus and run posteriomedially,attaching at the coccyx and anococcygeal ligament. As the fibres run inferiorly and medially, some fibres divide and loop around the prostate in males (levator prostatae) and around the vagina in females (pubovaginalis). Some also terminate in the perineal body.

Answer 89

The iliococcygeus has thin muscle fibres, which start anteriorly at the ischial spines and posterior aspect of the tendinous arch. They attach posteriorly to the coccyx and the anococcygeal ligament.

Answer 90

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.

Answer 91

The layers of the abdominal wall consist of (external to internal): Skin. Superficial fascia (or subcutaneous tissue). Muscles and associated fascia. Parietal peritoneum.

Answer 92

There are five muscles in the abdominal wall. They can be divided into two groups: Vertical muscles – There are two vertical muscles, situated near the mid-line of the body. Flat muscles – There are three flat muscles, situated laterally.

Answer 93

There are three flat muscles; the external oblique, internal oblique and transversus abdominis. They are located laterally in the abdominal wall, stacked upon one another. These muscles act to flex, laterally flex and rotate the trunk. Their fibres run in differing directions and cross each other – strengthening the abdominal wall and decreasing the risk of herniation.

Answer 94

The largest and most superficial flat muscle in the abdominal wall. Its fibres runinferomedially. As the fibres approach the mid-line, they form an aponeurosis (a broad flat tendon). In the mid-line, the aponeuroses of all the flat muscles become entwined, forming the linea alba. This is a fibrous structure that extends from the xiphoid process of the sternum to the pubic symphysis.

Answer 95

This muscle lies deep to the external oblique. It is smaller and thinner in structure, with its fibres running superiormedially (perpendicular to the fibres of the external oblique). Near the midline it forms aponeurotic fibres which contribute to the linea alba.

Answer 96

The deepest of the flat muscles, with transversely running fibres. Like the other flat muscles, it contributes aponeurotic fibres to the linea alba. Deep to this muscle is a well formed layer of fascia, called the transversalis fascia.

Answer 97

* rectus abdominis * pyramidalis

Answer 98

This is a long, paired muscle, found either side of the midline in the abdominal wall. It is split into two by the linea alba. The lateral border of the two muscles create a surface marking called the linea semilunaris. At several places, the muscle is intersected by fibrous strips, known as tendinous intersections. The tendinous intersections and the linea alba give rise to the ‘six pack’ seen in individuals with low body fat. As well as assisting the flat muscles in compressing the abdominal viscera, the rectus abdominus also stabilises the pelvis during walking, and depresses the ribs.

Answer 99

This is a small triangle shaped muscle, found superficially to the rectus abdominus. It is located inferiorly, with its base on the pubis bone, and the apex of the triangle attached to the linea alba. It acts to tense the linea alba.

Answer 100

The rectus sheath is formed by the aponeuroses of the three flat muscles, and encloses the rectus abdominus and pyramidalis muscles. It has an anterior and posterior wall for most of its length: The anterior wall is formed by the aponeuroses of the external oblique, and of half of the internal oblique. The posterior wall is formed by the aponeuroses of half the internal oblique and of the transversus abdominus. Approximately midway between the umbilicus and the pubic symphysis, all of the aponeuroses move to the anterior wall of the rectus sheath. At this point, there is no posterior wall to the sheath; the rectus abdominus is in direct contact with the transversalis fascia. The area of transition between having a posterior wall, and no posterior wall is known as thearcuate line.

Answer 101

There are five muscles in the posterior abdominal wall: the iliacus, psoas major, psoas minor, quadratus lumborum and the diaphragm.

Answer 102

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.

Answer 103

The psoas major is located near the midline of the posterior abdominal wall, immediately lateral to the lumbar vertebrae. **Attachments**: Originates from the transverse processes and vertebral bodies of T12 – L5. It then moves inferiorly and laterally, running deep to the inguinal ligament, and attaching to the lesser trochanter of the femur. **Actions**: Flexion of the thigh at the hip and lateral flexion of the vertebral column. **Innervation**: Anterior rami of L1 – L3 nerves.

Answer 104

The psoas minor muscle is only present in 60% of the population. It is located anterior to the psoas major. **Attachments**: Originates from the vertebral bodies of T12 and L1 and attaches to a ridge on the superior ramus of the pubic bone, known as the pectineal line. **Actions**: Flexion of the vertebral column. **Innervation**: Anterior rami of the L1 spinal nerve.

Answer 105

The iliacus muscle is a fan-shaped muscle that is situated inferiorly on the posterior abdominal wall. It combines with the psoas major to form the iliopsoas – the major flexor of the thigh. **Attachments**: Originates from surface of the iliac fossa and anterior inferior iliac spine. Its fibres combine with the tendon of the psoas major, inserting into the lesser trochanter of the femur. **Actions**: Flexion of the thigh at the hip joint. **Innervation**: Femoral nerve (L2 – L4).

Answer 106

The muscles of the tongue can be divided a couple of ways. You can divide them by where they attach (either internal to the tongue, or to external structures), or by the direction that the muscle fibres run: longitudinal (front to back), transverse (side to side), or vertical.

Answer 107

They only attach to other structures in the tongue. They are named by the direction in which they travel; superior longitudinal, inferior longitudinal, transverse and vertical.

Answer 108

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.

Answer 109

The muscles of mastication are a group of muscles associated with movements of the jaw (temporomandibular joint). They are one of the major muscle groups in the head – the other being the muscles of facial expression. There are four muscles of mastication – the masseter, temporalis, medial pterygoid and lateral pterygoid. Embryologically, the muscles of mastication develop from the first pharyngeal arch. Consequently they are innervated by a branch of the trigeminal nerve (CN V), the mandibular nerve.

Answer 110

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).

Answer 111

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).

Answer 112

The medial pterygoid muscle has a quadrangular shape, with two heads; deep and superficial. It is located inferiorly to the lateral pterygoid. * *Attachments**: The superficial head originates from the maxilla. The deep head originates from the lateral pterygoid plate of the sphenoid bone. Both parts attach to the ramus of the mandible, near the angle of mandible. * *Actions**: Elevates the mandible, closing the mouth * *Innervation**: Mandibular nerve (V3).

Answer 113

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).

Answer 114

The muscles of facial expression are located in the subcutaneous tissue, originating from bone or fascia, and inserting onto the skin. By contracting, the muscles pull on the skin and exert their effects. They are the only group of muscles that insert into skin. These muscles have a common embryonic origin – the 2nd pharyngeal arch. They migrate from the arch, taking their nerve supply with them. As such, all the muscles of facial expression are innervated by the facial nerve. The facial muscles can broadly be split into three groups; orbital, nasal and oral.

Answer 115

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.

Answer 116

This muscle surrounds the eye socket and extends into the eyelid. It can be functionally split into two parts; the outer orbital part and inner palpebral part. * *Actions**: The palpebral part of the muscle performs gentle closure of the eyelid, whereas the orbital portion closes more forcefully. * *Innervation**: Facial nerve.

Answer 117

The corrugator supercilii is a much smaller muscle, and is located posteriorly to the obicularis oculi muscle. * *Attachments**: It originates from the superciliary arch, running in an superolateral direction. It inserts into the skin of the eyebrow. * *Actions**: It acts to draw the eyebrows together, creating vertical wrinkles on the bridge of the nose. * *Innervation**: Facial nerve.

Answer 118

The nasal group of facial muscles are associated with movements of the nose, and the skin around it. There are three muscles in this group, and they are all innervated by the facial nerve. They serve little importance in humans.

Answer 119

The nasalis is the largest of the nasal muscles. It is split into two parts; transverse and alar. **Attachments**: Both portions of the muscle originate from the maxilla. The transverse part attaches to an aponeurosis across the dorsum of the nose. The alar portion of the muscle attaches to the alar cartilage of the nasal skeleton. **Actions**: The two parts have opposing functions. The transverse part compresses the nares, and the alar part opens the nares. **Innervation**: Facial nerve.

Answer 120

The procerus is the most superior of the nasal muscles. It also lies superficially to the other muscles of facial expression. * *Attachments**: It originates from the nasal bone, inserting into the lower medial forehead. * *Actions**: Contraction of this muscle pulls the eyebrows downward to produce transverse wrinkles over the nose. * *Innervation**: Facial nerve.

Answer 121

This muscle assists the alar part of the nasali in opening the nostrils. * *Attachments**: It runs from the maxilla (above the medial incisor tooth) to the nasal septum. * *Actions**: It pulls the nose inferiorly, opening the nares. * *Innervation**: Facial nerve.

Answer 122

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.

Answer 123

The fibres of the orbicularis oris enclose the opening to the oral cavity. **Attachments**: Arises from the maxilla and from the other muscles of the cheek. It inserts into the skin and mucous membranes of the lips. **Action**: Purses the lips. **Innervation**: Facial nerve.

Answer 124

This muscle is located between the mandible and maxilla, deep to the other muscles of the face. Attachments: It originates from the maxilla and mandible. The fibres run in an inferomedial medial direction, blending with the orbicularis oris and the skin of the lips. Actions: The buccinator pulls the cheek inwards against the teeth, preventing accumulation of food in that area. Innervation: Facial nerve.

Answer 125

There are other muscles that act of the lips and mouth. Anatomically, they can be divided into upper and lower groups: The lower group contains the depressor anguli oris, depressor labii inferioris and the mentalis. The upper group contains the risorius, zygomaticus major, zygomaticus minor, levator labii superioris, levator labii superioris alaeque nasi and levator anguli oris.

Answer 126

The extraocular muscles are located within the orbit, but are extrinsic and separate from the eyeball itself. They act to control the movements of the eyeball and the superior eyelid. There are seven extraocular muscles – the levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, lateral rectus, inferior oblique and superior oblique. Functionally, they can be divided into two groups: Responsible for eye movement: Recti and oblique muscles. Responsible for superior eyelid movement: Levator palpebrae superioris.

Answer 127

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.

Answer 128

There are four recti muscles; superior rectus, inferior rectus, medial rectus and lateral rectus. These muscles characteristically originate from the common tendinous ring. This is a ring of fibrous tissue, which surrounds the optic canal at the back of the orbit. From their origin, the muscles pass anteriorly to attach to the sclera of the eyeball. The name recti is derived from the latin for ‘straight’ – this represents the fact that the recti muscles have direct path from origin to attachment. This is in contrast with the oblique eye muscles, which have an angular approach to the eyeball.

Answer 129

* *Attachments**: Originates from the superior part of the common tendinous ring, and attaches to the superior and anterior aspect of the sclera. * *Actions**: Main movement is elevation. Also contributes to adduction and medial rotation of the eyeball. * *Innervation**: Oculomotor nerve (CN III).

Answer 130

* *Attachments**: Originates from the inferior part of the common tendinous ring, and attaches to the inferior and anterior aspect of the sclera. * *Actions**: Main movement is depression. Also contributes to adduction and medial rotation of the eyeball. * *Innervation**: Oculomotor nerve (CN III).

Answer 131

* *Attachments**: Originates from the medial part of the common tendinous ring, and attaches to the anterio-medial aspect of the sclera. * *Actions**: Adducts the eyeball. * *Innervation**: Oculomotor nerve (CN III).

Answer 132

* *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).

Answer 133

There are two oblique muscles – the superior and inferior obliques. Unlike the recti group of muscles, they do not originate from the common tendinous ring. From their origin, the oblique muscles take an angular approach to the eyeball (in contrast to the straight approach of the recti muscles). They attach to the posterior surface of the sclera.

Answer 134

* *Attachments**: Originates from the body of the sphenoid bone. Its tendon passes through a trochlear, and then attaches to the sclera of the eye, posterior to the superior rectus. * *Actions**: Depresses, abducts and medially rotates the eyeball. * *Innervation**: Trochlear nerve (CN IV).

Answer 135

* *Attachments**: Originates from the anterior aspect of the orbital floor. Attaches to the sclera of the eye, posterior to the lateral rectus * *Actions**: Elevates, abducts and laterally rotates the eyeball. * *Innervation**: Oculomotor nerve (CN III).

Answer 136

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.

Answer 137

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.

Answer 138

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.

Answer 139

The serratus anterior is found more laterally in the chest and, forms the medial wall of the axilla. ## Footnote 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

Answer 140

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.

Answer 141

The teres major forms the inferior border of the quadrangular space – the ‘gap’ that the axillary nerve and posterior circumflex humeral artery pass through to reach the posterior scapula region. Attachments: Originates from the posterior surface of the inferior angle of the scapula. It attaches to the intertubecular groove of the humerus. Innervation: Lower subscapular nerve. Actions: Adducts at the shoulder and medially rotates the arm.

Answer 142

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.

Answer 143

* *Attachments**: Originates from the supraspinous fossa of the scapula, attaches to the greater tuberosity of the humerus. * *Innervation**: Suprascapular nerve. * *Actions**: Abducts the arm 0-15o, and assists deltoid for 15-90o

Answer 144

* *Attachments**: Originates from the infraspinous fossa of the scapula, attaches to the greater tubercle of the humerus. * *Innervation**: Suprascapular nerve. * *Actions**: Laterally rotates the arm.

Answer 145

* *Attachments**: Originates from the subscapular fossa, on the costal surface of the scapula. It attaches to the lesser tubercle of the humerus. * *Innervation**: Upper and lower subscapular nerves. * *Actions**: Medially rotates the arm.

Answer 146

* *Attachments**: Originates from the posterior surface of the scapula, adjacent to its lateral border. It attaches to the greater tubercle of the humerus. * *Innervation**: Axillary nerve. * *Actions**: Laterally rotates the arm.

Answer 147

The three muscles in the anterior compartment of the arm are the biceps brachii, coracobrachialis and brachialis. They are all innervated by the musculocutaneous nerve. A good memory aid for this is BBC – biceps, brachialis, coracobrachialis.

Answer 148

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.

Answer 149

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).

Answer 150

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.

Answer 151

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.

Answer 152

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.

Muscles Flashcards

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