Efferent Innervation of Skeletal Muscle

The efferent innervation of skeletal muscle is carried out by a lower motor neuron, its efferent nerve endings, and the motor end plate, which is the site of the neuromuscular junction. Individual lower motor neurons in the spinal cord supply a number of muscle fibers, widely distributed throughout a muscle, with axon terminal nerve endings. The transmission of efferent nerve impulses is done through the motor end plate at the neuromuscular junction.

In certain skeletal muscle, as few as three to five muscle fibers are supplied by each neuron. The regulation of contraction of such muscles, such as the extrinsic ocular muscles responsible for the delicate eye movement, is correspondingly precise. When efferent impulses stimulate skeletal muscle fibers to contract, these fibers always shorten to their fullest extent. Graded contractions of skeletal muscles depend on the number of muscle fibers stimulated to contract, and not on partial contraction of individual fibers.

The motor unit is the key to the efferent innervation of skeletal muscle. It consists of a lower motor neuron, the motor end plate, and skeletal muscle fibers that are innervated. Efferent impulses from the neuron cause all the muscle fibers to contract fully. When there are no impulses coming from the neuron, none of the fibers contracts at all. Therefore, the strength of a skeletal muscle contraction is the function of a number of motor units participating in the efferent innervation.

Below, schematic image of efferent innervation of skeletal muscle. You can see that upper motor neurons can also take part in such action in a more complex way. Upper motor neurons are located in the primary motor gyrus, or pre-central gyrus, in the frontal lobe of brain.

Muscles of Thenar Eminence

The muscles of thenar eminence are a group of four short muscles located on the lateral aspect of palm of human hand, at the base of the thumb (radial side of palm). They are four in number and they are innervated by the median (C6-C7) and ulnar (C8-T1) nerve. Their source of blood supply are the palmar branch of radial artery. Remember: the muscles of thumb are eight in number as four of them are located in forearm, while the other four lies at the base of thumb (thenar) but all of them move the short digit of hand.

1) Oppenens pollicis muscle.- Triangular in shape, it arises from the crest of the trapezium bone and the flexor retinaculum, and it is inserted into the first metacarpal bone. Action: it opposes the thumb in relation to the fingers, especially the little and ring finger.

2) Flexor pollicis brevis.- It is a superficial muscle which lies medially beside the abductor pollicis brevis. It arises from the flexor retinaculum, the trapezium and trapezoid bones. It is inserted into the base of proximal phalanx of thumb. Action: it flexes the proximal phalanx of thumb.

3) Adductor pollicis muscle.- Lying deep in the palm of hand, it emerges from the radiate carpal ligament, the capitate bone, and the third metacarpal bone. It is inserted into the base of proximal phalanx of thumb. Action: it adducts the thumb (it pulls it medially), assisting in flexing the proximal phalanx.

4) Abductor pollicis brevis.- It lies superficially, arising from the tendon of the abductor pollicis longus muscle and tubercle of trapezium. It is inserted into the lateral side of proximal phalanx of thumb. Action: it abducts thumb (it draws it away from the medial plane) and holds it in mild position.

Below, view of palm of right hand, showing the muscles of thenar eminence. Notice that the abductor pollicis muscle was cut off to expose the opponens pollicis.

Flexor Digitorum Sublimis

The flexor digitorum sublimis is one of the nineteen muscles of the forearm, and it belongs to the second layer of muscles. It lies under the palmaris longus and the flexor carpi radialis muscle, which leave grooves on it. It flexes the second phalanges of the four fingers of the hand.

The flexor digitorum sublimis muscle originates by two heads; the humero-ulnar head, which is long and narrow, arises from the medial epicondyle of the humerus and the coronoid process of ulna; while the radial head, which is wide and short, arises from the proximal palmar surface of radius. Then the two heads join to form a common belly which runs downwards, dividing into four long tendons. These tendons travel over to the hand, running through the carpal tunnel to be inserted into the bases of the middle phalanges of the fingers. At the level of the proximal phalanges, each tendon splits into two and, therefore, has two points of insertion at the base of the middle phalanges.

Action

The flexor digitorum sublimis flexes (bends) the middle phalanx of the index, middle, ring, and little finger.

Innervation

The flexor digitorum sublimis is innervated by the median nerve (C6-C7-T1), which arises from the brachial plexus.

Blood Supply

This long muscle is supplied by collateral branches of the radial and ulnar artery.

Below, image of muscles on palmar (anterior) aspect of forearm. You can see that the flexor digitorum sublimis is partially covered by the flexor carpi radialis and the palmaris longus muscle.

Opponens Pollicis

The opponens pollicis is a short muscle of the ball of thumb, on the radial side of palm. It is shaped like a thin triangular sheet, which lies under the abductor pollicis brevis muscle. It arises from the crest of the trapezium (carpal bone) and from the anterior annular ligament. Then it runs downwards and laterally to be inserted into the whole length of the radial border of the first metacarpal bone (of thumb).

Action

The opponens pollicis pulls the first metacarpal bone inwardly towards the center of palm, opposing the other four fingers.

Innervation

This small muscle is innervated by the median nerve, which emerges from C6 and C7 of brachial plexus.

Blood Supply

It is supplied by a palmar branch of radial artery, which forms the deep palmar arch.

Below, image of palm of right hand, showing the opponens pollicis muscle. The abductor pollicis brevis has been cut away to expose it.

Muscles of Thumb

The muscles of thumb are those which control the movement of this short digit of the human hand, such as flexing, adduction, and abduction. Some of them are located in the forearm, and some at the base of the thumb (thenar muscles) on palm of hand. Thus, some are long and powerful, and others are short.

The muscles of thumb are eight in number. There are three flexors, one adductor, two abductors, and two extensors. They are voluntarily controlled with precision by a large area in the precentral central gyrus (motor strip) of the brain frontal lobe. The great precision and strength of these muscles are the result of the human brain cortex evolution. Thus, the muscles that move the thumb are:

1) Flexor pollicis longus.- It flexes the thumb when you close it tightly, drawing it towards the palm of hand. It is supplied by a branch of the median nerve;

2) flexor pollicis brevis.- It also flexes the thumb to close it, pulling it inwardly towards the center of hand; it usually works together with the one mentioned above and the flexors of the four fingers when you grasp something. The first one is innervated by the anterior interosseous nerve, which is a branch of the median nerve, while the flexor pollicis brevis is supplied by a branch of the ulnar nerve;

3) oppenens pollicis muscle.- It arises from the crest of the trapezium bone and the flexor retinaculum, and it is inserted into the first metacarpal bone. It pulls the ball of thumb towards the center of palm. Hence, it is considered a flexor.

4) adductor pollicis.- It is a short broad muscle that adducts the thumb, drawing it sideways and inwardly towards the hand and base of the forefinger. It originates from by two heads from the capitate bone of wrist (the largest carpal bone) and the base of second metacarpal bone (of forefinger) and it is attached to the medial side of proximal phalanx of thumb. It is supplied by a deep branch of the ulnar nerve;

5) abductor pollicis brevis.- It opens up the thumb, pulling it away from the forefinger. It is innervated by a recurrent branch of the median nerve.

6) abductor pollicis longus.- This muscle works together with the brevis to open up the thumb, but it is innervated by a branch of the radial nerve.

7) extensor pollicis brevis.- It extends and abducts the thumb, pulling it away and backwards. It arises from dorsal aspect of distal radius and is inserted in the posterior side of base of thumb proximal phalanx. It is innervated by a branch of the posterior interosseous nerve.

8) extensor pollicis longus.- It extends the distal phalanx of thumb and is supplied also by a branch of the posterior interosseous nerve, which arises from the radial.

Below, view of right hand showing five muscles of thumbs.

Muscles of Tongue

Not only do the muscles of tongue play an important role in deglutition and tasting the food we eat but also in language production, since we use it to pronounce the letters of the alphabet. There are two types of muscles of tongue; extrinsic and intrinsic ones.

The extrinsic muscles are those located at the base of the tongue and they make it possible for us to swallow the food we eat; this is called deglutition. They are anchored to the hyoid bone, the mandible, and the styloid process and they are innervated by the hypoglossal nerve (CNXII) and receive oxygen-rich blood from the lingual artery, which originates from the external carotid artery. On the other hand, the intrinsic muscles constitute the body of the tongue and are involved in speech, whose center is located in the Broca’s area of the brain frontal lobe. They are also innervated by the hypoglossal nerve and supplied by branches of the lingual artery.

Extrinsic muscles

1) Genioglossus: it arises from the symphysis of mandible. Then it fans out as it runs up to insert at the base of tongue and at the hyoid bone. It depresses and protrudes the tongue.

2) Hyoglossus: it originates from the hyoid bone and goes up to insert between the intrinsic muscles of tongue. It draws back and down the tongue.

3) Stylohyoid: it emerges from the styloid process and is inserted into the sides of tongue. It pulls back this organ.

4) Chondroglossus: it originates from lesser horn of hyoid bone, inserting into the hyoglossus fibers.

Intrinsic muscles

1) Superior longitudinal

2) Transverse

3) Vertical

4) Inferior longitudinal

Below, two images of the muscles of tongue; the first one showing the extrinsic and the other the intrinsic muscles.

Intrinsic Muscles of Tongue

The intrinsic muscles of tongue are those muscular structures which form and constitute this organ of speech. They are inherent to the tongue proper, giving it shape. In other words, they give it the very well-known elongated, muscular consistency that we know, playing a key role in the articulation of human speech, especially in the pronunciation of consonant letters. The intrinsic muscles of tongue are four. From top to bottom, they are:

1) the superior longitudinal muscle of tongue, which travels from base to tip along the top of the organ with long fibers. Function: it bends the tongue, curling its tip backwards;

2) the inferior longitudinal muscle of tongue, which is long and narrow, lying in the tongue lateral of genioglussus muscle.

3) the transverse muscle of tongue (transversus linguae), which is made up of separate transverse muscle fibers, originating from the septum of tongue. Function: it raises the lateral aspects of tongue, making it convex, like a trough;

4) the vertical muscle, which is made up of short fibers lying between the dorsum and the inferior surface, with its function being flattening the tongue.

Action

The superior longitudinal muscle retracts the tongue and curls up its tip, while the transverse curls up the sides of this organ. The inferior longitudinal collaborates with the superior longitudinal muscle to draw back the tongue, making it thick. The vertical muscle flattens this organ sideways.

Nerve supply

They are innervated by a branch of the glossopharyngeal nerve (CN IX), which transmits sensory information, and by the hypoglossal nerve (CN XII), which supplies with motor innervation.

Blood supply

The intrinsic muscles of tongue are supplied by the deep lingual artery, which branches off the lingual artery, and this, from the external carotid artery.

Down below, inferior view of human tongue, showing the extrinsic muscles and only two of the intrinsic muscles of tongue: the inferior longitudinal and the transverse muscle.

Transverse Muscle of Tongue

The transverse muscle of tongue is a one of the four intrinsic muscles which form and give shape to this organ. It lies transversely (across) the whole length of the tongue. It originates from the septum of the tongue, which extends lengthwise along the middle of this organ, from the root to its tip. Then these separate transverse muscle fibers run laterally to end up in the mucous membrane of the lateral border and dorsum of tongue.

Action

The transverse muscle reduces the transverse diameter of the tongue and makes it transversely convex.

Innervation

It is innervated by terminal branches of hypoglossal nerve (CN XII).

Blood Supply

The transverse muscle of tongue is supplied by collateral branches of the lingual artery.

Below, view of inferior aspect of the organ of speech. Extrinsic and intrinsic muscles can be seen, with the transverse muscle fibers running across the length of tongue.

Inferior Longitudinal Muscle of Tongue

The inferior longitudinal muscle of tongue is a paired intrinsic muscle of this organ of speech. It is long, narrow and cylindrical. It lies on each of the inferior lateral borders of the tongue proper, medially of the hyoglossus and styloglossus but laterally of the genioglossus muscle fibers.

The inferior longitudinal muscle arises from the mucous membrane of the root of tongue. Then it runs forward along the full length of this muscular organ to its tip, right under the transverse muscle.

Action: it shortens tongue and pulls its tip downwards.

Innervation

The inferior longitudinal muscle of tongue is innervated by terminal branches of the hypoglossal nerve (CN XII).

Blood Supply

It receives oxygenated blood from secondary branches of lingual artery.

Below, view of inferior side of human tongue, showing its extrinsic and intrinsic muscles. The inferior longitudinal is clearly labeled.

Superior Longitudinal Muscle of Tongue

The superior longitudinal muscle of tongue is one of the four intrinsic muscles which form this muscular organ of the oral cavity. It underlies the superficial mucous membrane and submucous fibrous layer of the tongue. It is made up of a thin layer of oblique and longitudinal muscular fibers. It is also known as superior lingualis in older text books.

Origin and Insertion

The superior longitudinal muscle of tongue arises from the lesser horns of the hyoid bone, by two lateral slips, and from the anterior surface of epiglottis by a medial slip. Then these three slips converge and pass immediately under the mucous membrane, running along the whole dorsum of the tongue to its tip, interlacing with one another.

The oblique muscular fibers, which constitute the superior longitudinal muscle, runs forward obliquely and laterally to the edges of the tongue. Meanwhile, its longitudinal fibers runs straight forwards to the tip of tongue. Both types of fibers insert themselves in between the extrinsic muscular fiber ends of the styloglossus, palatoglossus, hyoglossus, and chondroglossus muscles, which constitute the base of the tongue.

Innervation and Blood Supply

The superior longitudinal muscle of tongue is innervated by the hypoglossal nerve (CN XII) and is supplied by a branch of the lingual artery.

Action

This longitudinal lingual muscle raises the tip of tongue, curls it backwards, and shorten it, making it thicker. Thus, it is important when it comes to speech, because we use it when we pronounce some consonant letters.

Down below, the human tongue, showing the superior longitudinal muscle (superior lingualis). The surface of tongue (superficial mucous membrane and the submucous fibrous) layer have been removed to expose it.

Extrinsic Muscles of Tongue

The extrinsic muscles of tongue make up the muscular base of this organ. Some anatomists also refer to them as the skeletal muscles of tongue, since they are attached to bone. They are four muscles as two of them take part in deglutition (process of swallowing food). They are innervated by the hypoglossal nerve (CN XII) and supplied by the deep lingual and sublingual arteries, which are branches of the lingual artery.

1) Styloglossus muscle– It originates from the styloid process of temporal bone and the stylohyoid ligament, traveling obliquely downwards and forwards, joining the lateral aspect of the root of tongue. Function: it pulls the tongue backwards and upwards.

2) Hyoglossus muscle– It is square in shape, rising from the superior border of the body and the greater horn of the hyoid bone, with its fibers running upwards to insert to the side of the tongue, between the styloglossus and inferior longitudinal muscle. Action: it pulls the tongue backwards and downwards.

3) Genioglossus muscle– Lying on both sides of septum of tongue, it arises from spina mentalis of mandible and then runs up as it fans out to insert into the lingual fascia and the mucous membrane of tongue. Its posterior fibers insert into the body of the hyoid bone. It pulls the tongue forwards and downwards.

4) Chondroglossus muscle– It originates from the lesser horn of the hyoid bone and runs upwards, together and confused with the hyoglossus fibers. It is inserted into the dorsum of tongue.

Below, schematic picture of extrinsic muscles of human tongue. The chondroglossus cannot be seen because it runs between the muscular fibers of the hyoglossus muscle.

Chondroglossus Muscle

The chondroglossus muscle is one of the four extrinsic muscles of human tongue. It arises from the lesser horn of the hyoid bone by a small muscular slip. Then its fibers travel up obliquely and anteriorly between the muscular fibers of the hyoglossus as they get mixed up. It is inserted into the dorsum of the tongue, interlacing with the fibers of the superior longitudinal muscle of tongue.

Action

The chondroglossus pulls the tongue downwards and backwards, working together with the hyoglossus.

Innervation and Blood Supply

It is innervated by the hypoglossus nerve (CN XII) and it receives oxygenated blood from small collateral branches of the lingual artery.

Below, right side of human face, exhibiting the extrinsic muscle of tongue. To expose the chondroglossus, the hyoglossus has been cut off.

Genioglossus Muscle

The genioglossus muscle is located at the base of the tongue on both side of its septum. Triangular in shape, it is one of the extrinsic muscles of this organ. It originates from the mental spine of the mandible (called symphysis), fanning out as it extends backwards to insert into the lingual fascia and the hyoid bone.

Action

The genioglossus protrudes (sticks out) and depresses the tongue, pulling it forwards and backwards. Not only does it contribute in the motor articulation of this organ to produce speech, but it is also one of the muscles involved in deglutition (swallowing) of food, a vital reflex action whose center is located in the medulla oblongata.

Innervation and Blood Supply

The genioglossus muscle is innervated by the hypoglossal nerve and is supplied by collateral branches of the lingual artery, which arises from the external carotid artery.

Below, right side of the human face, showing the genioglossus and other extrinsic muscles of the tongue.

Hyoglossus Muscle

The hyoglossus muscle is a paired extrinsic muscle of the human tongue. Flat and rectangular in shape, it is located laterally of the genioglossus, at the base and under this organ of speech.

The hyoglossus originates from the superior border of the body and the greater horn of the hyoid bone. Then its fibers travel upwards and anteriorly towards the lateral margins of the root and body of the tongue, where they run between the styloglossus and  inferior longitudinal muscle, some reaching the tip of the tongue.

Action

The hyoglossus muscle pulls the tongue backwards and downwards, especially when we swallow our food.

Innervation and Blood Supply

It is innervated by the hypoglossal nerve (XII CN) and it receives oxygenated blood from the suprahyoid artery (a branch of the lingual a.) and secondary branches of facial artery, both of which arise from the external carotid artery.

Below, two pictures of human tongue and face, showing the hyoglossus and other extrinsic muscles of this organ.

Styloglossus Muscle

The styloglossus muscle is one of the four extrinsic muscles of the human tongue. It arises from the styloid process and the stylohyoid ligament. Then it travels down obliquely and anteriorly, between the stylohyoid muscle and the pharynx. As it descends, it adjoins the lateral surface of root of tongue and the upper lateral surface of the hyoglossus muscle.

The thicker upper bundle of the styloglossus runs along the lateral margin of the tongue, all the way forward to its tip. Meanwhile, its thinner lower bundle penetrates the hyoglossus muscle and passes downward at the posterior part of tongue to interlace with the tendinous band of its contralateral muscle. This happens on both lateral sides of tongue, as it is a paired muscle.

Action/Function

The styloglossus muscle pulls the tongue backwards and upwards.

Innervation and blood supply 

It is innervated by the hypoglossal nerve and it is supplied with oxygen-rich blood by the sublingual artery, which is a small branch of the lingual.

Down below, illustrative image showing the location of styloglossus in relation to the other muscles of tongue.

Muscles Involved in Jumping

There are several muscles involved in jumping. They are among the largest, longest, and most powerful skeletal muscles of the human body. Also involved in sprinting, they are located in the pelvis, thigh, and leg regions. They are often used by soccer and basketball players when they leap or spring. According to their importance when performing this action, they are:

1) triceps surae, which is a muscle group made up of the gastrocnemius, which consists of two heads, and the soleus muscle, both sharing the same tendon: the Achilles tendon, that is inserted into the calcaneum bone. Action: plantar flexion, raising the body upwards when we stand on tiptoe, and off the ground at the moment of jumping. Innervation: tibial nerve (from sacral plexus);

2) quadriceps femoris, which is a group made up of four muscles (rectus femoris, vastus lateralis, vastus medialis and vastus intermedius); action: they prop up the full weight of the body when we flex the knee just before jumping high, extending the leg at the knee-joint at the moment of jumping. Innervation: femoral nerve (from lumbar plexus);

3) gluteus maximus, which arises from the back of pelvis (ilium) and is inserted in posterior side of proximal portion of femur; action: it extends the thigh, pulling the femur backwards when running and jumping. Innervation: inferior gluteal nerve (from sacral plexus);

4) posterior group of thigh muscles: semitendinosus, semimembranosus, and biceps femoris. Action: they extend the thigh at the hip-joint, flexing the leg at the knee-joint. Innervation: branches of the sciatic nerve (from L4-S3 of lumbo-sacral plexus).

Below, the triceps surae group: the gastrocnemius extending superficialis over the soleus.

 

Triceps Surae Muscle

The triceps surae muscle is located on the posterior side of leg, allowing us to walk on tiptoe and jump. Broad and powerful, it is composed of two well defined portions: the gastrocnemius and the soleus muscle, both being united into one by the Achilles tendon, which is inserted into the calcaneus (heel bone).

It is called ‘triceps’ because the former consists of two strong heads, which protrudes sideways in athletes, plus the latter, which lies underneath it. Lying on top of the soleus, both heads of the gastrocnemius originates from the distal end of femur, while the soleus arises from the upper portion of fibula and the shaft of tibia.

Action/function

The triceps surae is the muscle of athletes and ballet dancers as it accomplishes plantar flexion of the foot, pulling its tip downwards (when we are sitting) and raising the heel off the ground (when we are standing), allowing us to jump or walk in tiptoe.

Nerve Supply

It is innervated by the medial popliteal nerve (L4, L5; S1, S2), which originates from the sciatic.

Blood Supply

The triceps surae muscle receives oxygenated blood from the posterior tibial and peroneal artery.

Below, an schematic drawing the muscles of posterior aspect of leg, showing the gastrocnemius and the soleus muscle.

Gastrocnemius Muscle

The gastrocnemius is a strong muscle lying on the superficial and posterior aspect of leg. It consists of two heads, a medial and a lateral head. The medial head is stronger, arising from the popliteal surface of the femur. The lateral portion, on the other hand, originates from a point located right above the lateral condyle of the same bone. At their origins, both heads constitute the inferior border of the popliteal fossa.

The gastrocnemius muscle runs down along the posterior side of the leg, over the soleus. In the middle of leg, both heads unite into one muscle, which tapers into a strong, thick tendon in the lower third of the leg; it is the Achilles tendon, with which it shares with the soleus muscle. This sturdy tendon is inserted into the posterior surface of the calcaneus (heel bone).

Action/function

Along with the soleus, it performs two important functions: 1) it performs plantar flexion of the foot, pointing the toes downwards, raising the heel off the ground as when we walk on tiptoe; 2) it contributes to the biceps femoris muscle in the flexion of the leg backwards and upwards at the knee-joint.

Innervation

The gastrocnemius muscle is supplied by the tibial nerve, which is a branch of the sciatic nerve.

Blood Supply

It receives oxygen-rich blood from the posterior tibial and peroneal artery.

Below, image of posterior side of right leg, showing its superficial muscles: the gastrocnemius and the soleus, with the Achilles tendon, which joins them together at the heel.

Soleus Muscle

The soleus muscle is a flat skeletal muscle which is located on the posterior side of leg. It lies under the gastrocnemius and it can only be partially noticed at the medial and lateral aspect of leg.

The soleus muscle arises from the head and upper third of the shaft of fibula, and also from soleal line and the middle third of the shaft of tibia. Then this muscle stretches down towards the heel as it becomes narrower.

In the lower third portion of leg, the soleus muscle fuses together with the gastrocnemius, ending up in a powerful thick tendon; the Achilles’ tendon, which is inserted into the posterior surface of the calcaneus of tarsus (heel bone).

Action/function

The soleus muscle works in unison with the gastrocnemius, performing plantar flexion of the foot as they pull its tip downwards (like a ballet dancer). When one is standing, it raises the heel off the ground.

Innervation

This leg muscle is innervated by the tibial nerve (L4, L5; S1, S2), which arises from the sciatic.

Blood Supply

The soleus is supplied by branches of the posterior tibial and peroneal artery.

Below, an anatomical drawing which shows both the gastrocnemius and the soleus muscle beneath it.

Popliteal Fossa

The popliteal fossa (fossa poplitea, in Latin) is an anatomical region located on the posterior surface of the knee-joint region. It is rhomboid in shape. Superiorly and medially, it is bounded by the semimembranosus and semitendinosus muscle. Superiorly and laterally, it is limited by the biceps femoris muscle. Inferiorly, it is confined by both heads of the gastronemius muscle and the plantaris muscle. The floor of the fossa is constituted by the popliteal surface of the distal end of femur and the posterior surface of the knee-joint capsule.

The region of the popliteal fossa is crisscrossed by a network of arteries that supply the different muscles and bones of the distal portion of thigh and the leg. These are the branches of the popliteal artery, which in turn is the continuation of the femoral artery. It is innervated by the popliteal nerve as well as by the tibial and the common peroneal nerve, all of them being branches of the sciatic nerve.

Below, diagram showing the popliteal fossa region, with the different muscles, arteries and nerves.

Muscles of Thigh

The muscles of thigh are the longest and most powerful muscles of the human body. They consume a large amount of calories (glucose/fatty acid) when we run. Not only are the muscles of thigh long but some of them are also broad and spindle-shaped. The sartorius is the longest and narrowest, while the adductor magnum is the broadest, with the quadriceps femoris being the largest. They are innervated by branches of the femoral, the sciatic, the tibial, and the peroneal nerve and they are supplied by the femoral artery and its branches. Some of them arise from the different anatomical parts of pelvis, but others from the upper third portion of femur, inserting into the tibia.

Anatomically, they are classified into three groups: 1) anterior group; 2) medial group; 3) posterior group.

Anterior Group

The muscles of this group are located on the anterior aspect of thigh. It is formed by the sartorius, which is the longest muscle of the body and the most anterior of the thigh, arising from the anterior superior iliac crest and inserting into the tubercle of tibia (tibial tuberosity); and the quadriceps femoris, which is composed in turn of four muscular heads: the rectus femoris, which lies anteriorly; the vastus medialis, which is located towards the medial side of thigh; the vastus lateralis, lying towards the lateral aspect of upper limb; and the vastus intermedius, which also lies anteriorly but under the rectus femoris.

Medial Group

There are five muscles in this group as their function is the adduction of the thigh (pulling it inwardly as when we ride a horse); they all lie on the medial (inner) aspect of thigh. It is composed of the gracilis, which is long and flattened; adductor longus, which is also long but rather triangular in shape; the adductor brevis; adductor magnus, which is the broadest of them all; adductor minimus; and pectinius muscle, which is small, flat and rather square. These muscles originate from the pubic border of pelvis and insert into the middle line of femur, and into the tibia. They are innervated by branches of the femoral and obturator nerve and they are supplied by the femoral artery. 

Posterior Group 

Three long muscles make up this group. The biceps femoris, which is situated along the postero-lateral side of thigh; the semimembranosus, which lies along the medial border and posterior side of thigh; the semitendinosus, which is narrower than the other two muscles of the group, being situated along and over the semimembranosus. All three of them arise from the tuberosity of ischium (of pelvis) and are inserted into the superior portion of tibia. Action: they flex the leg and extend the thigh. They are innervated by the sciatic, tibial, and peroneal nerve. They are supplied by the medial circumflex, perforating, and the popliteal artery, which are branches of the femoral artery.

Below, anterior group of muscles of thigh. The sartorius and the quadriceps are visible in this picture of right thigh. The vastus intermedius cannot be seen as it is located under the rectus femoris. However, three muscles of the medial group can be observed (adductor longus, adductor magnus, and gracilis).

Below, medial group of muscles. View of medial aspect of right human thigh. The adductor brevis is not visible as it lies beneath the gracilis and the adductor longus.

Muscles of thigh. Posterior group: semitendinosus, semimembranosus, and biceps femoris. The adductor magnus and gracilis belong to the medial group.

Quadriceps Femoris

The quadriceps femoris is the strong extensor muscle which lies on the anterolateral aspect of thigh. It is made up of four smaller muscles; they are the rectus femoris, the vastus lateralis, the vastus medialis, and the vastus intermedius, forming a large dense mass covering the front and sides of the femur.

Each of the heads of these muscles arises independently, but as they reach the knee-joint the form one tendon. This means that the individual tendons of these four muscles that constitute the quadriceps fuse into a common tendon at the distal part of the thigh and inserts into the patella and the tibial tuberosity.

The rectus femoris occupies the anterior surface of thigh, arising from the anterior inferior iliac spine by a fine tendon. The vastus lateralis lies on the anterolateral aspect of thigh, originating from the greater trochanter and the lateral lip of linea aspera of femur. The vastus medialis is located on the anteromedial side of thigh, taking origin also from the lateral lip of linea aspera of femur. The vastus intermedius lies on the anterior side of thigh, beneath the rectus femoris muscle, arising from the anterior surface of femur.

Action

Contraction of all the heads of the quadriceps femoris muscle extends the leg at the knee-joint, while the rectus femoris alone flexes the hip-joint. All of them contract when we rise up from a sitting position, and when we run and do sit-ups in the gym.

Innervation

This group of four muscles is innervated by the femoral nerve (from L2, L3 and L4).

Blood Supply

The quadriceps femoris is supplied by the lateral circumflex femoral and the profunda femoris artery.

Below, a diagrammatic picture of right thigh, showing three of the four muscles that make up the quadriceps group. The vastus medialis cannot be seen because it lies underneath the rectus femoris muscle.

Posterior Group of Thigh Muscles

The posterior group of thigh muscles is sometimes referred to as the hamstring muscles. It is composed by three long powerful muscles, all of them arising from the ischial tuberosity of pelvis, stretching along the full length of femur. Their upper (proximal) portions are covered by the gluteus maximus. They are:

1- The semimembranosus muscle, which lies on the medial border of the posterior side of thigh. Origin: ischial tuberosity. Insertion: medial condyle of tibia and oblique posterior ligament of knee.

2- The semitendinosus muscle, which lies closer to the medial border, extending over the semimembranosus. Origin: ischial tuberosity. Insertion: tubercle of tibia.

3- The biceps femoris muscle, which extends vertically on the lateral border of posterior side of thigh. Long and flattish, it arises from the ischial tuberosity of pelvis ischium and get inserted into the proximal end of tibia.

Action/function

They extend the thigh at the hip-joint, flexing the leg at the knee, rotating medially and laterally.

Innervation

The posterior group of thigh muscles are innervated by the tibial (L4-L5-S1) and sciatic nerves (S1-S2).

Blood Supply

They receive oxygenated blood from branches of the medial circumflex femoral, perforating, and popliteal artery.

Below, the schematic picture of posterior aspect of right thigh, showing all three muscles of posterior group.

Biceps Femoris Muscle

The biceps femoris is a long muscle lying on the lateral border of posterior aspect of human thigh. Thus, it belongs to the posterior group of thigh muscles, together with the semitendinosus and semimembranosus muscle. It has two heads, a long and a short head, which fuse together to form a single common belly.

The long head of the biceps femoris muscle arises from the ischial tuberosity by a narrow, flat tendon. The short head originates from the lateral lip of linea aspera of the distal half of femur. Then the two heads get together to become a strong muscle belly, which stretches down along the posterior lateral border of thigh, parallel and next to the semitendinosus muscle. The distal portion of the biceps femoris becomes a long narrow tendon, which curves around the lateral epicondyle of femur to be inserted into the head of fibula.

However, some bands of its distal tendon runs almost horizontally to be inserted into the edge of superior articular surface of the tibia. The lower bursa of the biceps femoris muscle is lodged between its tendon and the lateral ligament of the knee.

Action/Function

It extends the thigh at the hip-joint. It also flexes the leg at the knee-joint, rotating it laterally.

Innervation

The long head of the biceps femoris in innervated by branches of the tibial and sciatic nerve (S1, S2). The short head receives branches from the common peroneal nerve (L4, L5, S1).

Blood Supply

It receives oxygenated blood from the medial circumflex femoral, perforating, and popliteal artery.

Above, a schematic picture of posterior side of right thigh, showing the biceps femoris muscle. You can observe that its proximal (upper) portion is covered by the gluteus maximus.

Semitendinosus Muscle

The semitendinosus muscle belongs to the posterior group of muscles of human thigh. It is long and narrow and stretches along the full length of femur, over the semimembranosus muscle. It lies closer to the medial (inner) border of the posterior aspect of thigh, next and parallel to the biceps femoris mucle. Its proximal end is covered by the gluteus maximus muscle.

The semitendinosus muscle arises from the tuberosity of ischium, traveling downwards along the length of thigh, partially covering the semimembranosus muscle. At its distal extremity, it ends up in a long tendon that curves around the medial femoral epicondyle as it runs down slightly beyond the knee-joint. Then the tendon stretches on to the anteromedial surface of tibia to be inserted into its tuberosity.

Action/Function

The semitendinosus muscle flexes the leg at the knee-joint and it also extends the thigh at the hip joint.

Blood supply

It is supplied by the perforating arteries, which are branches arising from the deep artery of thigh, also known as the deep femoral artery.

Innervation

It is innervated by branches springing from the tibial nerve (L4, L6, S1, S2)

Below, diagrammatic picture that shows the thigh posterior side muscles, which include the semitendinosus, semimembranosus, and biceps femoris muscle.

 The superficial aspect of posterior side of side. The semitendinosus muscle can be perceived as it stands out distintively under the skin in athletic humans, such as soccer and football players.

Semimembranosus Muscle

The semimembranosus muscle lies on the medial border of posterior side of the human thigh. Its lateral half is covered by the semitendinosus muscle, leaving a mark in the form of a wide longitudinal groove. With the medial margin of the muscle being free, it stretches along the full length of the femur. It is part of the posterior group of muscles of the thigh.

The semimembranosus muscle originates from the ischial tuberosity of pelvis by a flat, strong tendon. Then it travels downwards vertically along the length of thigh, partially covered by the semitendinosus. It ends up in a distal flat tendon which narrows gradually. This tendon winds around the medial epicondyle as it runs to the anteromedial surface of tibia where it becomes wider and divides into three bands; the first one is inserted into the medial condyle of tibia; the second band fuses with the fascia covering the popliteus muscle; and the third one is inserted into the oblique posterior ligament of knee. 

Function/action 

It extends thigh straight at the hip-joint. It also flexes and rotates leg medially. 

Nerve supply 

The semimembranosus  muscle is innervated by the tibial nerve, which is a major branch of the sciatic nerve. 

Blood supply 

It receives oxygen-rich blood from a branch from the deep femoral artery, which arises from the femoral, and the gluteal arteries, which spring from the internal iliac artery.

Below, posterior aspect of muscles of right thigh, showing the semimembranosus, semitendinosus, and biceps femoris muscle.

The semimembranosus muscle, with the semitendinosus cut away to expose the groove along its lateral half.

Middle Meningeal Artery

The middle meningeal artery arises from the superior side of first part of maxillary artery (mandibular portion), being its largest branch. Then it travels upwards and passes through the foramen spinosum into the cavity of the skull, where it divides into a frontal and a parietal branch. These two main branches extend across the external surface of dura mater in the arterial sulci of the cranial bones. They supply the sulci as well as the temporal, frontal, and parietal areas of dura mater.

Along its course, the middle meningeal artery gives off the following branches: 1) the accessory meningeal artery, which originates from the extracranial part of the middle meningeal to supply the pterygoid muscles, the pharyngotympanic tube, and the muscles of palate; 2) superior tympanic artery, which supplies the mucous membrane of tympanic cavity; 3) superficial petrosal branch, which arises above the foramen spinosum and then stretches laterally and to the back to supply bone tissue.

Below, a picture of the right side of face showing the maxillary and the middle meningeal artery.

Branches of Maxillary Artery

All the branches of maxillary artery carry about 50% of the blood supply to the face and ear. Arising from the external carotid artery, the maxillary has a rather long and tortuous course. For this reason, it can be divided into three portions for a better comprehension.

First Portion (mandibular part)

As soon as it springs from the external carotid, the maxillary gives off five branches, with the first four arising from its superior side; 1) the deep auricular artery, which runs upwards to supply the auricular capsule of the mandibular joint, the inferior wall of the external auditory meatus, and the tympanic membrane; 2) the anterior tympanic artery, which travels up and enters the tympanic cavity through the squamotympanic fissure to supply its mucous membrane; 3) the middle meningeal artery, which is its largest branch, running upwards through the foramen spinosum into the skull to supply a large part of the dura mater that covers the frontal part of the brain; 4) the inferior alveolar artery, which is the only one that originates from the inferior side of first portion of maxillary as it travels downwards through the mandibular foramen to supply the chin and lower teeth.

Second Portion (pterygoid part)

The second part of the maxillary gives off several branches which originate both from its superior and inferior side. 1) The posterior deep temporal artery, which arises from its superior aspect and runs upwards to supply the temporal muscle, periosteum, and bone of the temporal fossa; 2) The anterior deep temporal artery, which also originates from the superior side of maxillary and irrigates the temporal muscle 3) the pterygoid branches, originating within the pterygoid bone, with one branch traveling upwards and the other downwards in the oppossite direction, to supply the lateral and medial pterygoid muscle respectively; 4) the messeteric artery, which descends through the mandibular notch to provided the messeter muscle with oxygenated blood; 5) the buccal artery, which also descends to supply the buccinator muscle and the upper portion of cheek.

Third Portion (pterygopalatine part)

The third and final section of the maxillary artery is located in the pterygopalatine fossa. There, several smaller branches arise from it to provide the upper and medial part of face with oxygenated blood. 1) The posterior superior alveolar artery, which originates from its inferior side and travels downwards and obliquely to supply the superior premolar and molar teeth, gingiva (gum), and maxillary sinus; 2) the descending palatine artery, which first gives off the artery of the pterygoid canal, then it divides into the greater and lesser palatine artery that supply the soft and hard palate as well as the gum and bone of the lower and posterior part of maxilla; 3) the infraorbital artery, which travels down to supply the roots of the superior incisors and canine teeth; 4) the sphenopalatine artery, being the terminal branch of the maxillary that runs through the sphenopalatine foramen to supply the posterior part of nasal cavity and the septum.

Below, schematic picture showing the branches of maxillary artery.