Snouted Cobra

The Snouted Cobra (Naja annulifera) is a large brown snake of the savanna of southeast Africa. Its glands produce venom with powerful neurotoxins, which cause death from respiratory failure. However, it is not as aggressive as other cobras. It is nocturnal, coming out at dusk to pray on rodents and other small animals.

Physical Characteristics

The Snouted Cobra is light brown in color, but it goes through a banded phase, in which it is black, with yellowish cream bands. A distinctive dark throat can be observed in juveniles. The scales are smooth, with 19 rows at mid body and the ventral side has 175 rows. The head is broad, and the eye pupils are round. It is characterized by having a row of scales between the eye and upper labials.

The female of the Naja annulifera lays 20 eggs in Summer. When it feels threatened, it spreads its broad hood and is always ready to bite. However, it does not spit, as other species do. It inhabits the dry and moist savanna of south and southeast Africa and the woodland, between sea level and the 1,600 m of altitude.

Below, the Snouted Cobra, in its banded phase.

The adult of the Naja annulifera, which is yellowish brown in color.

Cervical Plexus

The cervical plexus is a network of spinal nerve fibers that supply the region of the neck. It consists of fibers from the ventral rami of nerves from C1 to C5. Their branches innervate the skin of the neck and head, as well as the diaphragm and some muscles of neck. The cervical plexus gives off six important nerves:

1) the lesser occipital nerve, which supply the skin of lateral scalp;

2) the greater auricular nerve, which innervates the skin around the external ear;

3) the transverse cervical nerve (also called superficial cervical N.), supplying the skin of ventral and lateral neck;

4) the ansa cervicalis, which is a nerve loop that gives off branches to supply the omohyoid, sternohyoid, and the sternothyroid muscle;

5) the supraclavicular nerve, which innervates the skin of shoulder and central chest;

6) the phrenic nerve, which innervates the diaphragm. The origin of this nerve is found in grey nuclei located in the medulla oblongata and pons.

 

Elapidae

Elapidae, or elapids, is a taxonomical family of snakes, most of which are very dangerous for humans. They have immovable fangs located at the front of the upper jaw. Their bites are of medical significance as their glands produce powerful neurotoxic venom, which can cause death quickly if untreated.

Genera and Species

The family Elapidae include around 50 genera and 375 species, which are distributed world-wide in tropical regions. They comprise the mambas (Dendroaspis), which are found in Africa, the cobras, the King Cobra (Ophiophagus hannah), the coral snakes, the Australian brown snakes and taipans (Oxyuranus), sea snakes (Hydrophiinae), kraits (Bungarus), and African garter snakes. All African land elapids belong in turn to the sub-family Elapinae. The sub-family Hydrophiinae consist of the Yellow-bellied sea snake and the Australian terrestrial elapids.

Physical Characteristics

The great majority of elapids snakes have long, slender body. Their scales are smooth and usually smaller in size than those of the family Viperidae. They have round eye pupils and their heads are covered by very large scales or shields, being rather elongated and not triangular, as is the case with the viper snakes. Some of them have hood, which they spread out when they feel threatened. Many of them are burrowers, some live on grassy plains, such as the African savanna, others are arboreal. Their females are oviparous, meaning that they lay eggs. Most of them are diurnal (active during the day).

Below, a famous member of the family Elapidae; a cobra, one species from Africa in this case.

Body Tissue Repair

The body tissue repair begins right after the acute inflammatory reaction, which is the result of tissue damage. It is the replacement of dead cells by new viable ones. These new cells may originate from the damaged parenchyma (an organ inherent cellular structure) or from connective tissue in the damaged area.

But parenchymal regeneration is very slow, since the cells that work together to perform the organ main function are stable and it takes a long time for them to multiply, as is the case with hepatocytes, the cells that constitute the liver. When this organ is damaged by either a viral infection or alcohol, it is the organ connective tissue cells that does the repair as they multiply much faster than the parenchymal cells. However, body tissue repair through proliferation of connective tissue is not good, especially for organs such as the liver, lungs, and the heart.

Unfortunately, when the liver is repeatedly wounded by a chronic disease or alcoholism, the liver parenchymal cells (hepatocytes) do not have time to undertake the repair, naturally regenerating, and are overtaken by massive connective tissue cells proliferation; and overtime, the organ become fibrous and rigid, rendering the organ unable to perform its functions. Thus, fibrosis is due to connective tissue repair. Fibrosis in the liver is cirrhosis.

Black Mamba

The Black Mamba (Dendroaspis polylepis) is a long, slender snake which inhabits the different regions of sub-Saharan Africa. It is the most feared snake in that continent. According to recorded hospital statistics, there are an average of 2,500 Black Mamba's bites per year, with 30 deaths, in Africa.

It belongs to the Elapidae family of snakes, like the cobras. Thus, its glands secretes a potent neurotoxic venom. It can bite any part of the victim's body because it has the fangs located well forward on its upper jaw. It is diurnal and feeds mainly on rats and other rodents. It is usually found in the savannas and other grassy plains.

Physical Description

The Black Mamba is dark grey or olive in color, with the belly being creamy or pale green. The upper portion of the body is often speckled with black blotches, especially on the flanks. The adult can measure up to 3.50 m long, but the average length is 2.50 m. It has smooth scales, with 23-25 rows at mid body. Rows of ventral scales are between 239 and 281.

The head is elongated and 'coffin-shaped'. It has round pupils and a pronounced brow ridge. The inside of the mouth is dark bluish or black. Although it is not really black, it is called Black Mamba due to the black mouth lining. The female lays a clutch of 12-18 large eggs each year, with the hatchlings measuring between 45 and 60 cm in length.

Habitat and Distribution

The Dendroaspis polylepis is usually encountered in either the moist and dry savanna areas. However, it can also be found in the coastal bush and the woodland. Although it is usually found in the southern third portion of Africa, it is widespread in this continent. Since this species is widespread, its presence was also reported in the southern border of the Sahara desert. An experienced snake collector in Burkina Faso was bitten three times and killed by a Black Mamba; he had never encountered one before and did not think it was aggressive. This snake moves fast, very fast, and one has to be very careful.

Below, a photo of a Black Mamba taken in the woodland of South Africa.

Lateral Superior Genicular Artery

The lateral superior genicular artery is one of several blood vessels supplying the knee. It arises from the lateral side of popliteal artery. First, it extends laterally, running under the distal portion of the biceps femoris muscle. Then it travels anteriorly as it curves around and above the lateral condyle of the femur bone, hugging it.

When it has reached the frontal aspect of knee, the lateral superior genicular artery divides into several smaller branches, just above the patella. These smaller branches anastomose with other arterial branches to become part of the knee-joint vascular network.

The lateral superior genicular artery supplies the vastus lateralis muscle and the lower part of femur, forming an anastomotic arch across the front of this bone with the highest genicular and the medial inferior genicular arteries.

Below, image of arteries that supply the knee, showing the femoral, the descending genicular, the popliteal, and the lateral superior genicular artery. It is an anterior (frontal) aspect drawing, as you can see the popliteal running down behind the knee-joint.

 

Artery

An artery is a blood vessel which carries oxygenated blood from the heart left ventricle to the rest of the body. It supplies every tissue and organ with oxygen and nutrients. Its smooth muscle, which forms its middle layer, makes it elastic as its walls can expand outwards when blood pressure increases. It has to be like this, since it must withstand the pressure exerted by the pump (heart), when the ventricular muscle of the heart suddenly contracts during the systole to send blood to every part of the body. Thus, when blood pressure is measured, it is always done on an artery, never on a vein. In anatomical drawings and diagrams, arteries are red colored, while veins are light blue.

The main artery of the body is the aorta, which arises from the left ventricle, ascending and forming an arch, which gives off important branches that supply the head and the upper limbs. Then it runs down parallel to the spinal column as it sends secondary arteries that supply the internal organs. At the base of the abdomen, the aorta divides into two important branches, which are the common iliac arteries. The main artery of the lower limb (thigh and leg) is the femoral artery, while the main artery of the upper limb (arm) is the brachial artery. Meanwhile the head, which include the brain, is supplied by the common carotid and basilar artery.

As it extends throughout the body, the artery keeps giving off secondary branches, just like a tree, forming a network, as it gets smaller and smaller in size, until it becomes so thin that it is called arteriole, which can be thinner than a hair. Finally, the arteriole ends up in a capillary, which is the tiniest blood vessel of the circulatory system. In order to efficiently supply an organ, an artery sends off lateral side branches that link up with another nearby artery; this is called anastomoses, which form a network of arterial blood vessels supplying an organ tissue.

Structure

The artery is made up of three layers of three different tissues: 1) the tunica intima, which is the innermost layer that lines the lumen (opening) of the artery; 2) the tunica media, which is the middle layer; and 3) the tunica adventitia, which is the external coating of the artery. The tunica intima is an endothelial layer, which means it is made up of endothelium (flat epithelial cells that line the inner walls of blood vessels and organs). The tunica media is formed by smooth muscle, which gives the artery elasticity. Meanwhile, the tunica adventitia consists of connective tissue, which give the artery form and consistency.

Innervation

The smooth muscle of tunica media is innervated by the peripheral nervous system (sympathetic and parasympathetic fibers), which means that its constriction and dilation do not depend on our will (cerebral cortex), but on adrenaline and acetylcholine, which are neurotransmitters of the peripheral nervous system.

Below, a diagram of the systemic blood circulation. Arteries are in red, while veins are in blue. The artery coming out of the heart left ventricle is the aorta.

 

Desert Mountain Adder

The desert mountain adder (Bitis xeropaga) is a venomous snake from the African continent. It is not well known because its natural habitat is the mountain region bordering the lower Orange River, in South Africa and Namibia. Since it belongs to the Viperidae family of serpents, its venom, which can be lethal, contain cytotoxins, which cause blood clots and destroy body tissues.

Physical Description

The desert mountain adder is a medium size snake, with the adult being no longer than 60 cm. It has a big triangular head, with a ridge running above each eye but it has no horns. Its body is greyish-yellowish brown, which is interrupted by multicolor rings composed of dark brown, white, and grey strips. However, its belly is dark grey patterned with dark speckles.

It usually dwells in nook and crannies under rocks and boulders and it never slithers under the sand. It hunts rodents, lizards, and other small animals. The female bears between 4 and 5 young every Summer. Even though it is not aggressive, it could bite you if it is cornered or stepped on.

Below, photo of the desert mountain adder (Bitis xeropaga)

 

Vastus Lateralis

The vastus lateralis is a long muscle of the anterolateral surface of the human thigh. It is part of the quadriceps femoris group. Its proximal end is covered by the tensor fasciae latae muscle.

The vastus lateralis muscle originates from the greater trochanter, the intertrochanteric line, and the lateral lip of linea aspera of femur. Next, it runs down laterally. Then its distal portion travels anteriorly, ending up in a wide tendon, part of which gets fused with the rectus femoris muscle tendon to be inserted into the lateral border of patella.

Action

The vastus lateralis muscle function is to extend the leg at the knee-joint. In doing so, it contributes to lift up the whole body when it is in a sitting position, as when we stand up from a chair, working together with the other muscles of the quadriceps.

Innervation

For the contraction, the vastus lateralis receives nerve fibers from the femoral nerve (L2-L4).

Blood Supply

It is supplied by branches arising from the profunda femoris artery, which include the lateral circumflex femoral and the perforating arteries.

Below, an anterior view of the right thigh. As you can see, the vastus lateralis muscle is partially covered by tensor fasciae latae

 

Vastus Intermedius Muscle

The vastus intermedius muscle is one of the four heads of the quadriceps femoris. It lies on the anterior aspect of thigh, between the vastus lateralis and vastus medialis. It is completely covered by the rectus femoris muscle.

The vastus intermedius muscle arises from the intertrochanteric line of head of femur. Then it travels downwards along the femur getting narrower as it goes. When it has reached the middle portion of thigh, it becomes a wide tendon, which fuses with the tendon of the rectus femoris to form the common tendon of the quadriceps femoris muscle.

Action

Extension of leg at the knee joint.

Innervation

This vastus intermedius muscle is innervated by nerve fibers arising from the femoral nerve (L2-L4).

Blood Supply

Like the other muscles of quadriceps, it receives oxygenated blood from the lateral circumflex and profunda femoris artery.

Below, two pictures of vastus intermedius; the first one with the vastus lateralis and the vastus medialis. The other without these muscles.

 

Rectus Femoris Muscle

The rectus femoris muscle is the longest head of the quadriceps femoris. It occupies the superficial and anterior side of the human thigh. It emerges from the anterior-inferior iliac spine and the superior border of acetabulum (of pelvis). Then it extends anteriorly, all the way downwards, covering the vastus intermedius muscle.

In the distal portion of thigh, the rectus femoris ends up in a narrow yet strong tendon, which fuses with the base and the anterior surface of the patella. Having run beyond the patella, this tendon is called patellar ligament, which is inserted into the tibial tubercle (tuberosity).

Action 

Its main function is the extension of the leg at the knee-joint.

Innervation and Blood Supply

The rectus femoris muscle is innervated by branches of the femoral nerve and it receives oxygenated blood from branches of the profunda femoris artery.

Regions of Abdomen

The regions of abdomen are the different parts into which the human venter (belly) is anatomically divided. The upper part of abdomen has an epigastric region (epigastrium), which is triangular, and two, left and right, hypochondriac regions. In the middle portion of the belly, two lateral abdominal, right and left, regions, and a middle umbilical region. The lower part of the abdomen, called hypogastrium, also has two lateral regions, which are called the inguinal regions (right and left), and a middle pubic region.

 Right and left costal arches are clearly outlined when the abdominal wall is pulled in. The xiphoid process is left in the angle formed by the cartilaginous costal arches, which is called infrasternal angle. The inguinal folds that correspond to the position of the inguinal ligaments are distinctively seen in the lower portion of abdominal wall. When the abdominal muscles are tensed, a groove get formed running vertically along the midline; it is the linea alba abdominis. The umbilicus lies right in the middle of the linea alba, on the level of the articulation between the third and fourth lumbar vertebrae.

The rectus abdominis muscles are outlined to both sides of the midline. The tendinous intersection of these muscles are defined clearly as three or four transverse constrictions. The slips of the external oblique muscle alternating with slips of serratus anterior and longissimus dorsi muscle are outlined on the upper part of the anterolateral portion of thoracic wall.

Below, you can see a schematic drawing of the regions of abdomen and the thorax.

 

Human Diaphragm

The human diaphragm is an unpaired broad and flat muscle which divides the thorax from the abdominal cavity. Being dome-shaped, it isolates the thoracic viscera, such as the lungs and heart, from the digestive organs (stomach, intestines, liver, and pancreas). It plays a vital role in breathing as it is innervated by the phrenic nerve, whose center is located in the medulla oblongata (see breathing centers).

Both its thoracic and abdominal surface are covered by fasciae, which in turn are covered by connective tissue. A relaxed diaphragm has a beveled spherical convexity, which faces the thoracic cavity with two domes; the right and left. The apex of the dome rises on the medioclavicular line to the level of the fourth intercostal space on the right side, and to the level of the fifth intercostal space on the left. When the diaphragm contracts, its domes flatten out, increasing the thoracic space volume and the capacity of the lungs to expand during the inspiration phase of breathing.

The muscular fibers of the diaphragm arise from the inner border of the outlet of thorax, which can be divided into a sternal, costal, and lumbar portion. The sternal part is the smallest, arising from the posterior surface of the xiphoid and is continuous with the central tendon. The costal portion originates from the inner surface of the bony and cartilaginous parts of the lower six ribs, with its fibers running upwards and inwards, being continuous with the central tendon. The lumbar portion of diaphragm arises from the anterolateral surface of the body of the first three lumbar vertebrae and from the medial and lateral arcuate ligament; at this point, there is the aorta diaphragmatic foramen (opening).

The muscular fibers of the human diaphragm, which runs towards the center, continue as tendons from the central tendon. This area of the diaphragm is trifoliate (having three leaf-like parts) in shape, with one leaf directed forwards and on which the heart lies, and the other two directed to the sides, with the lungs being located there. In the posterior part of the central tendon, to the right of the midline, there is the vena-caval opening for the inferior vena cava. The medial muscular bundles of both crura opens up to form the esophageal opening for both the esophagus and the vagus nerve. There are other smaller orifices in it for the splanchnic nerve and veins.

The lungs and heart lie on the thoracic surface of the diaphragm, while the liver, stomach, and spleen are in contact with its abdominal surface. The pancreas, duodenum, kidneys, and adrenal glands touch areas of the abdominal surface of diaphragm which are not covered by the parietal peritoneum.

Action/Function

The human diaphragm takes part in inspiration (breath in) as it becomes flat upon contraction, increasing the thoracic cavity volume and decreasing its inner pressure. This unbalance between the external atmospheric pressure and the thoracic inner pressure, causes a stream of air to flow into the lungs through the nose to balance it out.

Blood Supply

It is supplied by the phrenic arteries, which originate straight from the thoracic aorta, and by the musculophrenic artery, which springs from the internal thoracic artery.

Innervation

It is innervated by the phrenic nerve, which arises from vertebral roots C3, C4, and C5 as it is part of the cervical plexus.

Below, an anterior aspect of the human diaphragm.

 

Function of Glucagon

The function of glucagon is to raise the amount of glucose in your bloodstream to keep it up at normal levels. It does so by making the liver cells produce glucose from glycogen first, then from fat. This fat could be in the form of triglyceride you have stored in your adipose cells or from the glycerol obtained from the fat you eat in your diet; when you eat butter, for example. Thus, this hormone is vital for blood sugar regulation and metabolism as the function it performs is the opposite of that of insulin. Glucagon is secreted by the alpha cells of the islets of Langerhans in the pancreas.

When you run or work out for more than half an hour, glucose (sugar) levels in the bloodstream begin to drop. To avoid deadly hypoglycemia, the pancreas alpha cells automatically releases glucagon, which activates hepatocytes. These metabolic liver cells in turn convert the stored glycogen back into glucose. Glycogen is the first fuel reserve. But if you keep strenuously exerting your muscles for a long period, you also run out of glycogen. Then, your body resort to tap the second fuel reserve, which is the fat stored in the form of triglyceride. This time, glucagon activates an enzyme called lipase, which is also found in the adipose tissue.

Lipase breaks each one of the molecule of triglyceride into smaller molecules: two fatty acids and one glycerol is obtained from one triglyceride. In the liver, fatty acids is further metabolized into ketone bodies, which are high-octane fuel utilized by most of the body cell mitochondria to produce ATP, the cell energy. In other words, thanks to glucagon, your body is able to burn fat to obtain high-octane fuel to produce energy, just like a thermoelectric power plant, where the boilers and turbines use fuel (gas or carbon) to turn the generators to produce AC electricity. ATP (AdenosineTriphosPhate) is the cell "electricity". By burning both glycogen and the fat you have stored in your body, you never suffer from hypoglycemia, unless you suffer from type I diabetes.

Meanwhile, the liver hepatocytes also metabolize the glycerol obtained from the fat contained in the food you eat. They convert it into glucose through a slow process called gluconeogenesis, which is the generation of sugar from glycerol.

By Carlos B. Camacho

Blood Sugar Regulation

Blood sugar regulation is performed by an organ of the endocrine system; the pancreas. This small organ secretes two types of hormones to maintain the glucose (sugar) in your bloodstream at normal levels: insulin and glucagon. Thus, they regulate the amount of glucose in your blood, which must range from 80 to 110 milligrams per deciliters (mg/dL) for a healthy person. Above them, you are in a pre-diabetic stage.

Although glucose is an essential fuel for many cells to produce energy (ATP), too much sugar in your tissues is inflammatory and, over the years, can lead to serious damage, especially to your arteries inner walls, which are made up of endothelial cells. Too much sugar also hurts your eye retina and it can also cause ischemia in your toes and feet. To avoid it, the beta cells of pancreas release insulin, which induces the liver cells to convert the excess glucose into glycogen, thus, lowering the sugar to normal levels.

Glycogen is a kind of first fuel reserve that muscles and organs have at their disposal during physical exertion. If you keep eating too much carbs and if you lead a sedentary life, then the pancreas will continue producing insulin and the liver will convert the remainder of excess sugar into triglyceride, which is stored in your adipose cells as fat. Therefore, fat is the second fuel reservoir that the body has in store.

During fasting or famine, the pancreas alpha cells release glucagon, which is a hormone that activates the enzyme lipase in the adipose tissue. Lipase breaks down triglyceride into smaller molecules: glycerol and fatty acids. Then the liver hepatocytes mitochondria convert glycerol into glucose through a metabolic process called gluconeogenesis, also turning fatty acids into ketone bodies, which are high-octane fuel employed by muscle and nerve cell mitochondria to produce ATP.

By Carlos B. Camacho (anthropologist)

Horned Adder

The horned adder (Bitis caudalis) is a small-size venomous snake inhabiting the Kalahari region and its surrounding arid areas, Africa. It is easily recognized by the single horn set above each eye. Since it is an adder, the Bitis caudalis belongs to the family Viperidae. Although its glands secrete cytotoxic venom, it is mild and no human deaths have been reported as a consequence of its bite.

The adult horned adder measures between 25 and 35 cm in length. The color of its body varies from orange-brown in Kalahari to grey-olive in Karo and northern provinces, but in both cases the background color is blotched with dark spots and smaller white ones. It has a creamy white belly. Its triangular head has a darker ‘V’ shape on the crown.

The horned adder hunts lizards most of the time, and rodents. The female bears up to 27 young in the late summer each year.

Below, the Betis caudalis in its orange-brown variation.

 

Genus Bothrops

The genus Bothrops belong to the large family of snakes called Viperidae (vipers). They are among the most venomous in the world. They are found in the tropical and subtropical jungles and savannas of Central and South America. All of them have a cytotoxic and hemotoxic venom, which destroys tissue cells in large numbers, causing necrosis and blood clots as sometimes amputation of hand or foot are required. In some cases, the patient dies of kidney failure if the envenomation becomes systemic. The symptoms caused by a bite are fever, headache, vomiting, and high blood pressure.

Physical characteristics

Their length ranges from 70 cm to 1.90 m long (about 6 ft). Bothrops snakes have triangular head and sharp-angled snout, pointing upwards. They have retractable fangs, which means they fold back when they close their mouth, but they do not have rattle. They all have ventral and subcaudal scales as their skin have brown, grey, green and yellowish irregular markings, with the main one looking like an inverted 'V' (Λ).

There are more than thirty species of the genus Bothrops. The Brothrops alternatus, asper, amoditoides, atrox, and jararacussu are the most common and widely distributed species of this genus.

Below, a Bothrops asper, the species that inhabits the Central American jungle.

Descending Genicular Artery

The descending genicular artery is a long arterial branch located in the medial, distal portion of thigh and the knee joint region. It supplies the knee, the vastus medialis muscle, and distal parts of the sartorius, gracilis, semitendinosus, and semimembranosus muscle.

The descending genicular artery arises from the antero-medial wall of femoral artery in the subsartorial canal (canalis adductorius). Then it descends towards the knee, piercing together with the saphenous nerve the tendinous lamina as it emerges towards the surface. Next, it travels behind the sartorius muscle, curving around the medial condyle of femur. Sending off several branches, it ends up in the muscles of this region.

The descending genicular artery gives off the following branches: 1) the muscular branches which run deep into the surrounding muscles; 2) the saphenous branch, which travels deep into the vastus medialis muscle; 3) articular branches, which anastomoses the medial superior genicular and the middle genicular artery, contributing the arterial network that supplies the knee joint.

Below, schematic picture of arteries of thigh and knee, showing the descending genicular.

 

Vastus Medialis Muscle

The vastus medialis muscle occupies the anteromedial surface of lower half of thigh. It is the shortest head of the quadriceps femoris and it is partially covered by the rectus femoris. It is made up of muscle fibers that are directed obliquely downwards and anteriorly.

The vastus medialis arises from the medial lip of linea aspera of femur. Then it runs dowards to be continuous with a wide tendon, which partly fuses with the common tendon of the quadriceps femoris and it partly inserted into the medial border of patella to form the medial retinaculum of the patella.

Action

Together with the other three muscles that constitute the quadriceps femoris, the vastus medialis muscle extends the leg, assisting in rising/lifting the body from a sitting position.

Innervation

It is innervated by nerve fibers arising from the femoral nerve (L2-L4)

Blood Supply

The vastus medialis muscle receives oxygenated blood from branches of the profunda femoris and the descending genicular artery.

Popliteal Artery

The popliteal artery is the main artery of the knee and leg, supplying their ligaments, muscles, and bones. It is located behind the knee joint, in the popliteal fossa.

It arises from the distal end of femoral artery, being its continuation. As it descends behind the distal portion of thigh, the popliteal artery runs through the adductor canal to enter the popliteal fossa at the flexor side of the knee.

When the popliteal artery reaches the proximal portion of tibia, it divides into the anterior and posterior tibial artery. During its course, it gives off the lateral superior genicular, the medial superior genicular, the middle genicular, the sural branches, lateral inferior genicular, and the medial inferior genicular artery.

Below, diagram/drawing of popliteal artery and its main branches. It is the posterior side of the right knee-joint region.

 

Sartorius Muscle

The sartorius muscle is a long and superficial muscle of the human thigh. Strap-like, it lies on its anterior aspect, stretching over the rectus femoris, adductor longus, and vastus medialis muscle. It travels down from the hip to the leg.

The sartorius arises from the anterior superior iliac spine, on the lateral aspect of hip. Then it descends obliquely and medially. Curving around the back of the medial epicondyle, it ends as a flat tendon, which is inserted into the tubercle of the tibia.

Action

The sartorius muscle flexes the thigh and leg, rotating the thigh laterally, and the leg medially.

Innervation

It is innervated by branches of the femoral nerve, from L2 and L3 of lumbar plexus.

Blood Supply

The superior portion of this long muscle is supplied by lateral circumflex femoral artery. The middle part is irrigated by muscular branches from femoral artery, while the distal portion receives oxygen-rich blood from the superior genicular artery.

Below, a picture/drawing of the human right thigh, showing the sartorius muscle, among others.

Articularis Genus Muscle

The articularis genus muscle is a flat sheet of muscle fibers which occupies the anterior aspect of distal portion of femur. It lies under the long tendon of vastus intermedius muscle.

The articularis genus consists of three flat and narrow bands of muscular fibers which originate from the lower fourth of anterior surface of shaft of femur and is inserted into the suprapatellar bursa of knee.

Action

The articularis genus tenses the capsule of the knee-joint.

Innervation

It is innervated by deep nerve fibers arising from the femoral nerve.

Blood Supply

It is supplied by deep branches from the second and third perforating arteries.

Below, the articularis genus on anterior surface of distal end of femur

 

Knee Joint

The knee joint is the site of junction and articulation between the thigh and the leg. It is composed of three bones; the distal portion of femur, the proximal end of tibia, and the patella. These three bones are attached to one another by a series of ligaments and tendons, such as the cruciate ligaments, the menisci, fibular collateral ligament, tibial collateral ligament, capsular ligament, and the quadriceps femoral tendon and the patellar ligament. They allow the leg to fold backwards on the femur/thigh lower end, like a hinge.

The articular surfaces of the femur intercondyle are ellipsoid, with the medial condyle being more complex than the lateral one; meanwhile, the patellar surface is located right on the lower anterior surface of the bone, which is called facies patellaris in Latin. The superior articular surfaces of the tibial condyles are slightly concave, and they are incongruent with the convex articular surfaces of the femur condyles. This incongruence is corrected by the interarticular cartilages called menisci (the medial meniscus and the lateral meniscus), which lie on top of the tibia, being fused to the articular capsule.

The anterior and the posterior cruciate ligaments, which form a cross, provides the knee joint with rotary stability. The anterior cruciate ligament extends forwards from the lateral condyle of femur to the anterior intercondylar region of tibia. The posterior cruciate ligament, on the other hand, runs backwards from the medial surface of medial femoral condyle to the posterior intercondylar area of tibia, crossing anterior C. L.

Below, anterior view of right knee joint, exhibiting its ligaments and tendons.

 Below, a radiographic picture of the knee joint region. Here, ligaments and tendons cannot be seen. Only the distal portion of femur and the proximal extremity of tibia and fibula can be observed.

Cruciate Ligaments

The cruciate ligaments of the knee are a pair of bands of fibrous connective tissue located in the center of cavity of the knee joint. Being extremely tough, they connect and join the distal head of femur to the proximal head of tibia, providing support to the knee during rotation of tibia. They also hold the head of femur in place, preventing it from coming off the anterior edge of tibia.

The anterior cruciate ligament arises from the lateral condyle of femur, running forwards and medially to be attached to the tibia in the anterior intercondylar segment.

The posterior cruciate ligament originates from the medial surface of the medial femoral condyle as it travels backwards to be attached to the posterior intercondylar area of the tibia.

Below, diagram of anterior view of right knee-joint showing the anterior and posterior cruciate ligaments right in the middle, between the distal head of femur and proximal head of tibia. You can also observe the knee menisci.

Posterior view of right knee-joint exhibiting cruciate ligaments

Knee Meniscus

The knee meniscus is one of two intraarticular cartilage disks of the knee-joint (plural: menisci). Being crescent-shaped, they are located between the femoral and tibial condyles. They are cartilaginous trihedral plates, with their peripheral edge being thick and fused with the articular capsule. The menisci are attached anteriorly and posteriorly to the intercondylar eminence of the tibia. The anterior part of both menisci are joined by the transverse ligament of the knee.

The upper surface of the meniscus is concave, while the inferior surface is flat and lies on top of the tibial condyles. Therefore, the peripheral edges of the menisci follow the configuration of the superior border of the tibial condyles. As a result, the medial meniscus is crescent-shaped, while the lateral meniscus resembles a half of a circumference. Posteriorly, the posterior meniscofemoral ligament attaches the lateral meniscus to the intercondyle fossa of the femur.

Injury to one of the meniscus or both is very common in outdoor sports, such as soccer. Twisting or overextension of the knee-joint can severely tear them. If they get detached, a sudden blockage of the joint occurs, rendering hinge-like movement impossible. Sometimes it is necessary a surgical procedure.

Diagram of anterior aspect of the right knee-joint showing the medial and lateral menisci joined together by the transverse ligament of the knee.

Below, posterior aspect of the right knee-joint, where you can see the posterior miniscofemoral ligament anchoring the lateral meniscus to the femoral intercondyle fossa.

Below, superior aspect of the menisci of right knee showing the cruciate ligaments. Notice the crescent shape of the medial meniscus