Biceps Brachii

The biceps brachii is a strong, spindle-shaped muscle of the human arm. It lies along the full length of the anterior side of humerus, stretching over the coracobrachialis and the brachialis muscle. It originates by two heads; the long head arises by a long tendon from the supraglenoid tubercle of scapula (right above the glenoid cavity where the head of humerus articulates). Then it runs over the head of humerus, extending down laterally to fuse with the short head into one muscle.

The short head of the biceps brachii, on the other hand, originates from the coracoid process of scapula and travels down medially, over the coracobrachialis muscle, to join its contralateral portion halfway the length of humerus. Then the biceps brachii muscle keeps stretching down the lower half of humerus as one long fleshy belly, covering the brachialis, to be inserted by a sturdy tendon into the radial tuberosity in the proximal portion of radius.

Action

The biceps brachii folds the upper limb at the elbow-joint, pulling the forearm up towards the anterior side of arm (this is the muscle you use when you do curls at the gym). Along with the anterior portion of deltoid, it also raises the arm forwardly. It also assists the supinator muscle to twist around the forearm into the supine position.

Innervation

This powerful muscle is innervated by a side branch of the musculocutaneous nerve (C5-C6)

Blood Supply

The biceps brachii muscle is supplied by muscular branches of both axillary and brachial artery.

Below, muscles of the arm, showing the biceps brachii stretching superficially over the coracobrachialis and the branchialis muscle.

 

Naja naja

Also known as the spectacled cobra, the Naja naja is one of the most venomous snake in the world. Its natural habitat is India and other Southeast Asian countries. As a member of the Elapidae family, the glands of its fangs secrete neurotoxic venom, which interferes with its prey's post-synaptic jump, blocking the nerve impulses between two nerve cells. Therefore, someone who is bitten by this cobra, if not treated, could die of a asphyxia due to paralysis of respiratory muscles (diaphragm and intercostal muscles of ribcage).

Description

The adult of the Naja naja measures between 1.80 and 2.20 m in length. Right below its round head, there is a pair of hoods, which are spread out when disturbed, or feels threatened, as it rears up ready to bite. The color of its body varies from brown to dark grey. The scales of the dorsal side of body are smooth and arranged in an oblique pattern. It has a spectacles-shaped pattern on the back of hood, which is clearly distinguished when it is light brown in color.

The Indian cobra lurks under rocks, pile of logs, and rat holes. It preys on rodents such as rats.

Below, the Naja naja rearing up, with its hood spread out.

 

Elephant Trunk Snake

The elephant trunk snake (Acrochordus javanicus) is the largest aquatic serpent in Southeast Asia. The adult can measure between 2.50 and 2.70 m long. It lives in freshwater wetland, river, streams and estuaries. It belongs to the genus Acrochordus, subfamily Acrochordidae, and the larger family Colubridae. It does not pose any risk for humans for their bites lack either cytotoxic or neurotoxic venom.

Description

The elephant trunk snake has a thick, stout body, which is grayish black, with the head having darker lines. It also features two longitudinal stripes and elongated dark blotches which run along the sides of its body. However, its belly is cream in color. Its eyes are small, with vertical pupils. Mid-body scale rows are largest around the dorsal side. Tail is prehensile.

The elephant trunk snakes are found in Thailand, peninsula of Malay, Singapur, Java, and Borneo. They lurk at the bottom of rivers and estuaries, hunting for fish.

Below, the Acrochordus javanicus on the ground

 

Coracobrachialis

The coracobrachialis is a deep, spindle-shaped muscle of upper portion of arm. It lies beneath the short head of the biceps brachii muscle. Lying on the medial side of proximal portion of humerus, it arises from the apex of the coracoid process of scapula. Then it extends down along the upper part of humerus to be inserted into the medial surface of this bone, on the medial lip of the bicipital groove.

Action

The coracobrachialis muscle raises and adducts the arm (pulls it towards the side of trunk).

Innervation

This hidden muscle is innervated by side branches from the musculocutaneous nerve.

Blood Supply

It receives oxygenated blood from secondary branches of the deep brachial and brachial artery.

Below, the coracobrachialis muscle hidden by biceps brachii.

The coracobrachialis, with the bicepss brachii muscle romoved. You can also see the musculocutaneous nerve and brachialis muscle on the lower portion of humerus.

Below, another view of coracobrachialis, along with pectoral major muscle.

 

Musculocutaneous Nerve

The musculocutaneous nerve is one of the four nerves that supply the muscles and skin of the arm, forearm, and hand. The median, radial, and ulnar are the other three nerves. It arises from the lateral cord of brachial plexus as a side branch, at the level of the lower border of the pectoralis minor muscle. The musculocutaneous nerve innervates the coracobrachialis, biceps brachii, and the brachialis anticus muscle as well as the skin of forearm.

This important nerve is composed of fibers originating from the fourth, fifth, and sixth cervical roots (C4, C5, C6). Having emerged from the lateral cord, it perforates the coracobrachialis muscle in the upper portion of arm. Then it travels obliquely down between the biceps brachii and brachialis anticus muscle. Giving off side branches, the musculocutaneous nerve extends along the radial side of forearm as the lateral cutaneous nerve, running into the wrist, in front of the radial artery. There it divides into smaller nerve filaments that run over the carpal bones to come up to the surface to supply the subcutaneous tissue and a portion of skin of hand.

Below, schematic drawing of brachial plexus showing the musculocutaneous nerve.

 

Brachial Plexus

The brachial plexus is an intricate web of nerves which originate from the cervical and thoracic roots. Located in the antero-lateral region of neck and shoulder, it is formed by the junctions of the anterior primary divisions of the lower four cervical nerves (C4, C5, C6, C7), and the upper two thoracic (T1, T2). It consists of mixed nerve fibers which innervate the upper limb. Damage to one or more nerves that make up the brachial plexus can cause partial or total paralysis of arm, forearm and hand.

Branches

The plexus is composed of three nerve cords: the lateral (outer), medial (inner), and a posterior cord, which lies in the middle of the lateral and medial. These cords give off four nerve branches that supply the muscles and skin of the arm, forearm, and hand; they are the median nerve, which supplies the flexor muscles of anterior compartment of forearm and muscles of thumb; the ulnar nerve, which supplies the flexor carpi ulnaris and the flexor digitorum profundus; the radial nerve, which innervates the triceps brachii and the extensor muscles of posterior side of forearm; and the musculocutaneous nerve, which sends branches to the coracobrachialis and biceps brachii and the skin of arm.

Below, diagram of the brachial plexus of left side.

Radial Nerve

The radial nerve is the thickest branch of the brachial plexus. It innervates the muscles of the posterior side of arm (triceps brachii) and forearm (anconeous, brachioradialis, extensor digitorum, extensor carpi ulnaris, and extensor indicis muscle). Therefore, damage to this nerve, caused by a broken humerus, may result in the inability to extend the fingers and the wrist, which is called "wrist drop", and the fingers. In old text, it is also known as the musculospiral nerve.

The radial nerve originates from the posterior cord of brachial plexus. This posterior cord is formed by the union of nerve fibers arising from the fifth, sixth, seventh, and eighth cervical roots (C5-C6-C7-C8). Just as it emerges from the brachial plexus, it travels down behind the axillary artery and behind the upper portion of the brachial artery as well. Then it spirals around the arm, switching position from the medial to the lateral side of humerus in the musculospiral (radial) grooves, with the deep brachial artery.

The radial nerve winds around once again to position itself on the anterior aspect of distal portion of humerus. When it has reached the forearm, it forks into the superficial branch, which is basically an afferent nerve, and a deep branch, which is efferent, supplying the extensor pollicis brevis muscle (of thumb) in the hand. The superficial afferent branch supplies the skin and subcutaneous tissue of forearm.

Below, the site of origin of radial nerve in brachial plexus.

The course of radial nerve in the arm. You can see why it was called the musculospiral nerve. Image from Gray's Anatomy, updated.

Acrochordidae

The Acrochordidae is a taxonomical subfamily of snakes, which include the genus Acrochordus, with three species world wide. Two of these species are found in Southeast Asia; the wart (Acrochordus granulatus), and the elephant trunk snake (Acrochordus javanicus). They both can be identified for their thick and heavy bodies. This subfamily is included within the larger family Colubridae.

Physical Characteristics

The Acrochordidae snakes have their eyes located on top of their head and valvular nostrils. Their bodies have loose folded skin, with rough granular scales and bristle-tipped tubercles. They also have a skin flap for closing the lingual (tongue) opening of the mouth. All these physical traits are evolutionary adaptation for an aquatic environment.

They inhabit fresh waters, river and lakes, and sea coasts. They are nocturnal creatures who hide away beneath fallen logs and other underwater debris. They feed on crabs, fish, and smaller snakes. They are either harvested for their durable and valuable skin and caught by fishermen for the flesh as they are eaten by local population.

Below, a member of the Acrochordidae family, the wart snake.

 

Median Nerve

The median nerve is one of the four main nerves that supply the upper limb (arm, forearm, and hand). The others are the ulnar, musculocutaneous, and radial; all of them originating from the brachial plexus. The median nerve innervates all the flexor muscles lying in the anterior compartment of forearm: flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus, and flexor pollicis brevis muscle.

Origin and Course

It is a mixed nerve which originates by the merging of two side branches, one arising from the lateral, and the other from the medial cord of the brachial plexus. Before joining together into one, the lateral (outer) and medial (inner) branch straddle the last portion of the axillary artery, embracing it.

Nerve fibers from the fifth, sixth, and seventh cervical (C5-C6-C7) join together to make up the median nerve, traveling through the lateral and medial cord. First it runs along the medial side of the arm. Then it extends along the middle of forearm, stretching into the hand. As it runs through the arm, it first lies on the lateral side of the brachial artery. Then it switches over to the other side of this blood vessel to position itself on the medial side of the brachial artery.

Once it has reached the forearm, it gives off the anterior interosseous branch. Then the median nerve runs between the two heads of the pronator teres muscle, crossing the ulnar artery. Next, it extends between the flexor digitorum superficialis and the flexor digitorum profundus. Finally, it runs through the carpal tunnel, supplying the flexor pollicis brevis and the opponens pollicis of thumb and the second and first lumbrical muscles of hand.

Innervation

The median nerve gives off efferent branches to supply all the superficial muscles of forearm, except for the flexor carpi ulnaris, which is supplied by the ulnar nerve. It also supplies the muscles of the thenar (thumb), except for the adductor pollicis. Meanwhile, its afferent (sensory) nerve fibers innervate the skin of forearm.

Below, drawing showing the location in the arm of the median, ulnar, and musculocutaneous nerve.

Schematic drawing of brachial plexus, exhibiting the origin of the median, ulnar, radial, and musculocutaneous nerve.

Adductor Pollicis Muscle

The adductor pollicis muscle is the deepest of the thenar group. It arises by two heads, whose fibers are directed towards one another, at an angle. The oblique head originates from the radiate carpal ligament (at the capitate bone) and the palmar surface of the second and third metacarpal bone. The transverse head arises from the palmar surface of the second and third metacarpal bone. Then these two muscle bundles converge together at an angle to be inserted into the base of the proximal phalanx of thumb, the ulnar sesamoid bone, and the capsule of the metacarpophalangeal joint. Name in Latin: musculus adductor pollicis. "Thenar" is the fleshy portion at the base of thumb.

Action

Upon contraction, it adducts the thumb (it pulls it medially towards the radial border of palm of hand). It also assists in flexing the thumb proximal phalanx.

Innervation

The adductor pollicis muscle is innervated by branches of the ulnar nerve (C8). Let us remember that the ulnar nerve springs from the brachial plexus.

Blood Supply

It receives oxygenated blood from secondary branches of the superficial and deep palmar arches, which are the arterial anastomoses of the radial and ulnar artery.

Below, a picture of muscles of right hand, exposing the adductor pollicis, with its two heads

 

Flexor Pollicis Brevis

Flexor pollicis brevis is a short, thick muscle of the thumb. It is composed of two heads, with the superficial head lying directly under the skin, between the opponens pollicis and the adductor pollicis brevis muscle. The deep head is hidden from sight as it is located beneath the superficial portion and the adductor pollicis. Pollicis is the Latin word for thumb; and brevis means short.

The flexor pollicis brevis arises from the flexor retinaculum (a fibrous band forming the carpal tunnel), the trapezium, trapezoid, the capitate bones of carpus, and the base of the first metacarpal bone. The superficial fibers are inserted into the radial sesamoid bone, while the deep portion is inserted into both sesamoid bones of the metacarpophalangeal joint.

Action

The flexor pollicis brevis flexes the proximal phalanx of the thumb. It assists the flexor pollicis longus in closing it when we want to grasp something in the hand.

Innervation

It is supplied by nerve fibers originating from the median nerve (C6-C7), which is part of the brachial plexus.

Blood Supply

This thick muscle of the thumb receives oxygenated blood from the superficial palmar branch of the radial artery, and a branch of the deep palmar arch.

Below, schematic picture of the flexor pollicis brevis (superficial head), lying between the opponens pollicis and the adductor pollicis muscle.

Deep head of flexor pollicis brevis.

Dorsal interossei muscles

The dorsal interossei are four small deep muscles of the hand. They are spindle-shaped and bipennate, lying in the interosseous spaces, between the metacarpal bones, on the dorsal aspect of hand. Each one of them arises by two heads from the adjacent sides of the bases of the next two metacarpal bones.

The first dorsal interosseous muscle originates from the inner surfaces of the first (thumb) and second (index finger) metacarpal bone; it is inserted into the radial side of proximal phalanx of index finger. The second dorsal interosseous arises from the inner surfaces of the second (ulna side) and third (radial side) metacarpal bone and is inserted into the radial side of middle finger proximal phalanx. The third and fourth dorsal interossei originate from the inner surfaces of the third, fourth, and fifth metacarpal bone and are inserted into the ulnar side of the middle and ring fingers.

Action

The these small muscles pull the proximal phalanges of the index, middle, and ring finger towards the palm of hand.

Innervation

They are supplied by motor nerve fibers springing from the ulnar nerve, which originates from the brachial plexus, from C8-T1).

Blood Supply

They are irrigated by secondary arterial branches arising from the deep palmar arch.

Below, the dorsal interossei muscles

Carpal Bones

The carpal bones are the eight wrist bones, which make up the base of the human hand. They are small and very irregular in shape as they are tightly held together by cartilage and strong ligaments (bands of connective tissue). They are set in two rows and all together are called the carpus, lying between the distal end of radius-ulna bones and the metacarpal bones, with which they articulate.

In the proximal row, there are the scaphoid, lunate, triquetral, and pisiform (the smallest one). The scaphoid and the lunate bone articulate with the radius, while the pisiform and triquetral bone with the ulna. In the distal row, there are the trapezium, trapezoid, capitate, and hamate, which articulate with the metacarpus.

The metacarpal bones have rough spots on the palmar and dorsal sides which indicate the sites of attachment for the hand muscles tendons. Except for the pisiform, the rest of the wrist bones have six surfaces or facets, most of which articulate with other bones. The capitate, the scaphoid, and the hamate are the biggest and strongest ones.

Below, diagram of the carpal and metacarpal bones (palmar aspect of right hand) showing all the eight bones that make up the wrist.

Below, the dorsal side of right hand, showing the wrist bones.
 

Wart Snake

The wart snake (Acrochordus granulatus) is an ophidian reptile of Southeast Asia. Its natural habitat includes the coastal regions and river estuaries of Thailand, Cambodia, Peninsula of Malaysia, Myanmar, and New Guinea. It belongs to the family Acrochordidae, and the genus Acrochordus. Therefore, it is aquatic, spending most of the time in fresh and sea water.

Physical description

The wart snake average length is 100 cm (1 m). Its body color ranges from blue to grey and it is marked with transverse, creamy white bands. Its body is heavy and stout. The head is covered by small juxtaposed scales (arranged side by side). Both female and male have small eyes with a vertical pupil, like most snakes. On the ventral region, the mid body scales are larger than on the rest of body.

Since it inhabits the coastal waters of river and shallow seas, it feeds mostly on fish and frogs. The female can produce as many as 33 fully developed young, which are enclosed in egg-sacs, from which they hatch out before birth. It can swim underwater for more than one hour without pulmonary respiration.

Below, the wart snake on the ground.

Angiology

Angiology is the scientific study of the vascular system, which includes arteries, veins, capillaries, and lymphatic vessels. The pump that makes it work, the heart, is also the object of its study. From a morphological and functional point of view, it is usually classified into blood vascular system (systema sanguineum), or the circulatory system, and the lymphatic system, which drains the body tissues.

The blood vascular system is composed in turn of three types of vessels: arteries, veins, and capillaries. Arteries carry oxygenated blood from the heart to the body, and vein deoxygenated (oxygen-poor) blood from the body back to the heart. Thus, they are responsible for keeping keep our tissues and organs alive. They are arranged in a closed-circuit manner, with the capillaries being the bridge or junction point between arteries and veins. Meanwhile, the lymphatic vessels do not carry blood but lympha, which is the excess fluid that builds up in the tissues.

Angiology also studies the structure of blood vessels and the vascular diseases that affect them. From the size of their lumen point of view, there are two types of arteries and veins. Therefore, a very small artery is called arteriole, while a very small-caliber vein is called venules. Both of them have smooth muscle constituting their middle layer, while the capillaries are made up only of squamous endothelial cells. Many inflammatory conditions damage these structures and can provoke a collapse of the inner walls and their occlusion.

Angiology also study the anatomical location of every blood vessel.

 

Macromolecular Constituents of Cells

The macromolecular constituents of cells are important biochemical elements so that their organelles can perform their biological functions to keep them alive. Thus, aside from containing water and ions, cells are composed of four major organic constituents: 1) proteins; 2) carbohydrates; 3) lipids (fats); and 4) nucleic acids.

Proteins- They consist of one or more chains of amino acids, with each one having an amino (-NH2) and a carboxyl (COOH) group. Plants produce their own amino acids and proteins from carbon dioxide, nitrogen, and water. However, animals cannot synthesize them as they have to depend on dietary proteins obtained from animal and plant sources when they eat them.

Carbohydrates- Hepatocytes (liver cells) convert the simplest form of carbs, glucose, into glycogen whenever there is an excess. This is called stored carbohydrate. Glycogen is a polysaccharide which can quickly be turned back into glucose during fasting, whenever the body cells need it.

Lipids- The body cells store fat in its simpler form; fatty acid, which is released when lipase breaks down a molecule of fat in the duodenum: two molecules of fatty acid and one glycerol. When there is not enough glucose, many body cells mitochondria employ fatty acid as fuel to produce ATP (energy). The liver cells also use this molecule to synthesize ketone bodies, which are also used as fuel by muscle cells and neurons to produce ATP.

Nucleic acids- They are complex molecules, which are the basic components of DNA and ARN. They are the carrier of hereditary information and control the synthesis of proteins.

Loggerhead Turtle

The loggerhead turtle (Caretta caretta) is a Testudine egg-laying reptile which is frequently found on the east coast of South Africa. It breeds on protected beaches in northern Zululand. Females come ashore during dark nights and each one of them lay up to 500 eggs at 15-day intervals.

It is a large turtle, with a big head. Its scute (shell) is smooth and non-overlapping, except for the young whose scute is keeled. Each one of its limb has two claws. It measures between 70 and 100 cm in length. Both adult and young are brown. It hunts for crabs, molluscs, and sea urchins around reefs and rocky estuary.

Below the loggerhead turtle on a beach in South Africa.