human head

In anatomy, the head of an animal is the rostral part (from anatomical position) that usually comprises the brain, eyes, ears, nose and mouth (all of which aid in various sensory functions, such as sight, hearing, smell, and taste). Some very simple animals may not have a head, but many bilaterally symmetric forms do.

For humans, the head and particularly the face are the main distinguishing feature between different people, due to their easily discernible features such as hair and eye color, nose, eye and mouth shapes, wrinkles, etc. Human faces are easily differentiable to us due to our brains' predispositions toward discriminating human facial forms. When observing a relatively unfamiliar species, all faces seem to be nearly identical, and human infants are biologically programmed to recognize subtle differences in anthropic facial features.
People who are more intelligent than normal are sometimes depicted in cartoons as having bigger heads, as a way of indicating that they have a larger brain; in science fiction, an extraterrestrial having a big head is often symbolic of high intelligence. Outside of this symbolic depiction, however, advances in neurobiology have shown that the functional diversity of the brain means that a difference in overall brain size is not a reliable indicator of how much, if any, difference in overall intelligence exists between two humans.
The head is a source for many metaphors and metonymies in human language, including referring to things which are often located near the human head ( "the head of the bed"), things which are physically similar to the way an animal's (or human's) head is arranged spatially vis-a-vis its body ("the head of the table"), even if this is so metaphorically ("the head of the class/FBI"), and things which represent some characteristic we associate with the head, such as intelligence ("there are a lot of good heads in this company"). These examples are all from English, but only some are possible expressions in other languages (depending on the language). (See Lakoff and Johnson 1980, 1999)
The ancient Greeks had a method for evaluating sexual attractiveness based on the Golden Ratio, part of which included measurements of the head.

teeth

Teeth (singular tooth) are small, calcified, whitish structures found in the jaws (or mouths) of many vertebrates that are used to tear, scrape, and chew food. Some animals, particularly carnivores, also use teeth for hunting or defense. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of tissues of varying density and hardness.
Teeth are among the most distinctive (and long-lasting) features of mammal species. Paleontologists use teeth to identify fossil species and determine their relationships. The shape of the animal's teeth are related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing. Carnivores, on the other hand, need canines to kill prey and to tear meat.
Mammals are diphyodont, meaning that they develop two sets of teeth. In humans, the first set (the "baby," "milk," "primary" or "deciduous" set) normally starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth. Normal tooth eruption at about six months is known as teething and can be painful.
Some animals develop only one set of teeth (monophyodont) while others develop many sets (polyphyodont). Sharks, for example, grow a new set of teeth every two weeks to replace worn teeth. Rodent incisors grow and wear away continually through gnawing, maintaining relatively constant length. The industry of the beaver is due in part to this qualification. Many rodents such as voles (but not mice) and guinea pigs, as well as rabbits, have continuously growing molars in addition to incisors.

beatiful eyebrow

The eyebrow is an area of thick, delicate hairs above the eye that follows the shape of the lower margin of the brow ridges of some[which?] mammals. Their main function is to protect the eye, but they are also important to human communication and facial expression.[1] It is not uncommon for people to modify their eyebrows by means of hair addition or removal, make up, or piercings.


Function

Physical

The main function of the eyebrow is to prevent moisture, mostly salty sweat and rain, from flowing into the eye. The typical curved shape of the eyebrow (with a slant on the side) and the direction in which eyebrow hairs are pointed, make sure that moisture has a tendency to flow sideways around the eyes, along the side of the head and along the nose. The slightly protruding brow ridges of modern humans could also still play a supporting role in this process, in this way it helps them make expressions.[citation needed] Together with the brow ridges, the eyebrows also shade the eyes from sunlight. Eyebrows also prevent debris such as dandruff and other small objects from falling into the eyes, as well as providing a more sensitive sense for detecting objects being near the eye, like small insects.

Psychological

Eyebrows also have an important facilitative function in communication, strengthening expressions, such as surprise or anger. Many makeup artists view eyebrows as a major feature in defining the face. The eyebrows shape the human face and give definition to one's eyes and forehead. Depending on the shape of the eyebrows, it sometimes can cause what is known as a false facial expression (such as a person's eyebrows shaped to seem as if the person was angry, but really isn't).

Identification

In a study published by MIT, where subjects were asked to identify celebrities with either their eyes or their eyebrows digitally edited out, the subjects were able to recognize the celebrity 46% of the time with their eyebrows edited out, compared to 60% of the time with their eyes edited out. The findings indicate the importance of eyebrows in providing cues to an individual's identity.


Although in common usage, the human leg or leg can refer to the entire lower extremity or limb of the human body, including the foot, thigh and even the hip or gluteal region, the precise definition in human anatomy refers to the section of the lower limb extending between the knee and the ankle.
Legs are used for standing, walking, jumping, running, kicking, and similar activities, and constitute a significant portion of a person's mass.
In human anatomical terms, the leg is the part of the lower limb that lies between the knee and the ankle,[6] the thigh is between the hip and knee and the term "lower limb" is used to describe the colloquial leg. This article generally follows the common usage.
The leg from the knee to the ankle is called the cnemis (née'mis) or crus. The calf is the back portion and the shin is the front.

Evolution has provided the human body with two distinct features: the specialization of the upper limb for visually-guided manipulation and the lower limb's development into a mechanism specifically adapted for efficient bipedal gait. While the capacity to walk upright is not unique to humans, other primates can only achieve this for short periods and at a great expenditure of energy. The human adoption to bipedalism is not limited to the leg, however, but has also affected the location of the body's center of gravity, the reorganisation of internal organs, and the form and biomechanism of the trunk. In humans, the double S-shaped vertebral column acts as a shock-absorber which shifts the weight from the trunk over the load-bearing surface of the feet. The human legs are exceptionally long and powerful as a result of their exclusive specialization to support and locomotion — in orangutans the leg length is 111% of the trunk; in chimpanzees 128%, and in humans 171%. Many of the leg's muscles are also adopted to bipedalism, most substantially the gluteal muscles, the extensors of the knee joint, and the calf muscles.

stomach

The stomach lies between the esophagus and the duodenum (the first part of the small intestine). It is on the left upper part of the abdominal cavity. The top of the stomach lies against the diaphragm. Lying behind the stomach is the pancreas. The greater omentum hangs down from the greater curvature.
Two smooth muscle valves, or sphincters, keep the contents of the stomach contained. They are the esophageal sphincter (found in the cardiac region) dividing the tract above, and the Pyloric sphincter dividing the stomach from the small intestine.
The stomach is surrounded by parasympathetic (stimulant) and orthosympathetic (inhibitor) plexuses (networks of blood vessels and nerves in the anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretions activity and the motor (motion) activity of its muscles.
In humans, the stomach has a relaxed, near empty volume of about 45 ml. It is a distensible organ. It normally expands to hold about 1 litre of food, but will hold as much as 2-3 litres(whereas a newborn baby will only be able to retain 30ml).

hair

Hair is an outgrowth of filamentous cells, containing keratin, that grows from follicles found in the dermis. The human body, apart from the palms of the hands and soles of the feet, is covered in follicles which produce thick terminal and fine vellus hair. Most common interest in hair is focused on hair growth, hair types and hair care but hair is also an important biomaterial and the hair follicle is a well studied biological organ.
Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class.[1] Although other non-mammals, especially insects, show filamentous outgrowths, these are not considered "hair" in the scientific sense. So-called "hairs" (trichomes) are also found on plants. The projections on arthropods such as insects and spiders are actually insect bristles, composed of a polysaccharide called chitin. There are varieties of dogs, cats, and mice bred to have little or no visible fur. In some species, hair is absent at certain stages of life. The main component of hair fiber is keratin.
Hair often refers to two distinct structures (1) the part beneath the skin, called the hair follicle or when pulled from the head called the bulb. This organ is located in the dermis and maintains stem cells which not only re-grow the hair after it falls out but also are recruited to regrow skin after a wound[2]; and (2) the shaft, which is considered the part of the hair above the skin surface though it appears first in the epidermis. The hair shaft, in cross-section, can be divided roughly into three zones. Starting from the outside, (1) the cuticle which consists of several layers of flat, thin cells laid out like roof shingles, (2) the cortex which contain the keratin bundles in cell structures that remain roughly rod like and in some cases (3) the medulla, a disorganized and open area at the fibers center[3].

nose

The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils. On average the nose of a male is larger than that of a female.
The nose has an area of specialised cells which are responsible for smelling (part of the olfactory system). Another function of the nose is the conditioning of inhaled air, warming it and making it more humid. Hairs inside the nose prevent large particles from entering the lungs. Sneezing is usually caused by foreign particles irritating the nasal mucosa, but can more rarely be caused by sudden exposure to bright light (called the photic sneeze reflex) or touching the external auditory canal. Sneezing is a means of transmitting infections because it creates aerosols in which the droplets can harbour microbes.

human legs

Although in common usage, the human leg or leg can refer to the entire lower extremity or limb of the human body, including the foot, thigh and even the hip or gluteal region, the precise definition in human anatomy refers to the section of the lower limb extending between the knee and the ankle.
Legs are used for standing, walking, jumping, running, kicking, and similar activities, and constitute a significant portion of a person's mass.
In human anatomical terms, the leg is the part of the lower limb that lies between the knee and the ankle,[6] the thigh is between the hip and knee and the term "lower limb" is used to describe the colloquial leg. This article generally follows the common usage.
The leg from the knee to the ankle is called the cnemis (née'mis) or crus. The calf is the back portion and the shin is the front.

Evolution has provided the human body with two distinct features: the specialization of the upper limb for visually-guided manipulation and the lower limb's development into a mechanism specifically adapted for efficient bipedal gait. While the capacity to walk upright is not unique to humans, other primates can only achieve this for short periods and at a great expenditure of energy. The human adoption to bipedalism is not limited to the leg, however, but has also affected the location of the body's center of gravity, the reorganisation of internal organs, and the form and biomechanism of the trunk. In humans, the double S-shaped vertebral column acts as a shock-absorber which shifts the weight from the trunk over the load-bearing surface of the feet. The human legs are exceptionally long and powerful as a result of their exclusive specialization to support and locomotion — in orangutans the leg length is 111% of the trunk; in chimpanzees 128%, and in humans 171%. Many of the leg's muscles are also adopted to bipedalism, most substantially the gluteal muscles, the extensors of the knee joint, and the calf muscles.

ears

The ear is the organ that detects sound. The vertebrate ear shows a common biology from fish to humans, with variations in structure according to order and species. It not only acts as a receiver for sound, but also plays a major role in the sense of balance and body position. The ear is part of the auditory system.
The word "ear" may be used correctly to describe the entire organ or just the visible portion. In most animals, the visible ear is a flap of tissue that is also called the pinna and is the first of many steps in hearing. In people, the pinna is often called the auricle. Vertebrates have a pair of ears, placed symmetrically on opposite sides of the face. This arrangement aids in the ability to localize sound sources.

Audition is the scientific name for the sense of sound. Sound is a form of energy that moves through air, water, and other matter, in waves of pressure. Sound is the means of auditory communication, including frog calls, bird songs and spoken language. Although the ear is the vertebrate sense organ that recognizes sound, it is the brain and central nervous system that "hears". Sound waves are perceived by the brain through the firing of nerve cells in the auditory portion of the central nervous system. The ear changes sound pressure waves from the outside world into a signal of nerve impulses sent to the brain.
Anatomy of the human ear. The length of the auditory canal is exaggerated for viewing purposes.
The outer part of the ear collects sound. That sound pressure is amplified through the middle portion of the ear and, in land animals, passed from the medium of air into a liquid medium. The change from air to liquid occurs because air surrounds the head and is contained in the ear canal and middle ear, but not in the inner ear. The inner ear is hollow, embedded in the temporal bone, the densest bone of the body. The hollow channels of the inner ear are filled with liquid, and contain a sensory epithelium that is studded with hair cells. The microscopic "hairs" of these cells are structural protein filaments that project out into the fluid. The hair cells are mechanoreceptors that release a chemical neurotransmitter when stimulated. Sound waves moving through fluid push the filaments; if the filaments bend over enough it causes the hair cells to fire. In this way sound waves are transformed into nerve impulses. In vision, the rods and cones of the retina play a similar role with light as the hair cells do with sound. The nerve impulses travel from the left and right ears through the eighth cranial nerve to both sides of the brain stem and up to the portion of the cerebral cortex dedicated to sound. This auditory part of the cerebral cortex is in the temporal lobe.
The part of the ear that is dedicated to sensing balance and position also sends impulses through the eighth cranial nerve, the VIIIth nerve's Vestibular Portion. Those impulses are sent to the vestibular portion of the central nervous system. The human ear can generally hear sounds with frequencies between 20 Hz and 20 kHz (the audio range). Although the sensation of hearing requires an intact and functioning auditory portion of the central nervous system as well as a working ear, human deafness (extreme insensitivity to sound) most commonly occurs because of abnormalities of the inner ear, rather than the nerves or tracts of the central auditory system.[1]

eyes

Eyes are organs that detect light, and send electrical impulses along the optic nerve to the visual and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system.[1] Image-resolving eyes are present in molluscs, chordates and arthropods.[2]
The simplest "eyes", such as those in unicellular organisms, do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment.

mouth

Amouth smile is the facial expression that most engages others. With the help of the teeth — which provide structural support for the face muscles — the mouth also forms a frown and other expressions that show on your face.
The mouth also plays a key role in the digestive system, but it does much more than get digestion started. The mouth — especially the teeth, lips, and tongue — is essential for speech. The tongue, which allows us to taste, also helps form words when we speak. The lips that line the outside of the mouth both help hold food in while we chew and pronounce words when we talk.

With the lips and tongue, teeth help form words by controlling air flow out of the mouth. The tongue strikes the teeth as certain sounds are made.
The hardest substances in the body, the teeth are also necessary for chewing (or mastication) — the process by which we tear, cut, and grind food in preparation for swallowing. Chewing allows enzymes and lubricants released in the mouth to further digest food.
Here's how each aspect of the mouth and teeth plays an important role in our daily lives.