Head
From Freepedia
- For other uses of the word head, see head (disambiguation).
In anatomy, the head of an animal is the anterior part (from anatomical position) that comprises the mouth, the brain and various sensory organs (e.g. organs of sight, hearing, smell and taste).
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Bilateral symmetry
The very simplest animals do not have a head, but many bilaterally symmetric forms do. In vertebrates the contents of the head are protected by an enclosure of bone called the skull, which is attached to the spine. The front of the primate head is called the face.
Anatomy
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The front (ventrum) of the head, where the eyes and ears and mouth are located, is called the face. The area above the eyes is called the forehead (the front of the head). Below the mouth is the chin. Younger aged humans and some older humans heads have a continuing growing layer of hair covering the head. Most females of the human race do not lose this covering during the aging process, however some males can lose their head hair as they grow older.
Many animals have horns or tusks protruding from their head.
In most complex animals the head is joined to the rest of the body by the neck.
Human head anatomy
Basic osteology
The bones of the human head is collectively called the skull. The skull is divided into the cranium (all the skull except the mandible) and the mandible or jawbone. One feature that distinguishes mammals and non mammals is that there are also three ear bones (called ossicles) -
These ossicles are important components in the sense of hearing in mammals. Other animals have a single bone that is usually called the columella.
The cranium can be divided into a calvarium (a skull cap) and a cranial base. The cranium consists of several bones which fuse together at junctions called sutures. This process occurs in utero to protect the most important organ in the body - the brain. Although most fusing is complete before birth, there are large areas where this in incomplete until puberty. These areas are called fontanelles and one particularly easily palpable one is present in the area just above the forehead in newborn babies and young children. Fontanelles are areas of fibrous tissue.
The differentiated parts of the adult cranium are separated as
- 2 (one on each side of the head) maxillae. This bone covers an area inferior and medial (click anatomical position for explanations to what these terms mean) to the eye socket or orbit.
- 2 zygomatic bones, inferior and lateral to the orbit.
- 2 temporal bones, covering an area where the ears are located
- a frontal bone, superior to the orbit
- 2 parietal bones, posterior to the frontal bone and superior to the temporal bone
- an occipital bone at the back of the head
- several more internal bones which are not easily seen which are
- a sphenoid
- an ethmoid
- 2 lacrimal bones
- 2 nasal bones
- 2 palatine bones
- 2 nasal conchae (inferior)
- a vomer
an area where several sutures join up is called a pterion.
The rest of the skull is the mandible, a bone attached to the cranium at the temporalmandibular joint (TMJ). This is an important joint which allows the mandible to move, using the TMJ as a pivot, and so achieve certain actions such as chewing (mastication), eating and speech.
When viewed from below, (inferiorly), the skull contains several holes, by far the biggest of which is the foramen magnum, where the spinal cord passes through. Other holes allow for arteries, veins, and nerves (the cranial nerves) to pass through. When the skull cap or calvarium is removed the base of the skull is viewed from above, there are three clear impressions or fossa.
The most anterior of these is the anterior cranial fossa, where, amongst other things, the frontal lobe of the brain would lie on. The middle cranial fossa is the second most anterior depression, shaped like a butterfly. The wings are where the temporal lobes of the brain lie. The body of the butterfly houses an important structure, the sella turcica(Latin, Turkish saddle), also know as the pituiary fossa or the hypophyseal fossa. This is where the pituitary gland, the major player in the endocrine system, rests. The posterior cranial fossa is where the foramen magnum is located and where the posterior lobe of the brain and the cerebellum lie.
The face
The face is anatomically considered to strech from the point of the chin to the roots of hair. The skin is quite pliable and loose. Wounds tend to bleed quite freely as there is no deep fasia.
There are three orifices on the face - the two eyes and the mouth
The blood supply to the face and indeed the most of the scalp comes mainly from the external carotid artery.
The sensory supply to the face comes solely from the trigeminal nerve (fifth cranial nerve). There are three divisions to this nerve,
- the opthalmic division, which covers an area superior to the eye, forehead and most of the nose.
- the maixillary division, which covers an area inferior to the eye but above the mouth, the cheeks and some of the nose
- the mandibular division, which covers an area inferior to the mouth but also lateral to the cheeks all the way until the ears. This area does not cover the mandibular angle (the protrusion on the jawbone)
The muscles in the face are
- the frontal part of the occipitofrontalis muscle. This muscle is a large muscle which contains two parts, the occipital part and the frontal part (also just simply known as frontalis and occipitalis). Although the two muscles are separate and supplied by different nerves, they are connected by an aponeurosis (fibromuscular tissue) which stretches across the top half of the head and forms what is known as the scalp. The aponeurosis is also known as the galea aponeurotica, or aponeurosis of Galen and this arrangement of two different muscles attached together is called a digastric muscle.
- -the muscle is attached to the skin of the forehead and eyebrow anteriorly and the superior nuchal line posteriorly.
- -the muscle's frontal belly is supplied by the temporal nerve, a branch of the facial nerve (cranial nerve VII) and the occipital belly by the posterior auricular, also a branch of the facial nerve.
- -the action of the muscle is to wrinke the forehead and raise the eyebrow.
- Nasal muscles
- The mouth muscles
- Zygomatic muscles
Cultural import
People who are more intelligent than normal are sometimes depicted in cartoons as having bigger heads, as a way of indicating that they have more brains; in science fiction, an alien having a big head is often symbolic of high intelligence. However, minor changes in brain size do not have much affect on intelligence in humans.
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.
In English slang, sometimes a boastful individual is said to have a "big head."
Clothing
Unlike other parts of the body clothing is most often not worn on the head. The most common headwear is a hat. This may be either a woolen hat, designed to keep the head warm or a baseball cap, to protect against the sun. In some african and asian cultures a turban is worn by men the same way. Women from islamic cultures sometimes wear veils which cover the face. These two items are may be religiously mandatory.
Hoods or balaclavas are designed mainly to keep the neck warm but may also hide the face. Wearing of non-religious clothing that hides the face when not climatically necessary is often considered very offensive to strangers, because it affords the wearer a threatening anonymity. Terrorist or violent rebel organisations are sometimes famed for wearing balaclavas or other face covering material,such as a bandana.
Pseudoscientific study of the human head
Because the human head is the location of the thinking organ, it has been the subject of intense study. Some of the early modern research on the human head by German physician Franz Joseph Gall has resulted in the pseudoscience of phrenology, which reached its peak in the 19th century. It attributes character traits and mental abilities to the shape of the head. The measurement of the human head and skull, known as craniometry, gained popularity at the same time. Some, notably in Nazi Germany, have used these measurements and other comparative research as the underpinnings of racist, pseudoscientific theories.
The procedure of trepanation has also been advocated and practiced for pseudoscientific reasons.
References
- Mike Hunt, Human Evolution: An Introduction to Man's Adaptations, 4th edition
