Head and Neck

22 03 2015
  • Skeletal

The scull comprises the cranium and mandible . It houses and protects the brain and the eyes, ears, nose, and mouth. It encloses the first parts of the airway and of the alimentary canal, and provides attachment for the muscles of the head and neck.

Movements of these bones by the attached muscles of the head provide for facial expressions, eating, speech, and head movement.

The skull consists of 22 cranial and facial bones, which, with the exception of the mandible, are tightly fused together. The skull encases and protects the brain as well as the special sense organs of vision, hearing, balance, taste and smell.

The skeletal section of the head and neck forms the superior segment of the axial skeleton and comprises skull, hyoid bone, auditory ossicles, and cervical spine. The skull can be further subdivided into:head and neck

(a) cranium (8 bones: frontal, 2-parietal, occipital, 2-temporal, sphenoid, ethmoid), and
(b) facial bones (14 bones: 2-zygomatic, 2-maxillary, 2-palatine, 2-nasal, 2-lacrimal, vomer, 2-inferior conchae, mandible).

As the fetus develops, the facial bones usually form into pairs, and then fuse together. As the cranium fuses, sutures are formed that resemble stitching between bone plates.

In a newborn, the junction of the parietal bones with the frontal and occipital bones, form the anterior (front) and posterior (back) fontanelle, or soft spots. The separation of the cranial bone plates at time of birth facilitate passage of the head of the fetus through the mother’s birth canal, or pelvic girdle. The parietal bones, and occipital bone can overlap each other in the birth canal, and form the unusual looking “cone head” appearance in a newborn when delivered in a natural, or vaginal, delivery.

  • Muscular

The muscles of the head and neck perform many important tasks, including movement of the head and neck, chewing and swallowing, speech, facial expressions, and movement of the eyes. These diverse tasks require both strong, forceful movements and some of the fastest, finest, and most delicate adjustments in the entire human body.

The muscles of the face have very important functions. They open and close the apertures in our faces-eyes, noses, and mouths. They also  play an extremely important role in communication, and this is why this muscles are often known collectively  as “the muscles of facial expression.” These muscles are attached to bone at one end ,and skin at the other . It is these muscles that allow us to raise our eyebrows in surprise, frown ,or knit our brows in concentration, to scrunch up our noses in distaste to smile gently  or grin widely , and to pout. As we age and our skin form creases, and wrinkles, these reflect the expressions we have used throughout our lives. The wrinkles and creases lie perpendicular to the direction of the underlying muscle fibers.

The muscle of mastication (chewing) attach from the skull to the mandible (jawbone), operating to open an shut the mouth and o grind the teeth together to crush the food we eat. Human jaws don’t just ope and close , they also move from side to side.

In the head we see the soft palate, tongue pharynx ,and larynx, all of which contain muscles. The soft palate comprises five pair of muscles . When relaxed it hangs down at the back of the mouth but during swallowing it thickens and is drawn upward to block off the airway. The tongue is a great mass of muscle , covered in mucosa.

The pharyngeal muscles are important  in swallowing , and the laryngeal muscles control the vocal corde.

neck-face-musculor                      transverse section of the neck

  • Nervous

Compared to other animals humans  have massive brains for the size of our bodies. The human brain has grown larger and large over the course of evolution , and it is now so overblown that the frontal lobes of the brain lie right over the top of the orbits that contain the eyes. The lobes that make up each cerebral hemisphere are the frontal, parietal , temporal and occipital  lobes. The brain looks like a large pinkish grey , wrinkled walnut especially when viewed  from above . The outer layer of gray matter , called the cortex is highly folded. Underneath the brain we some other detail, including some of the cranial nerves that emerge from the brain itself. The brain is the most complicated organ in human body. Its true complexity is visible only through a microscope  revealing billions of neurons that connect with each other to form the pathways that carry our senses , govern our actions, and create our minds.

The largest part of the brain , the cerebrum, is almost completely divided into two cerebral hemispheres . This division is clearly seen when viewing the brain from the front ,back or top. The fissure between the hemispheres runs deep, but at the bottom of it lies the corpus callosum  which forms a bridge from two sides.

The brain is protected by three membranes called the meninges . The tough dura mater layer is the outermost covering, which surrounds the brain and the spinal corde. Under the dura mater is the cobweblike   arachnoid matteranatomy-of-the-human-brain-1  layer. The delicate pia mater is a thin membrane on the surface of the brain. Between the pia mater and thearachnoid mater there is a  slim gap -the subarachnoid space-which contains cerebrospinal fluid (CSF). CSF flows through the third ventricle into the fourth , where it can escape via small apertures into the subarachnoid space.

The 1 pair of cranial nerves emerge from the brain and brain stem, leaving through holes or “foramina” in the base of the skull. Some nerves are purely sensory  some have just motor functions , but most contain a mixture of motor and sensory fibers. A few also contain autonomic nerve fibers.

  • Respiratory

When we take a breath air is pulled in through our nostrils into the nasal cavities.Here the air is cleaned, warmed and moistened before its onward journey.The nasal cavities are divided by the thin partition of the nasal septum , which is composed of plates of cartilage and bone. The lateral walls of the nasal cavity are more elaborate with bony curls that increase the surface area over which the air flows. The nasal cavity is lined with mucosa , which producesMidsagittal-section-of-the-head-and-neck mucus . This often undervalued substance does an important job of trapping particles and moistening in the air . The nasal sinuses also lined with mucosa  open via tiny orifices into the nasal cavity.

The main vessels supplying oxygenated blood to the head and neck are the common carotid and vertebral arteries.The vertebral artery runs up through holes in the cervical vertebrae and eventually enters the skull through the foramen magnum . The common caretid artery runs up the neck and divides into two-the internal carotid artery suppliesthe brain and the external  carotid artery gives rise to a profusion of branches.

  • Cardiovascular 

The brain has a rich blood supply , which arrives via the internal carotid and vertebral arteries . The vertebral image024arteries join together to form the basilar artery. The internal carotid arteries and basilar artery join on the undersurface of the brain to form the Circle of Willis. From there three pairs of cerebral arteries make their way into the brain . The veins of the brain and the skull drain into venous sinuses , which are enclosed within the dura mater and form grooves on the inner surface of the skull. The sinuses join up and eventually drain out of the base of the skull, into the internal jugular vein.

  • Digestive

The mouth is the first part of the digestive tract, and it is here that the processes of mechanical and chemical digestion get underway. Your teeth grind each mouthful and you have three pairs of major  salivary  , glands-parotid, submandibular , and sublingual , that secrete saliva through ducts into the mouth. Saliva contains digestive enzymes that begin to chemically break down the food in your mouth. The tongue manipulates the food and also has taste buds that allow you to quickly make the important distinction between delicious food and potentially harmful toxins.

Resource: the complete human body encyclopedia

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