Head and neck anatomy
This article describes the anatomy of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat.The head rests on the top part of the vertebral column, with the skull joining at C1 (the first cervical vertebra known as the atlas).The skeletal section of the head and neck forms the top part of the axial skeleton and is made up of the skull, hyoid bone, auditory ossicles, and cervical spine.The (exocrine) glands secrete saliva for proper mixing of food and provides enzymes to start chemical digestion.Saliva is composed primarily of water, ions, salivary amylase, lysozymes, and trace amounts of urea.[citation needed] They line the oral, nasal, and external auditory meatus, (ear), providing lubrication and protection against pathogens.Specialized glial cells called astrocytes form a tight junction or protective barrier around brain blood vessels and may be important in the development of the BBB.Blood from the brain and neck flows from: (1) within the cranium via the internal jugular veins, a continuation of the sigmoid sinuses.There is the formation of an extensive network of nerve groups or tracts attaching to the spinal cord in arrangements called rami or plexus.The sensory branches of spinal nerves include: lesser occipital, C-2, great auricular, (C-2 and C-3); transverse cervical, C-2 and C-3; and supraclavicular, C-3 and C-4.Damage to a person's spinal cord above C-5 may result in respiratory arrest and death if medicinal aid does not intervene.Twelve pairs of cranial nerves emerge from the brain; these affect movements and sensation, and some special organs such as hearing of parts of the head and neck.In the neck are the thyroid and parathyroid glands, that secrete hormones that control metabolism and blood calcium levels.The respiratory system begins in the head and neck, with air entering and leaving the body through the mouth and nose.A critical junction between the respiratory and digestive systems is the epiglottis, a cartilage flap which shuts during swallowing to prevent aspiration.The epiglottis is normally open to support respiration and shuts during swallowing to prevent food and fluids from entering the trachea, activating the gag reflex or initiates the choking mechanism.For example, a person suffering from the eating disorder, bulimia nervosa may show signs of excessive tooth and gum erosion.Anaphylactic shock requires advanced medical care immediately; but other first aid measures include rescue breathing (part of CPR) and administration of epinephrine using an EpiPen for immediate administration of epinephrine (adrenaline) to reverse swelling and to keep the respiratory airway (trachea) open.
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