Head Anatomy: Cranium, Face, Muscles

• The head sits superior to the neck and rests upon the cervical vertebrae
• It consists of the cranium, soft tissues, and internal structures
• The cranium houses the cranial cavity, which contains the brain
• The head is divided into the neurocranium (bony box surrounding the brain) and the viscerocranium (the face)
• Viscerocranium contains organs such as the lacrimal glands, eyes, and salivary glands

Facial Muscles

• Muscles of the face are separated into muscles of facial expression and muscles of mastication
• Facial expression muscles move the skin to express emotions and are innervated by a specific cranial nerve
• Mastication muscles, such as the masseter, move the mandible for chewing, and are innervated by a different cranial nerve

Mid-Sagittal Section Anatomy

• A mid-sagittal section reveals internal facial structures, including the nasal cavity (for airflow to the lungs)
• The nasal cavity warms and humidifies air before it reaches the lungs, aided by bony shapes covered in vascularized mucosa
• The nasal cavity extends further back than expected
• The opening of the middle ear is located at the back of the nasal cavity (nasopharynx) and equalizes pressure in the ear
• Sinuses within the facial bones may humidify air, lighten the face, or affect voice characteristics
• Tonsils, like the pharyngeal (adenoid) tonsil, are part of the immune system and monitor the entrance into the body

Nose and Nasal Cavity

• The nose's shape is primarily formed by cartilage, with bone extending only partway
• The nasal cavity is divided into left and right spaces, each connected to a nostril
• Inflammation in the nasal cavity can cause swelling and blockage due to vasodilation
• Mucosa in the nasal cavity produces mucus (snot) to protect the lining

Oral Cavity

• The bone separating the nasal cavity from the oral cavity is the hard palate
• When the mouth is closed, the tongue fills the oral cavity
• The hard palate transitions into the soft palate, ending in the uvula
• The soft palate elevates during swallowing to separate the oral cavity from the nasal cavity, preventing food/drink from entering the nasal passage
• The tongue is a muscular structure covered in mucosa, containing special sensory cells for taste, temperature, and pain
• Muscles inside the tongue can change its shape and move the bolus of food in your mouth to help you chew and also clean your teeth
• Upper teeth reside in the maxilla, while the lower teeth are in the mandible, all contributing to inital stage digestion

Tonsils and Salivary Glands

• Tonsils, including the lingual and palatine tonsils, are part of the immune system
• Salivary glands (parotid, submandibular, and sublingual) produce saliva for digestion, each secreting into the oral cavity

Eye Anatomy

• The eye resides within the bony orbit and is moved by extraocular muscles anchored in the orbit
• The retina at the back of the eye senses light, with the macula providing high-density vision
• Intraocular muscles control pupil dilation/constriction and change the shape of the lens for focusing
• The anterior surface of the eye is kept moist by the lacrimal gland, which secretes tears that sweep across the eye and drain into the nasal cavity via the nasolacrimal duct

Ear Anatomy

• The external ear (fibrocartilaginous shape) has the external auditory meatus, containing the tympanic membrane which is sensitive to vibrations
• The middle ear is on the other side of tympanic membrane and contains tiny bones that transmit vibrations to the cochlea
• The inner ear has the cochlea, which has a long sheet with specialized neurons, and the semicircular canals (arranged on three axes)
• As you rotate your head, the fluid in semicircular canals moves which deflects hair cells and sends signals to the brain, telling the brain how your heads moving
• This mechanism helps keeps your eyes fixed on an object as you move your head

Blood Supply to the Head

• The internal jugular vein drains most of the blood from the head and brain
• The common carotid artery divides into the external carotid (to the face) and internal carotid (to the brain) arteries
• Two vertebral arteries also supply blood to the brain

Brain and Meninges

• Removing the skull cap reveals the dura mater, a thick connective tissue covering the brain
• The arachnoid mater lies under the dura mater, and the pia mater is the thin layer covering the brain, with arteries and veins in the subarachnoid space
• The dura mater consists of two layers, which separate in some places to form dural venous sinuses

Brain Structure and Lobes

• The brain is regionalized to give the brain more processing power
• The cerebrum is the largest part of the brain and is divided into lobes, consisting of the cerebral cortex(outside layer and highly folded with gyri and sulci to increase surface area), gray matter (neuronal cell bodies), and white matter
• Lobes - frontal, temporal, parietal, occipital
• The cerebellum, located on the posterior and inferior aspect of the cerebrum, is involved in movements and coordination
• The brainstem connects the cerebral hemispheres to the spinal cord, it maintains basic autonomic functions and consist of the medulla oblongata, pons, and midbrain

Cranial Nerves

• Cranial nerves emerge from the brainstem
• They connect to structures in the head which control those structures
• There are 12 cranial nerves that pass anteriorly or inferiorly to structures of the face/beyond to drive a motor function in a structure, or collect a sensory something from a structure
• Foramina are holes in the cranial cavity where these cranial nerves exit the brain

Cerebrospinal Fluid

• Ventricles create cerebral spinal fluid (CSF)
• The brain is floating in CSF, which cushions the brain to reduce force exerted on structures inferior to it