Head Anatomy: Cranium, Face, and Muscles

Head Anatomy Overview

• The head sits superior to the neck and cervical vertebrae.
• It comprises the cranium and associated soft tissues, including the brain within the cranial cavity.
• The head is divided into the neurocranium (bony box surrounding the brain) and the viscerocranium (the face, containing organs like eyes and salivary glands).

Facial Muscles and Innervation

• Muscles of facial expression move the skin to express emotions and are innervated by a specific cranial nerve.
• Muscles of mastication move the mandible for chewing and are innervated by a separate cranial nerve.

Mid-Sagittal Section of the Face

• A mid-sagittal section reveals the nasal cavity, extending further back than expected, primarily for airflow to the lungs.
• The nasal cavity contains bony shapes covered in vascularized mucosa to warm and humidify air before it reaches the lungs.
• The opening at the back of the nasal cavity connects to the middle ear, allowing pressure equalization.
• Sinuses in the facial bones contribute to humidifying air, lightening the face, and influencing voice characteristics.

Tonsils and the Immune System

• Tonsils (pharyngeal/adenoid tonsils) are part of the immune system, monitoring the entrance to the body for infections.
• The nose's shape is largely formed by cartilage, with a divider creating separate left and right nasal cavities.
• Inflammation in the nasal cavity can cause swelling, blocking airflow, and leading to mucus production by the mucosa.

Oral Cavity and Palate

• The oral cavity space is mostly filled by the tongue when the mouth is closed.
• The hard palate (bone covered in mucosa) separates the nasal and oral cavities.
• The soft palate (muscle ending in the uvula) elevates during swallowing to prevent food/drink from entering the nasal cavity.

Tongue and Swallowing

• The tongue is a muscular structure attached internally, covered in mucosa with sensory cells for temperature, pain, touch, and taste.
• Tongue muscles move in various directions, aiding chewing and cleaning teeth.

Teeth and Salivary Glands

• Teeth are located around the mandible (lower) and maxilla (upper).
• Salivary glands (parotid, submandibular, sublingual) secrete saliva into the oral cavity, initiating digestion.
• The parotid salivary gland has a duct that runs through the cheek into the oral cavity.

Pharynx

• The nasal cavity connects to the nasopharynx posteriorly, while the oral cavity connects to the oropharynx.

Eye Anatomy

• The eye resides in the bony orbit, moved by extraocular muscles anchored to structures in the orbit.
• Intraocular muscles control pupil dilation/constriction and lens shape for focusing on near/far objects.
• The lacrimal gland secretes tears, sweeping across the eye and draining into the nasal cavity via the nasolacrimal duct.
• The retina is at the back of the eye and senses light.
• The macula focuses the densest vision.

Ear Anatomy

• The external ear's fibrocartilaginous structure, with the external auditory meatus leading to the tympanic membrane.
• The tympanic membrane vibrates in response to sound, transmitting vibrations to tiny bones in the middle ear.
• These bones pass vibrations to the cochlea, a snail-shell-like structure with specialized neurons that perceive sound at different pitches.
• Semicircular canals with fluid and hair cells detect head rotation, aiding balance and eye fixation.
• The ear is divided into 3 parts: external ear, middle ear, and inner ear.

Blood Supply to the Head

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

Meninges and Brain Protection

• The brain is covered by three connective tissue layers called meninges: dura mater, arachnoid mater, and pia mater.
• Dura mater consists of 2 layers, with dural venous sinuses in between.
• Dura mater is a thick, tough covering that supports the brain, arachnoid mater is deep to that, and pia mater, a thin layer, covers the brain.
• Arteries and veins in the subarachnoid space supply blood to the brain.

Cranial Cavity and Pressure

• The rigid cranial cavity requires blood to be at a higher pressure to enter and supply the brain.
• Additional masses (blood, tumors, abscesses) increase pressure within the cranial cavity.

Brain Structure

• The cerebrum, consisting of lobes (frontal, temporal, parietal, occipital), has a cortex with gray matter (neuronal cell bodies and connections) and medulla.
• Gyri and sulci increase the surface area of the cortex, providing more gray matter and complexity.

Cerebellum and Brainstem

• The cerebellum coordinates movements, containing more neurons than the cerebrum.
• The brainstem connects the cerebral hemispheres to the spinal cord and controls basic autonomic functions (breathing, heart rate, blood pressure, consciousness).
• The brainstem consists of the medulla oblongata, pons, and midbrain.

Cranial Nerves

• Cranial nerves emerge from the brainstem, innervating structures in the head and face (e.g., eye movement, taste, salivary glands, facial muscles).
• Examples include the optic, trigeminal, facial, and hypoglossal nerves.
• The vagus nerve extends to the thorax and abdomen, while the accessory nerve innervates the trapezius muscle.
• Cranial nerves pass through foramina (holes) in the cranial cavity bones to reach their targets.

Cerebrospinal Fluid (CSF)

• The brain floats in cerebrospinal fluid (CSF) within the meninges, reducing its weight and pressure on inferior structures.
• CSF is produced in the ventricles by the choroid plexus and circulates through the brain and spinal cord.
• The fluid helps cushion and protect the nerves and arteries that supply blood to the brain.