Head and Neck Anatomy

• Introduction to the head, neck region, and cranial nerves
• Lecture by Prof. J. Ahenkorah

Objectives of the Lecture

• Appreciate the major structures and parts of the head and neck
• Examples include osteology, muscles, glands, nasal cavity, pharynx, larynx, and oral cavity
• Recognize specializations in this region
• Communication (vocal, facial, etc.)
• Special sensory organs for smell, vision, hearing, balance, and taste, along with general sensation
• Respiration
• Mastication and deglutition
• Protection of vital organs
• Defense including the lymphatic system
• Endocrine functions
• The head and neck region is anatomically difficult.
• It is a relatively small area packed with important structures.
• It is associated with proximal ends of the GIT and respiratory systems.
• It is also associated with special sense organs, vessels, and cranial nerves

The S.C.A.L.P

• This is the soft tissue that envelops the cranial vault.
• It extends from the external occipital protuberance and superior nuchal line to the supraorbital margins.
• The superficial fascia of the scalp is dense and firm.
• The fascia has fibroadipose tissues.
• The fascia is closely adherent to the skin and underlying structures, including the epicranial aponeurosis
• Laterally, the fascia is prolonged into the temple where it is loose in texture
• See the zygomatic arch

Layers of the Scalp

• Skin: Thick, with hair and numerous sebaceous glands.
• Connective Tissue: Dense connective tissue with collagen fibers attached to the outer walls of blood vessels and nerves.
• Aponeurosis: A.k.a. "Galeal Aponeurosis"
• Loose Areolar Region: Periosteum/Pericranium; this is the "Danger Area"
• Loose Areolar Tissue Zone allows infections to pass into the cranial cavity through emissary veins.
• The Skin, Connective Tissue, and Aponeurosis layers form a unit that can pull off the loose areolar layer.
• Lacerations to the scalp can result in profuse bleeding and gaping of wounds

Cutaneous Nerves

• Cutaneous nerves like supraorbital, supratrochlear, auriculotemporal, greater, lesser occipital, and third occipital supply different parts of the head.

Osteology

• This is the study of the skull, cranium, and mandible
• Also includes Cervical Vertebrae.
• Parts of the skull include the atlas and axis.
• Also includes the vertebra prominence and other reference points

The Skull

• It is composed of 28 bones, most of which are paired
• It includes a calvarium and a delicate facial skeleton.
• The inferior margin of the orbit and the superior margin of the external acoustic meatus of both sides of the cranium lie in the same horizontal plane called the orbitomeatal plane.
• Emissary veins are valveless veins that normally drain external veins of the skull into the dural venous sinuses
• Diploe is soft, spongy, or cancellated substance between the plates of the skull.

The Pterion

• This is the region where the frontal, parietal, squamous temporal, and greater wing of the sphenoid bones meet
• The relation is to the middle meningeal vessels nearby
• Bleeding from the middle meningeal vessels results in extradural/epidural hemorrhage.
• CEPHALHEMATOMA?
• CAPUT SUCCEDANEUM

Nasal Cavity and Paranasal Sinuses

• Requires the Osteology of the nasal cavity
• Related to the communications in external environment, nasopharynx, paranasal air sinuses, lacrimal apparatus
• Responsible for the functions of respiration, smell, and protection

The Neck Fascia

• The neck extends from the base of the cranium and the inferior border of the mandible to the thoracic inlet.
• The superficial fascia contains adipose tissue and the platysma muscle.
• The deep cervical fascia is divided into investing, pretracheal, and prevertebral layers.
• These layers define various potential spaces, above and below the hyoid bone.
• Infections can spread between the head and neck and between the tissue spaces of the face and mediastinum.
• Facial layers surround muscles of the neck to some degrees.
• A condensation of the deep fascia, or Carotid sheath, surrounds the common and internal carotid arteries.
• The sheath also surrounds the internal jugular vein, vagus, and ansa cervicalis.

Oral Cavity

• Design includes feeding, protection, mastication, and swallowing
• Requires Muscles, including the temporomandibular joint (TMJ) and teeth
• Related to communication (verbal and social)
• Contents includes tongue and salivary glands
• Connected to the pharynx and external environment

Muscles of Facial Expression

• Includes major social muscle, and muscles of communication
• Includes the orbicularis oculi and oris
• Includes the occipitalis and frontalis, platysma, and risorius
• Includes the Zygomaticus major and minor and mentalis
• Includes the levator labii superioris alaeque nasi, etc.

Muscles of Mastication

• Includes the Temporalis, Masseter, Lateral Pterygoid and Medial Pterygoid and Digastric

Glands of Head and Neck

• Includes the pituitary and lacrimal glands
• The salivary glands are included
• The thyroid and parathyroid glands are included
• Includes the superior and inferior glands
• Minor salivary glands are included

Lymphatics of Head and Neck

• Extensive everywhere, except the brain and the cornea
• Superficial lymphatics ring-occipital, preauricular (parotid), submandibular and submental
• DEEP or inner ring LYMPHATICS
• Lymphatic aggregations include pharyngeal tonsil (adenoids), tubal tonsils, lingual tonsil, Palatine tonsils.

Cranial Nerves

• Objectives include the ability to identify them and differentiate partial or full functional loss.
• There are 12 pairs of cranial nerves
• They are numbered with Roman numerals in a rostrocaudal sequence
• Some are functionally either purely sensory or purely motor.
• Others are functionally mixed.
• Some nerves carry pre- or post-ganglionic parasympathetic fibres
• These are secretomotor to salivary and lacrimal glands, or even motor to smooth muscle within the eyeball

The 12 Cranial Nerves

• CN I - Olfactory n.
• CN II - Optic n.
• CN III - Oculomotor n.
• CN IV - Trochlear n.
• CN V - Trigeminal n.
• CN VI - Abducens n.
• CN VII - Facial n.
• CN VIII - Vestibulocochlear n.
• CN IX - Glossopharyngeal n.
• CN X - Vagus n.
• CN XI - Accessory n.
• CN XII - Hypoglossal n.

Cranial Nerve I: Olfactory

• Responsible for Smell (Sensory)
• The sensory receptors are in the roof of the nasal cavity
• Olfactory Tract, to the brain direct instead of ending in thalamus
• Responsible for the social relations of emotions
• Responsible for hunger/apetite
• Sexual attraction or repulsion, body scent, perfume industry
• Protection (Defensive mechanism) and survival
• Detection of Narcotics etc (Dogs)
• Related to the loss of smell and related problems

Cranial Nerve II: Optic

• Vision (Sensory)
• Retina, Receptors (Rods and Cones), Bipolar Neurons, Ganglion (Multipoloar Neurons)
• Optic Nerve to the Thalamus
• Visual Cortex
• Responsible for Appreciation of Colour, Depth, Dimensions, Position, Height, Speed, etc.
• Also linked to Attraction and repulsion
• Also linked to Protection/Survival and Integrated with Smell, Sound, Touch, and Balance
• Related to the loss of vision

Cranial Nerve III: Oculomotor

• Motor to all extraocular muscles except the lateral rectus and superior oblique
• Motor to eyelid muscles, levator palpebral superioris
• Motor to intrinsic muscles, constrictor pupillae
• Ciliaris - relaxing the lens
• Damage results in the paralysis of ocular muscles
• including Squint (Strabismus) and Diplopia
• May also result in the paralysis of eyelid muscles like dense ptosis
• May additionally lead to dilation of pupils and blurred vision

Cranial Nerve IV: Trochlear

• Supplies the superior oblique muscle, helps to look down and out.
• Damage results in double vision and focusing difficulty
• Head movement to accommodate defect

Cranial Nerve V: Trigeminal

• V1 Ophthalmic - Skin above lateral angle of eye, cornea
• V2 Maxillary - Between Angle of Eye And Angle Of Mouth
• V3 Mandibular - Below Angle of Mouth (Sensory)
• Muscles of Mastication (Motor) Other Muscles (Tensor Veli Palatini; Tensor Tympani; Mylohyoid; Anterior Belly of Digastric)

Cranial Nerve VI: Abducent

• Distributed to lateral rectus
• Damage causes Squint (Strabismus)
• Double Vision and Blurred vision

Cranial Nerve VII: Facia

• It Supplies All Exocrine Glands Of The Head Except The Parotid Gland (Superior Salivary Nucleus)
• Is Primarily Responsible Muscles of Facial Expression. Additionally is responsible for the sensation of
• Taste, anterior 2/3 of tongue, part of external ear
• Damage To Facial Nerve/Nucleus

Cranial Nerve VIII: Vestibulo-Cochlea

• Connected to the Cochlea Apparatus and Semicircular Canals.
• Controls hearing, balance. Note That This Nerve Travels With Facial Nerve In The Internal Auditory Meatus
• Lesion In This Region Would Affect All Three Nerves (6 Functional Components)

Cranial Nerve IX: Glossopharyngeal Nerve

• Sensation of stylopharyngeus, visceral sensation pharynx
• Supplies The Parotid Gland (Inferior Salivary Nucleus)
• Provides sensation of Taste to Posterior 1/3 Of Tongue
• General Sensation, Posterior 1/3 Of Tongue

Cranial Nerve X: Vagus

• Dorsal Vagal Nucleus is responsible for
• Parasympathetic Distribution To Neck, Thorax; Abdomen Up To Proximal 2/3 Of Transverse Colon
• Additionally it is related to the pharyngeal and laryngeal muscles and the Visceral Afferents From Regions Of Parasympathetic Distribution.
• Relays Taste To Part Of Root Of Tongue and Part Of The External Auditory Meatus

Cranial Nerve XI: Accessory Nerve

• This nerve is a composite nerve of two parts: -- The cranial accessory is distributed through the vagus to to the palato-glossus and some muscles of the larynx and pharynx -- The spinal accessory supplies the sternocleidomastoid and trapezius muscles

Cranial Nerve XII: Hypoglossal

• Supplies All Muscles Of The Tongue Except The Palato - Glossus
• Specifically it supplies: the Genio-Glossus, Hyo-Glossus, and Stylo - Glossus and the Intrinsic Muscles Of The Tongue
• Damage: Deviation Of Tongue To The Same Side