The Head and Neck Anatomy

Abstract

The head consists of skull bones, mimic muscles, brain and many nerves, and blood vessels. All the functions we perform with our five senses such as sight, hearing, smell, touch, and taste take place in the head region. In addition, emotions are expressed thanks to the facial muscles. One of the most essential functions performed in the head area is speech. Speech is a fundamental human characteristic that enables communication and social engagement. The only movable bone in the head is the mandible. The movement of the head is mostly owing to its articulation with the neck. It acts as a bridge between the body and the head. Due to their proximity and directly linked functions, the head and neck regions are mentioned together. The head and neck areas are crucial to swallowing function. Therefore, the head provides the realization of many intertwined vital functions with both the contractile and noncontractile structures it contains in the head and neck region. In this chapter, the anatomy of the head and neck region, the muscles it contains, and evidence-based exercises for these muscles will be explained.

1 Noncontractile Structures in the Head and Neck Region

1.1 Head Bones

The skeletal system consists of bones, joints, and cartilage structures associated with them. Bone structures not only provide the body structure but also form a support surface for the soft tissue. The bones of the skull consist of cranial bones and facial bones. The cranial bones protect the brain by surrounding it. Through the cavities in the skull, blood vessels and nerves can pass. The facial bones form the face and provide support for functions such as chewing, speaking, and breathing. The head bones are given in the table (Table 8.1).

Table 8.1 Head bones

There are 22 bones in the human skull, excluding the middle ear bones. Except for the mandible, all other bones are immobile. Thanks to the temporomandibular joint it forms with the temporal and the mandible bones are mobile. The skull also articulates with the vertebral column in the neck region. When viewed from above, the skull displays a single piece of the frontal bone in the front, two connected pieces of parietal bone on the sides, and a single piece of the temporal bone in the back. The junction of bone structures is called a suture. Laterally, the sphenoid and ethmoid bones can be seen. In the anterior part of the skull are the facial bones, including the maxilla, mandible, and zygomatic bone (Fig. 8.1). The maxillary bone comprises the upper jaw. The mandible is the lower jaw. Several facial bones are shared by one or more soft tissues. An anomaly in the facial bone also affects many soft tissues.

Fig. 8.1

Frontal and lateral view of the skull (Quality Stock Arts/Shutterstock.com)

In the lower part of the skull are the foramen and the hard palate. The hard palate forms the floor of the nasal cavity and the roof of the mouth. The foramen provides a passageway for the cranial nerves that innervate the blood vessels supplying the head and neck. The mandibular branch of the nervus trigeminalis (V) passes through the foramen ovale. The internal carotid artery and the sympathetic carotid plexus pass through the carotid canal. Just behind the styloid process is the stylomastoid foramen, where the N. facialis (VII) emerges from the skull to the face. The jugular foramen, placed medial to the styloid process, allows the internal jugular vein, the N. glossopharyngeus (IX), the N. vagus (X), and the N. accessorius to pass through (XI). The spinal cord, vertebral arteries, and nerve accessory (XI) go via the foramen magnum, the largest clearance in the lower view (Fig. 8.2).

Fig. 8.2

Inferior view of the skull (sciencepics/Shutterstock.com)

1.2 Temporomandibular Joint (TMJ)

Ginglymoarthrodial diarthrosis formed between the mandible and the temporal bone is a joint. The TMJ consists of the joint capsule, articular disc, synovial fluid, and several ligaments. The temporal bone forms the cranial surface of the TMJ. The area of temporal bone where the condyle of the mandible articulates is known as the glenoid fossa. The articular disc is placed slightly below the glenoid fossa and covers the condyle of the mandible. It has a biconcave or oval shape. The anterior part of the disc contacts the joint capsule, articular eminence, condyle, and lateral pterygoid muscle. The margins of the cartilaginous disc surround the joint and partially fuse with the fibrous capsule. The joint disc facilitates and regulates the joint’s mobility during movement.

Three main ligaments connect the joint to the cranium: the temporomandibular, stylomandibular, and sphenomandibular ligaments. The temporomandibular ligament supports the lateral joint capsule and is regarded as the main connector for the joint. This ligament prevents the mandible from moving backward excessively. The stylomandibular ligament prevents excessive protrusion of the mandibula. The primary function of the sphenomandibular ligament is to hinder excessive translation of the TMJ condyle after the mouth is opened 10°. The other two ligaments tighten when the mandible protrudes, preventing excessive movement (Fig. 8.3). These bonds direct the forces on the TMJ and form proprioceptive afferents. Furthermore, joint capsule receptors, masticatory muscles, skin receptors, and periodontal ligaments contribute to joint proprioception.

Fig. 8.3

Temporomandibular joint (VectorMine/Shutterstock.com)

During the opening of the mandible, the joint undergoes two fundamental motions: rotation and translation. The first movement of the joint, a 20–25 mm rotation, is followed by translation, which refers to the forward sliding of the joint. A mouth opening of 40–50 mm is considered normal. Trismus refers to the pathology of opening fewer than 35 mm. The TMJ is involved in many functions such as sucking, chewing, swallowing, speaking, breathing, and facial expressions.

1.3 Neck Bones

The cervical vertebrae consist of 7 vertebrae located between the skull and the thoracic vertebrae. There are transverse foramens on either side of the vertebral foramen. The vertebral artery passes through these transverse foramens. The first (atlas) and second (axis) cervical vertebrae are specifically defined because of their proximity to the skull and their unusual anatomy. The atlas is in the form of an irregular ring connected by a short anterior arch and a longer posterior arch. The axis has a vertical projection called the dens anteriorly. The dens articulates with the anterior arch of the atlas (Fig. 8.4).

Fig. 8.4

(a, b) Atlantoaxial joint (stihii for both/Shutterstock.com)

Located at the level of the third cervical vertebral, anterior–superior to the thyroid cartilage, the hyoid bone does not articulate with any structure. Many muscles such as the suprahyoid and infrahyoid muscles connect to the hyoid. The hyoid bone with its connected muscles forms the base of the tongue. It takes part in functions such as swallowing, chewing, speaking, and breathing. The hyoid bone may rise and fall in response to muscle contraction and function. The epiglottis is the cartilage structure at the base of the tongue. This structure forms the root of the tongue and the anatomical cavity called the vallecula. It undergoes retroflexion with the effect of gravity during swallowing. The movement of the epiglottis is facilitated by the elevation of the larynx, its contact with the base of the tongue, and the weight and movement of food passing over it. Epiglottis movement helps to close the airway during swallowing. Vocal cords are responsible for primary phonation. During swallowing, it abducts and closes the airway (Fig. 8.5).

Fig. 8.5

Larynx (Alila Medical Media/Shutterstock.com)

2 Contractile Structures in the Head and Neck Region

Muscles contract and relax by innervation of the corresponding nerves. They cause movement of soft tissue or bones along with contraction. It is essential to understand where the muscle starts and where it ends. Origin is often connected to the structure that moves the least. The opposite end of the muscle, the insertion, is the more movable part. Generally, when the muscle contracts, it moves from the insertion to the origin. The head and neck region are divided into six main groups based on their functions: mimic muscles, chewing muscles, tongue muscles, hyoid muscles and pharynx muscles, and cervical muscles. The muscles of the ear, eye, and nose are not included.

2.1 Mimic Muscles

Mimic muscles are the muscles humans use to express themselves and their emotions (Fig. 8.6). These muscles also contribute to the functions of speaking, chewing, and swallowing. Innervation of all mimic muscles is provided by N. facialis (VII). Both halves of the face are innervated separately. Mimic muscles are given in the table (Table 8.2). The sensation of the face is received by the branches of the trigeminal nerve and cervical plexus.

Fig. 8.6

Mimic muscles (ORLY Design/Shutterstock.com)

Table 8.2 Mimic muscles

2.2 Chewing Muscles

The chewing muscles consist of four muscles attached to the mandible: M. masseter, M. temporalis, M. pterygoideus medialis, and M. pterygoideus lateralis (Fig. 8.7). The masseter is the strongest of the chewing muscles. The temporomandibular joint enables mandibular movements while chewing (TMJ). Therefore, pathologies of these muscles may be related to TMJ dysfunctions. The table below lists the chewing muscles (Table 8.3).

Fig. 8.7

(a, b) Chewing muscles (RuMax/Shutterstock.com) (a), (Alex Mit/Shutterstock.com) (b)

Table 8.3 Chewing muscles

2.3 Hyoid Muscles

The hyoid muscles attach to the hyoid bone and assist functions such as chewing, swallowing, and speaking. The muscles are divided into two based on the way they are attached to the hyoid bone from above or below: suprahyoid and infrahyoid. During swallowing, the suprahyoid muscles are primarily responsible for elevating the hyolarynx. By closing the airway in this manner, safe swallowing is maintained. The infrahyoid muscles, on the other hand, operate as a suspension during hyoid movement, ensuring smooth and fluent movement. Additionally, when the hyoid bone is fixed, the suprahyoid muscles also act as mouth opening. The hyoid muscles and their innervations are given in the table (Table 8.4).

Table 8.4 Hyoid muscles

2.4 Tongue Muscles

The tongue is a thick mass of voluntary muscles coated by a mucosal membrane and attached to the floor of the mouth by the lingual frenum. It performs intricate functions during speech, chewing, and swallowing. Two types of muscles make up the tongue: the extrinsic and intrinsic tongue muscles. Intrinsic muscles are placed inside the tongue, whereas extrinsic muscles are located outside. The insertions of the extrinsic muscles are located inside the tongue. In terms of their direction, intrinsic tongue muscles are classified as superior longitudinal, inferior longitudinal, vertical, and transverse. The contraction of these muscles changes the shape of the tongue. Extrinsic muscles attach the tongue to bony structures and move the tongue (Table 8.5). All tongue muscles are innervated by the hypoglossal nerve.

Table 8.5 Tongue muscles

2.5 Pharyngeal Muscles

The pharynx is the region bounded by the oral cavity anteriorly and the nasal cavity superiorly, extending to the upper sphincter of the esophagus. It establishes a passageway for both breathing and swallowing. It has three components: the nasopharynx, oropharynx, and laryngopharynx. The pharynx consists of the stylopharyngeus, salpingopharyngeus, soft palate muscles, and pharyngeal structures. Stylopharyngeus, salpingopharyngeus, and palatopharyngeus are laryngopharyngeal elevators. The stylopharyngeus begins from the styloid portion of the temporal bone and extends longitudinally and terminates at the pharyngeal wall. It is innervated by the glossopharyngeal nerve.

Pharyngeal structures compose the posterior and lateral pharyngeal walls. These structures consist of three parts upper, middle, and lower parts. Pharyngeal structures elevate the pharynx and larynx and create pharyngeal pressure to deliver nutrients to the esophagus. They are innervated by the pharyngeal plexus. As a continuation of the hard palate, the roof of the mouth is formed by the five pairs of soft palate muscles. Additionally, these structures are connected to the tongue. All muscles are involved in speaking and swallowing. The tensor veli palatini muscle is innervated by the mandibular branch of the trigeminal nerve, while all other soft palate muscles are innervated by the pharyngeal plexus (Fig. 8.8). Soft palate muscles are given in the table (Table 8.6). The pharyngeal plexus innervates the pharyngeal muscles. These muscles are formed by the pharyngeal plexus vagus and glossopharyngeal nerve branches. The glossopharyngeal nerve receives the sensation in the plexus, while the vagus performs its motor innervation. Only the stylopharyngeus is innervated by the glossopharyngeal nerve.

Fig. 8.8

Anterior faucial arch (Andrea Danti/Shutterstock.com)

Table 8.6 Soft palate muscles

2.6 Cervical Muscles

The cervical muscles are responsible for the mobility and stability of the neck. M. trapezius and M. sternocleidomasteideus are the largest and most superficial muscles (Fig. 8.9). Cervical muscles are given in the table (Table 8.7).

Fig. 8.9

Cervical muscles (Mister_X/Shutterstock.com)

Table 8.7 Cervical muscles

3 Neural Structures in Head and Neck Region

There are 12 separately defined cranial nerve pairs in the head and neck region. They innervate all striated and smooth muscles of the head and receive sensation. In addition, they are responsible for the sensations of sight, smell, and hearing, as well as structures such as the salivary and lacrimal glands. Cranial nerves and their functions are given in Chap. 5.

4 Movements in the Head and Neck Region

Knowing the movements of the head and neck region enables clinicians in the evaluation and treatment of very common diseases such as cervical disc herniation, headache, temporomandibular joint problems, and swallowing disorders.

4.1 Movements of the Head

Movements of the head are shown in Table 8.8.

Table 8.8 Movements of the head

4.2 Movements of the Temporomandibular Joint (TMJ)

The temporomandibular joint (TMJ) slides and rotates in front of each ear and consists of the mandible and the temporal bone. The TMJs along with several muscles allow the mandible to move up and down, side to side, and forward and back. When the mandible and the joints are properly aligned, smooth muscle actions, such as chewing, talking, and swallowing, can take place. When muscles, ligaments, the disk of the TMJ, and jaw and temporal bones are not aligned, several problems may occur. Movements of the temporomandibular joint are shown in Table 8.9.

Table 8.9 Movements of the temporomandibular joint

5 Head and Neck Palpation

The explanations of the anatomic structures of the head and neck and their palpation techniques are given in Table 8.10. In order not to cause/trigger pain, no more than 1.5 kg of pressure should be applied during palpation [painful range (2.0 kg of palpation); pain-free range (0.5 kg and 1.0 kg of palpation)]. Palpation should be performed bilaterally, in a relaxed and seated facing position, with the tip of the finger or by pincer palpation, when no underline bone support is present.

Table 8.10 Palpations of head and neck anatomic structures

6 Evidence-Based Exercises for the Head and Neck Region

Head and neck problems are common among people. It is often confused with the vertebral column and shoulder–arm complex problems, and so, neglected. The head/neck, one of the five kinetic chain checkpoints (head/neck, shoulders, lumbo–pelvic–hip complex, knees, and feet/ankles) is affected by and influences all movements of the other kinetic chain points. Evidence-based exercises for the head and neck region are shown in Table 8.11. Hyoid and hyolaryngeal mobilizations, Masako maneuver, and head lift exercises should be performed while lying on the back, while others should be performed in a sitting position.

Table 8.11 Evidence-based exercises for the head and neck region

7 Conclusion

All body functions are either directly or indirectly connected to the head and neck. This region is responsible for vital tasks such as feeding, breathing, hearing, speaking, seeing, and smelling. This region is frequently impacted by neurological diseases, head and neck cancers, and head traumas. All other systems are affected by the deterioration of nutrition and respiratory functions in particular. Due to the fact that the physiological actions that occur during swallowing are so distinct, this subject must be studied separately. The head and neck region is highly intricate owing to the presence of hundreds of muscles of different sizes and the connections between the brain and cranial nerves. Thorough knowledge of the anatomy and physiology of this region is essential for the development of a correct and effective rehabilitation program.