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Head and Neck Anatomy

3 Extrinsic Auricular Muscles

Quick review

The extrinsic auricular muscles were discussed in the muscles of facial expression section. As a quick summary, this group of muscles includes the superior, posterior, and anterior auricular muscles. They move the ear superiorly, posteriorly and anteriorly, respectively. The superior auricular muscle is the largest, and the anterior auricular muscle is the smallest.

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There are 6 main intrinsic auricular muscles: the helicis major and minor, tragicus, antitragicus, transverse and oblique muscles. The transverse and oblique muscles are located on the posterior surface of the ear. Each muscle name is easy to remember as it corresponds to its respective region of the ear.

1 The Structure of Salivary Glands

Overview

The salivary glands are an example of exocrine glands in the body, meaning that the contents in the gland are secreted into ducts and released into a body cavity. These glands release saliva, which contain enzymes, antibodies from residing immunological cells, electrolytes, and a combination of water and mucous. Saliva is important for breaking down food into a bolus to assist in mastication and swallowing, initiates the process of digestion, alters the pH of the oral cavity, and "cleans" the mouth.

Before looking at the gross anatomical salivary glands, it is important to first understand the histological structure of these glands by looking at cellular components and their organization. There are three main cells that will be discussed:

•Serous cell

Pyramidal in shape produce watery secretions with proteins and tend to stain dark histologically

•Mucous cell

These cells are usually larger than the serous salivary glands, are pyramidal in shape, and contain secretory granules with glycoproteins

Produce thicker, more mucous-like secretions

•Myoepithelial cell

Are thin contractile cells located at the basal end of cells

Contractions cause secretory contents within the acini to enter into the surrounding ducts

There are five main regions that are also relevant:

•Serous acinus

Ball or sac-shaped cavity comprised of many serous cells

•Mucous acinus

Ball or sac-shaped cavity comprised of many mucous cells

•Mixed acinus

Ball or sac-shaped cavity that contains a combination of serous and mucous cells

•Intercalated duct

The region that connects to the acini and are usually cuboidal epithelial cells

•Striated duct

The region that connects to the intercalated ducts where secretions are initially produced, and release contents into interlobular excretory ducts

Tend to contain columnar epithelial cells

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Figure 12.01 The histological organization of salivary glands

There are three major salivary glands that will be discussed in this section: the parotid, submandibular, and sublingual glands.

2 The Parotid Gland

Overview

The parotid gland is the largest of the three salivary glands. It is located within the retromandibular fossa, inferior to the zygomatic arch and posterior to the masseter.

•Features:

Contains a superficial and deep lobe which is separated by the facial nerve (CN VII)

Contains the facial nerve but does not innervate it!

External carotid artery

Retromandibular vein

•Innervation:

Parasympathetic fibers from inferior salivatory nucleus --> glossopharyngeal nerve (CN IX) lesser petrosal nerve --> otic ganglion --> auriculotemporal nerve (of CN V3)

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•Secretion:

Contains predominately serous acini resulting in watery secretions

Serous cells of parotid glands secrete

α-amylase causes hydrolysis of carbohydrates

•Duct:

Stenson's duct, which courses from the anterior aspect of the superficial lobe, over the masseter, and penetrates the buccinator muscle

Opens into the oral cavity near the maxillary second molar

Figure 12.02 A simplified diagram of the three salivary glands

3 The submandibular gland

Overview

When compared with the other two salivary glands, the submandibular gland is the second largest. It is located in the submandibular fossa on the medial aspect of the mandible by the mylohyoid line.

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•Features:

Contains a superficial and deep lobe that is divided by the mylohyoid muscle

Likely to experience sialolithiasis (salivary gland stone)

•Innervation:

Parasympathetic fibres from superior salivatory nucleus --> CN VII --> chorda

tympani --> lingual nerve (of CN V3) --> submandibular ganglion

•Secretion:

Contains a mix of both serous and mucous-secreting acini; slightly more mucous acini means the saliva produced is a bit thicker

Produces most of the saliva

Combination of α-amylase from serous acini and lysozyme (hydrolyses bacterial cell walls) plus mucin from mucous acini

•Duct:

Wharton's duct courses around the posterior aspect of the mylohyoid muscle, then superomedially towards the floor of the mouth on either side of the lingual frenulum

4 The Sublingual Gland

Overview

When compared with the other salivary glands, the smallest is the sublingual gland. It can be found on the floor of the oral cavity between the geniohyoid, hyoglossus, and mylohyoid muscles. It is bordered laterally by the mandible.

•Features:

Contributes minimally to the overall saliva production in the oral cavity

Lacks striated and intercalated ducts

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•Innervation:

Parasympathetic fibres from superior salivatory nucleus --> CN VII --> chorda

tympani --> lingual nerve (of CN V3) --> submandibular ganglion

•Secretion:

Contains some mucous and serous acini, though is more of a mucous-secreting gland

Amylase, lysozyme and mucins present

•Duct:

Bartholin's duct is responsible for transporting saliva into the oral cavity

-Joins Wharton's duct and thus drains into the oral cavity by the lingual frenulum

Since this gland lacks striated and intercalated ducts, saliva is also excreted near the plica fimbriata of the ventral tongue through the ducts of Rivinus

Figure 12.03 The surrounding structures and associated excretory ducts of the salivary glands

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Figure 12.04 The parasympathetic innervation of the saliva glands and other visceral motor pathways

INBDE Pro Tip:

To remember the information in the table above, a mnemonic can be used.

•Perry's 9 Salty Sandwiches

•Manny's 7 Weird Bananas

•Lucy's 7 Baked Macaroons

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5 Other Minor Salivary Glands

Overview

There are hundreds of small salivary glands that are accessory to the three major glands discussed above. They contribute minimally to the overall salivary production and are of lesser importance. Nonetheless, they still have a role to play in salivary production, and are mentioned here for completeness. They can be found in the submucosa of the:

•Sinonasal cavity

•Cheeks

•Soft and hard palate

•Tongue

•Nasopharynx

•Larynx

•Trachea

•Lips

1 Muscles of the Tongue overview

The muscles of the tongue are crucial to the functions of the tongue, which include speech, manipulating food during mastication, and swallowing. Though not related to the muscles of the tongue specifically, the tongue is also involved in taste.

Embryologically, this group of muscles is derived from the paraxial mesoderm which later form the occipital somites. These muscles are innervated by the either the vagus nerve (CN X) or the hypoglossal nerve (CN XII).

There are two main groups of muscles for this organ, intrinsic and extrinsic.

2 Intrinsic Muscles

Overview

These muscles can be found within the tongue. Unlike the extrinsic muscles, these are found within the tongue, and are responsible for finer, more complex movements. Generally, they can change the shape of the tongue, rather than provide mass movement of the organ. These muscles include the superior and inferior longitudinal, plus the transverse and vertical lingual muscles.

These muscles are all innervated by the hypoglossal nerve (CN XII).

INBDE Pro Tip:

To remember which muscles are intrinsic, pay attention to their names. Each have to do with a specific plane, which tells us something about the fibers, and thus the action, of that particular muscle.

Superior longitudinal

Located most superficially to the other intrinsic muscles of the tongue, below the lingual submucosa. Oriented longitudinally, or in a postero-anterior fashion.

•Origin: submucosa of posterior tongue

•Insertion: anterolateral aspect of tongue

•Action: shortens tongue, curls it upward

Figure 13.01 The intrinsic and extrinsic muscles of the tongue (coronal view)

This muscle is located inferior to all other intrinsic muscles of the tongue. Runs posteroanteriorly.

•Origin: root of tongue, body of hyoid bone

•Insertion: apex of tongue

•Action: shortens tongue, curls it downward

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Transverse lingual

Fibers run laterally from the medial aspect of the tongue.

•Origin: lingual septum

•Insertion: lateral aspect of tongue

•Action: elongates and narrows tongue

Vertical lingual

Fibers run vertically in an infero-superior fashion.

•Origin: root of tongue, genioglossus

•Insertion: lingual aponeurosis

3Extrinsic Muscles

•Action: flattens tongue

Overview

These muscles are located externally to the tongue. They are responsible for mass movements of the tongue, and are primarily involved in swallowing and mastication. These muscles include the genioglossus, styloglossus, hyoglossus, and palatoglossus.

Genioglossus

The word "genio" essentially means "chin," which is the general location for this muscle's origin.

•Origin: Mandible (superior mental spine)

•Insertion: lingual aponeurosis, body of hyoid bone, dorsum of tongue

•Action: protrusion of tongue

Styloglossus

"Stylo" refers to the styloid process, which is where the origin of this muscle is found.

•Origin: styloid process, stylomandibular ligament

•Insertion: inferior longitudinal muscle, hyoglossus muscle

•Action: retraction of tongue bilaterally

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Hyoglossus

The word "hyo" is associated with the hyoid bone, which is where this muscle originates.

•Origin: body and greater horn of hyoid bone

•Insertion: lateral tongue (inferior aspect)

•Action: depression and retraction of tongue

Palatoglossus

"Palato" is related to the word "palate," which points to this muscle’s origin.

•Origin: soft palate (palatine aponeurosis)

•Insertion: lateral aspect of tongue

•Action: elevation of posterior tongue, closure of oropharyngeal Isthmus, maintains palatoglossal arch

•*Innervation: The only muscle of the tongue innervated by the vagus nerve (CN X)

Figure 13.02 The extrinsic muscles of the tongue

INBDE Pro Tip:

All the extrinsic muscles of the tongue have a prefix that alludes to its origin, and a suffix that points to its insertion (though non-specific).

1 Muscles of the Soft Palate Overview

The muscles of the soft palate combine aponeurotic and muscular tissue to form the soft palate. The soft palate is considered an extension of the hard palate, which is comprised of bone, or more specifically, the palatine and maxillary bones. Generally, the soft palate is important for swallowing and breathing, but also contains mucous glands necessary for lubrication of the oral cavity.

These muscles are innervated by the vagus nerve (CN X), though the tensor veli palatini is innervated by the trigeminal nerve (CN V3).

There are 5 muscles that will be discussed, including the levator veli palatini, tensor veli palatini, palatoglossus, palatopharyngeus, and musculus uvulae.

INBDE Pro Tip:

The names of these muscles will tell you something important about them!

•For the palatoglossus and palatopharyngeus, the prefix is the origin, and the suffix is the insertion

•"Levator" means "to raise," "tensor" means "to tense," and veli means a "curtain" or a "veil", and "palatini" refers to the palate

2 Muscles of the Soft Palate

Levator veli palatini

•Origin: medial eustachian tube and temporal bone (petrous part)

•Insertion: palatine aponeurosis

•Action: elevates soft palate during swallowing (prevents food from entering nasopharynx); opens auditory tube opening during swallowing to equalize pressure between the middle ear and pharynx

Tensor veli palatini

•Origin: medial pterygoid plate of sphenoid, lateral cartilage of eustachian tube

•Insertion: palatine aponeurosis

•Action: tenses soft palate during swallowing (prevents food from entering nasopharynx); opens auditory tube opening during swallowing to equalize pressure between middle ear and pharynx

Palatoglossus

•Origin: palatine aponeurosis

•Insertion: posterolateral aspect of tongue

•Action: depresses soft palate, elevates posterior tongue to facilitate swallowing

1 Introduction to Muscles of the Neck

Collectively, the muscles of the neck are important for supporting and protecting the head and neck region, in addition to providing their movement. In total, there are three main types of neck muscle categories: anterior, lateral, and posterior. Muscles are organized into these categories based on their position, though it is also related to their function in most cases.

There are many muscles that can be discussed for this region, though more focus will be placed on the anterior neck muscles for the board exam.

2 Superficial Neck Muscles

Introduction

As the name suggests, these muscles will be found in the most superficial layer of the neck.

Platysma

The platysma is a thin muscle often referred to as the "shaving muscle" because its activation tenses the skin of the neck to facilitate shaving.

•Origin: skin/fascia of superior thoracic and shoulder regions (clavicle, acromial region, pectoralis major and deltoid muscles)

•Insertion:

Medial fibers: lower border of the mandible and the skin of the lower lip

Lateral fibers: skin of the perioral region, modiolus

•Action: lateral fiber contraction causes corners of mouth and lip to lower while medial fiber contraction may depress mandible and open the mouth

Sternocleidomastoid

This muscle of the neck conveys its origin and insertion points by its name alone.

•Origin:

Clavicular head: clavicle (medial third)

Sternal head: sternum (manubrium)

•Insertion: temporal bone (mastoid process)

•Action:

Bilateral contraction: lateral neck flexion ipsilaterally, lateral head rotation contralaterally

Unilateral contraction: neck flexion

•Innervation: spinal accessory nerve (CN IX), spinal nerves C2 and C3