S2 Neck Learning Objectives

1. Describe the neck. Understand the osteological features of the cervical spine and hyoid bone. Understand the unique features of cervical vertebrae and describe the particular features of C1, C2, and C7.

The neck is the region inferior to the head and superior to the thorax. The structure of the neck consists of a foundation of bone supported by skeletal muscles and connective tissues. The neck conducts several systems (chiefly, respiratory, GI, cardiovascular, and nervous systems) between the head and thorax.

Cervical Spine (C-Spine):

The principal skeletal structure of the neck is the cervical spine, the most superior portion of the vertebral column, consisting of seven cervical vertebrae separated from one another by intervertebral discs (IV discs). IV discs have two parts: the annulus fibrosus (a durable, fibrous layer) surrounding the nucleus pulposus (a gelatinous core). Intervertebral foramina (windows formed on the lateral surfaces of the vertebral column) allow for spinal nerves to pass from the spinal cord to regions of the body.

Individual vertebrae consist of parts:


Cervical vertebrae are unique from all other vertebrae in that they also have bifid spinous processes (typically C2-C6) and transverse foramina.

Among the cervical vertebrae, there are three of particular importance


C1, ‘Atlas’

C2, ‘Axis’

C7, ‘Vertebra prominens’

Hyoid bone:


The hyoid sits anterior to the c-spine (in the vicinity of C4), inferior to the skull, and posterior to the inferior limit of the mandible. The hyoid bone does not directly articulate with another bone, but serves as an important attachment site for muscles of the tongue, suprahyoid muscles, and the larynx.

2. Understand the major muscles and muscle groups of the neck with an emphasis on attachments, actions, and innervations.

It is important to have a foundational understanding of the major muscles and muscle groups on the neck.  

Platysma:

Sternocleidomastoid m. (SCM):



Trapezius m.:

Infrahyoid (strap) mm.:

Superficial infrahyoids

Sternohyoid m.

Omohyoid m.

Deep infrahyoids

Sternothyroid m.

Thyrohyoid m.

Scalene mm.


Suprahyoid mm.

Mylohyoid m. - Br. Trigeminal n. (CN V)

Pharyngeal mm.

Laryngeal mm.

3. Describe the fasciae associated with the neck. Describe the layers and distribution of the deep cervical fascia. Describe the boundaries and divisions of the retropharyngeal space.

Fascia is the term for grossly visible connective tissue collections or sheaths deep to the skin (epidermis + dermis). From superficial to deep, the tissues are organized:

Epidermis → Dermis → Superficial fascia → Deep fascia

Superficial fascia is commonly referred to as subcutaneous (subQ) tissue or hypodermis, and is typically a layer of loose areolar connective tissue with varying amounts of adipose. Specifically, in the anterior neck, the hypodermis contains the platysma m(uscle). Platysma m. is a muscle of facial expression with a primary action of neck tension, and also plays a role in weak depression of the mandible and lower lip. The platysma m., like all muscles of facial expression, is innervated by the facial n. (CN VII), specifically the cervical br(anch). This muscle is a part of the Superficial Musculo-Aponeurotic System (SMAS), a superficial layer of muscles, aponeuroses, and fascia that are contiguous over the anterolateral neck and face.

Deep fascia is typically denser than superficial fascia, and is devoid of adipose tissue (fat). This fascia is important in surrounding and supporting muscle, organs (viscera), and neurovasculature.

Deep cervical fascia is located specifically in the neck with some extensions superiorly and inferiorly.

Three main deep cervical fascial layers:

Fascial spaces are either actual or potential spaces between these layers that form planes through which tissues can be separated, which is of particular importance in surgeries. The fascial spaces can limit or allow the spread of infections, etc.


Retropharyngeal Space:

The retropharyngeal space is a potential space posterior to the muscular wall of the pharynx (and its investing buccopharyngeal fascia), anterior to the prevertebral fascia, and spanning the distance between the base of the skull and the mediastinum (within the thoracic cavity). The retropharyngeal space is actually comprised of two potential spaces, separated by the alar fascia:


Clinically, the retropharyngeal space is important, because it represents a potential pathway for metastasis of disease between the head & neck and the thorax. Specifically, the ‘danger space’ between the prevertebral and alar fascia is of particular clinical importance as this is a potential area for infections to spread between the pharynx and mediastinum (a space within the thorax, medial to the lungs).

4. Understand the locations and drainage patterns of the major superficial and deep veins of the neck.

The superficial veins of the neck, named for their relative position to the deep fascia of the neck, are extremely inconstant in size, appearance, and connection. There are two major superficial veins of the neck: the external jugular v. & anterior jugular v.

The external jugular v. (EJV) is typically the most obvious superficial vein in the neck. The EJV is formed by the junction of the posterior division of the retromandibular v. and the posterior auricular v. The EJV runs superficial to the sternocleidomastoid muscle (SCM), and drains into the subclavian v. lateral and deep to the SCM.

The anterior jugular v. is formed from the coalescence of the superficial submandibular vv. The anterior jugular v. descends anterior to the superficial infrahyoid mm., often nestling under the SCM before draining into the EJV or the subclavian v. directly. The anterior jugular v. is valveless.

The deep veins of the neck are more constant in size and location than the superficial veins. Paired internal jugular veins (IJV) descend the neck within the carotid sheaths. The IJV arise from dural sinuses in the cranial cavity, exiting the skull via the jugular foramen with cranial nerves IX, X, & XI. As they descend the neck, they may pick up tributaries.

The subclavian veins principally drain the upper limbs of blood, but they have tributaries from the head, neck, back, and thorax. 


The confluence of the internal jugular v. and the subclavian v. is known as the venous angle, and it is in this vicinity where lymph is returned to venous circulation. 


Brachiocephalic vv., are each formed by the confluence of the internal jugular (IJ) vv. and subclavian vv. The L. brachiocephalic v. is located immediately anterosuperior to the aorta, and has a longer and more oblique course than the R. brachiocephalic v. Formed by the confluence of brachiocephalic vv., the superior vena cava transmits blood from the head, neck, upper limbs, and thorax to the right atrium of the heart. 

5. Understand the locations and distribution patterns of the major arteries of the neck.

The common carotid a. is a major content of the carotid sheath in the neck and bifurcates into the internal and external carotid aa.

The internal carotid a. has no branches in the neck. It travels to the cranium, where it is transmitted through the carotid canal, and supplies blood to the brain, orbit, and forehead.

The external carotid a. is the primary source of blood to the face and superficial head. The external carotid has eight branches:

The subclavian a. (SCA) supplies blood to the neck, cranial cavity (& brain), anterior wall of the thorax (and abdomen), and upper limbs. The subclavian a. is conceptually divided into three parts by the anterior scalene m. 

The 1st part of the subclavian a. is an important source of blood to various regions, including the brain and the neck, including the following three branches:

6. Understand the ‘big picture’ of the peripheral nervous system (PNS) of the neck with an emphasis on nerve modality and targets. 

The neck contains many important features of the peripheral nervous system. The following are a few of the more significant features, some of which will be elaborated upon in upcoming sessions.


Cranial nerves

As you may recall, there are 12 pairs of cranial nerves. Most cranial nerves are contained by and act upon the head. Four cranial nerves have branches within and act upon targets in the neck: Facial n. (CN VII), Glossopharyngeal n. (CN IX), Vagun n. (CN X), and the Accessory n. (CN XI). The facial n. has a single br. (the cervical br. Of the facial n.) which innervates the platysma m.  


Glossopharyngeal n. (IX)

The glossopharyngeal n. exits the jugular foramen, sending out branches to the superior neck and oral cavity. It has several targets in the head and neck, including:

Vagus n. (X)

The vagus n. exits the jugular foramen, sending out branches to the neck, thorax, and abdominopelvic cavity. It has several targets in the head and neck, including:

Accessory n. (XI)

The accessory n. enters the skull via the foramen magnum and exits the jugular foramen, sending out branches to the neck. It has two main targets in the neck, including:

Cervical sympathetic trunk

The sympathetic trunks are chains of ganglia found anterolateral the bodies of vertebrae. The trunks are found from the superior neck to the coccyx. The trunks receive their input (preganglionic sympathetic fibers) from T1-L2 levels of the spinal cord via white rami communicantes and have postganglionic communications back to spinal nerves at every level of the spinal cord. Thus, the only source of input (preganglionic fibers) comes from the thoracic portions of the sympathetic trunks.


The cervical sympathetic trunks are found just posterior to the carotid sheaths and typically consist of three sets of fused ganglia, the most constant of which are the superior cervical ganglia, but middle and inferior ganglia may also be found. 


The superior cervical ganglion typically consists of C1-C4 fused ganglia and is the exclusive provider of all sympathetics to the head, which are distributed as postganglionic fibers among perivascular plexuses. These have two types of targets/actions:

Cervical plexus

The cervical plexus is a peripheral nervous plexus consisting of contributions of ventral primary rami (VPR) of cervical nerves C1-C4. The plexus has both major motor and sensory targets including:

Motor brs.

There are two major motor brs. of the cervical plexus, including:

Cutaneous brs.

The cutaneous brs. of  the cervical plexus typically emerge posterior to the midpoint of the SCM at the nerve (Erb’s) point of the neck and distribute to the regions of skin from which they receive somatic sensory fibers. These cutaneous nerves include:

Brachial plexus

The brachial plexus is another peripheral nervous plexus found in the neck region, which consists of contributions of ventral primary rami (VPR) of nerves C5, C6, C7, C8, & T1. These VPR (‘roots’) and their subsequent trunks (where roots may coalesce) exit the lateral neck between the anterior & middle scalene muscles on their way to the upper limbs, which are the targets of the brachial plexus.

7. Where are the thyroid and parathyroid glands located? What are the functions of these glands? Vascular supply/drainage?

The thyroid gland has two lobes connected by a central isthmus, and sits between the C5-T1 vertebra. Nearly 50% of people have an accessory (pyramidal) lobe, which varies in size and typically connects the isthmus of the thyroid gland to the hyoid bone (Moore et al., 7th edition).

The thyroid gland is an endocrine gland, meaning it secretes hormones and is ductless. The thyroid gland secretes thyroid hormones (increases rates of tissue metabolism) and calcitonin (decreases concentrations of blood calcium).

The thyroid gland is typically supplied by two sets of arteries: superior & inferior thyroid aa.

The thyroid gland is typically drained via 3 sets of veins:

Parathyroid glands may be found in a variety of locations, but are typically on the posterior aspect of the thyroid gland. There are typically four parathyroid glands (a superior pair and inferior pair), but there may be more or fewer. The superior parathyroids are the most constant in size and position. Parathyroid glands may be supplied by either set of thyroid arteries (as determined by location), but typically the inferior thyroid aa. supply the parathyroids. The parathyroid glands are also endocrine and produce parathyroid hormone (PTH), which increases blood calcium concentrations. The parathyroid glands are supplied by the inferior thyroid aa. 

8. What is the root of the neck (RON)? Which structures (e.g. neurovasculature, muscles, & bones) are associated with the RON, and what are the classic anatomical relationships of these structures to one another?

The root of the neck (RON) is the nexus between the neck, thorax, and upper limbs. The RON is the proximal attachment site for many neck muscles and transmits important neurovasculature (e.g. common carotid aa., jugular vv., subclavian aa. & vv., vagus nn., and trunks of the brachial plexus). The RON rests upon the 1st ribs, and has indistinct boundaries with the neck and upper limbs.

Anterior scalene m.

The anterior scalene m. is an important anatomical landmark for understanding the neurovasculature of the root of the neck. There are four classic anatomical relationships to understand:

Phrenic n.

The phrenic n. (C3,4,5) descends from the cervical plexus through the root of the neck (just anterior to, and upon the anterior scalene m.) before entering the thorax between the subclavian a. & v. The phrenic n. is efferent (motor) and afferent (sensory) to the diaphragm and afferent (sensory) to the pericardium and diaphragmatic pleura.

Vagus n. (CN X)

The vagus n. (CN X) is the major parasympathetic supply and conduit to the thorax and abdomen, and is the major innervation to muscles of the larynx and pharynx, and aspects of the head.

The R. and L. vagus nn. take different routes through the thorax. Both nerves descend the neck within the carotid sheaths, and cross anteriorly over the subclavian aa., deep to the first ribs. The R. vagus n. then sends a major branch (the R. recurrent laryngeal n.) inferiorly and then posteriorly around the R. subclavian a., lateral to the trachea, on a course for the larynx. The L. vagus n. sends the L. recurrent laryngeal n. inferiorly and then posteriorly around the concavity of the arch of the aorta, lateral to the trachea, also on a course for the larynx.

9. Describe the boundaries of the naso-, oro-, and laryngopharynx, and identify the major contents of these spaces. Describe how substances may travel among these spaces. Describe the muscular wall of the pharynx and how it is innervated by the pharyngeal plexus.

The pharynx is a common space for the conductive pathways of the respiratory (gasses) and digestive (food and drink) systems. As such, the pharynx shares borders with the nasal cavity , oral cavity , larynx , and esophagus.

The pharynx is divided into three regions, which reflect the above borders. They are the:

The muscular wall of the pharynx consists of two layers: an outer layer of predominantly circularly-oriented constrictors, and an inner layer of longitudinally-oriented elevators that together shorten and widen the pharynx, and elevate the larynx.

The three pharyngeal constrictor muscles in the external layer of the pharynx surround the pharynx, and meet along a posterior midline pharyngeal raphe. A raphe is a seam where two elements fuse together. The pharyngeal raphe is a posterior midline seam of investing muscular fascia of the pharyngeal constrictor muscles. 

Each muscle has a unique attachment to an osteological structure, which helps to reciprocally reinforce spatial relationships, including the:

When activated, the pharyngeal constrictor mm. serially constrict the lumen of the pharynx.

The three longitudinal muscles of the inner layer have a less coordinated anatomical arrangement than the constrictor muscles. These muscles elevate the larynx and by doing so shorten the pharynx. The most obvious among these muscles is the stylopharyngeus, which has classic anatomical relationships of:

With the exception of the stylopharyngeus mm., the muscles of the pharynx are innervated by the pharyngeal (neural) plexus, which includes contributions of:

The stylopharyngeus mm. are innervated exclusively (motor and sensory) by the glossopharyngeal nn. (CN IX).

The pharyngeal mucosa is afferently innervated by the pharyngeal plexus as well, with the exception of the mucosa of the nasopharynx, which is afferently innervated by a branch of V2, the maxillary division of the trigeminal n. (CN V).

The pharyngeal ‘gag’ reflex is modulated by the pharyngeal plexus.

10. Explain the major cartilaginous parts of the laryngoskeleton, and relate important features of these cartilages to the structure and functions of the larynx. Describe the major intrinsic laryngeal mm., their innervation, and their functions. Understand the intrinsic laryngeal membranes and their features. 

The larynx (colloquially, the voice box) is a dynamic element which serves as the conduit between the pharynx and trachea. The bulk of the larynx is the laryngoskeleton (laryngeal skeleton), which consists of a series of cartilages. Three singular (unpaired) cartilages (thyroid, cricoid, epiglottic) make up the bulk of the laryngeal skeleton, and a pair of cartilages (arytenoids) are the key to understanding most of the movements that affect phonation and movement of air (tension/relaxation and/or abduction/adduction of the vocal folds). The laryngoskeleton sits inferior to the hyoid bone, anterior to the laryngopharynx, and superior to the trachea.

Thyroid cartilage:

Cricoid cartilage:

Epiglottic cartilage:

Also important to the function of the larynx in phonation and the regulation of airflow are the:

Arytenoid cartilages:

Vocal ligaments connect arytenoid cartilages to the thyroid cartilage and are covered by mucosa to form the (true) vocal folds (=vocal cords). The vocal folds vibrate with exhaled air (in a slightly adducted position) for phonation. The vocal folds may be abducted to allow for a more patent (open) pathway for air to move. Proximal (superior) to the vocal folds are the vestibular (ventricular; false vocal) folds. The ventricular folds also connect the arytenoid cartilages to the thyroid cartilage, but are not involved in phonation.

In emergent situations when the airway is compromised proximal to the larynx (such as during an obstruction), one may create a temporary airway by incising the median cricoid ligament, a procedure known as a cricothyrotomy. There are no vascular issues for the incision and there are good, palpable landmarks for this procedure, including:

The arytenoid cartilages are acted upon by most (but not all) of the intrinsic laryngeal mm. 

Posterior crico-artytenoid mm.

Arytenoid mm.

Thyro-artyenoid mm.

Cricothyroid mm.

11. Diagram the arteries and nerves that serve the larynx and explain the specific targets of each nerve and their branches.

The larynx is exclusively innervated by the vagus n., specifically by means of the:

Blood supply to the larynx comes from two major sources:

Inferior laryngeal a. (1st part of Subclavian a. → Thyrocervical trunk → Inferior thyroid a. → Inferior laryngeal a.)