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1. Describe the cervical (neck) region. 

The cervical (cervix, Latin = neck) region is the region inferior to the head and superior to the thorax. The neck conducts several systems (chiefly, respiratory, gastro-intestinal, cardiovascular, lymphatic, and nervous systems) between the head and thorax.

Because of its importance in conducting elements of the respiratory pathway and cardiovascular system, understanding the anatomy of the neck is key to the maintenance of the airway and detecting carotid pulse. 

2. Describe the structure and composition of the bones of the neck, principally, the cervical spine (C-spine) and hyoid bone.

The principal skeletal structure of the neck is the cervical spine (c-spine), the most superior portion of the vertebral column, consisting of seven cervical vertebrae separated from one another by intervertebral (IV) discs. 

The c-spine gives the neck structure and protects important features like the spinal cord. Certain dislocations or fractures of the c-spine can have significant ramifications, including variable paralysis or death. 

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

Among the cervical vertebrae, there are three of particular importance:

C1, ‘Atlas’

• Lacks body & spinous process

• Articulates with occipital condyles of skull superiorly & C2 inferiorly

  • Atlanto-occipital joint (Occipital bone & Atlas)

    • Action at this joint: flexion and extension = nodding head (as if in agreement)

C2, ‘Axis’

• Dens / odontoid process

• Articulates with C1 superiorly & C3 inferiorly

  • Atlanto-axial joint (Atlas & Axis)

    • Action at this joint: Pivots head (as if in disagreement)

Hyoid bone:

The hyoid (huoeidēs, Greek = shaped like an upsilon) 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 does not directly articulate with another bone, but serves as an important attachment site for muscles of the tongue, suprahyoid muscles, and the larynx.

The hyoid bone supports the larynx from above. Fractures of the hyoid bone may endanger the airway.

3. Outline the significant muscles of the anterior neck with an emphasis on attachments, actions, and innervations.

Sternocleidomastoid m. (SCM):

The sternocleidomastoid (SCM) muscles form large, visible, lateral boundaries to the anterior versus lateral/posterior neck. 

The external jugular veins are located just superficial to the SCMs,, allowing distension to be easily visualized. This can be an indication of high pressure in the right atrium due to right sided heart failure, cardiac tamponade, tension pneumothorax, pulmonary embolism, etc.

• Superior attachments

  • Mastoid process (of temporal bone of the cranium)

  • Superior nuchal line (of occipital bone of the cranium)

• Inferior attachments

  • Manubrium of sternum

  • Medial 3rd of clavicle

• Innervation

  • Efferent (motor): Accessory n. (CN XI)

  • Afferent (sensory): C2 & C3 spinal nerves brs.

• Actions

  • Unilateral contraction:

    • Lateral flexion of neck

    • ‘Head tilt with chin up’

  • Bilateral contraction:

    • Flexion of c-spine

    • ‘Touching chin to chest’

Infrahyoid (strap) mm.:

The infrahyoid (strap) mm. are a group of anterior neck muscles that stabilize or depress the hyoid bone, or stabilize, elevate, or depress the larynx (voicebox). 

The infrahyoid mm.:

• Are located:

  • Inferior to hyoid bone

    • Hyoid is the superior attachment for most infrahyoid mm.

  • Superior to sternum

    • The manubrium of the sternum is the inferior attachment for half of the infrahyoid mm.

  • Medial to carotid sheaths and contents

    • Except for the inferior belly of omohyoid m.

  • Superficial to thyroid gland & larynx

• Are innervated by: 

  • Ansa cervicalis (most), 

• Are organized in two layers: superficial (sternohyoid & omohyoid) & deep (sternothyroid & thyrohyoid).

Owing to their positions in the anterior neck, the infrahyoid muscles must be delicately navigated during surgical procedures such as tracheostomy, thyroidectomy, or carotid endarterectomy.

4. Describe the location and composition of the carotid sheath and its major contents.

The carotid sheath is a condensation of deep cervical fascia, investing and surrounding some of the major vascular conduits and nerves of the neck. The carotid sheaths and their contents are located:

• Inferior to the cranium,

• Superior to the arch of the aorta & venous angles,

• Lateral & posterior to the infrahyoid mm., 

• Deep & medial to the sternocleidomastoid mm., &

• Anterolateral to the cervical sympathetic trunk & ganglia

The carotid sheath contains and protects critical neck neurovasculature. The contents of the sheath are typically avoided during surgical procedures of the neck, but the internal jugular vein may be accessed in the carotid sheath during IJV cannulation for central line placement. 

The major structures invested by the carotid sheath include the:

• Common & internal carotid aa.

• Internal jugular v. (IJV)

  • Associated deep cervical lymph nodes & jugular lymphatic trunk 

• Vagus n. (CN X) & brs. &

• Ansa cervicalis (variably)

5. Discuss the thyroid & parathyroid glands, with an emphasis on gross structure, relational positions, and blood supplies. 

The thyroid and associated parathyroid glands are the major endocrine glands of the neck. 

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

The thyroid gland has two conical lobes connected by a central isthmus, and is found deep to the sternothyroid m., superficial to the larynx & trachea, and approximately at the C5-T1 vertebral levels. Nearly half of people have an accessory (pyramidal) lobe, which varies in size and typically connects the isthmus of the thyroid gland to the hyoid bone.

With a central role in regulating metabolism, growth, and homeostasis, the thyroid gland is susceptible to hyperthyroidism and hypothyroidism. Abnormal enlargement of the thyroid (goiter) may have several etiologies and consequences on hormone production.

The thyroid gland is richly vascularized. typically supplied by two sets of arteries: superior & inferior thyroid aa., and several sets of thyroid veins of variable distribution. Approximately 10% of people also have a thyroid ima a., which tracheostomy may endanger. 

Parathyroid glands are small, lentiform (lens-shaped) endocrine glands found in a variety of locations, typically on the posterior aspects of the lobes 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. The parathyroid glands produce parathyroid hormone (PTH), which increases blood calcium concentrations.

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 inferior thyroid arteries have a close anatomical relationship with the recurrent laryngeal nn.. When ligating an inferior thyroid a., one must take care to not endanger the recurrent laryngeal n., thus risking ipsilateral denervation of most intrinsic laryngeal mm. and mucosa inferior to the vocal fold.

6. Demonstrate the structure and anatomical constituencies of the sympathetic division of the autonomic nervous system (ANS).

Overview

The basics of the sympathetic division (thoracolumbar outflow) of the autonomic nervous system includes:

1. Intermediolateral (IML) columns

2. White rami communicantes

3. Sympathetic chains/trunks (of paravertebral ganglia)

4. Gray rami communicantes

5. Splanchnic nn. 

6. Prevertebral (pre-aortic) ganglia

Intermediolateral (IML) columns are groups of neurons within the lateral horns of the gray matter of the spinal cord which contains preganglionic sympathetic neurons. Sympathetic preganglionic fibers originate in intermediolateral (IML) columns (aka lateral horns) of spinal cord levels T1-L2 and travel along spinal nn. T1-L2, and then leave the ventral primary rami (VPR) of spinal nerves to travel via white rami communicantes to paravertebral ganglia of the sympathetic trunks. 

Preganglionic fibers either synapse in the paravertebral ganglia of the sympathetic trunks, or in prevertebral (pre-aortic) ganglia associated with major arteries in the abdominal cavity. 

Postganglionic fibers originating in the sympathetic trunk may:

• exit the trunk via perivascular plexuses associated with arteries, 

• exit the sympathetic trunk via brs. to target tissues, or

• return to a spinal nerve via gray rami communicantes.

Many parts of the sympathetic pathway between the IML and target tissues are susceptible to disruption. The sympathetics of the head are from the superior-most paravertebral ganglion - the superior cervical ganglion. Disruptions of pathways to or from the superior cervical ganglion can result in the ipsilateral impairment or absence of sympathetic responses to the head, also known as Horner’s Syndrome. The classic symptoms of Horner’s include unilateral: ptosis (droopy eyelid), miosis (constricted pupil), and anhidrosis (lack of sweating).   

Succinctly, the sympathetic nervous system consists of:

1. The intermediolateral (IML) columns, which send preganglionic fibers via spinal nerves via

2. White rami communicantes to

3. Sympathetic chains/trunks (of paravertebral ganglia) where fibers may either

4. Synapse and postganglionic fibers may

   1. Exit the trunks via gray rami communicantes back to a spinal nerves to their targets

   2. Exit the trunks via perivascular plexuses which follow arteries

   3. Exit the trunks via brs. to target tissues

5. Or, not synapse, pass through trunks as splanchnic nn. which synapse in prevertebral (pre-aortic) ganglia in the abdomen, and

Participate in autonomic plexuses that are distributed via abdominal aorta brs. that serve the abdominopelvic viscera.

7. Describe the structure of the pharynx: pharyngeal subdivisions, structure, contents, and innervation.

The pharynx (throat) 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:

• Nasopharynx

  • Contents:

    • Pharyngeal tonsil (adenoid)

    • Opening to auditory (Eustachian) tube

• Oropharynx

  • Contents:

    • Uvula

    • Tonsillar fossa w/palatine tonsils

    • Root (pharyngeal part) of tongue and lingual tonsil

    • Epiglottic valleculae - shallow depressions between the root of the tongue and epiglottis

      • Collect saliva to prevent deglutition reflex

• Laryngopharynx

  • Contents:

    • Piriform recess

      • Common place for food/pills to get stuck

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

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

• Somatic motor (efferent) fibers from the vagus nn. (CN X)

• Somatic sensory (afferent) fibers from the glossopharyngeal nn. (CN IX)

• Autonomic fibers

  • Vagus nn. (parasympathetic) - increase mucosa secretions & blood flow,

  • Superior cervical ganglia of the cervical sympathetic trunks - decrease mucosal secretions & blood flow. 

The pharyngeal mucosa is afferently innervated by the pharyngeal plexus as well, with the exception of the mucosa of the nasopharynx. The pharyngeal ‘gag’ reflex is modulated by the pharyngeal plexus.

8. Describe the structure of the larynx, structure of the laryngoskeleton, airway, and relevant neurovasculature.

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:

• Most prominent cartilage

• Formed from two laminae, united anteriorly along the midline (posteriorly, the cartilage is incomplete)

• Suspended from the hyoid bone by the thyrohyoid membrane

• Inferior horns form the cricothyroid joint with the cricoid cartilage

• Joints with cricoid allow for thyroid cartilage to ‘tip’ forwards

Cricoid cartilage:

• Forms a complete ring around the airway

• Most robust posteriorly

Epiglottic cartilage:

• Leaf-shaped cartilage

• Sits posterior to thyroid cartilage

• Forms the epiglottis

• Forms a lid to cover the laryngeal inlet during deglutition (swallowing)

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

• Pyramid-shaped

• Sit atop the posterior cricoid 

• Muscular process (allows for intrinsic laryngeal muscle attachment & control)

• Vocal process (attaches to vocal ligament)

• Capable of either rotation or gliding for either abduction (wide open airway), or adduction (narrower airway) of vocal cords

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:

• Laryngeal prominence (superior), &

• Cricoid cartilage (inferior).

The larynx is exclusively innervated both afferently and efferently by the vagus n., by means of the:

• Superior laryngeal n.:

  • Efferent to cricothyroid m. (intrinsic laryngeal muscle)

  • Afferent from (and secretomotor to) laryngeal mucosa proximal to vocal folds

• Recurrent laryngeal n.:

  • Efferent to all intrinsic laryngeal mm. (except cricothyroid m.)

  • Afferent from (and secretomotor to) laryngeal mucosa distal to vocal folds

Blood supply to the larynx comes from two major sources:

• Superior laryngeal a. (from superior thyroid a.)

  • Accompanied by the internal br. of the superior laryngeal n. through the thyrohyoid membrane.

• Inferior laryngeal a. (from inferior thyroid a.)

  • Accompanied by the recurrent laryngeal n.