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:
Body - a robust, cylindrical part that is anterior
Pedicles - project posteriorly from the body and support the laminae
Laminae - plate-like pieces of bone that join along the posterior midline
Vertebral foramen - a space bounded by the laminae, pedicles, and body
Surrounds the spinal cord and spinal meninges
Sum total = spinal canal
Processes
Spinous process - projects posteriorly from the union of the laminae
Transverse processes - project laterally or posterolaterally
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’
Lacks body & spinous process
Articulates with occipital condyles of skull
Atlanto-occipital joint
Nods head
C2, ‘Axis’
Dens / odontoid process
Articulates with C1
Atlanto-axial joint
Pivots head
C7, ‘Vertebra prominens’
Prominent, non-bifid spinous process
Palpable
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:
Found within the anterior and lateral subcutaneous layer of the neck
Action: tenses neck
Weak depressor of mandible & lower lip
Innervation: Cervical br. of facial n. (CN VII)
Sternocleidomastoid m. (SCM):
Superior attachments
Mastoid process
Superior nuchal line
Inferior attachments
Manubrium of sternum
Medial 3rd of clavicle
Actions
Unilateral contraction:
Lateral flexion of neck
‘Head tilt with chin up’
Bilateral contraction:
Flexion of c-spine
‘Touching chin to chest’
Innervation
Efferent (motor): Accessory n. (CN XI)
Afferent (sensory): C2 & C3 spinal nerves brs.
Trapezius m.:
Proximal attachments
Occipital bone
Superior nuchal line
External occipital protuberance
Ligamentum nuchae & spinous processes C7-T12
Distal attachments
Clavicle
Spine of scapula
Actions:
Depend on which fibers contract
Retracts, depresses, elevates, & superiorly rotates scapula
Innervation
Motor: Accessory n. (CN XI)
Sensory: Brs. C3 & C4
Infrahyoid (strap) mm.:
Inferior to hyoid bone
Superior to sternum
Medial to carotid sheaths and contents
Except inferior belly of omohyoid m.
Superficial to thyroid gland & larynx
Innervation: Ansa cervicalis (most) & C1 fibers (thyrohyoid)
Superficial infrahyoids
Sternohyoid m.
Attachments:
Sternum (& medial clavicle)
Hyoid
Actions:
Stabilization of hyoid
Depression of hyoid
Innervation: Ansa cervicalis
Omohyoid m.
Attachments:
Scapula
Hyoid
Intermediate tendon to the clavicle
2 bellies (superior & inferior)
Actions:
Stabilization of hyoid
Depression of hyoid
Innervation: Ansa cervicalis
Deep infrahyoids
Sternothyroid m.
Attachments:
Sternal manubrium
Oblique line of thyroid cartilage
Action:
Pulls an elevated larynx inferiorly
Innervation: Ansa cervicalis
Thyrohyoid m.
Attachments:
Thyroid cartilage
Oblique line
Hyoid
Actions:
Depresses the hyoid
Elevates the larynx
Innervation is unique!
C1 (fibers travel with hypoglossal n.)
Scalene mm.
Attachments
Superior
Transverse processes of cervical vertebrae
Inferior
1st rib
Anterior & Middle scalene mm.
2nd rib
Posterior scalene m.
Actions
Flex & laterally flex cervical spine
Accessory respiratory mm.
Innervation:
Brs. of VPR of cervical spinal nn.
Suprahyoid mm.
‘Above hyoid’
Attach hyoid to skull
Elevate hyoid (swallowing)
Digastric m.
Anterior belly – Br. Trigeminal n. (CN V)
Posterior belly – Br. Facial n. (CN VII)
Stylohyoid m. - Br. Facial n. (CN VII)
Geniohyoid m. –C1 br. via Hypoglossal
Mylohyoid m. - Br. Trigeminal n. (CN V)
Pharyngeal mm.
Muscular walls of pharynx
Constrictor mm.
Longitudinal mm.
Affect shape of pharynx & position of larynx for swallowing & phonation
Mostly innervated by pharyngeal plexus
Glossopharyngeal n. (CN IX)
Vagus n. (CN X)
Cervical sympathetic trunk
Laryngeal mm.
Intrinsic mm. of larynx
Affect laryngoskeleton
Air movement for ventilation
Position and shape of vocal folds for phonation
Innervated by Vagus n. (CN X)
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:
Investing fascia
This is the most superficial layer of deep cervical fascia. As the name suggests, this layer invests the entirety of the neck deep to the skin and superficial cervical fascia (subcutaneous tissue).
Middle (pretracheal) fascia has 2 layers:
Muscular fascia: invests the infrahyoid mm. and is more anteriorly located
Visceral fascia: surrounds the majority of the viscera of the neck, including the thyroid gland, trachea, and esophagus
Buccopharyngeal fascia
Often described as a subdivision of the visceral part of the middle layer of deep cervical fascia or described separately
Surrounds muscles of the cheek and pharynx
Deep fascia has 2 divisions:
Alar fascia: anteriorly located and attached to transverse processes of cervical vertebrae
Prevertebral fascia: posteriorly located, and closely associated with the anterior surfaces of vertebral bodies and intervertebral discs
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:
anterior, the 'true' retropharyngeal space, and
posteriorly, the 'danger space.'
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:
superior thyroid a.
ascending pharyngeal a.
occipital a.
lingual a.
facial a.
posterior auricular a.
maxillary a.
superficial temporal a.
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:
Vertebral a. (Brain)
Internal thoracic a. (Thorax & Abdomen)
Thyrocervical trunk
Inferior thyroid a. (Thyroid, parathyroids,& larynx)
Ascending cervical a. (Deep neck mm.)
Transverse cervical a. (Trapezius m.)
Suprascapular a. (Supra- & Infraspinatus mm. & shoulder)
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:
Pharyngeal plexus (Somatic sensory fibers from)
Stylopharyngeus m. (Somatic motor fibers to)
Carotid sinus & Body (Visceral Sensory from)
Parotid gland (Preganglionic parasympathetic fibers to)
Posterior tongue
Somatic sensory fibers from
Special sensory (taste) fibers from
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:
Superior (cervical) cardiac brs. (Preganglionic parasymp. fibers)
Variably mix with sympathetic cardiac brs. in the neck
Inferior cardiac brs. (Preganglionic parasymp. fibers)
Brs. to Pharyngeal plexus (Somatic motor fibers to)
Superior laryngeal n.
Internal br. (Somatic sensory & Visceral motor)
External br. (Somatic motor)
Recurrent laryngeal nn. (RLN)
Right RLN loop @ Subclavian a.
Left RLN loop @ Concavity of aorta
Branches to cardiac, pulmonary, & esophageal plexuses
Vagus nerves become Vagal trunks (Visceral motor to gastro-intestinal tract)
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:
Sternocleidomastoid m. (Somatic motor fibers to)
Trapezius m. (Somatic motor fibers to)
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:
Vasomotor fibers to the smooth muscle of arteries (e.g. arterioles), &
Sudomotor fibers to sweat glands.
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:
Phrenic n.
Hemi-diaphragm
‘C3,4,5 keeps the diaphragm alive’
Ansa cervicalis
Infrahyoid mm.
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:
Lesser occipital n. (C2, [C3])
Posterior to the ear
Great auricular n. (C2, C3)
Inferior and anterior to ear
Transverse cervical n. (C2, C3)
Crosses neck medially
Supraclavicular nn. (C3, C4)
Inferior (descends) to clavicle
Clavicular & shoulder regions
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.
Superior thyroid a.
First branch of the external carotid a.
Several branches, one of which is the superior laryngeal a.
Inferior thyroid a.
Branch of the thyrocervical trunk (a branch of the first part of the subclavian a.).
Typically cross the recurrent laryngeal nn. deep to the thyroid gland in the vicinity of the larynx.
Primary blood supply to parathyroid glands
The thyroid gland is typically drained via 3 sets of veins:
Superior thyroid vv., typically drain into the internal jugular vv.,
Middle thyroid vv., typically drain into the internal jugular vv.,
Inferior thyroid vv., typically drain into the L. brachiocephalic v.
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:
the anterior scalene m. is sandwiched between the subclavian v. (anterior to) and subclavian a. (posterior to),
the anterior scalene m. establishes the borders for the divisions of the subclavian a.,
the anterior scalene m. is immediately posterior to (and closely associated with) the phrenic n. as the phrenic n. descends the neck and the root of the neck, and
the anterior scalene m. is separated from the middle scalene m. by the roots (ventral primary rami of spinal nn.) and roots and trunks of the brachial plexus and subclavian a.
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:
Nasopharynx (choanae; soft palate),
Contents:
Pharyngeal tonsil (adenoid)
Opening to auditory (Eustachian) tube
Oropharynx (soft palate; palatoglossal arch; epiglottis & pharyngo-epiglottic folds),
Contents:
Uvula
Fauces: region bounded anteriorly by the palatoglossal arch (folds) and posteriorly by the palatopharyngeal arch (folds). These folds are muscles of the soft palate covered by mucosa.
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 (epiglottis & pharyngo-epiglottic folds; entrance to esophagus; laryngeal inlet).
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:
Superior pharyngeal constrictor m. attaches to the skull,
Middle pharyngeal constrictor m. attaches to the hyoid bone, &
Inferior pharyngeal constrictor m. attaches to the larynx.
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:
Traveling between superior & middle pharyngeal constrictor mm., &
Traveling closely with the glossopharyngeal n. (CN IX).
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 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:
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
Vocal process (attaches to vocal ligament)
Muscular process (allows for intrinsic laryngeal muscle attachment & control)
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 arytenoid cartilages are acted upon by most (but not all) of the intrinsic laryngeal mm.
Posterior crico-artytenoid mm.
Abduction of vocal folds (only muscles that allow this)
Opens the airway
Arytenoid mm.
Transverse arytenoid mm.
Adduct arytenoids & vocal ligs
Oblique arytenoid mm.
Adduct arytenoids & vocal ligs
Ary-epiglottic part
Sphincter of laryngeal inlet
Innervated by recurrent laryngeal nn.
Thyro-artyenoid mm.
Protract arytenoids toward thyroid
Decrease tension, lower pitch
“Vocalis mm.”
Adjacent to vocal ligs
Increase lateral tension of vocal ligs
Affect timbre
Raise pitch
Thyro-epiglottic part
Ascend to ary-epiglottic fold
Dilate laryngeal inlet
Innervated by recurrent laryngeal nn.
Cricothyroid mm.
No connection to arytenoid cartilages
Tip thyroid cartilage anteriorly, which leads to increased tension on vocal ligaments
Increases pitch
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:
Superior laryngeal n.:
External br.
Efferent to cricothyroid m. (intrinsic laryngeal muscle)
Internal br.
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. (External carotid a. → Superior thyroid a. → Superior laryngeal a.)
Accompanied by the internal br. of the superior laryngeal n. through the thyrohyoid membrane.
Inferior laryngeal a. (1st part of Subclavian a. → Thyrocervical trunk → Inferior thyroid a. → Inferior laryngeal a.)