Dissector Answers - Larynx and Neck

Learning Objectives:

Upon completion of this session, the student will be able to:

1. Identify and list the attachments, innervation and action of the muscles of the neck: sternocleidomastoid, infrahyoid muscles, scalene muscles.
2. Identify the boundaries of the anterior and posterior cervical triangles and their subdivisions.
3. Describe the branches of the cervical plexus.
4. Identify the deep cervical fascia, its various component layers, and the resulting compartmentalization of the neck.
5. Locate and describe the specific features of the thyroid gland.
6. Give the position of the parathyroid glands and consider the thyroid/parathyroid gland relationship in terms of vascular supply and surgical intervention.
7. Identify and list the parts and branches of the subclavian artery and vein, and describe their course in the neck.
8. In the root of the neck, locate the vagus and phrenic nerves and describe their relationships to the organs, fascia, vessels, and viscera of the neck.
9. Describe the anatomy relevant to subclavian vein catheterization: surface landmarks and relationships of the subclavian vein to the clavicle, 1st rib, subclavian artery, brachial plexus, parietal pleura, phrenic and vagus nerves.
10. Identify the deep cervical lymph nodes and explain their significance.
11. Review the arrangement, distribution and function of the cervical sympathetic trunk.
12. Review the carotid sheath and contents.
13. List the basic functions of the larynx.
14. Identify the main cartilages and membranes that form the internal framework (skeleton) of the larynx.
15. Describe the actions of the intrinsic muscles of the larynx in tensing, relaxing, abducting or adducting the vocal folds.
16. Describe the innervation and vascular supply of the larynx.
17. Describe the anatomy relevant to cricothyroidotomy: locate the cricothyroid membrane and describe its relationships to the thyroid and cricoid cartilages, vocal cords, cricothyroid artery, and cricothyroid muscles.

Learning Objectives and Explanations:

1. Identify and list the attachments, innervation and action of the muscles of the neck: sternocleidomastoid, infrahyoid muscles, scalene muscles. (N27,N28,N29,N31, N30, N32, N33, N186, N192, N194, N429, TG7-12, TG7-13, TG7-15A, TG7-15B, TG7-16, TG7-17, TG7-18)

The names of these muscles are helpful in identifying their locations. For example: "omo" means shoulder, and omohyoid goes from the shoulder to the hyoid bone.

Muscles
Muscle	Origin	Insertion	Action	Innervation	Notes	Image
omohyoid (TG7-10, TG7-12)	inferior belly: upper border of scapula medial to scapular notch; superior belly: intermediate tendon	inferior belly: intermediate tendon; superior belly: lower border of hyoid lateral to sternohyoid insertion	depresses/stabilizes hyoid bone	ansa cervicalis	the intermediate tendon of omohyoid is tethered to the clavicle by a fascial sling
sternohyoid (TG7-12, TG7-13)	posterior surfaces of manubrium and sternal end of clavicle	lower border of hyoid bone, medial to omohyoid insertion	depresses/stabilizes hyoid bone	ansa cervicalis	sternohyoid overlies sternothyroid and thyrohyoid
sternothyroid (TG7-12, TG7-13)	posterior surface of manubrium below sternohyoid origin	oblique line of thyroid cartilage	depresses/stabilizes thyroid cartilage of larynx	ansa cervicalis	sternothyroid lies deep to sternohyoid
thyrohyoid (TG7-12, TG7-13)	oblique line of thyroid cartilage	lower border of hyoid bone	elevates larynx; depresses/stabilizes hyoid bone	C1&2 fibers running with hypoglossal nerve that leave XII anterior to the superior root of ansa cervicalis	thyrohyoid lies deep to the sternohyoid
sternocleidomastoid (TG7-12, TG7-13)	sternal head: anterior surface of manubrium; clavicular head: medial 1/3rd of clavicle	mastoid process and lateral 1/2 of superior nuchal line	draws mastoid process down to same side; turns chin up toward opposite side	spinal accessory nerve (XI), with sensory supply from C2 & C3 (for proprioception)	carotid sheath structures lie deep to it
scalene, anterior (N28, N30, N32, TG7-15A, TG7-15B, TG7-17, TG7-18)	anterior tubercles of transverse processes of vertebrae C3-C6	scalene tubercle of first rib	elevates first rib; flexes and laterally bends the neck	brachial plexus, C5-C7	a muscle of inspiration; anterior scalene inserts behind the subclavian vein, and anterior to the subclavian artery and roots of the brachial plexus (Greek, skalenos = uneven, having sides of unequal length)
scalene, middle (N28, N30, N32, TG7-15A, TG7-15B, TG7-17, TG7-18)	posterior tubercles of the transverse processes of vertebrae C2-C7	upper surface of first rib behind subclavian artery	elevates first rib; flexes and laterally bends the neck	brachial plexus, C3-C8	a muscle of respiration (inspiratory); also called scalenus medius; penetrated by the dorsal scapular n. and long thoracic n. (Greek, skalenos = uneven, having sides of unequal length)
scalene, posterior (N28, N30, N32, TG7-15A, TG7-15B, TG7-17, TG7-18)	posterior tubercles of the transverse processes of vertebrae C5-C7	lateral surface of second rib	elevates second rib; flexes and laterally bends the neck	brachial plexus, C7-C8	a muscle of respiration (inspiratory) (Greek, skalenos = uneven, having sides of unequal length)

Nerves and their relations to the scalene muscles and 1st rib:

• The relation of the scalene muscles to nerves mainly occurs between the anterior and middle scalene muscles. In the space between these two muscles, known as the interscalene triangle:
  • C3, C4, and C5 spinal nerves emerge and give off their contributions to the phrenic nerve, which runs inferiorly on the anterior scalene muscle
  • inferior to the three aforementioned spinal nerves, the roots of the brachial plexus (C5 through T1) emerge as well
• Another nerve that has a specific relation with the scalene muscles is the vagus nerve while it is contained in the carotid sheath. Plates N31, N32, TG7-14, TG7-20 show the vagus nerve descending on the origin of the anterior scalene muscle.
• Other relevant nerves are the dorsal scapular nerve and long thoracic nerve, both of which pass through the middle scalene muscle after branching off of the roots of the brachial plexus (C5 for dorsal scapular, C5-7 for long thoracic).

Arteries and veins and their relations to the scalenes and 1st rib:

• The most important relations to notice are those of the subclavian artery and vein. The subclavian arteries are separated from the veins by the anterior scalene muscle, with the artery being posterior to the muscle and the vein anterior to it. Both of these vessels start posterior to the sternoclavicular joint and parallel each other as they pass inferior to the clavicle and superior to the 1st rib to become the axillary artery/vein. Since both vessels rest on the 1st rib, there are grooves that mark their positions on the rib.
• As for the branches/tributaries of the subclavian artery/vein, three branches of the thyrocervical trunk (1st part of subclavian) rest on the anterior scalene muscle as they travel to their destinations. These branches are the transverse cervical artery, suprascapular artery, and ascending cervical artery (actually a branch of inferior thyroid artery, the third branch of the thyrocervical trunk). Veins parallel these arteries and ultimately reach the subclavian vein. (N32, TG7-15A, TG7-15B)

2. Identify the boundaries of the anterior and posterior cervical triangles and their subdivisions. (N 28, TG 7-02A, 7-02B)

• Anterior cervical triangle
  • boundaries:
    • medial: midline
    • lateral: anterior border of the sternocleidomastoid muscle
    • superior: lower border of the mandible
  • subdivisions:
    • muscular triangle
      • medial: midline
      • superolateral: superior belly of the omohyoid muscle
      • inferolateral: sternocleidomastoid muscle
    • submandibular triangle
      
      • anterior: anterior belly of the digastric muscle (this muscle is not in this lab, so for now it is sufficient to know its location as a reference for triangle borders).
      • posterior: posterior belly of the digastric muscle
      • superior: lower border of the mandible
    • submental triangle
      
      • lateral: anterior belly of digastric muscle
      • medial: midline
      • inferior: hyoid bone
    • carotid triangle
      
      • lateral: sternocleidomastoid muscle
      • superior: posterior belly of the digastric muscle
      • anterior: superior belly of the omohyoid muscle
• Posterior cervical triangle
  
  • boundaries:
    • anterior: posterior border of the sternocleidomastoid muscle (SCM)
    • posterior: anterior border of the trapezius
    • inferior: clavicle
  • apex:
    • where the SCM and trapezius meet on the superior nuchal line of the occipital bone
  • roof:
    • superficial layer of deep cervical fascia<
  • floor:
    • formed by the levator scapulae, middle scalene, and posterior scalene, which are all covered by the prevertebral layer of deep cervical fascia
  • subdivisions:
    • subclavian/omoclavicular triangle
      • superior: inferior belly of omohyoid muscle
      • anterior: sternocleidomastoid muscle
      • inferior: clavicle
      • contents:
        • third part of subclavian artery
        • part of subclavian vein
        • suprascapular artery
        • supraclavicular lymph nodes
    • occipital triangle
      
      • anterior: sternocleidomastoid muscle
      • posterior: trapezius muscle
      • inferior: omohyoid muscle
      • contents:
        • part of external jugular vein
        • posterior branches of cervical plexus of nerves
        • accessory nerve
        • trunks of brachial plexus
        • transverse cervical artery
        • cervical lymph nodes

3. Describe the branches of the cervical plexus. (W & B 191 and Fig 190; N 24,31,32,129,178, TG 7-11, 7-16A,7-16B, 7-13)

The cutaneous branches of the cervical plexus include the lesser occipital, the great auricular, the transverse cervical, and the supraclavicular nerves. They emerge along the lateral border of the sternocleidomastoid muscle in the order of lesser occipital, great auricular, transverse cervical, and supraclavicular (superior to inferior). (Note: Netter 31 incorrectly indicates that the great auricular is superior to the lesser occipital. The lesser occipital comes from C2 and the great auricular comes from branches of C2 and C3.)

Nerve	Source	Location	Area of distribution
Lesser occipital	C2	Ascends in the neck along the posterior border of the sternocleidomastoid muscle; pierces the cervical fascia near the muscle and divides into branches	Skin and subcutaneous tissue behind the ear
Great auricular	C2, C3	Appears at the lateral border of the sternocleidomastoid muscle just below the lesser occipital nerve and goes toward the auricle and the angle of the mandible	Skin of the ear and below the ear
Transverse cervical	C2, C3	Appears below the great auricular nerve at the lateral border of the sternocleidomastoid muscle; crosses the muscle horizontally to reach the anterior triangle deep to the platysma muscle and the external jugular vein	Skin of the neck anteriorly
Supraclavicular	C3, C4	Emerges below the transverse cervical nerve at the lateral edge of the sternocleidomastoid muscle; descends through the inferior part of the posterior triangle and divides into three branches that pierce the platysma near the clavicle	Skin of the root of the neck; upper chest and upper shoulder anteriorly

Cervical Plexus
Nerve	Source	Branches	Motor	Sensory	Notes
cervical plexus	ventral primary rami of spinal nerves C1-C4	brs. to: longus colli & capitis, sternocleidomastoid m., trapezius m., levator scapulae m., scalenus medius m., rectus capitis anterior and lateralis mm.; superior & inferior root of the ansa cervicalis, n. to the thyrohyoid m., n. to the geniohyoid m., lesser occipital n., great auricular n., transverse cervical n., supraclavicular nn. (medial, intermediate and lateral), contributions to the phrenic n. from C3 and C4	longus colli & capitis mm., rectus capitis anterior & lateralis mm., infrahyoid mm., thyrohyoid m., geniohyoid m., respiratory diaphragm	skin of the anterolateral neck; skin of the ear and skin behind the ear	close association of the supraclavicular nn. to the phrenic n. results in pain from the respiratory diaphragm referred to the shoulder

4. Identify the deep cervical fascia, its various component layers, and the resulting compartmentalization of the neck. (W & B 191-195 and Fig 3-6, N 35, TG 7-10,7-11)

Deep cervical fascia components:

• superficial (investing) layer: (Note: this is the superficial layer of the deep fascia, which is different from superficial fascia) extends between the trapezius and the sternocleidomastoid muscles in the posterior triangle and between the paired sternocleidomastoid muscles in the anterior triangle. It surrounds all the deeper parts of the neck and splits to enclose the trapezius and sternocleidomastoid muscles. It also splits above the manubrium to create the suprasternal space (the jugular venous arch connecting the anterior jugular veins goes through this space).
• infrahyoid (muscular) fascia: has a superficial layer which encloses the sternohyoid and omohyoid muscles and a deeper lamina which encloses the sternothyroid and thyrohyoid muscles. Both layers create a semi-circle on the anterior side of the neck and end superiorly at the hyoid bone. Inferiorly they pass behind the sternum onto the left brachiocephalic vein and the pericardium.
• visceral fascia: encloses the pharynx, esophagus, larynx, trachea, thyroid, and parathyroid glands. It has two components: pretracheal fascia anteriorly and the buccopharyngeal fascia posteriorly.
• carotid sheath: encloses the internal and common carotid arteries, internal jugular vein, and vagus nerve.
• prevertebral fascia: forms a complete enclosure of the cervical vertebrae and their associated longitudinal musculature, vessels, and nerves. There are also some interfascial spaces. The most important is the retropharyngeal space. This space is between the buccopharyngeal and prevertebral fascias and accommodates the movements of the pharynx and associated parts during swallowing.

5. Locate and describe the specific features of the thyroid gland. (W & B 197-8, N 74, TG 7-13, 7-14)

The thyroid gland is H-shaped with lateral lobes making up the vertical lines and the isthmus making up the middle bar. There also sometimes is a pyramidal lobe which extends upward from the isthmus or from the junction of the isthmus and one of the lateral lobes. The thyroid gland arches over the trachea and is bound posterolaterally by the carotid sheath contents and anterolaterally by the sternothyroid muscles. The upper parts of the lateral lobes are molded against the cricoid and thyroid cartilages.

Thyroid gland:

• composed of two populations of cells: follicles and the surrounding parafollicular cells
• produces two hormones
  • calcitonin: lowers calcium and phosphate levels in the blood and is regulated by serum calcium levels
  • thyroxine: increases basal metabolic rate. Also feeds back to decrease TSH and TRH synthesis and release from the pituitary and hypothalamus.

6. Give the position of the parathyroid glands and consider the thyroid/parathyroid gland relationship in terms of vascular supply and surgical intervention. (W & B 201; N 74, 75, TG 7-14)

The parathyroid glands are usually four (but may be two to six) small glands lying posterior (superior parathyroids) or inferior (inferior parathyroids) to the thyroid gland. Blood supply comes from branches of the inferior or superior thyroid arteries, or from the longitudinal anastomosis between these vessels. Venous drainage flows into the thyroid plexus of veins. Inadvertent removal or damage of the parathyroid glands can occur in surgery on the thyroid gland because of variable positions of the parathyroid glands. If the parathyroid glands atrophy or are all removed during surgery, the patient suffers from tetany, severe convulsive muscle spasms resulting from a fall in serum calcium levels.

Parathyroid gland:

• produces parathyroid hormone - increases blood calcium levels (opposite of calcitonin) and lowers phosphate levels (same as calcitonin). It is regulated by serum calcium levels

7. Identify and list the parts and branches of the subclavian artery and vein, and describe their course in the neck. (N33, N70, N74, N238, TG7-15A, TG7-15B)

The subclavian artery arises superiorly from the brachiocephalic trunk (right side) or the aortic arch (left side) and travels between the anterior and middle scalene muscles. It then travels inferiorly between the clavicle and first rib to enter the pectoral region, where it becomes the axillary artery. The subclavian artery is divided into three parts by the anterior scalene muscle (this is similar to the pectoralis minor dividing the axillary artery into three parts):

• The first part of the subclavian artery is medial to the anterior scalene muscle and gives off the following branches:
  • vertebral artery - the cervical part of the vertebral artery ascends just medial to the muscles and passes deeply at its apex to course through the foramina of the transverse processes of C1 through C6. The suboccipital part of the vertebral artery courses in a groove on the posterior arch of the atlas before it enters the cranial cavity through the foramen magnum.
  • internal thoracic artery - arises from the anteroinferior aspect of the subclavian artery and passes inferomedially into the thorax. The cervical part of this artery has no branches.
  • thyrocervical trunk - arises from the anterosuperior aspect of the first part of the subclavian artery, just medial to the anterior scalene muscle, and has three branches:
    • inferior thyroid artery
    • transverse cervical artery - sends branches to muscles in the posterior cervical triangle, the trapezius, and medial scapular muscles
    • suprascapular artery
• The second part of the subclavian artery is posterior to the anterior scalene muscle and only has one branch:
  • costocervical trunk - arises from the posterior aspect of the subclavian artery. It passes posterosuperiorly and divides into:
    • superior intercostal artery - supplies first two intercostal spaces
    • deep cervical artery - supplies posterior deep cervical muscles
• The third part of the subclavian artery is lateral to the anterior scalene muscle and only has one branch:
  • dorsal scapular artery - occasionally arises as a branch of the transverse cervical artery. When it is a branch of the subclavian, it passes laterally through the trunks of the brachial plexus, anterior to the middle scalene muscle, and then runs deep to the levator scapulae to reach the scapula and supply the rhomboid muscles.

The subclavian vein begins at the lateral border of the 1st rib as a continuation of the axillary vein and ends when it unites with the IJV, posterior to the medial end of the clavicle (SC joint). The important part of the subclavian vein is that when it meets the IJV, it forms the brachiocephalic vein. This union is known as the venous angle and is the site where the thoracic duct and right lymphatic duct drain their lymph into the venous circulation. The subclavian vein receives the external jugular vein, anterior jugular vein, and vertebral vein. The external jugular vein receives the suprascapular vein and the transverse cervical vein. One thing to note is that even though the inferior thyroid ARTERY is a branch of the thyrocervical trunk of the subclavian artery, the inferior thyroid VEIN drains into the brachiocephalic vein, separate from the other branches of the thyrocervical trunk, which drain into the subclavian vein.

8. In the root of the neck, locate the vagus and phrenic nerves and describe their relationships to the fascia, vessels, and viscera of the neck. (WB 220; N32, N33, TG7-13 TG7-14)

Vagus nerves - The vagus nerves pass anterior to the first part of the subclavian artery and posterior to the brachiocephalic vein and SC joint to enter the thorax. Higher in the neck, the vagus nerve runs between and posterior to the common carotid artery and the internal jugular vein in the carotid sheath (the artery is medial, the vein lateral). (N31, N32, TG7-13, TG4-45)

Recurrent laryngeal nerves - branches of the vagus nerves - The right recurrent laryngeal nerve loops inferior to the right subclavian artery at approximately the T1 vertebral level. The nerve then ascends in the tracheoesophageal groove to supply all the intrinsic muscles of the larynx, except the cricothyroid (will need to know this later). To better orient yourself, remember that the vagus nerve descends anterior to the subclavian artery and posterior to the vein. The left recurrent laryngeal nerve loops inferior to the arch of the aorta behind the ligamentum arteriosum at approximately the T4/T5 intervertebral disc level. Recurrent nerve ascends in the tracheoesophageal groove to supply all the intrinsic muscles of the larynx, except the cricothyroid (will need to know this later).

Phrenic nerve - arises by a large root from C4 and is reinforced by smaller contributions from C3 and C5. It passes out along the lateral border of the anterior scalene muscle and enters the chest along its medial border. It lies behind the prevertebral layer of deep cervical fascia and is crossed by the transverse cervical and suprascapular vessels. At the root of the neck, the phrenic nerve passes between the first portion of the subclavian vein and subclavian artery and in front of the internal thoracic artery and vein.

9. Describe the anatomy relevant to subclavian vein catheterization: surface landmarks and relationships of the subclavian vein to the clavicle, 1st rib, subclavian artery, brachial plexus, parietal pleura, phrenic and vagus nerves. (N72, N239, N266, TG7-74)

The subclavian vein lies beneath the proximal third of the clavicle. It lies on the first rib anterior to the insertion of the anterior scalene muscle on the scalene tubercle, and it becomes the axillary vein at the lateral border of the first rib. Proximal to the first rib and before its union with the internal jugular vein (which happens behind the sternoclavicular joint), it lies on the cupula, or the dome of cervical parietal fascia. Hence, a needle penetrating the cupula may cause a pneumothorax. Phrenic nerve lies on the anterior surface of the anterior scalene, so it may be impaled here. The subclavian artery lies behind the subclavian vein, and the anterior scalene muscle separates them. The vagus nerve is medial to the anterior scalene and passes between subclavian artery and vein. The roots of the brachial plexus lie behind the subclavian artery.

10. Identify the deep cervical lymph nodes and explain their significance. (N72, N239, N266, TG7-74)

The deep cervical nodes are mostly lateral and posterior to the IJV. The nodes are divided into superior and inferior subgroups at the point where the omohyoid muscle crosses over the IJV. Thus, those deep nodes above this crossing are the superior deep cervical lymph nodes and those below the crossing are the inferior deep cervical lymph nodes. (WB 208) Channels from the inferior deep cervical lymph nodes, also called supraclavicular nodes, join to form the jugular lymphatic trunks, which usually join the thoracic duct on the left side and the right lymphatic duct on the right side (sometimes it will enter the right venous angle directly).

11. Review the arrangement, distribution and function of the cervical sympathetic trunk. (WB 211-12; N 35, 128, 130, 131, 209, TG 7-10, 7-15, 7-95)

The left and right cervical sympathetic trunks:

• are a continuation of the thoracic sympathetic trunks
• lie behind and medial to the carotid sheath and in front of prevertebral muscles
• may be a solid trunk or strands connecting 2 or 3 cervical ganglia
• cervical ganglia represent consolidation of the original 1 ganglion per cervical spinal nerve, which is the pattern in the thorax. This consolidation of ganglia happens in areas where there are gray rami but no white rami, such as above T1 or below L2.
• there are only gray rami communicantes between the cervical trunk and spinal nerves C1-C8, because the highest level for white rami is T1. This means that all of the preganglionic fibers of the cervical sympathetic trunk originated at T1 or below (generally T1-T5). Postganglionic fibers in the cervical sympathetic trunk originate from one of the three cervical ganglia (or thoracic ganglia).
• much of the sympathetic innervation of the deep structures of the head occurs via perivascular sympathetic nerve plexuses that follow branches of the external and internal carotid arteries.

The superior cervical ganglion sends gray rami to C1-C4 spinal nerves (variable) and also gives off other branches. It lies opposite the transverse process of C2. Besides the gray rami to the spinal nerves, branches of the ganglion include:

• external carotid nerve reaches external carotid artery to form the external carotid plexus. These perivascular fibers follow branches of the external carotid to all the structures it supplies. For example, parotid gland sympathetic innervation comes via the perivascular external carotid plexus (vasoconstriction reduces salivation).
• internal carotid nerve, forming the perivascular internal carotid plexus to the brain, orbit, and forehead.
• branches to the carotid body.
• superior cervical cardiac nerve (accelerates heart rate and increases force of contraction).
• sympathetic contributions to glossopharyngeal (CN IX), vagus (CN X), and hypoglossal (CN XII) nerves.
• branches to join the pharyngeal plexus (along with glossopharyngeal and vagus).

The middle cervical ganglion (which may be absent) sends gray rami to C5-6 spinal nerves. It is at the level of the cricoid cartilage, often close to where the inferior thyroid artery crosses the sympathetic trunk. Besides the gray rami, branches include:

• middle cervical cardiac nerve, which has cardioaccelerator fibers, visceral afferent fibers to the heart, and fibers that go to the thyroid.

The cervicothoracic or stellate ganglion, the fusion of the inferior cervical and first thoracic ganglia, sends gray rami to C6,7,8 and T1. It lies anterior to the transverse process of C7 or the head of rib 1. Its other name, stellate ganglion, comes from the fact that its multiple branches spread out like light rays from a star. Branches include:

• inferior cervical cardiac n.
• perivascular fibers to vertebral a. and from there into the brain, onto basilar, posterior cerebral, and cerebellar aa.
• the ansa subclavia is a superficial strand that loops down from the middle cervical ganglion anteriorly around the subclavian artery and joins the inferior cervical ganglion behind the artery.
• this ganglion also receives a white ramus from T1.

Functions of the cervical sympathetic trunk:

• recall that sympathetic nerves cause vasoconstriction, secretion (sweat glands), pilomotor functions, and contraction of smooth muscle. Vasoconstriction can reduce output of glands like parotid by reducing blood flowing in. Specifically, the cervical sympathetic trunk controls:
• vasoconstriction of all the blood vessels of the brain and head (perivascular fibers)
• blood vessels to salivary glands and other oral glands (external carotid n.)
• acceleration of heart rate and strength of cardiac contraction through superior, middle, and inferior cervical cardiac nerves
• innervation of hair muscles and sweat glands on the head
• innervation of dilatator pupillae m. of the eye and superior tarsal m. of the eyelid. (Think about the eyes going wide with fright, a sympathetic-stimulating emotion.)

Horner's syndrome involves a lesion of the sympathetic trunk. Two of the more noticeable signs of this syndrome are constriction of the pupil and slight ptosis (drooping) of the eyelid.

12. Review the carotid sheath and contents. (WB 201,203,206; N 32, 33, 35, 125, 126, TG 7-17, 7-18, 7-13, 7-10)

The carotid sheath is a tube-shaped fascia wrapping the common carotid a. and internal carotid a., internal jugular v., and vagus n. Within the sheath, artery is medial, vein lateral, and nerve posterior and between the vessels. The carotid sheath lies anterolateral to the cervical sympathetic trunk, behind the sternocleidomastoid muscle. The sheath blends with the thyroid fascia anteromedially and with the deep surface of sternocleidomastoid anterolaterally. Posteriorly it is attached to prevertebral fascia along the tips of the transverse processes of vertebrae. It ends at the base of the skull where it attaches around the jugular foramen and carotid canal. It is here at the base of the skull that the internal carotid artery and internal jugular vein go their separate ways. Inferiorly, the carotid sheath fuses with scalene fascia, adventitia of great vessels, and the fibrous pericardium.

Through the middle neck levels, the superior root of the ansa cervicalis (from cervical plexus C1-2) lies in the sheath anteriorly. The carotid sheath is posterolateral to the thyroid gland and anterior to the prevertebral fascia. The sympathetic trunk lies behind the medial portion of the sheath. (N 75, TG 7-14,7-15)

The carotid sinus is the dilated terminal part of the common carotid artery, approx. 1 cm long. It is a baroreceptor in the elastic wall which responds to changes in blood pressure. The carotid sinus is innervated by a branch of the glossopharyngeal nerve.

The carotid body is an disc-shaped mass lying behind the bifurcation of the common carotid artery. It has a chemoreceptor sensitive to blood oxygen concentration. The carotid body is innervated by the nerve to carotid sinus from glossopharyngeal nerve, and also receives the nerve to carotid body, a branch of the vagus n. (CN X), as well as sympathetic fibers.

13. List the basic functions of the larynx.

The larynx connects the superior pharynx (oro- and naso-) with the trachea. It is specialized for producing voice, and a special part of the larynx - the epiglottis - protects the airway during swallowing. To achieve these added functions, the larynx has additional cartilages, muscles, ligaments, and mucous membranes.

14. Identify the main cartilages and membranes that form the internal framework (skeleton) of the larynx. (N 65, 66, 77, 78A, 78B, 78C, 78D, 78E, TG 7-22, 7-247-25, 7-28, 7-26, 7-27)

The larynx has nine cartilages (three unpaired and three paired):

• Thyroid cartilage - largest, unpaired. Extends laterally but is not continuous posteriorly, so it doesn't form a complete ring around the airway. Is composed of two quadrilateral laminae fused together in the anterior midline where there is a dip called the superior thyroid notch. This dip projects anteriorly to form the laryngeal prominence (Adam's apple). Along the lateral margins of the cartilage are the oblique lines running from the superior to inferior tubercles. The oblique line provides a point of attachment for the sternothyroid and thyrohyoid muscles anteriorly and the inferior pharyngeal constrictor muscle posteriorly. The superior border of the thyroid cartilage attaches to the hyoid bone by the thyrohyoid membrane. Inferior horns of the thyroid cartilage articulate with the lateral surface of the cricoid at the cricothyroid joints. The interior of the thyroid cartilage is covered by the mucous membrane of the interior of the larynx. The interior part of the thyroid cartilage deep to the superior notch is the point of attachment for the stem of the epiglottis, the vocal and vestibular ligaments, and three muscles: thyroarytenoid and its thyroepiglottic and vocalis parts.
• Cricoid cartilage - is an unpaired signet-ring-shaped cartilage with the narrow band (the arch) facing anteriorly and the broadened signet portion (the lamina) facing posteriorly. The cricoid is the only complete ring of cartilage to encircle the airway. Cricoid attaches to the thyroid cartilage by the median cricothyroid ligament and to the trachea below by the cricotracheal ligament. The cricothyroid muscle attaches to the anterior and lateral borders of the cricoid cartilage, and the inferior pharyngeal constrictor attaches to its posterior border. The posterior superior aspect of the cricoid is notched, and on either side of the notch are smooth surfaces for articulation with the bases of the 2 arytenoid cartilages. The inner surface of the cricoid is lined with mucous membrane.
• Arytenoid cartilages - paired, three-sided, pyramid-shaped bodies that lie on the superior margin of the cricoid lamina. The anterior protrusion of the pyramid is the vocal process which is connected to the vocal ligament. The muscular process protrudes laterally, to which are attached the posterior and lateral cricoarytenoid muscles. (Stretching between the posterior surfaces of the two arytenoids are the transverse and oblique arytenoid muscles. Attached to the anterolateral surface of the arytenoid are the thyroarytenoid muscle with its vocalis and thyroepiglottic parts.)
• Corniculate cartilages - paired, small cartilages that sit on top of the apices of the arytenoids.
• Cuneiform cartilages - paired, rod shaped bodies in the aryepiglottic fold lateral to the epiglottis.
• Epiglottic cartilage - an unpaired, spoon-shaped cartilage which is attached (by the thyroepiglottic ligament) at its inferior tapered end (tubercle of the epiglottis) to the superior thyroid notch. The superior end is free and curved anteriorly, while the anterior surface is attached to the hyoid bone by the hyoepiglottic ligament. It is covered by mucosa. The posterior surface of the epiglottis faces the vestibule of the larynx. It is pitted to accommodate small mucous glands.

Membranes of the larynx:

• Thyrohyoid membrane - suspends the thyroid cartilage and thus the larynx from the hyoid bone above. The median portion of this membrane is thickened, forming the median thyrohyoid ligament. Lateral thyrohyoid ligament on the sides of the larynx extends between the superior horn of the thyroid cartilage and to the end of the greater horn of the hyoid bone.
• Quadrangular membrane - above the vocal ligament is a thin sheet of connective tissue connecting the lateral part of the epiglottic cartilage with the arytenoid. Its lower free margin, above the vocal ligament, is the vestibular ligament of the false vocal (vestibular) folds.
• Conus elasticus - is an elastic membrane hanging down like a sheet from the vocal ligament above to the cricoid cartilage below. The lower attachment of this sheet stretches in a semicircle from the base of one arytenoid to the other. The thickened superior margins of the conus - the vocal ligaments - attach the vocal processes of the arytenoids to the inner surface of the laryngeal prominence, below the superior thyroid notch. This forms the V shape of the abducted vocal ligaments when seen from above.
• Hyoepiglottic and thyroepiglottic ligaments - attach the epiglottis to the hyoid bone and thyroid cartilage anteriorly.
• Cricotracheal ligament - connects the inferior border of the cricoid to the first ring of the trachea.

The laryngeal cavity extends superiorly from the laryngeal inlet at the border with the laryngopharynx to the inferior border of the cricoid. It is covered with a mucous membrane, which is continuous with the pharynx above and trachea below. It has three parts.

• The inlet and vestibule of the larynx are above the vestibular (false vocal) folds. The epiglottis, arytenoid cartilages, cuneiform and corniculate cartilages, aryepiglottic folds, and piriform recesses are components here. Just below the inlet is the widening called the vestibule, which ends below at the rima vestibuli, the aperture between the false vocal folds. The lateral walls of the vestibule are formed by the quadrangular membranes. The free inferior margins of the quadrangular membranes form the vestibular folds (or false vocal folds). The rima vestibuli, the opening between the vestibular folds, is wider than the rima glottidis or glottis, the space between the true vocal folds, below.
• The ventricle of the larynx is a cavity just below the vestibular folds and just superior to the true vocal folds. The ventricle functions as a resonance chamber.
• The infraglottic cavity extends from the glottis - the space between the vocal folds - to the beginning of the trachea below. The true vocal folds, at the superior end of the infraglottic cavity, are two mucous-membrane-covered vocal ligaments stretched between the vocal processes of arytenoids and the deep surface of the anterior angle of the thyroid cartilage. Vocalis and thyroarytenoid muscles lie lateral, parallel, and adjacent to the vocal ligaments. These are the parts of the larynx directly involved in making sound.

15. Describe the actions of the intrinsic muscles of the larynx in tensing, relaxing, abducting or adducting the vocal folds. (N 78C, 78D, 79, TG 7-26, 7-27, 7-28)

• Cricothyroid muscles (paired) - On the external surface of the larynx. Arise from the anterior arch of the cricoid cartilage and fibers travel backward and upward to insert into the inferior border of the thyroid cartilage. Action: pulls the thyroid cartilage down and toward the cricoid. Result: increases the distance between the arytenoids and the thyroid cartilage, tensing the vocal folds. Helps control pitch.
• Posterior cricoarytenoid muscles (paired) - Lie on the dorsal surface of the cricoid cartilage. Fibers originate near the posterior midpoint, and run laterally from there in both directions to attach to the back of the muscular processes of the arytenoid cartilages. Action: when muscles contract, they pull the muscular processes posteriorly and the vocal processes laterally. Result: Abduction of the vocal folds. These are the only abductors of the vocal folds. Without them, the vocal folds adduct permanently, and you suffocate.
• Lateral cricoarytenoid muscles (paired) - Originate from the upper anterior border of the cricoid cartilage. Fibers pass posteriorly left and right and insert on the anterior aspect of the muscular processes of the arytenoid cartilages. Action: Upon contraction, muscular processes are pulled anteriorly and vocal processes are pulled medially. Result: Adduction of the vocal folds.
• Arytenoid muscles (two, but unpaired) - These muscles, oblique and transverse, attach the posterior surfaces of the arytenoids to one another. Oblique fibers are continuous with the aryepiglottic muscles, which help to pull epiglottis down toward the larynx during swallowing. Action: Upon contraction, pulls the arytenoids medially (toward each other). Result: Adduction of the vocal folds.
• Thyroarytenoid muscles (paired) - Border the vocal ligaments. Arise from the anterior inner surfaces of the thyroid laminae, deep to the laryngeal prominence, and insert on the lateral borders of the arytenoid cartilages. Action: they pull the arytenoid cartilages closer to the thyroid cartilages, Result: reduced tension of the vocal ligament. In the process of shortening, these muscles also thicken and this helps seal the glottis. Thus they are considered sphincters of the glottis.
• Vocalis muscles (paired) - are composed of the fibers of thyroarytenoid muscles closest to the vocal ligaments. Each vocalis attaches to the elastic tissue of the vocal ligament. Action: Contraction affects frequency of vibration of the vocal ligaments. Result: Control of pitch and the fine adjustments required in vocalization.

16. Describe the innervation and vascular supply of the larynx. (N 76, 80, TG 7-26B, 7-26C, 7-28)

Innervation:

• Vagus, through superior laryngeal and inferior laryngeal nerves, innervates the entire larynx.
  • Superior laryngeal, internal branch: the principal sensory nerve of the larynx, sending fibers from the supraglottic portion of the larynx; also sends parasympathetic fibers to the mucous glands of the interior of the supraglottic portion of the larynx.
  • Superior laryngeal, external branch: only innervates the cricothyroid muscle.
  • Inferior laryngeal: Is the continuation of the left and right recurrent laryngeal nerves. It innervates all intrinsic muscles of the larynx except cricothyroid.

Vascular supply:

• Superior laryngeal artery, branch of the superior thyroid artery, pierces the thyrohyoid membrane along with the internal branch of the superior laryngeal nerve.
• Inferior laryngeal artery, branch of the inferior thyroid artery, passes under the inferior pharyngeal constrictor muscle along with the inferior laryngeal nerve.

17. Describe the anatomy relevant to cricothyroidotomy: locate the cricothyroid membrane and describe its relationships to the thyroid and cricoid cartilages, vocal cords, cricothyroid artery, and cricothyroid muscles. (N 76, 80, TG 7-26B, 7-26C, 7-28)

The cricothyroid membrane stretches between the thyroid and cricoid cartilages anteriorly. It is partially covered anterolaterally by the cricothyroid muscle. The cricothyroid membrane, but not the muscle, should be incised in a cricothyrotomy. If the incision is midline, the small cricothyroid artery, a branch of the superior thyroid artery, should not be involved, nor should the slender external branch of the superior laryngeal nerve which supplies the cricothyroid muscle and the lower portion of the inferior pharyngeal constrictor. Deep to the cricothyroid membrane, the conus elasticus will be incised in cricothyrotomy, but the vocal cords, which are the thickened upper edges of the conus elasticus, should not be harmed because they connect higher to the inner aspect of the thyroid lamina near the midline.

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Questions and Answers:

1. Are the external jugular, anterior jugular, jugular venous arch, and communicating veins bilaterally symmetrical in arrangement or size? Are they all present?

These veins are quite variable and are often asymmetrical. It will be unlikely that you will find all of them in one specimen. (N 31, 256, TG 7-11)

2. How does the innervation to the thyrohyoid muscle differ from the other strap muscles?

Thyrohyoid innervation comes from C1 & C2 via the hypoglossal nerve, arising after the superior root of the ansa cervicalis leaves the hypoglossal nerve. (N 32, 135, TG 7-13, 7-18)

3. Trauma to the external branch of the superior laryngeal nerve to the cricothyroid muscle during thyroid surgery may result in changes in voice quality. Why?

Because cricothyroid muscle tenses the vocal cords by pulling the thyroid and cricoid cartilages closer together anteriorly. (N 74,78, 126, TG 7-26, 7-18)

4. Is there a thyroidea ima artery present?

Only if your cadaver is in the lucky 10% containing this artery.

5. To what vessels do the middle and inferior thyroid veins drain?

Middle thyroid: internal jugular vein
Inferior thyroid: left and right brachiocephalic veins (N 74, TG 7-13)

6. At what foramen on the base of the skull does the internal jugular vein originate?

The internal jugular vein originates at the jugular foramen. (N8, TG7-06)

7. Can you identify the middle cervical ganglion?

This is occasionally absent. When present, it will lie near the level of the inferior thyroid artery and the cricoid cartilage and the transverse process of C6, just anterior to the vertebral artery. (N130, TG7-15)

8 Organize those parts of the cervical sympathetic trunk you have seen so far.

Inferior cervical ganglion - In approximately 80% of people, it fuses with the 1st thoracic ganglion to form the large stellate ganglion (a.k.a. cervicothoracic ganglion). It lies anterior to the transverse process of C7and the neck of the 1st rib on each side and posterior to the origin of the vertebral artery.

Middle cervical ganglion - This is occasionally absent. It lies near the inferior thyroid artery at the level of the cricoid cartilage and the transverse process of C6, just anterior to the vertebral artery.

Superior cervical ganglion - This is a huge ganglion that can be confused with the nodose ganglion of the vagus. This is found at the level of C1 and C2. (N130, N208, TG7-15, TG7-95)

9. Do you see connections (gray rami communicantes) between the trunk or ganglia and spinal nerves?

Yes, but you may NOT see any white rami communicantes because those are only present from T1 through L2. One white ramus reaches the stellate ganglion, only. (N130, TG7-15, TG7-95)

10. Are these (transverse cervical and suprascapular arteries) individual arteries or are they derived from a common trunk?

Both of these arteries should be branches of the thyrocervical trunk which is a branch of the first part of the subclavian artery. Sometimes they arise as a common trunk. Suprascapular vessels travel laterally immediately behind the clavicle, while the transverse cervical arches higher across the posterior triangle. (N33, TG7-15A, TG7-15B)

11. Study its (thyroid gland) relation to the sympathetic trunk and middle cervical ganglion.

The thyroid gland as a whole will be anteromedial to the sympathetic trunk as it ascends on the longus colli muscle. The inferior aspect of the thyroid gland should be just medial to the middle cervical ganglion. (N39, N130, TG7-14)

12. Define the interscalene triangle.

The interscalene triangle is defined as the area between the posterior border of the anterior scalene muscle, anterior border of the middle scalene muscle, and the superior border of the 1st rib. The major structures that are located in this structure are the trunks of the brachial plexus. (N34, TG7-15)

13. In forced inspiration, what muscle raises the second rib?

The posterior scalene muscle, since it inserts onto the second rib. Anterior and middle scalene muscles would effectively raise the second rib also, however they insert on the first rib. (N34, N186, TG7-15)

14. Identify the ascending pharyngeal artery (a branch of the external carotid) distributing to the dorsal wall of the pharynx. Do you find any lymph nodes (retropharyngeal)?

Retropharyngeal lymph nodes are usually present in the tissue between visceral and musculoskeletal parts of the neck, known as the retropharyngeal space, but difficult to find unless they are enlarged by disease. They are associated with the deep cervical nodes found in the carotid sheath just lateral to the space. (N 73, 136, TG 7-74)

15. Define nasal, oral and laryngeal portions of pharynx. What boundaries separate these regions?

The nasopharynx extends from the choanae anteriorly to the soft palate inferiorly; it is the respiratory portion of the pharynx. The oropharynx extends from the soft palate above to the epiglottis below and opens into the mouth anteriorly. The laryngopharynx extends from the epiglottis to the beginning of the esophagus below. It opens into the larynx anteriorly.

16. What structures lie immediately deep (lateral) to the palatine tonsil? Where is the lingual tonsil?

The superior pharyngeal constrictor muscle lies lateral to the palatine tonsil, along with the vessels supplying the tonsil. The lingual tonsil is in the submucosa on the superior surface of the root of the tongue just behind the sulcus terminalis. It is a large collection of lymphoid nodules that give the posterior one-third of the tongue its warty appearance.

17. The cartilages of the larynx along with their articulations and membranes constitute a separate, almost independent, musculoskeletal entity. What structural features differ in male and female?

The thyroid cartilage in male and female are different in shape. In the female, the two thyroid laminae meet in an angle of about 120 degrees. In the male, the thyroid laminae meet at an angle of 90 degrees. Thus the laryngeal prominence (the so called "Adam's apple") in the male is more obvious. The shape as well determines the length of the vocal cords and their consequent pitch; the cords being shorter in women and thus a higher pitched voice.

18. What is the action of the cricothyroid joint?

The cricothyroid muscle brings the arch of the cricoid and the thyroid cartilage together with the pivot at this joint. During this action the vocal folds become more tense and the pitch of the voice increases. Conversely paralysis of this muscle produces hoarseness of voice.

19. What is the glottis?

The glottis is defined as the space between the true vocal folds. It is also called the rima glottidis to differentiate it from the rima vestibuli, the space between the vestibular or false vocal folds.

20. What is the source of the inferior laryngeal nerve and the inferior laryngeal artery?

The inferior laryngeal nerve is the terminal end of the recurrent laryngeal nerve. It is motor to the intrinsic muscles of the larynx, while the recurrent laryngeal supplies the trachea and esophagus as well. The inferior laryngeal artery is a branch of the inferior thyroid artery; it accompanies the nerve into the space deep to the piriform recess.

21. Identify two structures that perforate the thyrohyoid membrane: the internal branch of the superior laryngeal nerve and the superior laryngeal artery. What is the source of each?

The internal branch of the superior laryngeal nerve is a sensory nerve to the interior of the larynx which arises from the vagus. The superior laryngeal artery and vein arise as the first branches of the superior thyroid vessels. (N 69, 74, 126, TG 7-26, 7-28)

22. Does the external branch of the superior laryngeal nerve pass through or give off a branch to the inferior pharyngeal constrictor muscle?

The external branch of the superior laryngeal nerve usually passes through the lower portion of the inferior constrictor muscle (this portion a.k.a. cricopharyngeus m.) supplying it and the cricothryroid muscle. (N 74, 75, 76, TG 7-20, 7-26)