Anatomy H&N Flashcards
Describe the the thyroid gland:
Function: Largest endocrine gland (also encompasses the histologicaly and functionally distant parathyroid), producing thyroid hormones (T3 & T4, metabolism) and calcitonin (Ca and PO4 homeostasis).
Appearance: Described as butterfly shaped due to two lobes either side of the midline of the neck, joined by an isthmus. There is often a pyramid of gland directed superiorly from the left or right lobe.
Position/Size: Spans C5-T1. Lies inferior to the thyroid cartilage and is encapsulated by a fibrous capsule which fuses the gland to the cricoid cartilage.
Capsule is enclosed in a loose sheath formed by the pretracheal layer of the deep cervical fascia.
Lies deep to sternothyroid and sternohyoid muscles
Right and left lobes anterolateral to the larynx and trachea
In close contact with the small parathyroid glands which are posterior.
The fibrous thyroid capsule lies within?
The pre tracheal layer of the deep cervical fascia.
Which is more superficial, the sternohyoid or sternothyroid muscle?
The sternothyroid is deeper as it attaches to the inferior edge of the thyroid cartilage, the sternohyoid passing over on its way caudal to the sternum.
Microscopic description of the thyroid:
● Numerous lobules comprising individual follicles
● Supporting stroma and vasculature
● Follicles consists of single layer of cuboidal surface epithelium comprising thyroid follicular cells surrounding a central lumen containing colloid
● 10% of follicular epithelium contain parafollicular C cells, neural-crest derived containing granules of calcitonin
What makes calcitonin? Where
Parafolicular C cells make up 10% of the surface cuboidal cells surrounding colloid.
Follicular cells secrete? Stimulated by what and from where?
Follicular cells secrete thyroglobulin (contains iodine), T4 (storage and transport form), and T3 (active form)
Stimulated by TSH from anterior pituitary
Relations of the thyroid gland:
Relations
● Anterolaterally: sternothyroid, sternohyoid, superior belly of omohyoid and SCM
● Posterolaterally: carotid sheath and contents: common carotid, IJV, vagus nerve
● Medially: larynx and trachea, pharynx and oesophagus, recurrent and superior laryngeal nerves
● Posteriorly: parathyroid glands, vertebral bodies
Arterial supply to the thyroid
Arteries lie between the fibrous capsule and loose fascial sheath
1) Superior thyroid artery = anterior and superior
■ branch of external carotid
2) inferior thyroid artery = Posterior and inferior
■ branch of the thyrocervical trunk from 1st part of the subclavian artery
In 10% people isthmus is supplied by the Ima artery, a branch of brachiocephalic
Venous drainage of the thyroid:
The 2 paired (superior and middle thyroid veins) and 1 unpaired (Inferior thyroid vein) form a venous plexus.
The Sup and middle drain to the IJV, the inferior to the brachiocephalic trunk.
Any exam question about the lymphatic drainage of the thyroid should begin with:
Lymphatic vessels in the interlobar connective tissue and capsule.
Lymphatic drainage of the thyroid:
Lymphatic vessels in the interlobar connective tissue and capsule are multidirectional complex and extensive. Drains initially into peri-thyroid nodes, somewhat ipsilaterally drain to: Pre laryngeal (midline so bilaterally to) -> superior deep cervical nodes Pre tracheal (midline so bilaterally to) -> inferior deep cervical nodes ***** Para tracheal (lateral so drain ipsilaterally) -> Inferior deep cervical nodes, supraclavicular nodes and upper mediastinal nodes
Relations between structures in the carotid sheath:
IJV lateral to common carotid, vagus posteriorly.
Deep carotid nodes lie on the anterior lateral surface of the IJV.
Course of the Right common carotid
Right: Branches from the bifurcation brachiocephalic trunk behind the sternoclavicular joint. Ascends in the neck along with the other structures in the carotid sheath until it bifurcates into external and internal branches at the SUPERIOR BORDER of the Thyroid cartilage where the External leaves the sheath on its more anterior course.
Course of the Right common carotid
Left. Arises from the aortic arch immediately before the left subclavian artery, Travels 2cm superiorly in the superior mediastinum before entering the neck posterior to the Left sternoclavicular joint. Ascends in the neck along with the other structures in the carotid sheath until it bifurcates into external and internal branches at the SUPERIOR BORDER of the Thyroid cartilage where the External leaves the sheath on its more anterior course.
Where does the external carotid artery begin and end?
Begins at the bifurcation of the common carotid at the superior border of the thyroid cartilage.
End when divides into terminal branches = maxillary artery and superficial temporal behind neck of mandible.
Major Branches of the external carotid arteries:
1) (Almost immediately) Ascending laryngeal (gives off laryngeal branches)
2) Superior thyroid
3) Lingual
At the same level 4) & 5)
4) Facial artery, dips to medial side of angle of mandible to give off ascending palatine and tonsillar branches. Then rises superficial to the body turning superiorly to become the angular artery.
5) Occipital artery
6) Posterior auricular artery
The end at bifurcation into Terminal branches (post to neck of mandible:
Maxillary artery - to ptygopalantine fossa
Superficial temporal
The internal carotid begins at what vertebral level? and can be divided into how many segments:
A more complex division:
Begins at C4. 4 segments: Cervical (continues in sheath w/o branches) Petrous Cavernous Cerebral
Bouthillier's divisions (surgical and radiological use) are in to 7. In the scheme above (no cerebral): Cervical Petrous ** Lacerum Cavernous ** Clinoid ** Ophthalmic ** Communicating
Mnemonic for the internal carotid artery:
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Cervical Petrous Lacerum Cavernous Clinoid Ophthalmic Communicating artery.
The cervical segment of the internal carotid ends at (what is anterior):
Describe the 1st part of common carotid
C1 ends at carotid canal posterior to JV
Bulges after origin (the carotid sinus/bulb)
Course of cervical Internal carotid:
Ascends anterior to transverse processes of C1-3
Deep to parotid gland and internal jugular vein
Lateral to pharynx
Enters cranial cavity through carotid canal.
At the base of the skull what lies between the jugular vein and the internal carotid?
At the base of the skull the glossopharyngeal, vagus, accessory, and hypoglossal nerves lie between the artery and the internal jugular vein.
Describe C2 and C3 of the internal carotid:
Petrous (C2) Lacerum (C3)
○ Extends to foramen lacerum
○ Ascends in the carotid canal in petrous temporal bone
○ curves forwards and medially
○ then upwards and medially above foramen lacerum
○ Related posteriorly with cochlea and tympanic cavity
○ ***** superiorly with trigeminal ganglion
○ Surrounded by carotid plexus of nerves (sympathetic)
○ Branches: caroticotympanic and pterygoid
Describe C4 and C5 of internal Carotid
Cavernous (C4) + Clinoid (C5) = Cavernous segment
Curves layers of the dura mater forming the cavernous sinus (covered by the lining membrane of the sinus):
- First ascends toward the posterior clinoid process,
- Then passes forward by the side of the body of the sphenoid bone,
- again curves upward on the medial side of the anterior clinoid process, and
- perforates the dura mater forming the roof of the sinus. The curve in the cavernous segment is called the carotid siphon.
This portion of the artery is medial to abducent nerve (VI)
The crinoid segment is a tiny little bit with no branches betten the cavernous sinus and where the artery enter sub-arachnoid space/
Describe the ophthalmic segment of the internal carotid
○ After perforating dura medial to the anterior clinoid process
○ Curves backwards below optic nerve
○ Passes between optic and oculomotor nerves
○ Divides into anterior and middle cerebral arteries and join the Circle of Willis
○ Branches: ophthalmic, anterior cerebral, middle cerebral, posterior communicating, anterior choroid.
What does the external jugular vein do?
Basic course:
Drains face and neck
Begins near angle of mandible from union of Posterior branch of the retromandibular vein, and posterior auricular vein.
Passes superficial to SCM where at inferior edge is joined by posterior external jugular vein.
Continues inferiorly. Right before is joins the SCV it is joined by the jugular venous arch.
The jugular venous arch arises from? Travels medially behind?
Gives off what big branch?
1st branch external jugular vein
Travels medially behind SCM and IJV
Gives of Anterior Jugular Vein
Mnemonics for branches of:
External Jugular vein
Internal Jugular vein
External Jugular: PAST = Posterior, anterior Jugular, Suprascapular Transverse Cervical (bifurcates into reteromandibular and post auricular)
Internal
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Branches of the internal jugular vein (where does it begin?):
Begins in the posterior compartment of the jugular foramen, by the union of the inferior petrosal and sigmoid sinuses.
Origin of the jugular vein?
Begins at the base of skull in the posterior compartment of the jugular foramen, by the union of the inferior petrosal and sigmoid sinuses.
What is the venous angle?
Venous angle = site where the thoracic duct (L) and right lymphatic trunk (R) join the systemic circulation. Behind the medial end of the clavicle, where internal jugular unites with the subclavian vein to form the brachiocephalic vein.
Branches (inferior to superior) of the internal jugular vein
Formed by confluence of sigmoid sinus and inferior petrosal veins then: 1) Pharyngeal vein 2) Lingual vein 3) Common facial 4/5) sup and middle thyroid 6) Occipital vein
Course of the Subclavian vein:
● Begins at the lateral border of the first rib
● Continuation of the axillary vein
● Passes anterior to anterior scalene and phrenic nerve
● Unites with IJV at medial border of anterior scalene, posterior to medial end of clavicle to form the brachiocephalic vein.
What is the posterior relation to the phrenic nerve in the lower half of the neck?
The anterior scalene.
Course of the recurrent laryngeal nerve:
The left RLN is longer than the right, because it crosses under the arch of the aorta at the ligamentum arteriosum.
Typically ascend in a groove at the junction of the trachea and esophagus.
Pass behind the posterior, middle part of the outer lobes of the thyroid gland and enter the larynx underneath the inferior constrictor muscle,passing into the larynx just posterior to the cricothyroid joint.
The terminal branch is called the inferior laryngeal nerve.[
What forms the borders of the carotid triangle?
Posterior = SCM
Anterior: Superior body of omohyoidius
Superior: Posterior body of digastric
What runs within the carotid triangle (there are shitloads of things):
Bifurcation of common carotid, Carotid sheath with its contents (i.e vagus, nodes, IJV, internal carotid), external carotid and most of its branches (ascending pharyngeal, sup thyroid, lingual, facial, occipital.
Hypoglossal nerve, which crosses the bifurcated carotid arteries, and accessory nerve.
The internal carotid artery enters the skull base through the carotid canal, where it begins a series of 90° turns which lead it to eventually terminate as?
Describe the turns
The middle and anterior cerebral arteries.
5 Turns:
1) 90° anteromedially within the carotid canal to run through the petrous temporal bone.
2) 90° superiorly within the cavernous sinus
3) 90° turn anteriorly to travel along the roof of the cavernous sinus, where it grooves the body of the sphenoid.
Think of an “s” tipped to the left
4) 90° turn superiorly to exit posterior to the anterior clinoid
5) 90° turn inferior to run lateral to the chasm terminating in middle and anterior cerebral arteries.
Describe the larynx
● Anterior midline structure from levels C3-C6
● Fibrocartillagenous skeleton with muscles interiorly
● Divided into supraglottis, glottis and subglottis.
● Valve with the following functions:
i) An open valve in respiration
ii) Partially closed valve in phonation
iii) Closed valve to protect the airway during deglutition and coughing. A closed airway also allows a raised intra-abdominal pressure during defecation, micturition and parturition
What vertebral levels does the larynx span?
C3-C6
Relations of the Larynx:
Anterior: Skin, platysma, superior part of thyroid (this extend C5-T1)
Lateral: Piriform fossa, Sternohyoid (anterolateral), SCM,, carotid sheath and contents, recurrent laryngyneal nerves. Superior part of lateral lobes of thyroid
Posterior: Layngopahrynx (aka hypo pharynx)
Inferior: Continuous with cervical trachea
Superior: Superior border epiglottis, hyoid bone, hypo pharynx.
What subsections can the larynx be divided into?
1) Supraglottis: from inferior surface of epiglottis to vocal folds (ie. the false vocal cords).
2) Glottis: vocal cords and 1cm below them. The openingbetween the vocal cords is known as rima glottidis, the size of which is altered by the muscles of phonation
3) Subglottis– From inferior border of the glottis to the inferior border of the cricoid cartilage
Borders of the larynx:
Superior: Inferior boarder epiglottis
Inferior: Inferior border of cricoid cartilage (same as hypo pharynx).
The openingbetween the vocal cords is known as?
The openingbetween the vocal cords is known as rima glottidis, the size of which is altered by the muscles of phonation
The lining of the larynx:
The vocal cords are non-keratinised stratified squamous epithelium (i.e. think vocal cord SCC),
The rest is respiratory epithelium: ciliated columnar epithelium.
Describe the unpaired components of the cartilaginous skeleton of the larynx:
There are 3 paired and 3 unpaired components
Unpaired (the easy ones)
1) Epiglottis - heart shaped covered in mucous membrane. Forms
2) Thyroid cartilage: 2 laminae fusing anteriorly to form the laryngeal prominence. Superior border at the level of C4 where thyrohyoid membrane suspends the larynx from the hyoid. Inferior border has thyrocricoid membrane.
3) Cricoid cartilage: Signet ring with band facing anteriorly. Only complete ring of cartilage along the airway. Suspended from thyroid cartilage. The fibrous capsule of the thyroid is fused with the anterior surface./
Describe the paired components of the cartilaginous skeleton of the larynx:
Paired:
1) Arytenoid: Pyramid shaped cartilages. Apex superiorly, vocal process anteriorly, muscular process laterally. Movements allow tensing and relaxing of the vocal cords
2) Cuneiform
3) Corniculate
The muscles of the neck can be divided into?
Based on?
Intrinsic and extrinsic:
Extrinsic muscles move the larynx as a whole
Intrinsic alter the length and tension of the vocal folds
The extrinsic muscles of the larynx can be broken into:
outer aspect and internal
Outer aspect into:
- The suprahyoid muscles elevate the larynx,
Includes stylopharyngeus
- The infrahyoid muscles depress it
A tracheostomy goes through what?
A cricothyroidotomy goes through the median cricothyroid ligaments (there is also a median thyrohyoid ligament) - so there is 2 extra ligaments to name in an exam.
What connects the arytenoid cartilage with the epiglottic cartilage?
What does it form?
Quadrangular membrane:
- connects the arytenoid cartilage with the epiglottic cartilage, forming skeleton of the aryepiglottic fold
- Its free inferior edge forms the vestibular ligament
What is “special” about the cricothyroid?
What about the other muscles
The cricothyroid is the only intrinsic muscle external to the larynx. It tenses the vocal cords
Also supplied by the external branch of the superior laryngeal nerve (all the rest of the intrinsic are supplied by a branch of the recurrent)
The remainder of the muscles form a sphincter around the laryngeal inlet.
Intrinsic muscles of the larynx:
(all are paired) Cricothyroid Thyroarytenoid Posterior cricoarytenoid (important) Lateral cricoarytenoids Transverse and Oblique Arytenoids
Which muscles abduct the vocal cords?
Only the POSTERIOR cricoarytenoids abduct the cords, all other muscles function to oppose the vocal folds.
Parts of the thyroid cartilage
Composed of two lateral plates (laminae) which meet in the midline anteriorly, forming the:
Laryngeal prominence
Posterior border of each sheet projectsuperiorly and inferiorly to form the:
Superior and
Inferior horns (also known as cornu)
Arterial supply to the Larynx:
Superior laryngeal artery
Branch of the superior thyroid artery
Inferior laryngeal artery,
branch of inferior thyroid artery
Venous supply to the larynx:
Superior laryngeal vein
drains to the internal jugular vein via the superior thyroid
Inferior laryngeal vein
drains to the left brachiocephalic vein via the inferior thyroid vein
Easy thing to remember about the blood supply to the larynx:
Superior and inferior aa/vv all drain to inf and sup thyroid aa/vv’s
Lymphatics is similar (but remember level 4, pre/paratrachial nodes drain to deep cervical)
Lymphatic drainage of the larynx:
Above vocal folds = Follow superior laryngeal artery to drain into superior deep cervical nodes. (levels III, occasionally level II)
Below vocal folds = follow similar pathways to tracheal lymphatics, and end in pre- or para-tracheal nodes (level VI). From here they drain to deep cervical nodes (levels III, IV).
There are no lymphatics of the vocal folds. If tumours in this region advance to the point of invading surrounding parts of the larynx, they may spread along either pathway.
