Lab 1 Exam-Day Review

✍️ Wording

Full names, anatomical directions. Spelling counts: sternocleidomastoid · omohyoid · sternothyroid · thyrohyoid · ansa cervicalis · thyrocervical · costocervical · cricothyroid · supraclavicular · great auricular.

★ High-yield traps

Ansa cervicalis (C1–C3) supplies sternohyoid, sternothyroid, omohyoid. Thyrohyoid = C1 via CN XII (not the ansa).
Carotid sheath: common carotid medial, internal jugular vein lateral, vagus posterior between them. Deep cervical nodes follow the internal jugular vein.
Anterior scalene: phrenic nerve + subclavian vein anterior to it; subclavian artery + brachial plexus trunks posterior (interscalene triangle).
Suprahyoid nerves: stylohyoid + posterior digastric = CN VII; mylohyoid + anterior digastric = V3.
Superior thyroid artery ↔ external laryngeal nerve; superior laryngeal artery ↔ internal laryngeal nerve; inferior thyroid artery ↔ recurrent laryngeal nerve.
Cricothyroid is the only intrinsic laryngeal muscle supplied by the external laryngeal nerve; all others = recurrent laryngeal.
Carotid body (chemoreceptor) + carotid sinus (baroreceptor) = CN IX.
Right recurrent laryngeal loops the right subclavian artery; left loops the aortic arch.

2 · Surface Anatomy, Fascia & Spaces

Surface landmarks

Mental protuberance — chin
Laryngeal prominence — Adam’s apple (thyroid cartilage)
Jugular notch — lowest palpable midline landmark (manubrium)
Mastoid process — posteroinferior to the ear; SCM attachment
SCM divides the neck into anterior and posterior triangles
Anterior border of trapezius — posterior boundary of the posterior triangle

Fascial layers

Superficial fascia: cutaneous nerves, vessels, lymphatics, fat, platysma
Investing: 360° collar; splits around SCM and trapezius
Pretracheal: thyroid, trachea, esophagus; posteriorly = buccopharyngeal fascia
Carotid sheath: common carotid, internal jugular vein, vagus
Prevertebral: vertebrae + deep neck muscles (encloses the phrenic nerve)
Alar: subdivides the retropharyngeal space

Space	Between	Extent	Infection spreads to
Pretracheal	Fascia over infrahyoid muscles ↔ pretracheal fascia	Anterior neck	Anterior mediastinum (pretracheal fascia blends with the fibrous pericardium)
Retropharyngeal	Buccopharyngeal fascia ↔ alar fascia	Skull base → T1–T2	Superior mediastinum; fluid here → difficulty swallowing
Danger space	Alar fascia ↔ prevertebral fascia	Skull base → diaphragm	Most dangerous route — widest extent

3 · Triangles of the Neck

Lateral view. The SCM splits the neck into anterior and posterior triangles; the digastric bellies and superior omohyoid carve the anterior triangle into four. CN XI and the cutaneous nerves (Erb’s point) cross the posterior triangle.

Triangle	Boundaries	Key contents
Anterior (overall)	Midline · anterior border of SCM · inferior border of mandible	Four sub-triangles below
Submandibular	Mandible · anterior + posterior bellies of digastric	Submandibular gland, lymph nodes, facial artery + vein, CN XII, mylohyoid, stylohyoid
Submental	Both anterior bellies of digastric · hyoid (floor = mylohyoid)	Lymph nodes, tributaries of anterior jugular veins
Carotid	Posterior digastric · superior omohyoid · anterior border of SCM	Carotid sheath contents, deep cervical nodes, CN XII, ansa cervicalis, superior laryngeal nerve branches, ECA branches
Muscular	Superior omohyoid · anterior border of SCM · midline	Infrahyoid (strap) muscles, thyroid gland
Posterior	Posterior border of SCM · anterior border of trapezius · clavicle	CN XI, cervical plexus cutaneous branches, brachial plexus, external jugular vein, subclavian artery; floor = splenius capitis, levator scapulae, scalenes

4 · Superficial Neck: Muscles, Veins & Cervical Plexus

Muscle	Attachments	Action	Nerve
Platysma	Pectoral fascia → inferior mandible (in superficial fascia)	Tenses the skin of the neck	CN VII (cervical branch) — facial expression muscle
Sternocleidomastoid	Sternal + clavicular heads → mastoid process	Unilateral: tilts head to the same side, rotates face to the opposite side. Bilateral: flexion/extension of the head	CN XI
Trapezius	Occipital bone → T12; inserts on clavicle + scapula	Elevates/depresses scapula; helps abduct arm >90°	CN XI

CN XI injury (posterior triangle)

Ipsilateral shoulder droop, weak shrug
Weak head turn to the opposite side against resistance
Difficulty abducting the arm above 90°

Exits the jugular foramen → SCM → crosses the posterior triangle superficially → trapezius.

Torticollis (wry neck)

Contracted SCM → head tilts toward the affected side, chin points to the opposite side. Congenital (SCM fibrosis, birth trauma) or spasmodic (cervical dystonia).

Cutaneous branch (C1–C4 ventral rami)	Course from Erb’s point (mid-posterior border of SCM)	Skin supplied
Lesser occipital nerve	Ascends along the posterior border of SCM	Neck + scalp posterior to the ear
Great auricular nerve	Crosses SCM ascending to the ear	Ear + mastoid area (at risk in neck dissection)
Transverse cervical nerve	Runs horizontally across SCM	Anterior triangle
Supraclavicular nerves	Descend to the clavicle + shoulder	Over the clavicle + shoulder

Superficial veins

External jugular vein = posterior auricular + retromandibular (posterior division); descends superficial to SCM → subclavian vein. Superficial cervical nodes follow it. JVD in right heart failure.
Anterior jugular vein — anterior neck → external jugular vein.

Deep vein

Internal jugular vein — lateral in the carotid sheath; + subclavian → brachiocephalic vein.
Tributaries: common facial vein, superior + middle thyroid veins.
Central line site (with the subclavian vein). Deep cervical nodes run along it.

5 · Suprahyoid & Infrahyoid Muscles, Ansa Cervicalis

Suprahyoid (elevate the hyoid in swallowing)

Stylohyoid	Styloid → hyoid; splits around the digastric tendon · CN VII
Posterior digastric	Mastoid → intermediate tendon · CN VII
Anterior digastric	Superficial to mylohyoid · V3 (nerve to mylohyoid)
Mylohyoid	Floor of the mouth · V3 (nerve to mylohyoid)

Pair them: stylohyoid + posterior digastric = CN VII; mylohyoid + anterior digastric = V3.

Infrahyoid “strap” muscles

Sternohyoid	Superficial, medial · ansa
Omohyoid	Superficial, lateral; scapula → hyoid (omo = shoulder); intermediate tendon under SCM · ansa
Sternothyroid	Deep; sternum → thyroid cartilage · ansa
Thyrohyoid	Deep; thyroid cartilage → hyoid · C1 via CN XII

★ C1 hitchhikers on CN XII

C1 fibers leave CN XII as (1) the superior root of the ansa, (2) the nerve to thyrohyoid, (3) the nerve to geniohyoid. A tag on thyrohyoid → answer C1 via CN XII, not the ansa.

6 · Carotid Triangle & Carotid Sheath

Common carotid bifurcation

Right: from the brachiocephalic trunk; left: from the aortic arch
Bifurcates at the superior border of the thyroid cartilage
Internal carotid — no neck branches → cranial cavity
External carotid — neck + face branches

Carotid body vs. carotid sinus (both CN IX)

Carotid body	Tissue mass at the bifurcation · chemoreceptor (O₂)
Carotid sinus	Dilation of the proximal ICA · baroreceptor (BP)

#	ECA branch (inferior → superior)	Direction	Supplies / travels with
1	Superior thyroid → superior laryngeal artery	Anterior	Superior pole of thyroid (with external laryngeal nerve); superior laryngeal a. pierces the thyrohyoid membrane with the internal laryngeal nerve
2	Ascending pharyngeal	Posterior (medial)	Deep pharynx
3	Lingual	Anterior	Tongue/oral cavity (deep to hyoglossus)
4	Facial	Anterior	Face (through the submandibular triangle)
5	Occipital	Posterior	Posterior scalp
6	Posterior auricular	Posterior	Behind the ear
7	Maxillary	Terminal	Deep face
8	Superficial temporal	Terminal	Temporal region + scalp

CN XII in the neck

Hypoglossal canal → descends between ICA and IJV → hooks forward superficial to the internal + external carotid arteries → carotid + submandibular triangles (deep to posterior digastric) → tongue. Gives off C1 fibers (superior root of the ansa, nerve to thyrohyoid).

7 · Vagus Nerve & Laryngeal Branches

	Internal laryngeal	External laryngeal	Recurrent laryngeal
Type	Sensory	Motor	Motor + sensory
Target	Laryngeal mucosa above the vocal folds	Cricothyroid only	All other intrinsic laryngeal muscles; mucosa below the vocal folds
Travels with	Superior laryngeal artery	Superior thyroid artery	Inferior thyroid artery
Injury	Loss of the cough reflex (afferent limb)	Decreased vocal range (can’t raise pitch) — “opera singer”	Hoarseness (unilateral); thyroidectomy risk

Cricothyroid muscle

External to the larynx, between the cricoid and thyroid cartilages. Tilts the thyroid cartilage → lengthens/tenses the vocal folds → raises pitch. Nerve: external laryngeal.

8 · Larynx Landmarks & Surgical Airway

Hyoid bone↓Thyrohyoid membrane (internal laryngeal n. + superior laryngeal a. pierce it)↓Thyroid cartilage (laryngeal prominence)↓Cricothyroid ligament (membrane) — cricothyroidotomy↓Cricoid cartilage (complete ring)↓1st tracheal ring → C-shaped rings

	Cricothyroidotomy	Tracheostomy
Where	Through the cricothyroid membrane (between thyroid + cricoid cartilages)	Incision between tracheal rings
When	Emergency when orotracheal intubation fails	Longer-term airway
Risk	Left too long → damage to vocal folds/larynx	—

9 · Thyroid & Parathyroid Glands

Anatomy

Anterolateral to larynx/trachea, deep to the strap muscles, in pretracheal fascia
Right + left lobes joined by the isthmus
Pyramidal lobe (variable) = remnant of the thyroglossal duct
4 parathyroids on the posterior surface

Thyroidectomy danger

Inferior thyroid artery ↔ recurrent laryngeal nerve → hoarseness
Superior thyroid artery ↔ external laryngeal nerve → lost high pitch
Horner syndrome (sympathetic trunk) is also possible

Vessel	Source / drains to
Superior thyroid artery	1st branch of the external carotid
Inferior thyroid artery	Thyrocervical trunk (subclavian)
Superior + middle thyroid veins	Internal jugular vein
Inferior thyroid vein	Brachiocephalic vein

10 · Root of the Neck

Anterior scalene syndrome (thoracic outlet)

Cervical rib, hypertrophied scalenes or trauma compress the subclavian artery + brachial plexus in the interscalene triangle → vascular + neurologic upper limb symptoms. The subclavian vein is spared (anterior to the muscle).

Phrenic nerve

C3, 4, 5 keep the diaphragm alive. Descends on the anterior scalene within prevertebral fascia → posterior to the subclavian vein, anterior to the subclavian artery → thorax. Motor to the diaphragm; sensory to fibrous pericardium + parietal pleura.

Subclavian part (by anterior scalene)	Branches — “VIT C D”	Notes
1st — origin → medial border	Vertebral · Internal thoracic · Thyrocervical trunk	Vertebral ascends through transverse foramina → foramen magnum. Internal thoracic descends beside the sternum.
2nd — behind the muscle	Costocervical trunk	Deep neck + thoracic wall
3rd — lateral border → 1st rib	Dorsal scapular (variable)	Passes through the brachial plexus trunks; may come from the transverse cervical artery (“sometimes D”)

Thyrocervical trunk→Inferior thyroid a. (medially, with recurrent laryngeal n.)·Transverse cervical a. (across anterior scalene → posterior triangle → back)·Suprascapular a. (across anterior scalene → scapula)

Right subclavian = brachiocephalic trunk; left = aortic arch. Continues past the 1st rib as the axillary artery.

Lymph ducts

Thoracic duct — left side; enters the left venous angle (IJV + subclavian)
Right lymphatic duct — right venous angle
Jugular trunks carry all head/neck lymph (deep cervical nodes along the IJV) to these ducts

Brachial plexus & scalenes

Plexus = ventral rami C5–T1; trunks emerge between anterior + middle scalenes
Anterior + middle scalene → 1st rib; posterior scalene → 2nd rib; all = cervical ventral rami
Posterior triangle floor: splenius capitis (dorsal rami), levator scapulae (dorsal scapular n.), scalenes

11 · Cervical Sympathetic Trunk & Horner Syndrome

Inferior cervical ganglion often fuses with the 1st thoracic → stellate ganglion.

★ Horner syndrome — “PAM Horner”

Ptosis (mild; superior tarsal muscle) · Anhidrosis · Miosis (dilator pupillae lost). Causes: Pancoast tumor at the lung apex, penetrating neck trauma, surgery (thyroidectomy, carotid endarterectomy).

Lab 1 Exam-Day Review — The Neck

1 · Exam-Day Rules & Top Traps