Anatomy Of The Neck IX, X and XI

Describe the platysma muscle, including its classification, nerve supply and functional relevance.

What it is

• A broad, thin, superficial muscle of facial expression

• Unique because it lies within the superficial fascia of the neck

Nerve supply

• Cervical branch of the facial nerve (CN VII)

Why it matters

• Facial nerve lesion affects it → loss of lower facial/neck expressions (e.g. grimacing)

Describe the cutaneous nerve supply to the posterior neck.

Main Supply

• Dorsal ramus of C2 = Greater occipital nerve

• Major sensory supply to the posterior scalp and upper posterior neck

Additional Supply

• Remaining posterior neck sensation comes from dorsal rami of C3-C6 (and occasionally C7)

Describe the cutaneous nerve supply to the anterolateral neck and name the specific branches.

Source

• Comes from the cervical plexus

• Ventral rami of C2-C4

Four key cutaneous branches

• Lesser occipital (C2)

• Great auricular (C2-C3)

• Transverse cervical (C2-C3)

• Supraclavicular nerves (C3-C4)

Landmark

• All 4 emerge around Erb’s point on the posterior border of the sternocleidomastoid

Name the superficial veins of the neck and their significance.

The two main superficial veins

• External jugular vein (EJV)

• Anterior jugular vein (AJV)

• Both linked by a communicating vein

Key features and significance

• EJV is visible under the skin

• Clinically important because distension = raised venous pressure

• AJVs run near the midline

• Important in midline neck surgery due to their variable but close position

Name the 3 compartments of the neck and their contents.

Posterior (Vertebral) Compartment

• Contents: Cervical vertebrae C1-C7, spinal cord, deep neck muscles

• Role: Support + protection - the neck’s backbone

Anterior (Visceral) Compartment

• Respiratory: Larynx, trachea, pharynx

• Digestive: Oesophagus

• Endocrine: Thyroid + parathyroid glands

• Functions: Breathing, speaking, swallowing, hormonal regulation

Lateral Vascular Compartments (Right and Left)

• Carotid artery

• Internal jugular vein

• Vagus nerve (CN X)

• Purpose: Protects major neurovascular bundles for brain perfusion, venous drainage and autonomic control

What muscles form the posterior cervical region?

Superficial layer

• Trapezius → the big, visible muscle forming the surface

Deep to trapezius

• Levator scapulae → elevates the scapula

• Splenius muscles (capitis and cervicis) → rotate and extend the head

• Semispinalis → strong head/neck extensor and rotator

• Erector spinae group (longissimus, spinalis) → extend the head and neck

Deepest layer: Suboccipital muscles

• Rectus capitis posterior major and minor

• Obliquus capitis superior

• Obliquus capitis inferior

Describe the borders of the lateral cervical region (posterior triangle) and its key contents.

Borders

• Anterior: Sternocleidomastoid muscle

• Posterior: Trapezius

• Inferior: Clavicle

• These 3 form the classic posterior triangle

Floor (muscular)

• Scalenes

• Levator scapulae

• Splenius muscles

Key contents

• Spinal accessory nerve (CN XI)

• Cervical plexus branches

• Inferior belly of omohyoid

• Roots of the brachial plexus

Describe the actions of the SCM muscle and the condition resulting from its pathological shortening.

Unilateral SCM action

• Tilts head to the same side

• Rotates head to the opposite side

Bilateral SCM action

• Flexes the neck forward

• Protrudes the chin

Pathological shortening

• Torticollis (“wry neck”)

• Head tilts toward the affected side

• Face rotates away

Describe the course of CN XI (spinal accessory nerve) in the neck.

Course in the Neck

• Origin:

• Starts in the spinal cord not the brainstem

• Enters skull:

• Ascends and enters through the jugular foramen with CN IX and CN X

• Neck pathway:

• Passes deep to SCM → innervates SCM

• Then travels superficially across the posterior triangle, superficial to levator scapulae

• Ends by innervating the trapezius

How is CN XI clinically tested?

Test the Trapezius

• Ask the patient to shrug their shoulders upward

• Apply downward resistance

• Look for strength + symmetry

Test the Sternocleidomastoid (SCM)

• Ask the patient to rotate their head to the opposite side of the muscle being tested

• To test right SCM → patient rotates left

• Apply resistance to assess strength

Describe the key neurovascular relationships around the scalene muscles.

Anterior to the Anterior Scalene

• Phrenic nerve

• Subclavian vein

• Internal jugular vein

• Branches of the subclavian artery

Scalene Interval (between anterior and middle scalenes)

• Subclavian artery

• Roots of the brachial plexus

• Cervical plexus contributions

Clinical link: Thoracic Outlet Syndrome

• Compression in the scalene interval

• Causes neurological + vascular symptoms in the upper limb (pain, numbness, weakness, reduced pulses)

What are the borders of the anterior cervical region (anterior triangle)?

Borders

• Lateral: Formed by the SCM muscle that’s easily palpable on either side of the neck

• Medial: Midline of the neck

• Superior: Inferior border of the mandible

List and classify the infrahyoid (strap) muscles, including their layers, actions and innervation.

Superficial layer

• Sternohyoid

• Omohyoid

Deep layer

• Sternothyroid

• Thyrohyoid

Main actions

• Depress the hyoid and larynx (especially after swallowing)

• Stabilise the hyoid to allow suprahyoids to work effectively

Innervation

• Ansa cervicalis (C1-C3) → supplies all except one

• Thyrohyoid → C1 fibres via hypoglossal nerve (CN XII)

List the suprahyoid muscles, their actions and nerve supply.

What they are

The suprahyoid muscles sit above the hyoid bone, linking it to the mandible and skull

Main actions

• Elevate the hyoid, larynx and floor of mouth during swallowing

• Help depress the mandible when the hyoid is fixed

Muscles + Nerve supply

• Anterior belly of digastric + Mylohyoid → CN V3 (mandibular division of trigeminal nerve)

• Posterior belly of digastric + Stylohyoid → CN VII (facial nerve)

• Geniohyoid → C1 fibres travelling with CN XII (hypoglossal nerve)

What are the contents of the submandibular and submental triangles?

Submental Triangle

Small triangle, chin + floor of mouth drainage

• Contains the mylohyoid

• Submental lymph nodes (drain floor of mouth and central lower lip)

• Small veins that form venous drainage of the chin

Submandibular Triangle

Big triangle, big gland

• Houses the submandibular gland

• Submandibular lymph nodes

• Facial artery and facial vein

• CN XII (hypoglossal nerve) runs through it

List the contents of the carotid triangle.

Arteries

• Common carotid artery

• Internal carotid artery

• External carotid artery + its branches

Monitoring structures

• Carotid sinus → BP sensor

• Carotid body → Chemoreceptor (O2/CO2)

Veins

• Internal jugular vein + key tributaries

Nerves

• CN XII → Hypoglossal

• CN IX → Glossopharyngeal

• CN X → Vagus

• Cervical plexus branches

Where does the common carotid artery bifurcate and what structures arise at this level?

Where it happens

• The common carotid artery bifurcates into the internal and external carotid arteries

• This occurs within the carotid triangle

Key structures at the bifurcation

• Carotid sinus → Baroreceptor

• Detects BP changes

• Located at the origin of the internal carotid artery

• Carotid body → Chemoreceptor

• Monitors O2, CO2 and pH

• Sits in the bifurcation cleft

List the branches of the external carotid artery using the mnemonic SALF-OP-MS.

Anterior branches - SALF

• S → Superior thyroid

• A → Ascending pharyngeal

• L → Lingual

• F → Facial

Supplies structures at front of neck and face

Posterior branches - OP

• O → Occipital

• P → Posterior auricular

Supplies the back of scalp and ear regions

Terminal branches - MS

• M → Maxillary

• S → Superficial temporal

Major suppliers of deep facial structures

Describe the origin and course of the internal jugular vein including its tributaries.

What it is

• A major vein that originates in the brain’s dural venous sinuses and runs straight down the neck

Main tributaries (what drains into it)

• Common facial vein

• Superior thyroid vein

• Middle thyroid vein

Where it ends

• Joins the subclavian vein → together they form the brachiocephalic vein

List the branches of the subclavian artery using the mnemonic VIT-CD.

• V → Vertebral artery - supplies the brain and spinal cord

• I → Internal thoracic artery - aka internal mammary

• T → Thyrocervical trunk - key branch: inferior thyroid artery

• C → Costocervical trunk

• D → Dorsal scapular artery - arises from cervicodorsal trunk

Describe the gross anatomy of the thyroid gland.

Basic shape

• Thyroid has 2 lobes connected by a thin bridge called the isthmus

Pyramidal lobe

• Present in 20% of people

• A cone-shaped extension that rises upward from the isthmus

• Its a remnant of the thyroglossal duct

What holds it in place

• The whole gland is anchored by the pre-tracheal layer of deep cervical fascia, keeping it firmly attached to the trachea

Describe the embryological development of the thyroid gland and the clinical implications.

How it develops

• The thyroid begins as an endodermal outgrowth from the floor of the pharynx

• It descends into the neck along a temporary tube called the thyroglossal duct

What normally happens

• The thyroglossal duct disappears as the gland reaches its final position

If development goes wrong

• Failure of the duct to disappear → thyroglossal duct cyst (most common congenital neck mass in children)

Common remnant

• Pyramidal lobe in 20% of people - leftover from its embryological descent

Describe the parathyroid glands: number, normal position, embryological origin and clinical considerations.

Number and Position

• Usually 4 parathyroid glands

• Found on the posterior surface of the thyroid gland

Embryological Origin

• Inferior parathyroids → from 3rd pharyngeal pouch

• Superior parathyroids → from 4th pharyngeal pouch

Clinical Importance

• Because they migrate during development, their final positions can vary

• Variability matters in parathyroid surgery especially for hyperparathyroidism

Describe the arterial supply to the thyroid and parathyroid glands.

Superior thyroid artery

• From external carotid artery

• Supplies the upper pole of the thyroid

Inferior thyroid artery

• From the thyrocervical trunk (branch of subclavian)

• Supplies the lower poles of the thyroid

• Main blood supply to the parathyroid glands

• Passes posterior to the carotid sheath

Variant artery

• Thyroid ima artery (3-10%)

• Runs midline, anterior to trachea

• Can arise from brachiocephalic trunk/aorta

• Clinically important → bleeding risk during tracheostomy

Describe the relationship between thyroid vessels and the laryngeal nerves and explain the surgical significance.

Superior thyroid artery

• Supplies the upper pole of the thyroid

• Runs close to the external branch of the superior laryngeal nerve

• If injured: the cricothyroid muscle is affected → trouble with high-pitched voice and pitch control

Inferior thyroid artery

• Supplies the lower pole of the thyroid

• Closely related to the recurrent laryngeal nerve

• If recurrent laryngeal nerve is damaged:

• Unilateral injury: hoarseness, weak voice

• Bilateral injury: stridor + airway obstruction

Describe the venous drainage of the thyroid and parathyroid glands.

Thyroid veins

• Superior thyroid vein → drains into the internal jugular vein

• Middle thyroid vein → drains into the internal jugular vein

• Inferior thyroid vein → drains into the left brachiocephalic vein

Parathyroid glands

• They mainly drain through the inferior thyroid vein pathway (left brachiocephalic vein)

Describe the motor innervation of the laryngeal muscles.

Main nerve

• Vagus nerve (CN X) supplies all laryngeal muscles

Recurrent laryngeal nerve

• Supplies all intrinsic laryngeal muscles except the cricothyroid:

• Posterior cricoarytenoid

• Lateral cricoarytenoid

• Transverse arytenoid

• Oblique arytenoid

• Vocalis

Superior laryngeal nerve

• External branch supplies the cricothyroid muscle

Describe the sensory innervation of the larynx.

Main nerve

• Vagus nerve (CN X) provides all sensory innervation to the larynx

Above the vocal folds

• Superior laryngeal nerve (internal branch)

• Supplies sensation to:

• Vestibule

• Ventricle

• Middle part of the larynx

Below the vocal folds

• Recurrent laryngeal nerve

• Supplies the infraglottic cavity

Name the muscles of the pharynx and their motor innervation.

Pharyngeal constrictors (3 circular muscles)

• Superior pharyngeal constrictor

• Middle pharyngeal constrictor

• Inferior pharyngeal constrictor

Innervation

• All by vagus nerve (CN X) via the pharyngeal plexus

Longitudinal muscles

• Stylopharyngeus → only muscle innervated by CN IX (glossopharyngeal)

• Palatopharyngeus → CN X

• Salpingopharyngeus → CN X

Describe the arterial blood supply to the pharynx.

Main source

• The external carotid artery is the primary supplier of the pharynx

Key ECA branches involved

• Superior thyroid artery

• Ascending pharyngeal artery

• Lingual artery

• Facial artery

• Maxillary artery

Additional supply

• Inferior thyroid artery (from thyrocervical trunk, branch of subclavian artery) also contributes