Embryology of neck structures Flashcards
Desribe the anatomy and function of the cervical plexus
Formed by anterior rami of C1-C4 in the prevertebral layer of cervical fascia (at posterior triangle of the neck).
Consists of deep muscular branches and superficial cutaneous branches.
Muscular branches of the plexus supply prevertebral and lateral vertebral muscles, and contributes to the ansa cervicals which innervates the infrahyoid muscles. Major deep branch is the phrenic nerve.
Cutaneous branches visible beneath the border of sternocleidomastoid, supply the skin of the ear, neck, scalp, parotid, clavicle and shoulder.
Function of cutanous branches of the cervical plexus
Lesser occipital - skin of the neck, scalp and posterior ear
Greater auricular - skin of the parotid, ear, mastoid
Transverse cervical - anterior and lateral parts of the neck
Supraclavicular nerves - skin over clavicle and shoulder
Phrenic nerves
Branches of the cervical plexus (C3-C5). Pass around lateral border of anterior scalene and continue inferiorly within the prevertebral layer of cervical fascia.
Each nerve passes between the subclavian vein and artery to enter the thorax and continue to the diaphragm.
Innervate diaphragm . Damage causes paralysis
Course of the Vagus nerves
Descend through the neck within the carotid sheath. In the lower part of the neck, the vagus gives off cardiac branches that pass into the thorax.
In the root of the neck each vagus nerve passes anterior to the subclavian artery and posterior to the subclavian vein as it enters the thorax. Parasympathetic supply to thoracic and abdominal viscera
Left and right reccurent laryngeal nerves are branches of the vagus nerve.
Describe the anatomy of the spinal accessory nerve
Exits the cranial cavity through the jugular foramen. Descends through the neck in obliquely and posteriorly to sternocleidomastoid then enters the posterior triangle to lie within the investing fascia.
Nerve crosses the fascia to the anterior border of trapezius.
Innervates sternocleidomastoid and trapezius
Becasue it lies superficially as it crosses the posterior triangle it is susceptible to injury.
Damage causes weakness of shrugging, weakness of turning head to contralateral side, long term scoliosis due to pull of trapezius on one side.
Describe the anatomy of the glossopharyngeal nerve
leaves the cranial cavity through the jugular foramen and descends between the internal carotid artery and internal jugular vein. It then curves to reach the base of the tongue and palatine tonsil.
As it passes through the anterior triangle it innervates stylopharyngeus muscle, sends a branch to the carotid sinus and supplies sensory innervation to the pharynx.
Sensory supply to the pharynx, tonsil, middle ear, pharyngotypmanic tube and posterior 1/3 of the tongue.
Symptoms of damage to CNIX
Glossopharyngeal nerve
Damage causes difficulty swallowing
Loss os taste in posterior tongue and pharynx
Loss of gag reflex
Increased risk of aspiration
Describe the sympathetic supply to the head and neck
The cervical part of the sympathetic trunk lies posterior to the carotid sheath. It is connected to each cervical spinal nerve by grey ramus communicans.
The three ganglia in the neck are superior cervical (C1-C4), middle cervical (C5-C6) and stellate (C7-C8)
This is the only route for sympathetic nerves to enter the head.
Compression or laceration of the chain above T1 causes Horner’s syndrome.
Hypoglossal nerve
Leaves the cranial cavity through the hypoglossal canal and is medial to internal carotid and internal juguar vein. It then moves anteriorly across the lateral surfaces of the carotid arteries to the posterior belly of digastric and stylohyoid to enter the hyoglossus muscle.
Innervates muscles of the tongue.
Nerve is at risk of damage during carotid artery surgery and lymph node removal
Damage causes ipsilateral paralysis of the tongue. Deviation of the tongue towards the affected side on protrusion.
Briefly describe the development of the thyroid gland
The thyroid gland arises from endoderm.
Development begins in the floor of the pharynx, on the tongue at the foramen caecum.
As the embryo grows, the thyroid gland descends in the neck, passing ventral to the hyoid bone and laryngeal cartilages. It remains connected to the tongue by a narrow thyroglossal duct. This normally geneerates by week 7
It reaches its final position in front of the trachea at week 7 where it develops into two lateral lobes connected by an isthmus.
Thyroglossal duct cysts
Due to persistence of the thyroglossal duct after birth.
Cysts can form anywhere along the duct in the midline of the neck.
Cysts move on swallowing and protrusion of the tongue.
Can be distinguished from thyroid gland lumps because these move on swallowing but not with tongue protrusion
Nerve point of the neck
Posterior border of the middle 1/3 of sternocleidomastoid.
Where cutaneous branches of the cervical plexus emerge. Can anaesthatise the neck at this point.
Describe the anatomy of the thyroid gland
Thyroid gland is in the anterior part of the neck - visceral compartment
Two lobes on the lateral surfaces of the trachea and cricoid cartilage, connected by an isthmus that crosses the the 2nd/3rd tracheal cartilage.
Supplied by superior thyroid artery (branch of external carotid), and inferior thyroid artery (branch from thyrocervical trunk/subclavian)
Venous drainage by superior thyroid vein, middle thyroid vein ( go to IJV) and inferior thyroid vein (brachiocephalic)
Lymph drainage to paratracheal nodes and deep cervical nodes.
Innervated by nerves from the cervical sympathetic chain. Vasomotor fibres that cause constriction of blood vessels. Endocrine secretion controlled by pituitary.
Explain why patients for thyroid surgery should have vocal cord position and movements and their voice checked before and after surgery
The thyroid gland is closely related to the recurrent laryngeal nerves. Can become damaged during thyroidectomy causing vocal cord paralysis.
RLN branch from the vagus and loop around the subclavian artery (right) and arch of the aorta (left) and ascend between the trachea and oesophagus.
Pass along the posteromedial side of the thyroid, closely assocaited with inferior thyroid arteries.
Parathyroid glands
Two pairs of small, ovoid, yellow glands on the lateral lobes of the thyroid gland.
Derived from 3rd and 4th pharyngeal pouches. Inferior from 3rd, superior from 4th.
Supplied by inferior thyroid arteries, drain to thyrocervical trunk.
Secrete PTH, increases serum Ca2+ levels.
Pharyngeal arches
Consists of mesenchymal tissue with ectoderm on the outer surface and endoderm on the inner surface.
Mesoderm of the arches gives rise to muscles of the face and neck.
Each arch is innervated by a cranial nerve and initially contains an artery from the aortic arch (some degenerate).
Organs and tissues derived from the arches must migrate to their final position.
Pharyngeal clefts - internal indentations
Pharyngeal pouches - external indentations
Nerve supply to pharyngeal arches
1st Arch - CN V
Anterior belly digastric & mylohyoid
Muscles of mastication
Malleus & incus
2nd Arch - CN VII
Facial expression muscles
Posterior belly of digastric & stylohyoid
3rd Arch - CN IX
Stylopharyngeus
4th Arch - CN X (External Laryngeal Nerve)
Cricothyroid
6th Arch – CNX (Recurrent Laryngeal Nerve)
Intrinsic laryngeal muscles
Branchial cysts
Due to branchial fistulas. Formed when the 2nd pharyngeal arch fails to grow over the 3rd and 4th arches leaving remnants of the 2nd, 3rd and 4th clefts in contact with the surface of the skin by a narrow canal.
Fistulas found on the lateral aspect of the neck, anterior to sternocleidomastoid. Provides drrainage for lateral cervical cyst.
Metastatic origins of lymphadenopathy in the neck
Submental: lip
Submandibular: anterior 2/3 tongue, floor of mouth, gums, cheek
Post- auricular: nasopharynx
Posterior triangle: nasopharynx, posterior scalp, ear, skull base
Cervical chain: oral cavity, pharynx, larynx, tonsil.
Supraclavicular: thyroid, upper GI
