Pharyngeal arches

pharyngeal pouches

pharyngeal grooves

pharyngeal membranes

When do the pharyngeal arches appear?

Mesenchyme of pharyngeal arches derived from

Pharyngeal arches appear in 4th and 5th weeks

Mesenchyme derived from mesoderm and neural crest cells.

(Mesorderm --> musculature

neural crest cells --> skeletal (including ligaments) components)

**Pharyngeal arches covered by ectoderm externally, and endoderm internally

5 pairs around pharynx - each has its own muscular components, cranial nerve, and arterial component.

clefts lined w/ ectoderm

pouches lined w/ endoderm

1st arch (maxillary and mandibular prominences):

premaxilla

maxilla

zygomatic bone

part of the temporal bone

incus and malleous (from Meckel's cartilage)

mandible

2nd arch:

stapes

styloid process

stylohyoid ligament

lesser horn and upper part of body of the hyoid (from Reichert's cartilage)

3rd arch:

greater horn and lower part of body of the hyoid

4th and 6th:

Laryngeal cartilages (thyroid, cricoid, arytenoid, corniculate, cuneiform)

1st arch:

muscles of mastication

mylohyoid

anterior belly of digastric

tensor palatine

tensor tympani

2nd arch:

stapedius

stylohyoid

posterior belly of digastric

auricular

muscles of facial expression

3rd arch:

stylopharyngeus

4th & 6th arch:

cricothyroid

levator palatini

constrictors of pharynx

intrinsic muscles of pharynx

1st: Trigeminal nerve (CN V) - 3 divisions (V1,V2,V3) and carries NO parasympathetics

2nd: Facial nerve (CN VII) - does carry parasympathetics

3rd: Glossopharyngeal nerve (CN IX)

4th & 6th: Vagus nerve (CN X) - gives off recurrent laryngeal nerve a a branch

1st:

Tympanic (middle ear) cavity

Auditory (eustachian) tube

2nd:

Palatine tonsils

Tonsillar fossa

3rd:

Inferior parathyroid gland

Thymus

4th & 6th:

Superior parathyroid glands (related to 4th pouch)

Ultimobranchial body (-->C-cells of thyroid gland)

Remnants of 2nd, 3rd, and 4th clefts

**Typically, 2nd arch grows over the 3rd and 4th - 2nd, 3rd, and 4th lose contact w/ the outside. 1st cleft persists to give rise to the external auditory meatus.

If 2nd, 3rd, and 4th clefts persist, they form the cervical sinus.

Failure of the 2nd arch to grow caudally over the 3rd and 4th arches, leaving remnants of clefts in contact w/ the surface by a narrow canal.

On the lateral aspect of the nect, anterior to the sternocleidomastoid muscle.

Usually provides drainage for a lateral cervical cyst (remnant of cervical sinus, most often just below the angle of the jaw)

**Rupture b/w the 2nd cleft and pouch results in an internal branchial fistula - rare, occurs when the cervical sinus is connected to the lumen of the pharynx by a small canal.

Where mesenchyme seperates the endoderm of pouches from the ectoderm of clefts

**1st pharyngeal membrane becomes the tympanic membrane

Begins as a median endodermal thickening in the floor of the pharynx b/w the 1st and 2nd pharyngeal pouches (originates at foramen cecum, which is at the base of the tongue).

Grows into a median diverticulum (d: outpouching of a hollow or fluid-filled structure) and grows caudally as a tubular duct (thyroglossal duct).

Bifurcates forming the isthmus and 2 lateral loves of the thyroid gland.

Remnant of the thyroglossal duct (tubular duct growing caudally from the foramen cecum - becomes the thyroid gland).

May be found at any point along the migratory pathyway of the thyroid.

Found in or near the midline, and most frequently in hyoid region.

any point along the migratory pathway of the thyroid.

Commonly found in the base of the tongue, just behind the foramen cecum.

**Subject to the same diseases as the thyroid gland itself.

Facial prominences formed by...

What and where are the facial prominences located?

neural crest-derived mesenchyme, formed mainly by the 1st pair of arches.

Maxillary prominences lateral to the stomodeum

Mandibular prominences caudal to the stomodeum

Frontonasal prominence is the upper border of the stomodeum

Nasal placodes form on both sides of the frontonasal prominence.

Nasal placodes invaginate to form nasal pits, creating nasal prominences (lateral and medial).

the 2 medial nasal prominences and the 2 maxillary prominences.

**Maxillary prominences grow medially, compress medial nasal prominences and the 2 fuse.

Upper lip aka philtrum

6th week: outgrowths from the maxillary prominences called palatine shelves appear and are directed downwards on each side of the tongue.

7th week: palatine shelves ascend and attain a horizontal position above the tongue and fuse, forming the secondary palate.

**Shelves fuse w/ the triangular primary palate

Midline landmark b/w the primary and secondary palates

and dividing landmark b/w anterior and posterior cleft deformities

Cleft lip:

Multifactorial, related to maternal age

1/1000 births

80% more common in males

Cleft palate:

Multifactorial, NOT related to maternal age; related to anticonvulsant drugs during pregnancy

1/2500 births

67% more frequent in females

Obliquus capitis superior= lateral border (transverse process of atlas to occipital bone b/w sup and inf nuchal lines

Obliquus capitis inferior= inferior border (spinous process of axis to transverse process of atlas)

Rectus capitis posterior major= medial border (spinous process of atlas to inf nuchal line)

**produce extension and lateral bending of head at atlanto-occipital joint and rotation of head at atlantoaxial joint.

Suboccipital nerve and vertebral artery

*Suboccipital nerve= dorsal rami of C1 and emerges b/w occipital bone and C1; innervates muscles of the suboccipital region

Anterior triangle: Ant border= median line of neck

Post border= ant border of SCM

Sup border= inf border of the mandible

Roof= investing layer of deep cervical fascia

Floor= larynx and pharynx

Posterior triangle: Ant border= post border of SCM

Post border= ant border of trapezius

Inf border= middle 1/3 of clavicle

Roof= investing layer of deep cervical fascia

Floor= muscles covered by prevertebral layer of deep cervical fascia

Posterior division of the retromandibular vein

and

Posterior auricular vein

**EJV seen when platysma pulled back

Muscular triangle: superolateral border= superior belly of omohyoid

inferolateral border= inf portion of SCM

medial border= median plan of neck

Contents= infrahyoid muscles, thyroid gland, and parathyroid glands

Carotid triangle: inferomedial border= sup belly of omohyoid

inferolateral border= ant border of SCM

superior border= post belly of digastric

Contents= internal jugular lymph nodes, carotid sheath (common and internal carotid arteries, IJV, vagus n), hypoglossal n, branches of external carotid a.

Submandibular triangle: superior border= inf border of mandible

anteroinferior border= ant belly of digastric

posteroinferior border= post belly of digastric

roof= investing layer of deep cervical fascia

floor= mylohyoid and hyoglossus muscles

Contents= submandibular gland, facial artery, facial vein, stylohyoid muscle, part of CN XII and lymph nodes.

Submental triangle:

superior belly of omohyoid attached to hyoid, inferior belly attached to superior border of scapula near the suprasternal notch

depresses the hyoid bone

The infrahyoid muscles:

sternohyoid: sternum to hyoid - depresses hyoid.

superior belly of omohyoid: lateral to sternohyoid - hyoid to supior border of scapula - depresses hyoid.

sternothyroid: sternum to oblique line of thyroid cartilage - depresses larynx.

thyrohyoid: oblique line of thyroid cartilage to hyoid - elevates larynx.

**All innervated by ansa cervicalis EXCEPT the thyrohyoid which is innervated by C1 via hypoglossal nerve.

Anterior belly of digastric attached to digastric fossa of the mandible.

Posterior belly of digastric attached to mastoid process of temporal bone.

Attached to each other by intermediate tendon, attached to greater horn of hyoid by a fibrous sling.

Anterior belly of digastric innervated by mylohyoid nerve (branch of the mandibular division of the trigeminal (V3)).

Posterior belly of digastric innervated by facial nerve (CN VII).

Elevates the hyoid bone and depresses the mandible.

Attached to styloid process of temporal bone and greater cornu of hyoid bone.

Innervated by CNVII (facial nerve).

Elevates the hyoid bone.

**Tendon of stylohyoid straddles the intermediate tendon of the digastric muscle as it attaches to the hyoid bone.

**W/in submandibular triangle

External carotid arteries main supply laryngeal and pharyngeal structures and the face.

Internal carotids and the vertebral artery mostly supply the brain.

Vertebral artery= branch of the subclavian artery

Ascends through transverse foramen of the cervical vertebrae, typically entering throug the transverse foramen of C6.

3 branches off the 1st part of subclavian a:

Vertebral

Internal thoracic

Thyrocervical (--> inferior thyroid, ascending cervical, transverse cervical, suprascapular)

**Both transverse cervical and suprascapular travel into the post. triangle and supply structures in the neck and back.

1 branch off the 2nd part of subclavian a:

Costocervical (--> Deep cervical, Highest intercostals)

1 branch off the 3rd part of the subclavian a:

Dorsal scapular (or--> transverse cervical)

Sternohyoid

omohyoid

sternothyroid

thyrohyoid

Vertebral a.

Internal thoracic a.

Thyrocervical a.

Thyrocervical branches-->

Inferior thyroid a.

Ascending cervical a.

Transverse cervical a.

Suprascapular cervical a.

**Transverse cervical and suprascapular cervical travel into the posterior triangle to supply structures of the head and back.

2nd part:

Costocervical a

--> Deep cervical branch

and Highest intercostal branches

3rd part:

Dorsal scapular a.

--> Transverse cervical

6 Anterior branches:

Superior thyroid a.

lingual a.

facial a.

maxiallary a.

transverse facial a.

superficial temporal a. (pulse at temples)

3 Posterior branches:

Ascending pharyngeal a.

occipital a.

posterior auricular a.

Common facial v.

Pterygoid plexus

Pharyngeal v.

Lingual v.

Thyroid v. (sup and middle)

and brain

Anterior scalene innervated by C4-C7

Middle scalene innervated by C3-C7

Posterior scalene innervated by C5-C7

Omohyoid (inf. belly) innervated by ansa cervicalis (C1-C3)

Levator scapulae innervated by C3,C4 and the dorsal scapular n. (C4,C5)

Splenius capitis innervated by dorsal rami of C3,C4

**Scalenes innervated by branches of the cervical plexus

Longus capitis innervated by C1-C3

Longus colli innervated by C2-C6

Lesser occipital (C2) - ascends posterior scalp

Great auricular (C2,C3) - ascends medially across SCM

Transverse cervical (C2,C3) - travels anteromedially over SCM

Supraclaviculars (C3,C4) - descends to shoulders

All arise from Erb's Point, posterior to posterior border of SCM.

Spinal segments that contribute to the following nerves

Phrenic

Dorsal scapular

Long thoracic

Brachial plexus

Phrenic n.= C3,C4,C5

(travels on ant. scalene and innervates the diaphragm)

Dorsal scapular n.= C5

(innervates the rhomboids and levator scapulae)

Long thoracic n.= C5,C6,C7

(innervates the serratus anterior)

Brachial plexus= C5-T1

Facial nerve -->

Posterior auricular n.

Digastric br.

Cervical br.

Marginal mandibular br.

Buccal br.

Zygomatic br.

Temprao br.

**Facial nerve travels on top of the zygomatic arch (very superficial)

Facial n. branches deep to SMAS and muscles innervated on undersurface EXCEPT for the deep facial muscles which are innervate on their surface (levator anguli oris, buccinator, mentalis)