Dissection 8 - Neck I

Dissection Guide

• Platysma is within the superficial fascia

Layers of the deep fascia

• Investing layer, pretracheal fascia, prevertebral fascia, carotid sheath

  • Investing layer: SCM and trapezius

  • Pretracheal anteriorly

  • Prevertebral posteriorly

  • Carotid sheath on either side

• Puncta nervosum located deep to the posterior border of SCM (some n. pass through platysma)

• Locate parts of the cervical plexus

  • Great auricular n.: Traveling towards ear parallel to EJV on surface of SCM

    • Innervates skin overlying angle of the mandible

  • Lesser occipital n.: Coursing toward the apex of the posterior cervical triangle

  • Transverse cervical n

  • Suprascapular n.

Anterior triangle

• Borders: Midline, SCM, and Omohyoid

• SCM unilateral contraction: lateral head rotation

• SCM bilateral contraction: head flexion

• Deep to SCM

  • Find accessory n. → Just inferior to the ear

• Order of ligaments/cartilage around thyroid

  • Thyrohyoid ligament, Laryngeal promince of thyroid cartilage, Cricothyroid ligament, Cricoid cartilage

• Omohyoid central tendon units superior and inferior belly and passes through fascical sling

• Infrahyoid m.: Sternothyroid, Thyrohyoid

  • Deep to them: Thyroid gland

Cartotid trangle

• Borders: SCM, Omohyoid, Posterior belly of digastric

• Ansa cervicalis within anterior wall of carotid sheath

  • Surrounds IJV

  • Superior root traces up to hypoglassal n.

• Hypoglossal n. courses anteroposteriorly at the most superior portion of the carotid triangle

• Branches of ECA (most clinical significance)

  • Superior thyroid a.: most inferior branch, descends to superior lobe of thyroid gland

  • Lingual a.: arises at level of hyoid

    • Loops upward and passes anteriorly deep tot the hyoglossus m. to reach the oral cavity

  • Occipital a.: arises posterior side of ECA near hypoglossal n. and superior root of ansa cervicalis

  • Facial a.: Visinle in facial dissection

  • Maxillary a.: Visible in infratemporal fossa dissection

  • Superficial temporal a. Visible in infratemporal fossa dissection

• Cricothyroid m.: Innervated by external branch of superior laryngeal n. of CN X

  • Contraction → Elongate vocal cord

  • Node that internal branch of superior laryngeal n. pierces thyrohyoid membrane

Bolded terms

Accessory n. (CN XI)

• SM innervation to SCM and trapezius

• On anterior side of donor, seen deep to SCM just inferior to the ear

Ansa cervicalis

• Loop formed by C1-3 provides SM to infrahyoid m.

  • Except for thyrohyoid

• Superior root: mainly C1

• Inferior root: C2-3

Anterior and carotid triangles

• Anterior triangle borders: Midline of neck, SCM, and omohyoid

  • Structures to know in the area: ligaments and cartilage around thyroid and infrahyoid muscles

• Carotid triangle borders: SCM, posterior belly of digastric, omohyoid

  • Structures to know in the area: Ansa cervicalis (see loop around IJV and joining onto hypoglossal n.) and ECA branches

Anterior scalene m.

• Muscle that phrenic n. runs superficial to

• Located deep to SCM

Carotid a. (common, external, and internal)

• R CCA branches off of brachiocephalic trunk

• L CCA branches directly off aortic arch

Carotid body

• Chemoreceptor located at ECA and ICA bifurcation

• Innervated by CN IX

Carotid sheath

• Contains CCA, CN X, and IJV

  • CCA more medial

• Located between pretracheal and prevertebral fascia (one on each side)

Carotid sinus

• Baroreceptor located at the ECA and ICA bifurcation

• Innervated by CN IX

Cricoid arch

• Anterior portion of cricoid cartilage

Cricoid cartilage

• Located inferior to cricothryoid ligament

• “Class ring” shape

Cricothyroid m.

• Muscle that goes from cricoid cartilage to thyroid cartilage

• Innervated by external branch of superior laryngeal n. of CN X

• Contraction → Lengthen vocal cords (high pitch sounds)

Deep cervical lymph nodes

• Located within carotid sheath located close to IJV

Deep fascia of the neck

• Deep to superficial fascia of the neck

• Includes the investing layer, pretracheal fascia, prevertebral fascia, and carotid sheath

External branch of superior laryngeal n. of CN X

• Provides SM to cricothyroid m.

External jugular v.

• Runs superficial to SCM

• Drains into subclavian v.

Facial a.

• Branch of ECA

• Tortuous around gonial angle (because lots of movement)

Glossopharyngeal n. (CN IX)

• Runs along stylopharyngus m. (provides SM)

• Has a pharyngeal branch and one that continues between the superior and middle pharyngeal constrictors to reach the carotid sinus and body

  • Pharyngeal branch branches into lingual and tonsillar branches

Hyoid bone

• Free floating bone held by muscles

• Moves up during swallowing, moves down after to resting position

Hypoglossal n. (CN XII)

• Provides SM to extrinsic and intrinsic tongue m.

• C1 hitchhikes on CN XII to reach thyrohyoid and geniohyoid muscles

Internal and external carotid arteries

• ECA has branches outside cranium

• ICA enters cranium → Enter through carotid canal

Internal branch of the superior laryngeal n.

• Pierces thyrohyoid membrane to innervate intrinsic laryngeal m. (except thyrohyoid)

Internal jugular v.

• Runs within the carotid sheath and empties into brachiocephalic v.

Investing layer

• Contain trapezius and SCm

Laryngeal prominence

• “Adam’s” Apple

• Located on thyroid cartilage

Lingual a.

• Branch off ECA

Maxillary a.

• Branch off ECA

Median cricothyroid ligament

• Ligament between thyroid and cricoid

• Where a crycothyrotomy would be performed

Mendian thyrohyoid membrane (ligament)

• Ligament between thyroid and hyoid

Occipital a.

• Branch of ECA that goes posteriorly

Omohyoid

• Has a superior and inferior belly connected by a central tendon

Phrenic n.

• Made of C3-5, provides SM and SS to diaphragm

• Runs anterior to scalene m.

Platysma

• Thin muscle part of superficial fascia

Pretracheal fascia

• Anterior to prevertebral fascia

• Within deep fascia

Prevertebral fascia

• Posterior to pretrachela fascia

• Within deep fascia

Puncta nervosum

• Cutaneous n. derived from cervical plexus

• Located deep to the posterior border of the SCM

• Some n. pass through platysma

Pyramidal lobe/thyroid isthmus

• Pyramidal lobe is a middle lobe in the thyroid that ½ of the population has

• Thyroid isthmus is a midline connection between the L and R lobe ½ of the population has it

Thyroid gland

• Located inferior to thyroid ligament

• Receives blood from superior and inferior thyroid a.

Sternocleidomastoid m.

• Within the investing layer

• Innervated by CN XI

Sternohyoid

• Infrahyoid m.

• Runs from sternum to hyoid

Superficial fascia

• Beneath dermis, contains platysma in neck

Superior root of the ansa cervicalis

• Made of C1 primarily

• Runs superiorly to join hypoglossal n.

Superficial temporal a.

• Terminal branch of ECA

• Runs superficial to temporalis

Superior thyroid a.

• First branch of ECA

Supraclavicular n.

• Branch of cervical plexus made of C3-4

Thyrohyoid m.

• Innervated by C1 after hitchhiking on CN XII

• Infrahyoid m.

• Runs from thyroid to hyoid

Thyroid cartilage

• Lies between thyrohyoid ligament and cricothyroid ligament

• Contains laryngeal prominence

Transverse cervical n.

• Branch of cervical plexus C2-3

Vagus n. (CN X)

• Runs between CCA and IJV in carotid sheath and continues inferiorly