L6: Anterior Triangle: muscles, innervation, major vessels Flashcards
Describe the boundaries of the anterior triangle of the neck
- Lateral border: Ant border of Sternocleidomastoid muscle
- Medial border: Midpoint of mandible to jugular notch (midline)
- Superior border: Inferior border of mandible
What are the 4 suprahyoid muscles and their innervations, insertions and origins from lateral to medial
- Digastric muscle:
a) Ant belly: Mylohyoid nerve from Mandibular V3.
b) Post belly: Facial CN7
(Digastric fossa inside mandible to shared tendon then mastoid notch)
- Stylohyoid muscle: Facial CN7
(Styloid process to hyoid bone)
- Mylohyoid muscle: Mandibular V3
(mylohyoid line on mandible to hyoid bone)
- Geniohyoid: Branch of ant. ramus of C1 (carried along hypoglossal CN12)
(Inferior mental spine on mandible to hyoid bone)
What is the order of suprahyoid muscles from superficial to deep and where is CN9, CN12, CNV3, CN7
On anterior aspect:
1.Ant belly of digastric-> CNV3 nerve running between-> 2.mylohyoid-> 3.geniohyoid
On Lateral aspect:
1. stylohyoid.
2.Post belly of digastric and
Between them = stylomastoid foramen = CN7
Deep to these muscles runs CN9 and CN12
What are the 4 infrahyoid (strap) muscles and their innervations and insertions/origins from lateral to medial
Superior root of Ansa cervicalis from C1
1. sup belly of Omohyoid
(hyoid bone)
Inferior root of Ansa cervicalis from C2,C3.
1. inf belly of Omohyoid: (sup border of scapula)
- Sternohyoid: (posterior SC joint + manubrium to hyoid bone)
- Sternothyroid: (Post sternum to oblique line thyroid cartilage)
- Ant ramus of C1 (carried along hypoglossal CN12)
Thyrohyoid: (oblique line to greater horn of hyoid bone)
What triangle are the suprahyoid and infrahyoid muscles associated with and what is their general action
Supra: submental and submandibular triangles
Go from hyoid bone to skull or mandible to raise the hyoid as occurs during swallowing
Infra: muscular triangle.
Go from hyoid bone to inferior structures to depress the hyoid bone
Describe the path of the major artery of Ant triangle- including branching in the anterior triangle (and to the skull)
- Right and left common carotid artery cross the sup thoracic aperture on either side of esophagus/trachea in the carotid sheath.
- Within the neck they give off no branches
- At level C3/4 the Com. carotids bifurcate into Internal and External carotid arteries
a) Internal carotid artery has no branches in the neck, continuing in the carotid sheath (1st branch is ophthalmic in the skull).
b) External carotid gives branches immediately after bifurcation. - External carotid divides into the Superficial temporal and Maxillary artery
5a) Sup. Temporal artery runs to the temporal region to supply temporalis muscle/scalp
b) Maxillary artery enters at the base of the skull going to the infratemporal and pterygopalatine areas, splitting into 16 branches - main one MMA.
What are the landmarks that show C3/4
C3 is the level of the hyoid bone which separates the supra and infrahyoid muscles
and C4 is the upper border of the thyroid cartilage.
What are the 6 branches of the external carotid artery before its bifurcation (going from base of neck to skull)
- First is Superior thyroid artery on ant aspect,
- Ascending pharyngeal artery on posterior
- Lingual artery
- Facial artery anteriorly
- Occipital artery
- Posterior Auricular artery
Describe the position of the int carotid artery within the carotid sheath and the special features around its origin
- Initially medial to the int. jugular vein. Anterior to vagus nerve.
- Origin is dilated: Carotid sinus with baroreceptors relaying pressure to medulla via CN9
- Behind the bifurcation is the carotid body: chemoreceptors for pH, PO2, PCO2
Describe the tributaries and path of the veins in the ant triangle
Trib:
- Inferior petrosal sinus +
- Facial, lingual,
- pharyngeal, occipital,
- superior thyroid and middle thyroid veins.
- Internal jugular vein begins as continuation of sigmoid sinus.
- Exits out of jugular foramen (with CN9,10,11) and enters the carotid sheath
- It joins the subclavian vein to form the brachiocephalic vein behind the sternoclavicular joint.
(External jugular vein is formed by posterior auricular and retromandibular vein around ear)
How do you differentiate the Phrenic nerve (C3-5) and the Vagus (CN10) nerve at the base of the neck
Phrenic nerve follows the course of the anterior scalene muscle, going lateral to the midline whereas
Vagus nerve crosses the anterior scalene anteriorly in a medial plane over the superior thoracic apeture
What are the nerves that are in the anterior triangle
CN V3, 7, 9, 10, 11, 12. Nerve loop from the (Ant rami of C1-C3 - motor part of cervical plexus) Ansa cervicalis + ant rami of C1
Describe the path of the glossopharyngeal nerve (CN9) from where it leaves the skull
Exit, travel, branches
- Leaves through jugular foramen and lies deep to styloid apparatus
- Travels within the carotid sheath initially then exits anteriorly deep to the lateral suprahyoid muscles.
- Runs between int. and ext carotid arteries down and forward, giving off carotid sinus branch, pharyngeal/plexus branches etc
- Curves around lat border of stylopharyngeaus and continues in ant to base of tongue.
Describe the path of the Vagus nerve (CN10) from where it leaves the skull
Exit, travel, branches
- Exits through jugular foramen between CN9 and 11.
- Travels down in the carotid sheath, gives off pharyngeal, internal and external superior laryngeal and cardiac branches
- At root of the neck it passes in front of the subclavian artery and ant scalene but behind the sub clav vein to enter mediastinum
Describe the path of the Accessory nerve (CN11) from where it leaves the skull
Exit, travel, branches
- Exits through jugular foramen posterior to CN10
2.Runs in carotid sheath initially, but exits posterolaterally across the int jugular vein, transverse process of C1,
(medially to styloid process and post belly of digastric)
- Runs between two heads/under SCM -> through post triangle-> deep to trapezius. With branch to those two muscles.
