Submandibular region l human anatomy revision for dental students

 

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The Submandibular Region

Introduction

• The submandibular  region (suprahyoid  region) is the  anatomical area which  lies between the body  of mandible and the  hyoidbone.
• It corresponds to the  Rt. and Lt. digastric  and the submental  triangles.
• ThesubmandibularRegion(Suprahyoidregion)

The 4 Suprahyoid Muscles

• They include : digastric, stylohyoid , mylohyoid and geniohyoid.

(1)The Digastric Muscle:

Origin: It has 2 bellies:

1. Anterior belly : arises from mandible close to the digastric fossa of the symphysis menti.
2. Posterior belly : arises from the digastric notch on the medial surface of the mastoid process.

Insertion :

• the 2 bellies are united by an intermediate tendon which is held by fibrous loop to the junction of the body and greater horn of the hyoid bone.

Important Relations of the Digastric Muscle:

• Of the anterior belly:Deep to it : mylohyoid muscle , mylohyoid Nerve and vessels.
• Of the posterior belly: Along its upper border : stylohyoid muscle and the posterior auricular artery. ,  Along its lower border :  occipital artery.

(2) Stylohyoid Muscle:

Origin :

• Arises from the back of the styloid process near its base.

Insertion :

• near its insertion its tendon divides to surround the intermediate tendon of digastric and is inserted into the hyoid bone at the junction of the body and greater horn.

 

3) Geniohyoid muscle

Origin:

• Inferior genial tubercle of the mandible.

Insertion:

• Anterior, upper surfaces of body of hyoid bone.

Nerve supply:

• C1 nerve via hypoglossal N.

Action:

1. Pulls the hyoid bone upwards and forwards.
2. Depresses the mandible.

4) Mylohyoid muscle

• It is a thin sheet of muscle that forms the floor of the mouth (diaphragma oris).

Origin:

• Whole length of mylohyoid line of the mandible.

Insertion:

1. Posterior (1/4 ) fibers: Body of hyoid bone.
2. Middle and anterior (3/4) fibers: Median-fibrous raphe (between symphysis menti & hyoid bone).

Nerve supply:

• Mylohyoid nerve.

Actions:

1. Elevates the floor of the mouth and hyoid bone during swallowing.
2. Depresses the mandible (when hyoid bone is fixed).

Relations:

• Superficially (inferiorly):

1. Skin, fasciae, platysma.
2. Anterior belly of digastric.

• Supetficial to digastric:

1. Submandibular salivary gland.
2. Submental artery , veins & Lymph Nodes.

• Deep to digastric:

1. Mylohyoid nerve.

• Deeply (superiorly):

1. Hyoglossus + structures anterior + structures lateral to it

• Vessel: lingual artery.
• Glands: - Deep part of submandibular gland & its duct. - Sublingual gland.
• Nerves:  Lingual Nerve. -Submandibular ganglion. - Hypoglossal nerve.
• muscles: Styloglossus. - Hyoglossus. - Geniohyoid. - Genioglossus.

 

Submandibular Salivary Gland

 

• It consists of 2 parts: Superficial and deep.

 

1-Superficial Part of Submandibular Gland

 

• The main part of the gland which lies superficial to the mylohyoid muscle.
• Position: It lies in the submandibular fossa of the mandible, extending from mylohyoid line (above), to overlap intermediate tendon of digastric (below), and from mental foramen (in front) to angle of mandible (behind).
• Surfaces and Relations: The gland is wedged between the body of mandible and mylohyoid muscle.

The gland has 3 surfaces (lateral, medial, and inferolateral)

• Lateral surface: It lies in contact with the inner surface of the body of mandible and has the following relations:

1. Submandibular fossa of the mandible.
2. Insertion of medial pterygoid muscle.
3. Facial artery notches the posterior end of the gland then runs between the gland and insertion of medial pterygoid.

• Medial surface: It has the following relations:

1. Anterior part  : Mylohyoid muscle  .
2. Intermediate part : Hyoglossus muscle with all structures on its lateral surface mainly lingual nerve above & hypoglossal nerve below
3. Posterior part : Styloglossus muscle, stylohyoid ligament and glossopharyngeal nerve .
4. The deep part of the gland and its duct project from this surface. These 2 structures run together between mylohyoid and hyoglossus muscles.

• Inferolateral surface: It lies superficially below the mandible and has the following relations:

1. Skin, platysma and deep fascia
2. Submandibular lymph nodes.
3. Facial vein.
4. Cervical branch of facial nerve.

2-Deep Part of Submandibular Gland

 

It is  process that extends along submandibular duct, deep to mylohyoid, on the lateral surface of hyoglossus, with lingual nerve & submandibular ganglion  above and hypoglossal nerve below.

It is continuous with the superficial part of the gland around the posterior border of mylohyoid muscle.

 

3-Submandibular Duct

It arises from the medial surface of the superficial part of the gland.

It is 5 cm long.

It runs forwards along the deep part of the gland between the mylohyoid and hyoglossus muscles, with the lingual nerve & submandibular ganglion (above) and hypoglossal nerve (below).

At the anterior border of hyoglossus, the lingual nerve hooks around the duct (lateral , below then medial to the duct i.e. triple relation ).

It then continues forwards deep to sublingual gland on genioglossus to open in the floor of mouth in the summit of the sublingual papilla on both sides of the frenulum of the tongue.

Arterial supply:

facial artery.

Nerve supply:

Parasympathetic:  

• chorda tympani from facial nerve

Sympathetic: 

• From sympathetic plexus around facial artery

Sensory: 

• From lingual nerve
• All these fibers pass through submandibular ganglion

 

Applied Anatomy:

• Salivary calculi are more common in the submandibular salivary gland because:

1. Flow of saliva against gravity.
2. The duct open in the floor of the mouth ® liability to be  blocked by foreign body.
3. Secretion is more viscid.

• Salivary calculi may affect the duct or the gland.
• Stone in submandibular duct can be felt as hard nodule in the floor of the mouth.
• Submandibular salivary gland swelling and pain increases by eating or sucking a lemon (as parotid salivary gland swelling and pain).
• Submandibular salivary gland swelling is the 2^nd common swelling in the submandibular triangle (after L.Ns enlargement).
• In submandibular salivary gland stones or inflammations, the opening of submandibular duct is seen red, raised and discharging pus or blood, in the sublingual papilla.
• Submandibular salivary gland swelling is differentiated from L.Ns enlargement by:

1. Single.
2. Can not be rolled over the lower border of the mandible.
3. Increased by eating and sucking a lemon.
4. On bimanual examination, it is better felt from the floor of the mouth.

• Pain due to submandibular salivary gland disease is felt below the mandible and may radiate to the anterior 2/3 of the tongue (both supplied by lingual nerve ) .
• Due to triple close relation of lingual nerve to submandibular duct (lateral, below then medial), a stone in the duct may irritate the lingual nerve ® pain is radiating to the anterior 2/3 of the tongue.
• Radiologically, submandibular duct can be seen by submandibular sialography.

Sublingual Gland

• It is almond shaped (3 cm long), which lies on genioglossus muscle and raises the mucous membrane of the floor of the mouth forming the sublingual fold.
• It has 8-12 fine ducts which open in the sublingual fold, but few of them open in the submandibular duct .

 

Relations:

1. Laterally: Sublingual fossa of the mandible .
2. Medially: Genioglossus muscle with submandibular duct and lingual nerve & vessels between the gland and the muscle.
3. Below: Anterior part of mylohyoid muscle.
4. Above: Mucous membrane of mouth forming sublingual fold containing the orifices of the ducts of the gland.

 

Blood supply:

• Sublingual and submental blood vessels.

 

Nerve supply:

1. Parasympathetic: From chorda tympani nerve
2. Sympathetic: From plexus around lingual artery
3. Sensory: From lingual nerve.

• All these fibers pass through the submandibular ganglion