Sternomastoid Muscle Flashcards
Sternomastoid muscle
Important landmark between anterior and posterior triangles
Origin
- Sternal head
- Clavicular head
Sternal head
Round and tendinous from front of upper part manubrium sterni
Clavicular head
Broad and fleshy
From upper surface medial 1/3 clavicle
Insertion
- Lateral surface mastoid process
- Lateral half superior nuchal line
Nerve supply
- Motor: spinal root accessory nerve
- Sensory: anterior ramifications C2,3
Action
One muscle:
1. Bends head same side
2. Rotates face to opposite side
Two muscles:
Flexes neck by:
1. Projecting head forwards
2. Raising head from supine
Relations
- Spinal root accesory nerve
- Superficial
- Deep
Spinal root accessory nerve
- Pierces muscle at junction of upper and middle thirds
- Runs within it about its middle
Superficially
- Skin and fascia (with Platysma)
- EJV (crosses it obliquely)
- Posterior auricular vessels
- Great auricular nerve
- Transverse cutaneous nerve neck
- Parotid Posteromedial surface
Deep
- Carotid sheath and its contents
- Cervical plexus
- Deep cervical lymph nodes
- Eight muscles
- Scalenus anterior muscle
- Subclavian artery
- Anterior jugular vein
- Thyroid gland lobe
- Mastoid process
Carotid sheath and its contents
- Common and internal carotid arteries
- Vagus nerve
- IJV
Deep cervical lymph nodes
Along IJV
Subclavian artery
1st and 2nd parts
Anterior jugular vein
In lower part
Scalenus anterior muscle
With
1. Phrenic nerve
2. Intermediate tendon omohyoid
3. Transverse cervical
4. Suprascapular
arteries on it
Eight muscles
3 infrahyoid:
1. Sternohyoid
2. Sternothyroid
3. Intermediate tendon omohyoid
3 in posterior triangle floor:
4. Scalenus medius
5. Levator scapulae
6. Splenius capitis
2 others:
7. Scalenus anterior
8. Anterior belly digastric
