Typically, muscles in the body lie deep to the skin and layers of subcutaneous tissue, otherwise known as the superficial fascia. The platysma is one muscle that does not. Instead, it runs just below the epidermis and dermis in the superficial layer of fascia in the cervical region. Because of its association with the skin, changes in the muscle and skin tension can mean it becomes clinically important with ageing. In addition, its very superficial location means surgical dissections of the neck need to account for underlying neurovascular structures.
To understand this muscle from a clinical perspective, this article will first look at the organizational layers of tissue in the neck, then the attachments of the muscle, its actions and nerve supply.
|Origins||Skin/Fascia of infra- and supraclavicular regions|
|Insertions||Lower border of mandible, Skin of buccal/cheek region, Lower lip, Modiolus, Orbicularis oris muscle|
|Innervation||Cervical branch of facial nerve|
|Actions||Depresses mandible and angle of mouth, tenses skin of lower face and anterior neck|
The article will then highlight the structures that lie deep to the platysma, and finally, discuss the clinical implications of this muscle and its associated structures.
Layers in the Neck
In the region of the neck, structures are organized in layers. Anterolaterally, moving from superficial to deep is the:
- skin (epidermis and dermis)
- subcutaneous tissue/superficial fascia
- investing layer of deep fascia (which encloses the sternocleidomastoid muscle)
- the hyoid muscles
- two more layers of deep fascia that create two separate compartments:
- Pretracheal layer – lies anteriorly and encloses the trachea and esophagus
- Carotid sheath – lies anterolaterally and encloses the internal jugular vein, common carotid artery, and vagus nerve.
- the deepest layer of deep fascia; the prevertebral fascia
- deep muscles of the neck
The platysma muscle lies within the subcutaneous tissue in the anterolateral neck. This tissue is a very superficial layer of fatty connective tissue. The platysma is considered to be one of the muscles of facial expression because of its association with the skin of the face and neck, and because it will join to muscles that surround the mouth. It is also known as “the shaving muscle” as it tenses the skin of the neck when contracted.
- Origin: fascia covering the superior portions of the pectoralis major and deltoid muscles below the clavicle.
- Insertion: medial fibers insert onto the lower border of the mandible, lateral fibers will attach to the skin, subcutaneous tissue, and muscles surrounding the mouth.
- Innervation: cervical branch of the facial nerve, cranial nerve 7 (CNVII).
- Actions: depresses the mandible, draws the corners of the mouth inferiorly, tenses the skin of the anterior neck.
Structures Deep to the Platysma
The anterolateral region of the neck is distinct for its concentration of neurovascular structures, and the fact that the skin and the superficial fascia, including the platysma muscle, are often the only structures located superficial to the neurovasculature.
The following structures lie deep to the platysma and superficial to the sternocleidomastoid (SCM) muscle and the investing fascial layer:
- External Jugular Vein: begins near the angle of the mandible and runs obliquely across the SCM to pierce the investing layer of deep fascia just superior to the clavicle and lateral to the posterior border of the SCM.
- Marginal mandibular branch of the facial nerve (CNVII): emerges from the inferior border of the parotid gland and runs along the lower border of the mandible to supply motor innervation to the muscles of facial expression of the lower lip and chin.
- Cervical branch of the facial nerve (CNVII): emerges from the inferior border of the parotid gland and runs inferior and anterior to supply motor innervation to the platysma and other muscles of the face.
- Lesser occipital nerve: this branch off the cervical plexus emerges from underneath the upper third of the posterior border of the SCM to ascend superficial to the SCM towards the region behind the ear. It carries sensory information from the skin behind the ear.
- Spinal accessory nerve (CNXI): appears from underneath the SCM just inferior to the lesser occipital nerve and descends obliquely to provide motor innervation to the trapezius and SCM.
- Great auricular nerve: this branch of the cervical plexus appears from underneath the middle portion of the posterior border of the SCM to ascend across the muscle towards the anterior aspect of the ear. It carries sensory information from the skin over the parotid gland and ear.
- Transverse cervical nerve: another branch of the cervical plexus that appears from underneath the SCM just inferior to the great auricular nerve and ascends obliquely across the SCM towards the anterior aspect of the neck. It carries sensory information from the skin of the anterior neck.
- Supraclavicular nerves: this branch of the cervical plexus emerges from beneath the SCM just inferior to the transverse cervical nerve. Branches of this nerve will run inferiorly towards the clavicle and shoulder and will carry sensory information from the skin in these regions.
Neck Lacerations or Surgical Dissections
Cuts through the skin and superficial fascia including the platysma can be clinically relevant for a number of reasons:
- Without careful suturing of the wound or incision, the tone of the platysma muscle can pull on the healing skin causing large scars.
- The platysma muscle and one of the muscles that also helps shape the mouth (the depressor anguli oris muscle) are both supplied by the cervical portion of the facial nerve, which runs just deep to the platysma below the mandible. Damage to this nerve could result in paralysis in these muscles, distorting the shape of the mouth and the skin over the anterior neck region.
- Damage to any of the nerves lying just deep to the platysma muscle could result in motor and/or sensory deficits and so care needs to be taken during surgical dissection to preserve these structures.
Platysma Bands and Ageing
As a person ages, changes in the tone of the skin, especially in the neck, can occur. An early sign of ageing in the skin of the neck is the appearance of platysma bands, or ridges in the skin that can run the length of the muscle. It has been thought that these bands appear as the skin starts to sag due to a loss of muscle tone in the platysma. In this case, a surgery would be performed to tighten the skin of the neck to reduce sagging and in turn reduce the appearance of the bands. Recently however, it has been suggested that the platysma bands may be caused by muscle activity rather than a loss of muscle tone. In this case, the suggested treatment would be denervation of the platysma muscle to relax the bands and the overlying skin.