The platysma is a superficial muscle found in the neck. It covers most of the anterior and lateral aspects of the neck. The platysma is a broad muscle that arises from the fascia that covers the upper segments of the deltoid and pectoralis muscles. Its thin muscle fibers cross over the clavicle and proceed obliquely superiorly, laterally, and medially over the neck. The platysma muscle fibers thin out anteriorly and attach just behind the symphysis menti. On the lateral side, the muscle fibers pass over the mandible, and some fibers insert into the bone, and other fibers merge in the subcutaneous tissues. Most of the platysma muscle fibers start to thin as they traverse the superior aspect of the lower face and merge or blend in with the muscles around the ankle and lower part of the oral cavity.[rx]
The actual functional role of platysma is still a topic of some debate. When stimulating the platysma, it may produce wrinkling of the skin surface on the neck. In some cases, it may create a slight depression of the skin of the mandible. In other individuals, it may cause slight drooping of the lower lip and angle of the mouth. However, it is worth noting that the platysma plays a minor role in lip depressor function, which is chiefly performed by the two depressor muscles, namely, the depressor anguli oris and the depressor labii inferioris.[rx]
Blood Supply
The blood supply to the platysma is from branches of the external carotid artery. The blood supply is rich: even minor trauma can cause bruising.[rx] During surgery, hemostasis of the platysma layer is essential before proceeding. Otherwise, constant bleeding can obscure the surgical field. The lymphatic drainage of the platysma is by superficial lymph nodes of the corresponding soft tissue and is irregular as it spans the entire distance of the neck and portions of the face.[rx][rx]
Nerves
Because the platysma is a muscle of facial expression, its innervation is via the facial nerve (cranial nerve VII). The facial nerve has several main branches: the temporal, zygomatic, buccal, marginal mandibular, and cervical branches.[rx] The primary innervation of the platysma is by the cervical branch; however, there are instances of aberrant innervation to some muscle fibers by the marginal mandibular branch. This branch of the facial nerve courses deep to the superior aspect of the platysma inferior to the mandible.[rx]
The supraclavicular nerves pierce the inferior portion of the platysma muscle superior to the clavicle. These are pure sensory nerves and provide sensation to the lower neck and upper chest.[rx]
Muscles
The platysma, innervated by the facial nerve, is a thin, sheet-like voluntary muscle.
- Origin – the muscle has a broad origin with fibers arising from the fascia of the upper thorax including the clavicle, acromial region, pectoralis major and deltoid muscles.
- Course – Its fibers run superiorly and medially from the deltoid and pectoral region in a rostral-caudal direction.
- Insertion – the muscle inserts on the mandible, the cheek skin, the commissure of the mouth, the orbicularis oris muscle, to the posterior border of the depressor anguli oris muscle, and in some cases higher as high as the orbicularis oculi muscle. This muscle only has a small bony insertion, which is on the anterior third of the mandible.
- Anatomical Variations – in 75%, the medial fibers in the submental area interdigitate with the contralateral platysma muscle for up to 1 to 2 cm below the chin. In 15%, the muscle fibers interdigitate all the way down to the thyroid cartilage, and in 10% the medial platysmal fibers do not interdigitate.
- Function – a contraction of the muscle causes elevation of the neck with accentuation of the platysmal bands and also lowers the midfacial tissues, including the lower lids and midface with deepening of the malar and nasolabial folds. It also lowers the mandible, thereby making the neck shorter and wider. This type of contracture conveys the emotion of surprise, horror, or disgust.
The striated muscle of the platysma can vary in thickness depending on gender, age, and size. In surgeries or dissections of the elderly or malnourished, the platysma can be indistinguishable from the overlying adipose.[rx] Muscles immediately deep to the platysma muscle are the sternocleidomastoid muscle and the digastric muscle. Medially, the first layer of strap muscles is encountered covering the larynx and thyroid.[rx]
References
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