Muscles of Head and Neck

Muscles of Head

Orbicularis Oculi

The orbicularis oculi is a large muscle that completely surrounds each orbital orifice and extends into each eyelid. It closes the eyelids. It has two major parts:

• The outer orbital part is a broad ring that encircles the orbital orifice and extends outward beyond the orbital rim.
• The inner palpebral part is in the eyelids and consists of muscle fibers originating in the medial corner of the eye that arch across each lid to attach laterally.

The orbital and palpebral parts have specific roles to play during eyelid closure. The palpebral part closes the eye gently, whereas the orbital part closes the eye more forcefully and produces some wrinkling on the forehead.

An additional small lacrimal part of the orbicularis oculi muscle is deep, medial in position, and attaches to bone posterior to the lacrimal sac of the lacrimal apparatus in the orbit

Frontalis Muscle

No doubt you have already seen patients with drooping upper lids who lift their eyebrows to provide a tiny bit more upper eyelid elevation. The frontalis muscle lifts the brows and is a weak retractor of the upper eyelids. The frontalis muscle is a part of the occipitofrontalis musculofascial complex (frontalis muscle, galea aponeurotica, and occipitalis muscle) of the scalp. This broad band of tissue extends across the top of the skull from the occiput to the eyebrows. The A in the mnemonic for remembering the layers of the “SCALP” is this aponeurosis (S, scalp, C, subcutaneous tissue, A, aponeurosis, L, loose areolar tissue, P, periosteum.)

The fibrous aponeurosis becomes the frontalis muscle inferior to the hairline. Contraction of the frontalis muscle causes the horizontal furrows in the forehead. You may notice that the forehead furrows do not extend to the temporal hairline. The frontalis muscle thins laterally and does not extend to the tail of the brow. The lack of frontalis pull over the tail of the brow explains the temporal brow ptosis seen so commonly in older adults.

Corrugator Supercilii

The fibrous aponeurosis becomes the frontalis muscle inferior to the hairline. Contraction of the frontalis muscle causes the horizontal furrows in the forehead. You may notice that the forehead furrows do not extend to the temporal hairline. The frontalis muscle thins laterally and does not extend to the tail of the brow. The lack of frontalis pull over the tail of the brow explains the temporal brow ptosis seen so commonly in older adults.

The corrugator supercilii typically creates strong vertical or slightly oblique wrinkles and vertical bulges on the glabella between the medial ends of the eyebrows. It also swells the skin at the medial end of the eyebrow into a wide, thick, crescent-shaped bulge. This action pulls the brows shelflike over the eyes, shading them from strong light.

A depression forms in the skin above the middle of the eyebrow (actually closer to the medial end) as the corrugator contracts. It often gives the eyebrow an S-shaped curve – the eyebrow develops a central downward dip (usually close to the medial end) as the muscle pulls the middle portion of the eyebrow downward and inward. This is especially noticeable if the medial portion of the frontalis is also lifting the medial end of the eyebrow.

Levator Palpebrae Superioris

This muscle is an eye opener. The levator palpebrae superioris muscle attaches into the tarsal plate and skin of the upper eyelid and is the primary elevator of the eyelid. Weakness in this muscle results in ptosis (drooping) of the upper eyelid and may reflect a problem with the oculomotor nerve. The oculomotor nerve provides the motor control for the levator palpebrae superioris and most (4 of 6) of the extraocular muscles. The levator palpebrae superioris is assisted by the superior tarsal muscle, a thin smooth muscle sheet in the upper eyelid innervated by sympathetic fibers.

Levator palpebrae superioris raises the upper eyelid. It is the most superior muscle in the orbit, originating from the roof. Its primary point of insertion is into the anterior surface of the superior tarsus, but a few fibers also attach to the skin of the upper eyelid and the superior conjunctival fornix.

Contraction of the levator palpebrae superioris raises the upper eyelid.

Orbicularis Oris

The orbicularis oris is a complex muscle consisting of fibers that completely encircle the mouth. Its function is apparent when pursing the lips, as occurs during whistling. Some of its fibers originate near the midline from the maxilla superiorly and the mandible inferiorly, whereas other fibers are derived from both the buccinator, in the cheek, and the numerous other muscles acting on the lips. It inserts into the skin and mucous membrane of the lips, and into itself.

The orbicularis oris surrounds the mouth, lying in the upper and lower lips. It is continuous with the muscle of the other side (in both the upper and lower lips). The orbicularis oris is well developed in the horse and ox, which use the lips for grazing, and less developed (less mobile) in the dog and feline.

Muscle of Mastication

The muscles of mastication are concerned with movements of mandible in the temporomandibular joints during mastication. They’re split into 2 groups:

Main muscles:

• Lateral pterygoid.
• Medial pterygoid.

Accessory muscles

Muscles of Submandibular Region

The muscles in the submandibular region create 4 muscular planes; from superficial to deep, from the perspective of surgical procedures these are:

• First muscular plane: created by the digastric and stylohyoid muscles.
• Second muscular plane: created by the mylohyoid muscle.
• Third muscular plane: created by the geniohyoid, hyoglossus and styloglossus muscles.
• Fourth muscular plane: created by the genioglossus and a part of superior constrictor of the pharynx.

Temporalis Muscle

This large fan-shaped muscle originates from the floor of the temporal fossa and inner aspect of the temporal fascia. Its fibres converge inferiorly and pass deep to the zygomatic arch to be added into the coronoid process of mandible.

Muscles of Neck

Sternocleidomastoid Muscle

It goes obliquely through the side of the neck, breaking up it into posterior and anterior triangles and is an important muscle of neck.

The muscle originates by 2 heads: Sternal and Clavicular.

Sternal head: It appears by a rounded tendon from the superolateral part of the front of the manubrium sterni and is tendinous, below the suprasternal notch and enters upwards, backwards and laterally in front of the sternoclavicular joint.

Clavicular head: It is flat and musculoaponeurotic. It goes vertically upwards deep to the sternal head with which it joins to make a fusiform abdomen. The point of origin is from the medial third of the superior outermost layer of the clavicle.

A small triangular gap exists between both heads above the sternoclavicularjoint. It’s termed lesser supraclavicular fossa. It includes the terminal part of the internal jugular vein, which can be entered at this site by a needle or catheter.

Suprahyoid and Infrahyoid Muscles of Neck

The suprahyoid muscles consist of following 4 matched muscles:

The infrahyoid muscles are ribbon like and contain following 4 matched muscles:

Prevertebral (Anterior Vertebral) Muscle

They are located in front of the cervical part of the vertebral column. All of them are supplied by ventral rami of cervical nerves and covered by prevertebral fascia. The posterior boundary of the retropharyngeal space is created by them. They bend the neck and the head on the neck, as a group.

The anterior vertebral group of muscles consists of:

• Rectus capitis anterior.
• Rectus capitis lateralis.
• Longus cervicis (longus colli).
• Longus capitis.

Paravertebral (Lateral  Vertebral) Muscle

From transverse processes of cervical vertebrae to the upper 2 ribs, the paravertebral muscles stretch out. They can, therefore, either bend the cervical part of the vertebral column laterally or elevate these ribs. These muscles create a thick mass behind the prevertebral fascia and supplied by twigs from ventral rami of the lower 5 or 6 cervical spinal nerves. The lateral vertebral group of muscles is composed of scalene muscles. The scalene muscles, generally 3 in number, are as follows:

• Scalenus posterior.
• Scalenus medius.
• Scalenus anterior.

The scalenus medius is the largest and scalenus posterior is the smallest.