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The muscles of facial expression are located in the subcutaneous tissue , originating from bone or fascia, and inserting onto the skin. By contracting, the muscles pull on the skin and exert their effects. They are the only group of muscles that insert into skin. These muscles have a common embryonic origin – the 2nd pharyngeal arch . They migrate from the arch, taking their nerve supply with them. As such, all the muscles of facial expression are innervated by the facial nerve . The facial muscles can broadly be split into three groups: orbital , nasal and oral ..

Orbicularis oculi Corrugator supercilli. !lnoo spelt10!q'C).

Orbital Group These muscles control the movements of the eyelids , important in protecting the cornea from damage. They are both innervated by the facial nerve. Orbicularis Oculi The orbicularis oculi muscle surrounds the eye socket and extends into the eyelid. It has three distinct parts – palpebral, lacrimal, and orbital. Actions: Palpebral part – gently closes the eyelids. Lacrimal part – involved in the drainage of tears. Orbital part – tightly closes the eyelids. Innervation – Facial nerve (CN VII, temporal and zygomatic branches) Corrugator Supercilii The corrugator supercilii is a much smaller muscle and is located posteriorly to the orbicularis oculi. Actions – Acts to draw the eyebrows together, creating vertical wrinkles on the bridge of the nose. Innervation – Facial nerve..

Clinical Relevance: Paralysis to the Orbital Muscles If the facial nerve becomes damaged, the orbital muscles will cease to function. As they are the only muscles that can close the eyelids, this has some serious clinical consequences. The eye cannot shut – this can cause the cornea to dry out. This is known as exposure keratitis . The lower eyelid droops, called ectropion . Lacrimal fluid pools in the lower eyelid and cannot be spread across the surface of the eye. This can result in a failure to remove debris, and ulceration of the corneal surface. The test for facial nerve palsy involves raising the eyebrows (frontalis muscle see scalp) and closing the eyelids.

Procerus Nasalis (Transverse) Nasalis (Alar) Depressor Septi Nasi.

Other Oral Muscles There are other muscles that act on the lips and mouth. Anatomically, they can be divided into upper and lower groups: The lower group contains the depressor anguli oris , depressor labii inferioris and the mentalis. The upper group contains the risorius, zygomaticus major, zygomaticus minor, levator labii superioris, levator labii superioris alaeque nasi and levator anguli oris ..

Oral Group: These are the most important group of the facial expressors: responsible for movements of the mouth and lips . Such movements are required in singing and whistling and add emphasis to vocal communication. The oral group of muscles consists of the orbicularis oris , buccinator, and various smaller muscles. Orbicularis Oris The fibres of the orbicularis oris enclose the opening to the oral cavity. Action: Purses the lips. Innervation: Facial nerve. Buccinator This muscle is located between the mandible and maxilla, deep to the other muscles of the face. Attachments : It originates from the maxilla and mandible. blending with the orbicularis oris and the skin of the lips. Actions : The buccinator pulls the cheek inwards against the teeth, preventing accumulation of food in that area (vestibule of the mouth). Blowing, whistling. Innervation : Facial nerve..

Ptergomandibular Raphe Buccinator Muscle Levator Anglui Oris Muscle Orbicularis Oris Musc.

Clinical Relevance: Paralysis to the Oral Muscles If the facial nerve is dysfunctional, the oral muscles can become paralyzed. The patient may present with difficulty eating , with food collecting between the teeth and cheeks. In addition, the tissue around the mouth and cheeks sags, and is drawn across to the opposite side while smiling..

Platysma is a broad, thin sheet like muscle that lies superficially at the anterolateral aspect of neck bilaterally. N.S: Cervical branch of facial nerve (CN VII) The actions of the platysma muscle include pulling down the mandible, which opens the mouth, and pulling the corners of the lips out to the side and down, which forms a frown . Additionally, the platysma muscle can form wrinkles in the neck as a person ages and their skin becomes less elastic and starts to sag..

2- Muscles of Mastication These four muscles move the mandible and are involved in chewing. Three of them, masseter, temporalis and medial pterygoid are powerful closers of the joint and account for the strength of the bite. The medial and lateral pterygoids move the mandible from side to side and also protrude the mandible. Lateral pterygoid is an opener of the mouth..

Muscle Origin Insertion action Masseter zygomatic arch Ramus of Mandible Elevates mandible Temporalis Temporal and frontal bones Mandible Elevates mandible Medial pterygoid Sphenoid (Lateral pterygoid plate) Mandible Elevates mandible; moves mandible side to side Lateral pterygoid Sphenoid (Lateral pterygoid plate) Mandible Opens jaws, protrudes mandible; moves mandible side to side.

3 - Muscles of the Neck.

Muscles of the Floor of the Mouth These muscles are part of the suprahyoid (above the hyoid) group of muscles. Together with the infrahyoid muscles (discussed below) these muscles fix the hyoid bone and this enables the hyoid bone to serve as a firm base for the attachment of the tongue. As a group these muscles also elevate the hyoid bone, the floor of the oral cavity, and tongue during swallowing..

A close-up of a human skull Description automatically generated with low confidence.

Muscle Origin Insertion Action Digastric Anterior belly from mandible and posterior belly from temporal Hyoid Elevates hyoid and/or depresses mandible Stylohyoid Temporal (styloid process) Hyoid Elevates larynx Mylohyoid Mandible Hyoid Elevates hyoid and floor of mouth; depresses mandible.

Extrinsic Muscles of the Larynx The extrinsic muscles of the larynx are also called infrahyoid muscles because they lie inferior to the hyoid bone. These muscles are sometimes called "strap" muscles because of their ribbonlike appearance. These muscles depress the hyoid bone and larynx during swallowing and speech..

A close-up of a person Description automatically generated with low confidence.

Muscle Origin Insertion Action Omohyoid Central tendon attaches to clavicle and 1st rib One belly attaches to hyoid; second to scapula Depresses hyoid and larynx Sternohyoid Clavicle and Sternum Hyoid As above Sternothyroid Sternum Thyroid cartilage As above Thyrohyoid Thyroid cartilage Hyoid Depresses hyoid; elevates thyroid.

Muscles that Move the Head Balance and movement of the head on the atlanto -occipital joint involves the action of several neck muscles. One example of these muscles is the sternocleidomastoid muscles..

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1 st cervical vertebra Sternocleido- mastoid occipital bone Mastoid process Middle scalene Anterior scalene Posterior scalene.

Scalene Triangle Anatomy.

Scalenus medius Brachial plexus Scalenus anterior Subclavian artery *achMeAnatomy.

Anatomical Relationships: The scalene muscles are an important part of the anatomy of the neck, with several important structures located between and around them. The brachial plexus and subclavian artery pass between the anterior and middle scalene muscles. This provides an important anatomical landmark in anaesthetics for performing an interscalene block . The subclavian vein and phrenic nerve pass anteriorly to the anterior scalene – the subclavian vein courses horizontally across it, while the phrenic nerve runs vertically down the muscle. The subclavian artery is located posterior to the anterior scalene..

The scalene muscles collectively act to elevate the first and second ribs, and in doing so they increase the intrathoracic volume . In patients with respiratory distress, the scalene muscles may be used as ‘accessory muscles of respiration’ to aid with breathing. By increasing intrathoracic volume, the patient can ventilate their lungs more effectively. However, they are not required in the respiration of a healthy individual, and so the use of accessory muscles is an important clinical sign of respiratory distress ..

Sternocleidomastoid Anterior scalene Middle scalene Phrenic nerve Brachial plexus Trapezius Clavicle (cut) Deltoid Subclavian vein 1st rib Subclavian artery.

The thoracic outlet is the space bounded by the manubrium, the first rib, and T1 vertebra. The interval between the anterior and middle scalene muscles and the first rib (scalene triangle) transmits the structures coursing between the thorax, upper limb and lower neck. The triangle contains the trunks of the brachial plexus and the subclavian artery..

Thoracic outlet syndrome results from the compression of the trunks of the brachial plexus and the subclavian artery within the scalene triangle. Compression of these structures can result from tumors of the neck (Pancoast on apex of lung), a cervical rib or hypertrophy of the scalene muscles. The lower trunk of the brachial plexus (C8, T1) is usually the first to be affected. Clinical symptoms include the following: • Numbness and pain on medial aspect of the forearm and hand • Weakness of the muscles supplied by ulnar nerve in the hand (claw hand) • Decreased blood flow into upper limb, indicated by weakened radial pulse Compression can also affect the cervical sympathetic trunk (Horner’s syndrome) and the recurrent laryngeal nerves (hoarseness)..

Note The subclavian vein and phrenic nerve (C 3, 4, and 5) are on the anterior surface of the anterior scalene muscle and are not in the scalene triangle..

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