4.1 Origin, Insertion, and Action
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125 Terms
Q: What is the origin of a muscle?
A: The end of the muscle attached to the least movable structure.
Q: What is the insertion of a muscle?
A: The end of the muscle attached to the more movable structure.
Q: What usually happens to the insertion when a muscle contracts?
A: The insertion generally moves toward the origin.
Q: What is the action of a muscle?
A: The movement produced when the muscle contracts.
Q: What are the major muscle groups of the head and neck discussed in the notes?
A: Cervical muscles, facial expression, mastication, hyoid, tongue, and pharynx.
Q: What are the two cervical muscles discussed in this chapter?
A: Sternocleidomastoid and trapezius.
Q: What do the cervical muscles help do?
A: Hold and stabilize the head and position the head.
Q: What type of muscle is the sternocleidomastoid?
A: A large, superficial cervical muscle.
Q: Why is the SCM important during an extraoral examination?
A: It is a major landmark of the neck.
Q: What does the SCM divide the neck into?
A: The anterior and posterior cervical triangles.
Q: What is the origin of the SCM?
A: The medial clavicle and the superior/lateral surfaces of the sternum.
Q: What is the insertion of the SCM?
A: Just posterior and inferior to the external acoustic meatus.
Q: What does one SCM do when it contracts?
A: Bends the head and neck to the same side and rotates the face to the opposite side.
Q: What happens when both SCM muscles contract?
A: They flex the neck and extend the junction between the neck and skull.
Q: What is the innervation of the SCM?
A: CN XI, the accessory nerve.
Q: What is the shape of the trapezius?
A: A broad, flat, triangular muscle.
Q: What is the origin of the trapezius?
A: External occipital bone and the posterior midline of the cervical and thoracic regions.
Q: What is the insertion of the trapezius?
A: The lateral third of the clavicle and parts of the scapula.
Q: What does the cervical part of the trapezius do?
A: Lifts the clavicle and scapula like shrugging.
Q: What is the innervation of the trapezius?
A: CN XI plus C3 and C4.
Q: What are facial expression muscles like?
A: They are paired, superficial muscles located in the fascia.
Q: Where do facial expression muscles generally originate?
A: From the surface of the skull, rarely from fascia.
Q: Where do facial expression muscles generally insert?
A: Into the dermis of the skin.
Q: What do facial expression muscles move?
A: They move the skin and create facial wrinkles.
Q: What nerve innervates the muscles of facial expression?
A: CN VII, the facial nerve.
Q: Why are facial expression muscles important during an extraoral examination?
A: Their movement can help identify problems with facial nerve function.
Q: What can inability to make facial expressions on one side indicate?
A: Damage to CN VII and facial paralysis.
Q: What are some possible causes of facial paralysis mentioned in the notes?
A: Stroke, Bell palsy, and possibly parotid salivary gland cancer.
Q: Why can parotid salivary gland cancer affect facial expression?
A: CN VII travels through the parotid gland.
Q: What are the two parts of the epicranial muscle?
A: Frontal belly and occipital belly.
Q: What separates the frontal and occipital bellies?
A: The epicranial aponeurosis, also called the galea aponeurotica.
Q: Can the frontal and occipital bellies act independently?
A: Yes
Q: What does the epicranial muscle do?
A: Raises the eyebrows and scalp.
Q: What facial expression can involve the epicranial muscle?
A: Surprise.
Q: What is the origin of orbicularis oculi?
A: Orbital rim, nasal process of frontal bone, and frontal process of maxilla.
Q: What is the insertion of orbicularis oculi?
A: Mostly the skin at the lateral canthus; inner fibers encircle the orbit.
Q: What is the action of orbicularis oculi?
A: Closes the eyelids.
Q: What happens when orbicularis oculi contracts strongly?
A: Squinting occurs and crow's feet can form.
Q: Where is the corrugator supercilii located?
A: Deep to the superior part of orbicularis oculi.
Q: What is the origin of corrugator supercilii?
A: Frontal bone in the supraorbital region.
Q: What is the insertion of corrugator supercilii?
A: Skin of the eyebrow.
Q: What is the action of corrugator supercilii?
A: Draws the eyebrow medially and inferiorly toward the nose.
Q: What facial expression does corrugator supercilii help create?
A: A frown.
Q: What type of wrinkles can corrugator supercilii create?
A: Wrinkles around the glabellar region and bridge of the nose.
Q: What three muscles are in the nasal region?
A: Nasalis, procerus, and depressor septi nasi.
Q: Which nasal muscle is the largest and best developed?
A: Nasalis.
Q: When is the nasalis active?
A: When the nares flare.
Q: What is the action of nasalis given in the notes?
A: Flares the nares.
Q: What information is given about procerus in the notes?
A: It is identified as one of the muscles of the nasal region.
Q: What information is given about depressor septi nasi in the notes?
A: It is identified as one of the muscles of the nasal region.
Q: What does orbicularis oris control?
A: Mouth opening and the position and movement of the lips during speech.
Q: Where are the fibers of orbicularis oris located?
A: Around the mouth between the skin and labial mucosa.
Q: Where do the vermilion zone fibers of orbicularis oris insert?
A: Into the skin of the lips at both labial commissures.
Q: What is the action of orbicularis oris?
A: Closes the lips, tightens and thins them, purses them, rolls them inward, and thrusts them outward.
Q: What lip movement can orbicularis oris produce?
A: Pouting or kissing.
Q: What can happen if orbicularis oris loses function?
A: The person may be unable to close the lips and may have excessive drooling.
Q: What can smoking and prolonged oral habits cause around the lips?
A: Defined wrinkling.
Q: What is incompetent lips or lip seal failure?
A: Inability to maintain a proper closed lip position.
Q: What can lip seal failure affect?
A: The position of the maxillary incisors, canines, and premolars.
Q: What can an open-mouth resting posture cause to the teeth?
A: Dehydration at the incisal edges.
Q: What type of muscle is the buccinator?
A: A thin, quadrilateral facial expression muscle.
Q: Where is the buccinator located?
A: In the anterior cheek and lateral wall of the buccal cavity.
Q: What is the origin of the buccinator?
A: Alveolar processes of the maxilla and mandible and the pterygomandibular raphe.
Q: What is the action of the buccinator?
A: Pulls the labial commissure laterally and shortens the cheek.
Q: What important function does the buccinator have during chewing?
A: Keeps food on the occlusal surface of the posterior teeth.
Q: What other function does the buccinator assist with?
A: Mastication.
Q: What is the pterygomandibular raphe?
A: A tendinous band that extends from the mandible to the junction of the hard and soft palate.
Q: Where is the pterygomandibular raphe located?
A: Posterior to the most distal mandibular molar.
Q: What is the pterygomandibular raphe called when seen intraorally?
A: The pterygomandibular fold.
Q: What is the origin of the risorius?
A: Fascia superficial to the masseter.
Q: What is the insertion of the risorius?
A: Skin at the ipsilateral labial commissure.
Q: What is the action of the risorius?
A: Retracts the labial commissure and widens the mouth.
Q: Does the risorius create a true smile?
A: No. It creates more of a grimace.
Q: What is the origin of levator labii superioris?
A: Infraorbital rim of the maxilla.
Q: What is the insertion of levator labii superioris?
A: Skin of the upper lip.
Q: What is the action of levator labii superioris?
A: Elevates the upper lip.
Q: What is the origin of Levator labii superioris alaeque nasi?
A: Frontal process of the maxilla.
Q: What is the insertion of Levator labii superioris alaeque nasi?
A: Skin of the ala of the nose and upper lip.
Q: What is the action of Levator labii superioris alaeque nasi?
A: Elevates the upper lip and nasal ala and dilates the nares.
Q: What facial expression can Levator labii superioris alaeque nasi help create?
A: Sneering.
Q: What is the origin of zygomaticus major?
A: Zygomatic bone lateral to the origin of zygomaticus minor.
Q: What is the insertion of zygomaticus major?
A: Skin at the ipsilateral labial commissure around orbicularis oris.
Q: What is the action of zygomaticus major?
A: Elevates the upper lip and assists smiling.
Q: What is the origin of zygomaticus minor?
A: Body of the zygomatic bone.
Q: What is the insertion of zygomaticus minor?
A: Skin of the upper lip near levator labii superioris.
Q: What is the action of zygomaticus minor?
A: Elevates the upper lip and assists smiling.
Q: Where is levator anguli oris located?
A: Deep to zygomaticus major and minor.
Q: What is the origin of levator anguli oris?
A: Canine fossa of the maxilla, usually above the maxillary canine root.
Q: What is the insertion of levator anguli oris?
A: Skin of the ipsilateral labial commissure.
Q: What is the action of levator anguli oris?
A: Elevates the labial commissure and assists smiling.
Q: What shape is depressor anguli oris?
A: Triangular.
Q: Where is depressor anguli oris located?
A: In the inferior oral region.
Q: What is the origin of depressor anguli oris?
A: Inferior border of the mandible.
Q: What is the insertion of depressor anguli oris?
A: Skin of the ipsilateral labial commissure.
Q: What is the action of depressor anguli oris?
A: Depresses the labial commissure and helps create a frown.
Q: Where is depressor labii inferioris located?
A: Deep to depressor anguli oris.
Q: What shape is depressor labii inferioris?
A: Small and quadrilateral.
Q: What is the origin of depressor labii inferioris?
A: Inferior border of the mandible.
Q: What is the insertion of depressor labii inferioris?
A: Skin of the lower lip.
Q: What is the origin of mentalis?
A: Mandible near the midline.