muscle striations

(redirected from facial muscle tonus)

muscle striations

(strīā´shənz),
n.pl the transverse alternating light and dark bands of skeletal muscles that result from differences in light absorption. The light bands contain actin and are called “I” bands because they are isotropic to polarized light. The dark areas contain myosin filaments and are called “A” bands because they are anisotropic to polarized light.
muscle, styloglossus
(stī´lōglôs´us),
n an extrinsic tongue muscle that originates from the styloid process and inserts on the lateral surface of the tongue. It is used to retract the tongue.
muscle, stylohyoid,
n suprahyoid muscle that extends from the styloid process to the hyoid bone and is used for mastication and swallowing. See also deglutition; mastication; muscles, hyoid.
muscle, thyrohyoid,
n infrahyoid muscle that extends from the thyroid cartilage to the hyoid bone and is used for mastication and swallowing. See also deglutition; mastication; muscles, hyoid.
muscle tonus,
n the steady reflex contraction that resides in the muscles concerned in maintaining erect posture. Tonus has its basis in the positional interactions of the muscle and its accompanying nerve structure; e.g., a muscle holds the body (mandible) in a given position, and the awareness of this position is constantly being relayed by the sensory approaches to the cortex. A change in position or contractility of the muscle that affects its tonus is immediately relayed by the sensory apparatus for readjustment. Also called tone.
muscle tonus, facial
(tō´nus),
n the tone of the facial musculature, which is a major factor in providing the esthetic values of the face. The configurations of the face, which are maintained by good muscle tonus, are the modiolus, philtrum, nasolabial sulcus, and mentolabial sulcus. These functional contours are present when the nerve tissue is intact. They are altered by the loss of teeth or impaired nerve function. Their presence is an indication of a good state of health of the nerve and possibly of the dental arch.
muscles, cervical,
n.pl the large muscles used to turn or lower the head or to shrug the shoulders. This group includes the sternocleidomastoid and trapezius muscles.
muscles, elevator,
n muscles of the body that serve to raise the body part with which they are associated. E.g., the mandibular elevator muscles raise the jaw.
muscles, facial,
n.pl these muscles are quite variable in contour, are widely distributed over the scalp and face, and tend to be especially concentrated around the orbits, outer ear, and lips. It is the mobility of the lips that has extended the usefulness of these muscles in expressing emotion, speech, and intelligence. The muscles, as a group, have only one bony origin in the facial skeleton. The muscles form a circular rim around the perimeter of the facial bones and extend anteriorly as a tube of tissue in which the lumen narrows and terminates in the orbicularis oris. Their structure may be regarded as a truncated cone in which the base rests on the skeleton (origin) in a fixed position, whereas the truncated top of the cone (insertion in the orbicularis oris) is variable in diameter and height. The lips are thus extensible and retractable and can constrict like a purse string. The facial nerve provides neurologic control. Also called the
muscles of expression, mimetic muscles, and
orofacial muscles.
muscles, hyoid
(hī´oid),
n.pl a group of muscles used in mastication and swallowing. These muscles are attached to the hyoid bone, which is suspended in the neck and forms the base of the tongue and larynx. The muscles are divided into
suprahyoid (superior) or
infrahyoid (inferior) groups relative to the bone.
muscles, levator labii superioris alaeque nasi
(livā´tər lab´ēī soo´-pērēor´is al´akū naz´ī),
n the muscle that elevates the upper lip and the alae of the nose, allowing the nostrils to dilate in a sneering expression.
muscles, levator veli palatini
(livā´tər vē´lī palatē´nē),
n the muscle located superior to the soft palate that extends from the inferior surface of the temporal bone to the median palatine raphe; it raises the soft palate, causing it to cover the opening of the nasopharynx during swallowing and speech.
muscles, masticatory
(mas´tikətôrē),
n.pl the powerful muscles that elevate and rotate the mandible so that the opposing teeth may occlude for mastication. Includes the temporal, masseter, lateral pterygoid, and medial pterygoid muscles. Also called the
muscles of mastication.
muscles, mimetic
n.pl See muscles, facial.
muscles, ocular, function of,
n.pl the action of the eye muscles in moving the eyeballs. The eyes are in a position of rest (their primary position) when their direction is maintained simply by the tone of the ocular muscles. This condition prevails when the gaze is straight ahead into distance and not directed to any particular point in space. The visual axes are then parallel. When the eyes view some distant definite object, they are turned by contraction of the ocular muscles and converge so that the visual axes meet at the observed object, and an almost identical image of the object falls on a corresponding point on each fovea, the centralis of the retina. The adjustment of the eye movements for acute observation is called fixation, and the point where the visual axes meet is the fixation point. Thus the interplay of the ocular muscles permits rapid, reciprocally controlled movement of the eyeballs for fixation.
muscles, orofacial,
n.pl See muscles, facial.
muscles, posterior suprahyoid
(sōō´prəhī´oid),
n the muscles situated superior to the hyoid bone and made up of the stylohyoid muscles and the posterior belly of digastric muscles; they are used during mastication.
muscles, suprahyoid and infrahy-oid,
n.pl the muscles grouped around the hyoid bone. They aid in depressing and fixing the mandible, hyoid bone, and larynx in the performance of their several respective functions.
muscle(s), tongue, extrinsic,
n.pl the muscles of the tongue that provide a scaffolding by which the intrinsic muscles can be moved around in the oral cavity while the latter are continuously modifying their dimension and contour. The extrinsic muscles are paired and originate from both sides of the cranial skeleton, mandible, and hyoid bone to radiate medially and insert into the body of the tongue, which consists principally of the intrinsic muscles.
muscle(s), tongue, intrinsic,
n.pl the muscles of the tongue that have no attachments in bone, terminating either within each other or in the extrinsic muscle group. The fibers of the intrinsic muscles also lie in all three planes of space and are called
longitudinal, vertical, and
transverse fibers to describe their distribution. They are capable of assuming an infinite variety of shapes. They depend, however, on the activity of the extrinsic muscles to be moved bodily through space.