1. The muscles of facial expression originate on the surface of the skull.
2. The pairs of extrinsic eye muscles include: (1) inferior and superior rectus muscles, (2) lateral and medial rectus muscles, and (3) inferior and superior oblique muscles. The superior rectus muscles move the eyes superiorly and medially, while the inferior rectus muscles move the eyes inferiorly and medially. The medial rectus muscle pulls the eye medially (adducts the eye). The lateral rectus muscle pulls the eye laterally (abducts the eye). The inferior oblique muscle elevates the eye and turns the eye laterally. The superior oblique depresses the eye and turns the eye laterally.
3. When the orbicularis oculi muscle contracts, you close your eyelid (wink, blink, or squint).
4. The depressor anguli oris pulls the corner of the mouth inferiorly into the frown position.
5. The lateral and medial pterygoid muscles elevate and protract the mandible and move it from side to side during chewing.
6. The extrinsic tongue muscles are used in different combinations to accomplish the delicate and complex tongue movements necessary for speech. Additionally, they manipulate food within the mouth in preparation for swallowing. The left and right genioglossus muscles protract the tongue. The left and right styloglossus muscles elevate and retract the tongue. The left and right hyoglossus muscles depress and retract the tongue. The left and right palatoglossus muscles elevate the posterior portion of the tongue.
7. The mylohyoid elevates the hyoid bone and elevates the floor of the mouth when it contracts.
8. Unilateral contraction of the sternocleidomastoid muscle causes lateral flexion and rotation of the head to the opposite side.
9. The erector spinae is the largest muscle mass in the back. It consists of three groups of muscles organized into columns: the iliocostalis(located laterally), longissimus (located intermediately), and spinalis (located medially). The muscles of the erector spinae maintain posture and help us stand erect after bending over at the waist.
10. The external intercostal muscles extend inferomedially from the superior rib to the adjacent inferior rib. They assist in expanding the thoracic cavity by elevating the ribs during inhalation. The internal intercostal muscles lie deep to the external intercostals, and their muscle fibers are at right angles to the external intercostals. The internal intercostals depress the ribs, but only during a forced exhalation; normal exhalation requires no active muscular effort.
11. The muscle of respiration that separates the thoracic and abdominal cavities is the diaphragm. The structure to which all diaphragm muscle fibers converge is the central tendon.
12. The muscles of the abdominal wall are the external oblique, internal oblique, transversus abdominis, and rectus abdominis.