PSIO 201 Required Handout Department of Physiology Naming skeletal muscles Early anatomists named skeletal muscles based on a number of different characteristics These characteristics include muscle shape size number of origins action location and the direction in which the muscle fibers run TABLE 1 Naming skeletal muscles Characteristic Description Direction of muscle fibers Size Location Shape Number of origins Action Deltoid Triangular shape Rhomboid Diamond shape Trapezius Trapezoid shape Biceps Two origins Triceps Three origins Quadriceps Four origins Named for the action that the muscle performs TABLE 2 Muscles of the face head and neck Muscle Location Occipitofrontalis Frontalis and Occipitalis Orbicularis oris Orbicularis oculi Zygomaticus major Platysma Temporalis Masseter Sternocleidomastoid Example Rectus Fibers run parallel to the midline Transverse Fibers run perpendicular to the midline Oblique Fibers run diagonal to the midline Maximus Largest Minimus Smallest Longus Longest Named for the bone s to which the muscle attaches or region within which the muscle is found Composite muscle that overlies the cranium the two muscles are connected by an aponeurosis Circular muscle that encircles the mouth Circular muscle that encircles each eye Originates on the zygomatic bone and inserts on the skin at the corners of the mouth Originates on the fascia of the chest and deltoid and inserts on the mandible and skin below the mouth Originates on the temporal bone and inserts on the mandible Originates on the maxillae and zygomatic bones and inserts on the mandible Originates on the sternum and clavicle and inserts on the mastoid process of the temporal bone Rectus abdominis Transverse abdominis External oblique Gluteus maximus Gluteus minimus Adductor longus Tibialis anterior Occipitalis Sternocleidomastoid Deltoid Rhomboid major Trapezius Biceps femoris Triceps brachii Quadriceps femoris Adductor magnus Levator scapulae Action Frontalis Raises the eyebrows Occipitalis Draws scalp posteriorly Puckers the mouth as in kissing Closes each eye as in blinking Pulls the corners of the mouth superiorly as in smiling Depresses the lower lip mandible tenses neck skin and Elevates and retracts the mandible Elevates and protracts the mandible If one side contracts the head rotates to the opposite side If both contract flexion of the head is the result PSIO 201 Required Handout Department of Physiology Muscles that move the vertebral column Contraction of the muscles of the anterior and posterior trunk creates movement of the vertebral column Abdominal muscles located on the anterior trunk include the rectus abdominis external oblique internal oblique and transverse abdominis The most superficial of these muscles the rectus abdominis often appears to have six different portions in lean individuals This appearance is due to the presence of tendinous intersections three connective tissue bands that extend across the rectus abdominis at three different points The abdominal muscles act to flex the vertebral column and compress the abdomen during forced expiration The muscles that extend the vertebral column belong to the erector spinae group These muscles run along either side of the spine and contribute to extension of both the head and vertebral column TABLE 3 Muscles that move the vertebral column Muscle Location Action Rectus abdominis Originates on the pubis and inserts superiorly on the lower ribs and xiphoid process Originates laterally on the lower ribs and inserts medially on the iliac crest and linea alba Flexes the vertebral column and compresses the abdomen External oblique Internal oblique Transverse abdominis Erector spinae Iliocostalis group Longissimus group Spinalis group Rotation of the trunk results if one side contracts If both sides contract together flexion of the vertebral column and compression of the abdomen is the result Located deep to the external oblique The internal oblique has the same the internal oblique originates laterally action as the external oblique at the iliac crests and inserts medially at the linea alba and lower ribs Located deep to the internal oblique the Contraction of the transverse transverse abdominis originates abdominis compresses the abdomen laterally on the iliac crest and the cartilages of the lower ribs It inserts medially at the xiphoid process and linea alba Composite group of muscles that When one side contracts the muscles individually originate on vertebral laterally flex and rotate the vertebral processes or ribs and insert on superior column When both contract the processes of the vertebral column muscles extend the vertebral column and maintain erect posture The linea alba is a connective tissue band formed at the juncture of the aponeuroses of the transverse abdominis and oblique muscles It extends from the xiphoid process to the pubic symphysis PSIO 201 Required Handout Department of Physiology Muscles of respiration The muscles of respiration are involved in the processes of inspiration and expiration The diaphragm is considered the primary muscle of inspiration because its contraction increases the dimensions of the thorax and results in the movement of air into the lungs Relaxation of the diaphragm causes expiration The external intercostals and the internal intercostals are only active during forced inspiration and expiration TABLE 4 Muscles of respiration Muscle Location Action Diaphragm Dome shaped muscle that originates on During inspiration the diaphragm the lower ribs and lumbar vertebrae and moves downward in the thoracic inserts medially at the central tendon cavity increasing the horizontal and vertical dimensions of the thorax External Located between the ribs the external Contraction pulls the ribs upward and intercostals intercostals originate on the inferior together to expand the dimensions of border of the superior rib and insert on the thorax during forced inspiration the superior border of the inferior rib Internal intercostals Located between the ribs the internal Contraction pulls the ribs down and intercostals originate on the superior together to decrease the dimensions of border of the inferior rib and insert on the thorax during forced expiration the inferior border of the superior rib Muscles that move the pectoral girdle The pectoral girdle consists of the clavicle and scapula Muscles that move the pectoral girdle insert on either the clavicle or the scapula or in some cases both bones TABLE 5