Gross Anatomy of Skeletal Muscles

Muscles of the Head and Neck Head muscles are grouped into 2 large groups Facial muscles Inserted into soft tissue such as other muscles or skin Chewing muscles Breakdown food for the body

Head & Neck Facial Chewing Neck Frontalis Masseter Orbicularis oculi Raise eyebrows and wrinkle forehead Orbicularis oculi Close your eyes, squint, blink, wink Orbicularis Oris The “kissing” muscle Buccinator The “chewing” muscle Zygomaticus The “smiling” muscle Masseter Closes the jaw by elevating the mandible Temporalis Acts as a synergist of the masseter in closing the jaw Neck Platysma Pulls the corners of the mouth inferiorly, producing a downward sag Sternocleidomastoid (2) If both sternocleidomastoind muscles contract at the same time, the bow your head If one muscle contracts, it is bowed to the opposite side

Superficial muscles of the face and neck

In some difficult births, these muscles may be injured and develop spasms. The baby is said to have torticollis, or wryneck

Trunk Muscles Include Those that move the vertebral column Anterior thorax muscles, which move the ribs, head, and arms Muscles of the abdominal wall

Anterior muscles Pectoralis major – Intercostal muscles Adducts and flexes the chest Intercostal muscles Depress the ribcage to move air out of the lungs when you exhale forcibly Abdominal Girdle Rectus abdominis (2) Flex the vertebral column and compress the abdominal contents during defecation, childbirth and forced breathing External oblique (2) & Internal oblique (2) Flex the vertebral column, rotate the trunk and bend it laterally Transverse abdominis Compresses the abdominal contents

Posterior Muscles Trapezius (2) Latissimus Dorsi (2) Extend the head Elevate, depress, adduct, and stabilize the scapula Latissimus Dorsi (2) Extends and adducts the humerus Erector Spinae (2) Act as back extensors Provides resistance that helps control the act of bending over Deltoid (2) Favorite injection site Prime movers of arm abduction

Muscles of the upper limb Divided into 3 groups 1. Muscles that arise from the shoulder girdle and insert into the humerus Move the arm Deltoid Pectoralis major Latissimus dorsi 2. Muscles that enclose the humerus and insert into the forearm bone. cause movement at the elbow joint 3. muscles of the forearm which insert into the hand bones and cause their movement Flexor carpi Flexor digitorum Extensor carpi Extensor digitorum

Muscles of the humerus that act on the forearm Biceps Brachii Bulges when the elbow flexes Prime mover for flexion of the forearm Brachialis Flexion of the elbow Brachioradialis Fairly weak muscle Triceps Brachii Prime mover of elbow extension Antagonist of the biceps brachii

Muscles of the lower limb Cause movement at the hip, knee, and foot joints Largest, strongest muscles in the body Specialized for walking and balancing the body Many span 2 joints and span two joints Muscles of the thigh are massive and help hold the body upright against the pull of gravity and cause movement at the hip joint. Let students know that there is a need for very little muscle to support the pelvis because they are composed of heavy, fused bones that allow little movememt.

Muscles causing movement at the hip joint Gluteus maximus Acts to bring the thigh in a straight line with the pelvis The most important muscle for extending the hip when power is needed Gluteus medius Important in steadying the pelvis during walking Iliopsoas Composed of 2 muscles – iliacus & psoas major Prime mover for hip flexion Acts to keep the body from falling backward when we are standing erect Adductor Muscles Adductor or press the thighs together Tend to become flabby very easily because of gravity

Muscles causing movement at the knee joint Hamstring Group Composed of 3 muscles Biceps femoris Semimembranosus Semitendinosus Sartorius Acts as a synergist to bring about the crossed leg position Quadriceps Group Composed of 4 muscles Rectus femoris 3 vastus muscles Acts to extend the knee Name hamstrings comes from butchers hanging hams for smoking

Muscles causing movement at the ankle and foot Tibialis anterior Acts to dorsiflex and invert the foot Extensor digitorum Prime mover of the toe Fibularis Muscles (3) Longus, brevis, tertius Plantar flexis and everts the foot Gastrocnemius Forms the calf Prime mover of the plantar flexion of the foot Lifts the heel Soleus Plantar flexor of the foot