Muscular System Notes

1. Muscular System Notes Part 6

2. Head Muscles • Grouped into two large categories: • Facial Muscles – Permit us to frown, smile, deliver a kiss, pout, etc… • Chewing Muscles – Begin the breakdown of food

3. Head Muscles- Facial Muscles • Orbicularis Oculi – Run in circles around the eye; Allows you to close your eyes, squint, blink, and wink • Orbicularis Oris – Circular muscle of the lips; It closes the mouth and protrudes the lips; Often called the “kissing” muscle

4. Head Muscles – Facial Muscles • Buccinator – Fleshy muscle that runs horizontally across the cheek and inserts into the orbicularis oris; It flattens the cheek (as in whistling or blowing) and compresses the cheek to hold the food between the teeth during chewing • Zygomaticus – Extends from the corner of the mouth to the cheek bone; It raises the corners of the mouth upward; Often referred to as the “smiling” muscle

5. Head Muscles – Chewing Muscles • Buccinator - Discussed with the facial muscles • Masseter – Covers the angle of the lower jaw as it runs from the temporal bone to the mandible; Closes the jaw by elevating the mandible • Temporalis – Fan-shaped muscle overlying the temporal bone and inserts into the mandible; Acts as a synergist of the masseter in closing the jaw

6. Neck Muscles • The neck muscles move the head and shoulder girdle; They are small and strap-like • Platysma – Single, sheetlike muscle that covers the anterolateral neck • Originates from the chest muscles and inserts into the area around the mouth • Its action is to pull the corners of the mouth inferiorly, which produces a downward sag of the mouth

7. Neck Muscles • Sternocleidomastoid – Paired muscles that are two-headed (one found on each side of the neck) • Of the two heads of each muscle, one arises from the sternum and the other arises from the clavicle. The heads fuse before inserting into the temporal bone • Action: • When both muscles contract together, they flex the neck • If just one muscle contracts, the head is rotated toward the opposite side

10. Trunk Muscles • Include : • Those that move the vertebral column • Most are posterior anti- gravity muscles • Anterior thorax muscles • Move the ribs, head, and arms • Muscles of the abdominal wall • Help to move the vertebral column and form the muscular “natural girdle” of the abdominal body wall

11. Trunk Muscles - Anterior • Pectoralis Major – Large fan-shaped muscle covering the upper part of the chest; Acts to adduct and flex the arm

12. Trunk Muscles - Anterior • Intercostal Muscles – Deep muscles found between the ribs • Action- • External Intercostals – Important in breathing because they help to raise the rib cage for breathing air in • Internal Intercostals - Depress the rib cage, which helps to move air out of the lungs when you exhale forcibly

13. Trunk Muscles - Anterior • Muscles of the Abdominal Girdle include - • Rectus abdominis • External oblique • Internal oblique • Transversusabdominis • These muscle together form a natural “girdle” that reinforces the body trunk. Taken together they resemble the structure of plywood. • The fibers of each muscle run in a different direction • The abdominal muscles form a muscular wall that is well suited for its job of containing and protecting the abdominal contents

14. Trunk Muscles – Anterior • Abdominal Girdle Muscles • Rectus Abdominis – Paired and straplike; Most superficial muscles of the abdomen • Run from the pubis to the ribcage • Action – Flex the vertebral column, also compress the abdominal contents during defecation and childbirth, are involved in forced breathing

15. Trunk Muscles – Anterior • Abdominal Girdle Muscles • External Oblique– Paired superficial muscles that make up the lateral walls of the abdomen • Action – Flex the vertebral column , rotate the trunk, and bend it laterally • Internal Oblique – Paired muscles deep to the external obliques • Their fibers run at right angles to those of the external obliques • Action – Same as those of the external obliques

16. Trunk Muscles – Anterior • Abdominal Girdle Muscles • Transversus Abdominis– Deepest muscle of the abdominal wall and has fibers that run horizontally across the abdomen • Action – Compresses the abdominal contents

17. Trunk Muscles – Posterior • Trapezius – Are the most superficial muscles of the posterior neck and upper trunk • When seen together they form a diamond or kite-shaped muscle • Actions – Extend the head, can also elevate, depress, adduct, and stabilize the scapula

18. Trunk Muscles – Posterior • Latissimus Dorsi– Large, flat muscle pair that covers the lower back • Action - Extends and adducts the humerus • Very important muscles when the arm must be brought down in a power stroke (such as swimming or striking a blow)

19. Trunk Muscles – Posterior • Erector Spinae – Group of deep muscles that are a prime mover of back extension • Action – Powerful back entensors and also provide resistance that helps control the action of bending over at the waist • Following injury to back structures, these muscles go into spasms, a common source of lower back pain

20. Trunk Muscles – Posterior • Deltoid– Fleshy, triangle-shaped muscles that form the rounded shape of your shoulders • Action – Prime movers of arm abduction • Because they are so bulky, they are a favorite injection site when relatively small amounts of medication must be given intramuscularly

21. Muscles of the Upper Limb • All anterior arm muscles cause elbow flexion. • Biceps Brachii – The powerful prime mover for flexion of the forearm and acts to supinate the forearm • Most familiar muscle of the arm because it bulges when the elbow is flexed

22. Muscles of the Upper Limb • Brachialis – Lies deep to the biceps muscle; Is as important as the biceps in elbow flexion • Brachioradialis – Fairly weak muscle; Resides mainly in the forearm

23. Muscles of the Upper Limb • Triceps Brachii– The powerful prime mover of elbow extension • The only muscle fleshing out of the posterior humerus • It contains three heads • It is the antagonist of the biceps brachii

24. Muscles of the Lower Limb • Gluteus Maximus– Superficial muscle of the hip that forms most of the flesh of the buttock • It is a powerful hip extensor that acts to bring the thigh in a straight line with the pelvis • It is the most important muscle for extending the hip when power is needed (as when climbing stairs or jumping)

25. Muscles of the Lower Limb • Gluteus Medius– Runs beneath the gluteus maximus beneath for most of its length • Action - Is a hip abductor and is important in steadying the pelvis during walking • Important site for giving intramuscular injections when more than 5 ml is administered

26. Muscles of the Lower Limb • Iliopsoas – Fused muscle composed of two muscles (iliacus and the psoas major) • Action – Prime mover of hip flexion and acts to keep the upper body from falling backward when we are standing erect

27. Muscles of the Lower Limb • Adductor Muscles– The muscles of the adductor group form the muscle mass at the medial side of each thigh • Action – Adduct or press the thighs together • Since gravity does most of their work for them, they tend to become flabby very easily. Special exercises are usually needed to keep them toned.

28. Muscles of the Lower Limb • Hamstring Group– The muscles forming the muscle mass of the posterior thigh • Action: Extends the thigh and flexes the knee • Consists of three muscles: • Biceps Femoris • Semimembranosus • Semitendinosus

29. Muscles of the Lower Limb • Sartorius – Thin, straplike muscle that is the most superficial muscle of the thigh • Action – Weak thigh flexor

30. Muscles of the Lower Limb • Quadriceps Group– The group as a whole acts to extend the knee powerfully (as when kicking a football) • Consists of four muscles that flesh out the anterior thigh: • Rectus Femoris • Three Vastus Muscles

31. Muscles of the Lower Limb • Tibialis Anterior– Superficial muscle on the anterior lower leg • Action - Acts to dorsiflex and invert the foot • Extensor Digitorum Longus– Lateral to the tibialis anterior • Action - Prime mover of toe extension and a dorsiflexor of the foot

32. Muscles of the Lower Limb • Fibularis Muscles – Found on the lateral part of the leg • Action - Group as a whole plantar flexes and everts the foot • Consists of three fibularis muscles – the longus, brevis, and tertius

33. Muscles of the Lower Limb • Gastrocnemius – Two-bellied muscle that forms the curved calf of the posterior leg • Arises by two heads (one from each side of the distal femur) and inserts through the Achilles tendon into the heel of the foot • Action – Prime mover for plantar flexion of the foot • If its insertion tendon is cut, walking is very difficult (the foot drags because the heel cannot be lifted)

34. Muscles of the Lower Limb • Soleus – Located deep to the gastocnemius • Action – Strong plantar flexor of the foot