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
Transversus abdominis
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