1. Gross Anatomy and Functions of Skeletal Muscles
Chapter 9B
Gross Anatomy and Functions of Skeletal Muscles

2. Back Muscles
These muscles extend, laterally flex, and rotate the vertebral column. They also hold the vertebral column erect
A superficial group of muscles, the Erector spinae, runs from the pelvis to the skull, extending from the vertebrae to the ribs
Consist of three subgroups on each side of the vertebrae: Iliocostalis, Longissimus, and Spinalis
Lateral bending of the back is accomplished by unilateral contraction of these muscles

3. Fig. 9.10

4. Tab. 9.6

5. Abdominal Wall Muscles
The abdominal wall is composed of four paired muscles (Internal and External obliques, Transversus abdominis, and Rectus abdominis), their fasciae, and their aponeuroses
Fascicles of these muscles run at right and oblique angles to one another, giving the abdominal wall added strength
In addition to forming the abdominal wall, these muscles:
Are involved with lateral flexion and rotation of the trunk
Aid in functions such as forced expirations (coughing and screaming), vomiting, defecation, urination, and childbirth

6. Fig. 9.11

7. Tab. 9.7

8. Pelvic Floor and Perineum
The pelvic diaphragm is composed of two paired muscles: Levator ani and Coccygeus
These muscles:
Close the inferior outlet of the pelvis
Support the pelvic floor
Elevate the pelvic floor to help release feces
Resist increased intra-abdominal pressure
Two sphincter muscles allow voluntary control of urination (External urethral sphincter) and defecation (External anal sphincter)
The Ischiocavernosus and Bulbospongiosus assist in erection of the penis and clitoris

9. Fig. 9.12

10. Tab. 9.8

11. Thoracic Muscles Mainly involved in the process of breathing
Diaphragm: most important muscle in respiration
External intercostals: more superficial layer that lifts the rib cage and increases thoracic volume to allow inspiration
Internal intercostals: deeper layer that aids in forced expiration

12. Fig. 9.13

13. Tab. 9.9

14. Scapular Muscles and Movements
The scapula is attached to the rest of the skeleton only by the clavicle
Six muscles attach the scapula to the trunk and enable the scapula to function as an anchor point for the muscles and bones of the arm
Trapezius
Levator scapulae
Rhomboideus (major and minor)
Serratus anterior
Pectoralis minor
Prime movers of shoulder elevation are the trapezius and levator scapulae

15. Fig. 9.14

16. Tab. 9.10

17. Upper Limb Muscles and Arm Movements
Nine muscles attach the humerus to the scapula. Two additional muscles attach the humerus to the trunk
Trunk muscles moving the arm:
Pectoralis major: flexes the extended shoulder and extends the flexed shoulder
Latissimus dorsi: adducts and medially rotates arm; shoulder extension
Muscles located in the shoulder moving the arm:
Posterior fibers of the deltoid: shoulder extension
Anterior fibers of the deltoid: shoulder flexion
Lateral fibers of the deltoid: arm abduction and rotation
Teres major: shoulder extension

18. Fig. 9.15

19. Fig. 9.16

20. Tab. 9.11

21. Upper Limb Muscles and Arm Movements
Muscles located in the shoulder that move the arm (cont):
Rotator cuff muscles: Supraspinatus, Infraspinatus, Teres minor, and Subscapularis (mnemonic SITS)
Function mainly to reinforce the capsule of the shoulder by holding the head of the humerus in the glenoid cavity
Secondarily act as synergists and fixators
Muscles located in the arm that move the arm
Coracobrachialis
Biceps brachii
Triceps brachii
Actions of the trunk, shoulder, and arm muscles on the shoulder and arm are summarized in Table 9.12

22. Fig. 9.17

23. Tab. 9.12

24. Upper Limb Muscles and Forearm Movements
Flexion and extension of the elbow are accomplished by three muscles located in the arm and two in the forearm
Most anterior muscles are flexors, and posterior muscles are extensors
Forearm flexion
Brachialis and Biceps brachii are the chief forearm flexors
The Brachioradialis acts as a synergist and helps stabilize the elbow
Forearm extension
The Triceps brachii is the prime mover of forearm extension
The Anconeus is a weak synergist
Supination and pronation are accomplished primarily by forearm muscles
The Supinator muscle is a synergist with the Biceps brachii in supinating the forearm
The Pronator teres and Pronator quadratus pronate the forearm

25. Fig. 9.18

27. Forearm Muscles and Wrist, Hand, and Finger Movements
Most anterior muscles are flexors, and posterior muscles are extensors
Forearm muscles
Muscles that originate on the medial epicondyle are responsible for flexion of the wrist and fingers
Muscles extending the wrist and fingers originate on the lateral epicondyle
Forearm muscles moving the wrist, hand and fingers are summarized in Table 9.14
Extrinsic hand muscles are in the forearm
Retinaculum: covers the flexor and extensor tendons and holds them in place around the wrist
Intrinsic hand muscles are in the hand
Thenar muscles, hypothenar muscles, midpalmar muscles

29. Fig. 9.19

30. Fig. 9.20

31. Hip and Lower Limb Muscles
Most anterior compartment muscles of the hip and thigh flex the femur at the hip and extend the leg at the knee
Posterior compartment muscles of the hip and thigh extend the thigh and flex the leg
The medial compartment muscles all adduct the thigh
These three groups are enclosed by the fascia lata

32. Hip Muscles and Thigh Movements
Gluteus maximus extends the hip
Gluteus medius and minimus help hold the hip level while walking or running
Deep hip muscles laterally rotate the thigh
Anterior hip muscles flex the hip
The thigh can be divided into three compartments
Anterior muscles flex the hip
Posterior muscles extend the hip
Medial muscles adduct the thigh

33. Fig. 9.21

35. Thigh Muscles and Leg Movements
Anterior thigh muscles
Quadriceps femoris: extends the knee
Sartorius: flexes the knee
Tensor fasciae latae: stabilizes the knee
Posterior thigh muscles flex the knee
One medial thigh muscle flexes the knee: Gracilis
Summarized in Table 9.16

36. Fig. 9.22

37. Tab. 9.16

38. Fig. 9.23

39. Tab. 9.17

40. Lower Limb Muscles and Ankle, Foot, and Toe Movements
The leg is divided into three compartments
Muscles in the anterior compartment cause dorsiflexion, inversion, or eversion of the foot and extension of the toes
Muscles of the lateral compartment plantar flex and evert the foot
Muscles of the posterior compartment flex the leg, plantar flex and invert the foot, and flex the toes
Intrinsic foot muscles flex or extend and abduct or adduct the toes
Summarized in Table 9.18

41. Fig. 9.25

42. Fig. 9.26