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Gross Anatomy and Functions of Skeletal Muscles

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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


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