The Muscular System: Part B 10 The Muscular System: Part B

Muscles of the Thorax Muscles of respiration External intercostals—more superficial muscles that elevate ribs for inspiration Internal intercostals—deeper muscles that aid forced expiration Diaphragm Partition between thoracic and abdominal cavities Most important muscle in inspiration Innervated by phrenic nerves

External intercostal (a) Internal intercostal Figure 10.10a

Xiphoid process of sternum Foramen for inferior vena cava Foramen for esophagus Costal cartilage Central tendon of diaphragm Diaphragm Foramen for aorta Lumbar vertebra 12th rib Quadratus lumborum (b) Psoas major Figure 10.10b

Muscles of the Abdominal Wall Four paired muscles; their fasciae and aponeuroses form the lateral and anterior abdominal wall Internal obliques External obliques Transversus abdominis Rectus abdominis

Transversus abdominis Pectoralis major Serratus anterior Linea alba Tendinous intersection Transversus abdominis Internal oblique Rectus abdominis External oblique Aponeurosis of the external oblique Inguinal ligament (formed by free inferior border of the external oblique aponeurosis) (a) Figure 10.11a

Muscles of the Abdominal Wall Fascicles of these muscles run at angles to one another, providing added strength All are innervated by intercostal nerves Actions of these muscles Lateral flexion and rotation of the trunk Help promote urination, defecation, childbirth, vomiting, coughing, and screaming

Rectus abdominis Internal External oblique oblique Lumbar fascia IIiac crest Pubic tubercle Lumbar fascia Transversus abdominis Inguinal ligament (b) Figure 10.11b

Muscles of the Pelvic Floor Pelvic floor (pelvic diaphragm) is composed of two paired muscles Levator ani Coccygeus Both are innervated by sacral nerves

Muscles of the Pelvic Floor Functions of the pelvic diaphragm Seals the inferior outlet of the pelvis Supports pelvic organs Lifts pelvic floor to help release feces Resists increased intra-abdominal pressure

Muscles of the Perineum Urogenital diaphragm Anterior half of perineum, inferior to pelvic floor Deep transverse perineal muscle External urethral sphincter (voluntary control of urination)

Anterior Pubococcygeus Symphysis pubis Levator ani IIiococcygeus Urogenital diaphragm Urethra Vagina Anal canal Obturator internus Coccyx Levator ani Piriformis Coccygeus Pelvic diaphragm Posterior (a) Figure 10.12a

Urethral opening External urethral sphincter Vaginal opening Inferior pubic ramus Deep transverse perineal muscle Central tendon Anus External anal sphincter Male Female (b) Figure 10.12b

Muscles of the Perineum Muscles of superficial perineal space Ischiocavernosus Bulbospongiosus Superficial transverse perineal muscles External anal sphincter (in posterior half of perineum)

Urethral opening Clitoris Vaginal Anus opening Penis Midline raphe Ischiocavernosus Bulbospongiosus Superficial transverse perineal muscle Levator ani Gluteus maximus Male Female (c) Figure 10.12c

Superficial Muscles of the Thorax Most are extrinsic shoulder muscles Act in combination to fix the shoulder girdle (mostly the scapula) and move it to increase range of arm movements Actions include elevation, depression, rotation, lateral and medial movements, protraction, and retraction Two groups of muscles: anterior and posterior

Superficial Muscles of the Thorax Anterior extrinsic shoulder muscles Pectoralis minor Serratus anterior Subclavius (Pectoralis major considered later with muscles that act on the humerus)

Sternocleido- mastoid Subclavius Clavicle Subscapularis Deltoid Pectoralis minor Pectoralis major Coracobrachialis Sternum Serratus anterior Biceps brachii Humerus (a) Figure 10.13a

Superficial Muscles of the Posterior Thorax Posterior extrinsic shoulder muscles Trapezius Levator scapulae Rhomboids (major and minor) (Latissimus dorsi considered later with muscles that act on the humerus)

Levator scapulae Trapezius Supraspinatus Clavicle Deltoid Spine of Rhomboid minor Infraspinatus Rhomboid major Teres minor Teres major Humerus Latissimus dorsi (c) Figure 10.13c