Chapter 10 The Muscular System Part B Shilla Chakrabarty, Ph.D.

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 Muscles that flex vertebral column and compress abdominal wall are: Internal obliques External obliques Transversus abdominis Rectus abdominis Origin Pubic crest and symphysis Insertion Xiphoid process and costal cartilage of ribs 5-7 Function Flex and rotate lumbar region of vertebral column

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

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

Superficial Muscles of the Posterior Thorax Posterior extrinsic shoulder muscles Trapezius Levator scapulae Rhomboids (major and minor) Trapezius (c) Levator scapulae Supraspinatus Clavicle Spine of scapula Infraspinatus Teres minor Humerus Deltoid Teres major Latissimus dorsi Rhomboid minor major

Muscles Crossing the Shoulder Joint Nine muscles cross the shoulder joint to insert on and move the humerus Some originate off the scapula; others originate off the axial skeleton Three are prime movers of the arm Pectoralis major Latissimus dorsi Deltoid Actions include flexion, extension, adduction, abduction, and rotation of humerus

Muscles Crossing the Shoulder Joint Four muscles are rotator cuff muscles Supraspinatus Infraspinatus Teres minor Subscapularis Reinforce the capsule of the shoulder Act as synergists and fixators Two additional muscles are synergists: coracobrachialis and teres major Muscles Crossing the Elbow Joint Posterior extensor muscles Triceps brachii—prime mover of forearm extension Anconeus—weak synergist

Muscles Crossing the Shoulder Joint Supraspinatus* Spine of scapula (b) Posterior view Deltoid (cut) Greater tubercle of humerus Infraspinatus* Teres minor* Teres major Triceps brachii: Latissimus dorsi Humerus Olecranon process of ulna Lateral head Long head Anconeus * Rotator cuff muscles Clavicle Deltoid Sternum Pectoralis major Medial head Coracobrachialis Biceps brachii Brachialis Brachioradialis (a) Anterior view

Muscles of the Forearm Actions: movements of the wrist, hand, and fingers Most anterior muscles are flexors Some forearm muscles act to produce pronation and supination of the forearm Biceps brachii Tendon of biceps brachii Pronator teres Brachioradialis Extensor carpi radialis longus Flexor pollicis longus Pronator quadratus Flexor retinaculum Medial head of triceps brachii Medial epicondyle of humerus Flexor carpi radialis Palmar aponeurosis Superficial transverse ligament of palm Palmaris longus Flexor carpi ulnaris Flexor digitorum superficialis (a)

Muscles of the Forearm Most posterior muscles are extensors Extensor Insertion of triceps brachii Anconeus Flexor carpi ulnaris Extensor carpi Extensor digiti minimi Extensor indicis Tendons of extensor carpi radialis brevis and longus Extensor expansion (a) Extensor pollicis longus brevis Abductor pollicis longus Extensor digitorum radialis brevis radialis longus Brachioradialis Tendons of extensor digitorum Most posterior muscles are extensors

Antero-medial Postero-lateral

Intrinsic Muscles of the Hand Small weak muscles Lie entirely within the palm of the hand Control precise movements of metacarpals and fingers (e.g., threading a needle) Abductors and adductors of the fingers Produce opposition—move the thumb toward the little finger

Muscles Crossing Hip and Knee Joints Most anterior muscles flex the femur at the hip and extend the leg at the knee (fore swing of walking) Most posterior muscles extend the thigh and flex the leg (backswing of walking) Medial muscles all adduct the thigh All three groups are enclosed by the fascia lata

Movements of the Thigh Include flexion, extension, abduction, adduction, circumduction, and rotation Thigh flexors pass in front of the hip joint Iliopsoas (iliacus and psoas major): prime mover of flexion Tensor fasciae latae Rectus femoris Assisted by medial adductors and sartorius Psoas minor Iliac crest Psoas major Iliopsoas 12th rib Quadratus lumborum Iliacus Anterior superior iliac spine Tensor fasciae latae Pectineus Sartorius Quadriceps femoris • Rectus femoris • Vastus lateralis • Vastus medialis (a) Adductor magnus Patella Patellar ligament Tendon of quadriceps femoris 12th thoracic vertebra 5th lumbar vertebra Adductor longus Gracilis

Movements of the Thigh Thigh extensors Hamstring muscles (prime movers of extension) Biceps femoris Semitendinosus Semimembranosus Gluteus maximus (prime mover during forceful extension)

Muscles of the Thigh that Move the Knee Joint Psoas minor Iliac crest Psoas major Iliopsoas 12th rib Quadratus lumborum Iliacus Anterior superior iliac spine Tensor fasciae latae Pectineus Sartorius Quadriceps femoris • Rectus femoris • Vastus lateralis • Vastus medialis (a) Adductor magnus Patella Patellar ligament Tendon of quadriceps femoris 12th thoracic vertebra 5th lumbar vertebra Adductor longus Gracilis Quadriceps femoris—sole extensor of the knee Hamstring muscles—flex the knee, and are antagonists to the quadriceps femoris

Muscles of the Anterior Compartment of the Leg Fibularis longus Gastrocnemius Tibia Tibialis anterior Extensor digitorum longus Soleus Extensor hallucis longus Fibularis tertius Extensor hallucis brevis Extensor digitorum brevis Superior and inferior extensor retinacula (a) Primary toe extensors and ankle dorsiflexors Tibialis anterior Extensor digitorum longus Extensor hallucis longus Fibularis tertius (not always present)

Muscles of the Posterior Compartment of the Leg Flexors of the foot and the toes Gastrocnemius Soleus Plantaris Popliteus Tibialis posterior Flexor digitorum longus Flexor hallucis longus Gastrocnemius Plantaris Medial head Lateral head Tendon of gastrocnemius Calcaneal tendon Medial malleolus Lateral malleolus Calcaneus (a) Superficial view of the posterior leg.

Anterior Posterior Muscles Origin Insertion Function Ilipsoas Transverse processes ofT12-L5; iliac fossa Lesser trochanter of femur Major flexion of thigh Sartorius Anterior superior iliac spine Proximal tibia Flexes and laterally rotates thigh

Lateral Medial