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Anatomy & Physiology 2e: 11.5 Axial muscles of the abdominal wall and thorax

Anatomy & Physiology 2e
11.5 Axial muscles of the abdominal wall and thorax
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table of contents
  1. Cover
  2. Title Page
  3. Copyright
  4. Table Of Contents
  5. Chapter 1. An Introduction to the Human Body
    1. 1.0 Introduction
    2. 1.1 How Structure Determines Function
    3. 1.2 Structural Organization of the Human Body
    4. 1.3 Homeostasis
    5. 1.4 Anatomical Terminology
    6. 1.5 Medical Imaging
  6. Chapter 2. The Chemical Level of Organization
    1. 2.0 Introduction
    2. 2.1 Elements and Atoms: The Building Blocks of Matter
    3. 2.2 Chemical Bonds
    4. 2.3 Chemical Reactions
    5. 2.4 Inorganic Compounds Essential to Human Functioning
    6. 2.5 Organic Compounds Essential to Human Functioning
  7. Chapter 3. The Cellular Level of Organization
    1. 3.0 Introduction
    2. 3.1 The Cell Membrane
    3. 3.2 The Cytoplasm and Cellular Organelles
    4. 3.3 The Nucleus and DNA Replication
    5. 3.4 Protein Synthesis
    6. 3.5 Cell Growth and Division
    7. 3.6 Cellular Differentiation
  8. Chapter 4. The Tissue Level of Organization
    1. 4.0 Introduction
    2. 4.1 Types of Tissues
    3. 4.2 Epithelial Tissue
    4. 4.3 Connective Tissue Supports and Protects
    5. 4.4 Muscle Tissue
    6. 4.5 Nervous Tissue
    7. 4.6 Tissue Injury and Aging
  9. Chapter 5. The Integumentary System
    1. 5.0 Introduction
    2. 5.1 Layers of the Skin
    3. 5.2 Accessory Structures of the Skin
    4. 5.3 Functions of the Integumentary System
    5. 5.4 Diseases, Disorders, and Injuries of the Integumentary System
  10. Chapter 6. Bone Tissue and the Skeletal System
    1. 6.0 Introduction
    2. 6.1 The Functions of the Skeletal System
    3. 6.2 Bone Classification
    4. 6.3 Bone Structure
    5. 6.4 Bone Formation and Development
    6. 6.5 Fractures: Bone Repair
    7. 6.6 Exercise, Nutrition, Hormones, and Bone Tissue
    8. 6.7 Calcium Homeostasis: Interactions of the Skeletal System and Other Organ Systems
  11. Chapter 7. Axial Skeleton
    1. 7.0 Introduction
    2. 7.1 Divisions of the Skeletal System
    3. 7.2 Bone Markings
    4. 7.3 The Skull
    5. 7.4 The Vertebral Column
    6. 7.5 The Thoracic Cage
    7. 7.6 Embryonic Development of the Axial Skeleton
  12. Chapter 8. The Appendicular Skeleton
    1. 8.0 Introduction
    2. 8.1 The Pectoral Girdle
    3. 8.2 Bones of the Upper Limb
    4. 8.3 The Pelvic Girdle and Pelvis
    5. 8.4 Bones of the Lower Limb
    6. 8.5 Development of the Appendicular Skeleton
  13. Chapter 9. Joints
    1. 9.0 Introduction
    2. 9.1 Classification of Joints
    3. 9.2 Fibrous Joints
    4. 9.3 Cartilaginous Joints
    5. 9.4 Synovial Joints
    6. 9.5 Types of Body Movements
    7. 9.6 Anatomy of Selected Synovial Joints
    8. 9.7 Development of Joints
  14. Chapter 10. Muscle Tissue
    1. 10.0 Introduction
    2. 10.1 Overview of Muscle Tissues
    3. 10.2 Skeletal Muscle
    4. 10.3 Muscle Fiber Excitation, Contraction, and Relaxation
    5. 10.4 Nervous System Control of Muscle Tension
    6. 10.5 Types of Muscle Fibers
    7. 10.6 Exercise and Muscle Performance
    8. 10.7 Smooth Muscle Tissue
    9. 10.8 Development and Regeneration of Muscle Tissue
  15. Chapter 11. The Muscular System
    1. 11.0 Introduction
    2. 11.1 Describe the roles of agonists, antagonists and synergists
    3. 11.2 Explain the organization of muscle fascicles and their role in generating force
    4. 11.3 Explain the criteria used to name skeletal muscles
    5. 11.4 Axial Muscles of the Head Neck and Back
    6. 11.5 Axial muscles of the abdominal wall and thorax
    7. 11.6 Muscles of the Pectoral Girdle and Upper Limbs
    8. 11.7 Appendicular Muscles of the Pelvic Girdle and Lower Limbs
  16. Chapter 12. The Nervous System and Nervous Tissue
    1. 12.0 Introduction
    2. 12.1 Structure and Function of the Nervous System
    3. 12.2 Nervous Tissue
    4. 12.3 The Function of Nervous Tissue
    5. 12.4 Communication Between Neurons
    6. 12.5 The Action Potential
  17. Chapter 13. The Peripheral Nervous System
    1. 13.0 Introduction
    2. 13.1 Sensory Receptors
    3. 13.2 Ganglia and Nerves
    4. 13.3 Spinal and Cranial Nerves
    5. 13.4 Relationship of the PNS to the Spinal Cord of the CNS
    6. 13.5 Ventral Horn Output and Reflexes
    7. 13.6 Testing the Spinal Nerves (Sensory and Motor Exams)
    8. 13.7 The Cranial Nerve Exam
  18. Chapter 14. The Central Nervous System
    1. 14.0 Introduction
    2. 14.1 Embryonic Development
    3. 14.2 Blood Flow the meninges and Cerebrospinal Fluid Production and Circulation
    4. 14.3 The Brain and Spinal Cord
    5. 14.4 The Spinal Cord
    6. 14.5 Sensory and Motor Pathways
  19. Chapter 15. The Special Senses
    1. 15.0 Introduction
    2. 15.1 Taste
    3. 15.2 Smell
    4. 15.3 Hearing
    5. 15.4 Equilibrium
    6. 15.5 Vision
  20. Chapter 16. The Autonomic Nervous System
    1. 16.0 Introduction
    2. 16.1 Divisions of the Autonomic Nervous System
    3. 16.2 Autonomic Reflexes and Homeostasis
    4. 16.3 Central Control
    5. 16.4 Drugs that Affect the Autonomic System
  21. Chapter 17. The Endocrine System
    1. 17.0 Introduction
    2. 17.1 An Overview of the Endocrine System
    3. 17.2 Hormones
    4. 17.3 The Pituitary Gland and Hypothalamus
    5. 17.4 The Thyroid Gland
    6. 17.5 The Parathyroid Glands
    7. 17.6 The Adrenal Glands
    8. 17.7 The Pineal Gland
    9. 17.8 Gonadal and Placental Hormones
    10. 17.9 The Pancreas
    11. 17.10 Organs with Secondary Endocrine Functions
    12. 17.11 Development and Aging of the Endocrine System
  22. Chapter 18. The Cardiovascular System: Blood
    1. 18.0 Introduction
    2. 18.1 Functions of Blood
    3. 18.2 Production of the Formed Elements
    4. 18.3 Erythrocytes
    5. 18.4 Leukocytes and Platelets
    6. 18.5 Hemostasis
    7. 18.6 Blood Typing
  23. Chapter 19. The Cardiovascular System: The Heart
    1. 19.0 Introduction
    2. 19.1 Heart Anatomy
    3. 19.2 Cardiac Muscle and Electrical Activity
    4. 19.3 Cardiac Cycle
    5. 19.4 Cardiac Physiology
    6. 19.5 Development of the Heart
  24. Chapter 20. The Cardiovascular System: Blood Vessels and Circulation
    1. 20.0 Introduction
    2. 20.1 Structure and Function of Blood Vessels
    3. 20.2 Blood Flow, Blood Pressure, and Resistance
    4. 20.3 Capillary Exchange
    5. 20.4 Homeostatic Regulation of the Vascular System
    6. 20.5 Circulatory Pathways
    7. 20.6 Development of Blood Vessels and Fetal Circulation
  25. Chapter 21. The Lymphatic and Immune System
    1. 21.0 Introduction
    2. 21.1 Anatomy of the Lymphatic and Immune Systems
    3. 21.2 Barrier Defenses and the Innate Immune Response
    4. 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types
    5. 21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies
    6. 21.5 The Immune Response against Pathogens
    7. 21.6 Diseases Associated with Depressed or Overactive Immune Responses
    8. 21.7 Transplantation and Cancer Immunology
  26. Chapter 22. The Respiratory System
    1. 22.0 Introduction
    2. 22.1 Organs and Structures of the Respiratory System
    3. 22.2 The Lungs
    4. 22.3 The Process of Breathing
    5. 22.4 Gas Exchange
    6. 22.5 Transport of Gases
    7. 22.6 Modifications in Respiratory Functions
    8. 22.7 Embryonic Development of the Respiratory System
  27. Chapter 23. The Digestive System
    1. 23.0 Introduction
    2. 23.1 Overview of the Digestive System
    3. 23.2 Digestive System Processes and Regulation
    4. 23.3 The Mouth, Pharynx, and Esophagus
    5. 23.4 The Stomach
    6. 23.5 Accessory Organs in Digestion: The Liver, Pancreas, and Gallbladder
    7. 23.6 The Small and Large Intestines
    8. 23.7 Chemical Digestion and Absorption: A Closer Look
  28. Chapter 24. Metabolism and Nutrition
    1. 24.0 Introduction
    2. 24.1 Overview of Metabolic Reactions
    3. 24.2 Carbohydrate Metabolism
    4. 24.3 Lipid Metabolism
    5. 24.4 Protein Metabolism
    6. 24.5 Metabolic States of the Body
    7. 24.6 Energy and Heat Balance
    8. 24.7 Nutrition and Diet
  29. Chapter 25. The Urinary System
    1. 25.0 Introduction
    2. 25.1 Internal and External Anatomy of the Kidney
    3. 25.2 Microscopic Anatomy of the Kidney: Anatomy of the Nephron
    4. 25.3 Physiology of Urine Formation: Overview
    5. 25.4 Physiology of Urine Formation: Glomerular Filtration
    6. 25.5 Physiology of Urine Formation: Tubular Reabsorption and Secretion
    7. 25.6 Physiology of Urine Formation: Medullary Concentration Gradient
    8. 25.7 Physiology of Urine Formation: Regulation of Fluid Volume and Composition
    9. 25.8 Urine Transport and Elimination
    10. 25.9 The Urinary System and Homeostasis
  30. Chapter 26. Fluid, Electrolyte, and Acid-Base Balance
    1. 26.0 Introduction
    2. 26.1 Body Fluids and Fluid Compartments
    3. 26.2 Water Balance
    4. 26.3 Electrolyte Balance
    5. 26.4 Acid-Base Balance
    6. 26.5 Disorders of Acid-Base Balance
  31. Chapter 27. The Sexual Systems
    1. 27.0 Introduction
    2. 27.1 Anatomy of Sexual Systems
    3. 27.2 Development of Sexual Anatomy
    4. 27.3 Physiology of the Female Sexual System
    5. 27.4 Physiology of the Male Sexual System
    6. 27.5 Physiology of Arousal and Orgasm
  32. Chapter 28. Development and Inheritance
    1. 28.0 Introduction
    2. 28.1 Fertilization
    3. 28.2 Embryonic Development
    4. 28.3 Fetal Development
    5. 28.4 Maternal Changes During Pregnancy, Labor, and Birth
    6. 28.5 Adjustments of the Infant at Birth and Postnatal Stages
    7. 28.6 Lactation
    8. 28.7 Patterns of Inheritance
  33. Creative Commons License
  34. Recommended Citations
  35. Versioning

11.5 Axial muscles of the abdominal wall and thorax

Learning Objectives

By the end of this section, you will be able to:

Identify the following muscles and give their origins, insertions, actions and innervations:

  • Axial muscles of the abdominal wall and thorax

AXIAL MUSCLES OF THE ABDOMINAL WALL AND THORAX

It is a complex job to balance the body on two feet and walk upright. The muscles of the vertebral column, thorax, and abdominal wall extend, flex, and stabilize different parts of the body’s trunk. The deep muscles of the body’s core help maintain posture as well as provide stability for movement of the limbs.

Muscles of the Abdomen

There are four pairs of abdominal muscles that make up the abdominal wall: the rectus abdominis, the external abdominal obliques, the internal abdominal obliques and the transverse abdominis (Figure 11.4.9 and Table 11.6).

The top panel shows the lateral view of the superficial and deep abdominal muscles. The bottom panel shows the anterior view of the posterior abdominal muscles.
Figure 11.5.1 – Muscles of the Abdomen: (a) The anterior abdominal muscles include the medially located rectus abdominis, which is covered by a sheet of connective tissue called the rectus sheath. On the flanks of the body, medial to the rectus abdominis, the abdominal wall is composed of three layers. The external oblique muscles form the superficial layer, while the internal oblique muscles form the middle layer, and the transverses abdominus forms the deepest layer. (b) The muscles of the lower back move the lumbar spine but also assist in femur movements.
Muscles of the Abdomen (Table 11.6)
MovementTargetTarget motion directionPrime moverOriginInsertion
Twisting at waist; also bending to the sideVertebral columnSupination; lateral flexionExternal obliques; internal obliquesRibs 5–12; iliumRibs 7–10; linea alba; ilium
Squeezing abdomen during forceful exhalations, defecation, urination, and childbirthAbdominal cavityCompressionTransversus abdominusIlium; ribs 5–10Sternum; linea alba; pubis
Sitting upVertebral columnFlexionRectus abdominisPubisSternum; ribs 5 and 7
Bending to the sideVertebral columnLateral flexionQuadratus lumborumIlium; ribs 5–10Rib 12; vertebrae L1–L4

Muscles of the Abdomen

Prime moverMovementTargetTarget motion directionOriginInsertion
External obliques; internal obliquesTwisting at waist; also bending to the sideVertebral columnSupination; lateral flexionRibs 5–12; iliumRibs 7–10; linea alba; ilium
Transversus abdominusSqueezing abdomen during forceful exhalations, defecation, urination, and childbirthAbdominal cavityCompressionIlium; ribs 5–10Sternum; linea alba; pubis
Rectus abdominisSitting upVertebral columnFlexionPubisSternum; ribs 5 and 7
Quadratus lumborumBending to the sideVertebral columnLateral flexionIlium; ribs 5–10Rib 12; vertebrae L1–L4

There are three flat skeletal muscles in the antero-lateral wall of the abdomen. The external oblique, closest to the surface, extend inferiorly and medially, in the direction of sliding one’s four fingers into pants pockets. Perpendicular to it is the intermediate internal oblique, extending superiorly and medially, the direction the thumbs usually go when the other fingers are in the pants pocket. The deep muscle, the transverse abdominis, is arranged transversely around the abdomen, similar to a belt. This arrangement of three bands of muscles in different orientations allows various movements and rotations of the trunk. The three layers of muscle also help to protect the internal abdominal organs in an area where there is no bone.

The linea alba is a white, fibrous band that is made of the bilateral rectus sheaths (see Figure 11.4.9) that join at the anterior midline of the body. These enclose the rectus abdominis muscles that originate at the pubic crest and symphysis, and extend the length of the body’s trunk. Each muscle is segmented by three transverse bands of collagen fibers called the tendinous intersections resulting in the look of “six-pack abs”.

The posterior abdominal wall is formed by the lumbar vertebrae, parts of the ilia of the hip bones, psoas major and iliacus muscles, and quadratus lumborum muscle. This part of the core plays a key role in stabilizing the rest of the body and maintaining posture.

Career Connection – Physical Therapists

Those who have a muscle or joint injury will most likely be sent to a physical therapist (PT) after seeing their regular doctor. PTs have a master’s degree or doctorate, and are highly trained experts in the mechanics of body movements. Many PTs also specialize in sports injuries.

If you injured your shoulder while you were kayaking, the first thing a physical therapist would do during your first visit is assess the functionality of the joint. The range of motion of a particular joint refers to the normal movements the joint performs. The PT will ask you to abduct and adduct, circumduct, and flex and extend the arm. The PT will note the shoulder’s degree of function, and based on the assessment of the injury, will create an appropriate physical therapy plan.

The first step in physical therapy will probably be applying a heat pack to the injured site, which acts much like a warm-up to draw blood to the area, to enhance healing. You will be instructed to do a series of exercises to continue the therapy at home, followed by icing, to decrease inflammation and swelling, which will continue for several weeks. When physical therapy is complete, the PT will do an exit exam and send a detailed report on the improved range of motion and return of normal limb function to your doctor. Gradually, as the injury heals, the shoulder will begin to function correctly. A PT works closely with patients to help them get back to their normal level of physical activity.

Muscles of the Thorax

The muscles of the chest serve to facilitate breathing by changing the volume of the thoracic cavity (Table 11.7). When you inhale your chest rises increasing the volume of the thoracic cavity. Alternately, when you exhale, your chest falls decreasing the volume of the thoracic cavity.

Muscles of the Thorax (Table 11.7)
MovementTargetTarget motion directionPrime moverOriginInsertion
Inhalation; exhalationThoracic cavityCompression; expansionDiaphragmSternum; ribs 6–12; lumbar vertebraeCentral tendon
Inhalation;exhalationRibsElevation (expands thoracic cavity)External intercostalsRib superior to each intercostal muscleRib inferior to each intercostal muscle
Forced exhalationRibsMovement along superior/inferior axis to bring ribs closer togetherInternal intercostalsRib inferior to each intercostal muscleRib superior to each intercostal muscle

Muscles of the Thorax

Prime moverMovementTargetTarget motion directionOriginInsertion
DiaphragmInhalation; exhalationThoracic cavityCompression; expansionSternum; ribs 6–12; lumbar vertebraeCentral tendon
External intercostalsInhalation;exhalationRibsElevation (expands thoracic cavity)Rib superior to each intercostal muscleRib inferior to each intercostal muscle
Internal intercostalsForced exhalationRibsMovement along superior/inferior axis to bring ribs closer togetherRib inferior to each intercostal muscleRib superior to each intercostal muscle

The Diaphragm

The change in volume of the thoracic cavity during breathing is due to the alternate contraction and relaxation of the diaphragm (Figure 11.4.10). It separates the thoracic and abdominal cavities, and is dome-shaped at rest. The superior surface of the diaphragm is convex, creating the elevated floor of the thoracic cavity. The inferior surface is concave, creating the curved roof of the abdominal cavity.

This figure shows the inferior view of the diaphragm with the major parts labeled.
Figure 11.5.2 – Muscles of the Diaphragm: The diaphragm separates the thoracic and abdominal cavities.

Defecating, urination, and even childbirth involve cooperation between the diaphragm and abdominal muscles (this cooperation is referred to as the “Valsalva maneuver”). While you hold your breath the diaphragm and abdominal muscles contract increasing the pressure of the peritoneal cavity and stabilizing the core. When the abdominal muscles contract, the pressure cannot push the diaphragm up, so it increases pressure on the intestinal tract (defecation), urinary tract (urination), or reproductive tract (childbirth).

The inferior surface of the pericardial sac and the inferior surfaces of the pleural membranes (parietal pleura) fuse onto the central tendon of the diaphragm. To the sides of the tendon are the skeletal muscle portions of the diaphragm, which insert into the tendon while having a number of origins including the xiphoid process of the sternum anteriorly, the inferior six ribs and their cartilages laterally, and the lumbar vertebrae and 12th ribs posteriorly.

The diaphragm also includes three openings for the passage of structures between the thorax and the abdomen. The inferior vena cava passes through the caval opening, and the esophagus and attached nerves pass through the esophageal hiatus. The aorta, thoracic duct, and azygous vein pass through the aortic hiatus of the posterior diaphragm.

The Intercostal Muscles

There are three sets of muscles, called intercostal muscles, which span each of the intercostal spaces. The principal role of the intercostal muscles is to assist in breathing by changing the dimensions of the rib cage (Figure 11.4.11).

This figure shows the muscles in the thorax. The left panel shows the ribs, the major bones, and the muscles connecting them. The right panel shows a magnified view of the sternum and labels the muscles.
Figure 11.5.3 – Intercostal Muscles: The external intercostals are located laterally on the sides of the body. The internal intercostals are located medially near the sternum. The innermost intercostals are located deep to both the internal and external intercostals.

The 11 pairs of superficial external intercostal muscles aid in inspiration of air during breathing because when they contract, they raise the rib cage, which expands it. The 11 pairs of internal intercostal muscles, just under the externals, are used for expiration because they draw the ribs together to constrict the rib cage. The innermost intercostal muscles are the deepest, and they act as synergists for the action of the internal intercostals.

Muscles of the Pelvic Floor and Perineum

The pelvic floor (also referred to as the pelvic diaphragm) is a muscular sheet that defines the inferior portion of the pelvic cavity. The pelvic floor extends anteriorly to posteriorly from the pubis to the coccyx and is comprised of the levator ani and the ischiococcygeus. Its openings include the anal canal and urethra, and the vagina in women.

The large levator ani consists of two skeletal muscles, the pubococcygeus and the iliococcygeus (Figure 11.4.12). The levator ani is considered the most important muscle of the pelvic floor because it supports the pelvic viscera. It resists the pressure produced by contraction of the abdominal muscles so that the pressure is applied to the colon to aid in defecation and to the uterus to aid in childbirth (assisted by the ischiococcygeus, which pulls the coccyx anteriorly). This muscle also creates skeletal muscle sphincters at the urethra and anus.

This image shows the superior view of the pelvic diaphragm.
Figure 11.5.4 – Muscles of the Pelvic Floor: The pelvic floor muscles support the pelvic organs, resist intra-abdominal pressure, and work as sphincters for the urethra, rectum, and vagina.

The perineum is the diamond-shaped space between the pubic symphysis (anteriorly), the coccyx (posteriorly), and the ischial tuberosities (laterally), lying just inferior to the pelvic diaphragm (levator ani and ischiococcygeus). Divided transversely into triangles, the anterior is the urogenital triangle, which includes the external genitals and the posterior is the anal triangle containing the anus (Figure 11.4.13). The perineum is also divided into superficial and deep layers with some of the muscles common to men and women (Figure 11.4.14). Women also have the compressor urethrae and the sphincter urethrovaginalis, which function to close the vagina. In men, the deep transverse perineal muscle plays a role in ejaculation.

The left panel shows the muscles of the perineum in the male, and the right panel shows the muscles of the perineum in the female.
Figure 11.5.5 – Muscles of the Perineum: The perineum muscles play roles in urination in both sexes, ejaculation in men, and vaginal contraction in women.
This table describes the muscles of the perineum that are common to men and women. The levator ani pubococcygeus and levator ani iliococcygeus control movements during defaction, urination, coughing, and giving birth. They originate in the pubis and ischium. The superficial transverse perineal supports the perineal body maintaining the anus at the center of the perineum. It originates in the ischium. The bulbospongiosus is a superficial muscle that causes an involuntary response that compresses the urethra when excreting urine in both sexes or while ejaculating in males; it also aids in erection of the penis in males. It originates in the perineal body. The ischiocavernosus is a superficial muscle that compresses veins to maintain erection of the penis in males and erection of the clitoris in females. It originates in the ischium, ischial rami, and pubic rami. The external uretral sphincter is a deep muscle that voluntarily compresses the urethra during urination. It originates in the ischial rami and pubic rami. The external anal sphincter is a deep muscle that closes the anus. It originates in the anoccoccygeal ligament.
Figure 11.4.14 Muscles of the Perineum Common to Men and Women

Muscles of the Perineum Common to Men and Women

MuscleOriginInsertionActionInnervation
Levator ani pubococcygeus; levator ani iliococcygeusPubis; ischiumUrethra; anal canal; perineal body; coccyxCompresses anal canal; defecation; urination; birth; coughingPudendal nerve; Spinal nerves S2-S3
Superficial muscles
Superficial transverse perinealIschiumPerineal bodyNone- supports perineal body maintaining anus at center of perineumPudendal nerve
BulbospongiosusPerineal bodyPerineal membrane; corpus spongiosum of penis; deep fascia of penis; clitoris in femaleInvoluntary response that compresses urethra when excreting urine in both sexes or while ejaculating in males; also aids in erection of penis in malsePudendal nerve
IschiocavernosusIschium; ischial rami; pubic ramiPubic symphysis; corpus cavernosum of penis in males; clitoris in femalesCompresses veins to maintain erection of penis in males; erection of clitoris in femalesPudendal nerve
Deep muscles
External urethral sphincterIschial rami; pubic ramiMale: median raphe; female: vaginal wallVoluntarily compresses urethra during urinationPudendal nerve spinal nerves S2-S4; pelvic splanchnic nerve
External anal sphincterAnoccoccygeal ligamentPernieal bodyCloses anusPudendal nerve spinal nerves S2-S4; pelvic splanchnic nerve

Chapter Review

Made of skin, fascia, and four pairs of muscle, the anterior abdominal wall protects the organs located in the abdomen and moves the vertebral column. These muscles include the rectus abdominis, which extends through the entire length of the trunk, the external oblique, the internal oblique, and the transversus abdominus. The quadratus lumborum forms the posterior abdominal wall.

The muscles of the thorax play a large role in breathing, especially the dome-shaped diaphragm. When it contracts and flattens, the volume inside the pleural cavities increases, which decreases the pressure within them. As a result, air will flow into the lungs. The external and internal intercostal muscles span the space between the ribs and help change the shape of the rib cage and the volume-pressure ratio inside the pleural cavities during inspiration and expiration.

The perineum muscles play roles in urination in both sexes, ejaculation in men, and vaginal contraction in women. The pelvic floor muscles support the pelvic organs, resist intra-abdominal pressure, and work as sphincters for the urethra, rectum, and vagina.

Review Questions

An interactive H5P element has been excluded from this version of the text. You can view it online here:
https://open.oregonstate.education/aandp/?p=1553#h5p-624

An interactive H5P element has been excluded from this version of the text. You can view it online here:
https://open.oregonstate.education/aandp/?p=1553#h5p-625

An interactive H5P element has been excluded from this version of the text. You can view it online here:
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Critical Thinking Questions

  1. Describe the fascicle arrangement in the muscles of the abdominal wall. How do they relate to each other?
  2. What are some similarities and differences between the diaphragm and the pelvic diaphragm?

Glossary

anal triangle
posterior triangle of the perineum that includes the anus
caval opening
opening in the diaphragm that allows the inferior vena cava to pass through; foramen for the vena cava
compressor urethrae
deep perineal muscle in women
deep transverse perineal
deep perineal muscle in men
diaphragm
skeletal muscle that separates the thoracic and abdominal cavities and is dome-shaped at rest
external intercostal
superficial intercostal muscles that raise the rib cage
external oblique
superficial abdominal muscle with fascicles that extend inferiorly and medially
iliococcygeus
muscle that makes up the levator ani along with the pubococcygeus
innermost intercostal
the deepest intercostal muscles that draw the ribs together
intercostal muscles
muscles that span the spaces between the ribs
internal intercostal
muscles the intermediate intercostal muscles that draw the ribs together
internal oblique
flat, intermediate abdominal muscle with fascicles that run perpendicular to those of the external oblique
ischiococcygeus
muscle that assists the levator ani and pulls the coccyx anteriorly
levator ani
pelvic muscle that resists intra-abdominal pressure and supports the pelvic viscera
linea alba
white, fibrous band that runs along the midline of the trunk
pelvic diaphragm
muscular sheet that comprises the levator ani and the ischiococcygeus
perineum
diamond-shaped region between the pubic symphysis, coccyx, and ischial tuberosities
pubococcygeus
muscle that makes up the levator ani along with the iliococcygeus
quadratus lumborum
posterior part of the abdominal wall that helps with posture and stabilization of the body
rectus abdominis
long, linear muscle that extends along the middle of the trunk
rectus sheaths
tissue that makes up the linea alba
sphincter urethrovaginalis
deep perineal muscle in women
tendinous intersections
three transverse bands of collagen fibers that divide the rectus abdominis into segments
transversus abdominis
deep layer of the abdomen that has fascicles arranged transversely around the abdomen
urogenital triangle
anterior triangle of the perineum that includes the external genitals

Solutions

Answers for Critical Thinking Questions

  1. Tendons of the infraspinatus, supraspinatus, teres minor, and the subscapularis form the rotator cuff, which forms a foundation on which the arms and shoulders can be stabilized and move.
  2. The muscles that make up the shoulders and upper limbs include the muscles that position the pelvic girdle, the muscles that move the humerus, the muscles that move the forearm, and the muscles that move the wrists, hands, and fingers.

Annotate

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11.6 Muscles of the Pectoral Girdle and Upper Limbs
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Anatomy and Physiology
Copyright © 2019 by Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick & Jon Runyeon

Anatomy & Physiology by Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick & Jon Runyeon is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

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