chap 10 lect flash cards
Chapter 10: The Muscular System
10.1 Structural and Functional Organization of Muscles
Expected Learning Outcomes:
Describe the various functions of muscular tissue.
Describe the connective tissue components of a muscle and their relationship to the internal organization of a muscle and compartmentalization of muscle groups.
Relate muscle fascicles to the shapes and relative strengths of muscles.
Name the types of muscle-bone attachments and explain the shortcoming of calling their attachments origins and insertions.
Distinguish between intrinsic and extrinsic muscles.
Describe the ways muscles work in groups to aid, oppose, and moderate each other's actions.
Describe in general terms the nerve and blood supply to skeletal muscles.
Explain how the Latin names of muscles aid in visualizing and remembering them.
10.1a The Functions of Muscles
Primary Functions of Muscles:
Movement: Muscles facilitate the movement of body parts and contents such as food during digestion, air during breathing, and blood during circulation. They are also involved in communication through speech and facial expressions.
Stability: Muscles help maintain posture and stabilize joints, ensuring that the body remains in a position.
Control of Openings and Passages: Muscles control the intake of food, movement of materials through the body, and elimination of waste, as well as the admission of light through the eyes.
Heat Production (Thermogenesis): Skeletal muscles generate about 20% to 30% of body heat at rest and up to 85% during vigorous exercise.
Additional Functions:
Hormone Secretion: Exercised muscles secrete hormones that stimulate glucose synthesis in the liver and the breakdown of visceral fat.
Glycemic Control: Skeletal muscles are responsible for absorbing, storing, and using a significant amount of the body’s glucose, helping to stabilize blood glucose concentration.
10.1b Muscle Connective Tissues, Fascicles, and Compartments
Components of Skeletal Muscles:
Skeletal muscles consist of muscular tissue along with connective tissue, nerves, and blood vessels.
Connective Tissue Components:
Endomysium: A thin sleeve of loose connective tissue surrounding each muscle fiber, providing space for capillaries and nerve fibers, as well as a chemical environment for muscle fibers and nerve endings.
Perimysium: A thicker layer of connective tissue wrapping fascicles, which are bundles of muscle fibers. It carries nerves, blood vessels, and stretch receptors.
Epimysium: A fibrous sheath encasing the entire muscle, blending with fascia and deeper connective tissues.
Fascia: Connective tissue sheets lying between muscles or muscle groups.
Fascicle Orientation and Muscle Strength:
The strength of a muscle and the direction of pull are influenced by the orientation of its fascicles:
Fusiform Muscles: Thick in the middle with fascicles converging towards tapered ends (e.g., biceps brachii).
Parallel Muscles: Uniform width with parallel fascicles (e.g., rectus abdominis).
Triangular (Convergent) Muscles: Broad at one end with fascicles converging to the narrow end (e.g., pectoralis major).
Pennate Muscles: Feather-shaped; fascicles attach obliquely to a tendon (e.g., rectus femoris).
Unipennate: Fascicles come from one side.
Bipennate: Fascicles approach from both sides.
Multipennate: Fascicles converge to a single point.
Circular Muscles (Sphincters): Fascicles form rings around body openings, constricting the opening when contracted.
Muscle Compartments:
Fascia: Fascial layers package groups of functionally related muscles into compartments, containing nerves and blood vessels that supply these muscle groups.
Intermuscular Septa: Some fascia between compartments appear extra thick.
10.1c Muscle Attachments
Types of Muscle Attachments:
Muscles can attach to bones either directly or indirectly:
Direct (Fleshy) Attachment: Minimal separation between muscle and bone.
Indirect Attachment: Utilizes tendons (fibrous cords) connecting muscle to bone, where collagen fibers from the muscle's connective tissue layers extend into the tendon and subsequently into the bone's periosteum:
Tendon: A cord-like structure connecting muscle to bone.
Aponeurosis: A broad, flat tendon (e.g., palmar aponeurosis).
Retinaculum: A connective tissue band that holds tendons from separate muscles in place.
Terminology of Attachments:
Traditional terms "origin" (stationary end) and "insertion" (moving end) are often not accurate. Some anatomists prefer terms based on an attachment's proximal/distal or superior/inferior orientation.
10.1d Functional Groups of Muscles
Muscle Functionality:
Some muscles are categorized as intrinsic or extrinsic based on their location relative to the organ they control:
Intrinsic Muscles: Completely contained within a specific region (e.g., muscles of the hand).
Extrinsic Muscles: Act on a designated region but originate from a different area (e.g., forearm muscles acting on the hands).
Muscle Action Categories:
Muscles usually act in groups, and the action produced by them falls into four main categories:
Prime Mover: The muscle producing the most force in a movement (e.g., brachialis for elbow flexion).
Synergist: A muscle that assists the prime mover (e.g., biceps brachii assists brachialis).
Antagonist: A muscle opposing the prime mover (e.g., triceps brachii extends the elbow).
Fixator: A muscle that stabilizes a bone during movement (e.g., rhomboid muscles stabilize scapula during biceps contraction).
10.1e Innervation and Blood Supply
Muscle Innervation:
Innervation refers to the nerve that stimulates a muscle, aiding in diagnosing injuries of nerves, spinal cord, and brainstem through muscle tests.
Muscles receive innervation from branches of spinal and cranial nerves:
Spinal Nerves: Arise from the spinal cord and branch into posterior and anterior rami, innervating below the neck.
Cranial Nerves: Emerge from the base of the brain and innervate head and neck muscles, numbered CN I to CN XII.
Blood Supply:
At rest, the muscular system receives about 1.24 L of blood per minute (approximately one-quarter of the cardiac output); during intense exercise, blood flow to muscles increases to over three-quarters (11.6 L/min). Capillaries extensively branch through the endomysium, supplying each muscle fiber.
10.1f Muscle Names and Learning Strategy
Muscle Naming:
Latin-based naming conventions typically describe distinctive aspects of structure, location, or action of a muscle. Examples include:
Depressor labii inferioris: Lowers the bottom lip.
Flexor digiti minimi brevis: Short muscle that flexes the smallest finger.
Learning Strategies for the Muscular System:
Examine muscle models, cadavers, or dissected animals; use photographic atlases; palpate muscles on oneself when possible.
Locate muscle attachments on an articulated skeleton; study etymology of each muscle name to remember locations, attachments, and actions better.
Pronounce muscle names aloud and practice correct spelling with study partners.
10.2 Muscles of the Head and Neck
Expected Learning Outcomes:
Identify the muscles responsible for facial expressions.
Locate the muscles used in chewing and swallowing.
Identify neck muscles that facilitate head movement.
Understand the attachments, actions, and innervations of these muscles.
10.2a Muscles of Facial Expression
Characteristics:
Muscles arise from the dermis and subcutaneous tissue, affecting skin texture and expression.
These muscles are innervated by the facial nerve (CN VII).
Distribution: Scalp, forehead, around eyes, nose, mouth, and neck.
Specific Muscles and Functions:
Occipitofrontalis: Composed of two bellies (frontal and occipital) connected by the galea aponeurotica; raises eyebrows and retracts scalp.
Orbicularis oculi: Encircles eyes, functioning as a sphincter, closing the eyelids.
Levator palpebrae superioris: Elevates the upper eyelid, located beneath the orbicularis oculi.
Orbicularis oris: Encircles the mouth; puckers lips; consists of interlacing muscles.
Mentalis: From mandible to chin skin, elevates protrusion of lower lip.
Buccinator: Compresses the cheek (involved in blowing and chewing).
Platysma: Thin, broad muscle in the neck that aids in facial expression, particularly in expressing surprise or fear.
10.2b Muscles of Chewing and Swallowing
Tongue Muscles:
Intrinsic Muscles: Located entirely within the tongue, responsible for altering its shape (e.g., vertical, transverse, longitudinal).
Extrinsic Muscles: Originate from outside the tongue, responsible for positioning it during actions like mastication and deglutition (swallowing).
Muscles Involved in Chewing:
Temporalis and Masseter: Major muscles responsible for elevating the jaw.
Pterygoid Muscles (medial and lateral): Responsible for grinding movements of the molars.
Functionality of chewing includes opening and closing the mouth, biting, grinding, and moving the jaw from side to side.
10.2c Muscles Acting on the Head and Neck
Muscles and Their Actions:
Sternocleidomastoid: Major muscle for neck flexion, extending from sternum and clavicle to mastoid process. Unilateral contraction rotates head to the opposite side, while bilateral contraction flexes the neck.
Scalenes: Located on the sides of the neck, aid in neck flexion and assist in elevating ribs, contributing to breathing.
10.2d Muscles of Respiration (Introduction)
Major Respiratory Muscles:
Diaphragm: Separated thoracic and abdominal cavities; contraction increases thoracic cavity volume for inhalation.
Intercostal Muscles: Involved in breathing, placed between ribs, composed of external (elevates ribs during inhalation), internal (depresses ribs during exhalation), and innermost layers.
10.3 Muscles of the Trunk
Expected Learning Outcomes:
Name and locate the muscles involved in respiration and their effects on airflow and abdominal pressure.
Identify muscles of the abdominal wall, back, and pelvic floor along with their attachments, actions, and innervations.
10.3a Muscles of Respiration
Breathing Mechanics:
Diaphragm: A dome-shaped muscle that expands during contraction, increasing space in the thoracic cavity and facilitating air intake.
External Intercostal Muscles: Superficial layer, elevating ribs during inhalation.
Internal Intercostal Muscles: Deeper than external; their intercartilaginous and interosseous components depress ribs during exhalation.
10.3b Muscles of the Abdominal Wall
Layers and Functions:
External Oblique: Most superficial; assists in rotation and lateral flexion of the waist.
Internal Oblique: Middle layer; fibers run perpendicular to external obliques, also aiding in rotation of the waist.
Transverse Abdominis: Deepest layer, providing stability to the spine and compressing abdominal contents.
Rectus Abdominis: Paired vertical muscles; flex the waist; known for the ‘six pack’ due to tendinous intersections.
10.3c Muscles of the Back
Actions:
Latissimus Dorsi: Prominent muscle aiding in upper limb movements, involved in extension, adduction, and internal rotation of shoulder joint.
Erector Spinae Muscles: Group of three paired muscles running vertically from the cranium to the sacrum, involved in extension and lateral flexion of the spine (iliocostalis, longissimus, spinalis).
10.4 Muscles Acting on the Shoulder and Upper Limb
Expected Learning Outcomes:
Identify muscles acting on the pectoral girdle, shoulder, elbow, wrist, and hand, as well as their actions corresponding to joint movements.
Muscles of the Shoulder:
Functional Groupings:
Pectoralis Minor: Protracts the scapula; originates from the ribs and attaches to the coracoid process.
Serratus Anterior: Also protracts the scapula, originates from ribs and connects to the medial border of the scapula.
Trapezius: Capable of elevating, retracting, and rotating the scapula depending on which fibers contract.
Muscles Acting on the Arm:
Rotator Cuff Muscles (SITS):
Supraspinatus: Initiates arm abduction.
Infraspinatus: External rotation of shoulder.
Teres Minor: Assists in shoulder external rotation.
Subscapularis: Internal rotation of shoulder.
Additional Arm Muscles:
Deltoid: Abducts, flexes, and extends the arm; site for intramuscular injections.
Latissimus Dorsi: Extends and internally rotates the arm.
Biceps Brachii: Key elbow flexor and assists in shoulder flexion.
Triceps Brachii: Principal elbow extensor.
10.5 Muscles Acting on the Hip and Lower Limb
Expected Learning Outcomes:
Identify the muscles acting on the hip, knee, ankle, and toe joints; relate their actions to joint movements.
Muscles Acting on the Hip and Thigh:
Iliopsoas: A prime hip flexor, composed of iliacus (from iliac crest) and psoas major (from lumbar vertebrae).
Gluteus Maximus: Major extensor of the hip, also involved in lateral rotation.
Adductor Group: Adducts the thigh, includes adductor longus, adductor brevis, and adductor magnus.
Tensor Fasciae Latae: Stabilizes the knee while walking; helps with abduction.
Muscles Acting on the Knee and Leg:
Quadriceps Femoris: Major knee extensor, has four heads: rectus femoris (hip flexor), vastus lateralis, vastus medialis, vastus intermedius.
Hamstring Group: Flexes the knee, includes biceps femoris, semitendinosus, semimembranosus.
Muscles Acting on the Foot:
Gastrocnemius: Major plantar flexor of the foot and assists in knee flexion.
Soleus: Works with gastrocnemius to flex the foot.
Tibialis Anterior: Dorsiflexes and inverts the foot.
Intrinsic Muscles of the Foot:
Layered Arrangement: Consists of various muscles including abductors, flexors, and interosseous muscles.
10.5e Common Conditions:
Carpal Tunnel Syndrome:
A condition resulting from compression of the median nerve within the carpal tunnel, usually due to repetitive motions. Symptoms include tingling and weakness in the hand. Treatments might include anti-inflammatories, wrist immobilization, or surgery.
10.5f Hernias:
Types of Hernias:
Inguinal Hernia: Most common; occurs when viscera protrude through the inguinal canal.
Hiatal Hernia: Stomach protrudes through diaphragm into thorax; common in overweight individuals.
Umbilical Hernia: Protrusion through the navel area.
Chapter 10: The Muscular System
10.1 Structural and Functional Organization of Muscles
10.1a The Functions of Muscles
Expected Learning Outcome and Answer:
Question: Describe the various functions of muscular tissue.
Answer: The functions of muscular tissue include:
Primary Functions: Movement (body parts, contents; communication), Stability (posture, joint stabilization), Control of Openings and Passages (food, waste, light), and Heat Production (Thermogenesis, \text{20%}-\\text{30%} at rest, up to \text{85%} during exercise).
Additional Functions: Hormone Secretion (stimulate glucose synthesis, breakdown visceral fat) and Glycemic Control (absorbing, storing, using glucose).
Primary Functions of Muscles:
Movement: Muscles facilitate the movement of body parts and contents such as food during digestion, air during breathing, and blood during circulation. They are also involved in communication through speech and facial expressions.
Stability: Muscles help maintain posture and stabilize joints, ensuring that the body remains in a position.
Control of Openings and Passages: Muscles control the intake of food, movement of materials through the body, and elimination of waste, as well as the admission of light through the eyes.
Heat Production (Thermogenesis): Skeletal muscles generate about \text{20%} to \text{30%} of body heat at rest and up to \text{85%} during vigorous exercise.
Additional Functions:
Hormone Secretion: Exercised muscles secrete hormones that stimulate glucose synthesis in the liver and the breakdown of visceral fat.
Glycemic Control: Skeletal muscles are responsible for absorbing, storing, and using a significant amount of the body
10.1b Muscle Connective Tissues, Fascicles, and Compartments
Expected Learning Outcome and Answer:
Question: Describe the connective tissue components of a muscle and their relationship to the internal organization of a muscle and compartmentalization of muscle groups.
Answer: Skeletal muscles include connective tissue, nerves, and blood vessels. The connective tissue components are:
Endomysium: Thin sleeve around each muscle fiber; provides space for capillaries and nerve fibers, and a chemical environment.
Perimysium: Thicker layer wrapping fascicles (bundles of muscle fibers); carries nerves, blood vessels, and stretch receptors.
Epimysium: Fibrous sheath encasing the entire muscle; blends with fascia and deeper connective tissues.
Fascia: Connective tissue sheets between muscles or muscle groups; packages functional muscle groups into compartments.
Compartmentalization: Fascial layers package groups of functionally related muscles into compartments, with nerves and blood vessels supplying these groups. Intermuscular septa are extra thick fascia between compartments.
Question: Relate muscle fascicles to the shapes and relative strengths of muscles.
Answer: The orientation of muscle fascicles determines muscle strength and direction of pull, including:
Fusiform Muscles: Thick in the middle, tapered ends (e.g., biceps brachii).
Parallel Muscles: Uniform width, parallel fascicles (e.g., rectus abdominis).
Triangular (Convergent) Muscles: Broad at one end, fascicles converge to a narrow end (e.g., pectoralis major).
Pennate Muscles: Feather-shaped; fascicles attach obliquely to a tendon.
Unipennate: Fascicles from one side.
Bipennate: Fascicles from both sides.
Multipennate: Fascicles converge to a single point.
Circular Muscles (Sphincters): Fascicles form rings around body openings, constricting when contracted.
Components of Skeletal Muscles:
Skeletal muscles consist of muscular tissue along with connective tissue, nerves, and blood vessels.
Connective Tissue Components:
Endomysium: A thin sleeve of loose connective tissue surrounding each muscle fiber, providing space for capillaries and nerve fibers, as well as a chemical environment for muscle fibers and nerve endings.
Perimysium: A thicker layer of connective tissue wrapping fascicles, which are bundles of muscle fibers. It carries nerves, blood vessels, and stretch receptors.
Epimysium: A fibrous sheath encasing the entire muscle, blending with fascia and deeper connective tissues.
Fascia: Connective tissue sheets lying between muscles or muscle groups.
Fascicle Orientation and Muscle Strength:
The strength of a muscle and the direction of pull are influenced by the orientation of its fascicles:
Fusiform Muscles: Thick in the middle with fascicles converging towards tapered ends (e.g., biceps brachii).
Parallel Muscles: Uniform width with parallel fascicles (e.g., rectus abdominis).
Triangular (Convergent) Muscles: Broad at one end with fascicles converging to the narrow end (e.g., pectoralis major).
Pennate Muscles: Feather-shaped; fascicles attach obliquely to a tendon (e.g., rectus femoris).
Unipennate: Fascicles come from one side.
Bipennate: Fascicles approach from both sides.
Multipennate: Fascicles converge to a single point.
Circular Muscles (Sphincters): Fascicles form rings around body openings, constricting the opening when contracted.
Muscle Compartments:
Fascia: Fascial layers package groups of functionally related muscles into compartments, containing nerves and blood vessels that supply these muscle groups.
Intermuscular Septa: Some fascia between compartments appear extra thick.
10.1c Muscle Attachments
Expected Learning Outcome and Answer:
Question: Name the types of muscle-bone attachments and explain the shortcoming of calling their attachments origins and insertions.
Answer: Muscles attach to bones either directly or indirectly.
Direct (Fleshy) Attachment: Minimal separation between muscle and bone.
Indirect Attachment: Uses tendons (fibrous cords) where collagen fibers from the muscle's connective tissue layers extend into the tendon and bone's periosteum.
Tendon: Cord-like structure connecting muscle to bone.
Aponeurosis: Broad, flat tendon (e.g., palmar aponeurosis).
Retinaculum: Connective tissue band holding tendons in place.
Shortcoming of "Origin" and "Insertion": Traditional terms "origin" (stationary end) and "insertion" (moving end) are often inaccurate because the roles can reverse or both ends may move. Some anatomists prefer terms based on proximal/distal or superior/inferior orientation.
Types of Muscle Attachments:
Muscles can attach to bones either directly or indirectly:
Direct (Fleshy) Attachment: Minimal separation between muscle and bone.
Indirect Attachment: Utilizes tendons (fibrous cords) connecting muscle to bone, where collagen fibers from the muscle's connective tissue layers extend into the tendon and subsequently into the bone's periosteum:
Tendon: A cord-like structure connecting muscle to bone.
Aponeurosis: A broad, flat tendon (e.g., palmar aponeurosis).
Retinaculum: A connective tissue band that holds tendons from separate muscles in place.
Terminology of Attachments:
Traditional terms "origin" (stationary end) and "insertion" (moving end) are often not accurate. Some anatomists prefer terms based on an attachment's proximal/distal or superior/inferior orientation.
10.1d Functional Groups of Muscles
Expected Learning Outcome and Answer:
Question: Distinguish between intrinsic and extrinsic muscles.
Answer: Muscles are categorized as intrinsic or extrinsic based on their location related to the organ they control:
Intrinsic Muscles: Completely contained within a specific region (e.g., muscles of the hand).
Extrinsic Muscles: Act on a designated region but originate from a different area (e.g., forearm muscles acting on the hands).
Question: Describe the ways muscles work in groups to aid, oppose, and moderate each other's actions.
Answer: Muscles usually act in groups, classified into four main action categories:
Prime Mover: The muscle producing the most force in a movement (e.g., brachialis for elbow flexion).
Synergist: A muscle that assists the prime mover (e.g., biceps brachii assists brachialis).
Antagonist: A muscle opposing the prime mover (e.g., triceps brachii extends the elbow).
Fixator: A muscle that stabilizes a bone during movement (e.g., rhomboid muscles stabilize scapula during biceps contraction).
Muscle Functionality:
Some muscles are categorized as intrinsic or extrinsic based on their location relative to the organ they control:
Intrinsic Muscles: Completely contained within a specific region (e.g., muscles of the hand).
Extrinsic Muscles: Act on a designated region but originate from a different area (e.g., forearm muscles acting on the hands).
Muscle Action Categories:
Muscles usually act in groups, and the action produced by them falls into four main categories:
Prime Mover: The muscle producing the most force in a movement (e.g., brachialis for elbow flexion).
Synergist: A muscle that assists the prime mover (e.g., biceps brachii assists brachialis).
Antagonist: A muscle opposing the prime mover (e.g., triceps brachii extends the elbow).
Fixator: A muscle that stabilizes a bone during movement (e.g., rhomboid muscles stabilize scapula during biceps contraction).
10.1e Innervation and Blood Supply
Expected Learning Outcome and Answer:
Question: Describe in general terms the nerve and blood supply to skeletal muscles.
Answer: Skeletal muscles receive nerve and blood supply as follows:
Innervation: Stimulated by branches of spinal and cranial nerves. Spinal nerves arise from the spinal cord to innervate muscles below the neck, while cranial nerves (CN I to CN XII) emerge from the brain's base to innervate head and neck muscles.
Blood Supply: At rest, muscles receive about (one-quarter of cardiac output), increasing to over (three-quarters) during intense exercise. Capillaries extensively branch through the endomysium to supply each muscle fiber.
Muscle Innervation:
Innervation refers to the nerve that stimulates a muscle, aiding in diagnosing injuries of nerves, spinal cord, and brainstem through muscle tests.
Muscles receive innervation from branches of spinal and cranial nerves:
Spinal Nerves: Arise from the spinal cord and branch into posterior and anterior rami, innervating below the neck.
Cranial Nerves: Emerge from the base of the brain and innervate head and neck muscles, numbered CN I to CN XII.
Blood Supply:
At rest, the muscular system receives about of blood per minute (approximately one-quarter of the cardiac output); during intense exercise, blood flow to muscles increases to over three-quarters (). Capillaries extensively branch through the endomysium, supplying each muscle fiber.
10.1f Muscle Names and Learning Strategy
Expected Learning Outcome and Answer:
Question: Explain how the Latin names of muscles aid in visualizing and remembering them.
Answer: Latin-based muscle names describe distinguishing aspects of a muscle's structure, location, or action, which helps visualize and remember them. For example: "Depressor labii inferioris" lowers the bottom lip, and "Flexor digiti minimi brevis" is a short muscle that flexes the smallest finger.
Muscle Naming:
Latin-based naming conventions typically describe distinctive aspects of structure, location, or action of a muscle. Examples include:
Depressor labii inferioris: Lowers the bottom lip.
Flexor digiti minimi brevis: Short muscle that flexes the smallest finger.
Learning Strategies for the Muscular System:
Examine muscle models, cadavers, or dissected animals; use photographic atlases; palpate muscles on oneself when possible.
Locate muscle attachments on an articulated skeleton; study etymology of each muscle name to remember locations, attachments, and actions better.
Pronounce muscle names aloud and practice correct spelling with study partners.
10.2 Muscles of the Head and Neck
10.2a Muscles of Facial Expression
Expected Learning Outcome and Answer:
Question: Identify the muscles responsible for facial expressions. Understand the attachments, actions, and innervations of these muscles.
Answer: Muscles of facial expression arise from the dermis and subcutaneous tissue, affecting skin texture and expression, and are innervated by the facial nerve (CN VII). Key muscles include:
Occipitofrontalis: Raises eyebrows and retracts scalp (connected by galea aponeurotica).
Orbicularis oculi: Encircles eyes; closes eyelids.
Levator palpebrae superioris: Elevates upper eyelid.
Orbicularis oris: Encircles mouth; puckers lips.
Mentalis: Elevates lower lip (from mandible to chin skin).
Buccinator: Compresses cheek (involved in blowing and chewing).
Platysma: Broad neck muscle aiding facial expression (surprise/fear).
Characteristics:
Muscles arise from the dermis and subcutaneous tissue, affecting skin texture and expression.
These muscles are innervated by the facial nerve (CN VII).
Distribution: Scalp, forehead, around eyes, nose, mouth, and neck.
Specific Muscles and Functions:
Occipitofrontalis: Composed of two bellies (frontal and occipital) connected by the galea aponeurotica; raises eyebrows and retracts scalp.
Orbicularis oculi: Encircles eyes, functioning as a sphincter, closing the eyelids.
Levator palpebrae superioris: Elevates the upper eyelid, located beneath the orbicularis oculi.
Orbicularis oris: Encircles the mouth; puckers lips; consists of interlacing muscles.
Mentalis: From mandible to chin skin, elevates protrusion of lower lip.
Buccinator: Compresses the cheek (involved in blowing and chewing).
Platysma: Thin, broad muscle in the neck that aids in facial expression, particularly in expressing surprise or fear.
10.2b Muscles of Chewing and Swallowing
Expected Learning Outcome and Answer:
Question: Locate the muscles used in chewing and swallowing. Understand the attachments, actions, and innervations of these muscles.
Answer: Muscles involved in chewing (mastication) and swallowing (deglutition) are:
Tongue Muscles:
Intrinsic Muscles: Within the tongue; alter its shape (e.g., vertical, transverse, longitudinal).
Extrinsic Muscles: Originate outside the tongue; position it during mastication and deglutition.
Chewing Muscles:
Temporalis and Masseter: Major muscles elevating the jaw.
Pterygoid Muscles (medial and lateral): Responsible for grinding movements of molars.
Actions: Chewing involves opening/closing the mouth, biting, grinding, and side-to-side jaw movement.
Tongue Muscles:
Intrinsic Muscles: Located entirely within the tongue, responsible for altering its shape (e.g., vertical, transverse, longitudinal).
Extrinsic Muscles: Originate from outside the tongue, responsible for positioning it during actions like mastication and deglutition (swallowing).
Muscles Involved in Chewing:
Temporalis and Masseter: Major muscles responsible for elevating the jaw.
Pterygoid Muscles (medial and lateral): Responsible for grinding movements of the molars.
Functionality of chewing includes opening and closing the mouth, biting, grinding, and moving the jaw from side to side.
10.2c Muscles Acting on the Head and Neck
Expected Learning Outcome and Answer:
Question: Identify neck muscles that facilitate head movement. Understand the attachments, actions, and innervations of these muscles.
Answer: Neck muscles facilitating head movement include:
Sternocleidomastoid: Major muscle for neck flexion, extending from sternum and clavicle to mastoid process. Unilateral contraction rotates the head to the opposite side, while bilateral contraction flexes the neck.
Scalenes: Located on the sides of the neck; aid in neck flexion and assist in elevating ribs, contributing to breathing.
Muscles and Their Actions:
Sternocleidomastoid: Major muscle for neck flexion, extending from sternum and clavicle to mastoid process. Unilateral contraction rotates head to the opposite side, while bilateral contraction flexes the neck.
Scalenes: Located on the sides of the neck, aid in neck flexion and assist in elevating ribs, contributing to breathing.
10.2d Muscles of Respiration (Introduction)
Major Respiratory Muscles:
Diaphragm: Separated thoracic and abdominal cavities; contraction increases thoracic cavity volume for inhalation.
Intercostal Muscles: Involved in breathing, placed between ribs, composed of external (elevates ribs during inhalation), internal (depresses ribs during exhalation), and innermost layers.
10.3 Muscles of the Trunk
10.3a Muscles of Respiration
Expected Learning Outcome and Answer:
Question: Name and locate the muscles involved in respiration and their effects on airflow.
Answer: Key muscles of respiration and their effects on airflow are:
Diaphragm: A dome-shaped muscle located between thoracic and abdominal cavities; expands during contraction, increasing thoracic cavity volume and facilitating air intake (inhalation).
External Intercostal Muscles: Superficial layer between ribs; elevate ribs during inhalation.
Internal Intercostal Muscles: Deeper layer; their intercartilaginous and interosseous components depress ribs during exhalation.
Breathing Mechanics:
Diaphragm: A dome-shaped muscle that expands during contraction, increasing space in the thoracic cavity and facilitating air intake.
External Intercostal Muscles: Superficial layer, elevating ribs during inhalation.
Internal Intercostal Muscles: Deeper than external; their intercartilaginous and interosseous components depress ribs during exhalation.
10.3b Muscles of the Abdominal Wall
Expected Learning Outcome and Answer:
Question: Identify muscles of the abdominal wall along with their attachments, actions, and innervations, and their effects on abdominal pressure.
Answer: Muscles of the abdominal wall contribute to abdominal pressure and movement:
External Oblique: Most superficial; assists in rotation and lateral flexion of the waist.
Internal Oblique: Middle layer; fibers run perpendicular to external obliques; also aids in waist rotation.
Transverse Abdominis: Deepest layer; provides stability to the spine and compresses abdominal contents.
Rectus Abdominis: Paired vertical muscles; flex the waist; known for the ‘six pack’ due to tendinous intersections.
Effect on Abdominal Pressure: These muscles compress abdominal contents, playing a role in forced exhalation, defecation, urination, and childbirth.
Layers and Functions:
External Oblique: Most superficial; assists in rotation and lateral flexion of the waist.
Internal Oblique: Middle layer; fibers run perpendicular to external obliques, also aiding in rotation of the waist.
Transverse Abdominis: Deepest layer, providing stability to the spine and compressing abdominal contents.
Rectus Abdominis: Paired vertical muscles; flex the waist; known for the ‘six pack’ due to tendinous intersections.
10.3c Muscles of the Back
Expected Learning Outcome and Answer:
Question: Identify muscles of the back along with their attachments, actions, and innervations.
Answer: Muscles of the back include:
Latissimus Dorsi: A prominent muscle aiding in upper limb movements, specifically extension, adduction, and internal rotation of the shoulder joint.
Erector Spinae Muscles: A group of three paired muscles (iliocostalis, longissimus, spinalis) running vertically from the cranium to the sacrum; involved in extension and lateral flexion of the spine.
Actions:
Latissimus Dorsi: Prominent muscle aiding in upper limb movements, involved in extension, adduction, and internal rotation of shoulder joint.
Erector Spinae Muscles: Group of three paired muscles running vertically from the cranium to the sacrum, involved in extension and lateral flexion of the spine (iliocostalis, longissimus, spinalis).
10.4 Muscles Acting on the Shoulder and Upper Limb
Expected Learning Outcome and Answer:
Question: Identify muscles acting on the pectoral girdle, shoulder, elbow, wrist, and hand, as well as their actions corresponding to joint movements.
Answer: Muscles acting on the shoulder and upper limb include:
On the Pectoral Girdle:
Pectoralis Minor: Protracts the scapula; originates from ribs, attaches to coracoid process.
Serratus Anterior: Protracts the scapula; originates from ribs, connects to medial border of scapula.
Trapezius: Elevates, retracts, and rotates the scapula.
On the Arm/Shoulder Joint:
Rotator Cuff Muscles (SITS):
Supraspinatus: Initiates arm abduction.
Infraspinatus: External rotation of shoulder.
Teres Minor: Assists in shoulder external rotation.
Subscapularis: Internal rotation of shoulder.
Deltoid: Abducts, flexes, and extends the arm; common intramuscular injection site.
Latissimus Dorsi: Extends and internally rotates the arm.
On the Elbow:
Biceps Brachii: Key elbow flexor, assists in shoulder flexion.
Triceps Brachii: Principal elbow extensor.
(Wrist and Hand muscles are not detailed in this section, but would be covered in similar fashion if present).
Muscles of the Shoulder:
Functional Groupings:
Pectoralis Minor: Protracts the scapula; originates from the ribs and attaches to the coracoid process.
Serratus Anterior: Also protracts the scapula, originates from ribs and connects to the medial border of the scapula.
Trapezius: Capable of elevating, retracting, and rotating the scapula depending on which fibers contract.
Muscles Acting on the Arm:
Rotator Cuff Muscles (SITS):
Supraspinatus: Initiates arm abduction.
Infraspinatus: External rotation of shoulder.
Teres Minor: Assists in shoulder external rotation.
Subscapularis: Internal rotation of shoulder.
Additional Arm Muscles:
Deltoid: Abducts, flexes, and extends the arm; site for intramuscular injections.
Latissimus Dorsi: Extends and internally rotates the arm.
Biceps Brachii: Key elbow flexor and assists in shoulder flexion.
Triceps Brachii: Principal elbow extensor.
10.5 Muscles Acting on the Hip and Lower Limb
Expected Learning Outcome and Answer:
Question: Identify the muscles acting on the hip, knee, ankle, and toe joints; relate their actions to joint movements.
Answer: Muscles acting on the hip and lower limb perform various joint movements:
On the Hip and Thigh:
Iliopsoas: Prime hip flexor (composed of iliacus and psoas major).
Gluteus Maximus: Major extensor of the hip, also involved in lateral rotation.
Adductor Group: Adducts the thigh (adductor longus, brevis, magnus).
Tensor Fasciae Latae: Stabilizes the knee while walking; aids abduction.
On the Knee and Leg:
Quadriceps Femoris: Major knee extensor (four heads: rectus femoris, vastus lateralis, medialis, intermedius).
Hamstring Group: Flexes the knee (biceps femoris, semitendinosus, semimembranosus).
On the Foot/Ankle:
Gastrocnemius: Major plantar flexor of the foot, assists knee flexion.
Soleus: Works with gastrocnemius to flex the foot.
Tibialis Anterior: Dorsiflexes and inverts the foot.
Intrinsic Muscles of the Foot: Layered arrangement including abductors, flexors, and interosseous muscles, acting on the toes and arch.
Muscles Acting on the Hip and Thigh:
Iliopsoas: A prime hip flexor, composed of iliacus (from iliac crest) and psoas major (from lumbar vertebrae).
Gluteus Maximus: Major extensor of the hip, also involved in lateral rotation.
Adductor Group: Adducts the thigh, includes adductor longus, adductor brevis, and adductor magnus.
Tensor Fasciae Latae: Stabilizes the knee while walking; helps with abduction.
Muscles Acting on the Knee and Leg:
Quadriceps Femoris: Major knee extensor, has four heads: rectus femoris (hip flexor), vastus lateralis, vastus medialis, vastus intermedius.
Hamstring Group: Flexes the knee, includes biceps femoris, semitendinosus, semimembranosus.
Muscles Acting on the Foot:
Gastrocnemius: Major plantar flexor of the foot and assists in knee flexion.
Soleus: Works with gastrocnemius to flex the foot.
Tibialis Anterior: Dorsiflexes and inverts the foot.
Intrinsic Muscles of the Foot:
Layered Arrangement: Consists of various muscles including abductors, flexors, and interosseous muscles.
10.5e Common Conditions:
Carpal Tunnel Syndrome:
A condition resulting from compression of the median nerve within the carpal tunnel, usually due to repetitive motions. Symptoms include tingling and weakness in the hand. Treatments might include anti-inflammatories, wrist immobilization, or surgery.
10.5f Hernias:
Types of Hernias:
Inguinal Hernia: Most
Chapter 10: The Muscular System
10.1 Structural and Functional Organization of Muscles
Expected Learning Outcomes:
Describe the various functions of muscular tissue.
Describe the connective tissue components of a muscle and their relationship to the internal organization of a muscle and compartmentalization of muscle groups.
Relate muscle fascicles to the shapes and relative strengths of muscles.
Name the types of muscle-bone attachments and explain the shortcoming of calling their attachments origins and insertions.
Distinguish between intrinsic and extrinsic muscles.
Describe the ways muscles work in groups to aid, oppose, and moderate each other's actions.
Describe in general terms the nerve and blood supply to skeletal muscles.
Explain how the Latin names of muscles aid in visualizing and remembering them.
10.1a The Functions of Muscles
Primary Functions of Muscles:
Movement: Muscles facilitate the movement of body parts and contents such as food during digestion, air during breathing, and blood during circulation. They are also involved in communication through speech and facial expressions.
Stability: Muscles help maintain posture and stabilize joints, ensuring that the body remains in a position.
Control of Openings and Passages: Muscles control the intake of food, movement of materials through the body, and elimination of waste, as well as the admission of light through the eyes.
Heat Production (Thermogenesis): Skeletal muscles generate about 20% to 30% of body heat at rest and up to 85% during vigorous exercise.
Additional Functions:
Hormone Secretion: Exercised muscles secrete hormones that stimulate glucose synthesis in the liver and the breakdown of visceral fat.
Glycemic Control: Skeletal muscles are responsible for absorbing, storing, and using a significant amount of the body’s glucose, helping to stabilize blood glucose concentration.
10.1b Muscle Connective Tissues, Fascicles, and Compartments
Components of Skeletal Muscles:
Skeletal muscles consist of muscular tissue along with connective tissue, nerves, and blood vessels.
Connective Tissue Components:
Endomysium: A thin sleeve of loose connective tissue surrounding each muscle fiber, providing space for capillaries and nerve fibers, as well as a chemical environment for muscle fibers and nerve endings.
Perimysium: A thicker layer of connective tissue wrapping fascicles, which are bundles of muscle fibers. It carries nerves, blood vessels, and stretch receptors.
Epimysium: A fibrous sheath encasing the entire muscle, blending with fascia and deeper connective tissues.
Fascia: Connective tissue sheets lying between muscles or muscle groups.
Fascicle Orientation and Muscle Strength:
The strength of a muscle and the direction of pull are influenced by the orientation of its fascicles:
Fusiform Muscles: Thick in the middle with fascicles converging towards tapered ends (e.g., biceps brachii).
Parallel Muscles: Uniform width with parallel fascicles (e.g., rectus abdominis).
Triangular (Convergent) Muscles: Broad at one end with fascicles converging to the narrow end (e.g., pectoralis major).
Pennate Muscles: Feather-shaped; fascicles attach obliquely to a tendon (e.g., rectus femoris).
Unipennate: Fascicles come from one side.
Bipennate: Fascicles approach from both sides.
Multipennate: Fascicles converge to a single point.
Circular Muscles (Sphincters): Fascicles form rings around body openings, constricting the opening when contracted.
Muscle Compartments:
Fascia: Fascial layers package groups of functionally related muscles into compartments, containing nerves and blood vessels that supply these muscle groups.
Intermuscular Septa: Some fascia between compartments appear extra thick.
10.1c Muscle Attachments
Types of Muscle Attachments:
Muscles can attach to bones either directly or indirectly:
Direct (Fleshy) Attachment: Minimal separation between muscle and bone.
Indirect Attachment: Utilizes tendons (fibrous cords) connecting muscle to bone, where collagen fibers from the muscle's connective tissue layers extend into the tendon and subsequently into the bone's periosteum:
Tendon: A cord-like structure connecting muscle to bone.
Aponeurosis: A broad, flat tendon (e.g., palmar aponeurosis).
Retinaculum: A connective tissue band that holds tendons from separate muscles in place.
Terminology of Attachments:
Traditional terms "origin" (stationary end) and "insertion" (moving end) are often not accurate. Some anatomists prefer terms based on an attachment's proximal/distal or superior/inferior orientation.
10.1d Functional Groups of Muscles
Muscle Functionality:
Some muscles are categorized as intrinsic or extrinsic based on their location relative to the organ they control:
Intrinsic Muscles: Completely contained within a specific region (e.g., muscles of the hand).
Extrinsic Muscles: Act on a designated region but originate from a different area (e.g., forearm muscles acting on the hands).
Muscle Action Categories:
Muscles usually act in groups, and the action produced by them falls into four main categories:
Prime Mover: The muscle producing the most force in a movement (e.g., brachialis for elbow flexion).
Synergist: A muscle that assists the prime mover (e.g., biceps brachii assists brachialis).
Antagonist: A muscle opposing the prime mover (e.g., triceps brachii extends the elbow).
Fixator: A muscle that stabilizes a bone during movement (e.g., rhomboid muscles stabilize scapula during biceps contraction).
10.1e Innervation and Blood Supply
Muscle Innervation:
Innervation refers to the nerve that stimulates a muscle, aiding in diagnosing injuries of nerves, spinal cord, and brainstem through muscle tests.
Muscles receive innervation from branches of spinal and cranial nerves:
Spinal Nerves: Arise from the spinal cord and branch into posterior and anterior rami, innervating below the neck.
Cranial Nerves: Emerge from the base of the brain and innervate head and neck muscles, numbered CN I to CN XII.
Blood Supply:
At rest, the muscular system receives about of blood per minute (approximately one-quarter of the cardiac output); during intense exercise, blood flow to muscles increases to over three-quarters (). Capillaries extensively branch through the endomysium, supplying each muscle fiber.
10.1f Muscle Names and Learning Strategy
Muscle Naming:
Latin-based naming conventions typically describe distinctive aspects of structure, location, or action of a muscle. Examples include:
Depressor labii inferioris: Lowers the bottom lip.
Flexor digiti minimi brevis: Short muscle that flexes the smallest finger.
Learning Strategies for the Muscular System:
Examine muscle models, cadavers, or dissected animals; use photographic atlases; palpate muscles on oneself when possible.
Locate muscle attachments on an articulated skeleton; study etymology of each muscle name to remember locations, attachments, and actions better.
Pronounce muscle names aloud and practice correct spelling with study partners.
10.2 Muscles of the Head and Neck
Expected Learning Outcomes:
Identify the muscles responsible for facial expressions.
Locate the muscles used in chewing and swallowing.
Identify neck muscles that facilitate head movement.
Understand the attachments, actions, and innervations of these muscles.
10.2a Muscles of Facial Expression
Characteristics:
Muscles arise from the dermis and subcutaneous tissue, affecting skin texture and expression.
These muscles are innervated by the facial nerve (CN VII).
Distribution: Scalp, forehead, around eyes, nose, mouth, and neck.
Specific Muscles and Functions:
Occipitofrontalis: Composed of two bellies (frontal and occipital) connected by the galea aponeurotica; raises eyebrows and retracts scalp.
Orbicularis oculi: Encircles eyes, functioning as a sphincter, closing the eyelids.
Levator palpebrae superioris: Elevates the upper eyelid, located beneath the orbicularis oculi.
Orbicularis oris: Encircles the mouth; puckers lips; consists of interlacing muscles.
Mentalis: From mandible to chin skin, elevates protrusion of lower lip.
Buccinator: Compresses the cheek (involved in blowing and chewing).
Platysma: Thin, broad muscle in the neck that aids in facial expression, particularly in expressing surprise or fear.
10.2b Muscles of Chewing and Swallowing
Tongue Muscles:
Intrinsic Muscles: Located entirely within the tongue, responsible for altering its shape (e.g., vertical, transverse, longitudinal).
Extrinsic Muscles: Originate from outside the tongue, responsible for positioning it during actions like mastication and deglutition (swallowing).
Muscles Involved in Chewing:
Temporalis and Masseter: Major muscles responsible for elevating the jaw.
Pterygoid Muscles (medial and lateral): Responsible for grinding movements of the molars.
Functionality of chewing includes opening and closing the mouth, biting, grinding, and moving the jaw from side to side.
10.2c Muscles Acting on the Head and Neck
Muscles and Their Actions:
Sternocleidomastoid: Major muscle for neck flexion, extending from sternum and clavicle to mastoid process. Unilateral contraction rotates head to the opposite side, while bilateral contraction flexes the neck.
Scalenes: Located on the sides of the neck, aid in neck flexion and assist in elevating ribs, contributing to breathing.
10.2d Muscles of Respiration (Introduction)
Major Respiratory Muscles:
Diaphragm: Separated thoracic and abdominal cavities; contraction increases thoracic cavity volume for inhalation.
Intercostal Muscles: Involved in breathing, placed between ribs, composed of external (elevates ribs during inhalation), internal (depresses ribs during exhalation), and innermost layers.
10.3 Muscles of the Trunk
Expected Learning Outcomes:
Name and locate the muscles involved in respiration and their effects on airflow and abdominal pressure.
Identify muscles of the abdominal wall, back, and pelvic floor along with their attachments, actions, and innervations.
10.3a Muscles of Respiration
Breathing Mechanics:
Diaphragm: A dome-shaped muscle that expands during contraction, increasing space in the thoracic cavity and facilitating air intake.
External Intercostal Muscles: Superficial layer, elevating ribs during inhalation.
Internal Intercostal Muscles: Deeper than external; their intercartilaginous and interosseous components depress ribs during exhalation.
10.3b Muscles of the Abdominal Wall
Layers and Functions:
External Oblique: Most superficial; assists in rotation and lateral flexion of the waist.
Internal Oblique: Middle layer; fibers run perpendicular to external obliques, also aiding in rotation of the waist.
Transverse Abdominis: Deepest layer, providing stability to the spine and compressing abdominal contents.
Rectus Abdominis: Paired vertical muscles; flex the waist; known for the ‘six pack’ due to tendinous intersections.
10.3c Muscles of the Back
Actions:
Latissimus Dorsi: Prominent muscle aiding in upper limb movements, involved in extension, adduction, and internal rotation of shoulder joint.
Erector Spinae Muscles: Group of three paired muscles running vertically from the cranium to the sacrum, involved in extension and lateral flexion of the spine (iliocostalis, longissimus, spinalis).
10.4 Muscles Acting on the Shoulder and Upper Limb
Expected Learning Outcomes:
Identify muscles acting on the pectoral girdle, shoulder, elbow, wrist, and hand, as well as their actions corresponding to joint movements.
Muscles of the Shoulder:
Functional Groupings:
Pectoralis Minor: Protracts the scapula; originates from the ribs and attaches to the coracoid process.
Serratus Anterior: Also protracts the scapula, originates from ribs and connects to the medial border of the scapula.
Trapezius: Capable of elevating, retracting, and rotating the scapula depending on which fibers contract.
Muscles Acting on the Arm:
Rotator Cuff Muscles (SITS):
Supraspinatus: Initiates arm abduction.
Infraspinatus: External rotation of shoulder.
Teres Minor: Assists in shoulder external rotation.
Subscapularis: Internal rotation of shoulder.
Additional Arm Muscles:
Deltoid: Abducts, flexes, and extends the arm; site for intramuscular injections.
Latissimus Dorsi: Extends and internally rotates the arm.
Biceps Brachii: Key elbow flexor and assists in shoulder flexion.
Triceps Brachii: Principal elbow extensor.
10.5 Muscles Acting on the Hip and Lower Limb
Expected Learning Outcomes:
Identify the muscles acting on the hip, knee, ankle, and toe joints; relate their actions to joint movements.
Muscles Acting on the Hip and Thigh:
Iliopsoas: A prime hip flexor, composed of iliacus (from iliac crest) and psoas major (from lumbar vertebrae).
Gluteus Maximus: Major extensor of the hip, also involved in lateral rotation.
Adductor Group: Adducts the thigh, includes adductor longus, adductor brevis, and adductor magnus.
Tensor Fasciae Latae: Stabilizes the knee while walking; helps with abduction.
Muscles Acting on the Knee and Leg:
Quadriceps Femoris: Major knee extensor, has four heads: rectus femoris (hip flexor), vastus lateralis, vastus medialis, vastus intermedius.
Hamstring Group: Flexes the knee, includes biceps femoris, semitendinosus, semimembranosus.
Muscles Acting on the Foot:
Gastrocnemius: Major plantar flexor of the foot and assists in knee flexion.
Soleus: Works with gastrocnemius to flex the foot.
Tibialis Anterior: Dorsiflexes and inverts the foot.
Intrinsic Muscles of the Foot:
Layered Arrangement: Consists of various muscles including abductors, flexors, and interosseous muscles.
10.5e Common Conditions:
Carpal Tunnel Syndrome:
A condition resulting from compression of the median nerve within the carpal tunnel, usually due to repetitive motions. Symptoms include tingling and weakness in the hand. Treatments might include anti-inflammatories, wrist immobilization, or surgery.
10.5f Hernias:
Types of Hernias:
Inguinal Hernia: Most common type, especially in males, where abdominal contents (e.g., viscera, fat) protrude through a weakened area in the lower abdominal wall into the inguinal canal. It often presents as a bulge in the groin area, which may cause pain or discomfort, particularly when coughing, bending over, or lifting heavy objects.
Hiatal Hernia: Occurs when a portion of the stomach pushes upward through the diaphragm into the chest cavity, often around the esophageal opening (hiatus). Frequently observed in overweight individuals, it can cause symptoms such as heartburn, acid reflux (regurgitation), difficulty swallowing, and chest pain. There are two main types: sliding (most common) and paraesophageal.
Umbilical Hernia: A protrusion of abdominal contents through the abdominal wall at the navel (belly button). Common in infants, where it often closes on its own, but can also occur in adults due to increased abdominal pressure (e.g., obesity, pregnancy, heavy lifting). It typically appears as a soft bulge near the belly button and may or may not be painful.
Femoral Hernia: Less common, these occur when tissue pushes through a weak spot in the lower abdomen into the femoral canal, near the groin and upper thigh. They are more prevalent in women and can be more prone to complications like strangulation.
Incisional Hernia: Develops at the site of a previous surgical incision in the abdominal wall. The abdominal tissues push through the weakened scar tissue, often presenting as a bulge under the skin. Risk factors include obesity, poor wound healing, and excessive strain after surgery.
Diaphragmatic Hernia: A general term referring to any hernia where abdominal organs protrude through the diaphragm. Hiatal hernia is a specific type. Congenital diaphragmatic hernias are severe birth defects where there is an opening in the diaphragm, allowing abdominal organs to move into the chest cavity.