Muscle Anatomy and Physiology Quiz
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Questions and Answers

Which muscle is primarily responsible for closing the eyelids?

  • Platysma
  • Orbicularis oculi (correct)
  • Zygomaticus major
  • Masseter

    • What type of muscle contraction occurs when the muscle length remains the same while developing tension?

  • Isometric (correct)
  • Eccentric
  • Concentric
  • Isotonic

    • Which muscle is considered the prime mover of breathing?

  • External intercostals
  • Internal intercostals
  • Sternocleidomastoid
  • Diaphragm (correct)

    • What is the primary role of calcium ions during muscle contraction?

    <p>To bind to troponin</p> Signup and view all the answers

    Which of the following muscles is part of the quadriceps femoris group?

    <p>Rectus femoris</p> Signup and view all the answers

    Which muscle is involved in moving the shoulder blade and is located on the posterior trunk?

    <p>Trapezius</p> Signup and view all the answers

    Which type of muscle fibers is known for endurance and is rich in mitochondria?

    <p>Red muscle fibers</p> Signup and view all the answers

    Which structure of a sarcomere marks the boundary between adjacent sarcomeres?

    <p>Z line</p> Signup and view all the answers

    Which neurotransmitter is involved in muscle contraction at the neuromuscular junction?

    <p>Acetylcholine</p> Signup and view all the answers

    Which condition is characterized by muscle weakness due to autoimmunity against acetylcholine receptors?

    <p>Myasthenia gravis</p> Signup and view all the answers

    Which type of cartilage is the primary component of costal cartilages that connect ribs to the sternum?

    <p>Hyaline cartilage</p> Signup and view all the answers

    What structure is primarily responsible for the cushioning between vertebrae in the vertebral column?

    <p>Intervertebral discs</p> Signup and view all the answers

    Which hormone is primarily responsible for promoting bone resorption?

    <p>Parathyroid hormone</p> Signup and view all the answers

    In the functional classification of joints, which category allows for the most movement?

    <p>Diarthroses</p> Signup and view all the answers

    What type of muscular tissue is involuntary and found in the heart?

    <p>Cardiac muscle</p> Signup and view all the answers

    Which type of synovial joint is characterized by the ability to rotate around a single axis?

    <p>Pivot joint</p> Signup and view all the answers

    What type of bone cell is primarily responsible for bone formation?

    <p>Osteoblast</p> Signup and view all the answers

    During endochondral ossification, what is the first step in the process of bone formation?

    <p>Formation of a bony collar</p> Signup and view all the answers

    Which part of the axial skeleton is directly involved in supporting the human head?

    <p>Cervical vertebrae</p> Signup and view all the answers

    The types of movements such as flexion, extension, and abduction belong to which classification of joint movement?

    <p>Angular movements</p> Signup and view all the answers

    What is the primary component of hyaline cartilage?

    <p>Collagen fibers and ground substance</p> Signup and view all the answers

    Which type of joint is classified as a synarthrosis?

    <p>Suture joint</p> Signup and view all the answers

    Which hormone promotes bone formation by stimulating osteoblasts?

    <p>Growth hormone</p> Signup and view all the answers

    What characterizes fibrous joints?

    <p>Connected by dense connective tissue</p> Signup and view all the answers

    Which type of bone is primarily found at the ends of long bones?

    <p>Cancellous bone</p> Signup and view all the answers

    What type of cartilage provides support and shape to the ear and epiglottis?

    <p>Elastic cartilage</p> Signup and view all the answers

    Which type of bone cell is responsible for the resorption of bone tissue?

    <p>Osteoclasts</p> Signup and view all the answers

    The structure of a typical vertebra includes which of the following components?

    <p>Vertebral body</p> Signup and view all the answers

    Which type of skeletal muscle fiber is primarily used for short bursts of strength and power?

    <p>Type IIb fibers</p> Signup and view all the answers

    What is the main function of the intervertebral discs?

    <p>Provide cushioning and stability</p> Signup and view all the answers

    What is the primary role of titin in muscle structure?

    <p>Provides elasticity and stability to the sarcomere</p> Signup and view all the answers

    Which muscle is primarily involved in lateral movement of the jaw?

    <p>Masseter</p> Signup and view all the answers

    What is a characteristic feature of isometric contractions?

    <p>Muscle length remains constant while tension increases</p> Signup and view all the answers

    Which function is primarily associated with the external intercostals?

    <p>Elevation of the ribs during inhalation</p> Signup and view all the answers

    Which type of muscle fibers have a high fatigue resistance and are suited for endurance activities?

    <p>Red muscle fibers</p> Signup and view all the answers

    What is the role of ATP during muscle contraction?

    <p>Provides energy for the detachment of myosin heads from actin</p> Signup and view all the answers

    In which type of muscle contraction does the muscle shorten while generating tension?

    <p>Concentric contraction</p> Signup and view all the answers

    What distinguishes smooth muscle from skeletal muscle?

    <p>Smooth muscle lacks striations and is involuntary</p> Signup and view all the answers

    Which muscle is involved in flexing the elbow joint?

    <p>Biceps brachii</p> Signup and view all the answers

    What condition is characterized by progressive muscle weakness due to genetic mutation affecting dystrophin?

    <p>Duchenne muscular dystrophy</p> Signup and view all the answers

    What is the primary function of titin in muscle structure?

    <p>Provides passive elasticity</p> Signup and view all the answers

    Which type of muscle is typically characterized by having a single nucleus and lacks striations?

    <p>Smooth muscle</p> Signup and view all the answers

    Which muscle is responsible for elevating the scapula and is located on the posterior trunk?

    <p>Trapezius</p> Signup and view all the answers

    Which statement correctly describes the sliding filament theory?

    <p>Actin filaments slide past myosin filaments.</p> Signup and view all the answers

    What is the main reason for rigor mortis after death?

    <p>Depletion of ATP in muscle fibers</p> Signup and view all the answers

    Which of the following muscles is primarily involved in flexing the hip joint?

    <p>Iliopsoas</p> Signup and view all the answers

    Which muscle is known as the prime mover for inspiration during respiration?

    <p>Diaphragm</p> Signup and view all the answers

    What condition is characterized by muscle weakness due to autoimmunity affecting acetylcholine receptors?

    <p>Myasthenia gravis</p> Signup and view all the answers

    Which type of muscle fiber is most likely to fatigue quickly and is suited for short bursts of high-intensity activity?

    <p>White muscle fibers</p> Signup and view all the answers

    What role does ATP play during muscle contraction?

    <p>It fuels the movement of myosin heads along actin.</p> Signup and view all the answers

    What is the primary function of cartilage in the human body?

    <p>Facilitating joint movement</p> Signup and view all the answers

    Which type of bone is characterized by a dense outer layer and inner spongy structure?

    <p>Compact bone</p> Signup and view all the answers

    Which of the following hormones is known to inhibit bone resorption?

    <p>Estrogens</p> Signup and view all the answers

    Which classification of joints allows for limited movement between the bones?

    <p>Amphiarthroses</p> Signup and view all the answers

    What is the primary role of the epimysium in muscle anatomy?

    <p>Encasing the entire muscle</p> Signup and view all the answers

    What are intervertebral discs primarily composed of?

    <p>Fibrocartilage</p> Signup and view all the answers

    Which type of joint is primarily involved in rotational movement?

    <p>Ball-and-socket joint</p> Signup and view all the answers

    During endochondral ossification, what occurs first during the bone formation process?

    <p>Formation of the bone collar</p> Signup and view all the answers

    What type of muscle tissue is characterized by striations and voluntary control?

    <p>Skeletal muscle</p> Signup and view all the answers

    Which of the following types of cartilage provides flexibility and support in structures such as the ear?

    <p>Elastic cartilage</p> Signup and view all the answers

    Which muscle is primarily responsible for elevating the mandible?

    <p>Temporalis</p> Signup and view all the answers

    What is the key role of tropomyosin in muscle contraction?

    <p>Blocks myosin-binding sites on actin</p> Signup and view all the answers

    Which type of muscle fibers are characterized by a high myoglobin content?

    <p>Red muscle fibers</p> Signup and view all the answers

    During a muscle twitch, what phase follows the latent period?

    <p>Contraction phase</p> Signup and view all the answers

    What distinguishing feature does smooth muscle have compared to skeletal muscle?

    <p>Involuntary control</p> Signup and view all the answers

    Which protein is crucial for the elasticity and stability of the sarcomere?

    <p>Titin</p> Signup and view all the answers

    What action is the iliopsoas muscle primarily responsible for?

    <p>Hip flexion</p> Signup and view all the answers

    Which muscle is primarily involved in the process of forced expiration?

    <p>Internal intercostals</p> Signup and view all the answers

    Which condition is characterized by a deficiency in the dystrophin protein?

    <p>Duchenne muscular dystrophy</p> Signup and view all the answers

    Which muscle group includes the pectoralis major and deltoid?

    <p>Anterior trunk muscles</p> Signup and view all the answers

    What is the primary function of hyaline cartilage in the skeletal system?

    <p>Forms a supportive structure that reduces friction in joints</p> Signup and view all the answers

    Which hormone is primarily involved in stimulating bone remodeling?

    <p>Parathyroid Hormone</p> Signup and view all the answers

    Which type of joint is classified as a diarthrosis?

    <p>Synovial</p> Signup and view all the answers

    What is the role of osteoclasts in bone homeostasis?

    <p>To absorb bone tissue</p> Signup and view all the answers

    Which characteristic is unique to spongy bone compared to compact bone?

    <p>Presence of trabecular structure</p> Signup and view all the answers

    What defines a synovial joint's structure?

    <p>Articular cartilage and a synovial capsule</p> Signup and view all the answers

    Which type of bone marking is typically found at the site of muscle attachment?

    <p>Process</p> Signup and view all the answers

    What characterizes endochondral ossification in bone development?

    <p>Replacement of cartilage with bone</p> Signup and view all the answers

    Which type of muscle tissue exhibits voluntary control?

    <p>Skeletal muscle</p> Signup and view all the answers

    What is a common result of osteoporosis in the skeletal system?

    <p>Fragility and increased risk of fractures</p> Signup and view all the answers

    Study Notes

    Bone Function

    • Supports and protects vital organs
    • Provides framework for movement
    • Stores mineral reserves
    • Produces blood cells (hematopoiesis)

    Cartilage Structure & Types

    • Hyaline cartilage: Smooth, glassy appearance found in ribs, nose, trachea, and articular surfaces of joints
    • Elastic cartilage: More flexible and found in the ear and epiglottis
    • Fibrocartilage: Strongest type, found in intervertebral discs and menisci of knee

    Bone Types

    • Compact bone: Dense, hard outer layer, provides strength and protection
    • Spongy bone: Lighter, porous inner layer, provides flexibility and contains red bone marrow for blood cell production

    Bone Classification

    • Long bones: Longer than they are wide. Examples: femur, humerus
    • Short bones: Cube-shaped, primarily for strength and stability. Examples: carpals, tarsals
    • Flat bones: Thin, flat, curved for protection or broad muscle attachment. Examples: skull bones, ribs, scapula
    • Irregular bones: Complex shapes that do not fit other categories. Examples: vertebrae, facial bones

    Structure of a Long Bone

    • Diaphysis: Long shaft of the bone
    • Epiphyses: Expanded ends of the bone
    • Epiphyseal plate: Growth plate made of hyaline cartilage, present during bone growth
    • Periosteum: Tough outer covering of bone, contains blood vessels and nerves
    • Endosteum: Lining of the medullary cavity, contains bone cells
    • Medullary cavity: Hollow space within diaphysis, filled with yellow bone marrow (fat storage)

    Microscopic Structure of Bone

    • Osteon: Functional unit of compact bone, consists of concentric rings of bone matrix called lamellae
    • Central canal: Runs through the center of the osteon, contains blood vessels and nerves
    • Lacunae: Small spaces within lamellae that house osteocytes (mature bone cells)
    • Canaliculi: Tiny canals that connect lacunae, allowing for nutrient and waste exchange

    Bone Cells

    • Osteoblasts: Immature bone cells that secrete bone matrix
    • Osteocytes: Mature bone cells that maintain bone matrix
    • Osteoclasts: Large, multinucleated cells responsible for bone resorption (breakdown)

    Bone Development

    • Intramembranous ossification: Bone formation directly from mesenchyme, how flat bones develop
    • Endochondral ossification: Bone formation from a hyaline cartilage model, how long bones develop

    Bone Growth

    • Interstitial growth: Growth in length by cartilage cells in the epiphyseal plate
    • Appositional growth: Growth in width by adding bone matrix to the surface

    Bone Remodeling

    • Continuous process of bone breakdown and formation
    • Regulated by hormonal factors and mechanical stress

    Bone Resorption

    • Performed by osteoclasts
    • Releases calcium and phosphate into the bloodstream

    Bone Diseases

    • Osteoporosis: Decreased bone density and increased fracture risk, often associated with aging, hormonal imbalances, or vitamin deficiency
    • Osteomalacia: Softening of bones due to inadequate mineralization
    • Osteopenia: Reduced bone density, not as severe as osteoporosis

    Types of Bone Fractures

    • Simple (closed): Bone does not break the skin
    • Compound (open): Bone protrudes through the skin

    Bone Markings

    • Projections: Sites of muscle attachment or articulation
    • Depressions: Hollows or indentations that allow passage of blood vessels or nerves

    Axial Skeleton

    • Skull: Protects the brain and provides attachment for facial muscles
      • Cranium (8 bones): Frontal, parietal (2), temporal (2), occipital, sphenoid, ethmoid
      • Facial bones (14 bones): Maxillae (2), palatine bones (2), zygomatic bones (2), nasal bones (2), lacrimal bones (2), inferior nasal conchae (2), vomer, mandible
      • Foramina: Openings in the skull for passage of nerves, blood vessels, and other structures
      • Foramen magnum: Large opening in the occipital bone, allows passage of the spinal cord
      • Skull sinuses: Air-filled cavities within the skull bones, lighten the skull and modify voice resonance
      • Sutures: Joints between the skull bones, allow for growth and flexibility
    • Hyoid bone: Small, U-shaped bone in the neck, supports the tongue and aids in swallowing
    • Vertebral column: Provides support and protection for the spinal cord, flexible and curved
      • Cervical vertebrae (7): Neck region, support the head, allow for flexion and extension
      • Thoracic vertebrae (12): Chest region, articulate with ribs, more rigid than cervical vertebrae
      • Lumbar vertebrae (5): Lower back region, bear the most weight of the body, large and robust
      • Sacrum (5 fused vertebrae): Forms the back portion of the pelvis, helps transfer weight to the lower limbs
      • Coccyx (4 fused vertebrae): Tailbone, provides attachment for some muscles
      • Abnormal curvatures: Scoliosis, lordosis, kyphosis
      • Primary curvatures: Develop in the fetus - thoracic and sacral curvatures
      • Secondary curvatures: Develop after birth - cervical and lumbar curvatures
      • Structure of a typical vertebra: Body, vertebral arch (pedicles, laminae), spinous process, transverse processes, articular processes
      • Intervertebral discs: Fibrocartilaginous cushions between vertebrae, shock absorbers
    • Sternum: Breastbone, provides attachment for ribs and pectoral muscles
    • Rib cage: Protects the heart and lungs, allows for breathing movements, composed of 12 pairs of ribs

    Appendicular Skeleton

    • Pectoral (shoulder) girdle: Connects upper limbs to axial skeleton, provides for movement and support
      • Clavicle (collarbone): Supports shoulder joint
      • Scapula (shoulder blade): Provides attachment for muscles of the back and shoulder
    • Bones of upper extremities:
      • Humerus: Upper arm
      • Radius and ulna: Forearm
      • Carpal bones: Wrist
      • Metacarpal bones: Palm
      • Phalanges: Fingers

    Pelvic Girdle

    • Coxal bone: Hip bone, composed of ilium, ischium, and pubis
    • Bones of lower extremities:
      • Femur: Thigh bone, largest and strongest bone in the body
      • Patella: Kneecap, protects the knee joint
      • Tibia and fibula: Lower leg
      • Tarsal bones: Ankle
      • Metatarsal bones: Sole of the foot
      • Phalanges: Toes

    Skeletal Articulations (Joints)

    • Functional classification: Based on the degree of movement allowed
      • Synarthroses: Immovable joints, found in the skull
      • Amphiarthroses: Slightly movable joints, found in the vertebrae
      • Diarthroses: Freely movable joints, found in the limbs
    • Structural classification: Based on the type of connective tissue that binds the bones together
      • Fibrous joints: Bones connected by fibrous tissue
        • Sutures: Found in the skull
        • Syndesmoses: Joints between bones connected by ligaments, example: distal tibiofibular joint
        • Gomphoses: Joints between teeth and bone, example: tooth socket
      • Cartilaginous joints: Bones connected by cartilage
        • Synchondroses: Bones connected by hyaline cartilage, example: epiphyseal plate
        • Symphyses: Bones connected by fibrocartilage, example: pubic symphysis
      • Synovial joints: Most movable joint types
        • Structure: Synovial cavity, articular cartilage, joint capsule (fibrous capsule and synovial membrane), ligaments, menisci, bursae, tendons
        • Location: Found in the limbs, skull, and vertebral column
        • Degree of movement allowed: Vary depending on the type of joint
    • Bursa: Fluid-filled sac that reduces friction between bones, tendons, and muscles
    • Tendon sheath: Tubular bursa that surrounds tendons, reduces friction during movement

    Classification of Diarthrotic Joints

    • Uniaxial joints: Allow movement in one plane
      • Plane joint: Flat surfaces that slide over one another, example: carpals, tarsals
      • Hinge joint: Allows for flexion and extension, example: elbow, knee
      • Pivot joint: Allows for rotation, example: proximal radioulnar joint
    • Biaxial joints: Allow movement in two planes
      • Condyloid joint: Allows flexion, extension, abduction, adduction, and circumduction, example: wrist, knuckles
      • Saddle joint: Allows similar movement to condyloid joint but with greater range of motion, example: carpometacarpal joint of thumb
    • Multiaxial joints: Allow movement in all planes
      • Ball-and-socket joint: Allows for wide range of motion, example: shoulder, hip

    Types of Synovial Joints

    • Shoulder joint: Ball-and-socket joint, allows for a wide range of movements, prone to instability
    • Hip joint: Ball-and-socket joint, very stable, allows for a wide range of movements
    • Elbow joint: Hinge joint between humerus and ulna, allows for flexion and extension
    • Knee joint: Large, complex hinge joint, allows for flexion, extension, and some rotation

    Joint Disorders

    • Bursitis: Inflammation of the bursa
    • Tendonitis: Inflammation of a tendon
    • Arthritis: Inflammation of a joint
      • Rheumatoid arthritis: Autoimmune disorder that attacks joint tissues
      • Osteoarthritis: Degenerative joint disease, wear and tear on joint cartilage
      • Gouty arthritis: Excess uric acid in blood crystallizes in joints

    Types of Muscle Tissue

    • Skeletal muscle: Attached to bones, responsible for voluntary movements, striated, multinucleated
    • Cardiac muscle: Found in the heart, involuntary, striated, branching with intercalated discs
    • Smooth muscle: Found in the walls of hollow organs, involuntary, non-striated, single-nucleated

    Functional Characteristics of Muscles

    • Excitability: Ability to respond to stimuli
    • Contractility: Ability to shorten and thicken
    • Extensibility: Ability to be stretched
    • Elasticity: Ability to return to its original shape after stretching

    Functions of Muscles

    • Movement: Responsible for all types of body movement
    • Maintain posture: Hold the body in position against gravity
    • Support soft tissues: Provides support and protection for internal organs
    • Regulate body temperature: Muscle contraction generates heat
    • Controls passage of substances: Smooth muscles control the movement of substances through body cavities

    Skeletal Muscle Anatomy

    • Origin: Attachment of a muscle to the more stationary bone
    • Insertion: Attachment of a muscle to the more movable bone
    • Tendons: Connective tissue that attaches muscle to bone
    • Aponeuroses: Broad, sheet-like tendons
    • Muscle coverings:
      • Endomysium: Surrounds individual muscle fibers
      • Perimysium: Surrounds bundles of muscle fibers called fascicles
      • Epimysium: Outermost covering of the muscle, merges with the tendon
      • Deep fascia: Sheets of dense connective tissue that surround groups of muscles

    Skeletal Muscle Fiber Structure

    • Sarcolemma: Plasma membrane of a muscle fiber
    • Sarcoplasm: Cytoplasm of a muscle fiber
    • Sarcoplasmic reticulum: Network of tubules that stores calcium ions
    • Myofibrils: Contractile units of the muscle fiber, composed of sarcomeres

    Sarcomere Structure

    • Myofilaments: Protein filaments within the sarcomere, composed of:
      • Actin: Thin filament
      • Myosin: Thick filament
    • Sarcomere: Functional unit of a myofibril, extends from one Z-disc to the next
    • Bands and lines/discs: Regions within the sarcomere with different protein arrangements:
      • A band: Dark band containing both myosin and actin filaments
      • I band: Light band containing only actin filaments
      • H zone: Central region of the A band containing only myosin filaments
      • M line: Midpoint of the H zone, anchors thick filaments
      • Z disc: Separates adjacent sarcomeres, anchors thin filaments

    Muscle Proteins

    • Actin: Provides binding sites for myosin heads
    • Myosin: Thick filament, contains myosin heads that bind to actin
    • Tropomyosin: Covers binding sites on actin when muscle is relaxed
    • Troponin: Binds to calcium ions, moves tropomyosin off the binding sites on actin, allowing for muscle contraction
    • Titin: Connects myosin to the Z disc, provides elasticity and stability to the sarcomere
    • Actinin: Acts as a structural protein, connecting actin filaments to the Z disc
    • Dystrophin: Helps link the sarcomere to the sarcolemma, strengthens the muscle fiber

    Neuromuscular Junction

    • Synaptic transmission: Communication between a nerve and a muscle fiber
    • Motor neuron: Nerve that stimulates a muscle fiber
    • Motor end plate: Region of the muscle fiber where the neuron makes contact
    • Synaptic cleft: Small space between the neuron and the motor end plate
    • Neurotransmitter: Chemical messenger released by the neuron, acetylcholine

    Skeletal Muscle Physiology

    • Sliding filament theory: Mechanism of muscle contraction
      • Myosin heads bind to actin filaments, pull them toward the M line, shortening the sarcomere
      • Requires calcium ions and ATP
    • Excitation-contraction coupling: Sequence of events that links the nerve impulse to muscle contraction
    • Mechanism of muscle contraction:
      • Nerve impulse releases acetylcholine at the neuromuscular junction
      • Acetylcholine binds to receptors on the sarcolemma, initiating an action potential
      • Action potential travels along the sarcolemma and into the T-tubules (invaginations of the sarcolemma), which are connected to the sarcoplasmic reticulum
      • Calcium ions are released from the sarcoplasmic reticulum, bind to troponin, shifting tropomyosin off the binding sites on actin
      • Myosin heads can now bind to actin, pulling it toward the M line, shortening the sarcomere
    • Rigor mortis: Stiffening of muscles after death due to lack of ATP, preventing myosin from detaching from actin
    • Energy demands of muscles: Muscle contraction requires a lot of energy (ATP)
      • ATP is produced by aerobic respiration (with oxygen) and anaerobic respiration (without oxygen)
      • Creatine phosphate and glycogen are used to provide energy for short-term muscle contraction
    • Types of muscle fibers:
      • Red muscle fibers: Slow-twitch, oxidative, contain a lot of myoglobin (red pigment that stores oxygen), fatigue resistant, used for endurance activities
      • White muscle fibers: Fast-twitch, glycolytic, contain less myoglobin, fatigue more easily, used for short bursts of activity
      • Pink muscle fibers: Intermediate fibers, have characteristics of both red and white fibers
    • Graded muscle contractions: Varying strength of muscle contraction, determined by:
      • Number of motor units recruited: More motor units = stronger contraction
      • Frequency of stimulation: Higher frequency = stronger contraction
    • Muscle twitch: Contraction of a single muscle fiber in response to a single stimulus
      • Types of twitches:
        • Latent period: Short delay between stimulus and contraction
        • Contraction period: Muscle shortens
        • Relaxation period: Muscle returns to its resting length
    • Isometric contraction: Muscle tension increases but length remains the same, example: holding a heavy object
    • Isotonic contraction: Muscle tension remains constant while the muscle changes length, example: lifting a weight

    Smooth Muscle

    • Structure: Spindle-shaped fibers, not striated, single nucleus, lack sarcomeres
    • Function: Controls involuntary movements of internal organs, regulates blood flow, and propels substances through body cavities
    • Differences from skeletal muscle:
      • Slower contraction speed
      • Can sustain a prolonged contraction with less fatigue
      • Regulated by autonomic nervous system
    • Myasthenia gravis: Autoimmune disorder that attacks acetylcholine receptors at the neuromuscular junction, results in muscle weakness and fatigue
    • Duchenne muscular dystrophy: Genetic disorder that weakens muscles over time due to a lack of dystrophin, affecting mainly boys

    Muscles of the Head and Neck (Selected muscles):

    • Epicranius (occipitofrontalis): Raises eyebrows, wrinkles forehead
    • Orbicularis oculi: Closes the eyelids
    • Orbicularis oris: Closes the mouth, purses lips
    • Zygomaticus major and minor: Smiling muscles
    • Mentalis: Pouts the lower lip
    • Platysma: Draws the corners of the mouth down, tenses the skin of the neck
    • Masseter: Closes the jaw
    • Temporalis: Closes the jaw, elevates and retracts mandible
    • Buccinator: Compresses cheeks, helps with chewing, holds food between teeth
    • Sternocleidomastoid: Flexes the neck, rotates the head to the opposite side

    Anterior Trunk Muscles that Move the Arm and Shoulder (Selected muscles):

    • Pectoralis major: Flexes, adducts, and rotates the arm medially
    • Deltoid: Abducts, flexes, extends, and rotates the arm
    • Serratus anterior: Protracts and rotates the scapula upward
    • Pectoralis minor: Depresses and protracts the scapula
    • Biceps brachii: Flexes the elbow, supinates the forearm
    • Brachioradialis: Flexes the elbow

    Posterior Trunk Muscles that Move the Arm and Shoulder (Selected muscles):

    • Trapezius: Elevates, depresses, retracts, and rotates the scapula; extends the head
    • Latissimus dorsi: Extends, adducts, and rotates the arm medially
    • Triceps brachii: Extends the elbow
    • Infraspinatus: Externally rotates the arm
    • Teres major: Extends, adducts, and rotates the arm medially
    • Teres minor: Externally rotates the arm
    • Rhomboids major and minor: Retract and elevate the scapula

    Muscles that Move the Wrist and Hand (Selected muscles):

    • Flexor carpi ulnaris: Flexes and adducts the wrist
    • Flexor digitorum superficialis: Flexes the middle phalanges of the fingers
    • Extensor digitorum: Extends the fingers
    • Extensor carpi ulnaris: Extends and adducts the wrist

    Trunk Muscles that Move the Abdomen (Selected muscles):

    • Rectus abdominis: Flexes the vertebral column, compresses the abdomen
    • External oblique: Rotates and flexes the vertebral column, compresses the abdomen
    • Internal oblique: Rotates and flexes the vertebral column, compresses the abdomen
    • Transversus abdominis: Compresses the abdomen

    Muscles of Respiration (Selected muscles):

    • External intercostals: Elevate ribs during inspiration
    • Internal intercostals: Depress ribs during forced expiration
    • Diaphragm: Prime mover of inspiration

    Anterior Muscles that Move the Leg at the Hip and/or Move the Knee (Selected muscles):

    • Iliopsoas: Flexes the hip joint
    • Sartorius: Flexes, abducts, and laterally rotates the hip joint; flexes the knee
    • Gracilis: Adducts the hip joint; flexes the knee
    • Adductor longus: Adducts the hip joint
    • Quadriceps femoris: Extends the knee
      • Rectus femoris: Extends the knee and flexes the hip
      • Vastus lateralis: Extends the knee
      • Vastus medialis: Extends the knee
      • Vastus intermedius: Extends the knee

    Posterior Muscles that Move the Leg at the Hip and/or Move the Knee (Selected muscles):

    • Gluteus maximus: Extends and laterally rotates the hip
    • Gluteus medius: Abducts the hip, prevents the pelvis from dipping when walking
    • Gluteus minimus: Abducts and medially rotates the hip
    • Hamstring muscles: Flex the knee and extend the hip
      • Biceps femoris: Extends the hip, flexes the knee, laterally rotates the leg
      • Semitendinosus: Extends hip, flexes the knee, medially rotates the leg
      • Semimembranosus: Extends the hip, flexes the knee, medially rotates the leg
    • Gastrocnemius: Plantar flexes the foot
    • Soleus: Plantar flexes the foot
    • Tibialis anterior: Dorsiflexes and inverts the foot
    • Peroneus longus: Plantar flexes and everts the foot
    • Peroneus brevis: Plantar flexes and everts the foot

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