Bone Structure and Function Quiz
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Questions and Answers

Which statement about compact bone is true?

  • Compact bone is characterized by a dense and strong structure. (correct)
  • Compact bone has a high number of osteons.
  • Compact bone contains many blood vessels within its matrix.
  • Compact bone is primarily found in the epiphysis of long bones.

    • What is the primary function of canaliculi in osteons?

  • To allow blood vessels to enter the bone.
  • To form the outer layer of bone.
  • To store adipose tissue.
  • To provide communication between osteocytes. (correct)

    • During intramembranous ossification, which cell type directly differentiates into osteoblasts?

  • Mesenchymal cells (correct)
  • Fibroblasts
  • Osteocytes
  • Chondrocytes

    • What structure is specifically associated with spongy bone?

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

    What begins the process of endochondral ossification?

    <p>Development of cartilage model in fetal development.</p> Signup and view all the answers

    Which type of bone fracture is characterized by a break that does not fully break through the bone?

    <p>Greenstick fracture</p> Signup and view all the answers

    Which condition is characterized by the thinning of bone density, making bones more susceptible to fractures?

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

    What process involves the transformation of cartilage into bone, primarily occurring in long bones?

    <p>Endochondral ossification</p> Signup and view all the answers

    Which hormone is primarily responsible for increasing calcium levels in the blood by stimulating bone resorption?

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

    Which zone in the epiphyseal plate is responsible for the formation of new cartilage cells?

    <p>Zone of proliferation</p> Signup and view all the answers

    What is the primary method by which bone width increases during growth?

    <p>Bone resorption by osteoclasts and formation by osteoblasts</p> Signup and view all the answers

    Which fracture type refers to a break that results in multiple fragments of bone?

    <p>Comminuted fracture</p> Signup and view all the answers

    What role does calcitonin play in bone health?

    <p>Lowers blood calcium levels</p> Signup and view all the answers

    Which part of a long bone is primarily responsible for the production of yellow bone marrow?

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

    What is the significance of the periosteum's inner osteogenic layer?

    <p>It is involved in the formation and resorption of bone.</p> Signup and view all the answers

    Which bone cells are primarily responsible for the breakdown of bone tissue?

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

    In the process of ossification, what do osteoblasts secrete to provide tensile strength to the bone?

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

    What type of cartilage covers the ends of long bones at the epiphyses?

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

    What is one of the main functions of the endosteum?

    <p>To facilitate bone growth and remodeling</p> Signup and view all the answers

    Which hormone is primarily involved in regulating calcium levels in the bone?

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

    What is the role of osteocytes within the bone tissue?

    <p>To maintain the bone matrix and communicate with other cells</p> Signup and view all the answers

    What is the primary function of the paranasal sinuses?

    <p>To lighten the skull and act as resonating chambers for speech</p> Signup and view all the answers

    Which of the following conditions describes inflammation of the membranes in the paranasal sinuses?

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

    What are the five regions of the vertebral column?

    <p>Cervical, Thoracic, Lumbar, Sacrum, Coccyx</p> Signup and view all the answers

    What are the two primary curvatures of the vertebral column?

    <p>Thoracic and Sacral</p> Signup and view all the answers

    What role do intervertebral discs serve in the vertebral column?

    <p>They absorb shock and allow for movement between vertebrae</p> Signup and view all the answers

    What is one of the primary functions of fontanels in infants?

    <p>To allow the skull to compress during delivery</p> Signup and view all the answers

    Which cranial fossa is responsible for holding the temporal lobes of the brain?

    <p>Middle fossa</p> Signup and view all the answers

    How many major fontanels are identified in an infant's skull?

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

    What are sutures primarily characterized as?

    <p>Immovable joints between skull bones</p> Signup and view all the answers

    Which of the following bones is not involved in the anterior cranial fossa?

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

    What is the role of tiny bones found within cranial sutures?

    <p>To form additional ossification centers</p> Signup and view all the answers

    Which cranial structure is primarily held in the posterior cranial fossa?

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

    What are the sutures in the skull primarily composed of?

    <p>Bone and dense fibrous connective tissue</p> Signup and view all the answers

    What are the two main parts of an intervertebral disc?

    <p>Nucleosus pulposus and annulus fibrosus</p> Signup and view all the answers

    What is the primary role of the annulus fibrosus in the intervertebral discs?

    <p>Holding successive vertebrae together</p> Signup and view all the answers

    What characterizes a herniated disc?

    <p>Protrusion of the nucleosus pulposus</p> Signup and view all the answers

    Which region of the vertebral column does not have a body (centrum)?

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

    Which group correctly identifies the types of ribs?

    <p>True, false, and floating ribs</p> Signup and view all the answers

    What is the primary function of intervertebral discs?

    <p>Cushion and allow movement of the spine</p> Signup and view all the answers

    Which process might involve percutaneous laser disc decompression?

    <p>Herniated disc treatment</p> Signup and view all the answers

    How is the strength of the annulus fibrosus best described?

    <p>Strong and resistant to tension</p> Signup and view all the answers

    Which type of movement is characterized as nonaxial, involving slipping movements without an axis?

    <p>Gliding movement</p> Signup and view all the answers

    Which type of angular movement allows movement only in one plane?

    <p>Uniaxial movement</p> Signup and view all the answers

    Which types of movements are included in multiaxial movements?

    <p>Both A and C</p> Signup and view all the answers

    What characterizes rotational movements in synovial joints?

    <p>Circular movement around an axis</p> Signup and view all the answers

    Which of the following is considered an angular movement?

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

    What type of movement occurs when the foot moves upward towards the shin?

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

    Which of the following joints primarily exhibits rotational movement?

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

    What is the defining feature of gliding movements between two bones?

    <p>Slipping or gliding motion</p> Signup and view all the answers

    Which type of joint allows only flexion and extension movements?

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

    Which joint is characterized by a convex condyle fitting into a concavity, allowing biaxial movement?

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

    Which synovial joint is considered the most freely movable?

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

    Which of the following joints is NOT an example of an uniaxial joint?

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

    Which type of joint would allow for rotational movement?

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

    What type of joint movement occurs at the carpo-metacarpal joint of the thumb?

    <p>Biaxial movement</p> Signup and view all the answers

    Which synovial joint type is characterized by both convex and concave surfaces?

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

    How would you describe the movement allowed by a plane joint?

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

    Which joint movement involves turning the palm upward?

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

    Which movement describes the sole of the foot turning inward?

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

    What does the term 'opposition' refer to in joint movements?

    <p>Moving the thumb to touch other fingers</p> Signup and view all the answers

    Which of the following movements would be characterized as elevation?

    <p>Lifting the arms above the head</p> Signup and view all the answers

    Which movement is specifically described by pushing the shoulders backward?

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

    What characterizes the movement associated with the term 'pronation'?

    <p>Turning the palm downward</p> Signup and view all the answers

    In what type of movement is the arm raised sideways away from the body?

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

    What is the primary characteristic of the movement known as 'depression'?

    <p>Moving a body part downward</p> Signup and view all the answers

    Which characteristics define muscle fibers?

    <p>Cylindrical, multinucleate, contain mitochondria</p> Signup and view all the answers

    What is the function of the sarcolemma in muscle fibers?

    <p>Serves as the muscle fiber's plasma membrane</p> Signup and view all the answers

    What is the primary role of epimysium in skeletal muscles?

    <p>To encapsulate the entire muscle belly</p> Signup and view all the answers

    Which connective tissue layer surrounds each muscle fiber?

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

    What functional characteristic of muscles allows them to return to their original shape after stretching?

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

    Which of the following statements correctly describes skeletal muscle attachment?

    <p>Origin is typically on an immovable bone, and insertion is on a movable bone</p> Signup and view all the answers

    What type of muscle fibers are typically characterized as having multiple nuclei?

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

    What connective tissue surrounds the fascicles of skeletal muscles?

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

    What is the primary feature of the all-or-none phenomenon in muscle contractions?

    <p>Muscle fibers contract fully or not at all.</p> Signup and view all the answers

    What occurs during the latent phase of a muscle twitch?

    <p>No obvious changes in muscle length happen.</p> Signup and view all the answers

    Which term describes a sustained muscle contraction that occurs when the rate of stimulation is high enough for the twitches to fuse?

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

    In which type of muscle contractions does the length of the muscle change while maintaining constant tension?

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

    What is the key function of calmodulin in smooth muscle contraction?

    <p>Binds to calcium to activate MLCK.</p> Signup and view all the answers

    What distinguishes single-unit smooth muscle from multi-unit smooth muscle?

    <p>Single-unit muscle fibers are connected by gap junctions.</p> Signup and view all the answers

    Which of the following best describes the role of dense bodies in smooth muscle?

    <p>They anchor the thin filaments during contraction.</p> Signup and view all the answers

    During which process do muscle fibers primarily lose their ability to maintain a contraction?

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

    What type of myofilament is anchored to Z-discs in a sarcomere?

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

    Which structure runs through thick filaments and provides elasticity to the sarcomere?

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

    Which protein binds to calcium ions and is part of the troponin complex?

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

    What is the primary role of actinin in muscle fibers?

    <p>Binds actin filaments to Z-discs</p> Signup and view all the answers

    In terms of sarcomere anatomy, what does the H-zone represent?

    <p>The region containing only thick filaments</p> Signup and view all the answers

    Which protein is responsible for connecting muscle cytoskeletal elements to the extracellular matrix?

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

    What component of the troponin complex is primarily responsible for maintaining the position of the actin-tropomyosin complex?

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

    Which part of the sarcomere is primarily responsible for the structural alignment of myofilaments?

    <p>Z-disc</p> Signup and view all the answers

    Which muscle is primarily responsible for elevating the mandible during mastication?

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

    Which muscle is part of the anterior trunk and is involved in moving the upper arm?

    <p>Pectoralis major</p> Signup and view all the answers

    Which of the following muscles is involved in the function of respiration?

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

    Which muscle has the ability to close the eyelids?

    <p>Orbicularis oculi</p> Signup and view all the answers

    Which muscle is known to assist in the lateral movement of the head?

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

    Which anterior muscle is primarily responsible for flexing the elbow?

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

    Which muscle is classified as a trunk muscle that contributes to movements of the abdomen?

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

    Which of the following muscles is responsible for moving the thigh at the hip?

    <p>Gluteus maximus</p> Signup and view all the answers

    Which muscle is part of the hamstrings group?

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

    Which of the following muscles is a flexor of the wrist?

    <p>Flexor carpi ulnaris</p> Signup and view all the answers

    Which muscle is NOT part of the rotator cuff?

    <p>Teres major</p> Signup and view all the answers

    Which muscle primarily aids in inhalation during breathing?

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

    Which group of muscles is included in the quadriceps femoris?

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

    Which muscle contributes to the action of extending the knee?

    <p>Vastus medialis</p> Signup and view all the answers

    What is the primary function of the external intercostals?

    <p>Facilitate inhalation</p> Signup and view all the answers

    Which muscle is responsible for dorsiflexion of the foot?

    <p>Tibialis anterior</p> Signup and view all the answers

    What is the primary function of supporting cells in the nervous system?

    <p>Support and protect neurons</p> Signup and view all the answers

    Which type of neuron is primarily responsible for transmitting sensory information to the central nervous system?

    <p>Afferent neurons</p> Signup and view all the answers

    Which of the following are types of supporting cells found in the central nervous system?

    <p>Astrocytes and oligodendrocytes</p> Signup and view all the answers

    What is the significance of Nissl's bodies in neurons?

    <p>They represent rough endoplasmic reticulum</p> Signup and view all the answers

    What distinguishes unipolar neurons from other types of neurons?

    <p>They originate as bipolar cells during development</p> Signup and view all the answers

    What is the structural characteristic of multipolar neurons?

    <p>Multiple dendrites and a single axon</p> Signup and view all the answers

    Which part of the neuron is primarily responsible for receiving signals?

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

    What is the primary role of glial cells in the nervous system?

    <p>Support and insulate axons</p> Signup and view all the answers

    What is the typical resting membrane potential of most neurons?

    <p>-70 to -90 mV</p> Signup and view all the answers

    What type of ion channels are opened in response to changes in the membrane potential?

    <p>Voltage-gated channels</p> Signup and view all the answers

    What characterizes the 'All-or-None' phenomenon in action potentials?

    <p>Action potentials are generated only if a certain threshold is reached.</p> Signup and view all the answers

    Which ions primarily diffuse across the membrane during the action potential's depolarization phase?

    <p>Na+ and K+</p> Signup and view all the answers

    What type of synapse contains neurotransmitter junctions between neurons and muscles?

    <p>Neuromuscular junctions</p> Signup and view all the answers

    What is the primary role of the Na+-K+ pump in neurons?

    <p>To maintain ion concentration gradients across the membrane.</p> Signup and view all the answers

    What is the effect of saltatory propagation on the conduction of action potentials?

    <p>It allows action potentials to jump between nodes of Ranvier, increasing conduction speed.</p> Signup and view all the answers

    What happens during the absolute refractory period?

    <p>No action potentials can be generated regardless of the stimulus strength.</p> Signup and view all the answers

    Which type of muscle tissue is involuntary and found in the heart?

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

    What is the primary functional classification of joints that allows for the most movement?

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

    Which hormone is involved in promoting bone growth by stimulating osteoblast activity?

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

    What kind of cartilage is primarily found at the ends of long bones and provides a smooth surface for joint movement?

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

    Which part of the vertebra allows for articulation with other vertebrae?

    <p>Articular processes</p> Signup and view all the answers

    Which condition results from a deficit of vitamin D, affecting bone mineralization?

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

    What type of joint is characterized by a cylindrical bone rotating within a ring formed by another bone and a ligament?

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

    Which type of skeletal muscle fiber is primarily involved in endurance activities?

    <p>Slow-twitch fibers</p> Signup and view all the answers

    Which muscle is primarily responsible for elevating the mandible during chewing?

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

    Which protein interacts with actin to allow muscle contraction?

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

    What is the main role of calcium ions in muscle contraction?

    <p>Expose binding sites on actin</p> Signup and view all the answers

    Which type of muscle fibers is characterized by high endurance and slow contraction?

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

    Which contraction type involves a change in muscle length?

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

    What condition is characterized by weakness of the skeletal muscles due to an autoimmune attack on receptors at the neuromuscular junction?

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

    During which phase of muscle contraction is rigor mortis most likely to occur?

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

    Which muscle is considered the prime mover of breathing during inspiration?

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

    Which protein is not included in the muscle proteins listed?

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

    What is the primary role of Ca2+ in muscle contraction?

    <p>Triggering the interaction between actin and myosin</p> Signup and view all the answers

    Which type of muscle fiber is primarily responsible for endurance activities?

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

    Which muscle is classified as a prime mover of breathing?

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

    What best describes isometric contractions?

    <p>Tension increases without changing muscle length</p> Signup and view all the answers

    Which muscle group is primarily responsible for moving the arm at the shoulder?

    <p>Pectoralis major and minor</p> Signup and view all the answers

    What is the main difference between smooth muscle and skeletal muscle?

    <p>Smooth muscle is involuntary and non-striated, while skeletal muscle is striated and voluntary</p> Signup and view all the answers

    Which condition is characterized by an autoimmune response leading to muscle weakness?

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

    Which type of joint allows for the greatest range of motion?

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

    What type of cartilage is primarily found in the intervertebral discs?

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

    Which hormone decreases bone resorption and helps maintain bone density?

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

    What is the primary structure that connects muscle to bone?

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

    What is the main characteristic of synovial joints?

    <p>They contain synovial fluid.</p> Signup and view all the answers

    Which of the following muscles is classified as cardiac muscle?

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

    What type of bone development occurs from a cartilage model?

    <p>Endochondral ossification</p> Signup and view all the answers

    Which of these is a function of the skeletal system?

    <p>Protection of internal organs</p> Signup and view all the answers

    Study Notes

    Intervertebral Discs

    • Cushion-like pads between vertebrae

    • Composed of two parts:

      • Inner semifluid nucleosus pulposus provides elasticity and compressibility
      • Outer annulus fibrosus is a strong collar made of collagen and fibrocartilage
        • Holds vertebrae together
        • Resists tension
        • Allows spinal movement

    • Herniated disc:

      • Annulus fibrosus ruptures
      • Nucleosus pulposus protrudes
      • Protrusion can compress spinal cord or nerve roots, causing pain

    Vertebrae

    • Each vertebra consists of:

      • Body (centrum)
      • Vertebral (neural) arch
      • Several processes

    • Cervical vertebrae:

      • Atlas: No body (centrum)
      • Axis: Dens or odontoid process

    • Thoracic vertebrae

    • Lumbar vertebrae

    • Sacral vertebrae

    • Coccyx vertebrae

    Hyoid Bone

    • Does not articulate with any other bone
    • Suspended in the neck by muscles and ligaments
    • Supports the tongue

    Thorax

    • Sternum, ribs, and costal cartilages form the bony framework of the thorax
    • Ribs:
      • True ribs: Connect directly to the sternum
      • False ribs: Connect indirectly to the sternum
      • Floating ribs: No sternal connection

    Paranasal Sinuses

    • Cavities in skull bones that communicate with the nasal cavity

    • Lined by mucous membranes

    • Functions:

      • Lighten the skull
      • Resonating chambers for speech

    • Sinusitis: Inflammation of the sinus membranes due to infection or allergy

    • Cleft palate and cleft lip:

      • Result from lack of fusion of palatine and maxillary bones during fetal development

    Vertebral Column

    • Distributed into five regions:
      • Cervical vertebrae
      • Thoracic vertebrae
      • Lumbar vertebrae
      • Sacrum
      • Coccyx

    Curvatures

    • Provide strength, support, and balance to the vertebral column

    • Primary curvatures: Thoracic and sacral

    • Secondary curvatures: Cervical and lumbar

    • Abnormal curves can lead to conditions such as scoliosis, kyphosis, and lordosis

    Cranial Fossae

    • Depressions on the internal surface of the skull

    • Anterior fossa:

      • Houses the frontal lobes of the brain
      • Made up of frontal, ethmoid, and sphenoid bones

    • Middle fossa:

      • Houses the temporal lobes of the brain
      • Made up of sphenoid, temporal, and parietal bones

    • Posterior fossa:

      • Houses the cerebellum and brainstem
      • Made up of temporal and occipital bones

    Sutures

    • Immovable joints found only between skull bones

    • Types:

      • Coronal
      • Sagittal
      • Lambdoid
      • Squamous

    • Tiny "Wormian" bones can be found within sutures, particularly in the lambdoid suture

    • Represent additional ossification centers in the expanding fetal skull

    • Craniosynostoses: Premature fusion of skull sutures

    Fontanels

    • Spaces between the cranial bones in fetuses and infants

    • Major fontanels:

      • Anterior
      • Posterior
      • Sphenoidal (anterolateral)
      • Mastoid (posterolateral)

    • Functions:

      • Allow the fetal skull to compress during birth
      • Permit rapid brain growth during infancy

    Skeletal Muscle

    • Responsible for movement, posture, stabilization, heat generation
    • Consists of muscle fibers (cells) with multiple nuclei
    • Contains nerves, blood vessels, and connective tissue
    • Origin: Attached to an immovable bone
    • Insertion: Attached to a movable bone
    • Direct attachment: Epimysium fused to bone
    • Indirect attachment: Via tendons, aponeurosis, or a fibrous raphe
    • Muscle fibers: Single, multinucleated cells with a sarcolemma (plasma membrane)

    Skeletal Muscle Fiber Structure

    • Endomysium: Surrounds individual muscle fibers
    • Perimysium: Surrounds fascicles (bundles of muscle fibers)
    • Epimysium: Surrounds the entire muscle
    • Deep fascia: Connective tissue that forms tendons, ligaments, and other structures
    • Superficial fascia (hypodermis): Subcutaneous layer that connects skin to muscle

    Sarcomere Structure

    • Myofibril: Made up of myofilaments
    • Thin filaments: Primarily composed of actin
    • Thick filaments: Primarily composed of myosin
    • Sarcomere: The functional unit of a muscle fiber
    • I-band: Contains only thin filaments
    • A-band: Contains both thin and thick filaments
    • Z-disc: Anchors thin filaments and separates sarcomeres
    • H-zone: Region within the A-band that contains only thick filaments
    • M-line: Middle of the H-zone, where thick filaments are linked

    Muscle Proteins

    • Actin: Forms thin filaments
    • Myosin: Forms thick filaments
    • Tropomyosin: Covers the myosin binding sites on actin filaments
    • Troponin:
      • TnT binds to tropomyosin
      • TnC binds calcium ions
      • TnI binds to actin
    • Titin: Elastic protein that holds thick filaments in place
    • Actinin: Non-elastic protein that anchors thin filaments to the Z-disk
    • Dystrophin: Links cytoskeleton to extracellular matrix
    • Myosin binding protein C: In heart, regulates cross-bridge formation

    Muscle Contraction

    • Sliding filament theory: Myofilaments slide past each other, causing muscle shortening
    • Neuromuscular junction: Where a nerve fiber meets a muscle fiber
    • Acetylcholine (ACh): Neurotransmitter released at the neuromuscular junction
    • Calcium ions: Released from the sarcoplasmic reticulum (SR)
    • Sarcoplasmic reticulum: Network of membranous channels that surrounds myofibrils
    • Cross-bridge formation: Myosin heads bind to actin filaments

    Graded Muscle Contractions

    • All-or-none principle: A muscle fiber contracts fully or not at all
    • Muscle twitch: A single, brief contraction in response to a stimulus
    • Summation: Increased force of contraction due to increased frequency of stimulation
    • Tetanus: Smooth, sustained contraction due to very high stimulation rates
    • Fatigue: Loss of ability to contract due to prolonged stimulation

    Types of Muscle Contractions

    • Isotonic: Muscle length changes, tension remains constant
    • Isometric: Muscle length stays constant, tension increases

    Cardiac Muscle

    • Found in the heart
    • Striated with sarcomeres
    • Involuntary: Controlled by the autonomic nervous system
    • Intercalated discs: Specialized junctions that connect cardiac muscle cells

    Smooth Muscle

    • Found in walls of hollow organs (e.g., blood vessels, digestive tract)
    • Non-striated: No sarcomeres
    • Involuntary: Controlled by the autonomic nervous system
    • Dense bodies: Anchor thin filaments and allow for contraction in three dimensions
    • Calcium ions: Needed for contraction, enter from extracellular fluid

    Myasthenia Gravis

    • Autoimmune disease that affects acetylcholine receptors
    • Causes muscle weakness
    • Affects muscles of the eyes, face, and limbs

    Human Muscular System

    • The human body has more than 600 skeletal muscles.
    • Muscles are named based on location, size, shape, fiber direction, number of origins, action, and origin/insertion.
    • Muscles are grouped based on their location and function.

    Muscles of the Face and Head

    • Epicranius (occipito-frontalis): Raises eyebrows and wrinkles forehead.
    • Orbicularis oculi: Closes eyes, helps blink and squint.
    • Orbicularis oris: Closes and protrudes lips, helps in kissing and whistling.
    • Zygomaticus major and minor: Elevates corners of mouth, helps in smiling.
    • Mentalis: Protrudes the lower lip, helps in expressing doubt.
    • Platysma: Depresses mandible and pulls mouth corners down, helps in frowning.
    • Masseter: Elevates the mandible, helps in chewing.
    • Temporalis: Elevates and retracts the mandible, helps in chewing.
    • Buccinator: Compresses cheeks, helps in sucking and blowing.
    • Sternocleidomastoid: Rotates and flexes the head, helps in turning head sideways.
    • Digastric: Depresses the mandible, helps in opening the mouth.
    • Stylohyoid: Elevates the hyoid bone, helps in swallowing.

    Muscles of the Anterior Trunk

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

    Muscles of the Posterior Trunk

    • Trapezius: Elevates, depresses, retracts, and rotates the scapula.
    • Latissimus dorsi: Extends, adducts, and rotates the arm medially.
    • Triceps brachii: Extends the elbow.
    • Infraspinatus: Laterally rotates the arm.
    • Teres major: Extends, adducts, and rotates the arm medially.
    • Rhomboids: Retracts and elevates the scapula.

    Muscles of the Wrist and Hand

    • Flexor carpi ulnaris: Flexes and adducts the wrist.
    • Flexor digitorum superficiales: Flexes the middle phalanges of fingers 2-5.
    • Extensor digitorum: Extends the metacarpophalangeal and proximal interphalangeal joints of fingers 2-5.
    • Extensor carpi ulnaris: Extends and adducts the wrist.

    Muscles of the Abdomen

    • Rectus abdominis: Flexes the vertebral column.
    • External oblique: Rotates and flexes the vertebral column, helps in compressing the abdomen.
    • Internal oblique: Rotates and flexes the vertebral column, helps in compressing the abdomen.
    • Transversus abdominis: Compresses the abdomen.

    Muscles of Respiration

    • External intercostals: Elevates the ribs, helps in inhalation.
    • Internal intercostals: Depresses the ribs, helps in exhalation.
    • Diaphragm: Flattens during contraction, helps in inhalation.

    Muscles of the Anterior Thigh

    • Iliopsoas: Flexes the hip.
    • Sartorius: Flexes, abducts, and laterally rotates the hip.
    • Gracilis: Adducts the hip.
    • Adductor longus: Adducts the hip.
    • 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.

    Muscles of the Posterior Thigh

    • Gluteus maximus: Extends, abducts, and laterally rotates the hip.
    • Hamstrings: Flex the knee and extend the hip.
      • Biceps femoris: Flexes the knee and laterally rotates the leg.
      • Semitendinosus: Flexes the knee and medially rotates the leg.
      • Semimembranosus: Flexes the knee and medially rotates the leg.

    Muscles of the Ankle and Foot

    • Tibialis anterior: Dorsiflexes and inverts the foot.
    • Extensor digitorum longus: Extends the toes.
    • Flexor digitorum longus: Flexes the toes.
    • Gastrocnemius: Plantar flexes the foot and flexes the knee.
    • Soleus: Plantar flexes the foot.

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