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Questions and Answers
What term describes a large rounded projection on a bone?
Which bone marking is characterized as a smooth, flat articular surface?
What is the term for a shallow, basin-like depression for articulation in bone anatomy?
Which term describes a round or oval opening in a bone?
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What is the correct name for a small rounded projection found on bones?
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What is a primary function of bones in the skeletal system?
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Which type of cartilage is known for its slight flexibility and is the most abundant type?
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What is the primary structural component of hyaline cartilage?
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Which characteristic is NOT associated with cartilage?
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Which type of bone is described as dense and forms the outer layer of bones?
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What percentage of water is found in cartilage?
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Which process is essential for maintaining healthy bone structure over time?
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Which of the following is NOT a function of bones?
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Which type of cartilage contains a large number of elastic fibers?
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Fibrocartilage is primarily found in which of the following structures?
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What is the main difference between appositional and interstitial growth of cartilage?
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Which statement best describes fibrocartilage?
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Which of the following bones is classified as a short bone?
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What key structural unit makes up compact bone?
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What distinguishes spongy bone from compact bone?
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Which of the following is NOT found in an osteon?
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What type of growth primarily involves chondroblasts secreting new matrix on the outer surface?
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Which classification of bone includes the vertebrae?
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What structure connects the lacunae in bone tissue?
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Which type of cartilage is primarily found in the larynx?
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Which type of bone development involves the differentiation of mesenchymal cells into osteoblasts?
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What primarily characterizes compact bone?
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What is the primary function of osteoblasts in bone tissue?
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How do bones become denser during growth?
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Which structure is characteristic of spongy bone rather than compact bone?
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What is the role of fontanelles in skull development?
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Which statement about endochondral ossification is true?
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Which of the following best describes interstitial lamellae?
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What is the process of endochondral ossification primarily responsible for?
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At what stage does the perichondrium become vascularized during endochondral ossification?
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In which zone of the epiphyseal plate does new cartilage form before being converted into bone?
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Which hormone is involved in increasing blood calcium levels?
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What is the primary function of osteoclasts in bone growth?
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Which of the following fractures is characterized by a break that occurs at a joint?
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What is the term for the transition zone between the diaphysis and epiphysis after growth has concluded?
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Which of the following is a potential consequence of low calcium levels in the body?
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During bone growth in width, which cells are responsible for bone formation?
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What type of fracture occurs when the bone is crushed under pressure?
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Which bones are included in the upper limbs of the appendicular skeleton?
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What is a component of the hip girdle in the appendicular skeleton?
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Which of the following bones is part of the lower limbs?
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Which statements about the shoulder girdle are accurate?
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Which of the following correctly identifies the bones in the lower limb?
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What does the axial skeleton primarily consist of?
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Which of the following bone types forms the framework of the face?
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Which of the following bones is NOT considered a cranial bone?
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What is one of the primary functions of the cranial bones?
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Which bones are classified as facial bones?
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What does the appendicular skeleton include?
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Which of the following is a function of facial bones?
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Which of the following bones is part of the cranial vault?
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Which bones are involved in the anterior cranial fossa?
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Which cranial fossa holds the temporal lobes of the brain?
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What is the primary function of fontanels in an infant's skull?
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What are sutures in the context of the skull?
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What is craniosynostosis?
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Which sutures are present in the human skull?
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Which of the following is NOT a major fontanel in infants?
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What do tiny bones found within sutures represent?
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What is the role of the posterior fossa?
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What is the primary purpose of the paranasal sinuses?
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What is sinusitis primarily caused by?
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Which of the following conditions results from a lack of fusion of the palatine and maxillary bones during fetal development?
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How many regions is the vertebral column distributed into?
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What contributes to the strength and support of the vertebral column?
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Which of the following are the primary curvatures of the vertebral column?
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What condition is characterized by abnormal development of the spinal column and can lead to incomplete closure of the spine?
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Which sinuses are known to potentially cause pain due to blockage of their outlets?
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What is a common sign of sinusitis?
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What role do the paranasal sinuses play in speech?
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What is the primary function of the annulus fibrosus in intervertebral discs?
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What happens when the annulus fibrosus ruptures in a herniated disc?
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What distinguishes the atlas from other cervical vertebrae?
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Which of the following is NOT a type of rib?
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What is a characteristic of intervertebral discs?
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What is the role of the nucleosus pulposus in intervertebral discs?
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How do vertebrae primarily differ from each other?
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Which characteristic is true about thoracic ribs compared to other rib types?
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What structural feature is unique to the cervical vertebrae?
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What characterizes rheumatoid arthritis?
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Which special movement involves the rotation of the palm to face upward?
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What is the main distinction between osteoarthritis and rheumatoid arthritis?
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Which of the following conditions is characterized by inflammation of the joints?
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What does a sprain involve?
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What type of joint is primarily characterized by the absence of a joint cavity?
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Which type of classification is based on the movement allowed at a joint?
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What type of fibrous joint allows only slight movement?
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Which type of joint is formed by hyaline cartilage uniting two bones?
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Which type of joint allows for the most movement?
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What is the primary characteristic of gomphoses?
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What type of cartilaginous joint is found in the pelvis and vertebral column?
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Which type of joint allows for considerable movement due to the length of the connecting ligament?
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What type of movement occurs between the carpals and tarsals?
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Which movement allows for flexion and extension?
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What characterizes uniaxial movements?
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Which joint movement involves turning a bone around its own axis?
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Which type of movement is classified as multiaxial?
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What movement is specifically described as decreasing the angle between body parts?
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Which of the following movements is NOT a type of angular movement?
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What is the primary feature of nonaxial movements?
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Which of the following is an example of a rotational movement?
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Which movement involves the distal end of a limb tracing a circular path?
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What type of joint is characterized by articulating bones being separated by a fluid-filled cavity?
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Which component of synovial joints provides a smooth surface for the opposing bone surfaces?
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What is the function of articular discs or menisci in synovial joints?
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Which type of ligaments provide strength and are often found outside the joint capsule?
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What structure is closely associated with synovial joints and is filled with lubricant?
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Which component is NOT part of the synovial joint structure?
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'Fat pads' in synovial joints serve what purpose?
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Which layer of the joint capsule is responsible for producing synovial fluid?
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What characteristic distinguishes intracapsular ligaments from other types of ligaments in synovial joints?
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What is the primary function of synovial fluid within a synovial joint?
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What type of ligament is the patellar ligament classified as?
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Which type of joint allows for uniaxial movement and permits only flexion and extension?
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What characterizes a pivot joint?
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Which of the following describes a ball-and-socket joint?
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What type of joint is the carpo-metacarpal joint in the thumb classified as?
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Which ligament is classified as a medial collateral ligament?
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Which of the following joints perform all angular movements in two planes?
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What describes the function of the anterior and posterior cruciate ligaments?
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What best describes a plane synovial joint?
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Which of the following statements about saddle joints is true?
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What characteristic describes the ability of muscles to return to their original shape after being stretched?
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Which type of muscle tissue is responsible for involuntary movements and is found in the heart?
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What is the primary function of the skeletal muscles listed?
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Which of the following best represents the components of muscle fiber structure?
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What type of muscle attachment involves a tendon or aponeurosis?
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What protein covers the myosin binding sites on actin filaments?
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Which part of the sarcomere is exclusively made of myosin filaments?
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What role does TnC play in the troponin complex?
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Which protein is known for its elastic properties and runs through thick filaments?
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Which component is responsible for binding actin filaments to the Z-disc?
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What is the primary role of dystrophin in muscle fibers?
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Which characteristic is associated with actin filaments?
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What is the primary functional unit of a myofibril?
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What occurs at the neuromuscular junction to initiate muscle contraction?
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Which statement accurately describes a motor unit?
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During synaptic transmission, what triggers the release of neurotransmitter from axonal terminals?
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What role does calcium ions play in muscle contraction?
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What happens to the sarcomeres during muscle contraction according to the sliding filament theory?
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What is a necessary requirement for the sliding filament mechanism to continue?
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What initiates the action potential at the neuromuscular junction?
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Which neural structure is responsible for transmitting signals to the muscle fibers?
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What happens immediately after action potential spreads along the sarcolemma?
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What is the primary cause of rigor mortis following death?
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Which type of muscle fiber is characterized by high fatigue resistance and slower contraction speed?
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What process primarily generates ATP for muscle activity during short-term intense exercise lasting 10 to 40 seconds?
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Which muscle fiber type is primarily used for activities like weightlifting and sprinting?
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What is the role of Ca2+ in muscle contraction?
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What is the main source of ATP during the initial 10 seconds of muscle activity?
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What happens to calcium ions after a muscle contraction has ended?
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What characterizes the energy system during the Krebs cycle?
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Which type of muscle fiber has a high content of myoglobin and is less fatigable?
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What physiological change occurs 24-36 hours after death?
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What best describes the all-or-none phenomenon in muscle contractions?
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During which phase of a muscle twitch does the muscle actually shorten and generate force?
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What occurs during tetanus in muscle contractions?
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Which statement best describes isotonic muscle contractions?
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What distinguishes single-unit smooth muscle from multi-unit smooth muscle?
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Which of the following is a significant characteristic of smooth muscle contraction?
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What is the primary effect of fatigue on muscle contractions?
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Which statement is correct regarding the role of extracellular calcium in smooth muscle contraction?
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What condition is characterized by weakness of the extrinsic eye muscles and facial expression muscles?
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What is the primary reason skeletal muscles are named?
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Which muscle group is primarily involved in facial expressions?
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Which muscle is commonly known for its role in elevating the mandible for chewing?
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What function does the deltoid muscle serve?
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Which muscle is identified for its action in mastication?
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Which muscle is primarily involved in moving the upper arm and shoulder?
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Which muscle does NOT belong to the group of trunk muscles moving the abdomen?
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What action is primarily associated with the biceps brachii muscle?
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Which of the following muscles helps in the process of respiration?
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Which of the following is a deep anterior muscle that moves the thigh at the hip?
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Which muscle is primarily responsible for extending the knee?
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Which muscles are involved in the process of respiration?
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Which muscle functions primarily to flex the wrist?
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Which muscle group is categorized as the hamstrings?
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Which muscle is part of the quadriceps femoris group?
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Which muscle can be identified as an antagonist to the flexor carpi ulnaris?
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Which muscle plays a significant role in hip flexion?
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Which of the following muscles is NOT part of the trunk muscles that move the abdomen?
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Which muscle group is primarily responsible for plantar flexion of the ankle?
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Which muscle primarily aids in the flexion of the digits?
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Study Notes
Bones and Skeletal Tissues
-
Bone: Hard, dense connective tissue that makes up the skeleton
- Compact bone: Dense and strong, found in the diaphysis (shaft) of long bones
- Spongy bone: Lighter and less dense, found in the epiphyses (ends) of long bones and in flat bones
-
Cartilage: Flexible connective tissue that provides support and cushioning
-
Types of cartilage:
- Hyaline cartilage: Most abundant, found in costal cartilages, laryngeal cartilage, tracheal and bronchial cartilages, nasal cartilages, articular cartilages (joints)
- Elastic cartilage: Found in ear pinna and epiglottis, contains elastin fibers for flexibility
- Fibrocartilage: Found in intervertebral discs and pubic symphysis, resists high pressures and contains lots of collagen
-
Types of cartilage:
Bone Functions
- Support: Provides framework for the body
- Protection: Protects vital organs
- Movement: Provides attachment points for muscles
- Mineral storage: Stores calcium and phosphorus
- Hematopoiesis: Production of blood cells in the bone marrow
Cartilage Structure
- Composition: 80% water, compressible, no blood vessels or nerves
- Covered by perichondrium: A dense connective tissue membrane
-
Cells:
- Chondroblasts: Immature cartilage cells that produce matrix
- Chondrocytes: Mature cartilage cells located in lacunae (cavities)
-
Extracellular matrix: Contains:
- Glucoseaminoglycans (GAGs): Chondroitin sulfate and hyaluronic acid
- Collagen and elastin fibers: Provide strength and flexibility
Cartilage Growth
- Appositional growth: Growth from the outside in, new matrix deposited by chondroblasts in perichondrium
- Interstitial growth: Growth from the inside out, chondrocytes divide and secrete new matrix
Bone Classification
- Small bones: Sesamoid bones (e.g., patella)
- Long bones: Longer than they are wide (e.g., femur, humerus)
- Large bones: Large and irregular in shape (e.g., pelvis)
- Flat bones: Thin and flattened (e.g., skull bones, ribs)
- Short bones: Cube-shaped (e.g., carpals, tarsals)
- Irregular bones: Complex shapes (e.g., vertebrae)
- Wormian bones: Small, irregular bones found in sutures of the skull
- Sesamoid bones: Small, round bones embedded in tendons (e.g., patella)
- Diploe: Spongy bone layer found in flat bones
Compact Bone Structure
-
Osteon: Basic structural unit of compact bone, also known as Haversian system
- Central canal: Contains blood vessels and nerves
- Concentric lamellae: Rings of bone tissue surrounding the central canal
- Osteocytes: Mature bone cells located in lacunae
- Lacunae: Small cavities that house osteocytes
- Canaliculi: Tiny canals that connect lacunae and allow for nutrient and waste exchange
- Perforating canals (Volkmann's canals): Connect central canals of adjacent osteons
- Interstitial lamellae: Remnants of old osteons
- Circumferential lamellae: Outermost layer of compact bone
Spongy Bone Structure
- Trabeculae: Irregularly arranged lamellae and osteocytes
- Few cells in thickness: No osteons are present
- Osteocytes: Located in lacunae and interconnected by canaliculi
Bone Development
-
Osteogenesis or ossification: Process of bone formation
-
Intramembranous ossification: Formation of bone directly from mesenchymal tissue
- Begins around 8th week of development
- Mesenchymal cells differentiate into osteoblasts
- Primary ossification centers form
- Osteoblasts secrete osteoid (bone matrix) and minerals
- Bony plates (diploe) form
- Fontanelles (soft spots) are present in infants
- Sutures (joints between skull bones) form
-
Endochondral ossification: Formation of bone from hyaline cartilage
- Begins around 8 weeks of development
- Perichondrium becomes vascularized
- Cartilage is replaced by bone
- Primary ossification center forms in the diaphysis of cartilage
- Bone collar, shaft, and medullary cavity develop
- Secondary ossification centers form at the ends of the bone (epiphysis)
- Epiphyseal plate (growth plate) is responsible for longitudinal bone growth
-
Role of epiphyseal plate in bone elongation:
- New cartilage forms first, then is converted into bone
- Zones of proliferation, hypertrophy, calcification, and ossification
- Epiphyseal line forms when growth stops
-
Intramembranous ossification: Formation of bone directly from mesenchymal tissue
Bone Growth in Width
- Bone resorption: Osteoclasts in endosteum break down bone tissue
- Bone formation: Osteoblasts in periosteum deposit new bone tissue
- Medullary cavity widens: As bone resorption outpaces bone formation on the inside
Bones and Hormones
- Parathyroid hormone (PTH): Increases blood calcium levels
- Calcitonin: Decreases blood calcium levels
- Growth hormone: Stimulates bone growth
- Thyroid hormones: Promote bone growth
- Estrogens: Promote bone growth and density
- Vitamin D3: Essential for calcium absorption
Bone Diseases
- Osteoporosis: Decreased bone density, leading to increased risk of fractures
- Osteopenia: Reduced bone density, not as severe as osteoporosis
- Osteomalacia: Softening of bones due to inadequate mineralization
Bone Fractures
- Colle's fracture: Fracture of the distal radius, usually caused by a fall onto an outstretched hand
- Pott's fracture: Fracture of the distal fibula, usually caused by an inversion injury of the foot
- Greenstick fracture: Incomplete fracture, common in children
- Comminuted fracture: Bone is broken into multiple pieces
- Compression fracture: Collapse of a bone due to compression, usually occurs in vertebrae
Bone Markings
- Tuberosity: Large rounded projection
- Crest: Narrow ridge
- Trochanter: Very large, blunt, irregular projection
- Line: Narrow line, less prominent than a crest
- Tubercle: Small rounded projection
- Epicondyle: Raised area above a condyle
- Spine: Sharp projection (e.g., vertebrae)
- Head: Rounded articular surface, often found at the end of a bone
- Facet: Smooth, flat articular surface
- Condyle: Rounded articular surface or projection
- Ramus: Arm-like bar of bone
- Meatus: Canal-like passageway
- Sinus: Air-filled cavity within a bone, lined with mucous membrane
- Fossa: Shallow, basin-like depression for articulation
- Groove: Furrow
- Fissure: Narrow, slit-like opening
- Foramen: Round or oval opening
Joints
- Sites where two or more bones meet
- Classified by structure and function
Structural Classification
-
Fibrous: Bones connected by fibrous connective tissue
- Sutures: Found between skull bones
- Syndesmoses: Connected by ligaments or sheets of fibrous tissue
- Gomphoses: Periodontal ligaments connect teeth to sockets
-
Cartilaginous: Bones united by cartilage
- Synchondroses: Hyaline cartilage connects bones
- Symphysis: Fibrocartilage connects bones
Functional Classification
- Synarthroses: Immovable joints
- Amphiarthroses: Slightly movable joints
- Diarthroses: Freely movable joints
Fibrous Joints
-
Mostly synarthrotic, meaning immovable
-
Lack a joint cavity
-
Three types:
- Sutures: Immovable joints found only in the skull
- Syndesmoses: Slightly movable joints (distal ends of tibia and fibula, radius and ulna)
- Gomphoses: Periodontal ligaments connect teeth to bone sockets.
Cartilaginous Joints
-
Lack a joint cavity
-
Two types:
- Synchondroses: Hyaline cartilage unites bones, allowing for bone growth during youth. Later ossify and become immovable.
- Symphysis: Fibrocartilage connects bones, providing shock absorption.
Synovial Joints
- Freely movable joints
- Consist of:
- Hyaline cartilage covering opposing bone surfaces
- Articular cavity filled with synovial fluid
- Joint capsule enclosing the articular cavity (outer fibrous layer, inner synovial membrane)
- Reinforcing ligaments for joint strength
- Intrinsic or capsular ligaments (thickened fibrous capsule)
- Extracapsular ligaments (outside the capsule)
- Intracapsular ligaments (covered by synovial membrane, not within the synovial cavity)
- Fat pads for cushioning
- Articular discs or menisci:
- Wedges of fibrocartilage found in knees and jaws
- Divide synovial cavity for better fit and joint stability
Bursae and Tendon Sheaths
- Bursa: Flattened sacs filled with lubricant, found near joints
- Tendon sheath: Similar to bursa, but encases tendons
Types of Synovial Joints
- Plane: Allows gliding movement (e.g., between carpals)
- Hinge: Uniaxial, allows flexion and extension (e.g., elbow, interphalangeal joints)
- Pivot: Uniaxial, allows rotation (e.g., between atlas and axis, proximal radio-ulnar joint)
- Condyloid: Biaxial, allows all angular movements (e.g., radius-carpal, metacarpo-phalangeal joints)
- Saddle: Allows greater freedom than condyloid, both surfaces have convex and concave areas (e.g., carpo-metacarpal joint of thumb)
- Ball-and-Socket: Multiaxial, allows most free movement (e.g., shoulder, hip joints)
Movements Allowed by Synovial Joints
- Gliding: Nonaxial movement, involves slipping of surfaces
-
Angular: Movement around an axis:
- Flexion: Decreases the angle between bones
- Extension: Increases the angle between bones
- Hyperextension: Increases the angle beyond anatomical position
- Abduction: Movement away from the midline
- Adduction: Movement towards the midline
- Circumduction: Combination of flexion, extension, abduction, and adduction
- Rotation: Movement around a bone's own axis
-
Special movements:
- Supination: Palm facing forward
- Pronation: Palm facing backward
- Inversion: Sole of foot inward
- Eversion: Sole of foot outward
- Protraction: Movement forward
- Retraction: Movement backward
- Elevation: Movement upward
- Depression: Movement downward
- Opposition: Thumb touching other fingers
Joint Injuries
- Sprain: Forcible twisting of a joint, stretching or tearing ligaments without bone dislocation
Inflammatory and Degenerative Disorders
-
Bursitis: Inflammation of a bursa
- Tendonitis: Inflammation of a tendon
Arthritis
- Rheumatoid Arthritis (RA): Autoimmune disease causing inflammation of synovial membrane, leading to joint stiffness, pain, and loss of function. - Affects people between 40-50 years old. - Aspirin and antibiotics can help manage symptoms.
-
Osteoarthritis (OA): Degenerative joint disease, "wear-and-tear" arthritis.
- Deterioration of articular cartilage and bone spur formation occurs, leading to pain and loss of function.
- Primarily affects weight-bearing joints and lumbar spine.
- Non-inflammatory.
Sarcomere Structure
- Muscle fibers are made of hundreds of cylindrical myofibrils.
- Myofibrils are made of protein filaments called myofilaments.
- Thin myofilaments are made of actin and are anchored to Z-discs.
- Thick myofilaments are made of myosin and are arranged tail-to-tail.
- Myofibrils are made of repeating contractile units called sarcomeres.
- Sarcomeres are composed of distinct bands: I-band, A-band, Z-disc, H-zone, and M-line.
Muscle Proteins
- Tropomyosin covers myosin binding sites on actin filaments.
- Troponin is a complex of three proteins: TnT, TnC, and TnI which are critical for muscle contraction.
- TnT binds to tropomyosin, forming a troponin-tropomyosin complex.
- TnC binds calcium ions.
- TnI binds to actin filaments, holding the actin-tropomyosin complex in place and blocking myosin binding sites.
- Titin is a large elastic protein that runs through thick filaments.
- Actinin is a non-elastic protein that anchors actin filaments to the Z-disc and cross-links thin filaments in neighboring sarcomeres to allow for coordinated contraction.
- Dystrophin connects the muscle cytoskeletal elements to the extracellular matrix and is involved in Duchenne Muscular Dystrophy.
- Myosin binding protein C helps limit the number of cross-bridges that can form in the heart.
Actin Filaments
- Thin filaments
- Actin monomers polymerize forming two twisted strands of F-actin.
- Each filament consists of 300-400 actin molecules.
- Actinin binds actin filaments to the Z-line.
Tropomyosin
- Associated with actin filaments
- Fills the groove between F-actin strands, providing stiffness.
Troponin
- Associated with tropomyosin and composed of three subunits: TnI, TnT, and TnC.
Neuromuscular Junction
- Myoneural junction is the connection between a motor neuron and a muscle fiber.
- Axons of motor neurons branch into axonal terminals.
- Each muscle fiber receives input from only one axonal terminal, forming a neuromuscular junction.
- A motor unit consists of a single motor neuron and all the muscle fibers it innervates.
- Small motor units are found in muscles requiring fine control, such as eye muscles and muscles in the hand.
- Large motor units are found in muscles requiring less precision, such as leg muscles.
Synaptic Transmission at Neuromuscular Junction
- An action potential travels down the motor neuron to the axonal terminal.
- This triggers the opening of voltage-gated calcium channels.
- Calcium influx causes the release of acetylcholine (ACh) from synaptic vesicles.
- ACh diffuses across the synaptic cleft and binds to ACh receptors on the muscle fiber's sarcolemma.
- This binding opens sodium channels, allowing sodium ions to enter the muscle fiber, generating an action potential.
- The muscle action potential travels along the sarcolemma and into T-tubules.
- This triggers the release of calcium from the sarcoplasmic reticulum (SR).
- Calcium ions bind to troponin C, causing a conformational change and exposing myosin binding sites on actin.
- Energized myosin heads bind to actin, forming cross-bridges.
- Acetylcholinesterase degrades ACh, terminating the signal.
Skeletal Muscle Physiology: Sliding Filament Theory
- Excitation-contraction coupling describes the process by which a stimulus triggers muscle contraction.
- Stimulus arrives at the neuromuscular junction.
- Action potential travels along the sarcolemma and T-tubules.
- Calcium ions are released from the SR.
- ATP powers the formation of myosin-actin cross-bridges, causing the filaments to slide past each other.
- Sliding continues as long as calcium and ATP are present.
- Sarcomeres shorten, I-band and H-zone decrease due to filament overlap.
- Connective tissue layers (epimysium, perimysium, endomysium) pull on the tendons, which in turn move the bone.
Muscle Relaxation
- Stimulus to the motor end plate ceases.
- Calcium ions are pumped back into the SR by an ATP-dependent Ca pump.
- Acetylcholinesterase degrades remaining ACh.
- Myosin heads detach from actin.
- Sarcomeres return to their resting length.
Rigor Mortis
- Occurs 6-24 hours after death due to lack of ATP.
- Calcium ions remain bound to troponin, keeping myosin heads bound to actin, creating a stiff muscle.
- Muscles become flaccid 24-36 hours after death due to the breakdown of muscle proteins by lysosomal enzymes.
Energy Demands of Muscles
- Short-term activity is powered by ATP already present in the muscle (10 seconds), myokinase, and creatine phosphate.
- Glycolysis provides energy for 10-40 seconds through anaerobic oxidation of glucose, producing 2 ATP and 2 NADH2.
- Muscle glycogen is broken down, leading to lactic acid accumulation and muscle fatigue.
- Krebs cycle provides a significant amount of ATP through the complete aerobic oxidation of glucose during extended work. This requires a constant supply of oxygen.
Types of Muscle Fibers
-
Slow Oxidative Fibers (Type I): Red, contain myoglobin, thin, aerobic fibers.
- Generate less force, are non-fatigable, contain slow-acting ATPase in the myosin head.
- Found in postural muscles.
-
Fast Oxidative Fibers (Type IIa): Pink, contain some myoglobin, thicker fibers.
- Generate medium force, less fatigable, contain fast-acting ATPase in the myosin head.
- Involved in light work and walking.
-
Fast Glycolytic Fibers (Type IIb): White, lack myoglobin, thick, glycolytic fibers.
- Generate a lot of force, easily fatigued, contain fast-acting ATPase in the myosin head.
- Used in weightlifting and sprinting.
Graded Muscle Contractions
- Muscles exhibit a graded contraction, meaning they can generate varying levels of force.
- Muscle twitch is the response to a single threshold stimulus and has three phases: latent phase, contraction phase, and relaxation phase.
- Summation: increased frequency of stimulus leads to increased force, with twitches fusing together.
- Tetanus: continuous smooth contraction due to very high stimulus frequency.
- Fatigue: muscle loses its ability to maintain contraction due to prolonged stimulation.
Isotonic and Isometric Muscle Contractions
- Isotonic contraction: muscle length changes while tension remains constant.
- Isometric contraction: muscle tension increases while length remains constant.
- Most muscle contractions are a combination of both isotonic and isometric contractions.
Myasthenia Gravis
- An autoimmune disease that affects ACh receptors, leading to muscle weakness.
- Primarily affects muscles of the eyes, eyelids, facial expression, chewing, talking, and swallowing.
Smooth Muscles
- Found in various organs like the GI tract, blood vessels, urinary bladder, uterus, urethra, and ureter.
- Individual cells are nucleated and contain irregularly arranged sarcomeres.
- Contract in three dimensions.
- Lack a SR and rely on extracellular calcium stored in caveolae for contraction.
- Dense bodies serve as anchor points for thin filaments (similar to Z-discs).
- Do not contain troponin.
- Calmodulin, a calcium-binding protein, activates MLCK (myosin light-chain kinase), leading to cross-bridge formation.
- Respond to hormones like oxytocin and epinephrine, as well as acetylcholine.
- Can remain extended without fatigue.
- Two types of smooth muscle: single-unit (smooth muscle cells contract together) and multi-unit (smooth muscle cells contract independently).
Skeletal Muscles
- Responsible for voluntary movement.
- Striated appearance due to the arrangement of sarcomeres.
- Muscles contain nerves, blood vessels, and connective tissue.
- Muscles are attached to bones via tendons or aponeuroses and have an origin (usually on a relatively stationary bone) and insertion (usually on a movable bone).
Cardiac Muscles
- Found only in the heart.
- Like skeletal muscles, cardiac muscles are striated, but they are branched and interconnected by intercalated discs.
- Cardiac muscle contractions are involuntary and rhythmic.
Smooth Muscles
- Found in walls of internal organs.
- Non-striated, involuntary, and generally slower contracting than skeletal muscles.
Functional Characteristics of Muscle Tissue
- Excitability or irritability: ability to respond to a stimulus.
- Conductivity: ability to transmit impulses.
- Contractility: ability to shorten.
- Extensibility: ability to stretch.
- Elasticity: ability to return to original length after stretching.
Functions of Muscle Tissue
- Produce physical movement.
- Maintain posture.
- Stabilize joints.
- Generate heat.
Skeletal Muscle Anatomy
- Each skeletal muscle is composed of muscle fibers, nerves, blood vessels, and connective tissue.
- Origin: usually the more stationary attachment point.
- Insertion: usually the more movable attachment point.
-
Attachments:
- Direct attachment: muscle epimysium fuses directly to the periosteum of bone or perichondrium of cartilage.
- Indirect attachment: muscle epimysium extends as a tendon or aponeurosis to attach to bone or cartilage.
- Attachment to fascia: muscle may attach to the fascia of other muscles via a fibrous raphe (e.g., linea alba).
Skeletal Muscle Fiber Structure
- Each muscle fiber is a single cell.
- Muscle fibers are unbranched, cylindrical, multinucleate, and contain mitochondria.
- The plasma membrane of a muscle fiber is called the sarcolemma.
-
Connective Tissue Layers:
- Endomysium: areolar connective tissue surrounding individual muscle fibers.
- Perimysium: fibrous connective tissue surrounding bundles of muscle fibers called fascicles.
- Epimysium: dense fibrous connective tissue surrounding the entire muscle.
- Deep fascia: fibrous connective tissue that forms tendons, ligaments, and other structures.
- Superficial fascia (hypodermis): subcutaneous layer.
Summary
This summary covered the structure and function of muscle tissue, including the three main types: skeletal, cardiac, and smooth muscle. It delved into the structure of a sarcomere, the proteins involved in muscle contraction, the neuromuscular junction, the sliding filament theory, energy demands, and the various types of muscle fibers. Additionally, it discussed the different types of muscle contractions and certain diseases related to muscle function, like Myasthenia Gravis. This information provides a comprehensive understanding of the intricate workings of muscle tissue and its vital roles in the human body.
Muscular System Overview
- Human body contains over 600 skeletal muscles
- Muscles named based on characteristics: location, size, shape, fiber direction, number of origins, action, origin and insertion
Muscle Grouping
- Muscles grouped based on location and function
- Facial expression
- Mastication
- Head movement
- Swallowing
- Respiration
- Abdomen movement
- Vertebral column movement
- Upper arm and shoulder movement (anterior and posterior)
- Forearm movement at elbow
- Hand and digit movement (anterior and posterior)
- Thigh movement at hip and/or knee (anterior/medial and posterior)
- Ankle and digit movement (anterior/lateral and posterior)
Selected Skeletal Muscles
Head and Neck
- Epicranius (aka occipito-frontalis)
- Orbicularis oculi
- Orbicularis oris
- Zygomaticus major and minor
- Mentalis
- Platysma
- Masseter *
- Temporalis
- Buccinator
- Sternocleidomastoid
- Digastric
- Stylohyoid
Anterior Trunk Muscles (arm and shoulder movement)
- Pectoralis major
- Deltoid *
- Serratus anterior
- Pectoralis minor
- Biceps brachii *
- Brachioradialis *
Posterior Trunk Muscles (arm and shoulder movement)
- Trapezius
- Latissimus dorsi
- Triceps brachii *
- Infraspinatus
- Teres major
- Rhomboids
Wrist and Hand Movement
- Flexor carpi ulnaris *
- Flexor digitorum superficiales *
- Extensor digitorum *
- Extensor carpi ulnaris *
Abdomen Movement
- Rectus abdominis
- External oblique
- Internal oblique
- Transversus abdominis
Respiration
- External intercostals
- Internal intercostals *
- Diaphragm *
Anterior Leg Muscles (hip and/or knee movement)
- Iliopsoas
- Sartorius
- Gracilis
-
Adductor longus
-
Quadriceps femoris
- Rectus femoris *
- Vastus lateralis *
- Vastus medialis *
- Vastus intermedius *
-
Quadriceps femoris
Posterior Leg Muscles (hip and/or knee movement)
-
Gluteus maximus
-
Hamstrings
- Biceps femoris *
- Semitendinosus *
- Semimembranosus *
-
Hamstrings
Ankle and Foot Movement
- Tibialis anterior *
- Extensor digitorum longus *
- Flexor digitorum longus *
- Gastrocnemius *
- Soleus
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Test your knowledge of bones and skeletal tissues with this quiz. Explore the different types of bone and cartilage, their functions, and the overall structure of the skeletal system. Perfect for students learning about human anatomy.