The Musculoskeletal System
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| What is the skeleton derived from? | the mesoderm
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| What are the 2 sections of our skeletal system divided into? | axial and appendicular sections
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| What does the axial skeleton consist of? | the skull, vertebral column, and ribcage, providing the central framework for the body
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| What does the appendicular skeleton consist of? | arms, legs, and pelvic and pectoral girdles that are attached to the axial skeleton for stability.
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| What are the two major components of the skeleton? | cartilage and bone
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| What does cartilage consist of? | a firm but elastic matrix called chondrin
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| What are chondrocytes? | cells that secrete chondrin, the elastic matrix that makes up cartilage
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| What parts of the body are made of cartilage? | ear, nose, walls of the larynx and trachea, and joints, as wells as much of the fetal skeleton
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| What causes arthritis? | degradation of cartilage in joints, causing bones to rub directly against each other
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| Cartilage is relatively avascular. What does that mean? | without blood and lymphatic vessels, not innervated
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| What are the types of bone structure? | compact bone and spongy/cancellous bone
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| What are trabeculae? | bony spicules (points) in the lattice structure of spongy bone
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| What are in the cavities of trabeculae? | bone marrow, which can be either red or yellow
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| What makes up red marrow? | hematopoietic stem cells, which are responsible for generation of all the cells in our blood
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| What is yellow marrow composed of? | fat, relatively inactive
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| What are the cylindrical shafts of long bones called? | diaphyses
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| What are the dilated ends of long bones called? | epiphyses
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| What are the peripheries of the epiphyses and diaphyses made of? | compact bone
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| What makes up the long bone diaphyses? | marrow
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| What makes up the epiphyses? | spongy bone core inside their compact bone sheath, for more effective dispersion of force at the joints
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| What separates the epiphysis and diaphysis in each bone? | the epiphyseal plate, a cartilaginous structure and the site of longitudinal growth
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| What is the periosteum? | a fibrous sheath that surrounds the long bone to protect it and to serve as a site for muscle attachment, and necessary for bone growth and repair
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| Where does the strength of compact bone come from? | the bone matrix, which has both organic and inorganic components
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| What are the organic components of the bone matrix? | collagen, glycoproteins, and other peptides
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| What are the inorganic components of the bone matrix? | calcium, phosphate, and hydroxide ions that harden together to form hydroxyapatite crystals
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| What else is stored in bone? | minerals such as sodium, magnesium, and potassium
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| What structural unit is the bony matrix ordered into? | osteons or Haversian systems
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| What makes up an osteon? | a central microscopic channel called a Haversian canal, surrounded by concentric circles of bony matrix called lamellae
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| What does the Haversian canal contain? | blood vessels, nerve fibers, and lymph
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| What are lacunae? | spaces interspersed within the bony matrix, which house mature bone cells called osteocytes
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| What are osteocytes? | mature bone cells involved in bone maintenance
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| What are canaliculi? | little canals that connect lacunae and allow for exchange of nutrients and wastes between them and the Haversian canals
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| How are bones formed? | through the hardening of cartilage, in a process called endochondral ossification; also through intramembranous ossification, in which undifferentiated embryonic connective tissue (mesenchymal tissue) is transformed into bone
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| What do osteoclasts and osteoblasts do? | Osteoblasts build bone and osteoclasts destroy or resorb bone
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| What happens to calcium and phosphate during bone reformation and resorption? | They are obtained from the blood during reformation, then released into the bloodstream during resorption
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| What is involved in the bone remodeling process? | endocrine hormones like parathyroid hormon and calcitonin as well as other compounds like vitamin D
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| What are the 2 kinds of joints? | movable and immovable
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| What strengthens movable joints? | ligaments, pieces of fibrous tissue that ocnnect bones to one another
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| What do ligaments consist of? | a synovial capsule that encloses the actual joint cavity (articular cavity)
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| What is synovial fluid? | It eases the movement of one structure over the other in joints, a lubricant
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| What does articular cartilage do? | it coats the articular surfaces of bones so that impact is restricted to the libricated joint cartilage rather than to bones
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| What are immovable joints? | bones that we would not want to move relative to one another, like in the skull
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| What are the three varieties of muscle? | skeletal, smooth, cardiac
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| What is the skeletal muscle innervated by? | the somatic nervous system
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| What is the basic contractile unit of a muscle? | the sarcomere
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| What are myofibrils? | they are built by sarcomeres put end to end
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| What is the sarcoplasmic reticulum? | a covering that surrounds myofibrils, a modified endoplasmic reticulum that contains a great deal of calcium
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| What is the sarcoplasm? | outside the SR, the modified cytoplasm of muscle cells
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| What is the sarcolemma? | the cell membrane of muscle cells, it is capable of propagating an action potential
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| What is a myocyte? | a muscle cell
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| What are T-tubules? | they’re connected to the sarcolemma and oriented perpendicularly to the myofibrils, allowing for ions to flow
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| What accounts for the striated appearance of skeletal muscle? | the alignment of Z-lines and their increased density relative to other structures
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| Skeletal muscles consists of what type of fibers? | red and white
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| Describe red muscle fibers? | aka slow twitch, they have a high myoglobin content (Mb is similar to Hb but consists of a single pp chain and binds O2 more tightly) and primarily derive their energy aerobically
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| Describe white fibers? | fast twitch, they are anaerobic and have much less Mb; they can contract more rapidly but are also easier to fatigue, they are mitochondria-poor
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| What are sarcomeres made of? | thick and thin filaments
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| What are thick filaments? | organized bundles of myosin
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| What are thin filaments? | actin and two other proteins, troponin and tropomyosin
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| What are Z-lines? | they define the boundaries of each sarcomere and are responsible for the striated nature of skeletal and cardiac muscles
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| What are M-lines? | they run down the center of the sarcomere
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| What is the I-band? | the region containing exclusively thin filaments
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| What is the H-zone? | exclusively contains thick filaments
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| What is the A-band? | contains thick filaments in their entirety, including any overlap with thin filaments
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| What happens to the sarcomere regions during contraction? | the H-zone, I-band, and distance between Z-lines become smaller, while the A-band’s size remains constant
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| How does muscle contraction begin? | A motor neuron sends a signal down until it reaches the nerve terminal (synaptic bouton), where the release of a neurotransmitter (e.g., acetylcholine) into the synapse results in contraction due to binding of the nt to its receptor on the muscle
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| What is the connection point between nerve and muscle called? | neuromuscule junction
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| What happens to the action potential generated at the neuromuscular junction? | it’s conducted along the sarcolemma and T-system, then transmitted into the muscle fiber itself
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| What happens when the muscle is depolarized? | the SR, full of Ca2+, is electrically responsive to depolarization, resulting in a massive release of calcium ions from the SR. Ca binds to troponin, causing tropomyosin to shift, exposing the myosin binding sites on actin.
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| What happens when the myosin binding sites on actin are exposed? | the free globular heads of myosin move toward and bind the exposed sites on actin. The actin-myosin cross bridges allow actin to pull on myosin which draws the thin filaments to the center of the H-zone and shorten the sarcomere
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| What does ATPase activity in the myosin heads do? | it provides the energy for the power stroke and results in dissociation of actin from myosin
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| How does myosin reset itself? | by binding another molecule of ATP, then free to bind another actin molecule
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| How do muscles relax? | Once SR’s receptors are no longer stimulated, calcium levels fall. The SR tightly controls intracellular calcium, so the muscles are only contracted when necessary. ATP is required for relaxation
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| What is tonus? | refers to muscles in a constant state of low-level contraction, essential for some voluntary and involuntary muscles
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| What is a simple twitch? | the response of a single muscle muscle fiber to a brief stimulus at or above the threshold
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| What are the three periods of a simple twitch? | latent period, contraction period, and relaxation period
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| What is the latent period? | the time between reaching threshold and onset of contraction. It is during this time that the action potential spreads along the muscle and allows for Ca2+ to be released from the SR
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| What is the refractory period? | period when muscle is unresponsive to stimuli. 2 types, absolute and relative
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| What happens during the absolute refractory period? | no amount of stimulus will generate a response because the muscle is restoring its resting potential
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| What happens during the relative refractory period? | the muscle can still be activated, but a higher than normal stimulus is required
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| What is frequency summation? | refers to the stronger and more prolonged contractions resulting from combination of contractions that happens when we expose our muscle fibers to frequent and prolonged stimulation without giving enough time to relax
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| What is tetanus? | refers to contractions becoming so frequent that there is no time for the muscle to relax, stronger than a simple muscle fiber twitch. Prolonged tetanus will result in muscle fatigue
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| What is smooth muscle eresponsible for? | involuntary action
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| What controls smooth muscle? | the autonomic nervous system
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| Where is smooth muscle found? | in the digestive tract, bladder, uterus, blood vessel walls, and many other locations
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| Describe smooth muscle. | They have a single centrally placed nuclei, contain actin and myosin, but not organized in a striated fashion, contract in the same way as skeletal muscles, but are capable of longer and more sustained contracts, can contract without nervous system input
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| What is myogenic activity? | the ability of smooth muscle to contract without nervous system input
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| What are the characteristics of cardiac muscle fibers? | uninucleate and involuntary like smooth muscle, striated like skeletal muscle, calcium is required for contraction, may also exhibit myogenic activity
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| What is creatine phosphate? | a high-energy compound that can derive energy for muscles
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| How is creatine phosphate stored? | by transferring a phosphate from ATP to creatine
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| How do we use creatine phosphate? | Take the phosphate and add it to ADP to rapidly generate ATP for muscle use, allowing for immediate creation of ATP that would have otherwise needed to be formed from glycolysis or the TCA cycle
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| What happens as exercising muscles run out of oxygen? | we use myoglobin’s reserves to keep aerobic metabolism going. Then when these reserves are exhausted, we have to ferment the remaining pyruvate to regenerate NAD+ and start glycolysis again
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| What is connective tissue composed of? | a sparsely scattered population of cells contained in an amorphous ground substance that may be liquid, jelly-like, or solid
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| What are the three types of fibers of connective tissue? | collagenous fibers, elastic fibers, reticular fibers
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| What are collagenous fibers made of and what do they do? | collagen, have great tensile strength
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| What are elastic fibers and what is their purpose? | elastin, endow connective tissue with resilience
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| What are reticular fibers? | branched, tightly woven fibers that join connective tissue to adjoining tissue
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| What are the two major cell types in loose connective tissue? | fibroblasts and macrophages
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| What are fibroblasts? | they are a cell type of loose connective tissue that secrete substances that are components of extracellular fibers
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| What are macrophages? | they are a cell type in loose connective tissue that engulf bacteria and dead cells via phagocytosis
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| What is dense connective tissue? | connective tissue with a high proportion of collagenous fibers, organized into parallel bundles that give great tensile strength. They form tendons and ligaments
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| What are tendons? | dense connective tissue which attaches muscle to bone
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| What are ligaments? | dense connective tissue which holds bones together at the joints
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| Insertion | the end of the muscle attached to the bone that moves during contraction (corresponds to the distal end in limb muscles)
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| orgin | the end of the muscle attached to the stationary bone (corresponds to the proximal end in limb muscles)
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| synergistic muscles | assist the principal muscles during movement
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| flexor muscles | contract to decrease the angle of a joint (e.g., the biceps will flex the elbow joint)
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| extensor muscles | contract to straighten the joint (e.g., the action of the triceps on the elbow)
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| abductor muscles | move a part of the body away from the body’s midline
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| adductor muscles | move a part of the body toward the midline
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