Podcast
Questions and Answers
What gives the light band in the myofibrils its isotropic property?
What gives the light band in the myofibrils its isotropic property?
Which statement is true regarding the A band of the myofibrils?
Which statement is true regarding the A band of the myofibrils?
Which protein primarily makes up the thick filaments in myofibrils?
Which protein primarily makes up the thick filaments in myofibrils?
What is the diameter range of the thick filaments in myofibrils?
What is the diameter range of the thick filaments in myofibrils?
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What is the function of the Z line in the sarcomere structure?
What is the function of the Z line in the sarcomere structure?
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Where is smooth muscle predominantly found in the body?
Where is smooth muscle predominantly found in the body?
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What main characteristic differentiates the A band from the I band in terms of refractive properties?
What main characteristic differentiates the A band from the I band in terms of refractive properties?
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Which of the following correctly describes the smooth muscle?
Which of the following correctly describes the smooth muscle?
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What is the shape of cardiac muscle fibers?
What is the shape of cardiac muscle fibers?
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Which proteins are primarily involved in muscle contraction?
Which proteins are primarily involved in muscle contraction?
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What is a distinctive feature of smooth muscle fibers compared to skeletal muscle?
What is a distinctive feature of smooth muscle fibers compared to skeletal muscle?
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What roles do the Golgi complexes serve in muscle fibers?
What roles do the Golgi complexes serve in muscle fibers?
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How are myofibrillar proteins classified?
How are myofibrillar proteins classified?
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What is the role of myosin heads during muscle contraction?
What is the role of myosin heads during muscle contraction?
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What unique structure is found at the position of Z-lines in cardiac muscle?
What unique structure is found at the position of Z-lines in cardiac muscle?
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Which of the following accurately describes smooth muscle fibers?
Which of the following accurately describes smooth muscle fibers?
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What is the significance of the actomyosin complex in postmortem muscle?
What is the significance of the actomyosin complex in postmortem muscle?
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Which protein constitutes 8-10 percent of the myofibrillar proteins along with tropomyosin?
Which protein constitutes 8-10 percent of the myofibrillar proteins along with tropomyosin?
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What is the approximate percentage of myofibrillar proteins that consists of actin and myosin?
What is the approximate percentage of myofibrillar proteins that consists of actin and myosin?
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At what pH does the isoelectric point of tropomyosin occur?
At what pH does the isoelectric point of tropomyosin occur?
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What is the fibrous nature of tropomyosin primarily due to?
What is the fibrous nature of tropomyosin primarily due to?
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How many G-actin molecules does a single tropomyosin molecule extend over?
How many G-actin molecules does a single tropomyosin molecule extend over?
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Where do troponin units locate in relation to tropomyosin on the actin filament?
Where do troponin units locate in relation to tropomyosin on the actin filament?
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What happens to cross bridges in muscle when it is at rest?
What happens to cross bridges in muscle when it is at rest?
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What characteristic describes the I band when viewed with polarized light?
What characteristic describes the I band when viewed with polarized light?
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What is the primary protein found in thick filaments of the sarcomere?
What is the primary protein found in thick filaments of the sarcomere?
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Which part of the sarcomere bisects the I band?
Which part of the sarcomere bisects the I band?
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How are the thick filaments described in terms of their diameter?
How are the thick filaments described in terms of their diameter?
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What structural feature occurs at the center of the A band?
What structural feature occurs at the center of the A band?
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What is the diameter range of myofibrils?
What is the diameter range of myofibrils?
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Which filaments are primarily made up of actin?
Which filaments are primarily made up of actin?
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What causes the alternating light and dark bands in myofibrils?
What causes the alternating light and dark bands in myofibrils?
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What is the total amount of protein indicated in the data?
What is the total amount of protein indicated in the data?
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Which myofibrillar protein has the highest quantity?
Which myofibrillar protein has the highest quantity?
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What type of lipids is recorded at 1.0?
What type of lipids is recorded at 1.0?
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Which non-protein nitrogenous substance has a value of 0.5?
Which non-protein nitrogenous substance has a value of 0.5?
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How much sarcoplasmic protein is indicated in the data?
How much sarcoplasmic protein is indicated in the data?
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Which connective tissue protein is listed with the highest value?
Which connective tissue protein is listed with the highest value?
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What is the total amount of lipids stated in the data?
What is the total amount of lipids stated in the data?
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Which enzyme is not included in the soluble sarcoplasmic & mitochondrial proteins?
Which enzyme is not included in the soluble sarcoplasmic & mitochondrial proteins?
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What accounts for the striated appearance of skeletal muscle?
What accounts for the striated appearance of skeletal muscle?
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What happens to muscle pH during postmortem glycolysis?
What happens to muscle pH during postmortem glycolysis?
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What is the ultimate pH range typically observed in muscle postmortem?
What is the ultimate pH range typically observed in muscle postmortem?
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What can contribute to a pale, soft, and exudative (PSE) condition in muscle?
What can contribute to a pale, soft, and exudative (PSE) condition in muscle?
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Which condition is characterized by muscles maintaining a consistently high pH postmortem?
Which condition is characterized by muscles maintaining a consistently high pH postmortem?
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What physiological change does rigor mortis refer to?
What physiological change does rigor mortis refer to?
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What factor can enhance the rate of pH decline in muscle postmortem?
What factor can enhance the rate of pH decline in muscle postmortem?
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Which statement is true about myofibrils in skeletal muscle?
Which statement is true about myofibrils in skeletal muscle?
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Study Notes
Gross Structure
- Meat animals have approximately 600 distinct muscles
- Muscles vary in size, shape (e.g., triangular, fusiform), attachments (bones, cartilages, ligaments), blood/nerve supply, and function (fast, slow, intermittent)
- Variations allow for a wide range of movements, from limb movement to eye movements
- Muscles have a basic, common structural pattern despite variations
- Skeletal muscles are striated, showing parallel light and dark bands
- Muscles are composed of muscle fibers (cells), which are made of myofibrils, which are made of myofilaments
Connective Tissue Associated with Muscle
- Muscles are composed of muscle fibers (cells) which are the fundamental units
Histological Structure - Myofibre
- Muscle fibers are long, unbranched, and multinucleated, tapering slightly at the ends
- Muscles fibers can be several centimeters long, but typically 10-100µm in diameter
- Invaginations of the sarcolemma (transverse tubules, T-system) form a network throughout the fiber
- Motor nerve fibers terminate on the invaginations (myoneural junction), forming motor end plates
Organelles of the Muscle Fibre
- Sarcoplasm (muscle cytoplasm) contains water, organelles, and colloidal substances
- Nuclei regularly distributed (approximately every 5µm), concentrated at tendinous attachments and myoneural junctions
- Nuclei are typically ellipsoidal in shape
- Mitochondria are abundant, particularly around the periphery of the fiber and at motor end plates
- Lysosomes and Golgi bodies are also present
- Highly developed sarcoplasmic reticulum (endoplasmic reticulum) is present
- Myofibrils are unique, cylindrical structures
Myofilaments
- Different densities (light and dark bands) are visible within myofibrils
- Light bands (I bands) have only actin filaments are isotropic
- Dark bands (A bands) have both actin and myosin filaments and are anisotropic
- Z lines bisect I bands
- M line bisects the center of A bands
- Thick filaments (myosin) are about 14-16nm in diameter and 1.5µm long, and form the A band
- Thin filaments (actin) are about 6-8nm in diameter and 1µm long, and form the I band
Smooth Muscle
- Smooth muscle is involuntary and found in walls of vessels (arteries, lymph vessels), gastrointestinal tract, and reproductive tissues
- Fibers are long, unevenly thickened, and lack alternating dark and light bands (homogenous)
- No Z or M lines
Cardiac Muscle
- Cardiac muscle has rhythmic contractility from early embryonic development to death
- Properties of both skeletal and smooth muscle
- Fibers are rounded or irregular, branching, and mixed with other fibers
- Nucleus is centrally located in fibers
- Myofibrils show striations, similar to skeletal muscle
- Rich in mitochondria
- Intercalated discs found where Z lines are located
Golgi Complex
- Golgi complex is near nuclei of fibers and is responsible for “concentrating” and “packaging” metabolic byproducts
- Vesicles resemble sarcoplasmic reticulum membranes
Proteins of the Muscle
- Classified as contractile, regulatory, and cytoskeletal proteins
- Contractile- actin and myosin, about 65% of myofibrillar protein
- Regulatory- tropomyosin, troponin, M proteins are involved in regulating the actomyosin complex
- Cytoskeletal- titin, nebulin, C-protein, and others help maintain protein structure in register
Z Line Ultrastructure
- Actin filaments on one side of the Z-line lie between two filaments on the opposite side
- Actin filaments terminate at Z lines
- Z-filaments are material that connect with actin filaments above and below
- Each actin filament connects to four Z filaments passing through the Z line
Myofibril
- Myofibrils are cylindrical, bathed in sarcoplasm and are approximately 1-2µm in diameter
- Myofibrils have alternating light and dark bands, and appear as dots in a cross-section
- Thick filaments (myosin) and thin filaments (actin)
- Arrangement explains striated appearance and longitudinal orientation
Postmortem Glycolysis and pH Decline
- Absence of oxygen triggers anaerobic glycolysis, producing lactic acid which reduces muscle pH
- Rate and extent of pH decline vary based on species, pre-slaughter factors, and temperature
- Low pH desirable for microbial control (slowing spoilage)
- Elevated pH can result in undesirable "pale, soft, exudative" (PSE) and "dark, firm, dry" (DFD) conditions
Rigor Mortis
- Muscle stiffening after death due to actomyosin bond formation from depletion of ATP
- Stages: delay, fast onset, completion
- Rigor mortis is enhanced at higher temperatures
- Breakdown of proteins by enzymes, resolution, and return to a more tender state
Conversion of Muscle to Meat
- Meat results from biochemical and physical changes in muscle post-death
- Oxygen depletion stops oxidative phosphorylation
- The end processes to create meat are complex processes
Aging
- Holding carcasses below freezing (aging) results in improved tenderness and flavor as a result of protein and fat breakdown
- Enzymatic changes during aging
- Timing of ageing varies by species, with different durations for optimal results
- Techniques like electrical stimulation and calcium infusions can decrease the aging duration
Meat Fats
- Meat fat has essential fatty acids (EFAs) and is a good source for human needs
- Meat fat contains oleic, palmitic, and stearic acids
- Some cholesterol content (high in organ meats)
Minerals
- Meat is a source of various minerals like potassium and phosphorus
- Iron vital for haemoglobin and other enzymes
Vitamins
- Lean meat is a good source of B-vitamins
- Vitamin C and fat-soluble vitamins are less abundant in the lean meat
- Liver is a particularly good source of a variety of vitamins
Chemical Composition of a Typical Animal Muscle
- Composition of a typical animal muscle (water, proteins, myofibrillar proteins, sarcoplasmic proteins etc.)
- Percentage breakdown of components in a typical sample
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Description
Test your knowledge on the gross structure and histological aspects of muscles. This quiz covers the distinct types of muscle fibers, their variations, and the associated connective tissues. Prepare to understand the intricate details of muscle anatomy and their functionalities.
