Muscle Anatomy and Structure Quiz

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