Structure of muscle tissue week 3 Flashcards
What is muscle tissue specialized for? What are the 3 histologically distinct types of muscle?
- specialized for contractility and excitability in order to perform movements. muscle cells are elongate and have membrane organelles specialized for contraction.
- skeletal: attach to bone and responsible for movement of body parts
cardiac
smooth: blood vessels, GI tract
Muscle contraction is also a source of ____.
heat
Muscle tissue can be striated or non-striated and voluntary or involuntary. What types of muscle fall into what categories?
skeletal: striated voluntary
cardiac: striated involuntary
smooth: non-striated involuntary
note: striated=light and dark bands on microscopic level
voluntary: under cerebral cortical control
involuntary: under autonomic nervous system control
What are the levels of structural organization of skeletal muscle? What is the functional unit of muscle?
- muscle (for example deltoid) is composed of numerous muscle fasicles that are composed of bundles of muscle fibers/muscle cells. muscle fibers/muscle cells/myofibrils are composed of myofibrils (organelle with repeating sarcomere units) that is composed of myofilaments (actin and myosin myofilaments
- sarcomere
What are characteristics of skeletal muscle cells? (include discussion of nuclei, organelles, cytoplasm) How are they formed?
- each muscle cell/muscle fiber/myofiber is a multinucleated cell with numerous peripherally located nuclei just beneath the plasma membrane. the plasma membrane in muscle is called the sarcolemma. cytoplasm, called sarcoplasm in muscle, is dominated by contractile filaments but is also rich in mitochondria. the sarcoplasmic reticulum is a specialized form or smooth ER and surrounds myofilaments (actin and myosin). functions in Ca2+ storage
- muscle cells are formed from the fusion of precursor cells called myoblasts which results in the long multinucleated fibers
What are the 3 connective tissue layers and what portions of muscle do they surround? What is their purpose?
epimysium: dense irregular connective tissue that surrounds all of the fasicles of a muscle (the entire muscle)
perimysium: thinner layer of dense irregular connective tissue that surrounds individual fasicles
endomysium: fine layer of reticular fibers that surround individual muscle fibers (cells)
connective tissue layers maintain the 3D structure of muscles and also serve as a route for nerve and circulatory supply to muscle tissue
How many skeletal muscle fiber types are there? How are they characterized?
3 diff skeletal muscle fiber types based on differences in contractile speed, metabolic profile, and fiber morphology. most muscles have all 3 types but proportion depends on function of a particular muscle
Myofibrils are composed of myofilaments. What are myofilaments?
individual polymers of myosin (thick filaments) and actin with its associated proteins (thin filaments)
What are the 3 major proteins of thin filaments?
- actin: a globular protein that polymerizes in a double helical structure forming the thin filament
- tropomyosin: protein that also forms a double helical structure that lies in the groove of the actin helix. acts with the troponin complex to regulate myosin-actin binding
- troponin complex: composed of 3 globular subunits
- TnI: actin binding protein that prevents binding of actin to myosin
- TnT: tropomyosin binding protein that holde troponin complex to actin
- TnC: calcium binding protein, essential step in initiation of muscle contraction
What are the 3 major proteins of thick filaments?
- myosin heavy chain: large protein with 2 portions-an alpha helical “rod” portion and a globular “head” protion containing ATP and actin binding sites
- myosin light chain 1
- myosin light chain 2
light chain phosphorylation helps regulate calcium stimulation of contraction. is more important in smooth muscle
Myofilaments are linked into a highly structured organization called the ____, a unique structural feature of striated muscle. ____ (same as previous blank) line up end to end along the length of the muscle fiber in small parallel bundles called ____. The highly organaized arrangement of thick and thin filaments in a specific banding pattern forms the basis for muscle contraction
- sarcomere
- sarcomeres
- myofibrils
True or false: There are additional accessory proteins that regulate spacing, attachment, and alignment of myofibrils.
True.
Give definitions of each and be sure to discuss which change sizes during contraction and whether or not they contain overlap of filaments:
A (anisotropic) band
I (isotropic) band
Z-line or disc
M-line
H-band/zone
A-band: darker stained band seen in histological slides (dArK=A band) that is equivalent to the length of the myosin (thick) filament. It contains both the thick filament and the portion of the thin filament that overlaps. The extent of overlap depends on the degree of muscle contraction. Stays the same length regardless of muscle contraction!!!
I-band: lighter stained band (light=I-band) seen in histological slides and is equivalent to the portion of thin filaments in adjacent sarcomeres that are not overlapping with thick filaments. Shorten during contraction and elongate during muscle stretch!!!
Z-line/disc: serves as an anchor for thin filaments. defines boundaries of sarcomere (sarcomere is from one Z-line to the next)
M-line: located at center of sarcomere. where myosin filaments are anchored by accessory proteins
H-zone: distance between end of actin molecules from opposite ends of sarcomere (no overlap of actin & myosin). Shorten during contraction and elongate during muscle stretch!!!
Summary: During contraction, the I and H bands shorten and the Z-lines move together thus shortening the entire sarcomere. The opposite occurs with stretch or lengthening. The lenght of the A-band never changes.
Identify the bands and zones of a sarcomere in this electron micrograph.
Identify the stuctures in this electron micrograph of muscle.