Muscle Tissue Flashcards
- Characterized by aggregates of specialized, elongated, cells arranged in_____ _____ that have the primary role of contraction
- ________ interaction is responsible for the muscle contraction
parallel array
Myofilament
2 types of myofilaments:
o Thin filaments- actin
o Thick filaments- myosin II
- The filaments occupy the bulk of the ______ (cytoplasm)
- Classification of muscle is by appearance of _______ cells
sarcoplasm
contractile
What are the types of muscle? (3)
o Smooth muscle
o Striated muscle
- Skeletal muscle attached to bone
- Visceral striated muscle in the tongue, pharynx, diaphragm, oesophagus
- Cardiac muscle
- Each muscle cell is a ________ syncytium
- These muscle fibers are formed during development by the fusion of _______
- Diameter ranges from 10 to 100 μm and length varies from 1m to 1mm
- Nuclei located in sarcoplasm immediately beneath ________
- Skeletal muscle consists of striated muscle fibers held together by connective tissue
- Connective tissue is important in force __________ and is rich in nerve and blood supply
multinucleated
myoblasts
sarcolemma
transduction
What are the types of connective tissue in skeletal muscle?
- Endomysium
- Perimysium
- Epimysium
What is Endomysium? (2)
o Reticular fibers immediately surrounding individual muscle fibers
o Small-diameter blood vessels and fine neuronal branches run parallel to muscle fibers
What is Perimysium? (2)
o Thicker connective tissue surrounding a group of fibers to form a fascicle (function unit of muscle fibers)
o Larger blood vessels and nerves present
What is epimysium? (2)
o Sheath of dense connective tissue surrounding a collection of fascicles
o Major vascular and nerve supply penetrates the epimysium
What are myofibrils? (3)
o The structural and functional subunit of the muscle fibre
o Longitudinally arranged
o Composed of bundles of myofilaments
What are Myofilaments? (3)
o Individual filamentous polymers of Myosin II and actin
o Surrounded by sarcoplasmic reticulum
o Mitochondria and glycogen deposits are located between the myofibrils
The functional unit of the myofibril is the ________.
sarcomere
What are the components of the sarcomere? (5)
o The segment between 2 adjacent Z lines
o Myosin II thick filament is the A band
o Thin filaments attach to Z line making the I bands
o Z band is zigzag structure
o Thin filaments bind to Z line by a-actinin
Contractile apparatus primary proteins:
* Thin filaments
o ________- a double helix bound to Z line by a-actinin
o ________- double helix of 2 polypeptides located in the groove between actin filaments
o _______- complex composed of 3 globular units
- Troponin-C (TnC)- smallest and binds ______ ions
- Troponin-T (TnT)- binds to _______ and anchors the complex
- Troponin-I (TnI)- binds to actin and prevents _____-______ interaction
F-actin-
Tropomyosin
Troponin-
Calcium ions
tropomyosin
actin-myosin
- Thick filaments
o Myosin ___ - 2 _______ heavy chains
- Twisted together as myosin tails
- Each has a globular head at one end
- Head has actin-binding site and ATP binding site
- 4 polypeptide light chains
- 2 types- essential light chains and regulatory light chains
- 1 _____ head has 1 _____ and 1 ______ light chain associated with it
II
polypeptide
myosin
regulatory
essential
Contraction and its regulation
* Thin filaments are pulled towards the M line by the myosin heads using ATP
What is the process? (5)
Contraction and its regulation
* Thin filaments are pulled towards the M line by the myosin heads using ATP
What is the process? (5)
How does the regulation of Ca2+ take place?
- Ca2+
o Must be available for the reaction between actin
and myosin
o After contraction, it must be removed
What is the Sarcoplasmic reticulum? (3)
o Arranged as repeating series of networks around
myofibrils
o Each network extends from one A-I junction to the
next within a sarcomere
o At A-I junction, terminal cisterna forms
o Terminal cisternae
- Reservoir for Ca2+
- contains many gated Ca2+-release channels
What is the transverse tubular system? (4)
o Consists of numerous tubular invaginations of the
Sarcolemma called T Tubules
o T tubules are located between adjacent terminal
cisternae at the A-I junctions
o Contain voltage-sensor proteins
o Depolarization of the T tubule membrane triggers
release of Ca2+ from the terminal cisternae
What is the triad?
Triad- complex of T tubule and 2 adjacent terminal cisternae
What are the events leading to the contraction of skeletal muscle?
What is cardiac muscle?
- Branching fibrous cells with communication between extended processes
- Strong, quick and continuous contraction
- Endomysium present with capillaries
Structure of cardiac muscle: (3)
- Cardiac muscle nucleus lies in the center of
the cell - Numerous large mitochondria and glycogen
stores are adjacent to each myofibril - Mitochondria extend the full length of the
sarcomere
What are Intercalated discs? (2)
o Represent junctions between cardiac
muscle cells
o Consists of short segments arranged in
a step-like fashion
What are Specialized junctions within the intercalated discs? (3)
- Fascia adherens- holds cardiac muscle cells at their ends (transverse component)
- Maculae adherentes- Prevent cells from pulling apart during contractions (transverse and lateral components)
- Gap junctions- Provide ionic continuity between cells
(lateral component)
What is the sarcoplasmic reticulum? (7)
o Extends from Z line to Z line
o T tubules penetrate at the level of Z line
o Only 1 tubule per sarcomere
o Small terminal cisternae of sER near T tubules at Z line
o T tubule + terminal cisternae form a diad at Z line
o T tubules are larger and more numerous in ventricles
than atria
o Passage of Ca2+ from lumen of T tubule to the
sarcoplasm which triggers sER Ca2+ release is
essential for contraction
What are the purkinje fibres?
o Allows for spontaneous rhythmic contractions
o Generate and rapidly transmit contractile impulses to myocardium in a precise sequence
What is smooth muscle? (5)
- Occurs as bundles of elongated fusiform cells with finely tapered ends
- From 20 μm in small blood vessel walls to 200 μm in the intestinal wall
- Smooth cells are interconnected by gap junctions
- Single centrally placed nucleus shaped like a corkscrew
- Organelles found at the ends of the nucleus
Structure of smooth muscles: (4)
- Thin filaments
- Thick filaments
- Dense bodies
- Intermediate filaments
What are the thin filaments? (3)
o Actin
o Tropomyosin
o 2 smooth muscle-specific actin-binding proteins: caldesmon and calponin
What are the thick filaments? (2)
o Myosin II
o Side-polar myosin filament
- Arranged in one direction on one side and in the
opposite direction on the other side
- Has a central bare zone
What are dense bodies? (4)
o Contains attachment proteins for thin and intermediate filaments to the sarcolemma
o Play an important role in transmitting contractile forces to cell surface
o Analogous to Z line
o Rich in a-actinin
What are Intermediate filaments?
o Desmin and vimentin attached to dense bodies
How does smooth muscle contraction work?
- Smooth muscles lack a T system
- Presence of many invaginations of the cell membrane called caveolae
- beneath caveolae are cytoplasmic vesicles- together act analogous to T system
- contraction initiated by Ca2+
