Lecture 17 Skeletal Muscle Tissue Flashcards
What are the three muscle types?
Skeletal, Smooth, and Cardiac
Skeletal Muscle Characteristics
Multinucleated syncytium Peripheral nuclei Sarcomeric arrangement Each fiber innervated via a single motor axon "all or none" contraction Troponin C
Formation of skeletal muscle cells (fibers)
Formed during embryonic development; hundreds of individual mononucleated myoblasts join end to end to form a myotube
Myotube matures into cylindrical myocyte w/ hundreds of nuclei
Describe Type I Myofibers
Intense staining for oxidative enzymes Rich in NADH transferase, myoglobin, ATPase Many Mitochondria Primarily use Oxidative Phosphorylation Slow & continuous contractions Referred to as dark or red fibers
Describe Type IIA Myofibers
Intermediate staining for oxidative enzymes
Aerobic and anaerobic respiration for ATP
Contract more rapidly than Type I
Resistance to fatigue
Describe Type IIB Myofibers
Light staining for oxidative enzymes Primarily anaerobic respiration for ATP Contract more rapidly than Type I or Type IIA Fatigue quickly Referred to as white or light fibers
Smooth Muscle Characteristics
Single mononucleated cells No sarcomeric arrangement Cells innervated via ANS Do not respond "all or none" Cell connected via Gap Junctions
Cardiac Muscle Characteristics
Single mononucleated cells Centrally positioned nuclei Branching Sarcomeric arrangement Gap Junctions (intercalated disks) Not directly innervated
A muscle is composed of many ______
fascicles
A fascicle is a bundle of _____
myofibers
A myofiber is bundle of ______
Myofibrils
A myofibril is a linear array of ______
Sarcomeres
A sarcomere is made up of what two types of filaments?
Thin = actin Thick = myosin
A muscle is covered by a CT tissue sheet called the ______
epimysium (abundance of type I collagen)
A fascicle is covered by a CT sheet called the ______
Perimysium
What does the perimysium consist of?
Fibroblasts and type I collagen
A myofiber is a muscle cell and is surrounded by a cell membrane called the ________
Sarcolemma
The ______ covers the muscle fiber, including the sarcolemma
Endomysium
The endomysium consists of:
A basal lamina and reticular collagen fibers
The basal lamina is secreted by:
Muscle cells
What is the function of the basal lamina?
Anchors muscle fibers to each other
Helps distribute the force of contraction
Review the structure of a Sarcomere
Slide 31
Review Sliding Filament Theory
Slide 33
Thick filaments are made up of:
Myosin
Describe Myosin
Dimeric protein with long tails and two head groups
Each myosin head group has:
Actin binding region
ATP-Binding Region
Light-chain binding region
(Review slide 38 for more detail)
Describe the two pairs of light chains on myosin
Similar to calmodulin, but have lost ability to bind Calcium
Essential light chains (stability of heads)
Regulatory light chains (stability of myosin II; phosphate binding)
Thin filaments are made of:
actin
Describe F actin
Polymer of G actin
Each actin filament consists of 2 polymers in alpha-helix configuration
Plus end inserts on Z-disk
Name the two actin-associated molecules
Troponin
Tropomyosin
(Review slide 41)
What are the three troponin molecules?
Troponin I
Troponin C
Troponin T
What is the function of Troponin I?
Inhibits binding between actin and myosin
What is the function of Troponin C?
Binds calcium ions
What is the function of Troponin T?
Binds to tropomyosin
What do we call the enlargements of the sarcoplasmic reticulum?
Cisternae
What do cisternae do?
sequester calcium ions
What are T-tubules?
Extensions of the sarcolemma that extend down into the sarcoplasm
Located at the A-I junction
What is the function of T-tubules?
Provide electromechanical coupling for myofiber contraction by transferring the AP of the sarcolemma into calcium release from the cisternae
AB-Crystallin
Heat-shock protein that protects desmin from mechanical stress
Dystrophin
1 of the proteins that links a-actin/desmin complex to cytoplasmic side of sarcolemma
Anchors actin to sarcolemma
Reinforces sarcolemma during muscle contraction
Dystroglycan complex
Links dystrophin (intracellular) to laminin-2 (extracellular)
a-Actinin
Attached thin filaments to the Z line
Titin
Large fibrous protein
Extends from Z disk to middle of H-band & connects ends of thick filaments to Z-line
Provides myosin w/ elasticity
Centers thick filaments in the sarcomere
Desmin Intermediate Filaments
Framework of desmin filaments which surrounds the Z line & extends into each sarcomere
Links myofibrils laterally & to sarcolemma
Plectin
Binds desmin filaments
Nebulin
Extends from Z disc to end of actin filament
Serves as template to regulate length of actin filaments
Muscular Dystrophy
X-linked inherited disease, results in progressive degeneration of skeletal muscle
Dystrophin is either absent (Duchenne’s) or abnormal (Becker’s)
Satellite Cell attach to ______ before basal lamina is laid down.
Myotubes
Satellite cells function as:
Stem cells
Satellite cells can become _____ in times of stress
mitotic
C-Met receptor for HGF
Satellite cells give rise to:
Myogenic precursor cells
- Replace damaged muscle by proliferating, fusing, and differentiating into skeletal muscle fibers
Neuromuscular Spindle Components
Extrafusal Fibers Intrafusal Fibers Alpha Motor Neurons Gamma Motor Fibers/Neurons Primary and Secondary Afferent Fibers
Intrafusal Fibers
Nuclear bag region = sensory region
Nuclear bag fibers
Nuclear chain fibers
Alpha motor neurons
To extrafusal fibers
Gamma motor neurons
To intrafusal fibers
