Skeletal Muscle Tissue - Downing Flashcards
What is the name of a single muscle cell?
myofiber
General Features of skeletal muscle:
Striated T-tubule system Well developed sarcoplasmic reticulum multinucleated (can be several hundred) Nuclei at cell periphery
What lines define the sarcomere?
From one Z-line to the next Z-line
The a band of the muscle fiber is the:
dark zone
The I band the the:
light zone
What is the small white zone inside of the A band?
The H band
What is the line in the center of the H band?
The M-line
What subunits make up mysoin?
4 light chains and 2 heavy chains
light chains are associated with the head regions that forms the cross bridges to actin
heavy chains can be cleaved into heavy and light meromyosin
Heavy has piece that forms head and binds to actin
What regions of the myosin has no cross bridges?
The M-line, has no heads
What are the regulatory molecules of skeletal muscle and how do they regulate the muscle?
Tropomyosin
- Fibrous; arranged head to tail in a linear series
- Helically wound along grooves of F-actin helix
Troponin complex (3 subunits)
- TnT: binds entire troponin complex to tropomyosin
- TnC: great affinity for Ca++
- TnI: binds to actin, preventing actin-myosin interactions
Calcium
- Binds to TnC
- Binding to TnC induces a conformational shift in tropomyosin, exposing previously blocked active sites on the actin filament
What are the three connective tissue coats in skeletal muscle?
Endomysium
Sheath of fine c.t. around individual muscle fibers
Fine reticular fibers and ground substance
Perimysium
Connective tissue sheath around groups of muscle fibers (fasicles)
Continuous with tendon fibers
Epimysium
Outermost sheath of c.t.; surrounds entire muscle
What in the clinical presentation of Myasthenia Gravis?
Weakness and easy fatigue of muscles
Caused by autoimmune attack of ACh receptors
ADminstration of AChE inhibitors has diagnostic and therapeutic value
What does a motor unit consist of?
One motor neuron and all the muscle fibers it innervates
If a motor unit has a 1:1 ratio of motor neurons to muscle fibers, what do you know about this muscle?
It is used for VERY fine motor control
How does the muscle spindle work?
you have a small encapsulated group of specialized muscle cells (intrafusal fibers)
Inbedded in a large group of extrafusal fibers (normal muscle)
Within these specialized fibers you have 2 types of fiberss:
Nuclear chain fibers
Nuclear bag fibers
Surrounded by an internal and external capsule
Stretching the muscle spindle fibers will send a signal to contract the muscle
How does the golgi tendon organ work?
Sensory endings wedged between collagen fibers of the tendons
Protective to prevent overcontraction of a muscle
Tendon primarily continal with the…?
Perimysium
When you’re working out at the gym, why are your muscles getting bigger?
The fibers are increasing in size
NOT increasing in number of fibers
What is the muscle equivalent of the cytoplasm?
Sarcoplasm
What is the muscle equivalent of the Smooth ER ?
sarcoplasmic reticulum
In a myofibril, where do the myosin anchor, and where do the actin anchor at?
Myosin - the M line
Actin - The Z line
What bands get smaller during muscle contraction?
In muscle contraction the H band and I band are going to get smaller
The A band will stay the same length
Explain the importance of the sarcoplasmic reticulum and T-tubules:
- Network of cisterns and/or membranous tubules running between and around myofibrils
- Binds and releases Ca ++
- Invaginations along cell surface form the t-tubules
- T-tubule lumen continuous with extracellular space
- Form triads, connected to 2 cisternae of the sarcoplasmic reticulum on either side
- FACILITATE TRANSMISSION OF ELECTRICAL IMPULSE FROM SARCOLEMMA TO INTERIOR DEPTHS OF CELL
Two types of actin?
G-type (globular)
F-type (fibrous)
