Exam #3 first part Flashcards
What are muscle fibers?
Highly specialized cylindrical cells
What determines the strength of muscle fibers?
The diameter of the fibers
What determines the length of muscle fibers?
Length is highly variable and depends on functional architecture (demands)
What are the different fiber organizations?
Longitudinal: Run in straight lines (biceps)
Pennate: Run diagonally (vastus lateralis)
Multipennate: Run diagonally in different directions (gluteus medius)
Where do skeletal muscles attach and how?
Skeletal muscles attach to bones via tendons
What is basal lamina?
The scaffolding that surrounds muscle cell
What is endomysium?
The collagenous mesh-like tissue that surrounds fiber and basal lamina
What is the perimysium?
The membrane that surrounds organized bunches of muscle fibers called fascicles
What is the epimysium?
The membrane that surrounds bundles of fascicles for actual muscles
What part of them muscle feels pain?
Pain receptors are located in the membrane, the membrane and connective tissue feels the pain, not the muscle fibers
What organelles are responsible for the day-to-day needs of the muscle cells?
Nuclei (multiple nuclei per muscle cells)
What is the purpose of the many nuclei in muscle cells?
To regulate protein synthesis (up regulate under stress and use, down regulate under immobilization or lack of use)
What does the endoplasmic reticulum do for muscle cells?
It is responsible for transporting cellular materials outside the cell
Since the muscle manufactures components for its local use, the ER is not well developed
The Ribosomes are associated with the ER
What do the ribosomes do for the muscle cells?
They synthesize muscle proteins
What do mitochondria do for the muscles?
Source for aerobic energy (production of ATP)
How are mitochondria distributed in the muscle cells?
Type I: >20%
Type II: <20%
What is a neuromuscular junction?
Comprised of a motor end-plate
A chemical neurotransmitter is used to convey information from the nerve (presynaptic) to the junctional receptors of the muscle (postsynaptic) across a synaptic cleft
What are junctional receptors?
Specific proteins that integrate themselves into the sarcolemma
How are neuromuscular junctions formed?
During development, the nerve contracts the muscle fiber. Due to the contact, ACh receptors are attracted to the site of contact and become trapped by the nerve.
The result in decreasing the number of ACh receptors along the rest of the fiber, only having receptors at the location of contact.
How do the mechanism of the down regulation and supercompensation occur?
Down regulation: due to lack of use, the number of ACh receptors at the NMJ are reduced
Supercomprensation: due to repeated use and stimulation, the number of ACh receptors at theNML are increased
What are myofibrils?
Small filaments (1 micrometer) that are bound together to form a muscle fiber. Arranged in parallel.
What is a sarcomere?
Subunits of myofibrils (means muscle segment)
Arranged in series.
The interdigitation pattern gives skeletal muscle its striated appearance
What is a motor unit?
Comprised of one motor neuron and all the muscle fiber that it innervates
The number of fibers the neuron innervate varies
How are the movements generated by the motor units determined?
Fewer muscle fibers innervated by the motor neuron = finer but weaker movement
More muscle fiber innervated by the motor neuron = stronger but lesser coordinated movements
What defines a sarcomere length?
The area between the two Z-disks
What is the average sarcomere length at rest?
2.2 micrometers long
What compound within the myofibrils enables the stretch-shortening property of muscle?
Titin protein
What allows the mechanism of hypertrophy?
Increase in number of myofibrils leads to an increase in size of the muscle fibers, causing larger muscle belly. Muscle fibers do not increase in number.
What allows the mechanism of hypertrophy?
Increase in number of myofibrils leads to an increase in size of the muscle fibers, causing larger muscle belly. Muscle fibers do not increase in number.
What is myosin filament?
A polymer of myosin molecules
What is a myosin molecule?
Highly asymmetric molecules
One end is globular “motor” domain (head) which powers muscle contraction: HMM
Other end is rod-like “tail” permitting multiple molecules to assemble into the thick filament: LMM
What are HMM made up of?
HMM (the heavy chain) is made up of 2 subfragments (S-1 and S-2)
S-1 is the globular head (cross bridge)
How is actin structured?
Long alpha-helical arrangement of actin monomers with no middle section
In has a + and - end based on the direction of polymerization
How is actin structured?
Long alpha-helical arrangement of actin monomers with no middle section
In has a + and - end based on the direction of polymerization
What is special about the helical shape of Actin?
A groove is created by the groove, and the regulatory protein tropomyosin fits nicely in the groove
What is troponin?
A protein along the tropomyosin string Comprised of three subunits Tn-T: Binds troponin to tropomyosin Tn-C: Binds calcium during contraction Tn-I: Exerts an inhibitory influence on tropomyosin when calcium is not present
What are the steps in the power stroke contraction?
- Binding: myosin cross bridge binds to actin molecule
- Power stroke: Cross bridge bends, pulling thin myofilament inwards
- Detachment: Cross bridge detaches at the end of the power stroke and returns to original conformation
- Binding: Cross bridge binds to more distal actin molecule; cycle repeats
