Muscles Lecture 1
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What is refered to as a neuromuscular junction?
- The innervation of a myofiber by one branch of an alpha motor neuron
- -Usually these junctions are in the belly or center regions of the muscle
Two locations for mitochondria in skeletal muscles
What are the primary functions of these mitochondria
- 1. The ones right below the sarcolemma: maintain Na/K active transport pump and concentration gradient
- 2. The inter-myofibril ones: produce ATP important for the myosin head region, which has myosin-atpase activity to breakdown the ATP provided for sliding
What constitude a triad in a sarcoplastmic reticulum?
2 terminal tubules+1 t-tubule
1. A protein that forms Z-disc
2. The actin filament (f-actin) is made up of globular actin units called
- 1. alpha actinin
What support protein is right underneath the sarcolemma that functions as a support protein for the myofibrils?
What large protein is associated with aiding in the relaxation of pulling filaments back apart from each other during contraction?
What are the large structural proteins that lies around the outside of z-line and m-line regions around the sarcomere?
What protein is within the thin filaments that is structural in nature to give more cytoskeletal structure within the cell and maintain filament alignment?
What kind of mutation in a particular protein causes many forms of muscular dystrophy
Mutations in dystrophin
The specialized, post-synaptic region of the sarcolemma that is part of the neuromuscular junction (This post-synaptic region DOES NOT INCLUDE THE TERMINAL BUTTON OF THE AXON)
Motor End Plate
Motor end plate has a surface of_______.
Term for flattened out sarcolemma caused by damage to the nerve axon or by continued lack of use of the muscle? What's the opposite?
When an action potential comes down from the axon, what permeabilty changes by coming into the presynaptic neuron that causes tubular formation that results in migration of neurotransmitters from the pre-synaptic membrane?
What's a motor unit?
It consists of the neuron and ALL of the myofibers it innervates;
Are myofibers contracting in a all-or-none fashion?
Yes-- and each motor unit also is all-or-none.
BUT, each neuron has a different threshold depending on RECRUITMENT of the CNS that tells it how many myofibers are suppose to be recruited to contract
What are the two ways to increase muscle strength?
- 1. More motor units added to contraction (increase the number)
- 2. Send action potential more rapidly to give a summation effect (increase the frequency)
Which is the light band and which is the dark band? Which one changes width during contraction and which one doesn't?
- I is the light, A is dark; I moves, A doesn't
- During contraction, the thick myosin filament pulls the actin over it leading to a shortnening of each myofibril
Draw the "Time to Peak" tension graph
When the length of the muscle doesn't change although the froce of the muscle does, what is this type of contraction called?
What is causing the latent period in a time to peak graph?
- Series and parallel elastic elements
- This is basically the connective tissues at work, until these units stretch tight enough, the tension won't be generated
Give an example of series elastic element
slinky trying to lift up a book, until the slinky generates the same amount of tension as the book, it won't pick it up
Look at the 1/2 relaxation time" on the time peak tension graph, it tells you how the muscle relaxes, what increases the time it takes to relax
Define and give example of ratio of motor units
extra-ocular muscles vs. quadricep muscles
Define and draw the graphs for "Spatial Summation" and "Temporal Summation"
Explain why in temporal summation, you eventually reach a smooth sustained contraction, and what is this kind of contraction called?
What does calsequestin do?
It helps to bind to Ca2+ that aids in pumping the concentrated Ca2+ back into the SR; This is only used because we are pumping uphill with such a great concentration gradient
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