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Physiology Exam 1, Lecture 5: Muscle Contraction
Cell Physiology
47
Physiology
Graduate
08/26/2011

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Term
Define tendons
Definition
Cords of elastic connective tissue that transmit force from muscle to bone
Term
Define fascicles
Definition
Bundles of individual muscle cells surrounded by cell tissue
Term
What do muscle fibers have many of that most cells only have one of?
Definition
Many nuclei and mitochondria
Term
What is a sarcolemma analogus to?
Definition
A plasma membrane
Term
What is the sarcoplasm analogus to?
Definition
Cytoplasm
Term
What are the components of myofibrils?
Definition
Actin and myosin
Term
What are the terms for thick and thin filaments, respectively?
Definition
Myosin and actin
Term
What is the function of the sarcoplasmic reticulum?
Definition
A sac that stores calcium ions
Term
What is the function of T tubules?
Definition
To transmit signals from the sarcolemma to the myofibrils
Term
What are sarcomeres bordered by?
Definition
Z lines
Term
In a sarcomere, what are thick filaments connected by?
Definition
M lines
Term
What band spans the length of thick filaments and the six thin filaments around them?
Definition
The A band
Term
What is the space in the middle of an A band, and why does it appear lighter?
Definition
The H zone; it is missing thin filaments
Term
What occupies the space between A bands?
Definition
I bands
Term
What do I bands contain?
Definition
Thin filaments and the Z line that connects them
Term
Define tropomyosin
Definition
A long fibrous molecule that extends over actin to block the myosin-binding sites at rest
Term
What is the functions of the three proteins on troponin?
Definition
1. Attatches to actin strand, inhibitory (I),
2.Binds to tromyosin,(T)
3. contains the calcium binding site (C)
Term
What are the two sites on a myosin head?
Definition
An actin-binding site and an ATP-ase site that hydrolyzes ATP
Term
What is the function of titin?
Definition
To anchor actin to myosin and to exert an opposite force as sarcomeres lengthen so muscle fibers shorten
Term
What areas of a sarcomere shorten during muscle contraction?
Definition
The I band and H zone (thin filaments slide past thick)
Term
When is the high energy form of myosin?
Definition
After hydrolyzing ATP
Term
When is the low energy form of myosin?
Definition
After releasing the ADP after power stroke
Term
When does myosin hydrolyze an ATP?
Definition
After unbinding to actin
Term
When does myosin release an inorganic phosphate?
Definition
After binding to actin
Term
What immidiately precedes a powerstroke?
Definition
Myosin releasing an inorganic phosphate
Term
When does myosin release an ADP?
Definition
After the crossbridge cycle
Term
When does a new ATP attatch to myosin?
Definition
After rigor
Term
What ion is required for the binding of actin and myosin?
Definition
Calcium
Term
Define excitation-contraction coupling
Definition
The events that link an action potential to the contraction
Term
As an action potential travels down Transverse tubules, what are activated?
Definition
voltage-sensitive L-type Ca2+ channels
Term
What do L-type Ca2+ channels link to and stimulate, and what is its function?
Definition
Ryanodine, to allow calcium to flow out of the SR
Term
What is the effect of calcium binding onto a troponin?
Definition
Tropomyosin shifts, exposing the myosin-binding sites
Term
What causes calcium reuptake in skeletal muscle?
Definition
Ca-ATPase pumps Ca2+ back into the SR
Term
What causes the "burn" during exercise?
Definition
Accumuation of lactic acid
Term
Define recruitment
Definition
An increase in the number of active motor units
Term
Define the size principle
Definition
Both smaller motor units and smaller motor neurons are activated first
Term
What kind of muscle has no stritations?
Definition
Smooth
Term
Name three functions of smooth muscle
Definition
Peristalsis, vasoconstriction, and vasodialation
Term
Why does smooth muscle lack stritations?
Definition
Thick and thin filaments are not arranged in sarcomeres
Term
Define pacemaker potentials
Definition
Slow depolarizations caused by increased sodium, increased calcium, or decreased potassium permeability
Term
Which muscle types have gap junctions?
Definition
Single-unit smooth and cardiac
Term
Can muscle fibers repair themselves if injured?
Definition
Muscle fiber cell division stops at birth, however, fibers can increase in size. If muscle cells are injured, satellite cells can differentiate into muscle cells after birth.
Term
How are thin filaments oriented around thick ones within a myofibril?
Definition
In a hexagon
Term
During a muscle contraction, what bands shorten?
Definition
I-band shortens, but A-band length does not change, thick and thin filaments slide past each other, but thick and thin filaments do not shorten.
Term
What causes rigor mortis?
Definition
If no ATP is available, the cross bridge remains attached to the actin producing rigor mortis. Rigor mortis peaks approximately 12 hrs after death and disappears 48-60 hrs after death due to break down of muscle.
Term
Define Lateral sacs
Definition
enlargements at the end of sarcoplasmic reticulum and is associated with the transverse tubule.
Term
How long is a muscle twitch?
Definition
About 100msec
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