Muscle physiology Flashcards
The entire muscle is surrounded by the ___, a dense layer of collagen fibers
epimysium
Light areas of sarcomeres that contain only thin filaments are called ____-bands
I-bands
Myofilaments are organized into functional (not structural) units called ____.
sarcomeres
T/F: A muscle cell (fiber) may have a diameter of 100um and a length of 40cm or longer
true
As a result of arrival of an action potential at the motor end plate, calcium released from the sarcoplasmic reticulum binds to ____, causing exposure of the active sites on the ____ filament.
troponin; actin
The myosin head is reactivated (‘cocked’) when it splits ATP into ___.
ADP+pi
When ____ binds to the myosin head, it breaks the link between actin and myosin, re-exposing the active site on the actin.
ATP
The ___-zone is a lighter region on either side of the M-line that contains thick filaments but no thin filaments.
H-zone (sometimes called H-band)
____-lines are formed by connectins that connect thin filaments. They mark the boundaries between adjacent sarcomeres.
z-lines
What are the functions of T-tubules in muscle cells? Do they contain ECF or ICF?
T-tubules help depolarization to occur more rapidly, conducting membrane changes to the center of large muscle cells. They are continuous with the sarcolemma and contain ECF.
In a(n) _____ contraction, tension rises to a plateau that extends until relaxation occurs.
isotonic
How does the action potential in smooth muscle lead to contraction?
the smooth muscle membrane depolarizes, voltage-gated calcium channels open, calcium rushes into the cell, calcium binds to calmodulin, calcium calmodulin complex activates myosin light chain kinase. MLCD phophorylates myosin light chain which crosslinks with actin and causes contraction.
In a ____ centric isotonic contraction, the muscle tension exceeds resistance and the muscle shortens.
concentric
What is the other name for a cell membrane of a muscle fiber?
sacolemma
The central portion of each thick filament is connected to its neighbors by proteins that form the ______-line
M-line
T/F: The amount of tension produced by an individual muscle cell can be increased by summation of twitches.
true
T/F: A single skeletal muscle cell (fiber) may have hundreds of nuclei located just beneath the cell membrane.
true
The connective tissue fibers of the _____ divide the skeletal muscle into a series of compartments.
perimysium
In a ____ centric isotonic contraction, the muscle tension developed is always less than the resistance, resulting in stretching of the muscle.
eccentric
T/F: The length of the A band is equal to the length of the thick filament.
true
Myofibrils are bundles of actin-myosin protein molecules called ______
myofilaments
What name is given to the surface of the muscle cell where it meets a synaptic knob of the nervous system?
motor end plate
Muscle contraction is a result of cross-linking between which two proteins?
actin and myosin
Actin is found in ____ filaments, and myosin is found in _____ filaments
thin; thick
T/F: A resting skeletal muscle fiber contains a very high concentration of free calcium.
false, calcium is stored in the sarcoplamic reticulum at rest
T/F: Myofibrils are only 1 to 2 um wide but can be as long as the muscle cell.
true
What is the effect of sarcomere length on the amount of tension produced by a contraction?
very short sarcomeres and very long sarcomeres produce weaker tension due to less myosin-actin overlap. Optimum force is generated when sarcomere is neither too long or too short
T/F: During contraction, thick filaments slide along thin filaments, towards the center of the sarcomere
false, it is the thin filaments that slide along the thick filaments toward the center of the sarcomere.
Which motor units are recruited first when a large muscle group is to be activated slow or fast?
motor units that contain slow muscle fibers are recruited first.
How is myosin light chain phosphatase involved in skeletal muscle relaxation?
it dephosphorylates myosin light chain, making it less able to cross-bridge with actin allowing relaxation to occur
___ binds to the myosin head during a skeletal muscle contraction?
ATP
Which neurotransmitter is released at the neuromuscular junction?
ACh
After cross-bridge attachment has been made, the stored energy is released as the myosin head snaps towards the M-line, releasing _____.
ADP+Pi
Within each fasicle, the delicate connective tissue of the ____ surrounds the skeletal muscle fibers and ties adjacent muscle fibers together.
endomysium
Name the three layers of connective tissue that are part of each skeletal muscle, from outer to inner.
epimysium, perimysium, ednomysium
How many muscle cells are in a typical motor unit in a muscle that controls the eye? How many in a motor unit that controls the calf?
only three or four in the eye motor unit (provides fine control). Several thousand in the calf muscle.
Inside a muscle fiber (cell), branches of the T-tubules encircle cylindrical structures called _______.
myofibrils
T/F: The amount of tension produced by an individual muscle fiber during one twitch depends only on the number of cross-bridge interactions and cannot be otherwise regulated.
true
Dark areas of sarcomeres that contain the tick filaments and portions of thin filaments are called _____-bands
A bands
In an iso____ contraction, tension rises in the muscle, but the resistance does not move.
isometric
Each compartment created by the permysium contains a bundle of muscle fibers called a _____.
fasicle
