Chapter 12 concept questions Flashcards
Identify as many pairs of antagonistic muscle groups in the body as you can. If you cannot name them, point out the probable location of the flexor and extensor of each group.
Biceps/triceps,
hamstring (flexor)/quadriceps (extensor),
Tibialis anterior(flexor)/gastrocnemius (extensor)
Why are the ends of the A band the darkest region of the sarcomere when viewed under the light microscope?
Ends of the A bands are darkest because they are where the thick and thin filaments overlap.
What is the function of t-tubules?
T-tubules allow action potentials to travel from the sources of the muscle fiber to its interior.
Why are skeletal muscles described as striated?
The banding pattern of organized filaments in the sarcomere forms striations in the muscle.
What are the three anatomical elements of a neuromuscular junction?
A neuromuscular junction consists of axon terminals form one somatic motor neuron, the synaptic cleft, and the motor end plate on the muscle fiber.
What is the chemical signal at a neuromuscular junction?
The chemical signal at a neuromuscular junction is acetylcholine.
Each myosin molecule has binding sites for what molecules?
Each myosin molecule has binding sites for ATP and actin.
What is the difference between F-actin and G-actin?
F-actin is a polymer filament of actin made from gobbler G-actin molecules.
Myosin hydolyzes ATP to ADP and Pi. Enzymes that hydrolyze ATP are collectively known as _________.
Enzymes that hydrolyze ATP are ATPases
Name an elastic fiber in the sarcomere that aids relaxation.
Titin is an elastic fiber in the sarcomere
In the sliding filament theory of contracting, what prevents the filaments from sliding back to their original position each time a myosin head releases to the next actin binding site?
The cross bridges do not all unlink at one time, so while some myosin heads are free and swiveling, others are still tightly bound.
Which part of contraction requires ATP? Does relaxation require ATP?
The release of myosin heads from actin requires ATP binding. Energy from ATP is required for the power stroke. Relaxation does not directly require ATP, but relaxation cannot occur unless Ca2+ is pumped back into the sarcoplasmic reticulum using a Ca2+-ATPase.
What events are taking place during the latent period before contraction begins?
The events of the latent period include creation of the muscle action potential, release of Ca2+ from the sarcoplasmic reticulum, and diffusion of Ca2+ to the contractile filaments.
According to the convention for naming enzymes, what does the name creatine kinase tell you about this enzyme’s function?
Creatine is the substrate, and kinase tells you that this enzyme phosphorylates the substrate.
The reactions in figure 12.12 show that creatine kinase catalyzes the creatine-phosphocreatine reaction in both directions. what then determines the direction that the reaction goes at any given moment?
Because creatine kinase catalyzes the reaction in both directions, the relative concentrations of the reactants and products determine the direction of the reaction. The reaction ones the law of mass action and goes to equilibrium.
If K+ concentration increases in the extracellular fluid surrounidng a cell but does not change significantly in the cell’s cytoplasm, the cell membrane __________ (depolarizes/hyperpolarizes) and becomes ___________ (more/less) negative.
Increasing extracellular K+ causes the cell to depolarize and become less negative.
Summation in muscle fibers means that the _____________ of the fiber increases with repeated action potentials.
tenstion
Temporal summation in neurons means that the __________ of the neuron increases when two depolarizing stimuli occur close together in time.
strength of the graded potential.
Which type of runner would you expect to have more slow-twitch fibers, a sprinter or marathon runner?
marathon runner.. duh
What is the response of a muscle fiber to an increase in the firing rate of the somatic motor neuron?
Increased motor neuron firing rate causes summation in a muscle fiber, which increases the force of contraction.
How does the nervous system increase the force of contraction in a muscle composed of many motor units?
The NS increases the force of contraction by recruiting additional motor units.
One study found that many would-class athletes have muscle insertions that are farther from the joint than in the average person. Why would this trait translate into an advantage for a weight lifter?
If the muscle insertion point is farther form the joint, the leverage is better and a contraction create more rotational force.
What is the differentce in how contraction force is varied in multi-unit and single-unit smooth muscle?
Multi-unit smooth muscle increases force by recruiting additional muscle fibers; single-unit smooth muscle increases force by increasing Ca2+ entry.
When the circular muscle layer of the intestine contracts, what happens to the shape of the tube? when the longitudinal layer contracts, what happens to the shape?
Contraction of the circular layer decrease the diameter of a tube. Contraction of the longitudinal layer shortens the tube.
