Smooth muscle is under control of the autonomic nervous system (true/false) A mo
ID: 3522244 • Letter: S
Question
Smooth muscle is under control of the autonomic nervous system (true/false)
A motor unit is
one motor neuron
one motor neuron and the group of muscle fibers it innervates
several motor neurons and the group of muscle fibers it innervates
one motor neuron and only one muscle fiber
The thin filament is:
a bundle of myosin molecules
an actin filament
an actin filament with its associated troponin complex and tropomyosin
a bundle of tropomyosin molecules
Binding Ca2+ to the troponin complex causes ____________ to move
troponin
actin
the myosin binding site
tropomyosin
Which of the following components of the sarcomere is an ATPase?
actin
tropomyosin
troponin
myosin
alpha actinin
Explanation / Answer
Answer 1. True.
Explanation: smooth muscles are involuntary by nature that is they do not contract or relax according to our own will. They form a part of the major visceral or the soft organs and are controlled by the autonomic nervous system that is the sympathetic and parasympathetic nerve fibers.
Answer 2. A motor unit is one motor neuron and group of muscle fiber it innervates
Explanation: Motor unit is a neuron which transmits stimuli to the muscle tissues. It consists of a single motor neuron and a group of the muscle fiber to which it innervates.
Answer 3. The thin myofilament is : an actin filament with its associated troponin complex and tropomyosin
Explanation: sarcomere which is the functional and structural unit of the muscle contraction consists of the thick as well as the thin myofilaments which remains scattered throughout the sarcomere.
Thin myofilament have a diameter of around 70 angstrom and are composed of three different proteins namely; actin, tropomyosin and troponin
Answer 4. Binding of the calcium ions to the troponin complex causes the tropomyosin to move from the surface of actin proteins.
Explanation: In the relaxed state that is when a muscle is not contracting, the active grooves present on the surface of the actin proteins remains covered with the tropomyosin proteins which are a component of the thin myofibril. It thus prevents the binding of the actin to the myosin and hence keeps the muscles in a relaxed state. However upon the release of the calcium ions from the body the signal for a muscle to contract gets triggered and hence tropomyosin molecule gets altered due to which it can no longer bind to the surface of the actin molecule; hence actin myosin interaction occurs and likewise the contraction of muscles take place.
Answer 5. Myosin:
Explanation:Myosin is a protein which is made up of six polypeptide chains among which two are heavy chains and four are the light chains. The two heavy chains wrap spirally around each other to form a double helix although the other end of the heavy chains remains folded into a globular protein mass which is called as the myosin head. The head has an ATPase activity which helps in the formation of cross bridges to the active site present on the actin proteins in the presence of magnesium ions.
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