1. The myocardium contracts in response to action potentials that arise from: in
ID: 51182 • Letter: 1
Question
1. The myocardium contracts in response to action potentials that arise from:
innervation by vasomotor center neurons
autonomic motor neurons
cardiac pacemaker cells
2. Do neuronal action potentials differ in either amplitude or duration from those experienced by muscle fibers?
yes
no
3. Do muscle fiber action potentials differ in either amplitude or duration from those experienced by the myocardium?
yes
no
4. Does the mechanism of excitation-contraction coupling differ between skeletal and cardiac muscle?
yes
no
5. Does molecular motor operation differ between skeletal and cardiac muscle?
yes
no
6. Does molecular motor operation differ between skeletal and smooth muscle cells?
yes
no
Explanation / Answer
1.The myocardium contracts in response to action potentials that arise from cardiac pacemaker cells
Explanation:Myocardial contraction refers to the ncontraction of heart muscle cells.
The contraction is propagated through a system of intricate fibers and nodules each with their specific function and characteristics. Impulses generated by the SA node (sinoatrial node also called pacemaker cells of heart) - located medial to the opening of the vena cava - are passed to the AV node (atrioventricular node) - located medial to the right AV valve. The AV node further branches into two nerve bundles (left and right) that terminate at the apex of the heart into highly conductive Purkinje fibers that innervate the tip of the ventricles.
2.Yes, neuronal action potentials differ in either amplitude or duration from those experienced by muscle fibers
Explanation: Both types of action potentials in the heart differ considerably from action potentials found in neural and skeletal muscle cells. One major difference is in the duration of the action potentials. In a typical nerve, the action potential duration is about 1 ms. In skeletal muscle cells, the action potential duration is approximately 2-5 ms. In contrast, the duration of cardiac action potentials range from 200 to 400 ms.
Another difference between cardiac and nerve and muscle action potentials is the role of calcium ions in depolarization. In nerve and muscle cells, the depolarization phase of the action potential is caused by an opening of sodium channels. This also occurs in non-pacemaker cardiac cells.
3. No, they experienced almost similar amplitude and duration
Explanation: In the heart muscle cell, or myocyte, electric activation takes place by means of the same mechanism as in the nerve cell - that is, from the inflow of sodium ions across the cell membrane. The amplitude of the action potential is also similar, being about 100 mV for both nerve and muscle. The duration of the cardiac muscle impulse is, however, two orders of magnitude longer than that in either nerve cell or skeletal muscle. A plateau phase follows cardiac depolarization, and thereafter repolarization takes place. As in the nerve cell, repolarization is a consequence of the outflow of potassium ions.
4. yes, mechanism of excitation-contraction coupling differ between skeletal and cardiac muscle
Explanation- Excitation-contraction coupling in skeletal muscle is considered to be mediated by a voltage-dependent charge movement within the region of the sarcolemma (T-tubule): junctional sarcoplasmic reticulum. Depolarization of the sarcolemma initiates the charge movement which may result in a change in sarcoplasmic reticulum membrane potential and ion conductance which is associated with release of calcium to the myofibrils.
In cardiac muscle, excitation appears to be linked to contraction by a different although not mutually exclusive mechanism, ie, by a process of calcium induced-calcium release. Depolarization of the cardiac sarcolemma is associated with an influx of calcium into the cell which initiates the release of more calcium from the sarcoplasmic reticulum to activate the myofibrils.
5.No, molecular motor operation do not differ between skeletal and cardiac muscle but organization differs
Explanation: Cardiac, skeletal and smooth muscle contain myosins that are similarly arranged, although they are encoded by different genes. Organization of the molecular motor of Skeletal muscle differ from cardiac and smooth muscle.
both muscle contraction depend on the ATP-driven sliding of highly organized arrays of actin filaments against arrays of myosin II filaments
6. No, molecular motor operation do not differ between skeletal and smooth muscle cells, the only difference is organisation and genes encoding.
Explanation: The myosin-actin system of the sarcomere powers the contraction of various types of muscle, including skeletal, smooth, and cardiac muscle.
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