Question

Which of the following involves a skeletal muscle (whole muscle)?

1. Treppe
2. Multiple wave summation
3. Isotonic contraction

Consider the following events and choose the one that occurs last

1. Na+ ions diffuse into the skeletal muscle cells
2. ACH binds to receptor sites on Na+ ion channels
3. Membrane permeability to Na+ ions increased

The sphere of hydration is greater for

1. Na+
2. H+
3. He+
4. H2O

Which ectodermal cells use socium, Na+, as a component of depolarization?

1. Heart muscle
2. Smooth muscle
3. Integument
4. Motor neurons

Answer 1

1.C

There are different types of contractions associated with the skeletal muscles-

1. Isometric: A muscular contraction in which the length of the muscle does not change.
2. isotonic: A muscular contraction in which the length of the muscle changes.
3. eccentric: An isotonic contraction where the muscle lengthens.
4. concentric: An isotonic contraction where the muscle shortens.

In isotonic contraction,the tension remains same in the muscle and the muscle length changes during muscle contraction. It occur only when a muscle's maximal force of contraction exceeds the total load on the muscle. In this, the length of the muscle changes during contraction.Isotonic exercise includes stair climbing, push-ups, squats, and biceps curls.

Other options:

Treppe- This process does not involve the whole muscle since when a skeletal muscle has been dormant for an extended period and then activated to contract, with all other things being equal, the initial contractions generate about one-half the force of later contractions.The calcium ions become more available in the subsequent Contraction only.As the ions become available, more binding sites start opening.This tension increase is called treppe, a condition where muscle contractions become more efficient.

Wave Summation- Only the stimulated muscle Fibres contract.The excitation-contraction coupling effects of successive motor neuron signaling is added together.If the fibers are stimulated while a previous twitch is still occurring, the second twitch will be stronger.

2.A

In neuromuscular junction, nerve Fibres divide into many terminal branches, each terminal ending near to the muscle fibre.This is called the motor end plate.There are thousands of receptors present on the surface of the muscle fibre membrane.The nerve releases the neurotransmitter acetyl choline from the synaptic vesicles..The channels open to facilitate the Na+ ion flow into the motor end plate.This initiates the end plate potential.  

Two types of ion channels involved in the neuromuscular junction and end plate potentials:

1.voltage-gated ion channel and

2.ligand-gated ion channel.

Voltage gated ion channels are responsive to changes in membrane voltage which cause the voltage gated ion channel to open and allows certain ions to pass through. Ligand gated ion channels are responsive to certain molecules such as neurotransmitters. The binding of a ligand to the receptor on the ion channel protein causes a conformational change which allows the passing of certain ions.It induces the opening of the voltage-gated Na+ ion channels. The rapid influx of sodium ions causes the membrane potential to reach a positive charge. The membrane potential starts to peak, the potassium ion channels open and causes an out flux of potassium to counteract the influx of sodium.

3.B

Hydration sphere is the layer of water molecules that surrounds an ion. Because smaller ions are more hydrated due to their more intense electric field they tend to have larger hydrated radii than larger ions.Although helium is smaller than hydrogen, He+ is larger than H+ ion.Hence more hydration occurs with H+.The cations will have more hydration compared to anion due to the negative polarity of the oxygen atom in the water molecule binds with the positively charged ion in a confined space so that more hydration can occur further with other water molecules.

4.D

Motor neurons can undergo depolarization in response to a number of stimuli. These stimuli generate a positive potential inside the neurons. When the positive potential becomes greater than the threshold potential, it causes the opening of sodium channels to cause depolarization of motor neurons.

Heart muscle and smooth muscle use Ca2+ ion for depolarization.