Question

Which of the following are characteristics of an isotonic muscle twitch?

1. The length of the muscle remains constant
2. The length of the muscle remains constant and latent period than in an isometric twitch
3. The muscle shortens at a constant velocity and the length of the latent period is longer than in an isometric twitch
4. The muscle shortens at a constant velocity

The afferent division of the peripheral nervous system

1. Transmits action potentials to sensory organs
2. Conveys action potentials to the CNS
3. Neither transmits action potentials to sensory organs nor conveys action potentials to the CNS

The resting potential of a neuron. E.g. -70 mv:         

1. There is a net flux of positive ions out the cell
2. There is a net flux of positive ions into the cell
3. The influx of Na+ ions through its channel is equal to the efflux of K+ ions through K channels
4. The influx of Na+ ions through NA channel is greater than the efflux of K+ through K channels

Relative refectory period occurs when:

1. K+ gates are closed
2. K+ gates are open
3. Ca++ gates are open

Steroid hormones produce their effects by

1. Combining with receptors located on the surface of cell membranes
2. Causing cyclic AMP to be produced
3. Activating the action of genes

Answer 1

1. Option (C) is correct. The muscle shortens at a constant velocity and the length of the latent period is longer than in an isometric twitch.

In isotonic contractions, the tension in the muscle remains constant and the length of the muscle changes as a load is moved. A concentric contraction involves the muscle shortening to move a load.

2. Option (B) is correct. The afferent division of the peripheral nervous system conveys action potentials to the CNS.

The afferent or sensory division conveys impulses to the CNS from peripheral organs

3. Option (C) is correct. The resting potential of a neuron. E.g. -70 mv: The influx of Na+ ions through its channel is equal to the efflux of K+ ions through K channels.

The net electrochemical force for K+ produces a small efflux. This small K+ efflux is equal to the small Na+ influx.

4. Option (B) is correct. The relative refectory period occurs when K+ gates are open.

The K+ voltage-dependent channels have been opened until the membrane potentials reach K+ equilibrium potential. The cell is in the relative refractory phase when the K+ channels are open.

5. Option (C) is correct. Steroid hormones produce their effects by activating the action of genes.

Inside the cell, steroid hormones bind to the nuclear membrane receptors, thus creating an activated hormone-receptor complex. The activated hormone-receptor complex binds to DNA and activates specific genes, increasing protein production.