For the following true/false items, mark "A" for true and "B" for false. 61) Sympathetic pathways have very long post-ganglionic fibers. 62) Parasympathetic pathways have a ganglion very close to the target organ. 63) A touch receptor will generate an action potential. 64) A motor neuron will carry a graded potential down its axon. 65) Charged particles like ions can cross cell membranes more easily than nonpolar

61) Sympathetic pathways have very long post-ganglionic fibers. "A", True.

62) Parasympathetic pathways have a ganglion very close to the target organ. "A", True.

63) A touch receptor will generate an action potential. "A", True.

64) A motor neuron will carry a graded potential down its axon. "B", False.

65) Charged particles like ions can cross cell membranes more easily than nonpolar. "B", False.

Explanation:

61) The postganglionic axons of the sympathetic division are very long and unmyelinated. These fibers go toward the target effector organs.

62) The axons of the firsts parasympathetic neurons characterize for being very long and for reaching the target organ before they make contact with the second neuron. This means that the ganglion is in the organ or very close to it, and the axon of the second neuron is very short.

63) There are different kinds of sensory receptors. One of them is mechanoreceptors, that respond to touch or pressure. One of the most important characteristics of these sensory receptors is excitability. They can react to different stimuli triggering an action potential that is transmitted to the brain.

64) The neuron stimulation is a change in its membrane potential, known as graded potential. The graded potential occurs in the motor neuron's body and occurs before the neuron transmits the signal to the other neuron. A neurotransmitter joins an ion-channels allowing the entrance of positive ions like sodium (depolarization) or negative ions like chloride (hyperpolarization). The intensity of this graded potential is variable. If this intensity reaches the action threshold it will trigger the signal down the axon to the other neuron.

65) Charged particles like ions and nonpolar molecules can cross cell membranes by passive transport. They do not need the energy to cross, but they depend on gradients. Ions need channel proteins or carrier proteins to cross the membrane and depend on the electrochemical gradient, while uncharged molecules only depend only on the concentration gradient and they do not need any protein to cross.

Active transport is against the electrochemical gradient, so it does need energy to happen. Molecules go from a high concentration side to a lower concentration side. This process is always in charge of carrier proteins.

In general passive transport is easier than active transport as it does not need energy. But in the case of passive transport, nonpolar molecules cross the membrane easier than charged ions.