Which of the following components of a neuron is an insulative covering necessary for effective transmission of nerve impulses?

A. Myelin is a fatty substance that wraps around axons in many neurons. It acts as an insulative covering that speeds up the transmission of nerve impulses by enabling the signal to jump between gaps in the myelin (called nodes of Ranvier). This is the correct answer.

B. The synapse is the junction between two neurons where signals are transmitted. It is not involved in the insulative covering of a neuron.

C. The axon is the long, slender part of a neuron that transmits electrical signals, but it requires myelin to efficiently conduct those signals.

D. Dendrites are branched extensions of a neuron that receive signals from other neurons. They do not have an insulative function.

A. Peristalsis, the movement of food through the digestive tract, is inhibited by sympathetic stimulation. The "fight-or-flight" response prioritizes immediate physical needs over digestion, decreasing peristalsis.

B. Bladder tone decreases with sympathetic stimulation. The sympathetic nervous system causes the bladder to relax, inhibiting urination in stressful situations.

C. Heart rate increases with sympathetic stimulation. The sympathetic nervous system activates the "fight-or-flight" response, which includes increasing heart rate to supply more oxygen and nutrients to muscles.

D. Saliva production decreases with sympathetic stimulation. During stress or danger, the body reduces non-essential activities like salivation to focus on more critical survival functions.