Problem 4 - Animal Physiology

Question

The sympathetic and parasympathetic divisions of the autonomic nervous system employ the same neurotransmitter (acetylcholine) for preganglionic neurons, but different neurotransmitters for postganglionic neurons (norepinephrine for sympathetic, and acetylcholine for parasympathetic; see Figure 15.10). How would it affect autonomic function if the situation were reversed-that is, if the preganglionic neurotransmitters were different and the postganglionic neurotransmitters were the same?

Step-by-Step Solution

Answer

If the postganglionic neurotransmitters were the same in both the sympathetic and parasympathetic divisions, and the preganglionic neurotransmitters were different, it could potentially disrupt the specific 'fight or flight' and 'rest and digest' responses of the two systems, respectively. This could affect the body's ability to properly respond to different physiological demands.

Step 1: Understanding the Autonomic System's Function

First of all, it's important to understand that the autonomic nervous system controls the body's physiological responses. It is divided into two main parts: the sympathetic and parasympathetic systems. The sympathetic system prepares the body for 'fight or flight' reactions, while the parasympathetic system is responsible for 'rest and digest' functions. In terms of neurotransmitters, both systems use acetylcholine for the preganglionic neurons while use different neurotransmitters for postganglionic neurons. The sympathetic system uses norepinephrine, and the parasympathetic uses acetylcholine.

Step 2: Considering the Reversed Neurotransmitter Situation

In the scenario where preganglionic neurotransmitters were different and the postganglionic neurotransmitters the same, it would mean that both systems are using the same neurotransmitter for their most direct effect on organs and tissues. With postganglionic neurons directly interacting with organs and muscles, having the same neurotransmitter could lead to the lack of specificity in organ responses.

Step 3: Analysing the Consequences

If the postganglionic neurotransmitters were the same (let's say acetylcholine for both), and the preganglionic neurotransmitters were different, it could potentially lead to a lack of differential responses in organs. The roles of sympathetic and parasympathetic systems in regulating organ function might not be as effective, as there could be a conflict in commands. The unique 'fight or flight' and 'rest and digest' functions of the sympathetic and parasympathetic systems, respectively, could be impaired due to the shared postganglionic neurotransmitter. In short, this could adversely affect the body's ability to appropriately respond to different physiological demands.