Chapter 15 - Section 15.3 - Study Guide - Assess Your Learning Outcomes - Page 575: 5

The stability of neurotransmitters and their breakdown processes play a significant role in determining the duration of the effects of the sympathetic and parasympathetic divisions of the autonomic nervous system (ANS). The two primary neurotransmitters involved in the ANS are norepinephrine (noradrenaline) and acetylcholine (ACh), and their stability and metabolism influence the duration of their respective effects. 1. **Norepinephrine (Noradrenaline)**: - Norepinephrine is the primary neurotransmitter released by sympathetic postganglionic neurons. - Its effects are relatively short-lived because of its rapid degradation and removal from synaptic clefts. - Norepinephrine is taken back up into the presynaptic neuron via a process called reuptake. This reuptake quickly terminates the signal transmission, reducing the duration of sympathetic effects. - Additionally, norepinephrine can be broken down by enzymes like monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT), further limiting its presence in the synaptic cleft. Due to the rapid reuptake and enzymatic degradation of norepinephrine, sympathetic effects are generally short-lived and are designed for immediate responses to stress or danger. 2. **Acetylcholine (ACh)**: - Acetylcholine is the primary neurotransmitter of both the sympathetic and parasympathetic divisions, although the effects differ depending on the receptors involved. - The duration of ACh's effects can vary depending on the type of receptors activated. - In the parasympathetic division, ACh activates muscarinic receptors, which typically lead to slower, more prolonged effects through second messenger systems like cyclic AMP (cAMP) or calcium ions (Ca²⁺). - In the sympathetic division, ACh is also involved in the transmission of signals at certain synapses, such as at the sympathetic ganglia, but these effects are relatively short-lived due to the rapid enzymatic degradation of ACh by acetylcholinesterase (AChE). However, the subsequent release of norepinephrine from postganglionic sympathetic neurons can have more prolonged effects. In summary, the stability and metabolism of neurotransmitters like norepinephrine and acetylcholine influence the duration of their effects in the autonomic nervous system. Norepinephrine's effects are relatively short-lived due to rapid reuptake and enzymatic degradation, making it well-suited for immediate stress responses. Acetylcholine's effects can vary depending on the type of receptors involved but are also limited by enzymatic breakdown by acetylcholinesterase. This difference in neurotransmitter stability contributes to the different durations of sympathetic and parasympathetic effects in the ANS, with sympathetic effects being more immediate and parasympathetic effects being more prolonged and sustained.

The stability of neurotransmitters and their breakdown processes play a significant role in determining the duration of the effects of the sympathetic and parasympathetic divisions of the autonomic nervous system (ANS). The two primary neurotransmitters involved in the ANS are norepinephrine (noradrenaline) and acetylcholine (ACh), and their stability and metabolism influence the duration of their respective effects. 1. **Norepinephrine (Noradrenaline)**: - Norepinephrine is the primary neurotransmitter released by sympathetic postganglionic neurons. - Its effects are relatively short-lived because of its rapid degradation and removal from synaptic clefts. - Norepinephrine is taken back up into the presynaptic neuron via a process called reuptake. This reuptake quickly terminates the signal transmission, reducing the duration of sympathetic effects. - Additionally, norepinephrine can be broken down by enzymes like monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT), further limiting its presence in the synaptic cleft. Due to the rapid reuptake and enzymatic degradation of norepinephrine, sympathetic effects are generally short-lived and are designed for immediate responses to stress or danger. 2. **Acetylcholine (ACh)**: - Acetylcholine is the primary neurotransmitter of both the sympathetic and parasympathetic divisions, although the effects differ depending on the receptors involved. - The duration of ACh's effects can vary depending on the type of receptors activated. - In the parasympathetic division, ACh activates muscarinic receptors, which typically lead to slower, more prolonged effects through second messenger systems like cyclic AMP (cAMP) or calcium ions (Ca²⁺). - In the sympathetic division, ACh is also involved in the transmission of signals at certain synapses, such as at the sympathetic ganglia, but these effects are relatively short-lived due to the rapid enzymatic degradation of ACh by acetylcholinesterase (AChE). However, the subsequent release of norepinephrine from postganglionic sympathetic neurons can have more prolonged effects. In summary, the stability and metabolism of neurotransmitters like norepinephrine and acetylcholine influence the duration of their effects in the autonomic nervous system. Norepinephrine's effects are relatively short-lived due to rapid reuptake and enzymatic degradation, making it well-suited for immediate stress responses. Acetylcholine's effects can vary depending on the type of receptors involved but are also limited by enzymatic breakdown by acetylcholinesterase. This difference in neurotransmitter stability contributes to the different durations of sympathetic and parasympathetic effects in the ANS, with sympathetic effects being more immediate and parasympathetic effects being more prolonged and sustained.