Chapter 12 - Section 12.5 - Synapses - Before You Go On - Page 461: 19

Acetylcholine (ACh), gamma-aminobutyric acid (GABA), and norepinephrine (NE) are neurotransmitters that play distinct roles in neuronal communication by acting on different types of synapses. Here's a contrast of their actions at their respective synapses: **1. Acetylcholine (ACh):** - **Type of Synapse:** ACh is commonly found in neuromuscular junctions and cholinergic synapses in the central nervous system and peripheral nervous system. - **Action at Synapse:** ACh can have both excitatory and inhibitory effects depending on the receptor subtype it binds to. - At neuromuscular junctions, ACh is excitatory and triggers muscle contraction by binding to nicotinic ACh receptors on muscle cells. - In the central nervous system, ACh acts as an excitatory neurotransmitter in certain pathways involved in attention, memory, and learning. It binds to nicotinic and muscarinic ACh receptors. **2. Gamma-Aminobutyric Acid (GABA):** - **Type of Synapse:** GABA is the primary inhibitory neurotransmitter in the central nervous system and is found in inhibitory synapses. - **Action at Synapse:** GABA typically has inhibitory effects by binding to GABA receptors (GABA-A and GABA-B). - GABA-A receptors are ligand-gated chloride channels. When GABA binds to these receptors, chloride ions enter the postsynaptic neuron, hyperpolarizing it and making it less likely to generate an action potential. - GABA-B receptors are metabotropic receptors that activate intracellular signaling pathways, leading to postsynaptic inhibition. **3. Norepinephrine (NE):** - **Type of Synapse:** Norepinephrine is involved in adrenergic synapses, which are found in the sympathetic branch of the autonomic nervous system. - **Action at Synapse:** Norepinephrine primarily has excitatory effects in the sympathetic nervous system. - It binds to adrenergic receptors (alpha and beta receptors) located on target cells, such as smooth muscle, cardiac muscle, and some neurons. - The activation of adrenergic receptors can lead to various physiological responses, such as increased heart rate and blood pressure, bronchodilation, and vasoconstriction. In summary, acetylcholine can have both excitatory and inhibitory effects depending on the receptor subtype and the synapse it acts upon. GABA primarily acts as an inhibitory neurotransmitter by hyperpolarizing postsynaptic neurons. Norepinephrine, on the other hand, is primarily excitatory and plays a key role in the sympathetic nervous system's fight-or-flight response. These neurotransmitters have distinct roles and functions at their respective synapses, contributing to the complexity and diversity of neuronal signaling in the nervous system.

Acetylcholine (ACh), gamma-aminobutyric acid (GABA), and norepinephrine (NE) are neurotransmitters that play distinct roles in neuronal communication by acting on different types of synapses. Here's a contrast of their actions at their respective synapses: **1. Acetylcholine (ACh):** - **Type of Synapse:** ACh is commonly found in neuromuscular junctions and cholinergic synapses in the central nervous system and peripheral nervous system. - **Action at Synapse:** ACh can have both excitatory and inhibitory effects depending on the receptor subtype it binds to. - At neuromuscular junctions, ACh is excitatory and triggers muscle contraction by binding to nicotinic ACh receptors on muscle cells. - In the central nervous system, ACh acts as an excitatory neurotransmitter in certain pathways involved in attention, memory, and learning. It binds to nicotinic and muscarinic ACh receptors. **2. Gamma-Aminobutyric Acid (GABA):** - **Type of Synapse:** GABA is the primary inhibitory neurotransmitter in the central nervous system and is found in inhibitory synapses. - **Action at Synapse:** GABA typically has inhibitory effects by binding to GABA receptors (GABA-A and GABA-B). - GABA-A receptors are ligand-gated chloride channels. When GABA binds to these receptors, chloride ions enter the postsynaptic neuron, hyperpolarizing it and making it less likely to generate an action potential. - GABA-B receptors are metabotropic receptors that activate intracellular signaling pathways, leading to postsynaptic inhibition. **3. Norepinephrine (NE):** - **Type of Synapse:** Norepinephrine is involved in adrenergic synapses, which are found in the sympathetic branch of the autonomic nervous system. - **Action at Synapse:** Norepinephrine primarily has excitatory effects in the sympathetic nervous system. - It binds to adrenergic receptors (alpha and beta receptors) located on target cells, such as smooth muscle, cardiac muscle, and some neurons. - The activation of adrenergic receptors can lead to various physiological responses, such as increased heart rate and blood pressure, bronchodilation, and vasoconstriction. In summary, acetylcholine can have both excitatory and inhibitory effects depending on the receptor subtype and the synapse it acts upon. GABA primarily acts as an inhibitory neurotransmitter by hyperpolarizing postsynaptic neurons. Norepinephrine, on the other hand, is primarily excitatory and plays a key role in the sympathetic nervous system's fight-or-flight response. These neurotransmitters have distinct roles and functions at their respective synapses, contributing to the complexity and diversity of neuronal signaling in the nervous system.