5.6.3 Classifications of Neurotransmitters

Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron to another. They are classified as excitatory and inhibitory based on their effects on the postsynaptic membrane.

Definition

Neurotransmitters: Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron to another. They are released from synaptic vesicles in the presynaptic neuron and bind to receptors on the postsynaptic membrane.

Excitatory Neurotransmitters: Neurotransmitters that cause increased membrane permeability to sodium ions and, thus, trigger nerve impulses are said to be excitatory.

Inhibitory Neurotransmitters: Other neurotransmitters cause decreased membrane permeability to sodium ions, thus causing the threshold of stimulus to be raised. This action is called inhibitory.

Main Idea

• Neurotransmitters are classified as excitatory and inhibitory.
• Excitatory neurotransmitters increase membrane permeability to sodium ions and trigger nerve impulses.
• Inhibitory neurotransmitters decrease membrane permeability to sodium ions and raise the threshold of stimulus.
• Examples of excitatory neurotransmitters: acetylcholine, biogenic amines (epinephrine, norepinephrine, serotonin, dopamine).
• Examples of inhibitory neurotransmitters: GABA, glycine.
• Endorphins are peptides that function as both neurotransmitters and hormones.

Core Concept

• Excitatory neurotransmitters = increase Na⁺ permeability; trigger nerve impulses
• Inhibitory neurotransmitters = decrease Na⁺ permeability; raise threshold
• Acetylcholine = excitatory; peripheral nervous system
• Biogenic amines = excitatory; central nervous system
• Epinephrine, norepinephrine = increase heartbeat rate during stress
• Serotonin, dopamine = affect sleep, mood, attention, learning
• GABA, glycine = inhibitory
• Endorphins = decrease perception of pain

Detailed Explanation

Classification of Neurotransmitters

Neurotransmitters are classified as excitatory and inhibitory.

Excitatory Neurotransmitters

• Neurotransmitters that cause increased membrane permeability to sodium ions and, thus, trigger nerve impulses are said to be excitatory.
• Acetylcholine is an excitatory neurotransmitter of peripheral nervous system.
• Biogenic amines (amino acid derivatives) are important neurotransmitters in central nervous system.
• They include:
• Epinephrine
• Norepinephrine
• Serotonin
• Dopamine
• All of which also function as hormones.
• Epinephrine and norepinephrine increase the heartbeat rate during stress.
• Serotonin and dopamine affect sleep, mood, attention and learning.

Inhibitory Neurotransmitters

• Other neurotransmitters cause decreased membrane permeability to sodium ions, thus causing the threshold of stimulus to be raised.
• This action is called inhibitory; because it lessens the chance that nerve impulse will be transferred to an adjoining neuron.
• Examples: amino acids gamma-aminobutyric acid (GABA) and glycine.
• The endorphins are peptides that function as both neurotransmitters and hormones, decreasing our perception of pain.

Summary Table of Neurotransmitter Classification

Detailed Classification

Intermediate Level

Classification of Neurotransmitters

Excitatory Neurotransmitters

Inhibitory Neurotransmitters

Biogenic Amines

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Neurotransmitters are classified as excitatory and inhibitory.
• 2. Excitatory neurotransmitters increase Na⁺ permeability.
• 3. Excitatory neurotransmitters trigger nerve impulses.
• 4. Inhibitory neurotransmitters decrease Na⁺ permeability.
• 5. Inhibitory neurotransmitters raise the threshold.
• 6. Acetylcholine is an excitatory neurotransmitter.
• 7. Acetylcholine is in the peripheral nervous system.
• 8. Biogenic amines are excitatory neurotransmitters.
• 9. Biogenic amines are in the central nervous system.
• 10. Biogenic amines include epinephrine, norepinephrine, serotonin, and dopamine.
• 11. Epinephrine and norepinephrine increase heartbeat rate during stress.
• 12. Serotonin and dopamine affect sleep, mood, attention, and learning.
• 13. GABA and glycine are inhibitory neurotransmitters.
• 14. Endorphins are peptides.
• 15. Endorphins decrease perception of pain.
• 16. Endorphins function as both neurotransmitters and hormones.
• 17. The balance between excitatory and inhibitory neurotransmitters is essential.
• 18. Imbalance can lead to disorders.
• 19. Neurotransmitters are chemical messengers.
• 20. They transmit signals across a synapse.

Remember

• - Excitatory neurotransmitters = increase Na⁺ permeability; trigger nerve impulses
• - Inhibitory neurotransmitters = decrease Na⁺ permeability; raise threshold
• - Acetylcholine = excitatory; peripheral nervous system
• - Biogenic amines = excitatory; central nervous system
• - Epinephrine, norepinephrine = increase heartbeat rate during stress
• - Serotonin, dopamine = affect sleep, mood, attention, learning
• - GABA, glycine = inhibitory
• - Endorphins = decrease perception of pain
• - Endorphins = both neurotransmitters and hormones

Common Mistakes

• 1. Confusing excitatory and inhibitory neurotransmitters — Excitatory = trigger; inhibitory = prevent.
• 2. Mixing up the examples — Acetylcholine, epinephrine, norepinephrine, serotonin, dopamine = excitatory; GABA, glycine = inhibitory.
• 3. Forgetting the role of Na⁺ permeability — Excitatory increases; inhibitory decreases.
• 4. Confusing the functions — Epinephrine and norepinephrine = stress; serotonin and dopamine = mood.
• 5. Thinking endorphins are excitatory — Endorphins are inhibitory.
• 6. Mixing up the locations — Acetylcholine = peripheral; biogenic amines = central.
• 7. Forgetting that biogenic amines also function as hormones — They do.
• 8. Believing all neurotransmitters are excitatory — Some are inhibitory.
• 9. Mixing up GABA and glycine — Both are inhibitory.
• 10. Thinking the balance is not important — The balance is essential.

Quick Revision

Neurotransmitters are classified as excitatory and inhibitory. Neurotransmitters that cause increased membrane permeability to sodium ions and, thus, trigger nerve impulses are said to be excitatory. Acetylcholine is an excitatory neurotransmitter of peripheral nervous system whereas biogenic amines (amino acid derivatives) are important neurotransmitters in central nervous system. They include epinephrine, norepinephrine, serotonin and dopamine, all of which also function as hormones. Epinephrine and norepinephrine increase the heartbeat rate during stress. Serotonin and dopamine affect sleep, mood, attention and learning. Other neurotransmitters cause decreased membrane permeability to sodium ions, thus causing the threshold of stimulus to be raised. This action is called inhibitory; because it lessens the chance that nerve impulse will be transferred to an adjoining neuron e.g., amino acids gamma-aminobutyric acid (GABA) and glycine. The endorphins are peptides that function as both neurotransmitters and hormones, decreasing our perception of pain.

60-Second Revision

• Excitatory neurotransmitters = increase Na⁺ permeability; trigger nerve impulses
• Inhibitory neurotransmitters = decrease Na⁺ permeability; raise threshold
• Acetylcholine = excitatory; peripheral nervous system
• Biogenic amines = excitatory; central nervous system
• Epinephrine, norepinephrine = increase heartbeat rate during stress
• Serotonin, dopamine = affect sleep, mood, attention, learning
• GABA, glycine = inhibitory
• Endorphins = decrease perception of pain
• Warning: Endorphins are inhibitory and decrease perception of pain

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