Neurotransmitters and receptors
In this section, we'll discuss neurotransmitters—the chemicals that neurons use to communicate with one another—and the receptors they interact with.
1) Start with this video:
2) Read this article for some historical context:
History of Neuroscience - Otto Loewi
3) Answer these questions to test your understanding:
1. What was the first neurotransmitter to be discovered?
- A. dopamine
- B. acetylcholine
- C. glycine
- D. serotonin
Show Answer
Correct answer: B
In a famous experiment in 1921, Otto Loewi demonstrated that chemical signaling played a key role in neural communication by showing a chemical he called Vagusstoff could affect the activity of the vagus nerve. Prior to that experiment, many neuroscientists believed neural communication was only electrical. In 1936, Henry Dale isolated Loewi's Vagusstoff and named it acetylcholine.
2. The vast majority of serotonin-producing neurons are found in the:
- A. locus coeruleus
- B. nucleus basalis
- C. substantia nigra
- D. raphe nuclei
Show Answer
Correct answer: D
Serotonin neurons are primarily found in the brainstem in clusters of neurons called the raphe nuclei. Serotonin neurons from the raphe nuclei project throughout the brainstem and brain, and provide serotonin to the rest of the central nervous system.
3. GABA is often referred to as the main inhibitory neurotransmitter of the brain. Which of the following is a way that GABA, upon binding to a receptor, can reduce the likelihood of a neuron firing an action potential?
- A. GABA causes sodium (Na+) ions to flow out of the cell
- B. GABA causes chloride (Cl-) ions to flow into the cell
- C. GABA causes sodium (Na+) ions to flow into the cell
- D. GABA causes chloride (Cl-) ions to flow out of the cell
Show Answer
Correct answer: B
Upon binding to a receptor, GABA can cause the opening of an ion channel that is permeable to negatively charged chloride (Cl-) ions. When these negatively charged ions flow into the neuron, they cause the neuron to become slightly hyperpolarized. Thus, the neuron is less likely to fire an action potential, and GABA has had an inhibitory effect.
4. A neurotransmitter binds to a receptor and activates a G-protein, which then activates an enzyme inside the cell. What type of receptor did the neurotransmitter bind to?
- A. ionotropic
- B. tyrosine kinase receptor
- C. metabotropic receptor
- D. steroid receptor
Show Answer
Correct answer: C
Metabotropic receptors are also known as G-protein-coupled receptors. When a neurotransmitter binds to one, it activates a G-protein. The G-protein can then influence the opening of ion channels, activate enzymes, and initiate signaling cascades within the cell.
5. Which of the following is the primary mechanism by which serotonin is removed from the synaptic cleft?
- A. diffusion into the postsynaptic neuron
- B. active transport into glial cells
- C. enzymatic breakdown by monoamine oxidase (MAO) in the synaptic cleft
- D. reuptake into the presynaptic neuron via the serotonin transporter
Show Answer
Correct answer: D
Serotonin is primarily removed from the synaptic cleft by a transport protein called the serotonin transporter, or SERT.
