Identify the ONE correct statement about synaptic transmission.

Question

BlackTom AI · Accepted Answer

Glutamate is the principal excitatory neurotransmitter in the neocortex, and most excitatory synapses onto dendritic spines use glutamatergic transmission.

1) Relevant knowledge points and concepts
- Neurotransmitters: molecules released by presynaptic terminals that activate postsynaptic receptors to produce excitatory or inhibitory postsynaptic potentials. 
- Excitatory vs inhibitory: Glutamate produces depolarizing excitatory postsynaptic potentials (EPSPs); GABA is the main inhibitory neurotransmitter in the adult brain. 
- Synaptic anatomy: In the neocortex, the majority of excitatory synapses are formed on dendritic spines (small protrusions) and contain postsynaptic densities rich in glutamate receptors (AMPA, NMDA, kainate). 
- Receptor physiology: AMPA receptors mediate fast Na+ currents producing EPSPs; NMDA receptors permit Ca2+ influx and are voltage-dependent (Mg2+ block).

2) Step-by-step reasoning
- Cortical excitatory neurons (pyramidal cells) release glutamate at their axon terminals. 
- These terminals commonly synapse onto dendritic spines of target neurons in the neocortex. 
- Release of glutamate into the synaptic cleft binds postsynaptic AMPA and NMDA receptors, producing rapid depolarization (AMPA) and Ca2+-dependent signaling (NMDA). 
- Anatomical and electrophysiological studies consistently show that dendritic spines are the predominant sites of excitatory, glutamatergic synapses in cortex.

3) Calculations
- None required for this conceptual question.

4) Why the correct answer is correct
- The statement matches well-established anatomical, biochemical, and physiological evidence: glutamatergic transmission predominates at cortical spines, and glutamate is the major excitatory transmitter in neocortex.

5) Why other possible statements would be incorrect (brief)
- Any statement claiming GABA is the major excitatory transmitter would be false—GABA is inhibitory in adults. 
- Claims that excitatory cortical synapses are mainly on shafts rather than spines are incorrect—spines are the primary locus. 
- Suggestions that acetylcholine or glycine are the main cortical excitatory transmitters are incorrect; acetylcholine has modulatory roles and glycine acts mainly in spinal inhibition.

6) Conclusion
This reasoning confirms the correct answer: "Glutamate is the major excitatory neurotransmitter at synapses on synaptic spines in the neocortex."

Identify the ONE correct statement about synaptic transmission.单项选择题

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