交感神经系统节前纤维：

Question

交感神经系统节前纤维：

BlackTom AI · Accepted Answer

The question provided is: '交感神经系统节前纤维：' which asks about the nature or targets of sympathetic preganglionic fibers. However, no answer options were supplied in the data, so there are no alternative statements to evaluate one by one.

To build understanding from first principles: sympathetic preganglionic neurons are cholinergic, meaning they release acetylcholine (ACh) onto nicotinic acetylcholine receptors. The classic site of these synapses is the autonomic ganglia, where ACh binds to neuronal nicotinic receptors on postganglionic neurons. This is the general mechanism by which preganglionic sympathetic fibers influence postganglionic neurons.

A distinctive and notable exception in the sympathetic system is the adrenal medulla. Here, preganglionic sympathetic fibers form synapses directly onto chromaffin cells of the adrenal medulla, which also possess nicotinic receptors. Activation of these receptors leads to release of epinephrine (and some norepinephrine) into the bloodstream, rather than a direct synapse onto a postganglionic neuron.

Given the absence of alternative choices, there is nothing to critique column-wise. If an option list were present, we would evaluate each choice against this framework:
- If an option states that preganglionic sympathetic fibers synapse on autonomic ganglia via nicotinic receptors, that would align with standard physiology.
- If an option claims non-cholinergic transmission (e.g., using a different neurotransmitter) at the ganglionic level, that would be incorrect.
- If an option mentions direct adrenal medulla innervation with nicotinic receptors, that would be correct as a special case of preganglionic sympathetic output.
- Any option suggesting that preganglionic fibers terminate at targets other than ganglia or adrenal medulla (e.g., directly at smooth muscle or heart without a ganglionic relay) would be inaccurate for classic sympathetic pathways.

In summary, the typical depiction is that sympathetic preganglionic fibers are cholinergic and form nicotinic receptor-mediated synapses in autonomic ganglia, with a special adrenal medulla innervation via nicotinic receptors. The adrenal medulla response is a key exception where preganglionic fibers act on chromaffin cells rather than a postganglionic neuron.

PCOL2021（ND）

交感神经系统节前纤维：

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