Final answer:
The sympathetic preganglionics are mostly B fibers, which are part of the sympathetic nervous system that contributes to the fight-or-flight response, including pupil dilation and increased heart rate. The sympathetic fibers originate in the spinal cord and can interact with various receptors such as nicotinic and adrenergic.option b is correct
Step-by-step explanation:
The sympathetic preganglionics are mostly B fibers. These are small myelinated fibers that are faster than unmyelinated C fibers but slower than larger myelinated A fibers such as A-beta and A-delta.
The sympathetic nervous system plays a critical role in the body's fight-or-flight response, and sympathetic activation is associated with effects such as pupil dilation and increased heart rate. Most preganglionic neurons in the sympathetic pathway originate in the spinal cord, and they release neurotransmitters that interact with various receptors, including nicotinic and adrenergic receptors, affecting organs including the heart. A unique aspect of the sympathetic nervous system is the direct preganglionic sympathetic fibers projecting to the adrenal medulla, bypassing ganglionic synapses to stimulate hormone release into the bloodstream.
For contrast, the preganglionic parasympathetic fibers, which are involved in rest-and-digest functions, can be found in cranial nerves, such as the facial nerve (CN VII).