Question

Axons of preganglionic neurons in the human sympathetic nervous system emerge from which of the following regions of the spinal cord?
A. Cranial and sacral
B. Thoracic and lumbar
C. Cranial and thoracic
D. Lumbar and sacral

Answer 1

Hint: Nerve fibers that connect the central nervous system to the ganglia in the autonomic nervous system are termed as preganglionic neurons. Preganglionic neurons of the sympathetic nervous system are shorter than the parasympathetic nervous system and are closer to the spinal cord.

Step by step answer:Option A) Parasympathetic or craniosacral system has cell bodies originating from cranial nerves in the brain stem or from the sacral region of the spinal cord. The cranial nerves III, VII, IX, X, and sacral region S2, S3, S4 form the preganglionic neurons of the parasympathetic nervous system.
Option B) In the sympathetic nervous system the cell bodies of preganglionic neurons are located in the central nervous system, which originates from the lateral horns of thoracic ganglia 12 and lumbar ganglia 2 or 3. Thus the sympathetic nervous system is also called the thoracolumbar system. These preganglionic neurons form synapses with the postganglionic neurons and their innervations are followed to the target organ. The released neurotransmitter on the target organ shows the effect of the sympathetic nervous system.
Option C) There are 12 thoracic nerves originating from the thoracic vertebrae of the spinal cord and they take part in the preganglionic formation. Cranial nerves originate from the brain stem and there are in total 12 cranial nerves and provide signals for the smell, vision, taste, hearing, etc. The preganglionic neurons of the sympathetic nervous system do not originate from cranial and thoracic together.
Option D) Lumbar and sacral nerves originate from the lumbar and sacral segment of vertebrae. Preganglionic neurons of the sympathetic nervous system emerge from the lumbar but not from the sacral segment and preganglionic neurons of the parasympathetic nervous system originate from the sacral segment.
Hence, the correct answer is option (B)

Note: The preganglionic neurons of both the parasympathetic and sympathetic neurons are cholinergic but the postganglionic neurons of both differ. The sympathetic nervous system is responsible for the fight or flight signal and reaction.