Question

Non-myelinated nerve fibers occur in?
A.cranial nerves
B. Autonomic nerves
C. Optic nerves
D. Spinal nerves

Answer 1

Hint:
Non-myelinated nerves are present in the autonomic nervous system. In these nerves, there is no myelin sheath surrounding its axon.
Myelin is a lipid-rich and fatty substance. It is formed by glial cells in the central nervous system (CNS). These cells are called oligodendrocytes. It is also formed in the peripheral nervous system (PNS) by Schwann cells.
The substance Myelin insulates nerve cell axons and increases its speed at which information travels from one nerve cell body to another.

Complete answer:
Option A i.e, cranial nerves
These are pairs of nerves present in your brain. They connect your brain to different parts of your head, neck, and trunk. There are 12 of them. Each of them is named for its function or structure.

Option B i.e autonomic nerve. The pathway formed by autonomic nerves involves two nerve cells. One cell is located in the brainstem or spinal cord and the other cell is located in a cluster of nerve cells (called an autonomic ganglion). Nerve fibers from these ganglia make a connection with internal organs. These are not covered by myelin, therefore they are Non-myelinated.

Option C i.e, optic nerve
It is present in each of the second pair of cranial nerves. It is responsible for transmitting impulses to the brain from the retina at the back of the eye.

Option D i.e, spinal nerve
It is known as a mixed nerve. It carries all the signals (motor, sensory, and autonomic) between the spinal cord and the body. In the human body, there are 31 pairs of spinal nerves and they are present as one on each side of the vertebral column.

So, the correct answer is option B- 'autonomic nerves'.




Note:
The non-myelinated nerve fibers and its fine structure along with morphological organization were studied by ultra-thin sectioning and electron microscopy in peripheral nerves, autonomic nerves, and dorsal roots. Several non-myelinated fibers are known to share the cytoplasm of a Schwann cell.