Which one of the following is not part of nerve cell body?

Question

Accepted Answer

The correct option is 2: Centriole
The centriole is an organelle primarily responsible for organizing the mitotic spindle during cell division. Since most mature neurons in the central nervous system are post-mitotic, meaning they do not divide, they lack functional centrioles and the associated centrosome structure. The absence of this cell-division machinery is a key cytological feature of fully differentiated nerve cell bodies, making the centriole the component that is definitively *not* a part of the soma's internal structure. This fundamental lack of a cell-division organelle is why Centriole is the most accurate answer to the question of what is *not* part of the nerve cell body.

The incorrect option is 1: Nissel's body
Nissl bodies, also known as Nissl granules or tigroid substance, are highly characteristic and abundant features of a neuron's cell body and dendrites. They represent large aggregations of rough endoplasmic reticulum (RER) and free ribosomes. Their crucial function is protein synthesis, which is required for the high metabolic demands of the neuron, including the production of enzymes, neurotransmitters, and maintenance proteins. Therefore, Nissl bodies are an essential and defining component *of* the nerve cell body.

The incorrect option is 3: Lipochrome granules
Lipochrome granules, often referred to as lipofuscin pigments, are masses of residual material resulting from lysosomal digestion. These yellow-brown pigments accumulate in the cytoplasm of long-lived, differentiated cells, including neurons, particularly as the cell ages. Their presence is a normal, though often age-related, component of the nerve cell body's internal contents. Thus, they are considered a part of the soma, not an absent structure.

The incorrect option is 4: Myelin
The myelin sheath is a fatty, insulating layer that surrounds the *axon* of a neuron, not the cell body (soma). Its function is to drastically increase the speed of electrical impulse transmission. Myelin is formed by specialized glial cells—Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system—which wrap their membranes around the axonal projection. While the myelin sheath is *not* found *inside* the cell body, it is a structural component of the *axon*, which is a projection *from* the cell body, whereas the centriole is an *internal organelle* that is physically absent from the soma, making the latter a more accurate and fundamental answer for what is not part of the cell body structure.