Question

Which of the following pairs of structures distinguishes a nerve cell from other cell types?
A. Vacuoles and fibres
B. Flagellum and medullary sheath
C. Nucleus and mitochondria
D. Perikaryon and dendrites

Answer 1

Hint: The nervous system is a complex part of an animal. The nervous system transmits signals to and from different regions of the body to coordinate its sensory signals.

Complete answer:The nervous system consists of two prominent parts, the central nervous system and the peripheral nervous system. The central nervous system is the brain and spinal cord, whereas the peripheral nervous system mainly consists of nerve cells or also known as neurons. Neurons are considered the basic unit of communication in the nervous system. They have special structures that enable them to send signals in the form of electrochemical waves swiftly and precisely to different cells.
Neurons consist of a cell body known as the Perikaryon. The cell body encompasses a nucleus, an axon which is a branching fibre and dendrites. The brain and spinal cord neurons are embraced by a myelin sheath, which is a fatty material protecting the neurons.

Therefore, the correct option is D. Perikaryon and dendrites.
The electrochemical signals travel along the axons. This results in the generation of neurotransmitter chemicals and the synapses junction. Excitation, inhibition or modulation of cells occur due to these synaptic signals. The neurons present, connect with each other and form neural circuits, neural pathways and networks that determine the behavior of an organism and generate their perception of the world. Glial cells are another type of specialized cells present in the nervous system and they provide metabolic and structural aid to the individual.
Brain signals are transmitted by motor or efferent nerves, whereas the nerves generating signals to the central nervous system from the body are called the sensory or afferent nerves.
The peripheral nervous system is further divided into the autonomic, enteric, and somatic nervous system. The somatic nervous system facilitates voluntary body movement with the help of skeletal. The gastrointestinal system is authorized by the enteric nervous system. The autonomic nervous system is further classified into sympathetic and parasympathetic nervous systems. They are associated with the fight-or-flight mode of the body.

Note: Most multicellular organisms are composed of a complex nervous system. Some organisms on the other hand lack the existence of a nervous system in their bodies. For instance, mesozoans, sponges, and placozoans do not have a nervous system. Organisms such as cnidarians which include corals, hydras, jellyfish, etc. consist of a diffuse nerve net as their nervous system. Other than a few species of worms, every other organism comprises a brain, a central cord, and nerves in their nervous system.