Question

The longest cell in animal body is/an
A) Osteocyte
B) Neuron
C) Chromatophore
D) Lymph Corpuscle

Answer 1

Hint: There are certain cells in our body that are specialised to execute special functions which help various systems of the body to coordinate easily with each other.

Complete answer:
Neuron also known as a nerve cell is a cell that is the longest cell of animals which has the capability to get excited by electrical or chemical impulse. These cells help in communication inside the body. These cells are found in animals except sponges whereas plants and fungi lack these cells.
These cells are classified into three types:
Sensory Neurons: These respond to stimuli for example touch.
Motor Neurons: Controls the process like muscle contraction and coordinates with the brain and spinal cord.
Interneurons: These are the connection of neurons in the same region of the brain or spinal cord.

Structure of Neuron:
1) A typical neuron has three main parts:- cell body also known as soma, dendrites and axon.
2) Soma or cell body is a compact structure from which dendrites and axon eject. It also contains the nucleus and Nissl’s granules.
3) Dendrites help in receiving and the processing of the information. These signals can be either exciting or inhibitory depending on the need.
4) A single neuron has more than one dendrites which help it to receive thousands of signals.
5) Axon: These are long fibres which emerge from the cell body and consist of a branched distal end. Its space is filled with neurotransmitters which help in transmission and it terminates at the synaptic knob.
6) Some axons are covered by a sheath known as the myelin sheath. It is formed with a plasma membrane and helps to increase the transmission speed.
7) These myelinated sheath axons have a gap in between known as nodes of Ranvier.
8) The neurotransmitter molecules are present at the end of the axon.
9) Nissl’ s granules are rough endoplasmic reticulum which helps in the protein synthesis.
10) Schwann cells which are also known as neurilemma cells are responsible for the production of the myelin sheath.
11) Nerve ending or Axon terminal is the distal part of the neuron that comes in contact with other cells.

Additional information:
The function of Neurons: The main and the basic function of a neuron is to send and receive signals by using action potential and can be achieved by either chemical or electrical means. The site at which neurons come in contact with other cells is synapses.
Nerve cells are the connection in our body which helps to communicate the entire body with each other. These cells do not execute cell division and are very specialised.

So, the correct answer is ‘Neuron’

Note: Myelin is a lipid-rich substance that covers the axons. Most of the synapses use chemical messengers to communicate. Neurotransmitters are the chemicals that help in neurotransmission like acetylcholine.