What is a Neuron? MCQ - Practice Questions with Answers

• These are the structural and functional units of the nervous system. 

Structure- 

• A neuron consists of two parts i.e. cyton or cell body and neuron processes or neurites.

Cyton- 

• Cyton varies in size and form as it can be up to 13.5 micrometres in diameter and may be variously shaped.
• Cyton may be irregular, spherical, oval, rounded, star-shaped etc.
• It contains cytoplasm called neuroplasm with a prominent nucleus and other cell organelles like mitochondria, Golgi bodies, endoplasmic reticulum, ribosomes, lysosomes, fat globules, Nissl’s granules and neurofibrils. 
• Nissl’s granules are granules of ribosomes and ER which are involved in synthesising the proteins. 
• The functions of cyton are concerned with metabolic maintenance and growth.

Neurites- 

• The neuron processes are of two types i.e. axon and dendrites.
• Axon is a single, long process arising from the cell body. 
• The area in cell body from which axon arises is called axon hillock. It is the most sensitive part of the neuron.
• Axon contains neurofibrils but lack Nissl’s granules. 
• The cell membrane of axon is called axolemma and its cytoplasm is called axoplasm. 
• Axon ends in a group of branches the axon endings or axon terminals.
• The axon terminals join with the dendrites of neighbouring neurons to form a synapse. 
• The axons conduct nerve impulses away from the cell body and are called efferent processes.

On the basis of types of axons, there are two types of nerve fibres:
(a) Myelinated nerve fibres- Schwann cells form the myelin sheath around the axon. The gaps between two adjacent myelin sheaths are called nodes of Ranvier. These fibres are found in cranial and spinal nerves. 
(b) Non-myelinated nerve fibres- In these nerve fibres, the Schwann cells do not form myelin sheath and are without nodes of Ranvier. These are generally found in autonomous and somatic neural systems. 

Dendrites-

• The shorter, tapering and much-branched processes of a neuron. 
• Their number varies from one to several.
• They contain neurofibrils and Nissl granules.
• Dendrites conduct nerve impulses towards the cell body and are called afferent processes.