Biology · Neural Control and Coordination · NEET
No. The cell body (also called cyton or soma) is the whole main part of the neuron. It contains cytoplasm with the usual cell organelles, the nucleus, and special granular bodies called Nissl's granules. The nucleus is only one structure inside the cell body, not the whole cell body.
Dendrites carry impulses TOWARDS the cell body. They are short fibres that branch repeatedly and project out of the cell body, and they also contain Nissl's granules. Remember: Dendrite = Direction IN. The axon does the opposite job and carries impulses AWAY from the cell body.
Nissl's granules are granular bodies present in the cell body of a neuron, and they also extend into the dendrites. In NCERT they are simply called granular bodies in the cell body. They are made of rough endoplasmic reticulum and free ribosomes, so they are the site of protein synthesis. Important point for NEET: Nissl's granules are NOT present in the axon.
Yes. Cyton, soma and cell body are three names for the same part of the neuron. NCERT uses the term cell body. It is the part that holds the cytoplasm, organelles and Nissl's granules, from which dendrites and the axon arise.
A neuron has only ONE axon but can have one or many dendrites. This number is actually used to classify neurons: multipolar (one axon, two or more dendrites), bipolar (one axon, one dendrite), and unipolar (cell body with one axon only). So the axon count stays one, while the dendrite count changes the type.
The distal (far) end of the axon is branched, and each branch ends in a bulb-like structure called the synaptic knob. The synaptic knob holds synaptic vesicles that contain chemicals called neurotransmitters. This is how the axon passes the impulse to the next neuron at a synapse or to a muscle at a neuro-muscular junction.
Nissl bodies are mainly composed of
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A neuron is a highly specialised cell that can detect, receive and transmit stimuli. It is the structural and functional unit of the neural system, and it is made of three parts: the cell body, dendrites and the axon.
The three main parts are the cell body (with cytoplasm, organelles and Nissl's granules), the dendrites (short branched fibres carrying impulses towards the cell body), and the axon (one long fibre carrying impulses away from the cell body).
The axon carries the nerve impulse away from the cell body to a synapse (junction with another neuron) or to a neuro-muscular junction (junction with a muscle). Its far end is branched and each branch ends in a synaptic knob.
It is called the structural unit because the whole neural system is built from neurons, and the functional unit because a single neuron can carry out the full job of detecting a stimulus and transmitting the impulse. This is a common one-line NEET fact.
Dendrites carry impulses towards the cell body and contain Nissl's granules; the axon carries impulses away from the cell body and has no Nissl's granules. A neuron has many dendrites but only one axon.
