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Myelinated and Unmyelinated Fibres

The myelin sh...

Question

The myelin sheath around axon is formed by:

A

Nodes of ranvier

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B

Synaptic knob

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C

Schwann cells

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D

Both b and c

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Solution

The correct option is C Schwann cells
Schwann cells are responsible for forming myelin sheath around the axon. They are present in both myelinated nerve fibres and unmyelinated nerve fibres. However they form myelin sheath around the axon in the myelinated nerve fibres.
Nodes of Ranvier are the gaps between two myelin sheath, since it is not a continuous sheath. Synaptic knobs are bulb-like structures present at the distal branched end of the axon. These knobs are composed of synaptic vesicles containing certain chemical substances called neurotransmitters. Hence both nodes of ranvier and synaptic knobs have no role in formation of myelin sheath.

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Q. The myelin sheath around axon is formed by:

A myelinated nerve fibre is enveloped by Schwann cells, which form a myelin sheath around the axon.

An unmyelinated nerve fibre is not enclosed by a Schwann cell and hence does not form a myelin sheath around the axon.

Q. Read the given statements and select the correct option.
(i) Synaptic cleft of neurons secretes adrenaline.
(ii) Myelinated nerve fibres are enveloped with Schwann cells, which form a myelin sheath around the axon.
(iii) Non-myelinated nerve fibre is enclosed by a Schwann cells that does not form a myelin sheath.
(iii) Spinal and cranial nerves are made of non-myelinated nerve fibres

Q. Consider the following statements and find out coorect option:
(a) Three are two types of axons, namely myelinated and non myelinated
(b) Myelinated nerve fibres found in autonomous and the somatic neural systems
(c) The myelinated nerve fibres are enveloped with Schwann cells, which form a myelin sheath around the axon.
(d) The gap between two adjacent myelin sheaths are calleds nodes of Ranvier.
(e) Unmyelinated nerve fibre found in spinal and cranial nerves
(f) Unmyelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath around the axon.

Q. Consider the following statements and state true or false.
1. Synaptic cleft of neurons secrete adrenaline.
2. Myelinated nerve fibres and enveloped with Schwann cells, which form a myelin sheath around the axon.
3. Non-myelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath.
4. Spinal cord and cranial nerves are made up of non-myelinated nerve fibres.

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Myelinated and Unmyelinated Fibres

Standard XII Biology

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