Question

Which of the following statements is incorrect?

• A. Synaptic cleft of neurons secrete adrenaline
• B. Myelinated nerves fibres are enveloped with Schwann cells that form myelin sheath around axon
• C. Non-myelinated nerve fibres are enclosed by Schwann cells that do not form myelin sheath
• D. Spinal cord and cranial nerves are made of myelinated nerve fibres

Answer 1

The correct option is A Synaptic cleft of neurons secrete adrenaline

A neuron is made of three parts, namely, the cyton, dendrites and the axon. Cyton is the cell body of the neuron. Dendrites are the short fibres that can be seen projecting out from the cyton. Axon is the long fibre which branches into short fibre like structures at the end. The bulb-like structure at the end of each branch is called the synaptic knob. Each synaptic knob contains synaptic vesicles which carry various neurotransmitters like the norepinephrine, dopamine, serotonin and acetylcholine. Synaptic cleft is the gap present between the two neurons. During the conduction of a nerve impulse, the neurotransmitters are released into the synaptic cleft from the synaptic knobs. These neurotransmitters go and bind with their receptors present in the adjacent neuron.

Axons can be of two types. One type contains a lipid rich layer called the myelin sheath wrapped around their axons. This layer is formed by the Schwann cells that envelop the nerve fibres. This type of neurons are called the myelinated neurons. The spinal and the cranial neurons are examples of this type. Unmyelinated neurons contain Schwann cells that do not produce myelin sheath. Autonomic neural systems contain the non-myelinated type of nerve fibres.