Read the given statements and select the correct option.
(i)Synaptic cleft of neurons secreates 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 cell that does not form a myelin sheath.
(iv)Spinal and cranial nerves are made of non-myelinated nerve fibres.

Which of the following statemetn are correct and incorret 1. Synaptic cleft of neurons secrate adrenaline 2. Myelinated nerve fibres are enveloped with Schwann cells, which form a myelin sheath around the axon 3. Non- myrlineated nerve fibre is emclosed by a schwann cell that from a myelin sheath. 4. Spinal cord and cranial nerve are made of non-myelinated nerve fibres of the four statemets

Assertion : Myelinated nerve fibre are enveloped with Schwan cells, which form a myelin sheath around the axon Reason : Unmyelinated nerve fibre is not enclosed by a Schwan cell and hence does not form a myelin sheath around the axon.

Non-myelinated nerve fibres occur in

Schwann cells begin to form myelin sheaths around axons :

Schwann cells begin to form myelin sheaths around axons :

Nodes of Ranvier occur in non-myelinated nerve fibres.