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.