|Medullated (Myelinated) nerve fiber
|Non-medullated (Non-myelinated) nerve fiber
|It comprises of neuraxis, which is covered by two sheaths;
i) inner thick myelin sheath of fatty material called myelin
ii) outer thin neurilemma
|It comprises of neuraxis which is covered by a single sheath, the neurilemma. Myelin sheath is absent.
|They appear white in fresh state.
|They appear grey in fresh state.
|Nodes of Ranvier are present in intervals.
|Nodes of Ranvier are absent.
|Extracellular fluid is in contact with the axon only at the nodes.
|Extracellular fluid is in contact with the axon along its entire length.
|Voltage-gated ion channels are concentrated at the nodes.
|Voltage-gated ion channels are spread all over the axon.
|Ion exchange can occur only at the nodes.
|Ion exchange occurs all along the axon.
|Action potential doesn’t propagate over the internodes, and jumps from node to node.
|Action potential propagates all along the axon.
|Nerve impulse conduction is salutatory.
|Nerve impulse conduction is smooth.
|These carry nerve impulses much faster than non-medullated nerve fibers.
|These carry nerve impulses much slower than the medullated nerve fiber.
|These are present in the white matter of brain and spinal cord and in the cranial and spinal nerves.
|These are present in the grey matter of brain and spinal cord and in the autonomic nerves.
|Collateral nerve fibers are present.
|Collateral nerve fibers are absent.
|They are more common in vertebrates.
|They are found in few vertebrates and almost all the invertebrates.