Summary OCR A-Level Biology 5.3.2 Types of Neurons and Transmission

Types of Neurons
Myelination
 Myelinated neurons are wrapped in a myelin sheath made of a fatty substance called
myelin
 Individual cells in the myelin sheath are called Schwann cells
 Each Schwann cell wraps around the neurone so there are several layers of membrane
and cytoplasm making up the sheath
 The Schwann cells prevent the movement of ions across the neurone membranes and
insulate them from other neurones
 Between Schwann cells are gaps called Nodes of Ranvier
 Movement of ions can occur at nodes of Ranvier
 Action potentials jump from one node of Ranvier to the next, increasing the speed of
transmission
 Myelinated neurones conduct much faster than non-myelinated neurones



Saltatory Conduction
 Action potentials travel along a neurone by localised depolarisation – the impulse
causes voltage gated sodium ion channels to open which allow sodium to diffuse in and
open the next voltage gated sodium ion channel
 In myelinated neurones, the action potential jumps between nodes of Ranvier and only
has to polarise the channels at the nodes, not the entire length of the axon
 This is saltatory conduction