lecture 6 notes

Lecture 6: 

Excitable cels as electrical circuits 

• Axons can be modelled as electric circuits  

• There is resistance to current flow across the memrbane and along the axon --> the distance that electrotonic (passive) spread travels is a function of the magnitude of these two resistance in relation to one another --> if internal resistance is low in relation to transmembrane resistance, electrotonic spread will be further along the axon  

• Can make actino potential transmission faster by increasing the axon diameter --> current in solution is carried by ions and more ions means lower resistance. Lower resistance means greater spread and greater spread means faster conduction. And by having a larger diameter, it means theres more space for more ions which will in turn make the conductions faster  

• Or could just increase the transmembrane resistance very high so that the AP travels along the axon --> myelin increases axon insulation meaning it increases transmembrane resistance. The reduces the current leak across the axon membrane and allows the AP to flow across the axon   

• Myelin : internode = myelinated, node = unmyelinated 

• The axon has a high density of ion channels at the node but few ion channels under the myelin therefore transmembrane resistance is high under the myelin  

AP conduction  

• Conduction in myelinated axons are described as saltatory (jumping) 

• Jump from node to node  

Transmitters and their receptors on synaptic partners can be excitatory or inhibitory and not AP