Impulse transmission across unmylinated axon

Impulse transmission across unmylinated axon

Ion channels

➢ Ion channels open and close due to the presence of “gates.” 

➢ The gate is a part of the channel protein that can seal the channel pore shut 

or move aside to open the pore.

Types of ion channels:

1.leakage channel

➢ The potassium ion leakage channels are leakier than the sodium ion leakage 

channels. 

➢ Thus, the membrane’s permeability to K+

is much higher than its permeability to 

Na+.

2.ligand gated channel

➢ Ligand-gated channel opens and closes in response to a specific chemical 

stimulus. 

➢ A wide variety of chemical ligands— including neurotransmitters, hormones, 

and particular ions—can open or close ligand-gated channels.

3.Mechanical gated channel

➢ These channels open or close in response to mechanical stimulation in the 

form of 

○ Vibration and touch.

○ Pressure and tissue stretching.

4. Voltage gated channel

➢ A voltage-gated channel opens in response to a change in membrane 

potential (voltage). 

➢ These participate in the generation and conduction of action potential

Resting membrane potential (rpm)

➢ In neurons, the resting membrane potential ranges from -40 to -90 mV.

➢ A typical value is -70 mV. 

➢ The minus sign indicates that the inside of the cell is negative relative to the 

outside. 

➢ A cell that exhibits a membrane potential is said to be polarized.

Factors contributing to resting membrane potential (rpm)

➢ The resting membrane potential arises from three major factors:

○ Unequal distribution of ions in the ECF and cytosol.

○ Inability of most anions to leave the cell.

○ Electrogenic nature of the Na+

/K+ ATPases.