As mentioned previously, ion channels allow ions to move down their concentration gradients. The movement of ions across a membrane generates current as electrical charge accumulates on either side. Gates are portions of protein channels that allow the cell to control movement of these ions in response to various stimuli.
Graded and Action Potentials rely on 4 types of ion channels :
1. Leakage Channels:
Alternate between open and closed randomly. There are more K+ leakage channels than Na+ and the K+ are leakier. Therefore, the membranes permeability to K+ is much higher.
2. Ligand-Gated Channel
Opens and closes in response to chemical stimulus such as neurotransmitters, hormones, and particular ions. Ex: ACh
3. Mechanically Gated Channel
Opens and closes in response to mechanical stimulation such as vibration, touch, pressure, or tissue stretching. Ex: auditory receptors in the ears, receptors on the skin.
4. Voltage-Gated Channel
Opens in response to membrane potential (voltage).
Graded Potential vs. Action Potential
Graded Potentials
A graded potential is a small, localized deviation in the membrane potential that makes the membrane either more polarized (inside more negative) called Hyperpolarizing Graded Potential , or less polarized (inside less negative) called Depolarizing Graded Potential .
153
Made with FlippingBook Publishing Software