• Electrical signals
• Chemical signals 

• Loud
• Quiet 

• It is loud by allowing uneven distrubiton of Ions.
• When they are congregated on one side, it is a clear signal that this neuron is sending an excitatory signal.

• The neuron unevenly distributes the Ions in opposited way as during excited period.
• The uneven distribution of Ions during the resting potenial creats a sepration of charge and concentration which is the electrochemical basis for the potential.  

• ICF has lower concentration of Na+ and Cl- than ECF
• ICF has higher concentration of K+ and negatively charged proteins (A-) than ECF 

• Impermeable to A-
• Slightly permeable to Na+ (through leakage channels)
• 75 times more permeable to K+ (more leakage channels)
• Freely permeable to Cl- 

• Negative interior of the cell is due to much greater diffusion of K+ out of the cell than Na+ diffusion into the cell and (A-) inside the cell
• Sodium-potassium pump stabilizes the resting membrane potential by maintaining the concentration gradients of Na+ and K+ 

• Opposite charges attract
• Energy is required to separate opposite charges across a membrane
• Energy is liberated when the charges move toward on another
• If opposite charges are separated, the system has potential energy.  

• An excitatory NT interacts with its receptors
• Causes a Na+ channel to open, Na+ rushes in (gradient potential)
• Inside of the cell becomes less negative, becomes somewhat depolarized
• Over time the channel will close 

• Occur when a stimulus causes gated ion channels to open
•  -Receptor potentials, postsynaptic potentials
• Magnitude varies directly (graded) with stimulus stregnth
• Short-distance signals along dendrite/soma 

• Ligand-gated channels beginning in the axon hillock, there are also voltage-gated channels
• Opens if the local enviroment becomes depolarized past certian threshold
• If the graded potential, that ripple of depolarization caused by excitation at the dendrites/soma is big enough, it will depolarize the area around the axon hillock past threshold
• Channels opens, sodium rushes in 

Chemical Gated Channels

(Ligand-Gate Channels)

• Ions diffuse quickly across the membrane along their electrochemical gradients
• Along chemical concentration gradients from higher concentration to lower concentration 

When Gated Channels Open

Electrochemical Gradient

• Along electrical gradients toward opposite electrical charge.
• Both driving it through the cell
• Ion flow creates an electrical current and voltage changes across the membrane 

• An important feature of this AP is that once threshold of depolarization is passed for opening the first voltage-gated Na+ channel, it does not matter how much it passed, you still generate the same size AP
• All or nothing property of the axonal action potential 

• No single dendrites getting depolarized by an excitatory NT is going to make enough of a ripple to reach the axon hillock
• Its either lots of dendrites getting depolarized all at once
• Or a few of them getting depolarized over and over again 

• Only Leakage channels for Na+ and K+
• All gated channels are closed.

1. Depolarizing local currents open voltage-gated Na+ channels
2. Na+ influx causes more depolarization
3. At threshold (-55mV) positive feedback leads to opening of all Na+ channels, and a reversal of membrane polarity to +30mV(spike of action potenial, Action Potential) 

• Membrane is depolarized by 15 to 20mV
• Na+ permeability increases
• Na influx exceeds K+ efflux
• The positive feedback cycle begins (results in AP) 

• No
• Subthreshold stimulus- weak local depolarized that does not reach threshold
• AP is an all-or-none Phenomenon- action potential either happen completely, or not at all 

• Na+ channel gates close
• Membrane permeability to Na+ declines to resting levels
• Voltage-sensitive K+ gates open
• K+ exits the cell and internal negativity is restored 

• Restores the resting electrical conditions of the neuron
• Does not restore the resting ionic conditions
• Ionic redistribution back to resting conditions is restored by thousands of sodium-potassium pumps

• Time from the opening of the Na+ channels until the restting of the channels
• Ensures that each AP is an all-or-none event
• Enforces one-way transmission of impulses