Unit 2: Lecture 11: Neurophysiology Pt 2

Graded Potentials

temporary, short lived localized change in the RMP

Caused By Stimulus

Localized= does not travel far from site

Goal: Axon Hillock reaches threshold at -60 mv to fire AP

Strength varies in magnitude depending on stimulus

Local Potentials

Neurons stimulating another neuron

ligand/ions bind to a chemical regulated channel

Physical shape changes in a mechanical gated channel

small local disturbances in MP

Characteristics of a Local Potential

Graded

Decremental

Reversible

Excitatory/Inhibitory

Graded

Strength varies in magnitude depending on stimulus

open more channels

length of opening

Decremental

Signal weakens the further it travels

Distal from the axon hillock as it works towards the axon hillock

Reversible

Removal of signal can restore RMP

Excitatory/Inhibitory

Open Na+ channels will EXCITE; Depolarize

Open K+ channels will INHIBIT; Hyperpolarize

Depolarization

Na+ moves into the cell

Raises MP to approx -60 mv

Makes cell more (+)

Steps for Depolarization

1. 1. Na+ gated channels open due to stimulus

2. 2. Flow of Na+ ions enter cell and causes MP to increase since gate is open

3. 3. Na+ gated channels close once stimulus is removed

4. 4. Na+/K+ ATPase pumps Na+ out of the cell causing MP to decrease

5. 5. RMP is established due to Repolarization

Hyperpolarization

K+ moves out of the cell

Lowers MP to approx -80mv

Makes Cell more (-)

Steps of Hyperpolarization

1. 1. K+ gated channels open due to stimulus

2. 2. Flow of K+ ions leave the cell and causes MP to decrease since gate is open

3. 3. K+ gated channels close once stimulus is removed

4. 4. Cells work on chemical and electrical gradient by letting K+ enter the cell causing MP to increase

5. 5. RMP is established due to Repolarization