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Nervous System Cheat Sheet (DRAFT) by

Nervous System Cheat Sheet

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Defini­tions

Diffusion
The process of movement of molecules under a concen­tration gradient
Electrical gradient
An electr­ostatic force caused by the separation of electrical charge
Membrane potential
A separation of opposite charges across the plasma membrane
Action Potential
Brief all or nothing reversal in membrane potential, lasting on the order of 1 millis­econd
Propag­ation
Action potentials propagate when locally generated depola­rizing current spreads to adjacent regions of membrane causing it to depolarize
Contiguous Conduction
Propag­ation of action potentials in unmyel­inated fibers by spread of locally generated depola­rizing current to adjacent regions of membrane, causing it to depolarize
Myelin
A multil­ayered sheath of plasma membrane that wraps around axonal fibers and acts as an insulator to the flow of current
Saltatory Conduction
Propag­ation of action potentials in myelinated axons by jumping from node to node
Graded Potentials
Local changes in membrane potential that decay over short distance
Synapse
Junction between two neurons, or between a neuron and a muscle or gland that enables one cell to electr­ically and/or bioche­mically influence another cell
Electrical Synpase
Direct electrical connection between two cells, formed by a gap junction
Gap Junctions
made up of multiple proteins called connexins
 

Diffusion and Gradients

Diffusion is the process of movement of molecules under a concen­tration gradient.
There are five factors that affect the rate of diffusion: magnitude of the concen­tration gradient, permea­bility of the membrane, surface area of the membrane, molecular weight of the substance, and distance over which diffusion takes place
Concen­tration gradients are formed when there is a difference in concen­tration in two different areas; molecules typically move from an area of greater concen­tration to an area of lesser concen­tra­tion. Net diffusion is the difference between two opposing movements.
An electrical gradient is when electr­ostatic forces are caused by the separation of electrical charges.
An electr­och­emical gradient is the combined force of concen­tration and electrical gradients

Membrane Potential

A membrane potential (Vm) is a separation of opposite charges across the plasma membrane. The cell creates this charge separation when it: 1) establ­ishes and maintains concen­tration gradients for key ions 2) Ions diffuse through the membrane down their concen­tration gradient 3) Diffusion through the membrane results in charge separa­tion, creating a membrane potential 4) Net diffusion continues unti lthe force exerted by the electrical gradient exactly balances the force exerted by the concen­tration gradient 5) This potential that would exist at this equili­brium is "­equ­ili­brium potent­ial­"
Equili­brium Potential for K+
1. K+ Tends to move out of the cell 2. Outside of the cell becomes more positive 3. Electrical gradient tends to move K+ into the cell 4. Electrical gradient counte­rba­lances concen­tration gradient 5. No further net movement of K+ occurs 6. E(K+) = -90mV
Equili­brium Potential for Na+
1. Na+ tends to move into the cell 2. Inside of the cell becomes more positive 3. Electrical gradient tends to move Na+ out the cell 4. Electrical gradient counte­rba­lances concen­tration gradient 5. No further net movement of Na+ occurs 6. E(Na+)­=+60mV
Nernst equation
equation describing the equili­brium: Ei = RT/zF In [i]o/[i]i potential for a particular ion (i)
Resting Membrane Potential
Resting membrane potential is -70mV because: the membrane is 20-30 more permeable to K+ than Na+ and there is a large net diffusion of K+. It is created due to a balance of passive leak channels and active Na+/K+ ATPase.
Action Membrane Potential
Depola­riz­ation: change in membrane polari­zation to more positive values than rest. Repola­riz­ation: return to resting membrane potential after depola­riz­ation. Hyperp­ola­riz­ation: change in membrane polari­zation to more negative values than rest. There is a rising phase in which Na+ moves into the cell and the falling phase in which K+ leaves the cell with the help of voltag­e-gated Na+ or K+ channels.
 

Types of Channels

Leak Channels
Passive channels that permit ions to flow down concen­tration gradients
Na/K ATPase
Active channel that establ­ishes and maintains concen­tration gradients. It pumps 3 Na+ out of the cell for every 2 K+ pumped into the cell