Lecture 17 ECEN5341/4341

February 21, 2014

Nerve Cells

• 1. Neurons, carry information• 2. Glia Cells support functions of insolation

and clean up of unwanted materials•

A Neuron

Electrical Signal In the Body

• 1. Nerves and Action Potentials• 2. Activate Mussels • 3. Effect Growth Processes. • 4. Involved in Memory

• 1

Cell Membrane Cartoon

Cell Membranes

• 1 Classical nerve cell– Na+

outside =142mEq/L 1gr/dL=2.5mEq/L

– Na+inside = 14 mEq/L

– K+outside =4 mEq/L

– K+inside = 140 mEq/L

– Cl-outside = 103 mEq/L

– Cl-inside = 4mEq/L

– Enzymes also negative on the inside

Diffusion Potential

• 1. Basic equation

2. For J=0 xCqDECqJ k

kk

kin

koutTm C

CVV lnqkTVT

mVVm 90

Active Pumps to Maintain Concentration Differences

• 1. Na+ , K+ pumps• 2. Many other pumps for 80 substances?– Ca2+,Fe,I, Cl, Urate,sugars and amino acids

• 3. All require energy. • 4. These all require protein channels.• 5. Co-transport of molecules say Na +Glucose

into the cell.

Na+ , K+ Concentration Gradients

Relative Permeability of Membrane

Action Potential

• 1Trigered by• influx of Na+ as• summed by the • inputs from the • dendrites at • the cell body

• 2. Terminated by• Outflow of K+

Na+ Gate

Channels

Current Pulses

Action Potential

• 1 Propagates at constant • Amplitude for up to 3m• at speeds up to 100m/s• 2.Repeated and amplified • at the nodes of Ranvier

Synaptic Junction Output Neurotransmitters

A Different Approach to Cell Structure and the Function of Membranes.

• 1. Reference • Cells, Gels and the Engines of Life by Gerald H.

Pollack Published by Ebner and Sons Seattle Washington. 2001

• 2 On the Web Human Physiology - Cell structure and function for some good pictures and standard model with channels for Na , K

Outline of Material

• 1. Problems with the current model for cells• 2. Some properties water , H2O, Solutes , Ions

and cell potential• 3. Properties of Gels and Cytoplasm ,• 4. Phase Transitions a Mechanism for Action• 5. Action potentials.

Some Problems.

• 1. Not enough energy for all the pumps.• 2. Need 50 or more types of channels and

pumps• 2. the concentration ratios and voltages are

still there when the membrane is removed. • 3. You can still get an action potential to

propagate along a nerve cell with no Na or K if you have enough Ca.