2. Neurolemma – outer covering of axons
Polarized membrane – diff electrical charge in/out of membrane – resting membrane potential
Depolarized membrane – same elec. charge in/out of membrane
Ion channels – regulate movement across the plasma membrane

5. Resting Membrane Potential [RMP]
Conditions that constitute Resting Membrane Potential :
1. At rest – 10x as many sodium ions outside than inside (reverse for potassium)
Accomplished by Na-K pump (needs energy – ATP)
2. For every 3 Na ions out, 2 K ions are pumped in
3. Membrane is more permeable to K, so some K leaks back out
4. Chloride ions are inside the membrane (negative)
#1-4 contribute a RMP of –70 mV (battery is 1.5 V – 1500x as great)

7. Action Potential
Stimulus causes a change in the permeability of membrane to Na which rushes inside.
The inside becomes more positive – depolarized increases to +30 mV
This takes 1/1000 of a second (1 millisecond)
After it peaks – there is a diffusion of K ions out – this is repolarization
NA/K pump then takes over to finally restore RMP

10. A strong stimulus produces more frequent impulses
Initiating Stimulus
Threshold stimulus--stimulus must be of minimum strength to initiate A.P.
–If stimulus is not strong enough – subthreshold stimulus
A series of subthreshold stim., if rapid enough can stimulate an A.P. – summation
 A strong stimulus produces more frequent impulses
Saltatory conduction – impulse jumps from Node of Ranvier to next Node of Ranvier (like stone skipping on water)
Faster than unmyel. - provides for faster reaction times
The speed of an impulse of myelinated fibers – 130 m/s (300 mph)
Unmyelinated – 10 m/s (23 mph)

14. Neurotransmitters
– chemical that transmits an impulse from one neuron to another (or a muscle cell)
excitatory – increase permeability to Na+ so it can flow inward faster
– acetylcholine; norepinephrine
inhibitory – no effect on Na+
- allows Cl- (in) and K+ (out)
becomes hyperpolarized – decreases the chance of an impulse being transferred
- endorphins, enkaphalins (pain-killers, naturally produced by the brain)