The Resting (Polarized) Membrane

1. The Resting (Polarized) Membrane • Potassium Pumps pull K+ ions into the cell • Sodium Pumps push Na+ ions out of the cell • Potassium diffuses out through potassium channels • more rapidly than • Sodium diffuses in through sodium channels • i.e. membrane is more permeable to K+ than to Na+ • More positive ions outside the cell than inside means • outside is positive relative to inside • this results in a • Resting potential of -70 mV (milliVolts)

2. Depolarization Sodium (Na+) channels open while Potassium (K+) channels close Membrane becomes more permeable to Na+ than to K+ Sodium ions enter the neuron by diffusion and charge attraction Charge reversal occurs: inside of cell is now positive relative to outside Charge is now +40 mV (milliVolts)

3. Repolarization Sodium (Na+) channels close while Potassium (K+) channels open Membrane is once again more permeable to K+ than to Na+ Potassium again diffuses out through potassium channels more rapidly than Sodium diffuses in through sodium channels Potassium Pumps pull K+ ions into the cell Sodium Pumps push Na+ ions out of the cell Membrane potential returns to resting level of -70 mV

4. Nerve Conduction • Stimulus happens at dendrites and starts action potential process • Axons that transport the electrical signals can be very long or very small • Many, many of these going on at once, happens to the same neuron very quickly after refractory period

5. Nerve Conduction - Intensity • Considering all or none response, how do we perceive intensity??? • 1) Frequency of nerve impulse • Higher frequency = brain interprets as a more intense stimulus • 2) Summation • Intense stimulus from our receptors can cause more than one neuron to reach threshold level and create action potential

6. Synapse - Basics • A Synapse is the region between neurons (synaptic cleft) • Very small space but is still there

7. Synapse - Basics • Not for all neurons, some are connected • Single neuron may branch many times • Neuron --------- • May be a synapse between many neurons at the end of one (rarely only between 2 neurons)

8. Synapse - Process • Small vesicles containing transmitter chemicals are in endplates of axons • Impulse moves along the axon and chemicals are released by the endplates • Chemicals diffuse across the synapse and starts depolarization on that neuron and continues (post-synaptic neuron)

9. Synapse - Process • When there is a synapse, the electrical transmission of energy is slowed • The greater the number of synapse between the stimulus and the brain, the longer it takes to get there • Reflex’s have very few synapses

10. Transmitter Chemicals • Acetylcholine • typical transmitter chemical found in end plates • makes the postsynaptic membranes more permeable to Na+ • Cholinesterase • enzyme released from end plate of neurons shortly after acetylcholine • breaks down acetylcholine, neuron can recover

11. Transmitter Chemicals • Acetylcholine can be an excitatory or a inhibitory transmitter chemical • Excitatory ones allow impulse to travel • Inhibitory ones prevent post-synaptic neurons from becoming active (important process)

12. Transmitter Chemicals • The interaction of excitatory and inhibitory chemicals is what allows you to throw a ball • Triceps receives excitatory and contracts • Biceps receives inhibitory and relaxes

13. Transmitter Chemicals & Disorders • Inhibitory impulses in your CNS (brain) • Sensory concentrated on teacher • Not temperature or clothes, etc. • Disorders related to transmitter chemicals • Parkinson’s disease • Involuntary muscle contraction • Alzheimer’s disease • Deterioration of memory and processing • Decreased production of acetylcholine