The Nervous System
The nervous system has to deal effectively with information in 'real time'
how does it do this?
Break the problem down:
1. body detects stimulus (light, sound, touch, chemical, temperature, etc.)
2. sensory neuron translates this to something a cell would understand (a chemical/electrical
3. sends signal to Central Nervous System (CNS)
4. interneurons are used to filter, magnify, interpret, or ignore signal
5. CNS directs this modified signal through motor neurons to muscle cells, to endocrine cells (to
make hormones), etc.
Signal is one way. At axon terminus, it jumps to next cell
How does it work?
Axon membrane at rest has a negative membrane potential (-70)
FACT: diff. [ion] either side; more anions (-) inside
Voltmeter used to measure difference in charge between inside/outside of cell to determine membrane
dif. is maintained by Na+/K pump – for every three Na+ that leave cell, 5 K enter cell
Membrane resting potential = -70 mV
Neuron membrane setup:
-voltage-gated Na channel with 2 gates
--voltage-gated K channel
Na gate opens when membrane potential > -50 mV
Def: graded potential anywhere below -50 mV (& not at resting potential)
Fact: K gate opens when memb. pot. > +30 to +40 mV (approx.)
membrane repolarizes when K gates open
Starts when (enough) Na gates