1. Resting Membrane Potential
Nervous System Part 1
Organization
Resting Membrane Potential
Signaling
Graded Potentials
Action Potentials

2. Organization
Control System that receives info about internal and external environment, integrates, and directs activities to respond.
Divided into the CNS and the PNS.

3. Organization Consists of 2 classes of cells:
Neurons (20%) – communication
Neuroglia (80%) – many fnctns: structurally supporting, nurturing, insulating, & protecting neutons
Nerves – Bundles of neurons in the PNS

4. Organization 3 types on neurons: Afferent (sensory) neurons
Interneurons
Efferent (motor) neurons

5. Organization
Main parts of a neuron:

6. Resting Membrane Potential
A charge difference across the membrane of -70mV at rest.
Has the potential to do work.
K+ and Na + leak channels in the cell membranes establish electrochemical gradients.

7. Resting Membrane Potential

8. Resting Membrane Potential
If the cell only had K + channels the equilibrium potential of the cell would be –90mV.

9. Resting Membrane Potential
If the cell only had Na+ channels the equilibrium potential of the cell would be 60mV.

10. Resting Membrane Potential
There are more K+ leak channels so Vm is closer to EK than ENa.

11. Resting Membrane Potential
Active transport Na+/K+ pumps maintain the ion concentrations as seen in table 6-2.

12. Signaling
Changes in a cell’s membrane potential produce electrical signals.
Graded potentials – signaling over short distances.
Action potentials – signaling over long distances
Terms for the direction
of changes relative to resting potential are seen to the right.

13. Graded Potentials
Changes in membrane potential confined to a small region of a neuron.
They are graded, meaning they can vary in magnitude.

14. Action Potentials
If the minimum threshold voltage is reached, a graded potential becomes an action potential.

15. Action Potentials
Voltage-gated sodium and potassium channels are responsible for the depolarization and repolarization of the membrane.

16. Action Potentials

17. Action Potentials Always an all-or-nothing event.
Propagates away from a neuron’s trigger zone.

18. Nervous System Part 1 (cont.)
Action Potentials Review
Synapse

19. Action Potentials Review‘

20. Action Potentials Review
A typical neuron would have a resting membrane potential of about
(A) +70 mV
(B) +70 V
(C) -70 mV
(D) -70 V
(E) All of the above are observed at rest.

21. Action Potentials Review
At the peak of the action potential, the membrane potential is:
(A) exactly at the Na+ equilibrium potential
(B) close to but more positive than the Na+ equilibrium potential
(C) close to but less positive than the Na+ equilibrium potential
(D) exactly at 0 mV
(E) the same as the resting membrane potential

22. Action Potentials Review
True or False: Threshold voltage for opening is approximately the same for voltage-gated Na+ and K+ channels.
Voltage-gated Na+ and K+ channels open at the approximately the same threshold voltage… K+ channels are just much more slower at opening wide and closing completely than Na+ channels.

23. Action Potentials Review
Schwann cells are glia cells that that for the myelin sheath.
They insulate the axons of neurons and increase the rate of action potential propagation.

24. Synapse Synapse: the narrow gap b/w 1 neuron & the next.
Neurotransmitter: the chemicals that cross the synapse

25. Synapse

26. Synapse Response by postsynaptic cell depends on:
Type of neurotransmitter
Conc. of neurotransmitter
Type of receptor
Number of receptors
Responsiveness of the receptors

27. Synapse Many axon terminals synapse onto one neuron.
Excitatory and inhibitory signals are integrated
All synaptic potentials are graded potentials

28. Synapse EPSP: excitatory post-synaptic potentials; depolarization
IPSP: inhibitory post-synaptic potentials; hyperpolarizing
When threshold is reached an action potential is fired down the post-synaptic neuron.

29. Synapse
Neurotransmitters need to be removed ASAP after signal is complete.
Many helpers:
Diffusion
Enzymes
Protein pumps