2. Nerve Impulses (action potentials) Synaptic Transmission
Line
Neurotrophins
Nerve Impulses (action potentials)
Synaptic Transmission

3. Type
Nerve growth factors (NGF)
2. Brain derived neurotrophic growth factor (BDGF)

4. Type
3. Ciliary Neurotrophic factor (CNTF)
Found in neurological cells/ astrocytes and Schwann cells
Potent protective action on dopaminergic neurons
Used for treatment of Parkinson’s disease
4. Fibroblast growth factors:
Promoting fibroblastic growth

5. Type 5. Glial cell line- derived neurotrophic factor (GDNF)
Maintains mid bran dopaminergic neurons
6. Leukemia inhibitory factors (LIF)
Enhances the growth of neurons
7. Insulin like growth factor I (IGF-I)
8. Transforming growth factor
9. Fibroblast growth factor
10. Platelet – derived growth factors

6. Nerve Impulses (action potentials)

7. NEUROLEMMA is the name of the plasma membrane (outermost covering) of a neuron.
DENDRITES function to receive the signal and carry the nerve conduction toward the cell body.
SOMA (cell body) is where the nucleus, ribosomes, and most organelles are located
AXON HILLOCK is the area on the soma where the action potential (electrical charges) of the neuron builds up before it transmits the signal down the axon.

8. Nerve Impulses (action potentials)
AXON function is to transmit signals. Some cells have more than one axon, some axons are short, and some are long.
AXON TERMINALS (also called boutons or synaptic knobs) contain a neurotransmitter which, when released, stimulates another cell.
A SYNAPSE is where one neuron touches another neuron. Neurons may have a couple of synapses, or hundreds.
AXOPLASMIC TRANSPORT: Movement of nutrients, wastes, and organelles between the cell body and axon terminals

9. Nerve Impulses (action potentials)
A nerve impulse (called an action potential) is typically generated at the axon hillock, and is conducted along the axon to the axon terminals, where it causes the release of neurotransmitters into the extracellular space.
These neurotransmitters excite or inhibit the dendrites of the adjacent neuron (or the target organ).

10. Structure of a Typical LargeNeuron
Figure 12.4 10

11. The Nerve Impulse The Resting Potential of the Neuron
Resting potential: results from a difference in distribution of various ions between the inside and outside of the cell
Why a Resting Potential?
Prepares neuron to respond rapidly to a stimulus

12. The Nerve Impulse
Neurons are the functional units of the nervous system.
What is the property that allows them to interact with each other?
Neurons are capable of signaling neurons communicate by sending electrical signals called Action Potentials .
Action Potentials are produced by the movement of ions in and out of the neuron, through the cell membrane.
= Ions are charged particles: Positive charges: cations
Negative charges: anions

13. The Nerve Impulse
What are the forces that move the ions across the cell membrane?
Ions move along gradients of potential energy. What is potential energy?
In the neuron, ions are moved by two forces (potential energy):
1-Concentration Gradients: difference in distribution for various ions
between the inside and outside of the membrane
2-Electrical Gradient: the difference in positive and negative charges
across the membrane

14. The Nerve Impulse
The cell membrane is a lipid bilayer which does not allow the passage of ions
However, the membrane has protein channels that allow the passage of ions
-Protein channels are very selective

15. The Nerve Impulse Concentration gradient
Due to Concentration gradient between inside and oustside the membrane, K+, Na+, A-, Cl- ions tend to go:
K+: OUT
A- : OUT (large ions, proteins, RNA, DNA, etc, cannot leave)
Na+: IN
Cl- : IN

16. The sodium and potassium gradients for a resting membrane .
The Nerve Impulse
 The sodium and potassium gradients for a resting membrane .

17. The Nerve Impulse What happens to Na+?
CONCENTRATION & ELECTRICAL GRADIENTS PUSH NA+ IN !!
What happens if Na+ channels open? AN ACTION POTENTIAL !
Momentary reversal of potential: positive inside, negative outside
Na+ cannels closed Na+ channels open
Outside
membrane____________________________________________________
Inside
Resting Potential Action potential
(-70 mV inside) (+50 mV inside)

18. The Nerve Impulse Important Definitions
Hyperpolarization: increasing the negative charge inside the neuron
Depolarization: decreasing the negative charge inside the neuron
Threshold of excitation: Level above which a stimulation produces a sudden depolarization of the membrane
Action Potential: rapid depolarization and slight reversal of the usual polarization

19. Molecular Basis of the Action Potential
Sodium channels open once threshold is reached causing an influx of sodium: depolarization to +50 mv
Potassium channels open as the action potential approaches its peak allowing potassium to flow out of the cell: hyperpolarization to -70mv.

20. Refractory Periods
The Refractory Period: after an action potential, the neuron resists the production of further action potentials
Two Refractory Periods
1. Absolute Refractory Period (1-2 msec)
The sodium gates are firmly closed
The membrane cannot produce an action potential, regardless of the stimulation.
-Limits the maximum firing frequency: 1000/sec
-Action potential cannot reverse direction
2. Relative Refractory Period
A stronger than normal stimulus can result in an action potential.

21. Refractory Periods Absolute Refractory Period threshold
+40 mV
-60 mV
-70 mV
Absolute Refractory Period
threshold
Relative Refractory Period

22. Properties of the Action Potential
1-Is an “all or none” event: membrane potential either passes threshold or doesn’t
2-Is propagated down the axon membrane
Notion of successive patches of membrane
3- Has a fixed amplitude: AP’s don’t change in height to signal information (nondegremental)
4- Has a conduction velocity (meters/sec)
5-Has a refractory period in which stimulation will not produce an AP (limits the firing rate)

23. Na+ Na+ Na+ Direction of impulse Resting potential Depolarization23
Na+
Na+
Na+
Resting potential
Depolarization
Repolarization
Na+ enters and K+ leaves, so outside of membrane becomes negative charge. This is depolarization
When stimulus is over, Na+ leaves and K+ lenters the cell, so outside of membrane returns to positive charge. This is repolarization
Outside of membrane is positive charge at resting potential.
Direction of impulse

24. What would happen to the membrane potential of the cell when you open up a sodium channel?
If we instantly increase sodium permeability, sodium will enter the cell, changing the charge of the inside of the cell so that it goes from negative to positive. The outside layer of the cell membrane would then go from positive to negative . This is called DEPOLARIZATION.
However, when this occurs, Na+ will be in higher concentration on the inside of the cell, so it wants to diffuse back out of the cell.
Once it leaves the cell again, the membrane potential of the inside of the cell membrane will return to a negative charge. This is called REPOLARIZATION.

25. Spread of Depolarization

26. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 26
Direction of Depol
Resting Cell

27. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 27
Direction of Depol
Sodium channels open

28. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 28
Direction of Depol

29. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 29
Direction of Depol +

30. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 30
Direction of Depol + + +

31. - - - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 31
Direction of Depol

32. - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + + 32
Direction of Depol

33. - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + +33
Direction of Depol

34. 34
Direction of Depol

35. + + + + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - -35
Direction of Depol

36. + + + + + + + + + + + + + + + + + + + + + + + + - - - - - - - - -36
Direction of Depol

37. + + + + + + + + + + + + + + + + + + + + + + + + + + + + - - -37
Direction of Depol

38. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +38
Direction of Depol

39. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +39
Direction of Depol

40. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +40
Direction of Depol
Depol = spread of surface NEG charge

41. Direction of Repolarization41
Direction of Repolarization
When Na+ is pumped back out, Repolarization begins

42. Direction of Repolarization42
Direction of Repolarization
- - -

43. Direction of Repolarization43
Direction of Repolarization

44. Direction of Repolarization44
Direction of Repolarization

45. Direction of Repolarization45
Direction of Repolarization

46. Direction of Repolarization46
Direction of Repolarization
Repolarization= spread of positive surface charge

47. Direction of Repolarization47
Direction of Repolarization

48. Direction of Repolarization48
Direction of Repolarization

49. ACTION POTENTIAL
The action potential occurs when the membrane potential (how negatively charged the inside of the cell is) reaches a certain threshold.
When the Na+ rushes into the cell, the membrane potential becomes less and less negative. Eventually, it reaches zero charge, and as more Na+ enters the cell, the inside of the cell becomes positively charged.
When it becomes positively charged enough (+30 mV), an action potential will sweep down the length of the cell membrane, like a wave of electricity. This is how one neuron stimulates a cell (a muscle cell, gland, or another neuron).
If the neuron stimulates a muscle cell, it contracts. If it stimulates a gland, it secretes. If it stimulates another neuron, the action potential is carried further along the nerve pathway, until it reaches the target organ.

50. ACTION POTENTIAL
Healthy kidneys clean the blood and remove excess potassium so that the level of potassium in the blood remains within a very narrow range.
If potassium levels get too high, nerves begin to misfire.
This can cause irregular heartbeats and even heart attacks.
If a patient's potassium levels rise above 5.0 mg/dl, the nephrologist often suggests that he limit his potassium intake to prevent nerve problems.
Lethal injections are potassium.

51. The All-or-None Law
The size of an action potential (120 mv) and its speed are independent of the intensity of the stimulus that initiated it.

52. Overview of Neural Impulse

53. Fun Fact
Children under 3 years of age have twice as many synapses as adults. That is why they learn languages better.