SEC.B-01-M03-07 Human Nervous System: Impulse conduction in the Neuron (Electrical)

1 The Neuron is Electrically Charged
1. Potential Difference
  1. Positive and negative ions
  2. Fluid inside and outside the neuron is "potentially different"
2 Resting membrane potential
1. Resting membrane potential is a condition of readiness to fire in the neuron
2. Negative inside and positive outside the neuron
  1. Caused by movement of ions from a high concentration to a low consentration
  2. Caused by ions of similar charges attract each other an move away from the opposite charged ions
3. The neuron membrane contains mechanisms that allow some ions through and prohbits others
  1. Sodium ions are positive
    1. High concentration of sodium ions outside the neuron membrane creates a positive electrical charge
  2. Proteins and nucleic acid are negative
    1. More negative charged molecules inside the neuron, makes neuron negatively charged
4. When the neuron is inactive but polarised, and readyto receive electrical impulses
3 Action Potential
1. 1 Soma receives stimuli from synaptic connections with other neurons
2. 2 Stimuli comes in the form of changing potentials across the soma's membrane
3. 3 These changing membrane potentials propagete towards the axon hillock where the are summed
4. 4 When the total potential reaches a particular level in the axon hillock, an action potential is triggered in the axon
5. 5 the axon must have a resting membrane potential for an action potential to be triggered
6. 6 the summed potential in the axon hillock must exceed the resting potential by a particulal amount (threshold)
  1. Threshold
    1. Action potential is triggered only when the summed potential in the axon hillock reaches the treshold potential
    2. The threshold potential is more than the axon's resting membrane potential
7. 7 The action potential is triggered because the axon is at a resting membrane potential
8. 8 When the action potential is triggered the membrane becomes permeable to sodium ions
9. 9 Sodium ions rushes into the axon by moving from a high sodium concentration on the outside of the neuron to the low sodium concentration on the inside
10. 10 The influx of positively charged sodium ions means the neuron becomes less negative on the inside and causes the charges on the in and outside to even out
11. 11 The membrane is now depoolarised (there is no potential difference between the inside and the outside of the neuron)
12. 12 When the membrane is depolarised the influx of sodium ions stops when the inside is slightly ore poitive than the outside
13. 13 When the inside is slightly more positive than the outside the membrane ceases to be permeable to sodium ions but now becomes permeable to potassium
14. 14 The positively charged potassium ions move from the high concentration on the inside of the axon to the low concentration on the outside
15. 15 When the potassium moves out of the axon the outside becomes positive again because it gains positive ions
16. 16 When the potassium move out of the axon the inside becomes negative because it loses positive ions
17. 17 The movement continues untill there are more potassium ions on the outside than the sodium on the inside (hyperpolarised)
18. 18 While hyperpolarized, the neuron is in a refractory period
19. During the refractory period the membrane returns the potassium and sodium ions to their original state
20. The sodium is pumped to the outside of the neuron and the potassium back inside
21. Absolute refractory period is during the beginning of the refractory period when the neuron does not respond to any stimulus
  1. The axon cannot conduct an impulse during the absolute refractory period
22. The absolute refractory period ends when most of the sodium and potassium have been returned to the outside and inside respectively
23. Relative refractory period is when the sodium and potassium returns to the outside and inside respectively
  1. A very intense stimulus can trigger an mpulse
24. Polarised resting phase with a restored membrane potential. Sodium outside and potassium inside
25. The neuron stays in the resting phse until another action potential is triggered at the axon hillock
4 Characteristics of impulse conduction
1. All or nothing law affplies
2. Relation between stimmulus and impulse frequency
3. axon insulation effects conduction
Neurons and Impulse Conduction
1. Electrical impulse conduction
  1. Begins in the first segment of the AXON down the length of the axon to the terminals due to electrical events
2. Chemical impulse conduction
  1. The passage of the nerve impulse from one neuron to another

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SEC.B-01-M03-07 Human Nervous System: Impulse conduction in the Neuron (Electrical)

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	Created by Ria Georgiou over 8 years ago