← Back to Session

Time Completed: 01:08:33

Final Score 46%

83
97

Questions

  • Q1. Correct
  • Q2. X Incorrect
  • Q3. Correct
  • Q4. Correct
  • Q5. X Incorrect
  • Q6. Correct
  • Q7. X Incorrect
  • Q8. Correct
  • Q9. X Incorrect
  • Q10. Correct
  • Q11. Correct
  • Q12. Correct
  • Q13. Correct
  • Q14. Correct
  • Q15. X Incorrect
  • Q16. X Incorrect
  • Q17. Correct
  • Q18. X Incorrect
  • Q19. Correct
  • Q20. X Incorrect
  • Q21. X Incorrect
  • Q22. Correct
  • Q23. Correct
  • Q24. X Incorrect
  • Q25. Correct
  • Q26. Correct
  • Q27. Correct
  • Q28. X Incorrect
  • Q29. X Incorrect
  • Q30. X Incorrect
  • Q31. Correct
  • Q32. X Incorrect
  • Q33. X Incorrect
  • Q34. Correct
  • Q35. X Incorrect
  • Q36. X Incorrect
  • Q37. Correct
  • Q38. X Incorrect
  • Q39. X Incorrect
  • Q40. X Incorrect
  • Q41. Correct
  • Q42. X Incorrect
  • Q43. Correct
  • Q44. X Incorrect
  • Q45. Correct
  • Q46. X Incorrect
  • Q47. X Incorrect
  • Q48. X Incorrect
  • Q49. X Incorrect
  • Q50. Correct
  • Q51. Correct
  • Q52. Correct
  • Q53. Correct
  • Q54. Correct
  • Q55. X Incorrect
  • Q56. Correct
  • Q57. Correct
  • Q58. X Incorrect
  • Q59. Correct
  • Q60. Correct
  • Q61. X Incorrect
  • Q62. X Incorrect
  • Q63. X Incorrect
  • Q64. X Incorrect
  • Q65. X Incorrect
  • Q66. X Incorrect
  • Q67. Correct
  • Q68. X Incorrect
  • Q69. Correct
  • Q70. X Incorrect
  • Q71. Correct
  • Q72. Correct
  • Q73. X Incorrect
  • Q74. Correct
  • Q75. X Incorrect
  • Q76. X Incorrect
  • Q77. Correct
  • Q78. Correct
  • Q79. X Incorrect
  • Q80. X Incorrect
  • Q81. Correct
  • Q82. X Incorrect
  • Q83. X Incorrect
  • Q84. Correct
  • Q85. X Incorrect
  • Q86. X Incorrect
  • Q87. Correct
  • Q88. X Incorrect
  • Q89. Correct
  • Q90. Correct
  • Q91. X Incorrect
  • Q92. Correct
  • Q93. X Incorrect
  • Q94. X Incorrect
  • Q95. X Incorrect
  • Q96. Correct
  • Q97. X Incorrect
  • Q98. Correct
  • Q99. X Incorrect
  • Q100. Correct
  • Q101. X Incorrect
  • Q102. Correct
  • Q103. X Incorrect
  • Q104. X Incorrect
  • Q105. X Incorrect
  • Q106. X Incorrect
  • Q107. Correct
  • Q108. X Incorrect
  • Q109. Correct
  • Q110. X Incorrect
  • Q111. X Incorrect
  • Q112. Correct
  • Q113. X Incorrect
  • Q114. Correct
  • Q115. Correct
  • Q116. Correct
  • Q117. X Incorrect
  • Q118. Correct
  • Q119. X Incorrect
  • Q120. Correct
  • Q121. Correct
  • Q122. Correct
  • Q123. Correct
  • Q124. Correct
  • Q125. X Incorrect
  • Q126. Correct
  • Q127. X Incorrect
  • Q128. X Incorrect
  • Q129. Correct
  • Q130. Correct
  • Q131. X Incorrect
  • Q132. X Incorrect
  • Q133. X Incorrect
  • Q134. X Incorrect
  • Q135. X Incorrect
  • Q136. Correct
  • Q137. Correct
  • Q138. X Incorrect
  • Q139. X Incorrect
  • Q140. Correct
  • Q141. Correct
  • Q142. X Incorrect
  • Q143. Correct
  • Q144. X Incorrect
  • Q145. X Incorrect
  • Q146. X Incorrect
  • Q147. X Incorrect
  • Q148. X Incorrect
  • Q149. X Incorrect
  • Q150. Correct
  • Q151. X Incorrect
  • Q152. X Incorrect
  • Q153. Correct
  • Q154. X Incorrect
  • Q155. X Incorrect
  • Q156. X Incorrect
  • Q157. Correct
  • Q158. Correct
  • Q159. X Incorrect
  • Q160. X Incorrect
  • Q161. Correct
  • Q162. X Incorrect
  • Q163. X Incorrect
  • Q164. Correct
  • Q165. X Incorrect
  • Q166. X Incorrect
  • Q167. Correct
  • Q168. Correct
  • Q169. X Incorrect
  • Q170. X Incorrect
  • Q171. Correct
  • Q172. Correct
  • Q173. Correct
  • Q174. X Incorrect
  • Q175. Correct
  • Q176. Correct
  • Q177. Correct
  • Q178. X Incorrect
  • Q179. X Incorrect
  • Q180. X Incorrect

Physiology

Basic Cellular

Question 99 of 180

Which of the following creates the intial graded depolarisation moving the membrane potential of a neurone towards threshold potential:

Answer:

Action potentials are initiated in nerves by activation of ligand-gated Na+ channels by neurotransmitters. Opening of these Na+ channels results in a small influx of sodium and depolarisation of the negative resting membrane potential (-70 mV). If the stimulus is sufficiently strong, the resting membrane depolarises enough to reach threshold potential (generally around -55 mV), at which point an action potential can occur.

Generation of Action Potentials

Once triggered an action potential will travel over the entire surface of an excitable cell and will always have the same amplitude. An action potential is an all or nothing response; because the size of the action potential is constant, the intensity of the stimulus is coded by the frequency of firing of a neuron.

Threshold Potential

Action potentials are initiated in nerves by activation of ligand-gated Na+ channels by neurotransmitters. Opening of these Na+ channels results in a small influx of sodium and depolarisation of the negative resting membrane potential (-70 mV).

If the stimulus is sufficiently strong, the resting membrane depolarises enough to reach threshold potential (generally around -55 mV), at which point an action potential can occur.

Depolarisation

Voltage-gated Na+ channels open, causing further depolarisation and activating more voltage-gated Na+ channels and there is a sudden and massive sodium influx, driving the cell membrane potential to about +40 mV.

Repolarisation

The spike of the action potential is transient because as the membrane potential becomes positive, the voltage-gated Na+ channels inactivate preventing further sodium influx.

Voltage-gated K+ channels are also activated, causing the K+ permeability to again be much greater than that for Na+, and the potassium efflux leads to repolarisation.

Delayed closure of these rectifier K+ channels causes a transient hyperpolarisation.

Refractory Period

Following the action potential, Na+ channels remain inactive for a time in a period known as the absolute refractory period where they cannot be opened by any amount of depolarisation.

Following this there is a relative refractory period where the temporary hyperpolarisation makes the cell more difficult to depolarise and an action potential can be generated only in response to a larger than normal stimulus.

The refractory period limits the frequency at which action potentials can be generated, and ensures that, once initiated, an action potential can travel only in one direction.

By Original by en:User:Chris 73, updated by en:User:Diberri, converted to SVG by tiZom (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 , via Wikimedia Commons

Action Potential. (Image by Unknown. [CC-BY-SA-3.0 , via Wikimedia Commons)

Report A Problem

Is there something wrong with this question? Let us know and we’ll fix it as soon as possible.

Loading Form...

Close
  • Biochemistry
  • Blood Gases
  • Haematology
Biochemistry Normal Value
Sodium 135 – 145 mmol/l
Potassium 3.0 – 4.5 mmol/l
Urea 2.5 – 7.5 mmol/l
Glucose 3.5 – 5.0 mmol/l
Creatinine 35 – 135 μmol/l
Alanine Aminotransferase (ALT) 5 – 35 U/l
Gamma-glutamyl Transferase (GGT) < 65 U/l
Alkaline Phosphatase (ALP) 30 – 135 U/l
Aspartate Aminotransferase (AST) < 40 U/l
Total Protein 60 – 80 g/l
Albumin 35 – 50 g/l
Globulin 2.4 – 3.5 g/dl
Amylase < 70 U/l
Total Bilirubin 3 – 17 μmol/l
Calcium 2.1 – 2.5 mmol/l
Chloride 95 – 105 mmol/l
Phosphate 0.8 – 1.4 mmol/l
Haematology Normal Value
Haemoglobin 11.5 – 16.6 g/dl
White Blood Cells 4.0 – 11.0 x 109/l
Platelets 150 – 450 x 109/l
MCV 80 – 96 fl
MCHC 32 – 36 g/dl
Neutrophils 2.0 – 7.5 x 109/l
Lymphocytes 1.5 – 4.0 x 109/l
Monocytes 0.3 – 1.0 x 109/l
Eosinophils 0.1 – 0.5 x 109/l
Basophils < 0.2 x 109/l
Reticulocytes < 2%
Haematocrit 0.35 – 0.49
Red Cell Distribution Width 11 – 15%
Blood Gases Normal Value
pH 7.35 – 7.45
pO2 11 – 14 kPa
pCO2 4.5 – 6.0 kPa
Base Excess -2 – +2 mmol/l
Bicarbonate 24 – 30 mmol/l
Lactate < 2 mmol/l

Join our Newsletter

Stay updated with free revision resources and exclusive discounts

©2017 - 2024 MRCEM Success