← Back to Session

Time Completed: 01:07:02

Final Score 54%

98
82

Questions

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

Physiology

Cardiovascular

Question 51 of 180

In the ventricular myocyte action potential, depolarisation occurs through the opening of:

Answer:

An action potential (AP) is initiated when the myocyte is depolarised to a threshold potential of about -65 mV, as a result of transmission from an adjacent myocyte via gap junctions. Fast voltage-gated Na+ channels are activated and a Na+ influx depolarises the membrane rapidly to about +30 mV. This initial depolarisation is similar to that in nerve and skeletal muscle, and assists the transmission to the next myocyte.

Ventricular Myocyte Action Potential

The resting potential of ventricular myocytes is about -90 mV. An action potential (AP) is initiated when the myocyte is depolarised to a threshold potential of about -65 mV, as a result of transmission from an adjacent myocyte via gap junctions.

Depolarisation

Fast voltage-gated Na+ channels are activated and a Na+ influx depolarises the membrane rapidly to about +30 mV. This initial depolarisation is similar to that in nerve and skeletal muscle, and assists the transmission to the next myocyte.

Na+ channels and currents rapidly inactivate, but in cardiac myocytes, the initial depolarisation activates voltage-gated Ca2+ channels (slow L-type channels, threshold approximately - 45 mV) through which Ca2+ floods into the cell. The resulting influx of Ca2+ prevents the cell from repolarising and causes a plateau phase, that is maintained for about 250 ms until the L-type channels inactivate. The cardiac AP is thus much longer than that in nerve or skeletal muscle.

Repolarisation

Repolarisation occurs due to activation of voltage-gated K+ rectifier channels and a K+ efflux. As the AP lasts almost as long as contraction, its refractory period prevents another AP being initiated until the muscle relaxes, thus cardiac muscle cannot exhibit tetanus.

Image modified by FRCEM Success. [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Ventricular Muscle Action Potential. (Image modified by FRCEM Success. Original by Unknown [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/), via Wikimedia Commons)

Other Cardiac Action Potentials

Atrial myocytes have a similar but more triangular AP compared to the ventricles (less plateau). Purkinje fibres in the conduction system are also similar to ventricular myocytes, but have a spike at the peak of the upstroke reflecting a larger Na+ current that contributes to their fast conduction velocity.

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