Sun21November0735PM 1

When a patient inadvertently touches a very hot surface with a finger it is withdrawn, away from further damage.

Which of the following best describes the neural pathway of this response?

(Please select 1 option)

Thermoreceptors, Ad fibre efferent neurone (conduction velocity 60-120 m/s), dorsal horn, interneurone, afferent Aa fibre afferent neurone (conduction velocity (10-30 m/s) and effector

Thermoreceptors, C fibre afferent neurone (conduction velocity 10-30 m/s), dorsal horn, interneurone, afferent Aa fibre efferent neurone (conduction velocity (60-120 m/s) and effector

Thermoreceptors, Ad fibre efferent neurone (conduction velocity 10-30 m/s), dorsal horn, interneurone, afferent Aa fibre afferent neurone (conduction velocity (60-120 m/s) and effector

Thermoreceptors, Ad fibre afferent neurone (conduction velocity 10-30 m/s), dorsal horn, interneurone, afferent Aa fibre efferent neurone (conduction velocity (60-120 m/s) and effector This is the correct answer

Thermoreceptors, Ad fibre afferent neurone (conduction velocity 60-120m/s), dorsal horn, interneurone, afferent Aa fibre efferent neurone (conduction velocity (10-30 m/s) and effector Incorrect answer selected

Explanation

The neural pathway described is a simple primary reflex arc.

Thermoreceptors are specialised receptors in the dermis on the free endings of Ad and C fibres.

Afferent pathways are the small myelinated Ad fibres. These fibres are 2-5 µm in diameter and have conduction speeds of between 10 and 30 metres per second. These primary afferents enter the dorsal horn of the spinal cord (the cell body lies in the dorsal root ganglion). In the dorsal horn the primary afferent neurone synapses with an inter-neurone, which in turn synapses with the efferent pathway.

Efferent pathways are the thick myelinated A-alpha fibres. These fibres are 10-20 µm in diameter and have fast conduction speeds of between 60 and 120 metres per second. The effectors are the flexor and extensor muscle groups.

The C fibres are unmyelinated nerve fibres that are 0.5-1 µm in diameter and have the slowest conduction speeds of between 0.5 and 15 metres per second. They carry the modalities of touch, pressure, cold, warm and dull ache.

Answer Statistics

1

7%

2

24%

3

11%

4

31%

5

29%

Times answered: 269