L5 & L6: Cold exposure

Question 1

What is the mechanism behind vasoconstriction reducing blood flow to the surface

Answer 1

1. Increased sympathetic nervous activity
2. Closes arterio-venous anastomoses
3. redirection of venous blood close to arteries via deep veins
4. countercurrent heat exchange inhibits heat transfer to extremes.

Question 2

How does cold temperature effect internal and peripheral receptor sensitivity?

Answer 2

• between 25 and 8 degrees minor impairment occurs
• Rapid drop in sensitivity below 8 degrees
• Below 6 degrees nerve block occurs resulting in the loss of sensibility and thus manual dexterity.

Question 3

How does cold temperature effect nerve conductivity velocity?

Answer 3

• between 36 and 23 degrees a linear decrease in nerve velocity is seen
• Nerve block due to cold occurs below 10 degrees
• Nerves are deep structure and so equates to around 15 degrees skin temperature.
• PARTLY explains critical hand temperature of 15 degrees.

Question 4

How does cold temperature effect muscle?

Answer 4

1. Cold temperature reduce power, contraction velocity, speed and endurance of muscle
2. Below optimum temperature of 38 degrees muscle force production decreases
3. strong decrease below 28 degrees
4. for the same absolute intensity cooled peripheral muscle fibres are working at a higher intensity compared to non-cooled muscle, increased time to fatigue.