Question

Put the motor units (listed by innervation ratio) in order from first activated to last to be activated

a) 1:5
b) 1:2
c) 1:10
d) 1:20

Answer 1

Motor units in skeletal muscles are recruited from smallest to largest. The order of activation based on innervation ratios from first to last is: 1:2, 1:5, 1:10, and 1:20.

Step-by-step explanation:

In skeletal muscles, motor units are recruited in order of size, with smaller motor units (having lower thresholds) being activated first, followed by larger motor units as more strength is needed. The process of enlisting motor units from smallest to largest is known as recruitment. The innervation ratios provided correspond to the size of motor units, which dictates their order of recruitment.

• 1:2 - Smallest motor units with the lowest threshold, recruited first.
• 1:5 - Slightly larger motor units recruited after 1:2 units.
• 1:10 - Larger motor units recruited once those with lower innervation ratios have been activated.
• 1:20 - Largest motor units with the highest threshold, recruited last as more force is required.

Thus, the correct order of activation from first to last is: b) 1:2, a) 1:5, c) 1:10, d) 1:20.