2.Put these events in the correctchronological sequence:

1. Upper motor neuron fires an actionpotential

2. T-tubules convey action potentialsinto the interior of the cell.

3. Acetylcholine is released from thelower motor neuron.

4. Ca2+ is released from thesarcoplasmic reticulum.

A) 1, 2, 3, 4

B) 3, 1, 2, 4

C) 2, 1, 4, 3

D) 1, 3, 2, 4

E) 4, 3, 2, 1

4.Which of the following sequencesrepresent muscle contraction?

A)Action Potential leads to Ca++release- troponin pulls troposmyosin -Ca++ binds to troponin- awaythe myosin binding site- myosin heads pull actin toward the M line- myosin head binds to myosin binding site on actin

B)Action Potential leads to Ca++release- - myosin head binds to myosin binding site on actin- Ca++binds to troponin--troponin pulls troposmyosin away from the myosinbinding site - myosin heads pull actin toward the M line

C)Action Potential leads to Ca++release- Ca++ binds to tropomyosin-tropomyosin pulls troponin awayfrom the myosin binding site- myosin head binds to myosin bindingsite on actin- myosin heads pull actin toward the M line

D)Action Potential leads to Ca++release- Ca++ binds to troponin-troponin pulls troposmyosin awaythe myosin binding site- myosin head binds to myosin binding siteon actin- myosin heads pull actin toward the M line

E)Ca++ binds to troponin -ActionPotential leads to Ca++ release- -troponin pulls