Physiology of contraction

Question 1

what are motor units

Answer 1

motor neurons originating in the ventral (anterior) roots of the spinal cord, terminate at NM junction to innervate muscle
- defined as a single MN and all the muscle fibres it innervates

Question 2

are all the fibres within a given MU the same fibre type

Answer 2

yes
- all fibres in one MU are the same

Question 3

what are the three parts of contraction

Answer 3

innervation
excitation
activation

Question 4

what is innervation

Answer 4

when ACh is released at the NM junction and travels across the synaptic cleft to the motor end plate

Question 5

what is excitation

Answer 5

AP generated along the fibre
AP can travel in both directions in muscle fibres

Question 6

what is activation

Answer 6

AP causes release of calcium into the cell which triggers cross bridge cycling
level of activation is proportional to the amount of calcium in the cell

Question 7

what is the sliding filament theory

Answer 7

power stroke causes protein filametns to slide past one another

Question 8

why does rigor mortis occur

Answer 8

not enough ATP In the body
myosin stays bound

Question 9

what occurs to the different portions of the sarcomere when the muscle contracts

Answer 9

A band stays the same - length of myosin stays the same
I band gets smaller
H zone gets smaller
adjacent Z lines get closer together

Question 10

what are the steps of cross bridge cycling (5)

Answer 10

1. active site on actin is exposed when Ca2+ binds to troponin and moves tropomyosin out of the way
2. myosin head binds to actin
3. power stroke - myosin head bends and ADP and phosphate are released
4. new molecule of ATP attaches to the myosin head and cross bridge detaches
5. ATP hydrolyses to ADP and phosphate which returns the myosin to its original position