Excitation-contraction coupling in skeletal muscle

Question 1

steps in the contraction of skeletal muscle

Answer 1

1. Acetylcholine released at axon terminal of the motor
   neuron
2. Acetylcholine binds to nicotinic receptors
3. Action potential generation in muscle fiber
4. Inward spread of depolarisation along T-tubules

5.Ca2+ release from lateral sacs of sarcoplasmic
reticulum

6.Ca2+ binds to troponin; uncovering myosin
binding sites on actin

7. Formation of cross-linkages between actin &
   myosin & sliding of thin on thick filaments
   producing movement.

Question 2

latent period

Answer 2

the period when an action potential is stimulated before the muscle contract

Question 3

period of action potential/latent period

Answer 3

1-2 msec

Question 4

muscle twitch

Answer 4

time is taken from the muscle to contract and relax

Question 5

skeletal muscle relaxation steps

Answer 5

1. Acetylcholine is broken down by
   acetylcholinesterase= no action
   potential on the motor end plate
2. Ca2+ pumped back into
   sarcoplasmic reticulum
3. With Ca2+ no longer bound to
   troponin, tropomyosin slips
   back to its blocking positing
4. Cessation of interaction
   between actin & myosin

Question 6

In skeletal muscle, the contractile unit is the sarcomere.

Answer 6

true

Question 7

In skeletal muscle the tension developed during a tetanic contraction is
greater than that developed by a single twitch

Answer 7

true

Question 8

In skeletal muscle, an action potential has a duration that is equal to the
duration of a muscle twitch.

Answer 8

false

Question 9

In skeletal muscle calcium ions (Ca2+) are released from the endoplasmic
reticulum into the cytoplasm during contraction

Answer 9

false

Question 10

Skeletal muscle contraction is inhibited by antibodies binding to cholinergic nicotinic
receptors

Answer 10

true

Question 11

Skeletal muscle contraction is inhibited by nicotinic antagonists

Answer 11

true

Question 12

Skeletal muscle contraction is inhibited by adrenergic agonists.

Answer 12

false

Question 13

Skeletal muscle contraction is inhibited by muscarinic agonists.

Answer 13

false

Question 14

Skeletal muscle contraction is inhibited by organophosphates (acetylcholinesterase).

Answer 14

false, organophosphates inhibits acetylcholinesterase which results in the accumulation of acetylcholine in the synaptic cleft causing continuous skeletal muscle contraction until muscle fatigues and paralyzed occurs