Lecture 30- Muscle Contraction

Question 1

Excitation contraction coupling

Answer 1

Sequence of events by which an action potential on the sarcolemma results in the sliding of the myofilaments

Question 2

Four steps of excitation contraction coupling

Answer 2

A nerve impulse reaches the axon terminal, causing release of ACh to the synaptic cleft.

ACh binds to ACh receptors in the sarcolemma

Voltage-gated sodium channels open,allowing the generation of an action potential on the sarcolemma.

Transmission of the action potential along the T tubules, release of calcium ions

Question 3

Sliding filament model of contraction

Answer 3

during contraction, thin filaments slide past thick filaments. Overlap between myofilaments increases and sacromere shortens.

• Myosin pulls on actin, causing the thin filament to slide inward. As a result, the sarcomere shortens.

Question 4

Cross bridge cycling

Answer 4

• Energized myosin heads bind to actin and perform a power stroke, causing actin to slide over myosin.
• ATP connects to the myosin head, disconnecting the cross-bridge.
• The cycle repeats as long as ATP and Ca2+ is present.

Question 5

Cross bridge cycling steps

Answer 5

Calcium ions bind to troponin and expose active site on actin filaments. The myosin heads attach to actin binding sites, forming the cross bridge

The myosin head pulls the thin filament past the thick filament. During power stroke, phosphate and ADP are released. If shortage of ATP, muscle contraction stops at this step.

After new ATP molecule attaches to the myosin head, cross-bridge weakens and myosin detaches from the actin.

A high-energy phosphate from ATP primes myosin head so it is ready to bind to new actin binding site if troponin is still bound by calcium ions.

Question 6

Motor unit

Answer 6

consists of a motor neuron and all the muscle fibres it innervates.

Question 7

Muscle twitch

Answer 7

the response of a muscle to a single action potential on its motor neuron, and has
three phases:
the latent period, corresponding to the lag between stimulation and excitation- contraction coupling,

the period of contraction

and the period of relaxation. The speed and duration of contraction varies between muscles.

Question 8

Graded muscle responses - wave summation

Answer 8

occurs when impulses reach the muscle in rapid succession, preventing the cell from relaxing, a condition called tetanus.

Question 9

Multiple motor unit summation

Answer 9

involves the response of a muscle to increasing stimulus voltage