Lecture 4

Question 1

What is the neuromuscular junction?

Answer 1

The synaptic connection between a motor nerve and a skeletal muscle

Nerves that regulate skeletal muscle function are called motor nerves.

Question 2

What neurotransmitter is released at the neuromuscular junction?

Answer 2

Acetylcholine (Ach)

Question 3

What type of receptor does acetylcholine bind to on the muscle cell membrane?

Answer 3

Nicotinic acetylcholine receptor

Question 4

What ion enters the muscle cell when acetylcholine binds to its receptor?

Answer 4

Na+ (sodium)

Question 5

What are muscle fibres?

Answer 5

Very long, multi-nucleated cells that make up skeletal muscles

Question 6

What are fascicles?

Answer 6

Bundles of muscle fibres surrounded by connective tissue

Question 7

What are myofibrils?

Answer 7

Bundles of actin and myosin filaments within muscle fibres

Question 8

What is the sarcolemma?

Answer 8

The plasma membrane of a skeletal muscle cell

Question 9

What triggers the release of Ca2+ from the sarcoplasmic reticulum?

Answer 9

An action potential traveling down the T-tubules

Question 10

What are sarcomeres?

Answer 10

Repeating units of thick (myosin) and thin (actin) filaments

Question 11

What happens to the myosin-binding sites on actin during muscle contraction?

Answer 11

They are exposed after tropomyosin moves away

Question 12

What is the function of tropomyosin?

Answer 12

Covers myosin-binding sites on actin when muscle is relaxed

Question 13

What is the role of troponin in muscle contraction?

Answer 13

Binds to actin, tropomyosin, and Ca2+ to facilitate contraction

Question 14

What are the two binding sites on a myosin molecule?

Answer 14

• Actin-binding site
• ATPase site

Question 15

What is rigor?

Answer 15

The binding of actin to myosin with the myosin head in the low energy configuration

Question 16

What is required for the separation of actin and myosin?

Answer 16

ATP

Question 17

What occurs during a muscle twitch?

Answer 17

An increase in muscle tension in response to a single stimulus

Question 18

What is an isometric contraction?

Answer 18

Muscle tension develops but muscle does not shorten

Question 19

What is an isotonic contraction?

Answer 19

Muscle generates enough tension to lift a load and shortens

Question 20

What happens during an isometric contraction regarding the elastic components?

Answer 20

The shortening of contractile components is countered by stretching of the series elastic component

Question 21

What happens during an isotonic contraction regarding the elastic components?

Answer 21

Both contractile and elastic components shorten

Question 22

How long is a typical action potential in muscle?

Answer 22

Approximately 5 msec

Question 23

What is summation in muscle contraction?

Answer 23

Increased muscle tension triggered by a second action potential arriving before the first twitch has finished

Question 24

What is rigor mortis?

Answer 24

A condition where actin and myosin remain bound due to lack of ATP after death

Question 25

What is the result of an action potential in a muscle?

Answer 25

A muscle twitch (the development of tension in the muscle) ## Footnote Action potentials are short-lived events that lead to longer-lasting muscle twitches.

Question 26

What happens if a second action potential arrives before the first twitch has finished?

Answer 26

It triggers an increase in muscle tension that superimposes upon the initial increase in tension, known as summation. ## Footnote Summation occurs when multiple action potentials lead to greater muscle tension.

Question 27

What is tetanus in the context of muscle action potentials?

Answer 27

A tension plateau reached when action potentials arrive at a very rapid rate, making individual twitches indistinguishable. ## Footnote Tetanus results in sustained muscle contraction due to rapid stimulation.

Question 28

Fill in the blank: If action potentials arrive at a very rapid rate, tension increases significantly and individual twitches are no longer distinguishable from one another, resulting in _______.

Answer 28

[tetanus]

Question 29

What is the relationship between the duration of action potentials and muscle twitches?

Answer 29

Action potentials are short, while twitches are long, allowing multiple action potentials to arrive before the first twitch is completed. ## Footnote This timing is crucial for understanding muscle contraction dynamics.