Exam 4 | Musculoskeletal system & muscle contraction

Question 1

What are the function of the musculoskeletal system?

Answer 1

Allowing for local and whole-body movement

Aiding in the circulation of lymph (fluid) and blood throughout the body

Protecting the internal organs

Maintaining homeostasis through heat production (the muscles are the largest source of internal heat in the body)

Question 2

What are individual muscle cells called?

Answer 2

Muscle Fibers.

Question 3

What are muscle bundles?

Answer 3

Muscle fibers that are connected via connective tissue.

Question 4

Muscle bundles create the entire muscle, which is connected to bone via…

Answer 4

Tendons

Question 5

What are the 3 types of muscle tissues?

Answer 5

Skeletal muscle, Smooth muscle, and cardiac muscle

Question 6

Describe skeletal muscle.

Answer 6

striated & tubular, under voluntary contraction, and multinucleated

Question 7

Describe smooth muscle.

Answer 7

Non-striated & spindle shaped, under involuntary contraction, and uninucleated; usually covering walls of internal organs

Question 8

Describe cardiac muscle.

Answer 8

Striated & branched, under involuntary contraction, and uninucleate; only covering walls of heart

Question 9

Within muscle cells are specialized structures known as…

Answer 9

Myofibril which are loaded with mitochondria and the site for muscle contraction

Question 10

What are the key features of a myofibril?

Answer 10

Sarcoplasmic reticulum, thin (actin) filament, sarcomere, and thick (myosin) filament

Question 11

What’s the sarcoplasmic reticulum?

Answer 11

A specialized extension of the smooth endoplasmic reticulum (ER) designed for aiding in the transduction of electrical signals and storing Calcium (Ca2+) ions for muscle contraction.

Question 12

What’s the thin (actin) filament?

Answer 12

Actin filaments wrapped around specialized proteins troponin and tropomyosin, both of which are essential for muscle contraction

Question 13

What’s the sarcomere?

Answer 13

The basic “contractile unit” of the myofibril, where all the “action” happens during muscle contraction. Divided into two zones based on the contrast in striation: the Z-discs and the H-zone.

Question 14

What’s the thick (myosin) filament?

Answer 14

A more dense cytoskeletal element compared to the thin (actin) filament, consists primarily of a specialized motor protein known as myosin.

Question 15

How does calcium play an important role in muscle contraction?

Answer 15

When Calcium (Ca2+) binds to its active site on the special protein troponin, it causes a conformational (shape) change in the troponin-tropomyosin complex that opens up the binding site for myosin which is important for muscle contraction.

Question 16

Describe muscle contraction (cross-bridge cycling)?

Answer 16

1) Calcium (Ca2+) ions will bind to their active sites on the thin filaments, exposing the active site for myosin to bind to the thin filaments.

2) Myosin heads from the thick filaments will bind to their active site on the thin filaments.

3) The hydrolysis of ATP to ADP and a loose inorganic phosphate group (Pi) cause a conformational (shape) change in the myosin heads, resulting what is known as the “power stroke”, which causes a physical movement (akin to a rowing motion) of the Z-disk.

4) Finally, the myosin heads acquire new ATP and are released from the thin filaments to allow the process to repeat, leading to whole muscle contraction.

Question 17

What causes muscles to contract?

Answer 17

In order for a skeletal muscle ot contract, there needs to be a stimulus which comes from a neuron innervating a single muscle fiber.

Question 18

The connection between neuron and muscle fiber is known as…

Answer 18

Neuromuscular junction

Question 19

Neurons at the neuromuscular junction release a neurotransmitter called…

Answer 19

Acetylcholine

Question 20

What does the binding of acetylcholine do?

Answer 20

Acetylcholine binding to its receptors on the muscle fiber causes a change in the voltage (potential) of the muscle fiber; this allows for depolarization of cations

Question 21

So what happens once a muscle fiber has undergone a complete cross-bridge cycle?

Answer 21

It is essential that excess Acetylcholine be removed, or recycled, from the neuromuscular junction. An enzyme secreted by muscle and nerve cells, known as Acetylcholinesterase (AChE), binds to and recycles remaining ACh within the synapse to prevent prolonged muscle contraction, known as tetanus.

Question 22

The voltage change in a muscle fiber doesn’t stop until it reaches the…

Answer 22

The sarcoplasmic reticulum; this means that the muscle fiber is sequential

Question 23

How does the change in voltage impact the sarcoplasmic reticulum?

Answer 23

the sarcoplasmic reticulum is a specialized organelle rich in Calcium, the change in voltage triggers release of Calcium from the sarcoplasmic reticulum, allowing Calcium ions to diffuse and bind to their active sites on the thin filaments in the sarcomere.

Question 24

What’s myasthenia Gravis?

Answer 24

It’s a rare neuromuscular autoimmune disease that targets the acetylcholine receptors on the surface of skeletal muscle fiber membranes

Question 25

What are some common symptoms of the myasthenia gravis?

Answer 25

Muscle weakness, specifically in the face (eyes and mouth)

Question 26

How can you treat myasthenia gravis?

Answer 26

It can be treated with acetylcholinesterase inhibitors

Question 27

What’s a motor unit?

Answer 27

An individual motor neuron and all the muscle fiber it innervates

Question 28

What’s a motor pool?

Answer 28

A group of motor neurons that innervate a single muscle; larger than a motor unit