physiology of muscle contraction

Question 1

What type of muscle tissue is made up of long cylindrical cells that are multinucleate?

Answer 1

Skeletal muscle

Skeletal muscle cells start off as separate cells that fuse during development.

Question 2

How does cardiac muscle differ from skeletal muscle in terms of shape?

Answer 2

Cardiac muscle is branched

Unlike skeletal muscle, which is long and cylindrical.

Question 3

What is the shape of smooth muscle cells?

Answer 3

Fusiform

Smooth muscle cells are long and tapered at the ends.

Question 4

Where is skeletal muscle typically found in the body?

Answer 4

Attached to bone or skin

This distinguishes it from cardiac and smooth muscle locations.

Question 5

What type of control mechanism governs skeletal muscle contraction?

Answer 5

Voluntary control

Cardiac and smooth muscle contractions are involuntary.

Question 6

What is the membrane surrounding a muscle cell called?

Answer 6

Sarcolemma

The cytoplasm inside the muscle cell is referred to as sarcoplasm.

Question 7

What are the long slender contractile organelles inside a muscle cell called?

Answer 7

Myofibrils

Myofibrils are made up of smaller units called myofilaments.

Question 8

What are the smallest units contained inside myofibrils?

Answer 8

Myofilaments

Myofilaments are responsible for muscle contraction.

Question 9

What causes the striated appearance of skeletal muscle cells?

Answer 9

The arrangement of myofilaments

Striations are due to overlapping dark and light bands.

Question 10

What are the two types of myofilaments?

Answer 10

Actin and myosin

Actin is the thin filament, and myosin is the thick filament.

Question 11

What is the dark band in muscle tissue called?

Answer 11

A band

The A band contains overlapping actin and myosin filaments.

Question 12

What is the light band in muscle tissue called?

Answer 12

I band

The I band consists of actin and the elastic filament Titin.

Question 13

What is the smallest functional unit of a muscle cell?

Answer 13

Sarcomere

A sarcomere is defined from one Z disc to the next.

Question 14

What connects myosin filaments to the Z disc?

Answer 14

Titin

Titin is an elastic filament that helps stabilize myosin.

Question 15

What happens to the Z discs during muscle contraction?

Answer 15

They move closer to the M line

This results in the shortening of the sarcomere.

Question 16

What is the role of the myosin heads during muscle contraction?

Answer 16

They form cross bridges with actin

This interaction generates the force of contraction.

Question 17

What is the function of the sarcoplasmic reticulum?

Answer 17

Stores ionic calcium

It regulates calcium levels and releases calcium on demand for contraction.

Question 18

What are T tubules?

Answer 18

Elongated tubes that extend deep into the muscle cell

They facilitate the spread of action potentials throughout the muscle fibre.

Question 19

What does the sliding filament mechanism describe?

Answer 19

How muscle fibres contract

It explains the sliding action of thin filaments past thick filaments.

Question 20

What initiates muscle contraction at the neuromuscular junction?

Answer 20

Release of acetylcholine

ACh binds to receptors on the sarcolemma, causing depolarization.

Question 21

What is the first phase of muscle contraction?

Answer 21

Stimulation at the neuromuscular junction

This involves the action potential from a motor neuron.

Question 22

What does excitation-contraction coupling refer to?

Answer 22

Linking the electrical signal to muscle contraction

It involves calcium release and exposure of actin binding sites.

Question 23

What occurs during the end plate potential?

Answer 23

Local depolarization of the sarcolemma

This triggers sodium voltage gates to open, leading to an action potential.

Question 24

What is the role of calcium ions in muscle contraction?

Answer 24

They bind to troponin

This causes tropomyosin to shift and expose myosin-binding sites on actin.

Question 25

What initiates the process of excitation-contraction coupling?

Answer 25

The action potential generated at the neuromuscular junction propagates along the sarcolemma and down into the T tubules.

Question 26

What happens during the release of calcium ions in excitation-contraction coupling?

Answer 26

Calcium ions flow from the sarcoplasmic reticulum into the sarcoplasm, surrounding the filament proteins.

Question 27

What is the role of calcium in muscle contraction?

Answer 27

Calcium binds to troponin, removing tropomyosin's blocking action and exposing the active binding sites for myosin on actin.

Question 28

What is a cross-bridge in muscle contraction?

Answer 28

A cross-bridge is formed when myosin binds to the exposed actin binding site.

Question 29

List the four main steps involved in the cross-bridge cycle.

Answer 29

* Attachment of myosin to actin * Power stroke * Cross-bridge detachment * Cocking of the myosin head

Question 30

What happens to calcium levels in the cytosol after muscle contraction?

Answer 30

Calcium is pumped back into the sarcoplasmic reticulum, causing calcium levels in the cytosol to drop.

Question 31

What is a motor unit?

Answer 31

A motor unit is the motor neuron and all of the muscle fibers it innervates.

Question 32

True or False: A single motor neuron can innervate multiple muscle fibers.

Answer 32

True

Question 33

What is the size principle in muscle contraction?

Answer 33

The smallest motor units are recruited first, and progressively larger motor units are recruited to produce larger forces.

Question 34

Fill in the blank: The process called _______ refers to the increase in size of individual muscle fibers.

Answer 34

Hypertrophy

Question 35

What type of muscle contraction occurs when there is a change in length of the muscle?

Answer 35

Isotonic contraction

Question 36

Differentiate between concentric and eccentric contractions.

Answer 36

* Concentric: Muscle shortens * Eccentric: Muscle lengthens

Question 37

What is an isometric contraction?

Answer 37

An isometric contraction occurs when the muscle length does not change, despite tension being developed.

Question 38

What is the primary energy source used directly for contractile activities of a muscle?

Answer 38

ATP (adenosine triphosphate)

Question 39

List the three processes by which ATP is regenerated during muscle contraction.

Answer 39

* Direct phosphorylation of ADP by creatine phosphate * Anaerobic glycolysis * Aerobic respiration

Question 40

What occurs during direct phosphorylation of ADP?

Answer 40

Creatine phosphate transfers a phosphate group to ADP to regenerate ATP.

Question 41

What happens during anaerobic glycolysis?

Answer 41

Glucose is broken down to produce pyruvic acid and 2 ATP molecules in the absence of oxygen.

Question 42

What is the result of glycolysis when there is no oxygen present?

Answer 42

Pyruvic acid is converted into lactic acid.

Question 43

What is the significance of aerobic respiration in muscle contraction?

Answer 43

It produces a net gain of 32 ATP molecules in the presence of oxygen.

Question 44

What happens to muscle fibers during prolonged exercise?

Answer 44

They primarily utilize aerobic respiration for ATP generation.

Question 45

What are the three types of muscle fibers?

Answer 45

* Fast oxidative (FO) * Slow oxidative (SO) * Fast glycolytic (FG)

Question 46

What characterizes fast glycolytic fibers?

Answer 46

They rely mostly on ATP from glycolysis and are larger, providing greater force.

Question 47

What is the role of slow oxidative fibers?

Answer 47

They utilize oxygen for endurance and are rich in myoglobin and capillaries.

Question 48

How does exercise affect muscle fibers?

Answer 48

Aerobic exercise improves oxygen delivery and utilization, while resistance exercise builds strength and muscle size.

Question 49

What is muscle atrophy?

Answer 49

Muscle atrophy refers to a decrease in muscle size due to lack of use.

Question 50

What is the treppe effect?

Answer 50

It refers to the phenomenon where each muscle contraction builds on the previous one due to increased calcium availability.

Question 51

What are the characteristics of slow oxidative fibres?

Answer 51

They are red, have lots of myoglobin, and many capillaries ## Footnote They utilize oxygen to provide energy for endurance.

Question 52

What type of muscle fibres are fast glycolytic fibres?

Answer 52

They are white, fast twitch, and fatigable ## Footnote They are engaged in short duration activities.

Question 53

What characterizes fast oxidative muscle fibres?

Answer 53

They are pink and share characteristics of both fast glycolytic and slow oxidative fibres ## Footnote They are engaged in activities requiring a combination.

Question 54

Which muscle fibre type would a sprinter like Usain Bolt have a higher proportion of?

Answer 54

Fast glycolytic fibres ## Footnote These fibres allow for quick bursts of energy.

Question 55

Which muscle fibre type would a marathon runner like Lemi Hayle have a higher proportion of?

Answer 55

Slow oxidative fibres ## Footnote These fibres support endurance through aerobic respiration.

Question 56

What is the main energy source for fast glycolytic fibres?

Answer 56

Anaerobic glycolysis ## Footnote This occurs in the absence of oxygen.

Question 57

What is the primary pathway of ATP synthesis for slow oxidative and fast oxidative fibres?

Answer 57

Aerobic respiration ## Footnote This process utilizes oxygen.

Question 58

What is the role of myosin ATPase activity in muscle fibres?

Answer 58

It enables faster contraction in fast glycolytic fibres and slower contraction in slow oxidative fibres ## Footnote ATPase is the enzyme that breaks the cross bridge cycle.

Question 59

Define hypertrophy in relation to skeletal muscle.

Answer 59

Increase in muscle size due to exercise ## Footnote It often results from strength training.

Question 60

Define atrophy in relation to skeletal muscle.

Answer 60

Decrease in muscle size due to disuse or disease ## Footnote It can occur when muscles are not used for extended periods.

Question 61

Define hyperplasia in relation to skeletal muscle.

Answer 61

Increase in the number of muscle fibres ## Footnote This is less common than hypertrophy.

Question 62

Fill in the blank: Fast glycolytic fibres are engaged in ______ activities.

Answer 62

short duration

Question 63

Fill in the blank: Slow oxidative fibres are engaged in ______ activities.

Answer 63

long duration

Question 64

Fill in the blank: Fast oxidative fibres are engaged in activities requiring a ______.

Answer 64

combination

Question 65

True or False: Fast glycolytic fibres produce ATP through aerobic respiration.

Answer 65

False ## Footnote They produce ATP via anaerobic glycolysis.

Question 66

True or False: Slow oxidative fibres are fatigue resistant.

Answer 66

True