MUSCLE PHYSIOLOGY

Question 1

Requirements for skeletal muscle contraction (2)

Answer 1

• Neuromuscular junction (site where motor neuron’s axon terminal meets muscle fiber)
• Excitation-contraction coupling

Question 2

Neuromuscular junction

Answer 2

Action potential at motor neuron terminal triggers Ca2+ influx, releasing acetylcholine into synaptic cleft. Acetylcholine binds to sarcolemma, opening channels for positive ions, initiating depolarization and action potential propagation.

Question 3

Propagation of Action Potential

Answer 3

Action potential prompts Ca2+ release from SR, T tubules transmit it, leading to Ca2+ diffusion and muscle fiber contraction.

Question 4

T tubules

Answer 4

Extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells.

Question 5

Skeletal Muscle and Contraction & Relaxation PART 1 - SKELETAL MUSCLE CONTRACTION INITIATION (3):

Answer 5

• Action potential triggers Ca2+ release from SR
• Ca2+ binds to troponin, exposing myosin-binding sites on actin
• ATP sustains muscle contraction

Question 6

Skeletal Muscle and Contraction & Relaxation PART 2 - MUSCLE CONTRACTION PROCESS (3)

Answer 6

• Myosin heads pull actin, causing shortening of sarcomeres
• Cross bridge cycle involves myosin binding, power stroke and detachment
• ATP essential for myosin detachment and recocking

Question 7

Skeletal Muscle and Contraction & Relaxation PART 3 - MUSCLE CONTRACTION REGULATION (3)

Answer 7

• Troponin and tropomyosin regulate actin-myosin interaction
• Ca2+ presence allows crossbridge formation; absence blocks it
• Rigor mortis occurs due to ATP depletion, leading to sustained cross bridges

Question 8

Tropomyosin

Answer 8

Long rod like molecule that blocks muscle contraction

Question 9

Troponin

Answer 9

Promotes muscle contraction

Question 10

Cross bridge formation

Answer 10

The attachment of myosin with actin within the muscle cell

Question 11

Power stroke

Answer 11

Movement of when actin is pulled

Question 12

Creatine phosphate

Answer 12

Main high-energy, phosphate-storage molecule of muscle

Question 13

Glycolysis

Answer 13

Process which glucose is broken down to produce energy. Muscles turn to glycolysis as an ATP source once the ATP produced by creatine phosphate is depleted

Question 14

Aerobic cellular respiration

Answer 14

Breakdown of glucose or other nutrients in PRESENCE OF OXYGEN to produce carbon dioxide, water and ATP. 95% of ATP required for resting or moderately active muscles are provided by this

Question 15

Anaerobic respiration

Answer 15

Takes place in the absence of oxygen

Question 16

Skeletal muscle relaxation

Answer 16

Motor neuron stops releasing acetylcholine, muscle fibers repolarize and close gates, remove calcium ions from sarcoplasm via active transport and tropomyosin blocks myosin binding sites = no crossbridge formation

Question 17

Cardiac muscle

Answer 17

Only found in the heart, responsible for pumping blood throughout circulatory system. Cardiac muscle is not consciously controlled, but the pacemaker cells respond to signals from the ANS

Question 18

Cardiac muscle structure (3):

Answer 18

• Shorter branched shape that connect at ends to one another by intercalated discs
• Striated, organized into sarcomeres and posses many mitochondria
• One nucleus

Question 19

Intercalated disc

Answer 19

Part of sarcolemma and contain 2 structures important in cardiac muscle contractions; gap junctions and desmosomes

Question 20

Gap junction

Answer 20

AAllow the exchange of ions, second messengers, and small metabolites between adjacent cells

Question 21

Electric coupling

Answer 21

The joining formed by gap junction that allows quick transmission of action potentials and coordinated contraction of entire heart

Question 22

Syncytium

Answer 22

Functional unit of contraction

Question 23

Desmosomes

Answer 23

Anchor ends of cardiac muscle fibers together so that cells do not pull apart during stress

Question 24

Pace maker cells

Answer 24

Specialized cardiac muscle cells that directly control heart rate and are self excitable (set action potentials on their own; autorhythmicity). Connected to gap junctions so it can transfer depolarization to other cardiac muscle fibers in a coordinated manner

Question 25

Smooth muscle

Answer 25

Arranged in layers and the triggers include hormones, neural stimulation by ANS, and pH factors, etc. Found around hollow organs that produce slow and steady contractions known as peristalis, such as moving food in digestive tract. It is an involuntary muscle

Question 26

Smooth muscle structure (4)

Answer 26

• Spindle shaped
• No striations
• Single nucleus
• Thin (actin) and thick (myosin) filaments present

Question 27

Thin filaments of smooth muscle

Answer 27

Attached to sarcolemma by dense bodies

Question 28

Caveolae

Answer 28

Membrane indentations of smooth muscle where calcium ions are supplied by the SR

Question 29

Calmodulin

Answer 29

Regulatory protein in smooth muscle cells instead of tropon-tropomyosin complex

Question 30

Smooth muscle contraction mechanism (6):

Answer 30

• Calcium ions from SR and extracellular fluid bind to calmodulin
• Calmodulin activates enzyme that activates myosin heads
• Myosin heads attach to actin binding sites and pull thin filaments
• Thin filaments slide past thick filaments pulling dense bodies
• Dense bodies pull on intermediate filaments causing muscle fiber contraction
• Muscle fiber contracts with ends pulled towards the center causing midsection bulging inward

Question 31

Where do thin filaments get pulled towards during contraction

Answer 31

M-line

Question 32

Myoblast

Answer 32

Immature muscle cell