Detailed lectures 18 -

Question 1

Three types of muscle

Answer 1

1) Skeletal: Movement
2) Cardiac: Found in heart only
3) Smooth: Hollow organs and tubes

Question 2

Classification of muscle

Answer 2

1) Striation or unstriated

2) Voluntary or involuntary

Question 3

Striation v unstriation

Answer 3

Striated: With lines, cardiac
Unstriated: Smooth

Question 4

Voluntary v involuntary

Answer 4

Voluntary: Skeletal
Involuntary: Cardiac, smooth

Question 5

Skeletal mucle

Answer 5

• Controlled muscle contraction that allows purposeful movement
• Propulsion of contents through hollow internal organs
• Emptying contents of organs to external environment

Question 6

Structure of skeletal muscle

Answer 6

• Made of muscle fibers parallel to each other
• Muscle fibers held together with connective tissue
• Single skeletal muscle cell known as muscle fiber: multinucleated, cylindrically shaped, fibers extend full length of muscle

Question 7

Fast v slow twitch

Answer 7

• Fast: Few mitochondria, fatigue quickly, very strong (fine motor movements, eyes)
• Slow: More mitochondria, fatigue slowly (standing)

Question 8

Structure of skeletal muscle

Answer 8

• Sarcomere: Functional unit of skeletal muscle between two Z-bands
• Z-band: Hold protein together
• A-band: Thick and thin filaments (thin overlap thick ends)
• H-zone: No thin filaments
• M-line: Vertically down center of H-zone in A-band
• I-band: Thin filaments not in A band

Question 9

Myofibrils

Answer 9

• Cause muscle fiber to contract
• Regular arrangement of thick (myosin)/thin (actin) filaments (protein fibers)
• A-bands dark, I-bands light –> Striations

Question 10

Myosin

Answer 10

• Thick filament
• Two golf club shapes (intertwined) connected by tails
• Actin-binding site
• ATP-binding site: Energy contract muscle

Question 11

Actin

Answer 11

• Thin filaments
• Spherical
• Two proteins: Tropomyosin (covers myosin binding site) and troponin (site on tropomyosin)
• Each actin has binding site for myosin cross bridge

Question 12

Tropomyosin

Answer 12

• Regulatory protein
• Lie around grove of actin spiral
• Blocks interaction that leads to muscle contraction

Question 13

Troponin

Answer 13

• Made of 3 polypeptide units: tropomyosin, actin, Ca2+
• Ca2+ NOT bound: Blocks
• Ca2+ bound: Moves away from blocking position (contraction) because myosin and actin can now cross bridges

Question 14

Sliding filament mechanism

Answer 14

• Increase in Ca2+ starts filament sliding
• Decrease in Ca2+ turns off sliding process
• Thin slide towards A band and Z lines closer together, shortening sarcomeres (all shorten simultaneously)
• Thin filaments sliding closer together between thick filaments –> Contraction

Question 15

Conditions for continuous muscle contraction

Answer 15

• ATP available

- Ca2+ levels are high

Question 16

Muscle relaxation

Answer 16

• Re-uptake of Ca2+ into sarcoplasmic reticulum (SR)
• Acetylcholinesterase breaks down ACh at neuromuscular junction
• Muscle fiber action potential stops
• Local action potential no longer present —> Ca2+ moves back to sarcoplasmic reticulum

Question 17

Skeletal muscle mechanics

Answer 17

• Muscle made of muscle fibers bundled together and attached to bones
• Connective tissue covering muscle divides muscle into bundles

Question 18

Tendons

Answer 18

• Formed by connective tissue extending beyond end of muscles
• Anchor muscles to bones

Question 19

Muscle contractions

Answer 19

• Muscle contractions can vary in strength
• Twitch: Brief, weak, from single action potential
• Twitch summation: Sustained elevation of cytosolic tension
• Tetanus: Muscle fiber is stimulated too quickly and can’t relax between

Question 20

Muscle tension

Answer 20

• Produced internally within sarcomeres
• Transmitted to bone via connective tissue and tendons
• Origin: End attached to stationary part
• Insertion: End attached to moving skeletal part

Question 21

Lever systems

Answer 21

• Bones are levers
• Joints are fulcrums
• Skeletal muscles move bones

Question 22

Smooth muscle

Answer 22

• Found in walls of hollow organs/tubes
• No striations
• Cells in sheets
• 3 types of filaments: Think myosin, thin actin, intermediate filaments

Question 23

Multiunit v single-unit smooth muscle

Answer 23

• Multiunit: Neurogenic. Discrete independent units. Must be stimulated separately to contract.
• Single-unit: Can excite self. Also called visceral smooth muscle. Contraction slow and energy efficient.

Question 24

Motor unit

Answer 24

• Number of cells innervate by a single neuron
• Motor pool: All motor neurons that innervate a single muscle
• Small motor pool, large motor unit
• Large motor pool, small motor unit