SM_224a: Muscle Physiology and Mechanics

Question 1

Describe the three basic principles of muscle physiology/mechanics

Answer 1

• Total muscle force at any moment is proportional to the total number of attached crossbridges (only attached crossbridges can generate force)
• Muscle uses a diverse set of energy substrates for energy needed to power crossbridge interactions and produce force
• CNS controls muscle force via activation of motor units, not whole muscles or individual muscle fibers

Question 2

Total muscle force at any moment is proportional to the ______

Answer 2

Total muscle force at any moment is proportional to the number of attached crossbridges

Question 3

Muscle uses ____ energy substrates to power crossbridge interactions and produce force

Answer 3

Muscle uses many energy substrates to power crossbridge interactions and produce force

Question 4

CNS controls muscle force via activation of _____

Answer 4

CNS controls muscle force via activation of motor units

(not whole muscles or individual muscle fibers)

Question 5

Describe the three main points about muscle physiology/mechanics

Answer 5

• Muscle has mechanical characteristics (spring-like and viscous-like) that allow it to be a good motor for movement
• Muscle energy utilization varies with intensity and duration of movement and exercise
• Motor units within a single muscle form a heterogeneous population, with systematic differences in force output, contraction speed, and fatigue resistance

Question 6

______ and _____ mechanical characteristics of muscle allow it to be a good motor for movement

Answer 6

Spring-like and viscous-like mechanical characteristics of muscle allow it to be a good motor for movement

Question 7

Muscle energy utilization varies with _____ and _____ of movement and exercise

Answer 7

Muscle energy utilization varies with intensity and duration of movement and exercise

Question 8

Motor units within a single muscle form a _____ population, with systematic differences in _____, _____, and _____

Answer 8

Motor units within a single muscle form a heterogeneous population, with systematic differences in force output, contraction speed, and fatigue resistance

Question 9

Ca binds to the ______ complex

Answer 9

Ca binds to the troponin/tropomyosin complex

Question 10

Movement of the _____ causes actin and myosin to slide past each other

Answer 10

Movement of the myosin head causes actin and myosin to slide past each other

Question 11

Myosin is an ____ase

Answer 11

Myosin is an ATPase

(hydrolyzes ATP)

Question 12

____ is the most important regulator of number of attached crossbridges

Answer 12

Ca level is the most important regulator of number of attached crossbridges

Question 13

Describe how the nervous system controls muscle

Answer 13

Nervous system controls muscle at single fiber level

1. Motor command causes AP in motor neuron
2. AP travels down the motor neuron to NMJ
3. NMJ releases ACh
4. ACh binds to receptor on muscle fiber
5. AP in muscle fiber travels downt T tubule to sarcomplasmic reticulum
6. Ca release from sarcoplasmic reticulum
7. Muscle contracts

Question 14

Mechanical events are _____ than electrical events

Answer 14

Mechanical events are slower than electrical events

(muscle fiber AP duration longer than motor neuron AP duration)

Question 15

There is a ____ force the muscle fiber can generate

Answer 15

There is a maximum force the muscle fiber can generate

Question 16

Most important regulator of number of attached crossbridges is _____

Answer 16

Most important regulator of number of attached crossbridges is Ca levels

(length of muscle and how fast the muscle moves also regulate number of attached crossbridges)

Question 17

Muscle-tendon unit behaves like a _____

Answer 17

Muscle-tendon unit behaves like a spring

(triceps serae is most efficient for locomotion due to tendons, tendons are important for locomotion)

Question 18

Describe energy utilization by muscle fibers

Answer 18

Energy utilization by muscle fibers

1. ATP used up in a few seconds
2. Creatine kinase used up within 10 seconds
3. Anaerobic glycolysis
4. Aerobic glycolysis: mitochondria generate a lot of energy
5. Aerobic fat: fat has high energy density

Question 19

Motor unit consists of _____ and _____

Answer 19

Motor unit consists of motor neuron and the muscle fibers it controls

Question 20

Fast motor units fatigue ____

Answer 20

Fast motor units fatigue quickly

Question 21

Slow motor units are used for _____

Answer 21

Slow motor units are used for large scale motions like posture

(b/c they do not fatigue, always active)