Muscles

Question 1

What are the three types of muscles?

Answer 1

1. cardiac
2. skeletal
3. smooth

Question 2

What is the most abundant tissue in the human body?

Answer 2

• skeletal tissue is responsible for about 40-45% of total body weight
• human body has more than 430 pairs of skeletal muscle

Question 3

What is the structural unit of skeletal muscle?

Answer 3

the multinucleated muscle cell or fiber

Question 4

What is the basic contractile unit of the muscle?

Answer 4

muscle fibers consist of myofibrils

Question 5

Myofibrils consists of _____

Answer 5

myofilaments (actin and myosin)

Question 6

What is a thin filaments?

Answer 6

actin

Question 7

What is a thick filaments?

Answer 7

myosin

Question 8

What is the functional unit of muscle contraction?

Answer 8

• Composed of motor neuron and all muscle cells (fibers) innervated by motor neuron
• Follows “all-or-none” principle

Question 9

What is the size principle?

Answer 9

• smallest motor units recruited first & w/ smaller stimulation frequencies
• larger motor units recruited later w/ increased frequency of stimulation and increased need for greater tension

Question 10

What are tonic units?

Answer 10

smaller, slow twitch, rich in mitochondria, highly capillarized, high aerobic metabolism, low peak tension, long time to peak (60-120 ms)

Question 11

What are phasic units?

Answer 11

larger, fast twitch, poorly capillarized, rely on anaerobic metabolism, high peak tension, short time peak (10-50 ms)

Question 12

What is the weakest voluntary contraction?

Answer 12

a twitch

Question 13

Wha determines the force of contraction in a single fiber?

Answer 13

the overlap of actin and myosin

Question 14

What accounts for the force of contraction for the whole muscle?

Answer 14

active (contractile) and passive (series and parallel elastic elements) components

Question 15

What are parallel connective tissue?

Answer 15

• tissues surrounding contractile elements
• acts like elastic band
• slack when muscle at resting length of less

Question 16

What are series elastic tissue?

Answer 16

• tissues in series with contractile component

- tendon forms series elastic element of skeletal muscle

Question 17

What are musculotendinous unit?

Answer 17

-tendon and connective tissues in muscle are viscoelastic

Question 18

What does viscoelastic structures help with?

Answer 18

They help determine mechanical characteristics of muscles during contraction and passive extension

Question 19

What are the functions of elastic elements of muscle?

Answer 19

• Keep “ready” state for muscle contraction
• Contribute to smooth contraction
• Reduce force buildup on muscle and help prevent muscle injury
• Helps muscle absorb, store, and return energy

Question 20

How does synchronization affects force potential?

Answer 20

• number of motor units active at one time

- the more –> greater force potential

Question 21

How does the size of motor units affects force potential?

Answer 21

motor units with larger number of fibers have greater force potential

Question 22

How does the type of motor units affects force potential?

Answer 22

type IIA and IIB increases force potential, type I decreases force potential

Question 23

How does summation affects force of contraction?

Answer 23

increase frequency of stimulation, to some limit, increases the force of contraction

Question 24

What is the size principle - tension decrease?

Answer 24

Last recruited motor units drop out first

Question 25

What are the four types of muscle contraction?

Answer 25

1. concentric
2. eccentric
3. isokinetic
4. isometric

Question 26

What is concentric muscle contraction?

Answer 26

Force of the muscle contraction, greater resistance;

positive work; muscle movement and angular velocity of joint in the same direction

Question 27

What is eccentric muscle contraction?

Answer 27

Force of muscle contraction, lesser resistance;
negative work;
muscle moment and angular velocity of joint in opposite direction

Question 28

What is isokinetic muscle contraction?

Answer 28

Force of muscle contraction is equal to resistance;

constant angular velocity; positive work; muscle movement and angular velocity of joint in the same direction

Question 29

What is isometric muscle contraction?

Answer 29

Force of muscle contraction is lesser resistance; series elastic component stretch
no mechanical work; physiological work

Question 30

What is length-tension relationship?

Answer 30

-difficult to isolate single agonist

Question 31

When does concentric contraction (muscle shortening) occur?

Answer 31

Occurs when the force of contraction is greater than the resistance (positive work)

Question 32

When does eccentric contraction (muscle lengthening) occur?

Answer 32

Occurs when the force of contraction is less than the resistance

Question 33

What is a fusiform muscle?

Answer 33

• fibers parallel to long axis of muscle
• Many sarcomeres make up long myofibrils
• advantage for length of contraction
• tends to have a smaller PCSA

Question 34

What is a pennate muscle?

Answer 34

• fibers arranged obliquely to long axis of muscle
• uni-, bi-, and multi-pennate
• advantage for force of contraction
• tends to have larger PCSA