Chapter 10 (Muscular Tissue X)

Question 1

Twitch Contraction

Answer 1

The brief contraction of the muscle fibers in a motor unit in response to an action potential
Twitches last from 20 to 200 msec

Question 2

Latent period (2 msec)

Answer 2

A brief delay between the stimulus and muscular contraction

The action potential sweeps over the sarcolemma and Ca++ is released from the SR

Question 3

Contraction period (10–100 msec)

Answer 3

Ca++ binds to troponin
Myosin-binding sites on actin are exposed
Cross-bridges form

Question 4

Relaxation period (10–100 msec)

Answer 4

Ca++ is transported into the SR
Myosin-binding sites are covered by tropomyosin
Myosin heads detach from actin
1- Muscle fibers that move the eyes have contraction periods lasting 10 msec
2- Muscle fibers that move the legs have contraction periods lasting 100 msec

Question 5

Refractory period

Answer 5

When a muscle fiber contracts, it temporarily cannot respond to another action potential
1- Skeletal muscle has a refractory period of 5 milliseconds
2- Cardiac muscle has a refractory period of 300 milliseconds

Question 6

Muscle Tone

Answer 6

A small amount of tension in the muscle due to weak contractions of motor units
Small groups of motor units are alternatively active and inactive in a constantly shifting pattern to sustain muscle tone
Muscle tone keeps skeletal muscles firm, helps maintain posture

Question 7

Types of Contractions

Answer 7

Isotonic and Isometric

Question 8

Isotonic contraction

Answer 8

The tension developed remains constant while the muscle changes its length
Used for body movements and for moving objects
Picking a book up off a table

Question 9

Isometric contraction

Answer 9

The tension generated is not enough for the object to be moved and the muscle does not change its length
Holding a book steady using an outstretched arm