Practice Questions for Muscle (Chapter 9) 19-42

Define motor unit.

A motor neuron and all of the muscle fibers it innervates

What molecule must be present for the myosin head to detach from actin?

ATP

In a whole skeletal muscle, increasing the frequency of stimulation results in __

Increases the force of contraction.

Contraction that increases muscle tension without changing muscle length is called __.

Isotonic Contraction

Which type of muscle contraction moves the load

Isotonic Contraction

For a skeletal muscle fiber to contract, it must be stimulated by a __.

Motornueron

In the neuromuscular junction, what separates the axonal terminal from the motor end plate?

Synaptic cleft

Name three important things found on the heads of myosin molecules?

a site that binds to actin, a binding site for ATP, and ATPase enzymes

Name the neurotransmitter released by motor neurons to stimulate muscle contraction.

acetylcholine (ACh)

The heads of myosin molecules are also called ___ ___ because they attach to binding to sites on actin.

cross bridge

Name the molecule that blocks the binding site on actin?

tropomyosin

Describe the steps involved in the contraction of a skeletal muscle fiber. Begin with an action potential in a motor neuron and end with calcium sequestration by the sarcoplasmic reticulum.

-Somatic motor neuron releases ACh into synaptic cleft -ACh diffuses across synaptic cleft, - ACh binds to ACh receptors on motor endplate of muscle cell, -chemically gated Na+ channels open, -voltage-gated Na+ channels open, -action potential in the sarcolemma, action potential in T tubules, -Ca2+ release from sarcoplasmic reticulum, -Ca2+ binds to troponin, troponin changes shape, rolls tropomyosin off binding sites, cross-bridge formation, -myosin head pivot, detach, reattach. Cycle will continue as long as calcium and ATP are available.

In a whole skeletal muscle, name two ways the force of contraction can increase

Recruitment and increased stimulation by Motor nueron

when A body stiffens @ 3 hours peaks at 12 hours softening of tissue is due to breakdown of muscle protein. Calcium influx after death causes cross-bridge attachment - cannot detach because there is no ATP

Rigor Mortis

Describe the difference between slow oxidative and fast glycolytic muscle fibers.

Slow Oxidative- -aerobic respiration, -high concentration of myoglobin molecules -slow to fatigue. Fast- -Most energy generated through glycolysis -Few myoglobin molecules -quick to fatigue.

Describe the relationship between T-tubules and the sarcoplasmic reticulum.

T-tubules are invaginations of sarcolemma carries current from nerves stimulate release of calcium from sacroplasmic reticulum

Name the three polypeptides that comprise troponin. Which component attaches to actin? Which component attaches to tropomyosin? Which component binds to calcium?

Tnl (attaches to actin) TnT (attaches to tropomyosin) TnC (binds to calcium)

What enzyme inactivates ACh in the neuromuscular junction?

acetylcholinesterase

Describe the role of myoglobin and creatine phosphate in muscle metabolism.

myoglobin-binds to oxygen Creatine- transfers phosphate to ADP when activity begins. ATP + CP can provide energy for about 15 seconds.

What happens when the binding site on actin is exposed?

myosin attaches

Do smooth muscle and cardiac muscle have to be innervated in order to contract?

no

What type of organelle is the sarcoplasmic reticulum? What is the function of SR in skeletal muscle?

smooth ER. regulates intracellular calcium levels.

What type of muscle is smooth and involuntary?

smooth Muscle

When is the binding site on actin exposed?

when TnT pulls tropomyosin so that binding sites on actin are exposed