Chapter 12

What is the role of the series elastic component in muscle contraction?

Elastic recoil and help return the muscle to its resting length after contraction.

The thin filaments are primarily composed of the protein

actin

The energy for muscle contraction is most directly obtained from

aerobic respiration

Sarcoplasmic reticulum

calcium release channels open

What stimulates the release of calcium from the sarcoplasmic reticulum in cardiac muscle cells?

Extracellular calcium from the opening of the voltage gated Ca++ channels

Structures in order from largest to smallest subunit

Fascicle Fiber Myofibril Myofilament Globular actin

During sarcomere contraction, the A band remains the same length while the __ band and the __ band get shorter

I,H

Which of the following influence the strength of contraction in a muscle?

Initial resting length of fiber Number of fibers stimulated Frequency of stimulation Thickness of muscle fiber

Double reciprocal innervation:

Involves muscles controlled by different spinal cord segments Occurs in complex reflexes

Titin:

Is responsible for elastic recoil of muscle after contraction. Is anchored into the Z disk Is bound to the thick filament.

During an _________ contraction, the tension that is produced by the muscle is not sufficient to move the load; consequently, the muscle does not contract.

Isometric

Which of these statements about muscle fatigue is true?

It may be caused by a loss of muscle cell Ca2+ it may be caused by the accumulation of extracellular K+ It may be a result of lactic acid production.

The contractions of smooth muscle are slow and sustained due to their ability to enter a ____ state where less ATP is hydrolyzed.

Latch

During the _____ period, the action potential stimulates the release of calcium but the muscle has not begun to shorten

Latent

Calcium Release Channel

Located in the terminal cisternaeof SR; releases calcium in response to shape changes of another ion channel Release calcium through passive diffusion

Alpha motoneuron

Lower motor neuron that innervated extrafusal muscle fibers

Gamma motoneuron

Lower motor neuron that innervates intrafusal muscle fibers or muscle spindle fibers

A reflex arc includes:

Lower motor neurons An alpha motor neuron A sensory Neuron

The ____ _____ are produced by protein filaments located at the center of the thick filaments and serve to anchor the thick filaments thus helping them to stay together during contraction.

M Lines

Which of these muscle types is striated and contains gap junctions?

cardiac muscle

Which of these types of muscle cells are capable of spontaneous depolarization?

cardiac muscle single-unit smooth muscle

Another name for an isotonic contraction where the muscle produces a tension greater than the load causing the muscle to shorten is:

concentric contraction

Which of the following actions apply to the myosin cross bridge heads?

Part of the myosin protein Bind to and pull on actin

which of the following are examples of isotonic contractions?

Picking up a pencil. Picking up your leg during walking.

When ______ ______ form between myosin and actin, they pull the actin towards the M line of the sarcomere.

cross bridges

When sarcomere lengths are greater than 2.2 micro-meters, the tension produced by the muscle during contraction:

decreases because there are fewer interactions between the actin and myosin.

Which of the following is an example of an eccentric muscle contraction?

flexing the arms when bench-pressing to allow the weight to return to the chest

Which of the following are characteristics of single unit smooth muscle?

Respond to stretch. Display pacemaker activity. Many gap junctions.

The series-elastic component of muscle contraction is responsible for

increased muscle shortening to successive twitches. a time delay between contraction and shortening. the lengthening of muscle after contraction has ceased.

The optimal muscle length:

is close to the normal resting length of muscle due to tendon insertion points. is the length where the most actin and myosin interactions can take place and the most force generated.

The contraction of smooth muscle cells:

is graded dependent upon the concentration of calcium. is slow and sustained.

The stimulation of gamma motoneurons produces

isometric contraction of intrafusal fibers

The contractions of skeletal muscles produce movements of bones and joints, the joints act as ____ to move the loads against which the muscle's force is exerted.

levers

Voltage gated calcium channel

located in the transverse tubules; opens in response to the action potential

Which of these muscles have motor units with the highest innervation ratio?

muscles that move the fingers

Within each muscle fiber densely packed, subunits known as _______ extend in parallel rows from one end of the cell to the other leaving no room between for other organelles

myofibrils

In a single reflex arc involved in the knee-jerk reflex, how many synapses are activated within the spinal cord?

one

A reflex

produces a response that varies with the stimulus strength. Produces the same result no matter the original strength of the stimuli

Asynchronous activation of different motor units in a muscle:

produces a smooth, sustained contraction prevents muscle fatigue

Stronger muscle contractions are produced by the process of __________ during which the body stimulated more muscle fibers to contract.

recruitment

Electrical excitation of a muscle fiber most directly causes

release of Ca2+ from the sarcoplasmic reticulum

Skeletal muscle

striated, innervated in motor units, multinucleate

Most of the calcium in skeletal muscle cells is stored in the

terminal cisternae

The calcium release channels found in the _______ _______ are responsible for the diffusion of calcium ions into the sarcoplasm which initiates fiber contraction

terminal cisternae

A graded whole muscle contraction is produced in vivo primarily by variations in

the number of fibers that are contracting

During the power stroke component of skeletal muscle contraction:

the thin filament moves towards the M line.

Spastic paralysis may occur when there is damage to

the upper motor neurons

When a muscle is at rest, the majority of the active sites for myosin binding on the actin molecule are covered by the protein

tropomyosin

When a muscle is stimulated to contract Ca2+ binds to

troponin

Smooth Muscle

unstriated, no sarcomeres, myogenic

Monosynaptic stretch reflex

1. Stretching of the spindle fibers of a muscle 2. distorting of central bag or chain region 3. Stimulus of sensory neurons 4. APs travel to spinal cord via sensory neuron 5. Somatic motor neuron stimulated 6. Contraction of extrafusal fibers stimulated

_______ or flower spray endings, which are located over the contracting poles of the nuclear chain fibers are continually stimulated throughout the stretch event.

Secondary

Afferent neuron

Sensory neuron that conducts signals

The elastic structures of muscle and tendons, called the _____ ______ ______, must be pulled tight before a muscle contraction can result in shortening.

Series Elastic Component

Which of the following is true of both temporal summation and motor unit recruitment?

They increase the force that a muscle generates

Varying the number of muscle fibers participating in a contraction will produce:

A graded contraction

What is used both to orient myosin into the correct position for the power stroke and to break the bond between actin and myosin after the power stroke?

ATP

Which of the following must be present to allow a muscle fiber to relax?

ATP

In smooth muscle, the receptors for autonomic neurotransmitters are located

Across the entire surface of the cell

In smooth muscle, the receptors for autonomic neurotransmitters are located:

Across the entire surface of the cell

The action of the Ca++ ATPase pumps:

Allows the fiber to relax Moves calcium against its gradient. Moves calcium into the SR

The transverse tubules or T-tubules:

Are formed from the sarcolemma Conduct action potentials.

In order for a muscle to contract and shorten, the tension produced by the muscle must _______ the load on the muscle.

Be equal to be greater than

Troponin

Calcium binds causing shape change that moves tropomyosin

what protein binds with calcium and regulates the binding of myosin and actin?

Calmodulin

When is calcium used during contraction?

To bind to troponin and allow for the movement of tropomyosin

What is the function of tropomyosin in muscle contraction?

To block myosin from binding to actin when there is no contraction signal

What is the function of troponin in muscle contraction?

To move/lever tropomyosin off the active site of actin so that myosin can bind to it.

What is the H band of the sarcomere?

The area that contains only thick filaments.

Which of the following must occur for a muscle fiber to relax?

The concentration of calcium in the cytoplasm must increase

Which of the following are true of cardiac muscle but not of skeletal muscle?

The entire myocardium contracts as a unit. Signal to contract is passed between cells via gap junctions.

When a muscle contracts isometrically

The load is greater than or equal to the tension that the muscle can produce. The muscle does not shorten.

During an isotonic contraction:

The muscle shortens The tension produced by the muscle is greater than the load.

In an isotonic muscle contraction

The muscle tension remains constant

In cardiac muscle, the initial signal to contract is generated by _______

The pacemaker or SA node

In smooth muscle, calcium regulates ________ while in skeletal muscle calcium regulates the availability of actin binding sites.

The phosphorylation of myosin cross bridges.

Which of the following analogies best explains how actin and myosin cycle within a cell

The power strokes are asynchronous and attach alternately as in the actions of a team engaged in a tug of war.

How does smooth muscle differ from skeletal muscle?

The thin filaments in smooth muscle cells are much longer. The myosin in smooth muscle fibers is stacked perpendicular. Smooth muscle does not have sarcomeres.

Excitation-contraction coupling pairs:

There generation of an action potential with the release of calcium to begin contraction

Which of the following statements is a characteristic of smooth muscles?

They are able to conduct graded depolarizations. They can enter a latch state. They produce graded contractions in response to graded depolarizations.

Which of the following statements about the Ca2+ release channels in the sarcoplasmic reticulum is true?

They are also called ryanodine receptors. They are opened by Ca2+ release channels in the transverse tubules. They permit Ca2+ to diffuse into the sarcoplasm from the sarcoplasmic reticulum.

A muscle _____ occurs when the muscle is stimulated with a single electric shock.

Twitch

Transverse tubules

Voltage gated calcium channels open

At what point will the velocity of shortening be the greatest?

When the load is zero

Sliding filament theory

1. Ca++ is released from the sarcoplasmic reticulum (SR) 2. Ca ++ binds to troponin C 3. Myosin cross bridges bind to actin 4. The myosin head pivots towards the center of the sarcomere 5. The myosin head binds an ATP molecule and detaches from the actin.

Which of these statements about cross bridges is true?

They are composed of myosin. they contain an ATPase They split ATP before they attach to actin.

In a _______ reflex, the signal crosses two synapses from sensory neuron to interneuron to motor neuron

Disynaptic

_____ _______ innervation occurs when the muscles involved in the reflex are controlled by more than one segment of the spinal cord or are located on different limbs of the body

Double reciprocal

Which of the following statements about myosin are correct?

Each globular myosin head has a binding site for actin as well as for ATP. At rest, each globular myosin head is not attached to actin. The myosin heads act as myosin ATPase enzymes.

In a __________ reflex, the sensory neuron detecting the change synapses only with the motor neuron that activates the muscle responding to the change.

Monosynaptic

Efferent neuron

Motor neuron that conducts signals from the CNS to muscle or effector organ

The power stroke:

Moves actin towards the center of the sarcomere. is produced by the myosin cross bridge. generates the contractile force in the muscle cell.

What makes up the thick filaments?

Myosin

_______ reflexes maintain muscles at their optimal length

Stretch

Cardiac muscle

Striated, myogenic, intercalated discs

When a muscle is repeatedly stimulated to contract before it completely relaxes, the muscle will remain contracted. What is this called?

Summation

The ________ _________ of the sarcoplasmic reticulum function in the storage and release of calcium ions during muscle contraction

Terminal Cisternae

When a skeletal muscle shortens during contraction, which of these statements is true?

The A bands shorten The H bands shorten The sarcomeres shorten

During muscle contraction:

The actin and myosin overlap each other