A & P Ch 9 Muscular System 2/3

Cardiac muscle is ____-_____ and rhythmic. A pattern of contraction and ____ repeats, generating the rhythmic contraction of the heart.

self-exciting; relaxation

While summation increases the force of contraction of a ____ muscle fiber, a whole muscle can generate more force if more muscle fibers are involved in the ____.

single; contraction

The contractile response of a __ muscle fiber to a single ___ is called a ____.

single; impulse; twitch

A ____ action potential conducted down a ____ neuron normally releases enough ___ to bring the muscle fibers to threshold, generating an ____.

single; motor; ACh; impulse

Smooth muscle is _____ to contract and ____ than skeletal muscle, yet smooth muscle can ____ contract longer with the ____ amount of ATP.

slower; relax; forcefully; same

At higher frequencies of _____, as the time spent in relaxation becomes very ____, a condition called partial ____ results

stimulation; brief; tetany

At higher intensities of ____, other motor neurons respond, and more motor ____ are activated. Such an increase in the number of activated motor units is called ____ motor ___ summation, or _____

stimulation; units; multiple; unit; recruitment

The length to which a muscle fiber is ___ before stimulation affects the ___ it will develop.

stretched; force

If a skeletal muscle fiber is ___ well beyond its normal ___ length, the force will ___. This is because ___ of that fiber become so ___ that some myosin heads cannot reach binding sites on the ___ filaments and cannot ____ to contraction.

stretched; resting; decrease; sarcomeres; extended; thin; contribute

Even when a muscle appears to be at rest, its fibers undergo a certain degree of ___ contraction. This continuous state of partial contraction is called muscle ____ (tonus), and it is a response to impulses originating _____ in the spinal cord and conducted along ____ to a few muscle fibers.

sustained; tone; repeatedly; axons

Smooth muscle cells do not have ____ _____, and their ______ reticula are not well developed.

transverse tubules; sarcoplasmic

The number of muscle fibers in a motor unit ____ considerably. The fewer muscle ___ in the motor units, however, the more ____ the movements that can be produced in a particular muscle.

varies; fibers; precise

Also, cardiac muscle becomes non-responsive (____) after stimulation until the ____ ends. Therefore, sustained or tetanic contractions do not occur in the ____ muscle.

refractory; contraction; heart

the events leading up to a twitch is called a?

myogram

Summation and recruitment together can produce a ____ contraction of _____ strength.

sustained; increasing

During sustained contractions smaller motor units, whose neurons have smaller-_____ axons, are more _____ stimulated and are recruited ____. Larger motor units, whose neurons have larger-diameter ____, respond later and with ____ force.

-diameter; easily; first; axons; greater

Once threshold is reached, an ____ potential is generated, resulting in an ____ that spreads throughout the muscle fiber, releasing enough ____ ions from the _______ reticulum to activate cross-bridge formation and ____ the fiber.

action; impulse; calcium; sarcoplasmic; contract

Sustained contractions of whole muscles enable us to perform everyday activities, but the force generated by those contractions must be _____.

controlled

Visceral smooth muscle is the more ____ type of smooth muscle. It is found in the walls of ____ organs, such as the stomach, _____, urinary bladder, and uterus.

common; hollow; intestines

A twitch consists of a period of ___, during which the fiber pulls at its _____, followed by a period of _____, during which the pulling force declines

contraction; attachments; relaxation

A twitch has a brief ___ between the time of stimulation and the ____ of contraction. This is the ____ period, which in human muscle is approximately 2 ______

delay; beginning; latent; milliseconds

Smooth muscle cells are ____ with tapering ends and contain thick and thin ____, but these filaments are not organized into _____. Therefore, smooth muscle cells lack _____ and appear "smooth" under the microscope

elongated; filaments; myofibrils; striations

Understanding how individual muscle ____ contract is important for understanding how ___ work, but such contractions by themselves are of little significance in ___-___-____ activities. Rather, the actions we need to perform usually require the contribution of ___ muscle fibers simultaneously

fibers; muscles; day-to-day; multiple

For example, holding a paper cup of coffee ___ enough to keep it from slipping through our fingers, but not so forcefully as to crush it, requires precise control of ____ force. In the whole muscle, the force developed reflects (1) the ____ at which individual muscle fibers are stimulated and (2) how many fibers take part in the overall _____ of the muscle.

firmly; contractile; frequency; contraction

The calcium ions in transverse tubules come from the ___ outside the cardiac muscle ____. In this way, extracellular calcium partially controls the ____ of cardiac muscle contraction and enables cardiac muscle cells to contract _____ than skeletal muscle fibers can.

fluid; cell; strength; longer

When the resulting ______, sustained contraction lacks even partial _____, it is called complete (____) tetany (tetanus). Complete tetany does not occur in the ___, but can be demonstrated in the laboratory.

forceful; relaxation; fused; body

These two features of visceral smooth muscle—conduction of ____ from cell to cell and rhythmicity—are largely responsible for the wavelike motion called _____ of certain ____ organs

impulses; peristalsis; tubular

A muscle fiber exposed to a series of stimuli of _____ frequency reaches a point when it is unable to completely ___ before the next stimulus in the ___ arrives. When this happens, the individual ___ begin to combine, and the contraction becomes ____. In such a sustained contraction, the force of individual twitches combines by the process of _____

increasing; relax; series; twitches; sustained; summation

Intercalated discs help join cells and transfer the force of contraction from cell to cell, and also allow ____ to diffuse between the cells. This ion movement allows action potentials to ____ from cell to cell. In this way, when one portion of the cardiac muscle network is stimulated, the impulse ___ rapidly to other cells of the network, and the whole structure contracts as a unit or _____; that is, the network responds to stimulation in an ____-___-____ manner.

ions; travel; passes; syncytium; all-or-none

In the laboratory, when an ___ muscle fiber is exposed to a series of electrical ___ of increasing strength, the fiber remains ___ until a certain strength of stimulation called the ____ stimulus is applied

isolated; stimuli; unresponsive; threshold

On the other hand, the transverse tubules of cardiac muscle cells are ____ than those in skeletal muscle cells, and they release many ___ ions into the sarcoplasm in response to a single _____.

larger; calcium; impulse

Like muscle fibers, ___ neurons must be brought to ____ before an impulse is generated. Some motor neurons are more easily brought to threshold than others. If only the more ___ stimulated motor neurons are involved, few motor units ___.

motor; threshold; easily; contract

The two major types of smooth muscle are ____ and _____

multiunit; visceral

individual twitches do ___ normally occur. Partial ____ contractions of muscle fibers are common. On the whole-muscle level, contractions are smooth rather than irregular or jerky because the ____ cord stimulates contractions in different sets of motor units at different ____.

not; tetanic; spinal; moments

The ____ ends of cardiac muscle cells are connected by cross-bands called ____ discs. These bands are complex intercellular ____ that include components of _____ and gap junctions.

opposing; intercalated; junctions; desmosomes

During normal activities, muscle fibers contract at their ___ lengths, at which force of contraction will be ____

optimal; maximal

Most muscle fibers have only one motor end ____. Motor neuron axons, however, are densely ____, which enables one such ___ to control many muscle fibers. Together, a motor ____ and the muscle fibers it controls constitute a motor ___

plate; branched; axon; neuron; unit

Muscle tone contributes to maintaining _____. Tautness in the muscles of the neck, trunk, and _____ limbs enables a person to hold the ____ upright, stand, or sit. If tone is suddenly lost, such as when a person loses consciousness, the body _____.

posture; lower; head; collapses

As the intensity of stimulation increases, _______ of motor units continues until finally ____ motor units are activated in that muscle.

recruitment; all