9.9: Smooth muscle is nonstriated involuntary muscle

How is the contraction in smooth muscle similar to skeletal

- The final trigger for contraction is a rise in the intracellular calcium ion level. - Actin and myosin interact by the sliding filament mechanism. - ATP energizes the sliding process.

cell shape and appearance of cardiac muscle

Branching chains of cells; uni- or binucleate; striations

Connective tissue components of cardiac muscle

Endomysium attached to fibrous skeleton of heart

In smooth muscle fibers because they are arranged diagonally, the contract __________

In a twisting way

How is the activation of smooth muscle by a neural stimulus is identical to that in skeletal muscle?

Neurotransmitter binding generates an action potential, which is coupled to a rise in calcium ions in the cytosol.

What is a pacemaker

Some smooth muscle fibers in the stomach and small intestine

Describe smooth muscle tone

The smooth muscle in arterioles (small arteries) and other visceral organs routinely maintains a moderate degree of contraction,

True or False In most cases, adjacent smooth muscle fibers exhibit slow, synchronized contractions, the whole sheet responding to a stimulus in unison.

True

True or False Smooth muscle has low energy requirements, and as a rule, it makes enough ATP via aerobic pathways to keep up with the demand

True

True or False When norepinephrine, released by a different type of autonomic nerve fiber, binds to norepinephrine receptors on the same smooth muscle cells, the effect is inhibitory—the muscle relaxes, which dilates the bronchioles.

True

True or False some types of smooth muscle respond to neural stimulation with graded potentials (local electrical signals) only

True

True or False Smooth muscle takes 30 times longer to contract and relax than does skeletal muscle

True

True or False These pacemakers depolarize spontaneously in the absence of external stimuli.

True

Define calmodulin

a cytoplasmic calcium-binding protein.

Once pacemaker cell are excited___________

act as "drummers" to set the pace of contraction for the entire muscle sheet

In comparison to skeletal muscle, why is smooth muscle slower

because of ATPases and myofilaments latch together

What is involved in getting smooth muscle to stop contracting

calcium detachment from calmodulin, active transport of Ca21 into the SR and extracellular fluid, and dephosphorylation of myosin by a phosphatase enzyme, which reduces the activity of the myosin ATPases

How can neural and chemical stimuli affect pacemakers

can modify both the rate and the intensity of smooth muscle contraction.

smooth muscle layers depolarize spontaneously or in response to _____________

chemical stimuli that bind to G protein-linked receptors

Synchronized contraction sin most smooth muscle fibers reflect what?

coupling of smooth muscle cells by gap junctions that transmit depolarization from fiber to fiber.

In smooth muscle during excitation-contraction coupling, the SR releases Ca2+, but Ca2+ also moves_________

into the cell from the extracellular space via membrane channels

In all striated muscle types, calcium ions activate_________

myosin by binding to troponin.

How in smooth muscle does calcium activate myosin

myosin by interacting with a regulatory molecule called calmodulin

What is it called when calmodulin interact with kinase enzymes

myosin light chain kinase or myosin kinase

What does myosin light chain kinase do?

phosphorylates myosin light chains activating it

What regulates smooth muscle contraction

regulated by nerves, hormones, or local chemical changes.

____________ can maintain the same contractile tension for prolonged periods at less than 1% of the energy cost.

smooth muscle

In smooth muscle fibers bundles of contractile proteins crisscross within the smooth muscle cell so they ___________

spiral down the long axis of the cell like the stripes on a candy cane.

When acetylcholine binds to ACh receptors on smooth muscle in the bronchioles (small air passageways of the lungs), the response is ______________

strong contraction that narrows the bronchioles

when norepinephrine binds to smooth muscle in the walls of most blood vessels, it stimulates _____________

the smooth muscle cells to contract and constrict the vessel.

The effect of a specific neurotransmitter on a smooth muscle cell depends on____________

the type of receptor molecules on the cell's sarcolemma.

True or False Different autonomic nerves serving the smooth muscle of visceral organs release different neurotransmitters, each of which may excite or inhibit a particular group of smooth muscle cells.

true

true or false Some smooth muscle layers have no nerve supply at all.

true

Both skeletal and smooth muscle relax when

when intracellular Ca2+ levels drop

Which is longer and wider skeletal or smooth muscle

Skeletal muscle fibers are up to 10 times wider and thousands of times longer

Constricted breathing of asthma and for stomach cramps result from

Smooth muscle contraction

What is the response to stretch in smooth muscle

Stress-relaxation response

The intermediate filament-dense body networks forms _________ that harnesses the pull generated by the sliding of the thick and thin filaments

cable-like intracellular cytoskeleton

Although the SR does release some of the Ca21 that triggers contraction, most Ca21 enters through _________________

calcium channels directly from the extracellular space

True or False Skeletal muscle, which depends on extracellular Ca2+ for excitation-contraction coupling

False Correct: Skeletal muscle, which does not depend on extracellular Ca2+ for excitation-contraction coupling

True or False Smooth muscle fiber don't contain overlapping thick and thin filaments

False Correct: Smooth muscle fiber contain overlapping thick and thin filaments

True or False Smooth muscle fibers are large spindle-shaped cells.

False Correct: Smooth muscle fibers are small spindle shaped cells.

True or False Smooth muscle fibers have more elaborate SR and no T tubules.

False Correct: Smooth muscle fibers have less elaborate SR and no T tubules.

What are the speed of contractions in skeletal muscle

slow to fast

What does the sarcoplasmic reticulum of smooth muscle fibers lack ?

has no terminal cisterns and lacks a specific pattern relative to the myofilaments

What does contraction of smooth muscle in the rectum, urinary bladder, and uterus help with

helps those organs to expel their content

The ratio of thick to thin filaments is ___________ in smooth muscle than in skeletal muscle

much lower

In skeletal muscle is there presence of gap junctions

no

In smooth muscle fibers , each cell contains how many nucleus

one centrally located nucleus

Define Caveolae

pouchlike infoldings containing large numbers of Ca21 channels

What is the source of Ca2+ for contraction in skeletal muscle

sarcoplasmic reticulum ( SR)

What muscle is the highly structured neuromuscular junctions

skeletal muscle

What are the speed of contractions in cardiac muscle

slow

A small amount of fine connective tissue (endomysium) is secreted by _______________

smooth muscle themselves

Dense bodies at the sarcolemma surface also bind the muscle cell to the ___________

the connective tissue fibers outside the cell and to adjacent cells.

Describe chemical and mechanical events of contraction

the same in all muscle tissues, but smooth muscle is distinctive in several ways

What are the speed of contractions in smooth muscle

very slow

Where is cardiac muscle located?

walls of the heart

Where are endomysium located

between smooth muscle fibers

What does endomysium contain

blood vessels and nerves

Where is the site of calcium regulation in smooth muscle

Calmodulin in the cytosol

What is the response to stretch in skeletal muscle

Contractile strength increases with degree of stretch (to a point)

True or False Thick filaments of smooth muscle contain actin-gripping myosin heads along their entire length, a feature that makes smooth muscle as powerful as a skeletal muscle of the same size.

True

True or False Smooth muscle has calcium- binding troponin complex

True Correct: Smooth muscle doesn't have calcium- binding troponin complex

In smooth muscle what is the specific way myosin heads are oriented

in one direction on one side of the filament and in the opposite direction on the other side

Alternating contraction and relaxation of the longitudinal and circular layers mixes substances ____________________

in the lumen and squeezes them through the organ's internal pathway

Where is skeletal muscle located?

Attached to bones or (some facial muscles) to skin

What is the response to stretch in cardiac muscle

Contractile strength increases with degree of stretch

connective tissue components of skeletal muscle

Epimysium, perimysium, and endomysium

In smooth muscle does it elaborate sarcoplasmic reticulum

Equivalent to cardiac muscle (1-8% of cell volume); some SR contacts the sarcolemma

Define Gap Junction

Gap junctions are specialized cell connections that allow depolarization to spread from cell to cell.

Describe regulation of contraction in cardiac muscle

Involuntary; contraction initiated by intrinsic pacemaker cells; regulated by autonomic nervous system, hormones, and stretch

Describe regulation of contraction in smooth muscle

Involuntary; initiated by intrinsic pacemaker cells (in unitary muscle) or autonomic nerves (in multi unit muscle); regulated by local chemicals, hormones, and stretch

In cardiac muscle does it elaborate sarcoplasmic reticulum

Less than skeletal muscle (1-8% of cell volume); small terminal cisterns

Does skeletal muscle have rhythmic contraction

No

If there are no striations in smooth muscle, do they include sarcomeres

No

In skeletal muscle is there any presence of peacemakers(s)

No

Is there a presence of myofibrils composed of sarcomeres in smooth muscle

No, but actin and myosin filaments are present throughout; dense bodies anchor actin filaments

Is the presence and location of T tubules in smooth muscle

No; only caveolae

What is the source of Ca2+ for contraction in cardiac muscle

SR and from extracellular fluid

Cell shape and appearance of smooth muscle

Single, spindle shaped, uninucleate; no striations

Cell shape and appearance of skeletal muscle

Single, very long, cylindrical, multinucleate cells with obvious striations

Describe regulation of contraction in skeletal muscle

Voluntary via axon terminals of the somatic nervous system

Does cardiac muscle have rhythmic contraction

Yes

In cardiac muscle is there any presence of peacemakers(s)

Yes

Is there a presence of myofibrils composed of sarcomeres in skeletal muscle

Yes

In smooth muscle is there any presence of peacemakers(s)

Yes (in unitary muscle only)

Is there a presence of myofibrils composed of sarcomeres in cardiac muscle

Yes, but myofibrils are of irregular thickness

In cardiac muscle is there presence of gap junctions

Yes; at intercalated discs

In smooth muscle is there presence of gap junctions

Yes; in unitary muscle

In skeletal muscle does it elaborate sarcoplasmic reticulum

Yes; large terminal cisterns

Define Calmodulin

acts as the calcium-binding site in smooth muscle, due to the fact there is no troponin complex

What is the metabolism of cardiac muscle

aerobic

What is the metabolism of skeletal muscle

aerobic and anaerobic

Define dense bodies

also tethered to the sarcolemma, act as anchoring points for thin filaments and therefore correspond to Z discs of skeletal muscle

The intermediate filaments attach at regular intervals to cytoplasmic structures called _________

dense bodies

What does varicosities form ?

diffuse junctions that have wide synaptic clefts

Connective tissue components of smooth muscle

endomysium

How are most smooth muscles organized ?

into sheets of tightly packed fibers. These sheets are found in the walls of all but the smallest blood vessels and in the walls of hollow organs of the respiratory, digestive, urinary, and reproductive tracts.

Describe the longitudinal layer of smooth muscle fibers

layer, the muscle fibers run parallel to the long axis of the organ. Consequently, when these fibers con-tract, the organ shortens

What is the metabolism of smooth muscle

mainly aerobic

During contraction of smooth muscle fibers areas of the sarcolemma between the sense bodies bulge outward, ___________

making cell look puffy

True or False Epimysium and perimysium are present in smooth muscle fibers

False Correct: Epimysium and perimysium are not present

In contrast to skeletal muscle, smooth muscle has

- Smooth muscle fibers are small spindle-shaped cells. - Smooth muscle lacks the coarse connective tissue sheaths found in skeletal muscle. - Smooth muscle has varicosities instead of neuromuscular junctions. - Smooth muscle fibers have less elaborate SR and no T tubules. - Smooth muscle fibers are usually electrically connected by gap junctions.

How does smooth muscle myofilaments differ from skeletal muscle

- Thick and think filaments arranged diagonal - Intermediate filament-dense body network - No troponin complex in thin filaments - Thick filaments are fewer but have myosin heads along their entire length

In an example compare and contrast the neural input to skeletal and smooth muscles

- skeletal muscle gets high-speed internet while smooth muscle gets slow-speed dial-up

How many sheet of smooth muscle is form with their fibers oriented at right angles to each other ( like intestine)

2

What are the effect of nervous system stimulation in skeletal muscle

Excitation

What are the effect of nervous system stimulation in cardiac muscle

Excitation or inhibition

What is the source of Ca2+ for contraction in smooth muscle

Extracellular fluid and from SR

Where is the site of calcium regulation in cardiac muscle

Troponin on actin-containing thin filaments

Where is the site of calcium regulation in skeletal muscle

Troponin on actin-containing thin filaments

True or False In smooth muscle fibers hick and Thin filaments arranged diagonally

True

True or False Intermediate filament-dense body network in smooth muscle fibers

True

True or False Skeletal muscle fibers are electrically isolated from one another

True

True or False Smooth muscle fibers are usually electrically connected by gap junctions.

True

True or False Smooth muscle has varicosities instead of neuromuscular junctions.

True

True or False Smooth muscle lacks the coarse connective tissue sheaths found in skeletal muscle.

True

True or False The sarcolemma has multiple caveolae

True

True or False The varicosities simply "sprinkle" neurotransmitter in the general area of the smooth muscle cells.

True

True or False No troponin complex in thin filaments in smooth muscle fibers

True

Where is smooth muscle located?

Unitary muscle in walls of hollow visceral organs (other than the heart); multi unit muscle in intrinsic eye muscles, airways, large arteries

Does smooth muscle have rhythmic contraction

Ye sin unitary muscle

Is the presence and location of T tubules in cardiac muscle

Yes; one per sarcomere at Z disc; larger diameter than those of skeletal muscle

Smooth muscle fibers contain ______________________ taht resist tension

a lattice-like arrangement of noncontrac-tile intermediate filaments

Describe the circular layer of smooth muscle fibers

the fibers run around the circumference of the organ. Contraction of this layer constricts the lumen (cavity inside) of the organ.

The muscle in the walls of all the body's hollow organs is almost entirely smooth muscle except _________

the heart, which is made of cardiac muscle

Define varicosities

the innervating nerve fibers of the autonomic (involuntary) nervous system have numerous bulbous swellings

The calcium channels that allow Ca2+ to enter are a major source for what ?

the major source of Ca2+ for smooth muscle contraction.

Describe the difference between myosin and actin in smooth muscle

the myosin filaments are a lot shorter than the actin filaments and the type of myosin contained differs from skeletal muscle.

Is the presence and location of T tubules in skeletal muscle

yes; two per sarcomere at A-I junctions