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
