Smooth Muscles & Muscle Metabolism Flashcards by Milleth Jane CAPANGPANGAN

composed of small fibers that are usually 1 to 5 micrometers in diameter and only 20 to 500 micrometers in length.

smooth muscle

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In contrast to skeletal muscle fibers
are as much as 30 times greater in diameter and hundreds of times as long.

smooth muscle

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has thick and thin filaments that are not arranged in sarcomeres; therefore, they
appear homogeneous rather than striated

smooth muscle

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Most important, essentially the same attractive forces between myosin and actin filaments cause contraction in smooth muscle as in skeletal muscle, but the___________ is different

internal physical arrangement of smooth muscle fibers

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is present in the iris, ciliary muscle of the lens, and vas deferens, arrector pili muscle
- behaves as separate motor units

Each fiber can contract independently of the others
and the control is exerted mainly by nerve signals

Multi-unit smooth muscle

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has little or no electrical coupling between cells.

is densely innervated; contraction is controlled by neural innervation (e.g., autonomic
nervous system)

Multi-unit smooth muscle

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In contrast, a major share of control
of unitary smooth muscle is exerted by ____________

non-nervous stimuli

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unitary smooth muscle, syncytial
smooth muscle, and visceral smooth muscle

Single-unit smooth muscle

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Muscle fibers contract together as a single unit

Cell membranes of adjacent fibers are connected
electrically by gap junctions

Single-unit smooth muscle

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is spontaneously active (exhibits slow waves) and exhibits “pacemaker”
- which is modulated by hormones and neurotransmitters.

■ has a high degree of electrical coupling between cells and, therefore, permits coordinated contraction of the organ (e.g., bladder).

Unitary (single-unit) smooth muscle

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is the most common type and is present in the uterus, gastrointestinal tract, ureter, and
bladder.

biliary tract, ureter , fallopian tube, blood vessels

Single-unit smooth muscle (unitary smooth muscle, syncytial smooth muscle, and visceral smooth muscle)

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has properties of both multi-unit and single-unit smooth muscle

vascular smooth muscle

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Smooth muscle does not have the same striated arrangement of actin and myosin filaments.

Actin filaments attach to dense bodies

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Dense bodies are dispersed in linking one dense body to another or attached to the cell membrane and form bonds with dense bodies of adjacent cells allowing______

force to be transmitted from one cell to another

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have similar functions to Z
disks in skeletal muscle.

Dense bodies

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are interspersed among actin filaments.

its filaments have a diameter that is more
than twice as large as that of the actin filaments.

Myosin filaments

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consist of actin filaments radiating from 2 dense bodies; these filaments overlap a single myosin filament that is located midway between the dense bodies.

Contractile units

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Most smooth muscle contractions are prolonged __________ones that sometimes last hours or even days.

tonic

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Slow cycling of the cross-bridges
Low energy requirement
Slow onset of contraction and relaxation
Increased maximum force of contraction
“Latch Mechanism”

MUSCLE CONTRACTION

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smooth muscle contracts 50-100
milliseconds after it is excited.

It has a long total contraction time of about ________, which is 30x stronger than skeletal muscle

1-3 seconds

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Increased force of contraction is postulated to
resolve due to the long period of attachment of the _____

myosin cross bridges to the actin filaments.

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Skeletal muscles have a useful distance contraction of only ¼-⅓ of its resting length, whereas smooth muscles often contract more than __________ of its stretch length.

⅔

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facilitates prolonged holding contractions; muscle can maintain its full force of contraction even when there is reduction in the degree of activation from the initial level

“Latch Mechanism”

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can maintain prolonged tonic contraction for hours with use of relatively low energy levels

“Latch Mechanism”

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Calcium ions combine with ___________ to cause activation of myosin kinase and phosphorylation of the myosin head.

Calmodulin (Counterpart of Troponin)

The calcium ions bind with calmodulin; the calmodulin-calcium complex then joins with and activates ______________

myosin kinase (phosphorylating enzyme)

One of the light chains of each___________ becomes phosphorylated in response to myosin kinase

myosin head (regulatory chain)

When the "regulatory chain" is phosphorylated, the HEAD has the capability of binding with the actin filament, causing _________

muscle contraction

is required for cessation of contraction

Myosin Phosphatase

Once ________ falls below a critical level, processes automatically reverse except for phosphorylation of the myosin head.

calcium ion concentration

Reversal of this step requires ___________, which splits the phosphate from the regulatory chain — relaxation then occurs

myosin phosphatase

neuromuscular junctions of the highly structured type found on skeletal muscle fibers are not present in smooth muscles due to the presence of:

1. Diffuse junctions formed by the autonomic fibers 2. Varicosities on the axon terminals distributed along the axis (loaded with transmitter substance) (- axon do not have typical branching) 3. Contact junctions in the multi unit of smooth muscles (similar to neuromuscular junction)

Neurotransmitters _________ & ____________ can have excitatory or inhibitory effects at the smooth muscle neuromuscular junction

acetylcholine and norepinephrine

○ Secreted by the autonomic neurons that innervate the smooth muscles ○ Subs are never secreted at the same time

acetylcholine and norepinephrine

excitatory transmitter for smooth muscle fibers in some organs but inhibitory in others

Acetylcholine

would inhibit some excitatory actions of the acetylcholine

Norepinephrine

depends of the smooth muscle and the momentary condition of the muscle is usually about -50 to -60 millivolts, or about 30 millivolts less negative than in skeletal muscle

RMP (Resting membrane potential)

Action Potentials occur in single-unit smooth muscle, such as visceral smooth muscle, in a manner similar to that of skeletal muscle, occurs in 2 forms:

1. Spike potentials 2. Action potentials with plateaus

—occurs in most types of single unit smooth muscle and can be elicited by electrical stimulation, stretch or the action of hormone/ transmitter subs, spontaneous generation from muscle fiber

Spike potentials

onset is similar of the spike, however depolarization is delayed for about several 100 milliseconds

Action potentials with plateaus

accounts for the prolonged period of contraction in the uterus, ureter, and some types of vascular smooth muscles

Action potentials with plateaus

are required for generating smooth muscle action potentials ○ Movement of Ca ions to the interior of the fiber is mainly responsible for the action potential

Calcium Ions

_______ in single unit smooth muscle can lead to generation of action potentials

Slow-wave potentials

are slow oscillations in membrane potentials. is not an action potential , but can LEAD or can CAUSE an action potential —> making muscle contract

Slow waves

Causes of slow waves:

1. The oscillation of sodium pump activity which causes membrane potential to become more negative (sodium is pumped rapidly) and less negative (sodium is pumped slowly) 2. The conductance of the ion channel may increase & decrease rhythmically

sodium is pumped rapidly

membrane potential become more negative

Action potential can be initiated when the potential of a slow wave raises above the threshold ___________

-35 millivolts

__________are often generated when visceral (Single-Unit) smooth muscle is stretched

Spontaneous Action Potentials

Spontaneous action potentials result from a combination of the normal SLOW WAVE potentials in addition to a decrease in the negativity of the membrane potential caused by the ____________

stretch (self-stimulus)

The response to stretch allows the GI wall when excessively stretched, to ______________ thereby resisting the stretch

contract rhythmically

______________ in blood vessels occurs in response to local tissue factors

Smooth Muscle Relaxation

is required for local control of blood flow

Vasodilatory response

Many circulating ________in the body affect smooth muscle contraction to some degree

hormones

A hormone causes contraction when the muscle cell membrane contains ____________ for the respective hormone

excitatory receptors

Conversely, the hormone causes relaxation if the membrane contains _________________

inhibitory receptors

Fibers are stimulated by certain:

neurotransmitters (acetylcholine & norepinephrine), hormones, or autorhythmic signals (eg in the GIT system to move food along)

Action Potentials are transmitted via

gap junction

- Walls of arteries and veins ○ Walls of Hollow organs ○ Walls of airway to the lungs ○ (Arrector pili) Muscles that attach to hair follicles ○ Muscles that adjust pupil diameter ○ Muscles that adjust focus of the lens in the eye

smooth mucles

Layers of Smooth Muscle (2) oriented at right angles to each other:

○ Longitudinal layer — causes organ dilation & shortening ○ Circular layer — causes organ constriction & elongation

in skeletal muscle cell, which has neuromuscular junction, in smooth muscle cells you see these _________

varicosities

in skeletal muscle you have somatic nerve fibers, in smooth muscle -

autonomic nerve fibers

series of neurotransmitter-filled bulges an axon courses through smooth muscle, loosely forming motor units ([link]). releases neurotransmitters into the synaptic cleft.

varicosities

With sympathetic innervation, usually the neurotransmitter is ________

norepinephrine

parasympathetic innervation, generally the neurotransmitter will be _________.

acetylcholine

Contains both thick filaments and thin filaments - Not arranged in orderly sarcomeres - Arranged diagonally - No regular pattern of overlap - not striated

SMOOTH MUSCLE TISSUE

_________in the sarcolemma instead of T tubules

Caveolae

why smooth muscles are not striated?

thick filaments and thin filaments are not arranged in orderly sarcomeres No regular pattern of overlap

__________in the sarcolemma instead of T tubules

Caveolae

not may SR in smooth muscle tissue so most of the calcium will come out from _____________

extracellular fluid

instead of Z disks, it has _______

dense bodies

functions same as Z disks, During contraction the filaments pull on the _________ causing a shortening of the muscle fiber

dense bodies

protein used to bind calcium in the cytosol (instead of troponin) then activates myosin kinase, which phosphorylates myosin head

Calmodulin

During contraction, the __________ do get pulled closer to each other

dense bodies

There is an ion channel that allows calcium inside. Remember, most of your calcium will come from the _________, but some will still come from the SR

extracellular fluid

calcium makes its way into the ______

cytosol

calcium becomes available, __________ will activate

calmodulin

This activated calmodulin can then activate __________. and they can then catalyze the transfer of this phosphate from ATP onto myosin

myosin light chain kinases

the activated kinase enzymes catalyze transfer of phosphate to myosin, activating the

myosin ATPases

Starts slower and lasts much longer than skeletal muscle contraction

SMOOTH MUSCLE TISSUE - physiology

Prolonged presence of calcium in the cell provides for a state of continued ___

partial contraction

calcium moves slowly out of the muscle fiber, delaying _________

relaxation

delay relaxation is important in ___________ where a steady pressure is maintained on the contents of the tract

Gastrointestinal tract

delay relaxation is important in the _________ which maintain a steady pressure on blood

walls of blood vessels

Smooth muscle fibers contract or relax in response to:

- Action potentials - Stretching - Hormones - Changes in pH, oxygen and carbon dioxide levels - Temperature

Action potentials is from the ________ unlike skeletal system that uses somatic nervous system

autonomic nervous system

cold temperature can cause muscle contractions

true

Pupil constriction due to increased light energy is an example of

action potential

Food in digestive tract stretches intestinal walls initiating peristalsis

stretching

_________ causes relaxation of smooth muscle in the air-ways and in some blood vessel walls

Epinephrine

______________of the cell membrane opens voltage-gated Ca2+ channels and Ca2+ flows into the cell down its electrochemical gradient, increasing the intracellular [Ca2+].

Depolarization

Hormones and neurotransmitters may open ligand-gated Ca2+channels in the cell membrane. They also directly release Ca2+ from the SR through_______

inositol 1,4,5-triphosphate (IP3)-gated Ca2+ channels

Ca2+ binds to calmodulin. The Ca2+–calmodulin complex binds to and activates myosin light-chain kinase. When activated, myosin light-chain kinase phosphorylates myosin and allows it to bind to actin, thus initiating cross-bridge cycling. The amount of tension produced is proportional to the intracellular Ca2+ concentration.

A decrease in intracellular [Ca2+] produces relaxation

Upstroke of action potential in skeletal muscle and smooth muscle is Inward Na+ current in cardiac muscle:

Inward Ca2+ current (SA node) Inward Na+ current (atria, ventricles, Purkinje fibers)

Plateau in skeletal muscle and smooth muscle is NO (absent) in cardiac muscle:

No (SA node) Yes (atria, ventricles, Purkinje fibers; due to inward Ca2+ current)

Duration of action potential in skeletal muscle is 1msec smooth muscle is 10msec cardiac muscle:

150 msec (SA node, atria) 250–300 msec (ventricles and Purkinje fibers)

Excitation–contraction coupling in smooth muscle:

Action potential opens voltage-gated Ca2+ channels in cell membrane Hormones and transmitters open IP3– gated Ca2+ channels in SR

Molecular basis for contraction

Ca2+–calmodulin ↑ myosin light-chain kinase