Ch 8: Muscles Flashcards
3 types of muscle
cardiac, skeletal, and smooth
a single skeletal muscle cell is known as a ____
muscle fiber
a skeletal muscle consists of:
a number of muscle fibers lying parallel to each other and bundled together by connective tissue
during embryonic development of vertebrates, the huge skeletal-muscle fibers are formed by the fusion of many smaller cells called _______
myoblasts
is skeletal muscle multinucleate?
yes
what are myofibrils?
- part of skeletal muscle fibers
- specialized contractile elements
- cylindrical intracellular organelle
- extend the full length of the muscle fiber
Can muscle fibers with a low percentage of myofibrils generate a high degree of tension? what do they have a high ability to do?
No. But they are generally associated with the ability to turn muscles on and off quickly or to generate prolonged activity.
How are male cicadas able to produce their loud mating song and tail-shaking rattlesnakes move their muscles so fast?
because they have a lower percentage of myofibrils in their muscle fibers.
2 cytoskeletal elements of myofibrils
thick and thin filaments
Thick filaments are special assemblies of the protein ____, while thin filaments are made up primarily of the protein ____.
Thick filaments are special assemblies of the protein MYOSIN, while thin filaments are made up primarily of the protein ACTIN.
dark bands are also known as ______ and light bands are known as _____
dark bands are known as A BANDS and light bands are known as I BANDS
What leads to the striated appearance of a skeletal muscle fiber?
the bands of all the myofibrils lined up parallel to each other
What does an A band consist of?
a stacked set of thick filaments along with the portion of thin filaments that overlap on both ends of the thick filaments.
What defines the outer limits of a given A band?
where thick filaments end
What is the H zone?
The lighter area within the middle of the A band , where the thin filaments do not reach.
What does the I band consist of?
the remaining portion of thin filaments that do not project into the A band.
The visible line in the middle of each I band is called the _________
Z line
The area between two Z lines is known as a _____
sarcomere, which is the functional unit of skeletal muscle (i.e., the smallest component of muscle that is capable of contraction).
What is a functional unit?
the functional unit of any organ is the smallest component that can perform all the functions of that organ.
What is the Z line?
a flat cytoskeletal disc made from a cytoskeletal protein complex that CONNECTS THE THIN FILAMENTS OF TWO ADJOINING SARCOMERES.
T/F. during growth of a vertebrate, the size of the sarcomere increases.
false. A muscle increases in length by adding new sarcomeres.
The system of supporting proteins which hold thick filaments together vertically within each stack is found in the ______
M line
a myosin molecule is a protein consisting of ___ identical subunits, each shaped like a _____
a myosin molecule is a protein consisting of TWO identical subunits, each shaped like a GOLD CLUB WITH TWO HEADS.
Two important myosin sites crucial to the contractile process:
- an actin-binding site
2. an ATPase site
Myosin filaments are linked to the Z lines by the gigantic, elastic protein, ________
TITIN.
Connects Z disc to M line
What is the cell membrane of a muscle fiber called?
sarcolema
Thin filaments consist of 3 proteins:
actin, tropomyosin, and troponin
What shape are actin proteins?
spherical
what forms the backbone of thin filaments?
the backbone of thin filament is formed by ACTIN MOLECULES joined into TWO STRANDS and TWISTED TOGETHER.
kinda like two chains of pearls wrapped around each other.
Wife: you’re “actin” strange by giving me those pearls, husband.
Each actin molecule has sites for both ____ and ____ myosin attachment with a myosin cross bridge.
weak and strong
What types of bonds exist in the weak binding site of actin?
primarily electrostatic.
What are tropomyosin molecules?
threadlike proteins that lie end-to-end alongside the groove of the actin spiral.
It covers the actin sites that bind with the cross bridges, blocking interaction that leads to muscle contraction.
3 polypeptide units in troponin:
- one that binds to tropomyosin
- one that binds to actin
- one that can bind to Ca2+
What occurs when troponin binds to Ca2+?
When troponin is NOT bound to Ca2+, it stabilizes tropomyosin in its blocking position over actin’s cross-bridge binding site.
When troponin BINDS TO Ca2+, there is a SHAPE CHANGE that allows tropomyosin to slide away from its blocking position, ALLOWING MYOSIN HEAD TO BIND TO ACTIN TO FORM CROSS BRIDGES, resulting in a MUSCLE CONTRACTION.
Why are troponin and tropomyosin called “regulatory proteins?”
because of their role in preventing or permitting contraction/binding between actin and myosin.
Troponin molecules consist of ___ small, spherical subunits
3
explain what occurs when a muscle fiber is excited.
- Ca2+ is released
- released Ca2+ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site
- Cross-bridge binding occurs
- Binding of actin and myosin cross bridge triggers POWER STROKE that pulls THIN FILAMENT inward during contraction
Explain the changes in banding pattern during muscle shortening
- Sarcomere shortens
- A band stays the same width
- I band shortens
- H zone shortens
- Z lines get closer together
Tropomyosin is held in place over actin binding site by _______
Troponin (unbound to Ca2+)
When myosin and actin make contact at a cross-bridge, the bridge changes shape, bending _____ degrees (inward/outward?), “stroking” (towards/away from?) the center of the sarcomere.
When myosin and actin make contact at a cross-bridge, the bridge changes shape, bending 45 degrees INWARD, “stroking” TOWARDS the center of the sarcomere.
Describe a single cross-bridge cycle (power stroke)
- Binding: myosin cross bridge binds to actin molecue
- Power stroke: corss bridge bends 45 degrees, pulling thin filaments inward.
- Detachment: Cross bridge detaches at the end of the power stroke and returns to original conformation.
- Binding: Cross bridge binds to more distal actin molecule; cycle repeats.
What prevents “slip back” of thin filaments?
There will always be at least a few myosin heads attaching to actin while others detach
Skeletal muscles are stimulated to contract by release of ______ at _________ ________ between motor neuron terminals and muscle fiber.
Skeletal muscles are stimulated to contract by release of ACETYLCHOLINE at NEUROMUSCULAR JUNCTIONS between motor neuron terminals and muscle fiber.
Which enzyme destroys ACh to shut off signal?
Acetylcholinesterase
Two important membranous structures in the muscle
Transverse tubules (T tubules) and sarcoplasmic reticulum (SR)
Location of transverse tubules
at each end of the A band
What are t tubules? what do they do?
- deep dips in the surface membrane
- runs perpendicularly from the surface of the muscle cell membrane into the central portions of the muscle fiber.
- Because the t tubule membrane is continuous with the surface membrane, an AP on the surface membrane also spreads down the t tubule, providing a means of RAPIDLY TRANSMITTING THE SURFACE ELECTRIC ACTIVITY INTO THE CENTRAL PORTIONS OF THE FIBER.
- AP in the T tubules induces permeability changes in the SR (ACTIVATES SR).
Location of SR
fine network of interconnected tubules SURROUNDING MYOFIBRIL like a mesh sleeve.
Runs longitudinally along myofibril.
Separate segments of SR are wrapped around each A band and each I band.
What is stored in the SR’s lateral sacs?
Calcium
Spread of an AP down a T tubule triggers release of ___ from the SR into the ___ to trigger contraction.
Spread of an AP down a T tubule triggers release of Ca2+ from the SR into the CYTOSOL to trigger contraction
How does calcium return to the SR?
via the Ca2+-ATPase pumps
The greater the speed of conduction, the ____ the volume of SR in a muscle fiber.
GREATER.
i.e., more SR = faster
What proteins contain 4 subunits, bridge the gap between the lateral sac of the SR and the T tubule, and serves as a Ca2+ release channel?
foot proteins!
What receptor fits into foot proteins?
dihydropyridine receptor of T tubule
The ATPase site of the myosin cross bridge is an _____ site which can bind the carrier _____ and split it into ____ and ____, releasing ____ in the process
The ATPase site of the myosin cross bridge is an ENZYMATIC site which can bind the carrier ATP and split it into ADP and Pi, releasing ENERGY in the process.
Does the breakdown of ATP occur before or after the binding of the myosin cross bridge with actin?
BEFORE
When are Pi and ADP released from the crossbridge?
Pi is released during the power stroke.
ADP is released after the power stroke is completed.
What allows for the detachment of the cross bridge from the actin molecule following a power stroke?
The actin and myosin remain linked until a molecule of ATP attaches to the myosin at the end of the power stroke.
Binding of myosin to a new ATP allows for the detachment of the cross bridge and myosin returns to its original conformation, ready for the next cycle.
What occurs to cross bridges when a person dies?
Since no fresh ATP is available, myosin cross bridges are unable to detach from actin molecules and remain bound in a RIGOR COMPLEX.
When is the contractile process turned off?
When Ca2+ is returned to the LATERAL SACS via the SR Ca2+-ATPase pump.
Mitochondria, which are positioned close to the calcium release sites on the SR, also take up Ca2+.
Stored energy in myosin cross bridge is converted into _____ energy and ___ ___ occurs
Stored energy in myosin cross bridge is converted into MECHANICAL energy and POWER STROKE occurs
What occurs to tropomyosin once no more Ca2+ is present?
with no Ca2+ on troponin, tropomyosin moves back to original position, blocking myosin cross bridge sites on actin.
Mitochondrial volume is _____ that of the SR and is positioned near _____________, so it plays a significant role in Ca2+ reuptake
Mitochondrial volume is FIVE FOLD that of the SR and is positioned near Ca2+ RELEASE SITES, so it plays a significant role in Ca2+ reuptake
High speed muscles have:
- increased density of Ca2+ ATPase pumps
- calcium binding proteins (calsequestrin)
Gulf toadfish swim bladder function
- holds gases to help determine buoyancy
- rapidly contracts and relaxes and makes sound
- vocalization is caused by rapid muscle contraction (for mating calls and other purposes)
Adaptations of gulf toadfish swim bladder
Calcium:
- maximal density Ca2+ pumps in SR
- different Ca2+ pump isoforms which pump at different rates
- High volume of SR (about 30% of muscle volume)
- Exclusion of mitochondria
Myosin cross bridges:
- Troponin isoforms with lower Ca2+ affinity INCREASE BEAT FREQUENCY by releasing Ca2+ faster
- Low proportion of cross-bridges are attached at any given instant
- muscle strength is weak
A single AP in a skeletal muscle fiber results in a ___
twitch
The delay of a few milliseconds between stimulation and the onset of contraction is known as the ____ ____
Latent period
What is the contraction time?
Time from the onset of contraction until peak tension is developed.
The time from peak tension until relaxation is complete is the _____ _______
relaxation time
For a contracted muscle to expand, there are three basic mechanisms:
- an ANTAGONISTIC MUSCLE typically found on the opposite side of a skeletal joint, WHOSE CONTRACTION STRETCHES OUT THE OTHER MUSCLE.
- FLUID PRESSURE created by distant muscles that push on and re-extend a contracted muscle.
- SERIES ELASTIC ELEMENTS: springlike structures that get stretched or compressed by a contracting muscle and then “rebound” to release their stored energy and thereby stretch out that muscle.
Muscle organ is covered by a sheath of __ ___
connective tissue
Connective tissue extends beyond the ends of the muscle to form tough, collagenous ______
tendons
What do tendons do?
attach muscles to bones
permit greater dexterity
In arthopods, muscles attach to _____ rather than tendons
apodemes (ridges that project from the inner face of the exoskeleton)
Flexors ___ a limb, and extensors ___ a limb
Flexors BEND a limb, and extensors STRAIGHTEN a limb out
The greater the number of muscle fibers contracting, the ___ the total muscle tension
greater
T/F: a muscle fiber can be innervated by multiple motor neuron.
FALSE. One motor neuron innervates a number of muscle fibers, but each vertebrate muscle fiber is supplied by only one motor neuron.
What composes a motor unit?
one motor neuron and all the muscle fibers it innervates.
What do small motor units (e.g., one nerve innervating only 12 or less muscle fibers) allow for?
very fine degree of control over muscle tension.
e.g., external eye muscles and hand muscles in humans
What does the number of muscle fibers participating in the whole muscle’s total contraction depend on?
the number of motor units recruited and the number of muscle fibers per motor unit.
Explain asynchronous recruitment of motor units
The brain alternates motor unit activity so as to prevent muscle fatigue.
Gives motor units which had been active a chance to rest while others take over.
Which motor units are recruited first during weak or moderate endurance-type activities (aerobic activities)?
The motor units which are most resistant to fatigue
What occurs when a second AP is elicited in a muscle before the first AP comes to rest?
The second one piggybacks” onto the first one.
The two twitches SUMMATE to produce a greater tension in the fiber than that produced by a single AP.
Why is twitch summation possible?
Because the duration of the AP is much shorter than the duration of the twitch.
In other words, the AP and refractory period are done far before the twitch is completed.
What is tetanus?
When a muscle fiber is stimulated so rapidly that it does not have time to relax between stimuli, a smooth, sustained CONTRACTION OF MAXIMAL STRENGTH (tetanus) occurs.
Shortening of the sarcomeres stretches the series-elastic components (____, ____, ____) and transmits muscle ____ to skeleton
Shortening of the sarcomeres stretches the series-elastic components (TITN, Z-LINE, TENDON) and transmits muscle TENSION to skeleton
2 primary types of contraction:
- isotonic
2. isometric
Work =
force x distance
What occurs during an isotonic contraction?
- MUSCLE TENSION REMAINS CONSTANT
- MUSCLE CHANGES LENGTH
- MUSCLE DOES WORK
What occurs during an isometric contraction?
- MUSCLE LENGTH REMAINS CONSTANT
- TENSION INCREASES
- NO WORK DONE
define the two types of isotonic contractions:
- concentric: muscle shortens
2. eccentric: muscle lengthens
Two primary factors are adjusted to accomplish gradation of whole-muscle tension:
IMPORTANT FOR EXAM
- number of fibers contracting:
- number of motor units recruited
- number of muscle fibers per motor unit
- number of muscle fibers available to contract (size of muscle). - Tension developed by each contracting fiber
a. frequency of stimulation
b. length of fiber at the onset of contraction
c. extent of fatigue
d. thickness of fibers
T/F, every muscle has an optimal length
true
When can the greatest degree of tension be achieved during tetanus?
-When beginning at the OPTIMAL MUSCLE LENGTH
-less tension in tetanus when beginning with the muscle less or grater than ts optimal length
(length-tension relationship)
Conditions of optimal length
Optimal length is when optimal tension can be developed.
At this length, A MAXIMAL NUMBER OF CROSS BRIDGE SITES ARE ACCESSIBLE TO THE ACTIN MOLECULES FOR BINDING AND BENDING.
Why is maximum achieved tetanus tension less when muscle length is GREATER than its optimal length?
When the muscle is stretched, the thin filaments have been pulled out from between the thick filaments, decreasing the number of sites for cross bridge binding.
Several actin sites thus go unused.
Why is maximum achieved tetanus tension less when muscle length is LESS than its optimal length?
Less tension can be developed when the muscle is compressed shorter than its optimal length because:
- thin filaments from the opposite sides of the sarcomere become overlapped, decreasing number of actin sites exposed to the cross bridges.
- Thick filaments become forced against Z lines, further shortening is impended
- Less Ca2+ is released
The contraction/relaxation process requires ATP at three different steps:
- splitting of ATP by myosin ATPase
- binding of a new ATP molecule to myosin to permit detachment from actin (it is subsequently split)
- Active transport of Ca2+ back into SR during relaxation
3 pathways to supply ATP:
- phosphagen
- ox phosphorylation
- glycolysis
Phosphagens
- creatine phosphate and arginine phosphate
- provide an immediate supply of ATP
- first energy storehouse tapped at the onset of contractile activity.
- they contain a high energy phosphate group which is transferred to ADP to form ATP
Creatine phosphate and ADP mechanism
creatine kinase
creatine phosphate + ADP creatine + ATP
How many ATPs are produced in oxidative phosphorylation?
approx 30 per glucose molecule
The O2 required for oxidative phosphorylation in vertebrates is primarily delivered by the ___
blood
How is increased O2 made available during aerobic activity?
- enhanced breathing brings in more O2
- heart contracts more rapidly and forcefully to pump more oxygenated blood to tissues
- more blood is diverted to exercising muscles by dilation of the blood vessels supplying them
- the hemoglobin molecules release more O2 in exercising molecules
Oxidative phosphorylation is fueled by ____ or ___
glucose or fatty acids
which process can be anaerobic? ox. phosph. or glycolysis?
glycolysis
Which ATP-yielding process supports high intensity activity? (eg. burst swimming in fish)?
glycolysis
Advantage of glycolysis for supplied ATP as opposed to ox. ph.?
- faster
- does not require oxygen
- it is the ONLY WAY TO SUPPORT HIGH INTENSITY ACTIVITY
Glycolysis produces ______ which ______ pH
Glycolysis produces LACTATE which LOWERS pH
main source of ATP when oxygen is present? when it’s not present?
When O2 is present, oxidative phosphorylation.
When O2 is NOT present, glycolysis.
What does muscle fatigue protect against?
the full depletion of ATP in muscles, leading to rigor mortis
When does central fatigue occur? What happens?
Central fatigue occurs when the CNS no longer adequately activates the motor neurons supplying the working muscles.
The animals slows down or stops exercising, even if the muscles are still able to perform.
What is muscle fatigue?
muscle fatigue occurs when an exercising muscle can no longer respond to stimulation with the same degree of contractile activity.
what is one way to protect against fatigue?
switching between motor units can delay fatigue
5 primary reasons thought to cause muscle fatigue
- local increase of ADP and Pi from ATP breakdown may interfere with cross bridge cycling and release/reuptake of Ca2+
- Accumulation of lactate from ATP hydrolysis may inhibit key enzymes
- Accumulation of extracellular K+
- depletion of glycogen energy reserves
- fiber type of muscle (some types fatigue sooner than others….SO, FO, FG)
Three major groups of skeletal muscle:
- Slow-oxidative (type I)
- fast-oxidative (type IIa)
- fast-glycolytic (type IIx)
Fast vs slow fibers
-fast fibers have more myosin-ATPase activity than slow fibers because of different myosin isoforms. This results in faster twitch
Two factors determine the speed at which a muscle can contract:
- the load (load-velocity relationship
2. the myosin ATPase activity of contracting fibers (fast or slow twitch)
Myosin-ATPase activity in SO vs FO vs FG fibers:
SO: low
FO: high
FG: high
Resistance to fatigue in SO vs FO vs FG fibers:
SO: high
FO: intermediate
FG: low (i.e., quickly fatigued)
Enzymes for anaerobic glycolysis in SO vs FO vs FG fibers:
SO: low
FO: intermediate
FG: high
Mitochondria in SO vs FO vs FG fibers:
SO: many
FO: many
FG: few
capillaries in SO vs FO vs FG fibers:
SO: many
FO: many
FG: few
myoglobin content in SO vs FO vs FG fibers:
SO: high
FO: high
FG: low
color of SO vs FO vs FG fibers:
SO: red
FO: red
FG: white
glycogen content in SO vs FO vs FG fibers:
SO: low
FO: intermediate
FG: high
Fast fiber twitch peaks at ___, whereas slow fiber twitch peaks at ___
Fast fiber twitch peaks at 20-40ms, whereas slow fiber twitch peaks at 60-100ms
Fibers with greater capacity to form ATP are more resistant to ____
fatigue
why are oxidative fibers more resistant to fatigue than glycolytic fibers?
Because oxidative phosphorylation yields more ATP from each nutrient molecule processed than glycolysis and thus DOES NOT DEPLETE ENERGY STORES.
Also no lactate accumulation.
Explain how energy requirements of muscle fibers change as the Icelandic horse gait changes from walk to a canter
Walking - type I (SO) fibers used and energy requirements are minimal. PRIMARILY USES FAT AS FUEL.
Trot - Type IIa (FO) fibers recruited. GLYCOGEN SERVES AS PRIMARY ENERGY SOURCE (because fat cannot be burned anaerobically)
Gallop - Type IIx (FG) fibers recruited. ATP generation almost exclusively ANAEROBIC.
most muscle fibers in fish are _________, with some ______ fibers near their lateral line
most muscle fibers in fish are FAST GLYCOLYTIC, with some SLOW OXIDATIVE fibers near their lateral line
3 types of changes can be induced in muscle fibers:
- changes in their ATP-synthesizing capacity
- changes in myosin isoforms and thus sontractile speed
- changes in their diameter
How to improve oxidative capacity of an oxidative fiber:
- increase number of mitochondria
- increase number of capillaries
Naked mole rat does endurance digging in hypoxic conditions. It has these two adaptations which improve its oxidative capacities compared to the white rat:
It has a 30% higher capillary density and 50% higher mitochondrial density that the white rat.
What is muscle hypertrophy?
- an increase in diameter of fast-glycolytic fibers
- as a result of regular bouts of anaerobic, short duration, high intensity training
- this causes synthesis of myosin and actin filaments for more cross bridge interactions
- endurance is not improved, but strength for brief periods is
What muscle fiber type do people with paralysis stop using?
lose their slow muscles.
Why do mammalian males have larger muscles than females?
- due to testosterone
- TESTOSTERONE PROMOTES THE SYNTHESIS AND ASSEMBLY OF MYOSIN AND ACTIN
2 form of muscle atrophy:
- disuse atrophy
2. denervation atrophy
When does disuse atrophy occur?
when a muscle experiences metamorphosis or if it not used for a long period of time even though THE NERVE SUPPLY IS STILL INTACT
When does denervation atrophy occur?
after the nerve supply to a muscle is lost
Three levels of input control motor neuron output in vertebrates:
- input from afferent neurons (spinal reflexes)
- input from the primary motor cortex (neurons descend from cortex and terminate on motor neurons; corticospinal motor system)
- input from the brainstem (multineuronal motor system; a number of complex interactions and several brain structures used)
Two types of proprioceptors:
muscle spindles
golgi tendon organs
Proprioceptors measure changes in muscle ____ and ____
Proprioceptors measure changes in muscle LENGTH and TENSION
Muscle length is monitored by ________, whereas changes in muscle tension are detected by _________
Muscle length is monitored by MUSCLE SPINDLES, whereas changes in muscle tension are detected by GOLGI TENDON ORGANS.
muscle spindles are distributed throughout specialized muscle fibers known as _____________, which lie within spindle-shaped connective tissue capsules parallel to the “ordinary” _____ fibers.
muscle spindles are distributed throughout specialized muscle fibers known as INTRAFUSAL FIBERS, which lie within spindle-shaped connective tissue capsules parallel to the “ordinary” EXTRAFUSAL fibers.
Briefly describe the stretch reflex
- muscle passively stretched, causing intrafusal fibers to stretch
- this increases rate of firing of the afferent nerve fibers whose sensory endings terminate on the stretched spindle fibers.
- Afferent neuron directly synapses onto an alpha motor neuron that innervates the extrafusal fibers of the same muscle, causing it to contract.
- THIS SERVES AS A LOCAL NEGATIVE FEEDBACK MECHANISM
Where are golgi tendon organs located?
in the tendons of the muscle
Golgi tendon organs respond to changes in the muscle’s externally applied ___ rather than to changes in its length
Golgi tendon organs respond to changes in the muscle’s externally applied TENSION rather than to changes in its length
Steps of golgi tendon organ activation
- tension on tendon activates sensory neuron
- sensory neuron stimulates interneuron in CNS
- interneuron inhibits apha motor neuron
- tension on tendon is reduced
Vertebrate muscle types
- STRIATED:
a. skeletal
b. cardiac - SMOOTH
smooth muscle is under control of which nervous systems?
enteric and autonomic
Skeletal muscle is under control of:
somatic NS
cardiac muscle is under control of:
autonomic ns
are smooth muscle cells multinucleated?
NO. each cells contains ONE nucleus
Majority of smooth muscle cells are found in _______ and_________
Majority of smooth muscle cells are found in HOLLOW ORGANS and TUBES
T/F: smooth muscle cells extend the full length of the muscle
FALSE. they are arranged in sheets
what shape do smooth muscles have?
spindle-shaped
2 types of smooth muscle:
- mult-unti: multiple discrete units that function independently
- single-unit: “visceral” smooth muscle
Smooth muscle cells are (small/large?) and (striated/unstriated?)
smooth muscle cells are SMALL and UNSTRIATED
smooth muscle has 3 types of filaments:
- thick myosin filament (longer than those found in skeletal muscle)
- thin actin filaments (which contain tropomyosin but not troponin)
- intermediate filaments (that do not participate in contraction)
Rather than Z lines, smooth muscles have _____, containing the same proteins found in the Z line
dense bodies
Actin filaments are anchored to the ___ ___ in smooth muscle
dense bodies
Which contains more actin? skeletal or smooth muscle cells?
Smooth
Location of skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
- Skel: attached to skeleton
- multiunit sm: large blood vessels, eyes, hair follicles
- single-unit sm: walls of hollow organs in digestive, reproductive, and urinary tracts and in small blood vessels.
cardiac: heart only
function of skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
- skel: movement of body in relation to external envir.
- multi-unit sm: varies with structure involved
- single-unit sm: movement of contents within hollow organs
cardiac: pumps blood out of heart
Mechanism of contraction in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
ALL SLIDING FILAMENT MECHANISM
level of control in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
all under INVOLUNTARY CONTROL, except for skeletal muscle, which is VOLUNTARY
initiation of contraction in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
skel: neurogenic
multi-unti sm: neurogenic
single-unit sm: MYOGENIC (pacemaker potentials and slow-wave potentials)
cardiac: MYOGENIC (pacemaker potentials)
T/F: skeletal, MU smooth, SU smooth, and cardiac muscle ALL have thick myosin and thin actin filaments present
TRUE
Striated? skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
Skeletal: yes
Multi-unit sm: no
Single-unit sm: no
Cardiac: yes
Presence of tropomyosin and troponin in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
sk: yes
smooth: tropomyosin only
cardiac: yes
Presence of t tubules in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
Sk: yes
Smooth: no
cardiac: yes
Level of development of SR in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
Sk: well developed
smooth: poorly developed
cardiac: moderately developed.
Cross bridges of all muscle types are turned on by ____
Ca2+
Source of increased cytosolic Ca2+ in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
Sk: Sarcoplasmic reticulum
smooth and cardiac: ECF and sarcoplasmic reticulum
Site of Ca2+ regulation in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
Sk: Troponin in thin filaments
Smooth: myosin in thick filaments
Cardiac: troponin in thin filaments
Mechanism of Ca2+ action in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
Sk: physically repositions troponin-tropomyosin complex to uncover actin cross bridge binding sites.
Smooth: Chemically brings about phosphorylation of myosin cross bridges so they can bind with actin
cardiac: physically repositions troponin-tropomyosin complex
Presence of Gap Junctions in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
Sk: no
Multiunit sm: yes (very few)
Single unit sm: yes
cardiac: yes
Myosin ATPase activity; Speed of contraction in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
Sk: fast or slow, depending on fiber type
Smooth: very slow
cardiac: slow
Means by which gradation is accomplished in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
- Sk: varying number of motor units contracting (motor unit recruitment) and frequency at which they are stimulated (twitch summation)
- Multi-unit sm: varying number of muscle fibers contracting and varying cytosolic Ca2+ concentration in each fiber by AUTONOMIC and HORMONAL influences.
- Single-unit sm: Varying cytosolic Ca2+ concentration throughout myogenic activity and influences of the ANS, hormones, mechanical stretch, and local metabolites
- Cardiac: Varying length of fiber (depending on extent of filling of the heart chambers) and varying cytosolic Ca2+ concentration through autonomic, hormonal, and local metabolite influence.
Presence of tone in absencec of external stimulation in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle
sk: no
multi-unit sm: no
Single-unit sm: yes
cardiac: no
is there a clear-cut length-tension relationship in skeletal vs multiunit smooth vs single-unit smooth vs cardiac muscle?
sk: yes
smooth: no
cardaic: yes
How are the thick and thin filaments oriented in smooth muscle?
Thick and thin filaments are oriented slightly DIAGONALLY from side to side in an ELONGATED, DIAMOND-SHAPED LATTICE.
Sliding of thin filament during contraction of smooth muscle causes the lattice to _____ in length and _______ ___ ___ __ ____
Sliding of thin filament during contraction of smooth muscle causes the lattice to REDUCE in length and EXPAND FROM SIDE TO SIDE
How do smooth muscle cells contract without troponin?
- Myosin heads have LIGHT CHAINS near the “neck”
- smooth muscle myosin heads can ONLY INTERACT WHEN THE MYOSIN LIGHT CHAIN IS PHOSPHORYLATED
Biochemical events for the phosphorylation of the myosin light chain
- Ca2+ bind with CALMODULIN
- Ca2+-calmodulin complex binds to and activates MYOSIN LIGHT CHAIN KINASE (MLC kinase)
- MLC kinase phosphorylates the MYOSIN LIGHT CHAIN
How many ATPs needed to bend a cross bridge and bind myosin to actin?
one for bending, one for binding
Two types of smooth muscle depending on how its cytosolic Ca2+ concentration increases and its level of ongoing contractile activity:
- Phasic: contracts in BURSTS OF ACTIVITY
2. Tonic: maintains an ONGOING LEVEL of contraction
Phasic smooth muscle is most abundant in:
digestive tract
Tonic smooth muscle examples:
in walls of arterioles, maintains BP
Phasic smooth muscle
- contracts in BURTSTS
- triggered by APs that lead to increased cytosolic Ca2+
- mix food with digestive juices and propel mass forward for further processing
Tonic Smooth Muscle
-Partially contracted at all times (tone)
-
What is tone?
partial contraction even in resting state
Why does tone exist in tonic smooth muscle?
Because they have relatively low resting potentials of -55mV to -40mV.
Some surface Ca2+ channels are open at these potentials, allowing for constant flow of Ca2+ into cell, making it maintain a partial contraction.
Does maintenance of tone in tonic smooth muscle depend on action potentials?
no
All multi-unit smooth muscle is (phasic/tonic?)
phasic
i.e., baseline for contraction = 0
Single-unit smooth muscle is (phasic/tonic?)
could be ohasic or tonic
Single-unit smooth muscle is (neurogenic/myogenic?)
myogenic
Multi-unit smooth muscle is (neurogenic/myogenic?)
Neurogenic
why is single-unit muscle called “visceral?”
because it is found in the walls of hollow organs or viscera
Why are they called single-unit muscles?
because the muscle fibers which comprise them become excited and contract as a SINGLE UNIT
_______ electrically link the muscle fibers in single-unit sm
Gap junctions
Functional syncytium
AP can occur anywhere in the sheet of sing;e-unit muscle cells and can be propagated.
Cells contract in unison.
2 major types of spontaneous depolarization displayed by self-excitable cells:
- pacemaker potentials
- slow-wave potentials
What are pacemaker potentials?
membrane potential gradually depolarizes on its own due to shift in ionic fluxes accompanying automatic changes in channel permeability .
Whendepolarization reaches threshold, an AP is initiated.
After repolarization, the membrane potential once again depolarizes to threshold.
Cycle continues
What are slow-wave potentials?
Gradually alternating HYPERPOLARIZATNG and DEPOLARIZING swings in potential caused by automatic cyclic changes in the rate at which Na+ is actively transported across the membrane.
Constantly moves away from and towards threshold.
If threshold is reached, a BURST OF APs occurs at the peak of the depolarizing swing.
Startiing point is influences by NEURAL and LOCAL factors
What occurs one an AP is generated by pacemaker cells?
It is conducted to contractile, non-pacemaker cells of the functional syncytium via GAP JUNCTIONS
Nerve-independent contractile activity initiated by the muscle itself is called ____ activity
myogenic
Tension in single-unit smooth muscle is modified by varying____
cytosolic Ca2+
More cytosolic Ca2+ leads to what, in single-unit smooth muscle?
More cross bridges brought into play
MORE TENSION
How does the ANS modify the activity of smooth muscle?
They have a distribution of cholinergic and adrenergic receptors throughout cells.
Each terminal branch of a POSTGANGLIONIC AUTONOMIC FIBER travels across the surface of one or more smooth muscle cells, RELEASING TRANSMITTER from the vesicles within its multiple VARICOSITIES as an AP passes along the terminal.
The NT diffuses to the many receptor sites
