Exam 3: Chapter 20: Muscle Flashcards
What is muscle made up of?
Contractile cells
What two muscle components combine to allow movement?
Molecular motor myosin and energy from ATP
What contractile proteins generate force?
Actin and myosin
Where is striated muscle found?
Skeletal and cardiac muscle
The striated muscles found in skeletal and cardiac muscles have what?
Sarcomeres
What do skeletal muscles consist of?
Bundles of longitudinally arranged muscle fibers (cells)
What are 3 main characteristics of smooth muscle?
- Not striated
- Uses actin and myosin for contractions
- Surrounds organs, intestine, and blood vessels
Every muscle fiber contains what?
Myofibrils
What does each myofibril have?
Cross- striations, which are sarcomeres
What kind of muscle fibers make up vertebrate skeletal muscle cells
Long muscle fibers
What are the 5 main characteristics of vertebrate skeletal muscle regarding its structure and function?
- Made up of long muscle fibers
- Connective tissue forms tendons that attach to the muscles and bones
- Transmit force
- Have many nuclei
- Surrounded by a membrane called the sarcolemma.
What is the name of the membrane that surrounds vertebrate skeletal muscles?
Sarcolemma
What forms the tendons that attach to the skeletal muscles and bones
Connective tissues
What does each myofibril have in terms of bands?
Regularly repeating transverse bands
What are the names of the major bands in the myofibrils/ muscle fibers of the skeletal muscles?
Dark A and light I
What is the name of the functional unit of striated muscles?
The sarcomere
What is the Z line?
The line in the middle of each I band
The line in the middle of each I band is the …..
Z line
What is between the Z lines
The sarcomere
The sarcomere is between what lines?
Z lines
What contributes to the striated appearance of skeletal muscle?
The major bands (the dark A and the light I) and the lines/discs in sarcomere
Myofilaments are made up of….
Thick and thin parts
How many myosin proteins make up thick filaments?
200-400
What are thin filaments made up of?
Actin
What is found in the middle of the A band?
The H zone and the M line
Muscle filaments come in …..
Different sizes and length
What does the protein desmin do?
It holds the Z lines together of different filaments
What holds the Z lines together of different filaments?
The protein desmin
What is the protein desmin a part of and what does it aid in?
It is part of the cytoskeleton below the cell membrane, nucleus, and mitochondria and it aids in organization during contraction
What generates contraction?
Myosin protein’s many cross- bridges that make contact with actin
What proteins align myosin and actin?
Titin and nebulin
What do titin and nebulin do?
They are proteins that align the myosin and actin
What is the protein that binds the M line to the sarcoplasmic reticulum?
Obscurin
What does the protein obscurin do?
It binds the M line to the
sarcoplasmic reticulum
What are troponin and tropomyosin? What do they do?
They are actin associated proteins that control contraction
What does the sliding- filament theory of muscle contraction say?
-Thick and thin filaments are polarized polymers of individual protein molecules
-The polarized organization of the thick and thin filaments has the cross-bridges connecting to the thin filament like
oars to pull the thin filaments to the middle of the sarcomere
-The force of contraction is generated by the cross-bridges connecting to the thin filaments
What do muscles require in order to be able to contract?
ATP
Myosin has binding sites for what two things?
Actin and ATP
The binding site for ATP found on myosin is called what? What does it do and what does it enable?
- ATPase
- It converts ATP to ADP, releasing energy
- This energy enables cross- bridge activity
In muscle contraction, how much ATP is consumed per cycle?
1
What is the intent in muscle contraction in vertebrate skeletal muscle?
To pull the thin filaments to the center of the sarcomere
A single cross- bridge cycle uses ________ molecule of ATP and moves the actin filament about _______
- One
- 10 nm
Along with the regulatory proteins tropomyosin and troponin, what else helps control contractions?
Calcium
How do tropomyosin (TM) and troponin (TN) control contraction?
They prevent contraction by blocking myosin from contacting actin
In terms of calcium, tropomyosin, and troponin, how do they all work together to help control and regulate muscle contraction?
- TM and TN prevent contraction by blocking myosin from contacting actin
- Troponin C binds Ca²⁺
- Contraction occurs when Ca²⁺ binds TN
- This causes a conformational change that now allows myosin to bind to actin
What does nerve excitation cause?
Skeletal muscles to contract
What causes skeletal muscles to contract?
Nerve excitation
What do the motor neurons form?
Endplates at each skeletal muscle fiber
What forms the endplates at each skeletal muscle fiber?
Motor neurons
What is excitation- contraction coupling accomplished by?
The interactions of the transverse tubules (t- tubules) and the sarcoplasmic reticulum (SR)
What two different membrane systems are involved in excitation- contraction coupling?
The sarcolemma and t- tubules
What is the sarcoplasmic reticulum (SR)?
A network of tubules within muscles
The ________________ are in contact with the muscle fibers
t- tubules
What happens when the sarcolemma is depolarized?
The t- tubules send this excitation into the muscle
What kind of ATPase pumps does the SRF membrane have and what do they keep?
The SR membrane has Ca2+ - ATPase pumps and keeps a much higher concentration of Ca2+ inside the SR
What receptors control Ca2+ movement?
The dihydropyridine receptors (DHPRs) on the t- tubules and the ryanodine receptors (RyRs) of the SR control Ca2+ movement
What do DHPRs act as? What happens to them when the t- tubules are depolarized?
They act as voltage- sensitive calcium channels and when the t- tubules are depolarized, they have have a conformational change.
Muscle level organization
- Thick/thin myofilaments
- Myofibril
- Many myofibrils
- Muscle fiber/ cell
- Sarcoplasmic reticulum
- Sarcolemma (cell membrane)
Where is the M line found?
In the middle of the sarcomere
What does the M line run through the center of?
The dark A band and the H- zone
What kind of myofilaments does the dark A band include?
Flanking ends of both thick (myosin) and thin (actin) filaments
What kind of myofilaments does the H- zone include?
Only thick filaments (myosin) w the M line running through the center
What kind of myofilaments does the light I band include?
Only thin filaments (actin) w the Z disc running through the center
From what line to what line is considered the sarcomere?
Z disc to Z disc
What are the steps in a single- cross bridge cycle? (6)
- Rigor is a transient state
- ATP binding dissociates myosin from actin
- The myosin ATPase hydrolyzes ATP to ADP, and energy is transferred to the cross bridge (ADP and Pi remain bound to myosin and the myosin head moves to the cocked position and loosely binds to a G- actin)
- When Ca2+ is present, the cross bridge attaches tightly to G- actin and goes through another cycle
- The myosin head releases Pi as it swivels in the power stroke, moving the thin filament 10 nm toward the center of the sarcomere
- Myosin unbinds ADP after the power stroke and stays attached to actin in rigor
What controls contractions?
Calcium and regulatory proteins tropomyosin and troponin
What is going on with the myofilaments/ muscle fiber when no Ca2+ ions are present in the cytoplasm?
- Primed myosin head attaches loosely to the thin filament
2. Tropomyosin blocks myosin binding sites on G- actin
What is going on with the myofilaments/ muscle fiber when Ca2+ ions are released from the SR, permitting cross- bridge action?
- Ca2+ binds to tropomyosin
- Myosin binding sites are exposed by shift of tropomyosin
- Myosin head binds tightly and makes the power stroke
- Thin filament moves ~10 nm toward center of sarcomere
What does nerve excitation cause?
It causes skeletal muscles to contract
What do motor neurons form at each skeletal muscle fiber?
End plates
How is excitation- contraction coupling accomplished?
By the interaction of two different membrane systems, the transverse tubules (t- tubules) and the sarcolemma/ sarcoplasmic reticulum (SR)
What do the transverse tubules (t- tubules) make contact with?
They contact the muscle fibers
What is the sarcoplasmic reticulum (SR)?
A network of tubules within the muscle cells
What are the 10 steps in excitation- contraction coupling?
- ACh is released from the presynaptic region and attaches
to the receptors in the post-synaptic area - A resulting permeability change creates a depolarization
and a resulting action potential - When the sarcolemma is depolarized, the t-tubules send
this excitation into the muscle - The SR membrane has Ca²⁺ -ATPase pumps and keep a much
higher concentration of Ca²⁺ inside the SR with the ryanodine receptors (RyRs) of the SR controlling Ca2+ movement - The dihydropyridine receptors (DHPRs) on the t-tubluesact as voltage-sensitive calcium channels and when the t-tubules is depolarized, the DHPRs have a
conformational change - This alteration opens the RyRs and Ca²⁺ moves out to the
cytoplasm - Ca²⁺ is then available for muscle contractions
- Ca²⁺ binds to TN at high level causes muscle contractions
- When the action potential ends, the RyRs close and the Ca²⁺ level
decreases - The Ca²⁺ -ATPase pumps help lower the cytoplasmic calcium
concentration
What is the immediate source of energy for powering muscle contraction?
ATP
What are the 3 roles ATP plays in the contraction- relaxation process?
- ATP hydrolysis energy enables the calcium pump to move Ca²⁺ into the SR
- ATP hydrolysis primes myosin cross- bridge to enable it to bind actin for contraction
- ATP binding to cross-bridges required to remove myosin from actin
How much ATP does muscle naturally contain, allowing it contract for only more than a few seconds? What does this mean?
2-4 mM, so ATP must be made in the muscle while it’s active
What are the 3 metabolic pathways that supply ATP for muscle contractile activity?
- Creatine phosphate: Donates a P and converts ADP to
ATP - Anaerobic glycolysis: Makes 2 ATP per glucose
- Aerobic catabolism (oxidative phosphorylation): Makes ATP by oxidative phosphorylation
What is the peak rate of ATP synthesis, total possible yield of ATP in one episode of use, and the rate of acceleration of ATP production like when creatine phosphate/ phosphagen is used as the principal mechanism of ATP generation in vertebrate muscles?
- Peak rate of ATP synthesis: Very high
- Total possible yield of ATP in one episode of use: Small
- Rate of acceleration of ATP production: Fast
What is the peak rate of ATP synthesis, total possible yield of ATP in one episode of use, and the rate of acceleration of ATP production like when anaerobic glycolysis is used as the principal mechanism of ATP generation in vertebrate muscles?
- Peak rate of ATP synthesis: High
- Total possible yield of ATP in one episode of use: Moderate
- Rate of acceleration of ATP production: Fast
What is the peak rate of ATP synthesis, total possible yield of ATP in one episode of use, and the rate of acceleration of ATP production like when aerobic catabolism (oxidative phosphorylation is used as the principal mechanism of ATP generation in vertebrate muscles?
- Peak rate of ATP synthesis: Moderate
- Total possible yield of ATP in one episode of use: High (maintained indefinitely)
- Rate of acceleration of ATP production: Slow
Bc creatine phosphate, anaerobic glycolysis, and aerobic catabolism (oxidative phosphorylation) make ATP at different rates ….
The work rate of muscle decreases over time with vigorous activity
What do vertebrate muscle fibers vary in?
Their use of ATP
What kind of muscle fibers are the most common? How do they work?
Twitch muscle fibers -> They have an action potential and cause a twitch
What are the 3 kinds of twitch muscle fibers?
Slow oxidative (SO), fast glycolytic (FG), fast oxidative glycolytic (FOG)
For slow oxidative (SO) muscle fibers:
- How do they make ATP?
- Fatigue rate
- Amount of myoglobin
- Color
- Amount of mitochondria
- How they stain
- Diameter
- Amount of capillaries
- How do they make ATP: Aerobically
- Fatigue rate: Fatigue resistant/ fatigue slowly
- Amount of myoglobin: Rich
- Color: Red
- Amount of mitochondria: Abundant
- How they stain: Dark
- Diameter: Small
- Amount of capillaries: Abundant
For fast glycolytic (FG) muscle fibers:
- How do they make ATP?
- Fatigue rate
- Amount of myoglobin
- Color
- Amount of mitochondria
- How they stain
- Diameter
- Amount of capillaries
- How do they make ATP: Anaerobically .: Lactic acid builds up
- Fatigue rate: Fatigue quickly
- Amount of myoglobin: Few
- Color: White
- Amount of mitochondria: Few
- How they stain: Light
- Diameter: Moderate
- Amount of capillaries: Few
For fast oxidative glycolytic (FOG) muscle fibers:
- How do they make ATP?
- Fatigue rate
- Amount of myoglobin
- Color
- Amount of mitochondria
- How they stain
- Diameter
- Amount of capillaries
- How do they make ATP: Aerobically
- Fatigue rate: Fatigue resistant/ fatigue slowly
- Amount of myoglobin: Abundant
- Color: Red
- Amount of mitochondria: Abundant
- How they stain: Dark
- Diameter: Large
- Amount of capillaries: Abundant
What is the only way in which SO and FOG muscle fibers differ?
Their diameter -> SOs have a small diameter whereas FOGs have a large diameter
What kinds of things can vary within the 3 types of muscle fibers?
Even within the 3 types there can be variation, with varied
isoforms of troponin, tropomyosin and other proteins. Cross conversion can also occur
Muscles often have a mixture of….
The different types of muscle fibers
Role of SO muscle fibers
Isometric postural roles and slow, small movements
Example of SO muscle fiber role in the soleus of a cat
The cat hind limb has 3 muscles, ankle extensors -> The soleus, medial gastrocnemius and lateral
gastrocnemius ->The soleus has only SO fibers
Role of FG muscle fibers
Fast, strong movements
Role of FOG muscle fibers
Have a role in locomotion
Example of FG and SO/ FOG roles in the medial and gastrocnemii of a cat
The medial and lateral gastrocnemii are faster and have
mixed composition:
- The medial has 45% FG, 25% FOG and 25% SO
-FG fibers are larger, so their 45% equates to 75% of the
maximum total tension of the medial
- Although, walking and running use only 25% of the
maximum tension of the medial -> This is the total amount used by both the FOG and SO.
Different animals employ different types of muscles that….
Contribute to their achieving success
Example of how different animals employ different types of muscles that
contribute to their achieving success
Sound producing muscles of bats are faster than flight
muscle contraction-relaxation cycle of hummingbirds
15ms
What are 3 factos that aid in fast rates of contraction?
- Myosin isoforms with fast cross-bridge cycling
- Troponin isoforms with low affinity for Ca²⁺ binding, so
Ca²⁺ unbinds quickly - Higher number of Ca²⁺ -ATP pumps in the SR for rapid
relaxation
In conclusion, what is required for contraction
A great deal of ATP is required, mitochondria and
capillaries
In most locomotion muscles what makes up 90% of the space? What makes up the other 10%
- 90% of the space consists of
myofibrils - Mitochondria, glycogen and SR fill up the
remaining 10%
Myofibirls make up what percentage of the space in most locomotion muscles?
90%
Mitochondira, glyocgen, and SR make up what percentage of space in most locomotion muscles?
10%
When do skeletal muscles only contract?
When they are stimulated by motor neurons
What is the vertebrate plan based on?
Muscles organized into motor units
About how many motor neurons innervate skeletal muscle?
Bt 100- 1000
Each axon of a motor neuron connects to how many muscle fibers?
One
What does a motor unit consist of?
A single motor neuron and all of the muscle fibers it innervates (motor neuron contact to a muscle fiber) .
Each muscle fiber receives what from a motor neuron terminal branch?
A single end- plate contact
The amount of __________ ___________ varies from animal to animal
Tetanic tension
In many vertebrates how much higher is the tetanic tension than the twitch tension?
2-5x higher
Varying the amount of motor- units: Tension increases as…….
More motor units join in
What helps with exact smooth movements?
Timing of activation
What are the homeostatic functions of vertebrate smooth (unstriated) muscle?
- In GI, respiratory, reproductive, urinary tracts and blood
vessels - Moving materials along a tube (intestine)
- Maintain tension (arterioles and sphincter muscles)
4.Also in the eye, with roles in size of pupil and the shape
of the lense
In terms of myofilaments and innervation, how is vertebrate smooth (unstriated) muscle different from vertebrate skeletal muscle?
Smooth muscles uses actin and myosin to generate tension and it receives innervation from the autonomic nervous system, but it has no sarcomeres or striation
Is there more actin or myosin in smooth muscle? What does it attach to?
Actin, it attaches to dense bodies in the cytoplasm
In vertebrate smooth (unstriated) muscle, myosin has what? What powers it?
It has myosin cross- bridges along its entire length and myosin ATPases that hydrolyze ATP to power the cross- bridges
How is are vertebrate smooth muscle cells shaped?
Spindle- shaped
How many nuclei do vertebrate smooth muscle cells have?
Single nucleus
What regulatory proteins does smooth muscle lack in comparison to skeletal muscle?
Transverse tubules (t- tubules), troponin, and nebulin
Is smooth muscle more or less energy efficient than skeletal muscle
Smooth muscle is more energy efficient
Does smooth muscle work slower or faster than skeletal muscle? Does smooth muscle hold contractions for shorter or longer periods of time
Smooth muscle works more slowly and it hold contractions for a longer time than skeletal muscles
Smooth muscles cells are broadly classified into what two main types?
Single and multi unit
How are single unit smooth muscle cells coupled and how do they depolarize?
They are coupled electrically by gap junctions and depolarize together, meaning they function as a unit
How are multi unit smooth muscle cells coupled and how do they depolarize?
-They have few gap junctions and act independently
- They are innervated autonomically, they may be activated by
hormones, or chemically
Where are multi unit smooth muscle cells located?
In the hair, eyes, large arteries and the respiratory system
Which type of smooth muscles are not excitable and where are they located?
Tonic muscles and they are located in airways
Which type of smooth muscles are excitable? Why? Where are they located?
Phasic muscles bc they have gap junctions and they are located in the stomach and small intestine
What does action potentials lead to?
Increased intracellular Ca2+
What controls controls smooth muscle contraction? Through what kind of regulation does it do this?
Ca²⁺ availability controls smooth muscle contraction by myosin- linked regulation
What 3 things does myosin- linked regulation require?
Ca2+ ions, calmodulin, and myosin light chain kinase (MLCK)
What decides how much force is produced by cytoplasmic proteins in smooth muscle?
The amount of available cytoplasmic Ca2+
What are the 9 steps taken in smooth muscles to make graded contractions?
1.Ca²⁺ controls phosphorylation of myosin light chains (MLC)
2. Ca²⁺ works with calmodulin (A cytoplasmic protein that binds Ca2+ ions) to activate myosin light chained
kinase (MLCK) phosphorylating myosin
3. Increased intracellular Ca2+ leads to increased levels of Ca2+- calmodulin, which activate MLCK
4. Activated MLCK phosphorylates MLK, which activates myosin’s ATPase activity
5. As long as MLK stay phosphorylated, myosin ATPase catalyzes repeated cross- bridge cycles to produce tension
6. Relaxation occurs when the calcium concentration
lowers
7.Ca²⁺ disassociates from calmodulin
8. MLCK becomes inactive
9. MLCP dephosphorylates the light chains -> Signaling molecules may also have a role with G protein
RhoA and ROK inhibiting MLCP
What does vertebrate cardiac muscle form? What is the structures it forms?
Forms the walls of the heart with a role in moving the
blood in the venous system
How is vertebrate cardiac muscle similar to vertebrate skeletal muscle?
- Striated with its’ myofibrils in sarcomeres
- Same regulatory proteins as in skeletal muscle
How is the shaped of vertebrate cardiac muscle cells? How many nuclei do they have?
They are branched and have a single nuclei
What do vertebrate cardiac muscle cells have in between them? What do these include?
Have intercalated discs between cells, which include gap junctions and adhesions termed desmosomes
What does the adhesion through the desmosomes allow for?
Mechanical strength so contractions
can be transmitted from cell to cell
How do all the cells connected by gap junctions contract/ beat?
They beat in unison
What causes the cells to contract/ beat in unison?
Their connection via gap junctions
How long do long duration action potentials last? What do they ensure?
100-500ms and they ensure prolonged contraction
When are cardiac cells refractory?
During long action potentials
How are cardiac cells during long action potentials?
Refractory
At times, cardiac cells generate…..
Endogenous action potentials
Specialized pacemaker cells with fast endogenous rates…..
Force their rhythm on the contractile activity of the rest of the heart
