Bio 220 - Chapter 12 Muscles
Peripheral fatigue arise between what two elements?
neuromuscular junction contractile elements
A myogenic contraction describes the opening of ________ channels in smooth muscle cells in response to a distortion of the cell membrane that is commonly observed in ________.
stretch activated, blood vessels
inward extensions of the muscle cell membrane
t-tubules
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
voltage-gated calcium channels
How many mV do Smooth Muscle resting membrane potential display?
-40mV & -80mV
What are the series elastic elements?
Elastic fibers in the muscle that stretch during isometric contraction.
What is an example of a paracrine signal?
Epinephrine, a neurohormone that relaxes smooth muscle and dilates the airway.
What are examples of tonic smooth muscles?
Esophagus, Urinary Bladder, Sphincters; Constantly contracted and closed until a situation demands they relax.
Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?
Excitation refers to the release of calcium ions from the sarcoplasmic reticulum.
Which loss of function would occur if you introduced a chemical that functioned as an inhibitor of the ryanodine receptor channel?
Myosin would not be able to bind to actin in order to cause shortening of the sarcomere
Is fatigue caused by depletion of ATP?
No
A motor unit consists of _____________________.
One motor neuron + All muscle fibers it controls
Central fatigue is ______________.
Psychological
One repeating unit of the banding pattern is called a _________.
Sarcomere
Which of the following structures would NOT change size during a muscle contraction? a.) sarcomere b.) H zone c.) A band c.) I Band
A band
What is an Isotonic contraction?
A contraction that creates force AND moves load.
What is an isometric contraction?
A contraction that creates force but DOES NOT move load.
What is the Contraction-Relaxation Cycle?
Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together: The Sliding Filament Theory
A change in membrane voltage that travels down the T-tubule to cause opening of Ca2+ channels
Action Potential
Where does peripheral fatigue occur?
Below the neck; neuromuscular junction, ECC, Ca2+ signaling, contraction-relaxation phase.
The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?
Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell.
An increase of what molecule initiates contraction in the smooth muscle?
Ca2+
The relaxation of skeletal muscle relies on the activity of the ________, which decreases cytoplasmic calcium concentration.
Ca2+ ATPase.
What causes Muscle Relaxation?
Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites.
Describe the role of calcium (Ca2+) in the excitation-contraction coupling reaction?
Ca2+ will bind to troponin, which leads to a shift in tropomyosin, allowing for myosin to attach to actin.
The contraction cycle is triggered by the rise in ________ released from the sarcoplasmic reticulum (SR).
Ca2+.
What is an example of a channel in a smooth muscle?
The Ryanodine Receptor (RyR) calcium release channel opens in response to Ca2+ entering the cell. It is a receptor that calcium binds to that triggers the SR to release calcium: Calcium-Induced Calcium Release.
What are two types of fatigues?
Central Fatigue Peripheral Fatigue
In muscles, what enzyme is used to transfer a phosphate group to make ATP?
Creating Kinase (Enzyme)
What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?
Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
Smooth muscles depolarize as a result of a transmembrane current of ________.
calcium ions
Where does central fatigue occur?
The Brain; In the CNS
What causes the latent period during excitation-contraction coupling?
Time is required for calcium release, diffusion, and binding to troponin.
What is the function of a smooth muscle?
To influence the movement of material in and out and within the body.
Muscles that continuously contract are called________________.
Tonic Smooth Muscles.
Smooth muscle lacks which protein?
Troponin
Compared to skeletal muscle, contraction of smooth muscle cells is
a slower response to a stimulus and sustained without fatigue.
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
acetylcholine (ACh)
A myosin head binds to which molecule to form a cross bridge?
actin
Each myosin head has a binding site for
actin and ATP.
The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a
channel for both Na+ and K+.
The action potential traveling along the t-tubule is detected by the
dihydropyridine (DHP) receptor (L-type calcium channel).
Which of the following is NOT a correct comparison of cardiac myocytes to other muscle cell types? a.) Like skeletal muscle cells, actin and myosin are organized into sarcomeres. b.) Like smooth muscle cells, cardiac muscle is under hormonal control. c.) Like smooth muscle cells, some cardiac myocytes have pacemaker potentials. d.) Like some smooth muscle cells, cardiac myocytes are electrically coupled. e.) Like skeletal muscle, contraction of cardiac muscle is under autonomic nervous control.
e.) Like skeletal muscle, contraction of cardiac muscle is under autonomic nervous control.
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
exocytosis
a bundle of adjacent muscle cells
fascicle
Groups of adjacent fibers bundled together into units are called ________. These bundles are surrounded by the proteins ________ and elastin as well as ________ that deliver nutrients to the muscle cells.
fascicles, collagen, blood vessels
Which fibers fatigue sooner?
fast-twitch fibers.
Which fibers generate more force?
fast-twitch fibers.
Motor units that control skeletal muscles involved with fine motor movements (eye muscles or the hands) have ________ muscle fibers than motor units that control more gross movements (gastrocnemius muscle of the lower leg).
fewer
The tension generated in a skeletal muscle fiber is directly proportional to the number of
high energy crossbridges formed.
The gap junctions in cardiac muscle are part of specialized cell junctions that are localized to the
intercalated disks.
What is the signal that initiates muscle contraction?
intracellular calcum signals
Smooth muscle fibers can sustain a contraction without fatigue by allowing dephosphorylated myosin to remain attached to actin in what is called the ________ state.
latch
The brief period of time between the beginning of the action potential in the muscle and the beginning of contraction is referred to as the
latent period.
Within a single fiber, the tension developed during a twitch depends upon the
length of the sarcomeres prior to contraction.
Bones form __________________. Joints form ___________________.
levers fulcrums
Which of the following is a characteristic of slow-twitch oxidative skeletal muscle fibers?
long contraction duration and high capillary density.
Which structural protein of skeletal muscle also acts as an enzyme?
myosin heavy chain
This protein is activated by the Ca2+-calmodulin complex to phosphorylate the myosin light chain protein.
myosin light chain kinase
The thick filament of the myofibril is composed of ________ molecules whereas ________ is a protein that makes up the thin filaments.
myosin, actin
the muscle cell membrane
sarcolemma
Striated muscles are so-called because of a repeating pattern of light and dark bands. One repeating unit of the banding pattern is called a
sarcomere.
When a skeletal muscle cell contracts and the muscle shortens,
some myosin heads are forming crossbridges as others are releasing them.
Skeletal muscle cells are usually attached to bone by
tendons.
The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell?
terminal cisterns (cisternae) of the sarcoplasmic reticulum
What happens at the Neuromuscular Junction?
From somatic motor neurons, Acetylcholine is converted into electrical signaling in the muscle fibers.
What does Nebulin do?
Help align the filaments of the sarcomere and is an inelastic protein.
Tension generated in skeletal muscle fiber is directly proportional to the ______________________.
High Energy Cross bridgess formed.
What does summation mean?
Increase of fiber tension.
An area of muscle fiber membrane that is in close association with the axon terminal of the motor neuron, contain receptors for acetylcholine
Motor End Plate
What are the two important events for skeletal muscle contractions?
Motor Neuron Excitation Myofilament Contraction
What is the function of cardiac muscles?
Moving blood through the circulatory system.
Smooth muscles that are not linked electrically and function independently are called __________________.
Multi-Unit Smooth Muscle
What does Excitation-Contraction Coupling do?
Muscle action potentials initiate CA2+ signals that activate a contraction-relaxation cycle.
Where does the muscle get ATP?
Muscles contain a small pool already Phosphocreatine (backup energy) Glucose => Pyruvates Fat (Requires Oxygen)
What proteins does a myofibril have?
Myosin (motor protein) Actin (Thin Microfilaments) Troponin (Regulatory Protein) Tropomyosin (Regulatory Protein) Titin (Accessory Protein) Nebulin (Accessory Protein)
Dephosphorylation of the myosin light chain is caused by what enzyme?
Myosin light chain phosphatase
Depolarizations that create regular rhythms of contraction are called ______________.
Pacemaker Potentials
Muscles that undergo periodic contraction-relaxation cycles are _______________.
Phasic Smooth Muscles.
________ is the backup energy molecule that can be rapidly converted to ATP in active skeletal muscle.
Phosphocreatine
Lever and Fulcrum Force Calculation
Rotational Force (up) = Rotational Force (down) Muscle force x #cm (length of fulcrum) = #kg (force) x #cm (length of lever)
Example of control of smooth muscle contraction
Signal Ligand >Membrane Receptor > Modulatory Pathways > Alter MLCK or Myosin Phosphatase > +or- = Muscle Contraction
Smooth muscles that are electrically connected by gap junctions are called ____________________.
Single-Unit Smooth Muscle
What type of muscle fibers do we have?
Slow Twitch Fibers Fast Twitch (Oxydative Glycolitic) Fibers Fast Twitch (Glycolitic) Fibers
Cells that exhibit cyclic depolarization and depolarization of their membrane potential are called ______________.
Slow Wave Potentials
Is there more Actin in Smooth or Skeletal muscles?
Smooth Muscles
What are Slow-Twitch fibers used for?
Maintaining Posture
Are there T-Tubules in Smooth Muscles?
No
Put these events in the correct chronological sequence: 1. End-plate potentials trigger action potentials. 2. Transverse tubules convey potentials into the interior of the cell. 3. Acetylcholine binds to receptors on the motor end plate. 4. Ca2+ is released from the sarcoplasmic reticulum.
3, 1, 2, 4
Steps of Excitation and Contraction Together
1. Acetylcholine is released from motor neuron 2. Action potential travels down the T-tubule 3. Ca2+ is released from the sarcoplasmic reticulum 4. Myosin generates the power stroke 5. Ca2+-ATPase channels actively pump Ca2+ back into the sarcoplasmic reticulum 6. Ca2+ unbinds from troponin 7. Actin filament slip back to rest position
Events of Contraction in Order
1. An action potential that travels down the T-tubule changes the structural confirmation of the DHP L-type Ca2+ channel 2. Ryanodine receptor channels open 3. Ca2+ leaves the sarcoplasmic reticulum 4. Acting and myosin bind to one another 5. Myosin heads utilize energy from ATP hydrolysis to produce the power stroke 6. Actin filaments slide toward the M line, shortening the sarcomere
Events at the Neuromuscular Junction in Order
1. Somatic motor neuron delivers action potential 2. Acetylcholine is released from the axon terminal onto the motor endplate 3. Net Na+ influx through nicotinic receptors 4. Muscle fiber depolarizes 5. Action potential travels down the T-tubule of the muscle fiber
Events of Smooth Muscle Contraction
1.) Increase in intracellular Ca2+ 2.) Ca2+ binds to Calmodulin 3.) Cascade of Phosphorylations 4.) Phosphorylation of myosin light chain kinase (enzyme)DeDe 5.) Active MLCK phosphorylation myosing using ATP 6.) Active myosin binds to actin
________ is composed of multiple globular molecules polymerized to form long chains or filaments.
Actin
A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?
A series of proteins that control calcium release.
A structure that when bound to a ligand opens a divalent channel for the movement of both Na+ and K+
ACh receptor-channel
The heavy chain of myosin contains two important regions: the first acts as ________ to convert energy into movement whereas the second binds to ________.
ATPase, actin
What is the enzyme that breaks up Acetylcholine?
Acetylchholine Estarase
Which of the following is not a correct statement concerning the muscles in the body? a.) All types of muscle generate heat by shivering when we are cold. b.) The two common functions are to generate motion and to generate force. c.) Three types of tissues are skeletal muscle, cardiac muscle, and smooth muscle. d.) Both skeletal and cardiac muscle tissue are considered striated.
All types of muscle generate heat by shivering when we are cold.
What are Flexor-Extensor pairs called?
Antagonistic muscle groups
One way the nervous system avoids fatigue in sustained contractions is by ________________________.
Asynchronous Recruitment
What type of chemical signals influence smooth muscle activity?
Autonomic neurotransmitters Hormones Paracrine Signals
An area that contains many synaptic vesicles filled with acetylcholine
Axon terminal of a motor neuron
What molecule is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Calcium ions.
Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?
Calcium release from the sarcoplasmic reticulum initiates the contraction.
In the smooth muscle, what does Ca2+ bind to?
Calmodulin
What i an example of inherited muscular disorder?
Duchenne Muscular Dystrophy; the structural protein dystrophin that links actin to proteins is absent.
What are some differences in fast and slow twitch fibers?
Fast: Last about 7.5 milliseconds Used Occasionally Glycolytic fibers fatigue more easy Pale Red in color Slow: Last 10 times longer Used constantly Oxydative fibers do not depend on anaerobic, last longer More myoblobin; Red in color
What are Fast-Twitch (glycolitic) fibers used for?
Jumping; quick fine movements. THINK AGILITY!
An isometric contraction is called ________________.
Latched State
Recruitment is controlled by what system?
Nervous System
Where is the cardiac muscle located?
ONLY in the heart
Smooth Muscles vs. Skeletal Muscle functional areas (comparisons, 5 each on the test)
Smooth: -Operate over a range of lengths -May run in several directions -Contract & Relax more slowly -Use of ATP is lower, fewer mitochondria -Can maintain contraction without fatiguing -Small Spindled-shape cells with single nucleus -Not arranged in sarcomeres; lack sarcomeres. -Contraction initiated by electrical, chemical, or both -Controlled by the autonomic nervous system -Lack specialized receptor regions -Ca2+ for contraction comes from ECF & S.R. -Ca2+ signal initiates a cascade that ends with phosphorylation of myosin light chain and activation of myosin ATPase. Skeletal: -Operate over a narrow range of lengths -Arranged so that their contraction shortens the muscle. -Skeletal or Cardiac muscles Contract & Relax faster -Use of ATP is higher, more mitochondria -Fatigue faster than smooth muscles -Large multi-nucleated fibers -Arranged in Sarcomeres -Contraction initiated by an action potential -Controlled by the somatic motor division of nervous system -Contain specialized receptor regions: motor end plate -Ca2+ for contraction comes from the S.R. only -Ca2+ signal binds to troponin to initiate contraction.
5 ways smooth and skeletal muscles are different...
Smooth: -Use of ATP is lower, fewer mitochondria -Small Spindled-shape cells with single nucleus -Lack sarcomeres. -Contraction initiated by electrical, chemical, or both -Controlled by the autonomic nervous system Skeletal: -Use of ATP is higher, more mitochondria -Large multi-nucleated fibers -Arranged in Sarcomeres -Contraction initiated by an action potential -Controlled by the somatic motor division of nervous system
What is Asynchronis Recruitment?
Some motor units are on and some off which prolongs the contraction.
What does Titin do?
Stabilizes the position of the contractile filaments and is an elastic protein.
What are Fast-Twitch (oxidative glycolitic) fibers used for?
Standing, Walking
What is Tetanus?
State of maximal contraction.
Where are the smooth muscles located?
Stomach, Urinary Bladder, Blood Vessels, Airway Passages, Uterus, Eye
What is Temporal Summation?
Strength of graded potential increases.
What are 5 charactereistics of a cardiac muscle?
Striated Sarcomere Structure Fibers are shorter than skeletal muscle fibers single nucleus single unit smooth muscle linked with gap junctions
What is Motor Unit Recruitment?
The activation of more motor units.
What is Tension?
The force created by a contracting muscle.
What is the Contraction - Relaxation Cycle?
The sliding filament theory
What is a benefit of having T-Tubules?
They allow action potential to move rapidly from the cell surface, into interior of the fibers, reaching the tereminal cisternae for stimulations.
Where are your skeletal muscles located?
They are attached to our bones.
What is the function of a skeletal muscle?
They attach to bones enabling muscles to control body movement.
What when a myofibril contracts?
Thin and thick filaments slide past each other, but do not change in length.
Single-Unit Smooth Muscles are also called _________________.
Visceral Smooth Muscles
Calcium enters the smooth muscles from the ECF via what type of channels?
Voltage-Gated Ligand-Gated Mechanically Gated
How is muscle contraction / movement created?
When myosin uses ATP to change its shape (confirmation).
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
arrival of an action potential
The nervous system avoids muscle fatigue during submaximal contraction by
asynchronous recruitment.
In order for high force crossbridges to form in contracting skeletal muscle, calcium must
bind to troponin which moves the tropomyosin.
What causes the myosin head to disconnect from actin?
binding of ATP
In smooth muscle cells, Ca2+ binds to ________ which activates the enzyme ________ to phosphorylate myosin and increase force.
calmodulin, myosin light chain kinase
Store-operated calcium channels open in response to
depleted intracellular stores of calcium.
As ATP binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately
detaches from actin.
Components of the Neuromuscular Junction
motor neuron acetylcholine motor end plate ACh receptor-channels muscle fibers
Actin is made up of what?
multiple globular molecules polymerized to form long chains.
a single muscle cell
muscle fiber
A motor unit consists of
one neuron and all the skeletal muscle fibers it controls.
Central fatigue protects the brain from drops in ______________.
pH
The function of transverse tubules is to
rapidly conduct action potentials to the interior of the muscle fiber.
What causes the power stroke?
release of ADP and Pi (hydrolysis of ATP)
The molecular event that occurs immediately after the power stroke is the
release of ADP from the myosin.
The hydrolysis of ATP causes myosin to immediately
rotate into a position (cocked) to bind to actin.
How is acetylcholine (ACh) removed from the synaptic cleft?
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
What is name given to the regularly spaced infoldings of the sarcolemma?
transverse or T tubules
The binding of calcium to which molecule causes the myosin binding sites to be exposed?
troponin
Calcium, released by the sarcoplasmic reticulum, binds to ________ to move the ________, which allows actin to form a high-force crossbridge with myosin.
troponin C, tropomyosin
Smooth muscle cells lack which protein(s)?
troponin only
