muscle tissue chapter 10
Describe resistance training
- "Strength training" - moderate increase in the frequency of motor unit activation and a large increase in force production - fewer repetitions w/ heavier weight. - use of free weights or resistance - exercise machine
Describe peristalsis
- Circular and longitudinal layers produce rhythmic waves (contract and relax) - propels materials through hollow organs of digestive, urinary and reproductive systems
What are 2 potential sources of glucose for glycolysis?
- Glucose that enters the fibers from the bloodstream -storage form of glucose called glycogen.
Describe an isotonic eccentric contraction (plyometric)
- Greatest amount of tension and force - Muscle lengthening - force generated by the muscle is less than that of the external load (greater injuries)
What are the 3 MAIN ways smooth muscle differs from skeletal muscle?
- It lacks motor end plate - The SR is much less extensive - T- tubules are absent
Describe the structure of smooth muscle cells
- Lack striation and sarcomeres - HAS DENSE BODIES - thin < thick filaments - thin filaments lack troponin
What is the "latch state" during the relaxation state for smooth muscles?
- Maintains tension while consuming very little ATP - Maintains a state of energy efficient sustained contraction (sphincters)
What are the stimulations for smooth muscle contractions?
- Mechanical stimulation (stretch) - Hormonal stimulation - Nervous system stimulation
Describe multi-unit smooth muscle
- RARE - found in uterus, muscles in the eyes, arrector pili muscles - consists of individual muscle cells NOT joined by gap junctions - each cell contracts independently, permitting precise control of contractions
Describe how a smooth muscle cell turns into the relaxation state in relation to CALCIUM
- Removal of calcium ions from cytosol - Calcium ions dissociate from calmodulin - MLCK is inactivated - Enters latch state
What are the 2 types of smooth muscle?
- Single-unit (unitary) smooth muscle or visceral smooth muscle - Multi-unit smooth muscle
Describe the Length-Tension Relationship
- The # of crossbridges depends on the length of the sarcomere prior to contraction.
How can pacemaker cells depolarize and contract spontaneously?
- They have unstable membrane potentials that cause them to spontaneously depolarize - They are responsible for the waves of contraction.
What are some types of Type II fibers?
- Type IIa --> fast oxidative glycolytic (FOG) - Type IIx --> fast oxidative (FO) - Type IIb --> fast glycolytic (FG)
What are some of the factors of muscular fatigue?
- depletion of key metabolites --> Creatine Phosphate, glycogen, blood glucose - decreased availability of O2 to muscle fibers - accumulation of certain chemicals --> calcium ions accumulate in mitochondria - environmental conditions --> extreme heat
Type II fibers
- fast-twitch fibers - contract more rapidly - quickly fatigued - rely on glycolytic energy sources - less myoglobin - fewer mitochondria - less extensive blood supply - "white" meat of the chicken
What are the classes of skeletal muscle fibers?
- fast-twitch fibers - slow-twitch fibers
To return to homeostasis, the body must:
- heat dissipation - restoration of intracellular and a extracellular ion concentration - correction of blood pH - ALL OF THESE PROCESSES CONSUME ATP
What are the functions of muscle tone?
- maintaining erect posture - stabilizing joints - generating heat - ensuring that the muscle is ready to respond if movement is initiated
What are the function of smooth muscle?
- peristalsis - formation of sphincters - regulation of flow
Describe Single-Unit (unitary) smooth muscle or visceral smooth muscle
- predominant type - found in nearly ALL hollow organs - consists of 100-1000s of muscle cells whose plasma membranes are linked electrically via GAP JUNCTIONS, causing the muscle cells to contract in a coordinated wave and as a single unit - Has multiple types of stimulation
Describe the smooth muscle function of formation of sphincters
- rings in both digestive and urinary system - usually contracted but relax periodically to allow substances to pass through them
Describe Type I fibers
- slow-twitch fibers - contract slowly; less forcefully - requires the continual oxidative generation of large quantities of ATP - large quantities of myoglobin - many mitochondria - well-developed bloody supply - slow oxidative fibers - "dark meat" of chicken
Describe Cardiac Muscle
- striated - consists of sarcomeres - have BOTH T- tubules and SR - shorter, branched cells - one or two nuclei - abundant myoglobin - mitochondria is about 30% of cytoplasmic vol - has INTERCALATED DISCS - electrical activity is coordinated by PACEMAKER CELLS
What value best represents resting membrane potential of skeletal muscle cells?
-85 mV
What is the resting membrane potential?
-85 mV. The cytosol is about 85 mV more negative than the extracellular fluid.
What causes spasms to occur?
-dehydration -electrolyte imbalances -muscle injury -muscle overload
Describe the steps of the oxidative energy source
-electrons are removed from carbon-based molecules and the energy liberates is then used to fuel synthesis of ATP -final step: transfer of electrons to a moleculre of O2 (which is why it can also be called aerobic catabolism)
What are the immediate sources of energy for muscle contraction?
-immediate energy sourse for contractin of the muscle fiber --> ATP - Creatine Phosphate (CP): a molecule used in a reaction to regenerate ATP immediately - Creatine Phosphate reaction: ADP + Creatine Phosphate --> ATP + creatine (10 secs of maximal muscle activity i.e. 100- meter sprint.)
axon terminal or synaptic bulb
...
skeletal muscle mitochondria
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Name and describe the 4 steps of the crossbridge cycle
1. ATP hydrolysis "cocks" the myosin head 2. The myosin head binds to actin. 3. The power stroke occurs when the ADP and phosphate detach from the myosin head; myosin pulls actin toweard the center of the sarcomere. 4. ATP breaks the attachment of myosin to actin
Describe the steps of Muscle Relaxation
1. AchE degrades the remaining Ach, and the final repolarization occurs ----> ligand-gated ions channels in teh motor end plate close. 2. The sarcolemma returns to its resting membrane potential, and calcium ion channels in the SR close 3. Calcium ions are pumped back into the SR, returning the calcium ions concentration in the cytosol to its resting level (active transport pumps in SR consume ATP to pump calcium ions) 4. Troponin and the tropomyosin block the active sites of actin, and the muscle relaxes (with support from titin and other structural proteins, myofilaments then slide back into their original positions)
Calcium ions initiate:
1. Calcium ions bind to a protein in the sarcoplasm called calmodulin. 2. The calcium ion-cam complex activates an enzyme associated w/ myosin --> myosin light-chaine kinase (MLCK). e. MLCK causes the activatoin of myosin ATPase 4. Crossbridge cycles then ensue.
Describe the steps of the Contraction Phase: The cross bridge cycle of the Sliding-Filament Mechanism
1. Calcium ions bind to troponin 2. Tropomyosin moves, and the active sites of actin are exposed
How many components are there for muscle relaxation? Describe each component.
2 components. 1. ACh release stops and the remaining ACh in the synaptic cleft is broken down 2. Calcium ion concentration in the cytosol returns to its resting level.
What is the product of glycolysis and describe what it does w/ O2 and when there is no O2
2 molecules of pyruvate. w/O2: Enters the mitochondria for oxidative catabolism. w/o O2: Converted to 2 molecules of lactic acid (lactate). Less than 20% of the lactate is converted to glucose by the the liver.
What does a triad consist of?
2 terminal cisternae and 1 T-Tubule
How many times does the process of ATP breaking the attachment of myosin to actin occur for each myosin head in each sarcomere of the muscle fiber
20-40 times for each myosin head in each sarcomere of the muscle fiber
What do the postural muscles of the back or the gastrocnemius in call contain? (in regards to how many fibers per motor unit)
2000-3000 muscle fibers in each motor unit. NOT as precise.
How many subunits does troponin have and name the function of each
3 subunints. One binds to calcium ions, one binds to actin, and one binds to tropomyosin
How long does a muscle twitch last?
5 ms.
What is the dark area that has both thick and thin filament?
A band
Define atrophy
A condition in response to physical inactivity the diameter of the muscle fiber decreases due to loss of myofibrils.
Define voltage
A difference in electrical potential between 2 points (measured in volts)
Actin
A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.
Troponin
A globular protein that ssociated with tropomyosin as part of the thin filament of the sarcomere. Troponin binds Ca2+, which causes the conformaiton change in tropomyosin required to expose the myosin-binding sites on actin and initiate muscle contraction.
Tropomyosin
A helical protein that winds around actin helices in skeletal and cardiac muscle cells to form the thin filament of the sarcomere. In the absence of Ca2+, tropomyosin covers the myosin-binding sites on actin and prevents muscle contraction. When calcium is present, a conformation change in tropomyosin occurs so that the myosin-binding sites are exposed and muscle contraction can occur.
axon
A long, thin fiber that transmits signals away from the neuron cell body to other neurons, or to muscles or glands
What is the Principle of Myoplaticity?
A muscle will alter its structure to follow its function
What is a "cross bridge"
A myosin head bounds to an actin
Define hypotonia
A nervous system disorder that makes the tone in skeletal muscle abnormally low. - looks flattened, feels soft and loose - joints are hyperextended
Describe the neuromuscular junction
A neuromuscular junction is the connection between the motor neuron and muscle fiber. Here the muscle fiber membrane is specialized to for a motor end plate. In this region of the muscle fiber, nuclei and mitochondria are abundant and the cell membrane is extensively folded.
What is the recovery period?
A period of time to return to the pre-exercise state
Myosin
A protein present in muscle fibers that aids in contraction and makes up the majority of muscle fiber
What does a motor unit consist of?
A single motor neuron along w/ the muscle fibers it innervates
Describe what a motor neuron does in relation to muscles
A single neuron communicates w/ many muscle fibers. The connection is called a synapse.
What is a contraction?
A succession of crossbridge cycle and the resulting production of force
Describe the structure and function of a tendon
A tendon is a fibrous band or cord of white connective tissue at the ends of muscle fibers that serves to attach a muscle to a bone and other structure. Tendons are strong and flexible but inelastic.
Myofibril
A threadlike structure, extending longitudinally through a muscle fiber (cell) consisting mainly of think filaments (myosin) and thin filaments (actin, troponin, and tropomyosin)
Complete the reaction below: ADP + creatine phosphate → creatine + __________
ATP
What are possible products of glycolytic, or anaerobic, catabolism?
ATP, pyruvate, and lactic acid
Which molecule has an active site to which myosin heads bind?
Actin
What are thin filaments made up of?
Actin (active site), tropomyosin (covers active site), and troponin (holds tropomyosin in place.
What are dense bodies?
Actin filaments are arranged obliquely in the sarcoplasm and are anchored to proteins
Describe conductivity in relation to muscle cells
Allows electrical changes to spread (action potential propagation)
Describe extensibility in relation to muscle cells
Allows muscles to be stretched without damage
What is a myogram?
An instrument that records the twitch and generates a recording
Describe electrically excitable cells
An unequal distribution of electrically charged ions near the plasma membranes of the cells
H zone(s)
Are areas in the center of the A bands containing only thick filaments Contain myosin only Zones shrink during contraction
Describe "Recruitment"
As greater force is needed, more motor units are activated (slow motor units and if needed, fast motor units are "recruited")
What does the NMJ consist of?
Axon terminal, synaptic cleft, and motor end plate.
endomysium
Connective tissue surrounding a muscle fiber
Describe the intercalated discs of cardiac muscle
Connects cardiac muscle cells and contains desmosomes and gap junctions. Helps the heart contract as a UNIT
What does the larynx or fingers contain? (in regards to how many fibers per motor unit)
Contains as few as 10 muscle fibers per unit. Allows more PRECISE control over the amount and rate of tension produced.
What do myofilaments consist of?
Contractile proteins (produces tension), regulatory proteins (control contractions) , and structural proteins (holds myofilaments in place and ensures structural stability of the myofibril and muscle fiber.)
What are the 5 common properties of muscle cells
Contractility, Excitability, Conductivity, Extensibility, and Elasticity.
What is the M line? What does it consist of?
Dark line in the A bands. Consists of structural proteins that hold the thick filaments in place and serve as an anchoring point for the elastic filaments.
What is the Z-disc? What does is consist of?
Dark line in the I bands. It is composed of structural proteins that: anchor the thin filaments in place and to another. Is the attachment point for elastic filaments. It attaches myofibrils to one another across the whole diameter of the muscle fiber.
What does amitotic mean?
Does not undergo mitosis. These are mature skeletal muscle fiber nuclei.
Define membrane potential
Electrical potential across its plasma membrane.
Define the resting membrane potential
Electrical potential across the sarcolemma in a muscle fiber @ rest Membrane is considered to polarized during the resting phase because two sides of opposite charges are present (ex. magnet)
What are the 2 types of training?
Endurance training and resistance training
What is the terminal cisternae?
Enlarged portions of the SR
Identify and describe the 3 connective tissue layers associated with a skeletal muscle
Epimysium perimysium and endomysium
What are the 3 parts of process of muscle contraction
Excitation phase, Excitation-contraction coupling, and the Contraction phase
Describe isometric contraction
External load is equal to the force generated by the muscle. SAME LENGTH, CHANGING TENSION
What type of motor units does Type II muscle fibers contain?
Fast motor units
What are slow-twitch fibers? Give an example of one.
Fibers w/ low myosin ATPase activity (ex. postural muscles of the back)
Transverse (T) tubule
Folds of Sarcolemma that fold inwards across the muscle fibre and stick into the Sarcoplasm. These aid in spreading electrical impulses
Where is Creatine Phosphate found in?
Found in muscle fibers; 5-6 times more abundant than ATP in cytosol
Describe elasticity in relation to muscle cells
Give the ability to return to original shape after stretching.
Describe glycolysis in relation to muscles.
Glycolysis is a series of rxns that takes place in cytosol of all cells (30-40 secs of sustained muscle contraction). -Glucose is broken down to produce 2 ATP per molecule of glucose.
what is the area within that only has thick filaments
H zone
Are smooth and cardiac muscles voluntary or involuntary?
Involuntary
What are the types of general muscle contractions?
Isotonic contraction and isometric contraction.
What does the myosin head contain?
It contains: a site that binds to ATP, a site that binds to ATPase enzyme that hydrolyzes ATP to an ADP and a P (phosphate group) <-- ADP and P remains attached when "cocked"
Describe the Excitation phase
It involves transmission of a signal fro mthe motor neuron --> sarcolemma of a muscle fiber
What does AchE stand for and what does it do?
It is Acetylcholinesterase. It is an enzyme in the synaptic cleft that immediately degrades and inactivates ACh.
Why do action potentials happen?
It is for long-distance signaling. Action potentials don't stay in one place; rather, they are conducted, or propagated throughout the entire sarcolemma (ex. ripples in a pond)
Describe the depolarization stage
It is in response to a stimulus, voltage-gated sodium ions enters cell (membrane potential --> less negative) --> +30 mV.
Describe the motor end plate
It is the folded surface and contains many receptors (ligand-gated ion channels) for Ach (ligand)
What is the sarcolemma and what is it composed of?
It is the plasma membrane of the muscle cell. Composed of: phospholipid bilayer w/ multiple specialized integral and peripheral proteins.
Why do skeletal muscle fibers have multiple nuclei?
It is the result of embryonic origin of fiber, as each muscle fiber arises from the fusion of multiple embryonic cells (myoblasts)
what does the "cross bridge cycle" lead to?
It leads to a sliding of myofilaments
Where does "maximal tension production" occur?
It occurs in a narrow range of resting sarcomere lengths, near the optimal length of the sarcomere.
What is the endomysium?
It surrounds the extracellular matrix and holds the muscle cells together within muscle tissue
What happens to tension when a sarcomere is overly shortened or overly stretched?
Less tension will be produced.
What are the 2 types of gated channels?
Ligand-gated channels and volage-gated channels.
I band(s)
Light bands containing thin filaments only and extend from the A Band of one sarcomere to the A Band of the next sarcomere.
Skeletal muscle tissue is made up of:
Long, multinucleated muscle cells that are arranged parallel to one another. Attached by connective tissue to the skeleton. They are voluntary.
What is the protein line that stabilize and support thick filament?
M line
M Line
Middle of sarcomere, holds thick filament in place
M line
Middle of sarcomere, holds thick filament in place midline of myosin fibers
Describe the sarcoplasmic reticulum (SR)
Modified smooth ER. Forms a weblike network surrounding each myofibril
What types of fiber classes do most muscles contain?
Most muscles contain ALL fiber classes, each of which is stimulated under different conditions
skeletal muscle nucleus
Multiple nuclei in one cell (multinucleate) Dark structure inside endomysium
Latrotoxin, produced by the poisonous black widow spider, increases the release of acetylcholine. How do muscle cells respond?
Muscle cells will experience fused or complete tetanus when excess acetylcholine exists.
What are fast-twitch fibers? Give an example of one.
Muscle fibers w/ high myosin ATPase activity, they proceed rapidly through contraction cycles (ex. eyeballs)
Muscle tissues consists of:
Myocytes
Which statement best describes the function of myoglobin?
Myoglobin stores oxygen in muscle cells.
The molecule on which ATPase (enzyme that breaks down ATP into ADP) is found.
Myosin
What do thick filaments contain?
Myosin
What energy source is used for longer-lasting muscle activity?
Oxidative energy sources.
What are smooth muscle cells that are able to depolarize and contract spontaneously called?
Pacemaker cells
Describe Excess Postexercise O2 Consumption (EPOC)
Persisting increased rate of breathing
What causes a change in skeletal muscle performance?
Physical training
Describe isotonic contraction
Produces enough tension to initially move a load, such as a weight, and then maintains that same level of tension throughout the contraction SAME TENSION, CHANGING LENGTH
Describe an isometric ctraction
The length of the muscle doesn't change
What is "optimal length"?
The length of the muscle fiber @ which the most crossbridges can form allowing the fiber to generate almost 100% of the tension that is possible to produce.
What is the refractory period?
The muscle cannot respond to another stimulus.
What happens when immediate energy sources are depleted for muscles?
The muscle fibers turn to glycolysis (glycotic or anaerobic catabolism) to make ATP
Describe the synaptic cleft
The narrow space between the axon terminal and the muscle fiber into which Ach is released and enzymes that breaks down Ach.
motor end plate
The portion of the cell membrane at the neuromusclar junction; essentially the postsynaptic membrane at the synapse.
I band
The reginon of the sarcomere made up only of thin filaments. The I band is bisected by a Z line. I bands alternate with A bands to give skeletal and cardiac muscle a striated appearance. I bands get shorter (and may disappear completely) during muscle contraction.
H Zone
The region at the center of an A band of a sarcomere that is made up of myosin only. The H zone gets shorter (and may disappear) during muscle contraction.
H Zone & I Band
The region(s) of the sarcomere that shorten during muscle contraction.
What produces muscle tone?
The small amount of tension; due to involuntary activation of motor by the brain and spinal cord
sarcoplasmic reticulum
The smooth ER of a muscle cell, enlarged and specialized to act as a Ca2+ reservoir. The SR winds around each myofibril in the muscle cell.
What is the Neuromuscular Junction (NMJ) and what is its function?
The synapse of a motor neuron w/ a muscle fiber. Function: transmit a signal called a nerve impulse (action potential of the neuron).
Sarcomere
The unit of muscle contraction. Sarcomeres are bounded by Z lins, to which thin filaments attach. Thick filaments are found in the center of the sarcomere, overlapped by thin filaments over one another during contraction reduces the distance between Z lines, shortening the sarcomere.
What is the wave summation?
The waves of contraction added together. -Depends on the # of times per sec the muscle fiber is stimulated, we end up with one or two states: unfused tetanus and fused tetanus
What are satellite cells?
These cells have the ability to divide; these cells can help repair injured skeletal muscle.
Thin Filaments
These filaments are composed of actin, troponin, and tropomyosin.
Describe ligand-gated channels
They are in response to a chemical stimulus (ligands). They are also called chemically gated chemicals
Describe smooth muscle cells
They are long and flattened w 2 pointed end (spindle shaped). Single centrally located with an oval nucleaus. They line every hollow organ, line eyes, skin, and ducts of certain glands. They are linked by gap junctions. INVOLUNTARY.
Describe Action Potentials
They are quick/temporary change. Ability for the resting membrane potential to be altered to become more negative or positive.
Describe excitability:
They are responsive in presence of stimuli.
Cardiac muscle tissue is made up of:
They are striated muscles cells, shorter and wider, branched, only 1 or 2 nuclei, and has intercalated discs (contain gap junctions and tight). INVOLUNTARY
Describe intercalated discs
They contain gap junctions and are tight. They are found on cardiac tissue.
Describe Transverse tubules (T-Tubules)
They dive deeply into the muscle fiber and surround each myofibril. They for a tunnel-like network within the muscle.
Describe voltage-gated channels?
They respond to changes in membrane potential.
What are the 3 types of myofilaments?
Thick filaments, thin filaments, and elastic filaments.
Describe the Sliding-Filament Mechanism of Contraction
Thiin filaments slide past the thick filaments, generating tension throughout the whole sarcomere.
sliding filament mechanism
Thin filaments slide over thick filaments, by the z discs pulling together. The I band and H zone shorten, and the A band remains the same length
synaptic vesicles
Tiny pouches or sacs in the axon terminals that contain neurotransmitters
Describe endurance training
Training w/ a large increase in the frequency of motor unit activation and a moderate increase in force production - more repetitive w/ a lighter weight. (ex. cycling, jogging, cross-country skiing, distance swimming. Muscle fiber: - increased amounts of oxidative enzymes - more mitochondria and mitochondrial proteins - greater # of blood vessels - more Type I fibers
At rest, what holds the tropomyosin molecule in place?
Troponin
Which molecule does calcium bind to?
Troponin
What are the 2 main classes of skeletal muscle fibers?
Type I fibers and Type II fibers
Describe the type/s of smooth muscles and describe smooth muscles.
Type: smooth muscle. Smooth muscle cells lack striations. Located in the walls of hollow organs like the stomach and intestines. Line the vessels to cause vasoconstriction and vasodilation. They work automatically.
Name the types of striated muscles and describe striated muscle
Types: skeletal and cardiac. Striated muscles have striations (alternating light and dark bands)
What is the area within that has only thick filament?
What is the area within that has only thick filament?
I Band
What is the light area that has only thin filament?
What happens during a spasm?
When a muscle is unable to relax
Describe an isotonic concentric contraction (miometric contraction)
When the muscle shortens - the force generated by the muscle is greater than that of the external load.
What is the power stroke?
When the myosin pivots, pulling the actin toward the center of the sarcomere
Describe the electrical gradient or electrical potential
Where we have unequal #s of positive and negative ions separates by a barriers. represents a source of potential energy
Define hypertonia
a condition of the muscle may have abnormally high tone - feels rock hard - may shorten, causes painful joint contractures - occurs during shivering
Define myofibril
a long strand of cable like protein that contains thousands of actin - thin filaments and myosin - thick filaments
motor neuron
a neuron that sends an impulse to a muscle or gland, causing the muscle or gland to react (ACh released by a somatic motor fiber stimulates a skeletal muscle Acetylcholinesterase (AchE)= Responsible for degrading ACh and stopping the stimulation of the muscle fiber)
Epimysium
a sheath of fibrous elastic tissue surrounding a muscle.
Excitability
ability to respond to a stimulus
Contractility
ability to shorten when an adequate stimulus is received
The neurotransmitter used at the neuromuscular junction (NMJ) is__________.
acetylcholine
During muscle contraction, myosin crossbridges bind to active sites on:
actin
Thin filaments are composed of
actin, tropomyosin, troponin
Around how many muscle fibers does a motor unit contain?
around 150 muscle fibers.
Compared to Type I fibers, Type II fibers__________.
can generate faster, more powerful contractions
Thin Filiments
composed of: 3 proten molecules (actin, troponin, tropmyosin made up of primarily actin
M line(s)
connects thick filaments in a sarcomere; also run perpendicular to the long axis
Myofibrils
contains bundles of myofilaments which is inside repeating microscopic cylindrical units called sarcomers
sarcomere(s)
contractile units within myofibrils, the smallest contractile unit of a muscle
What does muscle tension do?
creates movement, maintains posture, stabilizes joints, generates heat, regulates the flow of materials through hollow organs.
The binding of a myosin head to an actin molecule is termed a:
crossbridge
A band(s)
dark areas, contain myosin and actin overlapping
What are the A bands?
dark region of a striation
terminal cisternae
dilated end-sacs of SR which cross the muscle fiber from one side to the other
Describe the 5 characteristics of skeletal muscle
excitability conductivity contractility elasticity Extensibility
Describe the axon terminal
extends an axon (long "arm) to muscle fiber. Axon swells to create axon terminal.
Describe the sarcomere
functional unit of contraction where muscle tension is produced. Extends from Z-disc to Z-disc. Includes: a full A band and half of two I bands.
What is the basic function of all muscle tissue?
generate muscle tension
What are myofilaments?
hundreds to thousands of protein bundles in a myofibril
Extensibility
is the ability of a cell that allows it to be stretched without being ruptured (up to 3 times their resting length without damage)
elasticity
is the ability of a cell that allows it to return to its original length after it has been stretched
Conductivity
is the ability of a cell to conduct electrical changes across the entire plasma membrane
The type of contraction in which length of the muscle fibers do not change is called:
isometric
The type of contraction that causes a skeletal muscle to lengthen is called__________.
isotonic eccentric contraction
What are the I bands
light region of a striation
The immediate result of acetylcholine binding to receptors on the motor end plate is_________.
local depolarization of the sarcolemma
myofibril
long protein cords that occupy sarcoplasm
Thick Filiments
made up of primarily myosin
What is the H zone?
middle area
What is the Na+/K+ ATPase pump
most important active transport pump for sodium and potassium. Moves 3 sodium ions out of the cell and 2 potassium ions into the cell (this needs ATP hydrolysis)
The folded region of sarcolemma found at the neuromuscular junction (NMJ) is called the_________.
motor end plate
Where are receptors for acetylcholine located?
motor end plate
A single motor neuron together with all the skeletal muscle fibers it innervates is called a:
motor unit
Larry's muscles weakened while he played tennis for hours on a hot summer afternoon. This inability to maintain intensity is defined as:
muscle fatigue
Thick filaments are composed of
myosin
Which of the following proteins is a component of thick filaments?
myosin
Which protein does NOT belong in a thin filament?
myosin
The synapse of a motor neuron with a muscle fiber is known as the:
neuromuscular junction
What are gated channels:
open or close only in response to some sort of stimulus.
What is the zone of overlap ?
over lapping filaments (where tension is generated during muscle contraction)
Through which ATP-generating mechanism can long-lasting muscle contractions be sustained?
oxidative catabolism
What is myoglobin?
oxygen-binding protein -binds to oxygen that has diffused into the muscle fiber from ECF and releases it as the available O2 is depleted by mitochondria performing oxidative catabolism (provides ATP for hours)
sarcolemma
plasma membrane of a muscle fiber
If a patient is given a drug that inhibits acetylcholinesterase (AChE), you would expect to see__________.
prolonged muscle contraction
Z Disc
provides anchorage for thin filaments and elastic filaments Separates the sarcomeres from each other A protein disc to which thin filaments and elastic filaments are anchored at each end of a sarcomere; appears as a narrow dark line in the middle of the I band.
Increase in tension by increasing the number of motor units that are stimulated is called_________.
recruitment
Define physical training
repetitive use of skeletal muscles that leads to changes in the structure and biochemistry of the muscle fibers.
During excitation contraction coupling calcium is released from the__________.
sarcoplasmic reticulum
The storage and release of calcium ions is the key function of the:
sarcoplasmic reticulum
Type I fibers lack:
speed
Describe the structure and function of Aponeurosis
strong flat white sheet of tissue that acts as a tendon to attach muscles to bone
When the sarcomere contracts and shortens__________.
the A band stays the same
Which of the following steps of the contraction cycle triggers ATP hydrolysis?
the binding of ATP to the myosin head
synaptic cleft
tiny gap between synaptic knob and muscle sarcolemma
What protein forms elastic filaments?
titin
What are elastic filaments composed of?
titin (resists excessive stretching, and provides elasticity)
The type of contraction represented by a single stimulus/contraction/relaxation sequence is a(n)__________.
twitch
What is the end line for each sarcomere?
z disk
identify the components of each line and band within the sarcomere
z line thin filaments thick filaments a band I band m line
Describe the smooth muscle function of regulation of flow
Controls the flow of materials through certain hollow organs by changing the diameter of teh tubes
Describe myofibrils
Cylindrical organelles; bundles of specialized proteins. Makes up 50-80% volume of the muscle cells.
sarcoplasm
Cytoplasm of a muscle fiber/cell
What is the sarcoplasm?
Cytoplasm of muscle cells that contains cytosol and all the organelles for the muscle cell.
Breakdown a muscle from big to small
Tendon --> Muscle (surrounded by epimysium) --> fascicle (surrounded by perimysium) --> muscle fiber (surrounded by endomysium) (sarcolemma is the cell membrane) --> myofibrils (sarcoplasm in between myofibrils) --> myofilaments ---> thick, thin, and elastic filaments.
Describe unfused tetanus
Tension pulsates, decreasing slightly and increasing a bit more w/ each successive twitch until a level of maximal tension is reached. Generates more tension than a single twitch contraction
Describe fused tetanus
Tension remains constant @ a maximal level, producing a sustained contraction. Tension is highest. Like unfused tetanus, it generates more tension than a single twitch contraction.
triad
The T Tubule and two terminal cisternae associated with it
Describe contractility
The ability to contract.
A Band
The band of the sarcomere that extends the full length of the thick filament. The A band includes regions of thick and thin filament overlap, as well as a region of thick filament only. A bands alternate with I bands to give skeletal and cardiac muscle a striated apperance. The A band does not shorten during muscle contraction.
A band
The band of the sarcomere that extends the full length of the thick filament. The A band includes regions of thick and thin filament overlap, as well as a region of thick filament only. A bands alternate with I bands to give skeletal and cardiac muscle a striated apperance. The A band does not shorten during muscle contraction.
Perimysium
The connective tissue that surrounds fascicles.
What does the end plate potential lead to?
The end plate potential leads to an action potential in the sarcolemma which in turn triggers events that result in contraction.
What enzyme catalyzes the Creatine Phosphate Reaction?
The enzyme creatine kinase catalyzes the reaction. Creatine phosphate donates a phosphate group to ADP, producing ATP
neuromuscular junction
The functional connection between the distal end of a nerve fiber and the middle of a muscle fiber ACh released, binds to ACh receptors ACh released by a somatic motor fiber stimulates a skeletal muscle
Define sarcomere
The functional contracting unit of skeletal muscle; the portion of myofibril between two Z lines
Where are intercalated discs only found in?
The heart
What is "muscular fatigue"?
The inability to maintain a given level of intensity of a particular exercise.
How many phases of muscle twitch are there? Describe each phase.
1. Latent period: 1- to 2-ms time that it takes for the action potential to spread through the sarcolemma. 2. Contraction period: this period is marked by a rapid increase in tension as cross bridge cycles occur repeatedly. 3. Relaxation period: tension decreases due to the decreasing calcium ion concentration in the cytosol.
Explain the functions of skeletal muscle
1. Produce skeletal movement 2. Maintain posture and body position 3. Support soft tissues 4. Guard entrances and exits 5. Maintain body temperature 6. Store nutrient reserves
What are the 3 processes of ATP regeneration?
1. Reactions in the cytosol that immediately add a phosphate group to ADP. 2. Glycolytic catabolism in cytosol. 3. Oxidative catabolism in mitochondria.
Describe the Exctitation-contraction coupling steps
1. The end-plate potential stimulates an action potential. 2. The action potential is propagated down the T-tubules. 3. T-tubule depolarization leads to the opening of calcium ion channel is in the SR, and calcium ions enter the cytosol.
Describe the steps of the Excitation phase
1. an action potential arrive @ the axon terminal (triggers exocytosis of the synaptic vesicles containing Ach) 2. synaptic vesicles relase Ach into synaptic cleft 3. Ach binds to ligand0gated ion channels in the motor end plate 4. ionchannels open and sodium ions enter the muscle fiber 5. entry of sodium ions depolarizes the sarcolemma locally, producing an end-plate potential (potential is simply a locaal depolarization in the area of the motor end plate.
Explain the function of blood vessels and nerves serving a muscle
Blood vessels deliver oxygen and nutrients to the muscle fibers, as well as remove waste from the muscle fibers. Nerves serve to allow muscles to move using motor neurons (voluntary muscles).
Define hypertrophy
Both # of myofibrils and diameter of the muscle fibers increase
Z disc
Separates the sarcomeres from each other A protein disc to which thin filaments and elastic filaments are anchored at each end of a sarcomere; appears as a narrow dark line in the middle of the I band.
What does autorhythmic mean?
Sets its own rhythm. An example would be PACEMAKER CELLS
The 3 types of muscle tissues and what they all have:
Skeletal, Cardiac, smooth. They all have muscle tension (a force)
What type of motor units does Type I muscle fibers contain?
Slow motor units
What is a muscle twitch?
Smallest muscle contraction is the response of a muscle fiber to a single action potential in a motor neuron.
Describe the repolarization stage
Sodium ion channels close while voltage gated potassium ion channels open and potassium ions leave the cell making membrane potential more negative again --> --85 mV
motor neuron
Somatic Motor Fibers: lead to the skeletal muscles
What is the primary function of the SR?
Storage and release of calcium ions (vital to muscle contraction and relaxation)
What are the 2 basic forms of muscle cells or fibers?
Striated and smooth
What is electrophysiology?
Study of electrical changes plasma membranes and the accompanying physiological processes.
Endomysium
Surrounds individual muscle fibers
