Chapter 11 Flashcards
Characteristics of all muscle cells?
Conductivity, contractibility, excitability, extensibility, elasticity
What is excitability?
Responding to stimulation w/ electrical charges
What is conductivity?
When a small local excitation sets off a wave that leads to contraction
What is contractibility?
Shortening when stimulated
What is extensibility?
Stretching between contractions
What is elasticity?
Returning to original rest length after being stretched
What is skeletal muscle?
The muscles that move our body. Voluntary, striated
What are striations?
Light and dark transverse bands on muscle, representing overlapping arrangements of contractile proteins
What does voluntary mean?
Muscles that are subject to conscious control (skeletal)
What does involuntary mean?
Muscles that are not under conscious control. Never attached to bones (cardiac and smooth)
What are skeletal muscle cells called?
Muscle fibers or myofibers
What is skeletal muscle composed of?
The muscular tissue as well as fibrous connective tissue (endomysium, perimysium, epimysium)
How do bones move?
A muscle contracts, pulling on the collagen fibers continuous with tendons and a bone matrix, moving the bone
What properties does collagen have?
It is somewhat extensible and elastic
How does collagen assist with muscle stretching?
It helps prevent excessive stretching
What happens with collagen when a muscle relaxes?
The elastic recoil helps the muscle return to its resting length
Does collagen’s recoil help muscles with power?
It’s unclear
What are tendons?
Attachments between muscle and bone
matrix
What is the plasma membrane of a muscle fiber?
Sarcolemma
What is the cytoplasm of a muscle fiber?
Sarcoplasm
What are the protein cords occupying most of the sarcoplasm?
Myofibrils
What is glycogen?
Found in sarcoplasm, a carb that provides energy for the cell during exercise
What is myoglobin?
A red, oxygen-binding pigment which provides oxygen during exercise
How many nuclei are in a muscle cell? Where are they?
Multiple, they’re pressed against the inside of the sarcolemma
What are myoblasts?
Specialized stem cells which fuse to produce muscle fibers
What are satellite cells?
Unspecialized stem cells between the muscle fiber and endomysium. They help regenerate damaged skeletal muscle
Where are the mitochondria of a muscle cell?
Packed into spaces between myofibrils
What is the smooth endoplasmic reticulum of a muscle cell?
Sarcoplasmic reticulum
What does sarcoplasmic reticulum do?
Form a network around each myofibril, and exhibit terminal cisterns
What are terminal cisterns?
Dilated end-sacs of SR which cross the muscle fiber from one side to the other
What do terminal cisterns do regarding calcium?
It acts as a reservoir. It releases calcium through channels to activate contraction
What are transverse tubules (T tubules)?
Tubular infoldings in the sarcolemma, which penetrate through the cell and emerge on the other side
What is a triad?
A T tubule and the 2 terminal cisterns associated with it
What is required for a muscle to contract?
Calcium ions (Ca+)
Where does a muscle cell store its calcium when at rest?
The sarcoplasmic reticulum, bound to calsequestrin
What happens to calcium when a cell is stimulated?
T tubules signal to ion gates in the SR membrane to open, flooding Ca+ into the cytosol
What are myofilaments?
Long proteins that fill most of the muscle cell. They make up myofibrils
What are thick filaments?
A type of myofilament. Made of several hundred molecules of a protein called myosin
How are thick filaments shaped?
2 chains of myosin make a tail and a double globular head that projects out from an angle. Each myosin is shaped like a golf club
What are thin filaments?
A type of myofilament. Composed of 2 intertwined strands of a protein called fibrous actin (F actin), and molecules of tropomyosin
How is F actin made?
By a string of subunits called globular actin (G actin)
How does G actin work?
It has active sites that can bind to the heads of myosin molecules
What is tropomyosin?
Found in thin filaments, it is released when a muscle fiber is relaxed, and blocks the active sites of actins so myosin cannot bind to them
What is bound to tropomyosin?
It has calcium-binding proteins called troponin bound to it
What are elastic filaments?
A type of myofilament, made of a huge spongy protein called titin
Where are elastic filaments?
Through the core of each thick filament, anchoring it to the Z disc at one and and M line at the other
What does titin do?
Stabilize the thick filament, centering it between thin filaments, preventing overstretching, and recoiling it like a spring after a muscle is stretched
What are contractile proteins?
Myosin and actin. Shorten the muscle fiber
What are regulatory proteins?
Tropomyosin and troponin. Act like a switch to determine when a muscle fiber can and cannot contract
What is dystrophin?
An accessory protein which is located between the sarcolemma and outermost myofilaments
What does dystrophin do?
Links actin in outermost myofilaments to endomysium
What happens to dystrophin when thin filaments move?
It gets pulled on, in turn pulling the extracellular connective tissues that lead to a tendon
How is muscular dystrophy caused?
Genetic defects in dystrophin
How is contraction activated?
Calcium is released into the sarcoplasm. It binds to troponin. Troponin changes shape and moves tropomyosin off of the actin’s active sites
What are striations?
Bands made from the organization of myosin and actin (contractile proteins) in cardial and skeletal muscle cells
What are A bands?
Dark bands of striated muscle. Thick and thin filaments overlap. Anisotrophic
What are I bands?
Light bands of striated muscle. Only thin filaments and elastic fibers. Isotrophic
What is the H band?
In the middle of an A band, a lighter region where it’s only thick filaments
What is the M line?
The middle of an H band
What is a Z disc?
An anchor for thin filaments and elastic fibers. Bisects the I bands
What is a sarcomere?
A segment of a myofibril from one Z disc to another. The functional contractile units of the muscle fiber
How do muscle cells shorten?
The individual sarcomeres shorten, pulling Z discs to one another. The dystrophin and linking proteins pull on the extracellular proteins of the muscle. They pull on the sarcolemma to achieve cell shortening
Do thick or thin filaments change length during shortening?
No, they just overlap more
What is denervation atrophy?
When a muscle degrades from being paralyzed for so long
What are skeletal muscle cells innervated by?
Somatic nerve cells
Where are the cell bodies of somatic nerve cells?
Brainstem and spinal cord
What is a motor unit?
One nerve cell and all of the muscle fibers innervated by it
What are small motor units for?
Fine control
What are large motor units for?
Strength
What is a synapse?
The point where a nerve fiber meets its target
What is a neuromuscular junction?
A synapse where the target cell is a muscle fiber
What is an axon terminal?
The point where a nerve fiber ends
What are synaptic vesicles?
Organelles in axon terminals where acetylcholine is found
What is acetylcholine?
AKA ACh, a neurotransmitter that acts as a chemical messenger from nerve cell to plasma cell
What is a synaptic cleft?
The gap between an axon terminal and sarcolemma
What are junctional folds?
Infolds in the sarcolemma that increase ACh-sensitive membrane’s surface area
What are ACh receptors?
Proteins embedded in the sarcolemma
What is a basal lamina?
Covering the NMJ, it separates the muscle fiber and nerve ending from surrounding connective tissue
What is acetylcholinesterase?
AKA AChE, an enzyme that breaks down ACh after it’s stimulated a muscle, so it can relax
Are muscle and nerve cells electrically excitable?
Yes
What is electrophysiology?
The study of the electrical activity of cells
What is voltage?
Difference in electrical charge from one point to another
What is polarized?
The intracellular fluid, it has more anions than the ECF
What is resting membrane potential usually at?
-90 mv in skeletal muscle cells
What happens to ion concentration when a nerve or muscle cell is stimulated?
Na+ ions flood into the cell, overriding the negative charge inside the membrane and turning it positive. AKA, depolarization
What happens to the ion concentration after depolarization?
K+ exits the cell, repolarizing the membrane. The loss of positive potassium ions turned the membrane negative again
What is action potential?
The quick shift in electrical charge within a membrane
How does action potential spread?
It acts as a wave, producing a nerve impulse
How can toxins cause paralysis?
They can bind to AChE and prevent it from degrading ACh, leading to spastic paralysis, or, they can compete w/ ACh for receptor sites, leading to flaccid paralysis
What is excitation?
Process in which nerve action potentials lead to muscle action potentials
What is excitation-contraction coupling?
Events that link the action potentials on the
sarcolemma to activation of the myofilaments, thereby preparing them to contract
What is contraction?
Step in which the muscle fiber develops tension and may shorten
What is sliding filament theory?
The mechanism of contraction. Thin filament slides over thick filament, pulling Z discs, shortening sarcomere, generating tension
What is the length-tension relationship?
The amount of tension generated by a muscle depends on how stretched or shortened it was before stimulation
What is optimum resting length?
2.0-2.25 µm
How does rigor mortis work?
Calcium is released into cytosol and it starts the myosin-actin crossbridging, but theres no ATP for the muscle to relax with
What happens during excitation?
A nerve signal opens the calcium channels, letting them enter the synaptic terminal. This tells the vesicles to release ACh, which binds to sarcolemma and opens the channel so Na+ can come in and K+ can go out, making an end-plate potential. Then, more channels for Na+ and K+ open in response, causing an action potential
What happens during excitation-contraction coupling?
A wave of action potentials hits the T tubules, bringing them down into the cell, opening ion channels in the T tubules. This in turn opens channels in the SR so calcium can enter the cytosol. Calcium binds to the troponin on thin filaments, changing the chape of the troponin-tropomyosin complex, so the active sites on actin are exposed and ready for myosin
What happens during contraction?
The myosin head needs ATP on it. Then, the ATP turns into ADP and phosphate, which also activates the head. The head binds to an active site on actin, making a crossbridge. It lets go of the ADP and P and bends down, pulling the thin filament with it (power stroke). Then a new ATP binds to myosin, breaking the bridge (recovery stroke), and the myosin attaches to a new active site farther down
What can contraction be compared to?
Pulling an anchor up by a rope
What happens during relaxation?
Nerve signals stop arriving at the NMJ, so ACh stops getting released. AChE breaks it down and it gets reabsorbed into the SR. The calcium levels fall dramatically and tropomyosin moves back to blocking active sites on the actin
What are myocytes?
Any type of muscle cell
What are cardiomyocytes?
Cardiac muscle cells
What’s the difference between cardiac and smooth muscle, and skeletal muscle?
Skeletal is voluntary, the others are not
Purpose of cardiac muscle?
Pump blood
What are intercalated discs?
Intercellular connections on cardiomyocytes. Allow electrical impulse conduction from cell to cell
What nervous system is associated w/ cardiac muscle?
Autonomic nervous system
What nervous system is associated w/ skeletal muscle?
Somatic nervous system
What nervous system is associated with smooth muscle?
Autonomic nervous system
How do cells in cardiac muscle contract?
In unison
How long do contractions of cardiac muscle need to last?
Long enough to expel blood
How do damaged cardiac muscle cells regenerate?
Fibrosis (scar tissue)
How does the autonomic nervous system affect cardiac muscle?
Increases or decreases heart rate/contraction strength
How do smooth muscles get nerve supply?
Some get it from autonomic fibers
How does smooth muscle regenerate?
Mitosis
What is smooth muscle for?
It lines the internal walls of viscera and does some fine control
What is unique to smooth muscle’s method of contraction?
It’s really slow but it can stay contracted for a while
What are dense bodies?
Protein plaques in place of Z discs in smooth muscle
What is a multiunit smooth muscle?
Autonomic innervation, branches synapse w/ myocytes to form a motor unit
What is a single-unit smooth muscle?
AKA visceral muscle, electrically couples to each other via gap junctions. Stimulate each other, so they contract as a unit
What excites smooth muscle?
Autonomic nervous system, chemicals, temperature, stretch, autorhythmicity
What is contraction triggered by, energized by, and achieved by?
Triggered by calcium ions, energized by ATP, achieved by sliding filaments
What is latch-bridge mechanism?
Heads of myosin molecules in smooth muscle don’t detach actin immediately and dont consume more ATP
What is muscular dystrophy?
Hereditary diseases where skeletal muscles degenerate and are replaced w/ fat and fibrous scar tissue
What is duchenne?
A form of muscular dystrophy, common in boys 2-10
What is myasthenia gravis?
A form of muscular dystrophy, antibodies attach NMJs and bind ACh receptors together. Women 20-40
