Skeletal muscle tissue, connective tissue, nerves and blood vessels.
Skeletal muscle 6 functions
1. Produce skeletal movement - pull on tendons.
2. Maintain posture and body posture.
3. Support soft tissue
4. Guard entrances and exits
5. Maintain body temperature
6. Store nutrient reserves
Three layers of connective tissue that are part of each muscle:
1. Epimysium - surrounds the entire muscle
2. Perimysium - divides the muscle into departments
3. Endomysium - surrounds individual muscle cells
Surrounds the entire muscle. Separates the muscle from surrounding tissues and organs.
Divide the skeletal muscle into a series of compartments called fascicle. Contains blood vessels and nerves.
Within fascicle, surrounds the individual skeletal muscle cells, or muscle fibers. Contains capillary networks, myosatellite cells and nerve fibers that control the muscle.
Embryonic stem cells that function in the repair of damaged muscle tissue
Bundle of collagen fibers from epimysium, perimysium and endomysium at each end of the muscle come together.
Characteristics of skeletal muscle fiber.
Sarcolemma, what does it surround?
Plasma membrane of a muscle fiber. It surrounds the sarcoplasm.
Through what is signal to contract?
Through Transvers tubules.
Responsible for skletal muscle fiber contraction. Consist of bundles of protein filaments called myofilaments - thick and thin filaments and titin.
The sarcoplasmic reticulum
Related to smooth endoplasmic reticulum. Forms a tubulat network around each individual myofibril. On either side is teminal cisternae.
Pair of terminal cisternae an transverse tubule.
What causes muscle contration to begin?
When stored calcium ions are released into the sarcoplasm. These ions then diffuse into sarcomeres.
The smallers functional units of the muscle. Contains: thick and thin filaments, proteins that stabilize the positions of the thick and thin filaments, proteins that regulate the interactions between thick and thin filaments. Each sarcomere has dark (A band) and light bands (I bands).
The A band
Located in the center of the sarcomere and contain thick and thin filaments, M-line, H-band and the zones of overlap.
The M line
Central portion of the sarcomere. Help stabilize the positions of the thick filaments.
Contains only thick filaments. Is bigger at reast and gets shorter when contracted.
Zone of overlap
Thin filaments are in between the thick elements. Each thin filaments is surrounded by 3 thick filament and each thick filament is surrounded by 6 thin filament.
The I band
Contains thin filaments and no thick filaments.
The Z line
Consist of proteins called actinins, which interconnect thin filaments. Mark the boundaries between adjacent sarcomeres.
Helps keep the thick and thin filaments in proper alignment and aids in restoring resting sarcomere length. Helps the muscle fiber resist extreme stretching that would otherwise disrupt the contraction mechanism.
Thin filaments contains
Actin, trompomyosin (blocks the myosin binding site - prevents cross bridge cycling until it is moved aside by troponin) and troponin (binds calcium ions and drags tropomyosin off the myosin binding sites on actin). Does the moving. Double helical chain.
Made of myosin molecules. Has a core of titin. Does the pulling. Has binding sites for actin and ATP. The binding of ATP transfers energy into ADP and phosphate.
The globular head of the myosin protein that composes the thick filament. Has the ability to flex or move back and forth
What happens when a skeletal muscle fiber contracts? 4
1. The H bands and I bands get smaller
2. The zones of overlap get larger
3. The z lines move closer together
4.The width of the A band remains constant.
Sliding filament theory
The thin filaments are slighting toward the center of each sarcomere, alongside the thick filaments.
Where does the communication between the nervous system and skeletal muscle occur?
At neuromuscular junction (NMJ)
A single contraction produced by single stimulation.
1. the latent period - begins at stimulation
2. contraction phase -tension rises to peak
3. relaxiation phase - tension falls to resting levels.
Skeletal muscle is stimulates a second time immediately after the relaxiation phase has ended, resulting slightly higher maximum tension.
Summation of twitches.
Second stimulus arrives before the relaxiation phase has ended and the second contraction is more powerful.
Stimulus continues and the muscle is never allowed to relax.
Higher stimulation frequency eliminates the relaxiation phase. Action potentials arrive so rapidly that the sarcoplasmic reticulum has no time to reclaim the calcium ions.
Size of motor unit is an indication of how fine the control of movement is. The fewer the # of fibers per neuron the finer the control. ie eye muscles (4-6)vs leg muscles(1000-2000).
1) ACh released, binding to receptors
2) Action potential reaches T tubule
3) Sarcoplasmic reticulum releases Ca2+
4) Active-site exposure, cross-bridge formation
5) Contraction begins
6) ACh removed by AChE
7) Sarcoplasmic reticulum recaptures Ca2+
8) Active sites covered, no cross-bridge interation
9) contraction ends
10) relaxation occurs, passive return to resting length
What is motor end plate?
Place where tips of a motor neuron axon contact a muscle cell to stimulate muscle contraction. Sarcolemma contains the motor end plate.
What is Rogor mortis and what causes it?
A fixed muscular contraction after death. When calcium builds up in the cytoplasm because it is no longer actively pumped back into sarcoplamic reticulum.
What are the 2 types of muscle contractions?
Isotonic ( concentric and eccentric) and isometric
What is a Isotonic contraction?
Tension rises and the skeletal muscles's lenth changes. muscle tension exceeds the load and the muscle lifts the load. In a concentric contraction the muscle tension exceeds the load and the muscle shortens.
In a eccentric contraction, the peak tension is less than the load and the muscle elongates. It controls the speed of the movement - can't overcome the tension.
The muscle does not change length and the tension produced never exceeds the load.
How do cells generate ATP? 2 ways
1. Through aerobic metabolism in mitochondria
2. Glycolysis in the cytoplasm
What is muscle fatigue?
When muscles can no longer perform a required activity
What are the 3 characteristics of muscle fatigue?
Exhaustion of metabolic reserves, High acidity from presence of lactic acid, and Damage to cell membrane & sarcoplasmic reticulum
What are the 3 types of Skeletal muscle fibers?
Fast, Slow, and Intermediate Fibers
What is Muscle Hypertrophy
growth from heavy training, increased diameter of muscle fibers, increased number of myofibrils, increased number of mitochondria & glycogen reserves, and increased power
Made by nerve cell at motor endplate
changes permeability of sarcolemma and triggers the contraction of the muscle fiber
Breaks down Ach
found in synaptic cleft and ssarcolemma
takes place in mitochondria
glucose + O2 yields CO2 +H2O +36 (17) ATP
via Krebs cycle
resting muscles use aerobic process
Glucose (no oxygen)yields CO2 +lactic acid
incomplete breakdown of glucose, also called glycolysis, lactic acid irratates muscles,nerves
produces 2 ATP (yeast produces CO2 +alcohol by fermentation
When muscles run out of oxygen
rising lactic levels lower tissue pH levels then muscles can no longer function normally
by-product of anaerobic respiration, build up lowers pH and interferes with contraction until the muscl fiber cannot continue to contract, recycled back to pyruvic acid when O2 available
What causes the myocin head to release from actin?
ATP binding to myocin
Resting tension in a skeletal muscle.
Breakdown of glucose to pyruvic acid in the cytoplasm, provides 2 ATP molecules and generates 2 pyruvic acid molecules from each glucose molecule.
When becomes glycolysis important?
It provides substrates for aerobic metabolism.
Whenenergy demands are at a maximum and the aailability of oxygen limits the rate of mitochondrial ATP production.
Fast fibers - white muscle fiber, fast-twitch, type II fibers
Large glycogen reserves, few mitochondria. Produce powerful contractions, fatigue rapidly. Prolonged activity is supported by anaerobic metabolism. Appear pale and are called white muscles.Have low resistance to fatigue and have twitches with a very brief contraction pahse.
Slow fibers - red muscle fibers, slow-twitch, type I fibers.
Surrounded by extensive network of capillaries, higher supply to support mitochondrial activity. Contain myoglobin - fibers dark red. Red muscles.
Intermediate fibers - Type II A fibers
Between fast and slow fibers, in appearance, resemble more fast fibers.
Lenght of time a muscle can continue to contract while supported by mitochondrial activity. Exercises dont require peak tension production - jogging, distance swimming.
Length of time muscular contraction can continue to be supported by glycolysis ad by the existing energy reserves of ATP. Stimulates muscle hypertrophy. Frequent, brief, intensive workouts.
Only found in heart. Cells contain organized myofibrils, striated appearance, single, centrally placed nucleus, no triads, SR lacks terminal cisternae, almost totally dependent on aerobic metabolism, large numbers of mitochondria, each cell contacts intercalated discs. Branchin cell.
The plasma membranes of two adjacent cardiac muscle cells are extensively intertwined and bound together by gap junctions and desmosomes. This greates a direct electrical connection between two cells. Action potential can travel across an intercalated discs quickly.
Forms sheets, bundles or sheaths around almost every organ. Has single, centrally located nucleus. No T tubules, myofibrils or sarcomeres - no striations. Thick filaments are scattered throughout the sarcoplasm, Have more myosin heads per thick filament. The thin filaments are attached to dense bodies. Spindle-shaped cell.
The membranous network that surrounds each myofibril is the
The binding of calcium ions causes ACh to be released from what structure?
For tropomyosin to be shifted off its position covering the active sites of G actin molecules, calcium ions must bind to which structure?
The binding of ACh to the motor end plate causes a change in membrane permeability to
What event in a muscle contraction marks the beginning of the relaxation of the muscle cell?
1. regeneration is possible: satellite cells become myoblasts which become myotubes which become muscle fibers
2. no regeneration beyond early childhood;; forms scar tissue with remaining myocytes hypertrophying
3. undergoes mitosis and regenerates
What is plasticity?
Atrophy is caused by?
hypertrophy is caused by?
what kind of muscle fibers do sprinters have? marathon runner?
plasticity - muscle adaptation
atrophy - disuse such as bed rest, immobilization, denervation
hypertrophy - increased loading, exercise
sprinter - fast twitch
marathon - slow twitch
Primary function of ATP
Trnsfer of energy from one location to another rather than long-term storage of energy.
Why would ATP transfer its energy to creatine?
ATP can't be stored but at rest, a skeletal muscle fiber produces more ATP than it needs. So the energy wouldn't get lost, ATP transfers its energy to creatine. The energy transfer creates anouther high-energy compound, creatine phosphate (CP).
ATP+creatine -ADP+creatine phjosphate
Small molecule that muscle cells assemble from fragments of amino acids.
What happens if after heavy exercise, energy reserves in a muscle are depleted?
An oxygen dept occurs.
What happens during anaerobic glycolysis?
ATP is produces, oxygen is not consumed and pyruvic acid is produced.
In response to action potentials arriving along the transverse tubules, the sarcoplasmic reiculum releases?
Acts as an energy reserve in muscle tissue.
Where is each skeletal muscle fiber controlled by a motor neuron?
At a single neuromuscular junction.
What is the function of T-tubules?
Extension of the sarcolemma, provides a pathway for the conduction of electrical signals deep into the muscle fiber to the sarcoplasmic reticulm. the t-tubules encircle each myofibril
What is the terminal cisternae?
Part of the SR which store and release calcium
What happens when calcium ion binds to troponin?
Tropomyosi moves into the groove between the helical actin strands.
When do active sites on the actin become available for binding?
After calcium binds to troponin.
Tissues of the body characterized by widel spaced cells with large amounts of intracellular matrix. The functions of these tissues vary, generally, they serve to support, bind, insulate, transport and provide storage.
Organizational levels of skeletal muscle - biggest to smallest
Whole muscl is surrounded by epimysium (connective tissue).
Fascicl is surrounded my perimysium (C tissue).
Muscle fiber is surrounded my endomysium (CT).
Myofibril contains myofilaments (thick and thin).
The neuromusclular junction
The place where a motor neuron stimulates a muscle cell. Skeletal muscle cells contract as a result of impulses from motor neurons.
Structures distributed throughout the sarcoplasm in a network of intermediate filaments composed of the protein desmin. The thin filaments in a smooth muscle cell are attached to it.
What happens when action potential arrives at the axon terminal?
When the action potential arrives at the axon terminal, the voltage change of the membrane opens voltage-gated calcium channels, allowing calcium ions to enter the axon terminal.
What structure contains ACh - acetylcholine?
Synaptic vesicles in the synaptic terminal.
Sequence of events at the neuromusclar junction.
1. Action potential arrives at axon terminal.
2. Calcium ions enter axon terminal.
3. Synaptic vesicles fuse to membrane of axon terminal.
4. Acetylcholine is released into synaptic cleft.
5. Acetylcholine binds to receptor sites on motor end plate.
6. Motor end plate becomes depolarized.
7. Action potential is initiated on sarcolemma.
8. Action potential propagates along sarcolemma and down T tubules.
9. Calcium ions are released from terminal cisternae.
10. Muscle cell contracts.
Six steps of cross bridge cycling
1. The influx of calcium, triggering the exposure of binding sites on actin.
2. The binding of myosin to actin.
3. The power stroke of the myosin head that causes the sliding of the thin filaments.
4. The binding of ATP to the myosin head, which results in the myosin head disconnection from actin.
5. The hydrolysis of ATP, which leads to the re-energizing and repositioning of the myosin head.
6. The transport of calcium ions back into the sarcoplasmic reticulum.
A chemical process in which an enzyme uses water to split one molecul into smaller parts.