Chapter 8: Muscle Tissue
muscle
A muscle is made up of bundles of fascicles. Each fascicle is made up of bundles of fibers. Each fiber is made up of bundles of myofibrils. Each myofibril is a bundle of thick and thin filaments (a myofibril) wrapped in a sarcoplasmic reticulum.
ATP
Cells use the molecule ATP as their energy currency molecule. If energy is needed in the cell, a molecule of ATP has one covalent bond broken, the bond joining the first phosphate to the second. But breaking the bond also releases energy. Breaking any bond would release energy, but the cell almost always breaks the bond holding the last phosphate onto ATP when it wants to release energy for cellular processes. If a cellular process requires work, it will require an input of energy. If an input of energy is required, ATP is converted to ADP and energy is released. The energy released when ATP is broken can be captured by the cell machinery and used to power the work that needs to be done.
ions
Changing the distribution of ions across any cell's membrane changes the electrical charge across the membrane. A change in the distribution of ions/distribution of charges across the muscle fiber's plasma membrane is what begins the contraction of the fiber.
What is tropomyosin doing when a muscle is at rest
blocking every actin active site.
What arrangement of fascicles occurs most frequently and most adudentely in skeletal muscle?
parallel fascicles
What sodium ions from the action potential signal the sacroplasmtic reticulum do?
release Ca^2+
What does the neuron attach to it signal the muscle to do?
release Ca^2+ into the fiber cytoplasm
What molecule is the energy currency of all cells?
ATP
Tendon
At the ends of muscles, the three types of muscle connective tissue - endomysium, perimysium, and epimysium - all come together. They fuse to form a connective tissue attachment that will connect up with a bone either a tendon (bundle) or aponeurosis (sheet).
8.2: Skeletal Muscle organization
Each individual skeletal muscle is entirely surrounded by a layer of DICTP called epimysium- what defines and separates different muscles. fascicles- Within the muscle, the actual muscle fibers (the cellular components) are grouped together in bundles. A single muscle can have 10 to 100 fascicles. perimysium- Wrapping around each fascicle is a layer of dense regular connective tissue proper. also fills the spaces between all the fascicles. Embedded in the perimysium surrounding the fascicles are blood vessels and nerves that will branch off and send smaller blood vessels and smaller nerves to every fascicle in the muscle.
What are bundles of muscle fibers called?
Fascicles
8.7: ATP supplies muscle energy
It requires an input of energy in order to do the work involved. The energy currency of all cells (including muscle fibers) is the molecule ATP. ATP is a single molecule made from various components. The critical components of ATP for energy considerations are three phosphates, or the triphosphate group.
8.1: Overview of skeletal muscle
Muscle tissue is one of the four main tissue types. Skeletal muscle is one of the three muscle types. tissues- epithelial, connective, nervous, muscle. muscle- cardiac, smooth, skeletal Skeletal muscles are attached to the skeletal system. The muscular organ system includes only skeletal muscles. Cardiac muscles are part of cardiovascular organ system. Smooth muscles are part of different organ systems, depending on which organ a particular smooth muscle contracts.
Which type of muscle are in the muscular muscle system?
Only skeleton
strength training/exercise
Strength training or exercise does not usually increase the number of muscle cells. The number of muscle fibers and fascicles in any one muscle usually stay constant. When muscles increase in size due to exercise, the existing fibers are getting larger due to increased number of myofibrils, which do the actual contracting. There may be some circumstances in which training increases the number of fibers, rather than just increasing their size, but it is unclear how frequently this occurs.
8.6: Muscle contract via sliding filaments
When a muscle contracts, many many myofibrils within individual muscle fibers are contracting simultaneously. Within each myofibril, thin filaments are being pulled across thick filaments, which stay in place. A bands always stay the same width, but I bands get shorter during a myofibril contraction. thin filaments in I bands are pulled over immobile thick filaments in A bands in all the sarcomeres throughout a myofibril. same pulling of thin filaments occurs in all the myofibrils in one fiber, shortening the whole myofibril. Then fiber as a whole will shorten and contract. •One end of the muscle is held in place (to an immobile bone, usually). •And the other end is attached to a bone that moves. •So the muscle moves by contracting towards the fixed end, moving the mobile bone, but not the fixed bone.
8.4: Naming the Microscopic features
When a muscle myofibril is examined under the microscope in longitudinal section(from side), it has patterns of light and dark bands. myofibril bands were involved in muscle contraction. A bands are the wide and dark bands. The A bands alternate with I bands, which are light and thin. Z lines (Z discs) are in the middle of the I band. A sarcomere is everything between two Z lines. each myofibril consists of apporximately 10,000 sarcomeres. Each sarcomere is the actual unit of contraction in a myofibril. With each contraction, each sarcomere shortens.
Endomysium
Within each fascicle are several individual muscle fibers, the smallest living unit of muscle. The muscle fibers within a fascicle are surrounded by and embedded in endomysium. also embeds: 1.Capillaries that go to every fiber in the fascicle. 2.Nerves that go to every fiber in the fascicle. 3. Myosatellite cells that serve as muscle stem cells
What are intercalated discs in cardiac muscle fibers?
plasma membranes with dense collections of desomes and gap junctions
What is the name given to the wave of voltage-gated sodium chanels opening?
action potential
What is the state of all skeletal muscles immediately after death?
all of the skeletal muscles are relaxed
Muscle fibers
are not single cells. Muscle fibers are single units created by the fusion of hundreds or more precursor cells during embryonic development. That is the reason each muscle fiber is multinucleate and can have hundreds or more nuclei. The embryonic stem cells that fuse to form muscle fibers are called myoblasts. Some myoblasts don't fuse during development and instead become myosatellite cells in fascicles that can act as adult stem cells and supply cells to rebuild damaged fibers. Remember: •Myoblasts are stems cells only found during embryonic development •Myosatellite cells are stem cells found throughout life.
8.5: Myofibrils consist of protein filaments
at the molecular level, molecules make up bands and zones of myofibrils within muscle fibers. 1.Thin filaments - found in I bands and A bands 2. Thick filaments - found in A bands only
What initiates muscle contraction?
calcium entering the cytoplasm
Myofibrils
cylindrical bundles of long protein complexes found inside the muscle fiber. The myofibrils are what will do the actual contracting when the muscle contracts. Each muscle fiber has hundreds to thousands of myofibrils. The myofibrils extend the length of the fiber and their ends fuse with the plasma membrane/sarcolemma of the fiber. And the plasma membrane/sarcolemma is attached to the muscle's tendon with cell adhesion proteins. When myofibrils contract: •They pull in the ends of the fiber, including the plasma membrane. •Which pull in tendons attached to the membrane. •Which pull in the bone attached to the tendon •Which moves that bone.
What does an agonist do?
produces a specific movement when it contracts.
What is a sacromere?
everything between two zed lines.
What do sarco and Myo mean respectively?
flesh for sacro and muscle for myo.
covalent bond
hold the phosphates onto the ATP are no different from any other covalent bond in any other molecule. But all covalent bonds in all molecules do work. prevent the atoms they join from diffusing away from one another - covalent bonds hold atoms in place, which is a form of work. works=energy If the atoms weren't joined by the bond, they would diffuse away, so energy is used to keep the atoms together(in form of covalent bond) all covalent bonds are a form of stored energy, doing work to keep atoms together. If any covalent bond is broken, that energy is released. work is no longer keeping them together. Breaking any covalent bond releases energy.
Transverse Tubules
indentations in the plasma membrane/sarcolemma of muscle fibers that extend into the fiber at right angles to the cell surface. create passageways through the fiber made up of plasma membrane/sarcolemma that encircle myofibrils.
Where does the calcium that triggers rigor mortis?
leaks from the sarcoplasmtic reticulum
Thin filaments
made up of 3 proteins 1. actin- A protein fiber arranged in two twisted rows. g-actin- The individual protein molecules that assemble into the fiber complex. f-actin: But when assembled into twisted double strands, the entire complex. 2. Tropomyosin- A very thin double-stranded protein fiber that wraps around the actin chains. 3. Troponins- Individual proteins (not grouped into fiber chains) bound to the tropomyosin chains. Have binding sites where they can bind Ca2+ ions if Ca2+ is present.
thick filaments
made up of one protein fiber. 1. Myosin: Each thick filament is a complex of about 300 myosin molecules twisted around each other to form a thick fiber. Each myosin has a long tail, which twists around the other myosins. Each myosin also has a roundish head, which sticks out from the tail and which can be moved back and forth.
What proteins are in thick filaments?
myosin
What happens after ATP binds a mysoin head group?
mysoin head group detaches from the actin active binding site.
Sacroplasmic reticulum
name given smooth endoplasmic reticulum in muscle fibers. It wraps around the portions of myofibrils that don't have transverse tubules of indented plasma membrane. In muscle fibers it serves as a reservoir of Ca2+ ions. muscle smooth ER (sarcoplasmic reticulum) is also the site of new membrane synthesis, but not involved in muscle contraction. Inside those chambers the Ca2+ concentration is 10,000x higher.
Sacromere
overlapping thin and thick filaments between two z lines
8.3: Muscle Fiber structures and jargon
sarcolemma- The plasma membrane surrounding a muscle fiber. myo=muscle sacro=flesh sacroplasm- The cytoplasm of a muscle fiber. has more negative ions & fewer positive ions than the extracellular environment outside its plasma membrane/sarcolemma. muscle cells have a net charge across their plasma membrane. More positive outside plasma membrane; less positive inside
What is the name of the tiny space between a neuron and it's target?
synapse
When bone is a lever, what serves as fulcrum?
the joint
What neurotransmitter signals skeletal muscle fiber to fire?
the neurontransmitter is the acetylcholine
What happens when calcium ions are removed from the cytoplasm of the muscle fiber?
the thin filaments slide make to their resting uncontracted position.
What are the thin filaments attached to in smooth muscle
they are attached to dense bodies
What do myosin head groups have to do in order to power stroke?
they first have to bind an actin active site.
What overall roll do calcium ions serve in muscle fibers?
they serve as on and off switches for muscle contraction.
What is happening when muscle fibers are sliding?
thin filaments are being pulled across thick filaments.
ATP continued
when a cell acquires new energy it is usually done by breaking food molecules down to CO2, releasing energy from bonds. The cell will capture that energy and use it to reattach phosphates onto ADP, regenerating ATP. Muscle movement will involve using energy, so it will require ATP be broken down to ADP + phosphate.