Muscle tissue

Caveolae

- pouchlike infoldings that sequester bits of extracellular fluid containing a high concentration of Ca2+ close to the membrane; when calcium channels open here Ca2+ influx occurs rapidly -It is thought that caveolae may be responsible for the direct entry of Ca2+ from outside the cells via ion channels and its removal by pumping. It is also likely that caveolae contain signaling complexes that trigger Ca2+ release or reuptake from smooth muscle endoplasmic reticulum.

Ca2+ induced Ca2+ release (CICR)

-Required for Heart Muscle -NOT required for contraction of skeletal muscle

Thick filaments (myosin)

-myosin molecules -twisted protein strands called heads Myosin II consists of: 2 heavy chains, -heads cross brigdes with thin filaments 2 alkali (or essential) light chains - Stabilise the myosin heads 2 regulatory chains -regulate ATPase activity of myosin

summation and tetanus

1. summation is where muscle contractions combine and become stronger and more prolonged 2. tetatnus is the continous sustained contraction where muscle cannot relax. will release if maintained. Tetanus arises when the time between successive action potentials is insufficient to return enough Ca2+ to the SR to lower [Ca2+]i below a level that initiates relaxation. In fact, a sustained increase in [Ca2+]i persists until the tetanic stimulus ceases.

PIC FROM CLASS

4 - RMP 0 - Depolarization 1- Na+ channel is closing 2 - Plateau - Ca++ and K+ cancel out each other 3 - repolarization 4 - RMP

Which of the following decreases in length during the contrac(on of a skeletal muscle fiber? 1. A band of the sarcomere 2. I band of the sarcomere 3. Thick filaments 4. Thin filaments 5. Z disks of the sarcomere

I band

Calsequestrin

calcium-binding protein within the sarcoplasmic reticulum which aids in storage of intracellular Ca2+ same as calrecticulin in smooth muscle

Colon ganglia cells

if you don't see this, the person could hirushbrung disease

superficial fascia

loose connective tissue that underlies the skin and attaches it to the superficial layer of muscles

Isotonic contraction

muscle shortens because muscle tension exceeds load (Depends on the load As the load increases the velocity decreases) - tension stays the same - lenght gets shorters - energy fluctuating *the regular weight-lifting contractions we know about*

Smooth muscle

muscle tissue in which the contractile fibrils are not highly ordered, occurring in the gut and other internal organs and under *involuntary control*. - found in blood vessels, digestive, respiratory, urinary and reproductive tracts - has a external lamina and endomysium - numerous gap junctions present - on contraction, cell become scalloped and nucleus distorted

types of skeletal muscle fibers

slow oxidative, fast oxidative, fast glycolytic

Three types of muscle tissue

-- skeletal muscle, (made up of multinucleated cells) -- cardiac muscle, (composed of multiple cells that make tight end to end connections) -- smooth muscle

cardiac muscle contraction

-Contractions via self-excitable "pacemaker cells" = autorythmycity -Contractions go up and down determined by autonomic nervous system -Long APs due to influx of Ca++ from extracellular fluid (tetanus very unlikely)

Features of smooth muscle

- Mitochondria seen near nucleus, RER, and golgi - Myosin has fewer crossbridges - Actin filaments have no troponin or tropomyosin - presense of calmodulin and myosin light chain kinase to cause contraction Actin filaments insert into anchoring cytoplasmic and plasmalemma associated Dense bodies contain alpha actinin and similar to Z disc • Intermediate filaments of desmin also attach to dense bodies thus transmit contractility to adjacent cells • Lack neuromuscular junction are , involuntary. Under the influence of oxytocin-uterus , and autonomic nerves • Synthesize collagen , elastin and proteoglycans non-striated Contractions of smooth muscle are slower and less powerful than the contractions of striated muscle, in part because the ratio of myosin to actin is four-to fivefold lower in smooth muscle have dense bodies where the myofilaments contract cells are adhered to each other at the dense bodies

Regeneration of muscle

- Myoblast-like skeletal muscle satellite cells have limited regenerative ability - Cardiomyocytes can divide at modest rate, but injured heart muscle is mostly replaced by connective tissue *(fibroblasts; scar formation)* - Smooth muscle regenerates throughout life

muscle contraction steps

1) Motor neuron releases acetylcholine into the neuromuscular junction and causes the depolarization of the sarcolemma. 2) Depolarization spreads down the sarcolemma to the T-tubules, triggering the release of Ca2+ ions from the L-type Ca2+ channels (Dihydropyridine channels). 3) Ca2+ binds to troponin C, causing a shift in tropomyosin and exposure of the myosin-binding site on the actin filament. 4) Shortening of the sarcomere occurs as the myosin head binds to the exposed sites of actin, forming a cross-bridge and pulling the actin filament along the thick filament, resulting in contraction. 5) Muscle relaxes when acetylcholine is degraded by acetylcholine esterase and the allowing Ca2+ is brought back into the SR. ATP binds to myosin head, allowing it to relax from actin.

energy sources for contraction

1. ATP reserves: small amount 2. Creatine phosphate: initial source of energy to regenerate ATP from ADP and P 3. Cellular respiration 4. glycogen degredation to pyruvate and lactic acid or thru the TCA

motor unit

All the Muscle Fibers Innervated by a Single Nerve Fiber

pic of smooth muscle contraction

Always Gq G-protein activate Phospholipase C PIP2 -> DAG + IP3 1P3 opens Ca+ receptor in the SR Relaxion is done by MLCP that deactivates MLCK and thus, Myosin head is dephosphorylated In skeletal muscle , Get rid of Ca++ to promote relaxation Smooth muscle Depends on Extracellular Ca++ similar to the Cardiac muscle

A sacromere

Basic contracting unit of muscle cell consits of actin and myosin filaments between z-lines in a muscle cell • A Band - thick myofilaments - myosin • I band -thin myofilaments - F actin

Ca+ channel in muscle

Caffeine and Ryanodine inhibit this channel

Connective tissue of the muscle fibers

Epimycium is around the muscle Paramycium is around each fasicle Endomycium is around each muscle fiber They are all made up of collagen, recticular cells and fibroblasts -Nerve, blood vessels and lymphatics are seen in this layer

Lateral plate visceral mesoderm

Forms smooth muscle of the gastrointestinal system

paraxial mesoderm

Give rise to Somites which are further divided into sclerotome, myotome, and dermatome. Myotome stem cells (myoblasts) migrate through the embryo and form skeletal muscle.

role of calcium in muscle contraction

In turn this triggers the sarcoplasmic reticulum to release calcium ions into the muscle interior where they bind to troponin, thus causing tropomyosin to shift from the face of the actin filament to which myosin heads need to bind to produce contraction.

cardiac muscle

Involuntary muscle tissue found only in the heart. -has a straited pattern intercalated disc with junctional complexes -presense of desmosomes and fasia adherens and gap junctions -Mitochondria is upto 40% of cell (more than skeletal muscle) , glycogen granules and lipfuscin granules present. -T tubules in ventricles is well developed . -SR is less organized . -Junction between terminal cistern and T tubules forms *dyads*. -Secretory granules found near atrial muscle nuclei. These release *Atrial natriuretic factor*

What has smooth muscle

Multiple, independent cells or groups of cells --multiunit smooth muscle iris and ciliary body of the eye, the piloerector muscles of the skin, and some blood vessels Unitary smooth muscle: -Unitary smooth muscle these cells contract as a single unit, this type of smooth muscle is called unitary smooth muscle Unitary smooth muscle is the predominant smooth muscle type within the walls of visceral organs such as the gastrointestinal tract, the uterus, and many blood vessels

Sliding filament theory

Muscle Contraction -Sarcomere shortens -Z lines get closer -A bands remain the same* -I bands narrow. -H zones also narrow

isometric contraction

Muscle contracts but there is no movement, muscle stays the same length -holding a dumbbell in one position and not moving your hand OR sitting on air

Sacroplasmic Reticulum (SR)

Network of smooth endoplasmic reticulum surrounding each myofibril Pairs of terminal cisternae form perpendicular cross channels Functions in the regulation of intracellular Ca2+ levels

Cardiac muscle, H&E and EM

Nucleus is central unlike skeletal muscle

Smooth muscle

Nucleus looks like an elongated nucleus

tropomyosin and troponin

Regulatory proteins bound to actin (thin filaments) • 1. Tropomyosin- two polypeptide coiled chains in the groove between the two twisted actin strands. • 2.Troponin complex has three subunits: TnT - binds to tropomyosin TnC -binds to Ca+, TnI regulates actin -myosin interaction by binding to actin and inhibiting contraction

A single contraction of skeletal muscle is most likely to be terminated by which of the following actions? a. Closure of the postsynaptic nicotinic acetylcholine receptor b. Removal of acetylcholine from the neuromuscular junction c. Removal of Ca++ from the terminal of the motor neuron d. Removal of sarcoplasmic Ca++ e. Return of the dihydropyridine receptor to its res(ng conformation

Removal of sarcoplasmic Ca++ If Ca++ is present then regardless of the others, contraction will take place so far as ATP is available

Skeletal vs cardiac muscle

Skeletal Muscle -*Large muscle cells*:skeletal muscle fibers are really large in fact most of them run the entire length of the muscle itself -*Cylindrical*: so if you isolated a single muscle fiber it would be long and rounded or cylindrical. -*Multinucleated (nucleus is at the periphery of the cell)*: -*Striated voluntary muscle*: they have that banded appearance.• you have conscious control over whether or not that muscle fiber contracts. The contraction of the muscle fiber is controlled by the nervous system however it says part of the nervous system that you have conscious control over. cardiac muscle -*Smaller muscle cells* -*Branched * -*One centrally placed nucleus* -*Striated involuntary muscle*: they're striated just like skeletal muscle cells however they are involuntarily controlled by the nervous system so in other words if I told you to consciously slow down or speed up the contraction of your heart you couldn't do it. -*Cells interconnected by intercalated discs* -Cardiac and skeletal muscle fibers are both invested with connective tissue that conveys nerves and capillaries

Termination of contraction

Taken up by the SERCA type Ca2+ pump of the SR Calsequesterin -

Titin and nebulin

Titin: -a protein that positions the myosin filament to maintain equal spacing between actin filaments supports the thick filaments and connects them to Z disc -Contributes to elasticity Nebulin- binds each thin myofilament laterally Binding them to alpha actinin

fast glycolytic fibers

contract quickly, have fast myosin ATPase, and are easily fatigued intense powerful movements such as hitting a baseball

fast oxidative fibers

contract quickly, have fast myosin ATPases, and have moderate resistance to fatigue - sprinting, walking

slow oxidative fibers

contract slowly, have slow acting myosin ATPases, and are fatigue resistant - endurance exercises e.g, running a marathon, maintaining posture

contraction of smooth muscle

contraction: Influx of calcium thru the caveolae binds to calmodulin -Ca++ / calmodulin stimulate Myosin light chain kinase which then phosphorylates myosin heads -Ca++ / calmodulin also binds to thin filaments and displaces the protein, Caldesmon, which prevent smooth muscle thick filaments from interacting actin Relaxation requires: Ca2+ detachment from calmodulin Active transport of Ca2+ into SR and ECF Dephosphorylation of myosin to reduce myosin ATPase activity

deep fascia

dense connective tissue on the surface of individual muscles - it is continuous with the connective tissue of the tendons at the Myotendinous junctions which join muscle to bone skin or another muscle

Cajal cells

pacemaker cells for smooth muscle

Myoblasts

stem cells that fused to form each muscle fiber early in development Come from mesenchymal cells They fuse to make myotubes which increases the nuclei. A satalite cell is added as a progenitor of muscle fibers in case of an injury where muscle fibers need to be repaired or replenished. (Found in the external lamina)

Skeletal muscle

striated and voluntary Long multinucleated cells - Nucleus are always in the periphery myoblasts -> Myotubes -> Myofibers -> Fascicles -> muscle

thick and thin filaments

structures containing the contractile proteins actin and myosin