Lecture: Chapter 9: Muscles and Muscle Tissue

4 total sources of ATP

1.) ADP + P (From creatine phosphate) 2.) Aerobic respiration 3.) Anaerobic respiration

Basic characteristics

-needle-like shaped cell, single centrally located oval nucleus -contains actin and myosin filaments, but arrangement is not as orderly - non-striated appearance, involuntary innervation dense bodies serve as attachment points for thin filaments caveoli pouch-like invaginations of plasma membrane traps extracellular Ca++

Both types can

-spontaneously contract (doesnt need nerve stimulation) -contract more slowly for a longer period of time then skeletal muscle -can stretch without developing tension (digestion of visceral organs without increasing pressure within organ) - innervated by autonomic nervous system

Gross Anatomy of Skeletal Muscle

-tons of MUSCLE cells (you are born w/ all your skeletal muscle cells) - All shapes and sizes - Muscles are discrete organs made of of several similar tissues: muscles cells, BV, Nerve fibers, CT

events of contraction cycle

1.) Cross Bridge Formation: Myosin Head attaches to actin -Ca is released from SR and Ca molecules bind to troponin molecules, this causes tropomyosin molecules to move revealing myosin attachment sites on actin myofilaments. Single phosphate attached to myosin heads is released as the heads move to connect with the attachment sites on the actin. 2.) The Power Working (Skills)- Myosin head pulls on actin -Remaining ADP is expended in Powerstroke where myosin heads pull actin inward. 3.) Cross Bridge Detachment- Myosin head releases actin when ATP binds to it Atp molecules attach themselves to myosin heads triggering the release of the myosin head from actin attachment 4.) Cocking of Myosin Head myosin is broken down to ADP phosphate as heads move back into their resting position The myosin is returned to the high energy position

Aponeurosis

Aponeurosis: Flat and broad CT (DICT) Strong multiple direction pull, weaker in one direction

Attachements - tendon, aponeurosis,

CT surrounding the muscles components is continuous with tendon or aponeurosis Tendon: cord shaped CT (DRCT) connects muscle to bones- very strong pull in one direction Aponeurosis: Flat and broad CT (DICT) Strong multiple direction pull, weaker in one direction Cause movement of insertion towards origin

Perimysium

Connective tissue surrounding a fascicle (bundle of muscle fibers) (separates muscle into groups of fascicles) DICT

Endomysium

Connective tissue surrounding a muscle fiber and wraps fibers individually. Made of fine areolar CT Consist of: 1.) Capillary network 2.) Myosatellite cells: stem cells 3.) Nerve fibers All supply fibers directly

aerobic respiration

Constant replenishment of ATP ATP production process occurs in the mitochondria but requires O2 (aerobic) Involves a process called oxidative phosphorylation this process will provide 95% more ATP from glucose than the anaerobic p/w but is a slower process end products are ATP+ (CO2 and H2O ) waste products sweated out - long-duration energy

anaerobic metabolism/ lactic acid fermentation

Does not utilize O2 - kicks in When the aerobic system is ineffective end products are 2 ATP and lactic Acid (causes initial soreness) 2.5 times faster than aerobic (fast supply for only one min).9iuujujhnb

Microscopic anatomy

Elongated, cylindrical multi-nucleated cell, larger than most other cells sarcolemma Sarcoplasm myofibrils sarcomeres myofilaments T-tubules Triad relationship

Contraction Period (10-100 MS)

From onset of contraction to peak - power strokes cause thin filaments to move closer towards M line, (I, H ban get smaller, Z comes closer)

Latent period (0-10 MS)

From stimulus to beginning of contraction -cross bridges are active but there is no tension

Slow twitch oxidative fibers: fatigue resistance

Highly aerobic -small red cells, myoglobin, mitochondria, capillaries Contract more slowly, smaller in diameter, better blood supply, more fatigue-resistant than fast-twitch Postural muscles, more in lower than upper limbs. example: marathon runner

graded muscle responses (potential/threshold)

How the muscle cell responds to two different types of stimuli Resting- . - Frequency of neural stimuli -Strength the neural stimuli

muscle fatigue

Inability of muscle to maintain its strength of contraction or tension; may be related to insufficient oxygen, depletion of glycogen, and/or lactic acid buildup increase if lactic acid due to deficit of O2/ATP leads to sustained contraction and cramping (myosin heads cannot detatch once ATP is regenerated myosin heads will detatch

smooth muscle

Involuntary muscle found inside many internal organs of the body

Fast twitch glycolic fibers: fatigable

Large white cells, powerful structure Highly anaerobic: large glycogen reserves (few mitochondria and capillaries), therefore, contracts more rapidly, but fatigues quickly (result: increase lactic acid, decreased ATP) example sprinter

Three phases of contraction (cycle)

Latent period Contraction period Relaxation period

Smooth Muscle (Location, Shape, Feature, Control, Function, Longevity)

Location: Forms walls of hollow internal organs Shape: Needle shape, uninucleated, (Special feature: found in sheets/work together) Control: Involuntary control Function: Help hollow organs contract Longevity: Almost tireless

Skeletal muscles (Location, Shape, Feature, Control, Function, Longevity)

Location: On or attached to bones Shape: Long, cylindrical, multi-nucleated, (special feature- parallel), with striations Control: Voluntary Function: Exert ounces to pounds of force Longevity: Fatigues quickly

Cardiac Muscle (Location, Shape, Feature, Control, Function, Longevity)

Location: Walls of heart Shape: Short branched, uninucleate, sometimes binucleated, cells with striations (special feature: has intracellular discs ie. specialized junctions) Control: Involuntary Function: Pacemaker, will beat regularly without any outside help Longevity: Tireless

fast-twitch oxidative fibers: intermediate fatigue resistant

Moderate (intermediate) fatigue resistant medium in size, red/pink cell moderate amount of mitochondria and capillaries much like slow twitch but fatigues more rapidly example: soccer player

Four main functions

Movement (locomotion:walking/running etc, blood circulation, food digestion, movement of fluids) Maintenance of posture: on going skeletal muscle contractions and adjustments Heat Production: Contractions to produce heat- helps maintain normal body temperature Joint Stability: Muscle tone to stabilize

sacromeres

Muscle parts chained together to make up myofibril (z to z disc) Smallest contractile units made of bundles of thin and thick myofilaments

The duration of phases depends upon

Muscle type fast/slow twtich

muscles cells contain

Myofibrils, sarcoplasmic rectulum, and T tubules

nerve and blood supply

Nerves: Each muscle receives a nerve, artery, and veins Consciously controlled skeletal muscle has nerves supplying every fiber to control activity Arteries and veins: Contracting muscle fibers require huge amounts of oxygen and nutrients provided through arteries. Removal of wastes by at least one vein

Binding sties

On Myosin for: ATP, ATPase, and for actin On Actin for: Myosin head Tropomyosin- blocks the binding site on the actin On Troponin for: calcium, which changes the shape of troponin and moves tropomyosin and uncovers the active site on actin

sarcoplasmic reticulum

Organelle of the muscle fiber that stores calcium. The network of enclosed tubules (Smooth ER) that run between and parallel to, around, sarcomeres (myofibrils) -ends of sac-like channels are called terminal Function: SR regulates intracellular levels of ionic calcium, storing and releasing Ca on demands when a muscle fiber is stimulated to contract. "Go signal for contraction"

Muscle attachments may be direct or indirect

Origin: immovable portion or bone attachment Insertion: the more movable portions or bones attachment Direct: epimysium is connected continuously with the periosteum or perichondrium Indirect: Surrounding CT of muscle is connected to the fascia surrounding other muscles, cartilage, or bones

Connective Tissue Sheaths Function

Protect, strengthen, binds, and attaches muscle to bone. CT serves as a pathway for BVs and N.N

When muscles contract they...

Pull on sheaths which transmit pulling force to bone to be moved. Contribute to natural elasticity of muscle tissue

muscle twitch

Rapid contraction of muscle from one neural stimulus

Multiple stimuli

Unfused: with partial relaxation is called incomplete/unfused tetanus Fused: without relaxation, with sustained contraction is called complete/fused tetanus

Regulation of Contraction

activity of smooth muscle under ANS control, depends on the type of neurontransmitter and receptor on the cell membrane -initiation of contractions may also be caused by pace maker (spontaneous depolarization) cells, hormones or Ca++ level changes - hyperplasia: increase in number of cells Special smooth muscle features: secretory function: smooth muscle cells produce and release protein, collagen, and elastic fibers, and proteoglycans, this allows them to make their own endomysium

Regulation of contraction

basic characteristics - Must have action potential to contract -the action potential travels along the sarcolemma and down T Tubules This impulse will cause Ca++ to be released from SR (terminal Cisternae) leading to an increase in levels in the sarcoplasm -Ca++ binds to troponin and moves tropomyosin away from actin active site which myosin can now bind ultimately causing contraction - the electrical signal is only part of the overall contraction mechanism

Neuromuscular junctions

composed of ANS neuron ending has varicosities that store and release neurotransmitters which cover a large area of sarcolemma diffuse junctions: wide synaptic cleft

thin filaments

composed of actin (blue) extend across I band and into A band. They consist of two strands of actin subunits twisted into a helix - troponin - tropomyosin -kidney shaped polypeptide subunits called G Actin, which have myosin binding sites-where myosin heads attach during contraction -F actin: fibrous g actin in chain, arranged in double stranded coils Tropomyosin- rod shaped, blocks myosin-binding sites on actin, gives actin its regidity Troponin- polypeptide composed of three subunits TnI: inhibitory subunit, binds to actin TnT: binds to tropomyosin TnC: binds to Ca receptor

cross bridges

connections between the heads of myosin filaments and receptor sites on the actin filaments during contractions globular heads link thick and thin filaments together forming a cross-bridge. Act as motors that generate force, myosin spits ATP and uses released energy to drive movement.

thick myofilaments

contain the protein myosin (RED)- extend length of A band and connect into the midline of M line rod-like tail or axis with a double globular head, cross the bridge contain sites for actin and ATP

Direct phosphorylation of ATP (By creatine phosphate)

creatine phosphate is a high energy molecule a coupled reaction using creatine phosphate and ADP -starts after the stored ATP in the muscle is depleted -Provides 4-9 seconds of ATP for a total of 10-15 seconds in combination with stored ATP

Sarcoplasm (two special organelles vital to muscle cell)

cytoplasm of a muscle cell, contains large amounts of glycosomes (produce glucose during activity for ATP production) and myoglobin (stores and transports oxygen and nutrients)

3 layers of CT in muscle

epimysium, perimysium, endomysium

excitation-contraction coupling is

events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract Electrical: action potential (sarcolemma and T-tubule) Chemical: Ca++ being released from SR into Sarcoplasm Mechanical: Contraction due to Ca, calcium control is what actually alows contraction. Note: Ca is transported back into sarcoplasmic reticulum by calsequestrin and or calmodulin almost as soon as it is released. Ca++ pump moves the Ca++ into SR.

Functional Characteristics of Muscles

excitability: receive/respond to stimuli due to neural, chemical, hormonal, ph changes, which initiate an action potential contractility: Ability to shorten forcibly as a result of an adequate action potential extensibility: Ability of a muscle to stretch when relaxed elasticity: Ability of muscle tissue to return to its original length after being stretched KEY FUNCTION: CONTRACT

Which fiber type can change into the other?

fast-twitch oxidative fibers & Fast-twitch glycolic fibers can train these cells to increase/ decrease capillaries/mitochondria to change into each other.

relaxation period (10-100 MS)

from peak to 0 as cross bridges become inactive as potassium and Ca leave cell, the depolarization phase begins (Absolute refractory period is not part of a muscle twitch)

Heat production by muscle

important for body temperature homeostasis (1/4 of energy is converted into work the rest is converted into heat)

Multi unit

individual cells can fire by themselves - functionally individual fibers each with its own motor nerve ending -found in by walls, erector pilli, iris of the eye fine control act seperatley

Sarcolemma ("flesh sheath")

muscle cell plasma membrane, envelops each muscle cell fiber

isometric contraction

no shortening; muscle tension increases but does not exceed the load there is no movement, the muscle stays the same length

Chartacteristics of myofilaments

no striations: myosin (thick) and Actin (thin) filaments do not parallel or overlap thick filaments (myosin) are very long and have many cross bridge heads along their length no troponin and no sarcomere dense bodies sometimes attach to sarcolemma dense bands- anchoring points for thin filaments kind of like a Z-disc contract in S shape like a worm

Sarcoplasmic reticulum is

present but less developed and does not contain CA++ or T-Tubules

Myofibrils

protein structures that makeup muscle fibers- one muscle fiber has 100-1000 myofibrils rod shape, run parallel to the length made of sarcomere chains striated appearance due to: overlapping thin and thick myofilaments A Bands (dark) with H zone (lighter part) I bands (light) with midline Z disc Zone of overlap

Muscle metabolism

provides energy for contraction (ATP); for cross bridge and detachment, energy of Ca2+ to pump in SR Muscles have about 6 seconds of stored ATP on reserve so it must and will be regenerated continuously when muscle contraction starts

3 types of muscles

skeletal, smooth, cardiac

Wave (temporal) summation

when two or more stimuli are applied (the second delayed until after the absolute refractory period, but before complete relaxation. The 2nd contraction will be greater than the first because the 2nd builds upon the 1st creating greater tension

multiple motor unit summation

will cause smooth ongoing muscle contraction by calling into play more and more motor units (need more force-recruit more muscle fibers) The MUSCLE not the FIBER will contract more strongly

Contraction

The interaction of actin and myosin generating force regardless of whether the muscle stays the same length shortens or lengthens

contraction of skeletal muscle

- "all or nothing" applies only to individual muscle fibers - not all fibers may be stimulated all in one interval - different combinations of contractions give different responses -whole muscle can contract to varying degrees

single unit smooth muscle

- found in sheets - forms hollow viscera (stomach, uterus, and urinary bladder) - physiological/functional syncytium: when nerve impulse stimulates one fiber, it spreads throughout the entire sheet in a wave, as though it was one cell (Whole sheet contracts as a single unit) - longer latent period - attached by gap junctions (ions can flow from cell to cell) - may exhibit spontaneous depolarization (make self contract without external stimuli)

Factors affecting the velocity and duration of contractions

- load: greater the load the longer the latent period therefore, the slower velocity of contraction and shorter the duration of contractions

General characteristics of muscle types

-Muscles are essential for all movements in the body through contracting and relaxing -Skeletal muscles cause movement by utilizing the bony framework for leverage and the mobility provided by joints -Also, cause movement of fluids and other substances through internal body organs - Muscle tissue makes up about 50% of the total body weight

contraction of skeletal fibers explained deepe

1.) Within the Axon terminals are mitochondria and vessels containing Acetylcholine. When action potential reaches the axon terminal, voltage rated Ca++ Chanels open. Ca++ enter axon terminal which causes Ach to be released by exocytosis. 2.) When a A signal, neurotransmitter (ACh) from motor neuron diffuses across the synaptic cleft and enervates muscle fiber. The membrane of the fiber will depolarize as positively charges sodium ions (Na+) enter. 3.) This triggers an action potential that depolarize rest of membrane, including T-Tubules. 4.) Ca++ ions are released from storage in the sarcoplasmic reticulum. The release of Ca++ ions initiates contraction, which is sustained by ATP. 5.) As long as Ca++ ions remain in the sarcoplasm to bind to troponin actin binding sites will remain unshielded, and as long as ATP is available to drive cross bridge cycling and the pulling of actin strands by myosin the muscle fiber will continue to contract. Muscle contraction stops when signaling from the motor neuron ends, depolarizing the sarcolemma and t-tubules. Ca++ ions are pumped back into SR causing tropomyosin to recover the actin binding sites. A muscle also can stop contracting when it runs out of ATP and becomes fatigued.

motor unit

A motor neuron and all of the muscle fibers it innervates motor units fire different muscle fibers

isotonic contraction

A muscle contraction that pulls on the bones and produces movement of body parts. Muscle shortens because muscle tension exceeds the load

skeletal muscle

A muscle that is attached to the bones of the skeleton and provides the force that moves the bones.

Changes in Sacromere during contraction

Actin is pulled towards the center by myosin heads resulting in sarcomere shortening. In a fully contracted muscle: - The ends of actin myofilaments overlap, - The H zones disappear, - The I band becomes very narrow, - The A band remains unchanged.

Muscle fibers types

Slow twitch oxidative fibers Fast twitch glycolic fibers fast twitch oxidative fibers

Myofilaments

Smaller structures within sarcomeres Thin and thick filaments contain contractile proteins, actin, and myosin, of muscle cells

Triads

T tubules and SR provide signals for contractions are tightly linked. AT triads portions from T tubules and SR link together across gap between two membranes -act as voltage sensors -impulse travels down T tubules and effects the voltage sensors. This communicates with Sarcoplasmic Rectum foot proteins open and release Ca from cisternae terminal of SR into intracellular space

Tendon

Tendon: cord shaped CT (DRCT) connects muscle to bones- very strong pull in one direction

Graded muscle responces

Variation in degree of muscle contraction (for smooth skeletal movement, produces by wave summation and multiple motor unit summation

Two types of smooth muscle

Visceral single unit and Multi unit

Treppe

Warm up Phenomenon: each successive twitch contracts more forcefully than the previous one with same strength stimulus This is due to increased availability of Ca++ in Sarcoplasm, heat, and/ or the enzyme, system works more efficiently

Epimysium

Wraps entire outside of a muscle and separates it from surrounding features Made of Dense Irregular Connective Tissue

complete (fused) tetanus

a sustained contraction that lacks even partial relaxation between stimuli - heavy lifting fatigues quickly

contractions of smooth muscle

actin and myosin interact by a sliding filament mechanism - increase level of intracellular Ca++ triggers contraction - the sliding process uses ATP energy -contractions of smooth muscle are slow, sustained, and fatigue resistant (30% longer than skeletal muscle) -very efficient (1% the energy that skeletal muscle uses)

rigor mortis

stiffness of the body that sets in several hours after death Dead cells cannot hold Ca in the SR so Ca floods the cytoplasm. Ca binds to troponin and allows active sites to be open for actin and myosin to bind. muscles get rigid muscle proteins breakdown 2-3 days, stiffness ends

incomplete (unfused) tetanus

sustained muscle contraction that permits partial relaxation between stimuli

sliding filament theory

the concept that a sarcomere shortens as the thick and thin filaments slide past one another Cross bridges (myosin heads) of thick myofilaments attach to actin binding sites of the thin myoflaments and move like oars causing thin filaments to slide past. The Z lines are pulled together and both H zone and I bands disapear

Force of velocity and duration of muscle contraction factors affecting the force

the number of muscle fibers contracting at once(units) the relative size of the muscles:greater cross sectional area ---> greater tension(strength) series-elastic element: how long it takes to create tension degree of muscle stretch: length tension relationship

elastic filaments

titin, Zdisc to the midline. help return the sarcomere to its original position after either relaxation or contraction

T tubules

tubular infolding of the sarcolemma which penetrate through the cell and emerge on the other side Function: They allow nerve stimuli from sarcolemma to reach sarcomere and stimulate the release of Ca++ from cisternae terminal allow changes in membrane potential to rapidly penetrate deep into muscle fiber, stimulates the release of Ca

oxygen debt

volume of O2 required after exercise to deal with the lactic acid in the muscles and the liver Muscles will not return to the resting state until all anaerobic processes have been reversed O2, ATP, CP stores must be replenished lactic acid ---> Pyruvic acid ----> glucose---> glycogen in the muscle cell and liver