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[Front]

a. movement of body b. Posture maintenance c. Heat production: 85% of body heat is generated by skeletal muscle; 25-40% converted to ATP; 60-75% converted to heat

[Back]

3 key functions of muscle

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Exam 2 Chapter 9 - Marcador

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Exam 2 Chapter 9 - Detalles

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A. movement of body b. Posture maintenance c. Heat production: 85% of body heat is generated by skeletal muscle; 25-40% converted to ATP; 60-75% converted to heat

3 key functions of muscle

1. Excitability: ability to receive and respond to a stimulus 2. Contracticility: ability to shorten (up to 50% of resting length) 3. Extensibility: ability to stretch (up to 20% of resting length) 4. Elasticity: ability to return back to original length

4 special properties of muscle tissue

Large portion of muscle with perimysium (surrounds group of cells)

Definition of a fascicle

Muscle cell; multiple nucleuses, surrounded by endomysium (surrounds each individual cell)

Definition of myofiber

Occupy most of muscle cell volume; Composed of sarcomeres arranged end to end -100-1000/cell

Definition of myofibril

Inside sarcomere; has thick (myosin) and thin filaments (actin, tropomyosin, and troponin); sliding of thick and thin produce muscle shortening

Definition of myofilament

Lack of exercise decreases myofibrils

Definition of muscle atrophy

Exercise increases myofibril production

Definition of muscle hypertrophy

6 polypeptide chains: 2 heavy 4 light; Heavy chains twist together to form myosin tail and each end forms a head that contracts and forms cross bridges

Myosin: how many polypeptide chains? What does head of myosin do?

1 polypeptide band; rod shaped protein that spirals over actin to help stiffen and stabilize it; blocks actin dead so it cannot contract during resting state

Tropomyosin: how many polypeptide bands? Function?

3 polypeptide units; one subunits attaches troponin to actin; another subunit binds tropomyosin and helps position on actin; third binds calcium ions

Troponin: how many polypeptide units? Function?

Main protein of thin filaments; kidney shaped polypeptide units called globular actin; myosin binding site

Actin function

Myosin + overlapping actin

A band

Only actin, troponin, and tropomyosin

I band

Through center of I band; anchors thin filaments

Z disc

Only myosin through center of A band

H zone

Middle of sarcomere

M line

Hexagonal arrangement of 6 THIN filaments surround each THICK filament and 3 THICK filaments enclose each thin filament

Explain how arrangement of thick and thin myofilaments from the observed sarcomere structural patterns of myofibril

Sarcolemma is the cell membrane and T tubules are the inavigation of sarcolemma that surrounds each myofibril at the A band and I band junction

Discuss connection between sarcolemma and transverse tubules

Sarcoplasmic reticulum: smooth endoplasmic reticulum that stores Ca; Each myofibril is surrounded by SR; releases Ca when muscle wants to contract; terminal cisternae: dilated end sacs of SR

Describe and give function and location of sarcoplasmic reticulum and terminal cisternae

Epimysium: outside of entire muscle (protects muscle from friction against other muscles and bones); Perimysium: divides muscle cells into fascicles (bundles) Endomysium: covers individual muscle cells

3 layers of CT that surrounds skeletal muscle and give function

Step 1: action potential arrives at axon terminal Step 2: voltage gated Ca channels open, enter the axon terminal, moving down electrochemical gradient Step 3: Ca entry causes ACh to be released by exocytosis Step 4: ACh diffused across synaptic cleft and binds to ACh receptors on the sarcolemma Step 4: Binding initiates a change in the electrical state of the muscle cell called action potential

5 steps of neuromuscular junction

Binds to ACh receptors in skeletal muscle membrane; competes with ACh but does not stimulate ACh receptor; results in muscle paralysis

Curare effects neuromuscular junction how?

Antibodies destroy ACh receptors; muscle paralysis

Myasthenia Gravis effects neuromuscular junction how?

Toxin prevent ACh release; muscle paralysis; dilute solution of botox can be injected to help muscle relax

Botulism effects neuromuscular junction how?

Produced toxin that blocks an inhibitory neurotransmitter in nervous system; causes muscle spasms and painful convulsions

Tetanus effects neuromuscular junction how?

Prevents acetylcholinesterase which inactivates ACh; muscle spasms

Oreganophosphates effect neuromuscular junction how?

Calcium is in SR (terminal cisternae); Troponin-tropomyosin prevents myosin from binding to sites on actin; ATP bonded to myosin cross bridges (concentration of ATP is high in relaxed muscle)

Describe conditions inside of a skeletal muscle cell at rest in regards to ATP, calcium, and state of myofilaments

Muscle action potential will be generated at NMJ due to neural stimulus; ACh binds to receptor on motor end plate; causes action potential that travels along sarcolemma down T tubules; production of AP leads to muscle contraction

Explain why the process of muscle contraction is called Excitation-Contraction coupling

Once AP reaches T-tubules, this causes terminal cisternae to release calcium into sarcoplasm; calcium binds to troponin; tropomyosin changes shape and myosin sites are revealed; myosin binds to actin; calcium activated ATP of myosin; ATPase of myosin activates power stroke movement

Explain what happens after AP gets to T tubules

Pulls actin inward (H zones and I bands narrow and may disappear; A band does not change in length); At end of power stroke, ATP binds to ATP binding site on myosin cross bridge, resulting in detachment of myosin from actin

Power Stroke Movement

A. As long as there is enough calcium and ATP is present, contraction will occur b. Occurs when ATP is hydrolyzed to ADP and phosphate c. Myosin head moves toward M line pulling actin with it i. As actin is pulled, filaments move toward M line (known as power stroke

Explain power stroke movement

Stiffening of the joints and muscles a few hours after death; calcium leaks into muscle fibers, causing muscles to contract; since body no longer circulates blood, body relies on anerobic respiration which produces much less ATP; muscles become rigid

Rigor Mortis

1. ACh is inactivated by acetylcholinesterase 2. Calcium is actively transported back into SR (requires ATP) 3. ATP attaches myosin cross bridge and releases from actin 4. Troponin-tropomyosin covers myosin binding sites on actin

List 4 steps of how muscle relaxes following contraction

As we begin to exercise vigorously, demand for ATP is high and the ATP stored in muscles is consumed within few twitches 1. Creatine phosphate is tapped to regenerate ATP while other metabolic pathways adjust to demand for ATP 2. Stored ATP and CP provide for max muscle power for about 15 seconds 3. Replenished through rest

Describe direct phosphorylation (3 points)

As stored ATP and CP are exhausted, more ATP is generated by breaking down glucose from blood or glycogen from muscles Glycolysis: initial breakdown of glucose-broken down to 2 pyruvic acids releasing small ATP amounts; happens in presence and absence of O2; when O2 and blood flow impaired pyruvic acid converts to lactic acid (anaerobic glycolysis)

Describe Anaerobic Pathway

O2 is impaired because bulging muscles compress blood vessels within them; happens when contractile activity reaches 70% (running 600 meters with max effort)

During anaerobic respiration, what happens when oxygen delivery is impaired

20-40 seconds

During anaerobic respiration, JUST glycolysis lasts how long?

1 minute

During anaerobic respiration, with glycolysis, ATP and CP, and lactic acid pathway, can support strenuous activity for how long?

During rest, and light to moderate exercise, even if prolonged, 95% of ATP is used for muscle activity 1. Requires oxygen and mitochondria, and involves chemical reactions that break bonds of fuel molecules that release energy to make ATP 2. Begins with glycolysis and is followed by reactions that happen in mitochondria (Glucose + oxygen= carbon dioxide + water + ATP 3. Carbon Dioxide released diffuses out of muscle into blood, removed by lungs

Describe Aerobic Respiration (3 points)

Direct phosphorylation: 15 seconds Anaerobic Pathway: 15 seconds with just ATP, 1 minute with glycolysis, ATP and CP, and lactic acid Aerobic Pathway: after 30 minutes, fatty acid becomes main energy levels (can continue as long as an hour as oxygen is being replenished

Discuss the relative durations of time that each form of ATP production provides for sustained activity

Amount of oxygen needed to metabolize the accumulated lactic acid and to restore ATP levels-- Muscle fatigue is result of ATP depletion and accumulation of lactic acid (80% of lactic acid diffused from skeletal muscle to blood and is transported to liver where it is converted back to glucose, 20% remains in muscle)-- Oxygen debt results in labored breathing (lactic acid decreases pH in blood which stimulated increased respiration)

Define oxygen debt and discuss the purpose of the elevated use of oxygen after exercise

Individual muscle cells of a motor unit will contract to its fullest extent of its immediate ability when stimulated by a nerve impulse (AP) of its threshold level

Define all or none principle

All or none principle does NOT apply to entire muscle but only to motor units motor neuron + skeletal muscle cells it services (5-2000 muscle cells); one entire muscle has many motor units; not all are stimulated at same time; small the number of muscle cells per unit, the more precise the control of the muscle cells

Motor Unit

1. size of load 2. number of motor units activated 3. initial length of fibers: more a muscle is stretched, the greater the contraction

Strength of contraction of an entire muscle depends on what (3 points)

Partial sustained contraction important in maintenance of posture; only fraction of motor units are activated at any one time; produces tautness instead of recognized contraction; maintain without fatigue because system of rotation; muscle tone can break down (flaccid)

What is muscle tone?

Increasing number of motor units can contract heavier force

Effect of increasing the number of active motor units on contraction force

Latent: first few milliseconds following stimulation when excitation-contraction coupling is occurring; cross bridges begin to cycle but muscle tension is not yet measurable so myogram does NOT show response

3 stages of a muscle twitch: LATENT

Cross bridges are active, but from the onset to the peak of tension development, and myogram begins to peak; lasts 10-100 milliseconds

Contraction phase of muscle twitch

Due to pumping back Ca into SR; because number of cross bridges are declining, contractile force is declining on myogram; lasts 10-100 milliseconds

Relaxation phase of muscle twitch

Period of lost excitability; short period of time where there is no response to additional stimuli -Short in skeletal muscle (.005 seconds) -Long in cardiac muscle (.3 seconds)

Define refractory period

Staircase phenomenon; reoccurring stimulus results in increasingly stronger; increased heat in warm up muscles increases speed of reactions; increased calcium in sarcoplasm activated sliding mechanism faster

Define Wave summation

Fusion of twitches; relaxation not allowed to occur; body normally delivers volleys of impulses in rapid succession, giving us smooth contractions; voluntary contractions (normal movements) are TETANIC contractions

Define Tetanus

Muscle shortens and can move load; tension exerted into contracting muscle on some object has to exceed load to move it; tension remains constant as muscle shortens; EX lifting weights (curls)

Isotonic Contraction definition

Develop increased tension in muscle but muscle does not shorten or there is minimal shortening; cross bridges formed but unsuccessful in moving thin myofilaments (cross bridges spinning wheels on same cross bridge binding site); length remains same; requires no movement; EX squat holds, plank holds

Isometric Contraction definition

Highly resistant to fatigue; contract slowly; slower myosin ATPase; fuel source is fatty acids; aerobic respiration; more mitochondria; high myoglobin (binds 02 and acts as reservoir for more O2 until needed by mitochondria); more capillaries; small diameter; EX long distance runners

Discuss slow oxidative fibers based on cellular components, fatigue resistance, duration of contraction, and ATPase reaction rate

Not resistent to fatigue; contract more rapidly; faster myosin ATPase; Fuel source is glucose; anaerobic respiration; fewer mitochondria, high glycogen, low myoglobin, fewer capillaries, large diameter; EX muscles of arms and legs

Discuss the fast glycolytic based on their cellular components, fatigue resistance, duration of contraction and ATPase reaction rate

Contract more rapidly, faster myosin ATPase, fuel source is glucose, anaerobic and aerobic respiration, more mitochondria,high glycogen, high myoglobin, more capillaries, intermediate diameter, most muscles have combo of bth types

Discuss the intermediate fatigue resistant fibers based on their cellular components, fatigue resistance, duration of contraction and ATPase reaction rate.

Endurance type exercises (running swimming) can transform fast twitch fatiguable into intermediate by producing more mitochondria and increased myoglobin

Examine how various types of exercise can induce changes in the fibers of skeletal muscle

Slower

Does smooth muscle had a slower or faster contraction than skeletal muscle?

Yes but not arranged in sarcomeres- NO TROPONIN

Does smooth muscle had actin and myosin and troponin?