Chapter 10

Aerobic endurance:

(Prolonged activity) -Supported by mitochondria Requires oxygen & nutrients Improves: -Endurance by training fast fibers to be more like intermediate fibers -Cardiovascular performance

What is Epimysium:

- Exterior collagen layer -Separates muscle from surrounding tissues -Connected to the deep fascia, a dense connective tissue layer

A thick filament contains:

-300 twisted myosin subunits -Contains titin strands that recoil after stretching

Anaerobic activiites:

-50 meter dash, weightlifting -Use fast fibers -Fatigue quickly with strenuous activity Improves: -Frequent, brief, intensive workout & cause hypertrophy

Sarcoplasmic Reticulum (SR)

-A membranous structure surrounding each myofibril -Helps transmit action potential to myofibril

Treppe

-A stair-step increased in twitch tension -Repeated stimulations immediately after relaxation phase

Excitation-Contraction coupling steps:

-Action potential in sarcolemma to begin a contraction -Action potential reaches a triad -Action potential triggers the release of calcium -Requires myosin heads to be in "cocked" position -Loaded by ATP energy

Titin:

-Are strands of protein -Reach from tips of thick filaments to Z line -Stabilize the filaments

Fiber shortening:

-As sarcomeres shorten, muscle pulls together, producing tension. -Muscle shortening occurs at both ends of the muscle or only one end of the muscle. (This depends on the way the muscle is attached at the ends)

The mysosin molecule tail:

-Bound to other myosin molecules in the thin filament

Initiating contraction:

-Calcium binds to receptor on troponin molecule -Troponin-tropomyosin complex changes -Exposes active site of F-actin

Relaxation phase:

-Calcium levels decreased, active sites covered by tropomyosin, & cross-bridges decline. -Tension decreases

M line:

-Center of the A band -At midline of sarcomere

What is Perimysium:

-Collagen & elastic fibers -Surrounds muscle fiber bundles (fascicles) -Contains blood vessel and nerves supply to fascicles

Troponin:

-Consists of 3 globular subunits *One subunit binds to tropomyosin, locking them together as troponin-tropomyosin complex *Second subunit binds to 1 G-actin, holding the troponin-tropomyosin complex in position *Third subunit has a receptor that binds 2 calcium ions

Fast fiber:

-Contract very quickly after stimulation -Have large diameter, contain densely packed myofibrils, large glycogen reserves, and few mitochondria -Fatigue rapidly b/c have few mitochondria to produce ATP -White muscle=white mean

Tropomyosin:

-Double strand -Covers the active sites on G-actin & prevents actin-myosin interaction

What is Endomysium:

-Elastic connective tissue layer that contains -Capillaries & nerve fibers contacting muscle cells & myosatellite cells (stem cells) that repair damage muscle tissue -Surrounds individual muscle cells (muscle fibers)

Functional characteristics of smooth muscle cell:

-Excitation-contraction coupling -Length-tension relationships -Control of contractions -Smooth muscle tone

Excitation-contraction coupling

-Free calcium in cytoplasm triggers contraction -Calcium binds to calmodulin (a calcium-binding protein) in the sarcoplasm. -Calmodulin activates myosin light chain kinase (which in turn enables myosin heads to attach to actin) -Enzyme breaks down ATP, initiates contraction

Wave summation:

-Increased tensions of twitches -Repeated stimuli arrive before the relaxation phase has been completed.

Structural characteristics of smooth muscle cell:

-Lack myofibrils & sarcomeres, as a result, this tissue has no striations called Nonstriated muscle -Thin filaments of smooth muscle cells are attached to dense bodies. -No tendons-corkscrew like contractions

Characteristics of smooth muscle cell:

-Long, slender spindle shaped -Have a single, central nucleus -Have scattered myosin fibers -Myosin fibers have more heads per thick filament

Myofibril:

-Made up of bundles of protein filaments -Responsible for skeletal and cardiac muscle fiber contraction

Smooth muscle tone

-Maintains normal levels of activity -Modified by neural, hormonal, or chemical factors -Ex. smooth muscle around blood vessels

Intermediate fibers:

-Mid size, low myoglobin -Have more capillaries than fast fibers, slower to fatigue -Pink muscles (mixture of all types)`

Isometric Contraction:

-Muscle does not change length and the tension produces never exceeds the load

The mysosin molecule head:

-Projects outward toward the nearest thin filament -Has 2 globular protein subunits

Recruitment:

The smooth, but steady increased in muscular tension produced by increasing the number of active motor units

Regions of a sarcomere:

A band, M line, H band, Zone of overlap, I band, Z line, Titin protein

Incomplete tetanus:

Twitches reach maximum tension & periods of relaxation are very brief

What is a fatigued muscle:

When a muscle can no longer perform a required activity

How would a drug that blocks acetylcholine release affect muscle contraction?

A drug that blocks ACh release would interfere with this cross-bridge formation and prevent muscle contraction.

Latent phase:

Action potential moves through the sarcolemma & the SR releases calcium ions -No tension produced

Identify the 3 types of skeletal muscle fibers

Fast fibers(white muscle fibers) Slow fibers(red muscle fibers) Intermediate fibers

3 major types of muscle fibers

Fast, slow, intermediate

Myofilaments:

Fine protein filaments composed primarily of the protein actin (thin filaments) & myosin (thick filaments)

How do we classify muscle contraction:

Isotonic & isometric

Atrophy:

Lack of muscle activity -Reduces muscle size, tone, & power

Identify the structural characteristics of smooth muscle tissue

Lack sarcomeres and is not nonstriated Thin filaments are anchored to dense bodies

3 phases of a single twitch

Latent, contraction, & relaxation

The A band contains:

M line, H band, & zone of overlap

Sustained muscular contraction is required

Many repeated stimuli

Skeletal muscle does:

Moves the body by pulling on our bones

When does a muscle contraction begin?

When stored calcium ions are released into the cytosol. These ions then diffuse into individual contractile units called Sarcomeres.

Predict what would happen to a muscle if the motor end plate failed to produce acetylcholinesterase (AChe) ?

The motor end plate would be continuously stimulated by acetylcholine, locking the muscle in a state of contraction.

Zone of overlap:

Where thick & thin filaments overlap

Summary on skeletal muscle contraction & relaxation

-Skeletal muscle fibers shorten as thin filaments slide between thick filaments -Free Ca2+ in the sarcoplasm triggers contraction -Sarcoplasmic reticulum release Ca2+ when a motor neuron stimulates the muscle fiber -Contraction is an active process -Relaxation and return to resting length are passive

Energy use & level of muscular activity

-Skeletal muscles at rest metabolize fatty acids & store glycogen -During light activity, muscles generate ATP through anaerobic breakdown of carbohydrates, lipids, & amino acids -At peak activity, energy is provided by anaerobic reactions that generates lactic acid

Slow fibers:

-Slow to contract & slow to fatigue -Small diameter, more mitochondria -Surrounded by capillaries; higher oxygen supply to support mitochondrial activity -Contains myoglobin(red pigment, binds oxygen) -Red muscle=dark meat

Structural characteristics of cardiac muscle cells:

-Small & branched -Have single nucleus -Have short, wide t-tubules, no triads -Have SR w/ no terminal cisternae -Have aerobic(^ in myoglobin, mitochondria) -Have intercalated discs.

The neuromuscular junction (NMJ):

-Special intercellular connection b/w the nervous system & skeletal muscle fiber -Controls calcium ion release into the sarcoplasm

Contraction phase:

-Tension increases to peak -Tension increases, calcium ions bind to troponin, active sites on thin filaments exposed, & cross-bridges interactions occur.

Length-tense relationships:

-The # of cross-bridges formed, depends on the degree of overlap b/w thick & think filaments. -# of cross-bridges determines the amount of tension produced -Increased/decreased length reduces the tension produced by reducing the size of overlap & # of cross-bridges

H band:

-The area around the M line -Has thick but no thin filaments

What is a sarcolemma?

-The cell membrane of a muscle fiber (cell) -Surrounds the sarcoplasm (cytoplasm of muscle fiber) -A change in transmembrane potential begins contractions

Z lines:

-The center of the I band -At two ends of a sarcomere

Sarcomere:

-The contractile units of muscle -Structural units of myofibrils -Form visible patterns within myofibrils -A striped or striated pattern within myofibrils

The amount of tension produced by an individual muscle fiber ultimately depends on:

-The fiber's resting length at the time of stimulation -The number of pivoting cross-bridges -The frequency of stimulation

Cori cycle:

-The removal & recycling of lactic acid by the liver -Liver converts lactate to pyruvate -Glucose is released to recharge muscle glycogen reserves

Muscle Tone:

-The resting tension in skeletal muscle (normal tension & firmness of muscle at rest)

Intercalated discs

-The sarcolemma of 2 adjacent cardiac muscle cells are extensively intertwined and bound together by jap junctions & desmosomes. -Cardiac muscle cells are physically, chemically, and electrically connected, functions as 1 enormous muscle cell

The amount of tension produced in the skeletal muscle is determined by:

-The tension produced by the stimulated muscle fibers -Total number of muscle fibers stimulated

Length-tension relationships

-Thick & thin filaments are scattered -Resting length not related to tension development -Functions over a wide range of lengths (plasticity) Adaptation is important b/c in digestive organs, like the stomach changes greatly in volume.

What does Transverse Tubules (T-Tubules) do?

-Transmit action potential through cell -Allow entire muscle fiber to contract simultaneously

As Ca2+ concentration in the cytosol fall, earlier events reverse themselves:

1. Calcium ions detach from troponin 2. Troponin returns to its original position 3. Active sites are re-covered by troponin

4 major functional specialties of cardiac muscle

1. Cardiac muscle tissue contracts w/o neural stimulation=Automaticity Specialized cardiac muscle cell, determines the timing of contractions=Pacemaker cells 2. Controlled by the nervous system 3. Extended contraction & relaxation time 4. Prevention of wave summation & tetanic contractions by cell membranes; long refractory period

The Contraction Cycle steps:

1. Contraction cycle begins 2. Active-site exposure 3. Cross-bridge exposure 4. Myosin head pivoting 5. Cross-bridge detachment 6. Myosin reactivation

Muscle fatigue is correlated to:

1. Depletion of metabolic reserves 2. Damage to sarcolemma & SR 3. Low pH (lactic acid) 4. Muscle exhaustion & pain

What is excitation-contraction coupling?

1. Neural stimulation of sarcolemma -Causes excitation-contraction coupling 2. Calcium release 3. Interaction of thick & thin filaments 4. Muscle fiber contraction 5. Tension production

What does it depend on?

1. Period of stimulation at the neuromuscular junction 2. # of free calcium ions in the cytosol 3. Availability of ATP

Identify the 6 major functions of skeletal muscle

1. Produce skeletal movement 2. Maintain posture and body position 3. Support soft tissues 4. Guard body entrances and exits 5. Maintain body temperature 6. Store nutrients

What happens to a sarcomere when a skeletal muscle fiber contracts?

1. The H & I band of the sarcomeres narrow 2. The zone of overlap widen 3. The Z line moves closer together 4. The width of the A band remains constant

A sarcomere contains:

1. Thick filaments 2. Thin filaments 3. Proteins that stabilize the positions of thick & thin filaments 4. Proteins that regulate the interactions between thick & thin filaments

F-actin is:

2 twisted rows of globular G-actin -The active sites on G-actin strands bind to myosin

How long does a contraction last?

A single stimulus has only a brief effect on a muscle fiber, b/c the ACh released as a result of a single action potential is rapidly broken down by AChE.

Twitch

A single stimulus-contraction-relaxation sequence in a muscle fiber -Lasts about 7-100 msec.

Why would a sprinter experience muscle fatigue before a marathon runner would?

A sprinter requires large amount of energy for a short burst of activity. To supply this energy, the sprinter's muscles rely on anaerobic metabolism, it is less efficient in producing energy than aerobic metabolism, and the process also produces acidic wastes; this combination contributes to muscle fatigue. Marathon runners derive most of their energy from aerobic metabolism, which is more efficient and produces fewer wastes than anaerobic metabolism does.

Which activity would be more likely to create an oxygen debt; swimming laps or lifting weights?

Activities that require short periods of strenuous activity produce the greater oxygen debt, because such activities rely heavily on energy production by anaerobic metabolism. B/c lifting weights is more strenuous over the short term than swimming laps, which is aerobic activity, lifting weights would produce a greater oxygen debt.

Cells produce ATP in 2 ways:

Aerobic metabolism: Breaks down fatty acids in mitochondria, primary energy source, produces 34 ATP molecules per glucose molecule Anaerobic glycolysis: In cytoplasm Glycolysis: Produces 2 ATP molecules per glucose molecule, breaks down glucose from glycogen

Motor unit:

All the muscle fibers controlled by 1 motor neuron -Contains few hundred muscle fibers that contract at the same time

Describe the neuromuscular junction

Also known as the myoneural junction, is the synapse between a motor neuron and a skeletal muscle cell (fiber). This connection enables communication between the nervous system and a skeletal muscle fiber.

How would serving the tendon attached to a muscle affect the muscle's ability to move a body part?

Because tendons attach muscles to bones, severing the tendon would disconnect the muscle from the bone, and so the muscle could not move a body part.

Why do skeletal muscle fiber appear striated when viewed through a light microscope?

Because the Z lines and thick filaments of the myofibrils within the muscle fibers are aligned.

Which type of muscle tissie is least affected by changes in extracellular Ca2+ concentration during contraction?

By changes in extracellular Ca2+ concentrations. -Most of calcium ions comes from SR -Most calcium ions that trigger a contraction in cardiac and smooth muscles come from the extracellular fluid

How do muscle cells continuously synthesize ATP?

By utilizing creatine phosphate (CP) & metabolizing glycogen and fatty acids. Most cells generate ATP only through glycolysis in the cytoplasm.

What feature of cardiac muscle tissue allows the heart to act as a functional syncytium?

Cardiac muscle cells are joined together by gap junctions, which allow ions and small molecules to flow directly between cells. As a result, action potential generated in one cell spread rapidly to adjacent cells. Thus, all the cells contract simultaneously, as if they were a single unit.

Control of contractions

Categorize smooth muscle cells as Multiunit smooth muscle or visceral smooth muscle cells -Multiunit=connected to motor neurons Visceral=Not connected to motor neurons *gap junctions *Rhythmic cycles of activity controlled by pacesetter cells

What is a triad?

Combination of a pair of terminal cisternae plus a T-tubule

Compare/contrast skeletal muscle tissue & cardiac muscle tissue

Compared, cardiac muscle (1) relatively small cells, (2) has cells with a centrally locked nucleus, (3) has T-tubules that are short & broad and do not form triads, (4)has an SR that lacks terminal cisternae & as tubules that contract the plasma membrane as well as T tubules, (5) has cells that nearly totally dependent on aerobic metabolism as a energy source, (6) contains intercalated discs that assist in stabilizing tissue structure and spreading action potentials

2 Types of isotonic contractions:

Concentric contraction: muscle tension exceeds the load & muscle shortens Eccentric contraction: The muscle get longer as it generates tension

Cross-bridge is:

During contraction, myosin head interact with actin filaments

Describe the structural components of a sarcomere

Each sarcomere has dark A bands and light I bands. The A band contains the M line, the H band, and the zone of overlap. Each I band contains thin filaments, but not thick filaments. Z lines mark the boundaries between adjacent sarcomeres

What is a terminal cisternae?

Enlarged areas of the sarcoplasmic reticulum surrounding the transverse tubules.

What are the 3 layers of connective tissues:

Epimysium, Perimysium, & Endomysium

A single thin filament contains what 4 proteins:

F-actin, nebulin, tropomyosin, & troponin.

What does Nebulin do?

Holds F-actin stands together

Where would you expect to find the greatest concentration of Ca2+ in resting skeletal muscle?

In the terminal cisternae of the sarcoplasmic reticulum

Which type of muscle fiber would you expect to predominate in the leg muscles of someone who excels at endurance activities, such as cycling or long-distance running?

Individuals who excel at endurance activities have a higher than normal percentage of slow fibers. Slow fibers are physiologically better adapted to this type of activity than fast fibers, which are less vascular and fatigue faster.

What is muscle fatigue?

Is a muscle's reduced ability to contract due to low pH (lactic acid buildup and its dissociation to lactate and a hydrogen ion), low ATP levels, or other problems.

Define oxygen debt:

Is the amount of oxygen required to restore normal, pre-exertion conditions in muscle tissue.

Hypertrophy:

Muscle growth from heavy training -Increased diameter of muscle fibers, number of myofibrils, and mitochondria, glycogen reserves

Thin filaments composed of:

Of protein actin

Thick filaments composed of:

Of protein myosin

Skeletal muscles are:

Organs composed of skeletal muscle tissues but also contain connective tissues, nerves, and blood vessels.

Cardiac muscle does:

Pumps blood through the cardiovascular system

Smooth muscle does:

Pushes fluids and solids along the digestive tract and other internal organs and regulates the diameters of small arteries.

Endurance:

The amount of time during which the individual can perform a particular activity

Describe the structural components of a sarcomere

Sarcomeres, the smallest contractile units of a striated muscle cell, are segments of myofibrils. Each sarcomere has dark A bands and light I bands. The A band contains the M line, the H band, and the zone of overlap. Each I band contains thin filaments, but not thick filaments. Z lines bisect the I bands and mark the boundaries between adjacent sarcomere.

Identify the 3 types of muscle tissues

Skeletal, Cardiac, Smooth

Complete tetanus:

Stimulus frequency is so high that the relaxation phase is eliminated

Isotonic Contractions:

Tension increases and skeletal muscle length changes

Oxygen debt:

The amount of oxygen required to restore normal, pre-exertion conditions (EPOC)=Excess post oxygen consumption

What would happen to a resting skeletal muscle if the sarcolemma suddenly became very permeable to calcium ions?

The cytosolic concentration of Ca2+ would increase and the muscle would contract. In addition, because the amount of calcium ions in the cytosol must decrease for relaxation to occur, the increased permeability of the sarcolemma to Ca2+ might prevent the muscle from relaxing completely.

Load and speed of contraction:

The heavier the load of the muscle, the longer it will take for the muscle to begin to shorten and the less the muscle will shorten.

Skeletal Muscle Contraction: What is the process of a contraction?

The link between the generation of an action potential in the sarcolemma and the start of a muscle contraction

Why can smooth muscle contract over a wider range of resting lengths than skeletal muscle can?

The loose organization of actin and myosin filaments in smooth muscle allows smooth muscle ton contract over a wider range of resting lengths.

Force:

The maximum amount of tension produced

Recovery period:

The time required after exertion for muscles to return to normal

Force & endurance depends on:

The type of muscle fiber & physical conditioning

4 tension productions:

Treppe, wave summation, incomplete tetanus, & complete tetanus

The I band contains:

Z line & titin

What is a tendon?

a bundle of strong fibrous collagen tissue attaching a muscle to a bone

What is aponeurosis?

a sheet of fibrous tissue that takes the place of a tendon in sheetlike muscles having a wide area of attachment.