Anatomy & Physiology II: Chapter 10: The Muscular Tissue w/ Lab Questions

2nd Step of The Contraction Cycle

Myosin heads bind to actin, forming cross-bridges2

1st Step of The Contraction Cycle

Myosin heads hydrolyze ATP and become reoriented and energized1

3rd Step of The Contraction Cycle

Mysoin cross-bridges rotate toward center of sarcomere (power stroke)3

Length decreases when sarcomere shortens.

I bands and H zone.

Rod-like structures within skeletal muscle fiber that contain thin and thick filaments organized into sarcomeres.

Myofibrils.

What covers the muscle fiber or fasicle?

Perimysium

How is the motor end plate different from other parts of the sarcolemma?

The motor endplate is a specific part of the sarcolemma that contains acetylcholine (ACH) receptors and helps form the neuromuscular junction (the region of the muscle cell where a motor neuron stimulates the cell to contract).

What are the similarities among and differences between skeletal and cardiac muscle?

The one similarity between the cardiac and skeletal muscles, is that they are both categorized as striated muscles. However, their major difference is that the skeletal muscle is controlled by the somatic nervous system, and the cardiac muscles are, by nature, involuntarily controlled.

What part of the sarcolemma contains acetylcholine receptors?

The part of the sarcolemma that contains acetylcholine receptors is the motor end plate.

Excitation-Contraction Coupling

The process of neural stimulation creating a muscle contraction. Excites & Connects the events of a muscle action potential with the sliding filament mechanism.

How do calcium ions and ATP contribute to muscle contraction and relaxation?

The sarcoplasmic reticulum releases 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.

Which structure shown here releases calcium ions to trigger muscle contraction?

The sarcoplasmic reticulum releases calcium ions to trigger muscle contraction.

How are the structures of thin and thick filaments different?

The thick filament, myosin, has a double-headed structure, with the heads positioned at opposite ends of the molecule. During muscle contraction, the heads of the myosin filaments attach to oppositely oriented thin filaments, actin, and pull them past one another.

Length does not change when sarcomere shortens.

Thick and thin filaments.

Why do you continue to breathe heavily for a period of time after stopping exercise?

This is due to oxygen debt. The body needs to then: 1. Replenish CP stores 2. Convert lactate into pyruvate 3. Reload O2 onto myoglobin

What are three functions of ATP in muscle contraction?

Three functions of ATP in muscle contraction are the following: (1) Its hydrolysis by an ATPase activates the myosin head so it can bind to actin and rotate; (2) its binding to myosin causes detachment from actin after the power stroke; and (3) it powers the pumps that transport Ca2+ from the cytosol back into the sarcoplasmic reticulum.

Weight training increases muscle fiber size by increasing the number of myofibrils. Explain.

Very forceful, repetitive muscular activity, such as strength training increases the production of myofibrils, mitochondria, sarcoplasmic reticulum, and other organelles, which enlarges existing muscle fibers. This is called muscular hypertrophy.

What are the differences between visceral and multiunit smooth muscle?

Visceral smooth muscle is found in the walls of many soft internal organs. The cells of visceral smooth muscle are linked to form large sheets in the walls of organs such as the stomach, intestines, uterus, & urinary bladder. Whereas, visceral smooth muscle is large & relatively powerful, multiunit smooth muscle is small & delicate. Instead of being formed into large sheets that function as a single large unit, multiunit smooth muscle is made up of individual smooth muscle cells or small groups of cells.

I band

lIghter, less dense area, of sarcomere that contains remainder of thin filaments but no thick filaments. A Z dic passes through center of I band.

Isometric Contractions

muscle contracts but does not change length

What are the contractile muscle proteins?

myosin and actin

H zone

narrow region in center of each A band that contain tHick filaments but no thin filaments.

Wave Summation

occurs when a second action potential triggers muscle contraction before the first contraction sea has finished

Fast Glycolytic Skeletal Muscle Fiber

primarily uses anaerobic glycolysis

The Neuromuscular Junction

produces a muscle action potential

M line

region in center of H zone that contains proteins that hold thick filaments together at center of sarcoMere

Cardiac Muscle vs. Skeletal Muscle

same arrangement as skeletal muscles, but also has intercalated discs

What is a motor unit consisted of?

somatic motor neuron and the muscle fibers it innervates

Twitch Contraction

the brief contraction of all muscle fibers in a motor unit in response to a single action potential

Muscle Fatigue

the inability to maintain force of contraction after prolonged activity

Muscular Hypertrophy

the muscle growth that occurs after birth occurs by enlargement of existing muscle fibers

Motor Unit Recruitment

the process in which the number of active motor units increases

What are the structural muscle proteins?

titin, nebulin, alpha-actin, myomesin, and dystrophin

What are the regulatory muscle proteins?

troponin and tropomyosin

Put a check mark next to the muscles that are skeletal muscles. Hint: Consider location and whether muscle contraction is voluntary or involuntary. 1. Arrector pili. 2. Tongue. 3. Muscle in gallbladder. 4. Muscles that control movement of the eyeball.

1. (smooth muscle) 2. √ 3. (smooth muscle) 4. √

Does the A band length change when a muscle contracts? Explain.

No. By definition, the A band is the length of the thick filaments; since the filament length does not change, the A band length does not change.

Do the lengths of the thin or thick filaments change when a muscle contracts? Explain.

No. Filament length does not change, but there is greater overlap of thin and thick filaments when the muscle fiber contracts (shortens).

Why are some skeletal muscle fibers classified as "fast" and others are said to be "slow"?

People have two general types of skeletal muscle fibers: slow-twitch (type I) and fast-twitch (type II). Slow-twitch muscles help enable long-endurance feats such as distance running, while fast-twitch muscles fatigue faster but are used in powerful bursts of movements like sprinting.

Connective tissue surrounding a fascicle.

Perimysium

Which connective tissue coat surrounds groups of muscle fibers, separating them into fascicles?

Perimysium bundles groups of muscle fibers into fascicles.

Regulatory Proteins

Proteins that help switch muscle contraction process on and off.

Structural Proteins

Proteins that keep thick and thin filaments of myofibrils in proper alignment, give myofibrils elasticity and extensibility, and link myofibrils to sarcolemma and extracellular matrix.

What are the functions of muscular tissue?

1. Producing body movements 2. Stabilizing body positions 3. Storing and moving substances within the body 4. Generating heat

Troponin

Regulatory protein that is a component of thin filament; when calcium ions (Ca2+) bind to *troponin, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin.

Tropomyosin

Regulatory protein that is a component of thin filament; when skeletal muscle fiber is relaxed, *tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin.

What are the types of Muscular Tissue?

Skeletal, Cardiac, Smooth

Why is the term recovery oxygen uptake more accurate than oxygen debt?

1. the elevated body temperatures after strenuous exercise increases the rate of chemical reactions throughout the body 2. the heart and muscles used in breathing are still working harder than they were at rest, they consume more ATP 3. tissue repair processes are occurring at an increased pace

This area is the length of thick filaments.

A band.

Why is tension maximal at a sarcomere length of 2.2 μm?

A sarcomere length of 2.2 μm gives a generous zone of overlap between the parts of the thick filaments that have myosin heads and the thin filaments without the overlap being so extensive that sarcomere shortening is limited.

2nd Step of the Neuromuscular Junction

ACh binds to ACh receptor2

Which proteins connect into the Z disc? Which proteins are present in the A band? In the I band?

Actin and titin anchor into the Z disc. A bands contain myosin, actin, troponin, tropomyosin, and titin; I bands contain actin, troponin, tropomyosin, and titin.

Which ATP-producing reactions are aerobic and which are anaerobic?

Aerobic respiration is far more energy-efficient than anaerobic respiration. Aerobic processes produce up to 38 ATP per glucose. Anaerobic processes yield only 2 ATP per glucose.

Why is a rich blood supply important for muscle contraction?

An inadequate supply of blood will not provide enough oxygen to keep up with the energy demands of contraction.

In what order are the various types of skeletal muscle fibers recruited when you sprint to make it to the bus stop?

Slow oxidative, fast oxidative-glycolytic, fast glycolytic

Which type of muscular tissue has the highest capacity for regeneration?

Smooth cells have the greatest capacity to regenerate of all the muscle cell types.

How are skeletal and smooth muscle similar? How do they differ?

Smooth muscles and skeletal muscles have different structures, functions, contraction regulation, and excitation-contraction coupling. Smooth muscles are not striated while skeletal muscles are striated. Smooth muscles are an involuntary muscle while skeletal muscles are voluntary muscles.

Which structures develop from myotomes, dermatomes, and sclerotomes?

Somite Development. In the developing vertebrate embryo, somites are masses of mesoderm that can be found distributed along the two sides of the neural tube. They will eventually become dermis (dermatome), skeletal muscle (myotome), vertebrae (sclerotome), and tendons and cartilage (syndetome).

α-Actinin

Structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules.

Titin

Structural protein that connects Z disc to M line of sarcomere, thereby helping to stabilize thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils.

Myomesin

Structural protein that forms M line of sarcomere; binds to titin molecules and connects adjacent thick filaments to one another.

Nebulin

Structural protein that wraps around entire length of each thin filament; helps anchor thin filaments to Z discs and regulates length of thin filaments during development.

Space between synaptic end bulbs of axon terminal and sarcolemma.

Synaptic cleft.

Parts of axon terminal that form neuromuscular junction.

Synaptic end bulbs.

Found in synaptic end bulbs of axon terminal; contains neurotransmitter molecules.

Synaptic vesicles.

Finger-like invaginations of plasma membrane; extend into interior of fiber and surround myofibrils.

T-tubules.

4th Step of The Contraction Cycle

As myosin heads bind ATP, the cross-bridges detach from actin4

Divides into synaptic end bulbs at neuromuscular junction.

Axon terminal.

Which of the following is the smallest: muscle fiber, thick filament, or myofibril? Which is largest?

The following are arranged from smallest to largest: thick filament, myofibril, muscle fiber.

Weak Motor Units vs. Strong Motor Units

Weakest motor units are recruited first followed by stronger motor units

What factors contribute to muscle fatigue?

With pyruvate accumulation, lactic acid production is also increased. This lactic acid accumulation in the muscle tissue reduces the pH, making it more acidic and producing the stinging feeling in muscles when exercising. This further inhibits anaerobic respiration, inducing fatigue.

Does the H zone length change when a muscle contracts? Explain.

Yes. The H zone is the portion of the thick filaments that does not overlap with thin filaments. As thin filaments are pulled over thick filaments, this zone becomes smaller and eventually disappears when muscle is fully contracted.

Does the I band length change when a muscle contracts? Explain.

Yes. The I band contains the portion of the thin filaments that does not overlap with thick filaments. When a muscle fiber contracts, thin filaments are pulled over the thick filaments, so there is more overlap of thin and thick filaments and a shorter I band.

Point of attachment for thin filaments.

Z disc.

This area contains overlapping thin and thick filaments.

Zone of overlap (ends of A band).

Muscular Atrophy

a decrease in size of individual muscle fibers as a result of progressive loss of myofibrils (coma)

Periosteum

a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints

Which sources provide ATP during a marathon race?

aerobic cellular respiration (pyruvic acid, fatty acids and amino acids)

How do motor units contract?

alternately to sustain contraction for longer period of time

A band

dark, middle part of sarcomere that extends entire length of thick filaments and includes those parts of A thin filaments that overlap thick filaments

Fascia

dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body

What is the strength of contraction dependent on?

how many motor units are activated

Regeneration of Muscle Tissue

mature skeletal muscle fibers cannot undergo mitosis

Rigor Mortis

muscular stiffening that begins 2 to 4 hours after death and last for about 4 days

Z discs

narrow, plate-shaped regions of dense material that separate one sarcomere from zeenext

Myoglobin

red-colored protein

Isotonic Contractions

tension is constant while muscle length changes

Somatic motor neurons

the neurons that stimulate skeletal muscle to contract

Acetylcholine

the neurotransmitter released at the neuromuscular junction

Fibrosis

the replacement of muscle fibers by fibrous scar tissue

Muscle Tone

when a skeletal muscle exhibits a small amount of tension; due to weak, involuntary contraction of motor units

Aponeurosis

when the connective tissue elements extend as a broad, flat sheet

Fast Oxidative Glycolytic Skeletal Muscle Fiber

which is an intermediate between slow oxidative and *fast glycolytic fibers

Why do you think a healthy 30-year-old can lift a 25-lb load much more comfortably than an 80-year-old?

Bones are stronger and less prone to osteoporosis or brittle bones.

Slow Oxidative Skeletal Muscle Fiber

Contract slowly but resist fatigue. Use ATP slowly and makes it quickly

What roles do contractile, regulatory, and structural proteins play in muscle contraction and relaxation?

Contractile proteins generate force for muscle contraction. The two contractile proteins in myofibrils are actin (part of the thin filament) and myosin (part of the thick filament). Muscle fibers or myofibrils are formed of three types of proteins which are (1) contractile, (2) regulatory, and (3) structural.

The diaphragm is a muscle that controls inspiration. Is control of the diaphragm voluntary, involuntary, or both?

Control of the diaphragm is both voluntary and involuntary. We can consciously move our diaphragm to breathe, but it is also moved subconsciously. Even when we aren't consciously thinking about it, our diaphragm continues to alternately relax and contract so that we don't stop breathing.

Connective tissue covering surrounding individual muscle fibers.

Endomysium.

Connective tissue covering surrounding the muscle.

Epimysium.

Where inside a skeletal muscle fiber are the events shown here occurring?

Glycolysis, exchange of phosphate between creatine phosphate and ADP, and glycogen breakdown occur in the cytosol. Oxidation of pyruvic acid, amino acids, and fatty acids (aerobic respiration) occurs in mitochondria.

This area disappears in a fully contracted muscle.

H zone.

This area only contains thick filaments.

H zone.

What would happen if ATP suddenly were not available after the sarcomere had started to shorten?

If ATP were not available, the cross-bridges would not be able to detach from actin. The muscles would remain in a state of rigidity, as occurs in rigor mortis.

Demonstrate an isotonic contraction. How does it feel? What do you think causes the physical discomfort you are experiencing?

In an isotonic contraction, tension remains constant as muscle length decreases and increases.

On a cellular level, what causes muscle hypertrophy?

Increased synthesis of thick and thin filaments

Why does muscle strength decrease with aging?

Lean body mass decreases. This decrease is partly caused by a loss of muscle tissue (atrophy). The speed and amount of muscle changes seem to be caused by genes. Muscles are less toned and less able to contract because of changes in the muscle tissue and normal aging changes in the nervous system.

Cardiac Muscle

Location: heart Function: pump blood Appearance: one nucleus, striated, & intercalated discs Control: involuntary

Skeletal Muscle

Location: skeleton Function: move bones Appearance: multi-nucleated & striated Control: voluntary

Smooth Muscle

Location: various organs (ex: GI tract) Functions: various functions (ex: peristalsis) Appearance: one nucleus & no striations Control: involuntary

Center point of attachment for thick filaments.

M line.

How does sarcomere length influence the maximum tension that is possible during muscle contraction?

Maximum tension during contraction occurs when the resting sarcomere length is 2.0-2.4 a muscle fiber develops its greatest tension when there is an optional zone of overlap between thick and thin filaments.

With age, the collagen-containing connective tissue coverings of skeletal muscle increases, and the number of muscle fibers decreases. Is meat from an older or a younger animal more tender? Explain.

Meat from a younger animal is more tender. The more collagen there is in the connective tissue of a muscle, the tougher it is to cut and chew.

Area of sarcolemma across from synaptic end bulbs of axon terminal; contains neurotransmitter receptors.

Motor end plate.

What is motor unit recruitment?

Motor unit recruitment refers to the activation of additional motor units to accomplish an increase in contractile strength in a muscle.

What is the effect of the size of a motor unit on its strength of contraction? (Assume that each muscle fiber can generate about the same amount of tension.)

Motor units having many muscle fibers are capable of more forceful contractions than those having only a few fibers.

3rd Step of the Neuromuscular Junction

Muscle action potential is produced3

Why is muscle tone important?

Muscle tone is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state. It helps to maintain posture and declines during REM sleep.

How do muscles derive the ATP necessary to power the contraction cycle?

1. Creatine phosphate 2. Anaerobic glycolysis 3. Cellular respiration

What are the properties of muscle tissue?

1. Electrical Excitability 2. Contractility 3. Extensibility 4. Elasticity

What types of fascia cover skeletal muscles?

1. Epimysium 2. Perimysium 3. Endomysium

What causes muscle fatigue?

1. Inadequate release of Ca2+ from SR 2. Depletion of CP, oxygen, and nutrients 3. Build up of lactic acid and ADP 4. Insufficient release of ACh at NMJ

What steps make up the force of contraction?

1. Latent Period 2. Contraction Period 3. Relaxation Period 4. Refractory Period

Using your textbook or another reference, for each condition below, indicate which part of the neuromuscular junction is affected: the motor end plate or the axon terminal: 1. Myasthenia gravis. 2. Curare poisoning. 3. Botulinum toxin poisoning.

1. Motor end plate. 2. Motor end plate. 3. Axon terminal.

Name the following nestled, cylindrical structures in order from largest (1) to smallest (5): Myofibril. Fascicle. Filaments. Muscle fiber. Muscle.

1. Muscle. 2. Fascicle. 3. Muscle fiber. 4. Myofibril. 5. Filaments.

Describe the Sliding Filament Mechanism:

1. Myosin pulls on actin, causing the thin filament to slide inward 2. Consequently, Z discs move toward each other and the sarcomere shortens 3. Thanks to the structural proteins, there is a transmission of force throughout the entire muscle, resulting in whole muscle contraction

Plasma membrane of skeletal muscle fiber.

Sarcolemma.

Smallest contractile unit within individual muscle fibers.

Sarcomere.

The area from Z disc to Z disc.

Sarcomere.

Stores calcium within muscle fiber.

Sarcoplasmic reticulum.

Which numbered steps in this figure are part of excitation-contraction coupling?

Steps 4 through 5 are part of excitation-contraction coupling (muscle action potential through binding of myosin heads to actin).

Two terminal cisterns and a T tubule.

Triad.

Length-Tension Relationship

The force of a muscle contraction depends on the length of the sarcomeres prior to the contraction.

Smooth Muscle vs. Skeletal Muscle

1. Smooth muscle contractions start more slowly and last longer than skeletal and cardiac muscle contractions 2. Smooth muscle can shorten and stretch to a greater extent

Describe what happens in the Neuromuscular Junction

1. Voltage-gated calcium channels open resulting in an influx of calcium. This causes exocytosis of neurotransmitter (NT) into the synaptic cleft. NT binds to ligand-gated Na+ channels on the motor endplate which cause an influx of Na+ into the muscle. This depolarizes it and results in Ca2+ release from the SR 2. NT gets broken down

4th Step of the Neuromuscular Junction

ACh is broken down4

1st Step of the Neuromuscular Junction

ACh is released from synaptic vessicle1

The contraction cycle will continue when __________.

ATP is available and Ca2+ levels in sarcoplasm are high

Calsequestrin

Stores calcium in the sarcoplasmic reticulum.

Dystrophin

Structural protein that links thin filaments of sarcomere to integral membrane proteins in sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers; thought to help reinforce sarcolemma and help transmit tension generated by sarcomeres to tendons.

What happens to the I band and H zone as muscle contracts? Do the lengths of the thick and thin filaments change?

The I bands and H zones disappear during muscle contraction; the lengths of the thin and thick filaments do not change.

Contractility

ability of muscular tissue to contract forcefully when stimulated by an action potential

Elasticity

ability of muscular tissue to return to its original length and shape after contraction or extension

Extensibility

ability of muscular tissue to stretch, within limits, without being damaged

Electrical Exicitability

ability to respond to certain stimuli by producing electrical signals called action potentials (impulses)

How are the sizes of motor units related to the degree of muscular control they allow?

all of the muscle fibers of a motor unit contract and relax together, the total strength of a contraction depends, in part, on the size of the motor units and the number that are activated at a given time