Chapter 12 Review Questions Flashcards
What generates muscle?
Muscles generates motion, force, and heat.
What are the three types of muscles
The three types of muscle are skeletal muscle, cardiac muscle, and smooth muscle. Skeletal and cardiac muscles are striated muscles.
Skeletal and cardiac muscles are striated muscles.
What are muscles controlled by?
Skeletal muscles are controlled by somatic motor neurons. Cardiac and smooth muscle are controlled by autonomic innervation, paracrine signals, and hormones. Some smooth and cardiac muscles are autorhythmic and contract spontaneously.
12.1 SKELETAL MUSCLE
What are skeletal muscles usually attached to?
Skeletal muscles are usually attached to bones by tendons. The origin is the end of the muscle attached closest to the trunk or to the more stationary bone. The insertion is the more distal or mobile attachment.
What are flexors and extensors?
At a flexible joint, muscle contraction moves the skeleton. Flexors bring bones closer together; extensors move bones away from each other. Flexor-extensor pairs are examples of antagonistic muscle groups.
What is a skeletal muslce?
A skeletal muscle is a collection of muscle fibers, large cells with many nuclei
What do T-tubules do in an AP?
T-tubules allow action potentials to move rapidly into the interior of the fiber and release calcium from the sarcoplasmic reticulum.
What are myofibrils?
Myofibrils are intracellular bundles of contractile and elastic proteins. Thick filaments are made of myosin. Thin filaments are made mostly of actin. Titin and nebulin hold thick and thin filaments in position.
What does myosin bind to?
Myosin binds to actin, creating crossbridges between the thick and thin filaments.
What are sarcomere, Z disks, I bands, A band, H zone, and M line?
A sarcomere is the contractile unit of a myofibril. It is composed of two Z disks and the filaments between them. The sarcomere is divided into I bands (thin filaments only), an A band that runs the length of a thick filament, and a central H zone occupied by thick filaments only. The M line and Z disks represent attachment sites for myosin and actin, respectively.
What is the force created by contracting muscle called?
The force created by a contracting muscle is called muscle tension. The load is a weight or force that opposes contraction of a muscle.
What is the sliding filament theory
The sliding filament theory of contraction states that during contraction, overlapping thick and thin filaments slide past each other in an energy-dependent manner as a result of actin-myosin crossbridge movement.
What does tropomyosin do in relaxed muscles?
In relaxed muscles, tropomyosin partially blocks the myosin-binding site on actin. To initiate contraction, Ca2+ binds to troponin. This unblocks the myosin-binding sites and allows myosin to complete its power stroke
What happens during relaxation
During relaxation, the sarcoplasmic reticulum uses a to pump back into its lumen.
What does myosin convert energy to?
Myosin converts energy from ATP into motion. Myosin ATPase hydrolyzes ATP to ADP and Pi.
What happens when myosin releases the myosin head?
When myosin releases the myosin head moves in the power stroke. At the end of the power stroke, myosin releases ADP. The cycle ends in the rigor state, with myosin tightly bound to actin
What happens in excitation-contraction coupling?
In excitation-contraction coupling, a somatic motor neuron releases ACh, which initiates a skeletal muscle action potential that leads to contraction.
DHP receptors
Voltage-sensing Ca2+ channels called DHP receptors in the t-tubules open RyR
Ca2+ release channels in the sarcoplasmic reticulum.
Single contraction-relaxation cycle
A single contraction-relaxation cycle is known as a twitch. The latent period between the end of the muscle action potential and the beginning of muscle tension development represents the time required for Ca2+ release and binding to troponin.
Phosphocreatine
Muscle fibers store energy for contraction in phosphocreatine. Anaerobic metabolism of glucose is a rapid source of ATP but is not efficient. Aerobic metabolism is very efficient but requires an adequate supply of oxygen to the muscles.
Muscle fatigue
Muscle fatigue is a reversible condition in which a muscle is no longer able to generate or sustain the expected power output. Fatigue has multiple causes.
Skeletal muscle fibers
Skeletal muscle fibers can be classified on the basis of their speed of contraction and resistance to fatigue into slow-twitch (oxidative) fibers, fast-twitch oxidative-glycolytic fibers, and fast-twitch glycolytic fibers. Oxidative fibers are the most fatigue resistant.
Myoglobin
Myoglobin is an oxygen-binding pigment that transfers oxygen to the interior of the muscle fiber.
Tension of a skeletal muscle
The tension of a skeletal muscle contraction is determined by the length of the sarcomeres before contraction begins.
Tetanus
Increasing the stimulus frequency causes summation of twitches with an increase of tension. A state of maximal contraction is known as tetanus.
Motor unit
A motor unit is composed of a group of muscle fibers and the somatic motor neuron that controls them. The number of muscle fibers in a motor unit varies, but all fibers in a single motor unit are of the same fiber type
Recruitment
The force of contraction within a skeletal muscle can be increased by recruitment of additional motor units.
12.2 MECHANICS OF BODY MOVEMENT
Isotonic contraction and isometric contraction
An isotonic contraction creates force as the muscle shortens and moves a load. An isometric contraction creates force without moving a load. Lengthening contractions create force while the muscle lengthens.
Series elastic elements
Isometric contractions occur because series elastic elements allow the fibers to maintain constant length even though the sarcomeres are shortening and creating tension
Levers and fulcrums
The body uses its bones and joints as levers and fulcrums. Most lever-fulcrum systems in the body maximize the distance and speed that a load can be moved but also require that muscles do more work than they would without the lever
Contraction is fastest when?
Contraction speed is a function of muscle fiber type and load. Contraction is fastest when the load on the muscle is zero
12.3 SMOOTH MUSCLE
What is smooth muscle?
Smooth muscle is slower than skeletal muscle but can sustain contractions for longer without fatiguing.
Phasic muscles and tonic smooth muscle
Phasic muscles are usually relaxed or cycle through contractions. Tonic smooth muscle is usually contracted
Single-unit smooth muscle
Single-unit smooth muscle contracts as a single unit when depolarizations pass from cell to cell through gap junctions. In multiunit smooth muscle, individual muscle fibers are stimulated independently.
Smooth muscle and skeletal muscle
Smooth muscle has less myosin than skeletal muscle. Each myosin is associated with about 12–15 actin molecules. Smooth muscle actin lacks troponin.
Smooth muscle sarcoplasmic reticulum has both
Smooth muscle sarcoplasmic reticulum has both RyR Ca2+ release channels and
IP3 channels. Calcium also enters the cell from the extracellular fluid.
In smooth muscle contraction what does Ca2+ bind to
In smooth muscle contraction, Ca2+ binds to calmodulin and activates myosin light chain kinase (MLCK)
MLCK phosphorylates what
MLCK phosphorylates myosin light chains, which activates myosin ATPase. This allows crossbridge power strokes
what happens to Ca2+ during relaxation
During relaxation, Ca2+ is pumped out of the cytosol, and myosin light chains are dephosphorylated by myosin phosphatase.
Smooth muscle calcium sensitivity
Smooth muscle calcium sensitivity can be altered by changing myosin phosphatase activity
What happens in myogenic contraction
In myogenic contraction, stretch on the cell depolarizes it and opens membrane
channels.
what happens in unstable membrane potentials
Unstable membrane potentials in smooth muscle take the form of either slow wave potentials or pacemaker potentials
What happens in pharmacomechanical coupling
In pharmacomechanical coupling, smooth muscle contraction initiated by chemical signals can take place without a significant change in membrane potential.
what are smooth muscle contractions influenced by?
smooth muscle contraction is influenced by sympathetic and parasympathetic neurons and a variety of hormones and paracrine signals
12.4 CARDIAC MUSCLE
Cardiac muscle fibers
Cardiac muscle fibers are striated, have a single nucleus, and are electrically linked through gap junctions. Cardiac muscle shares features with both skeletal and smooth muscle.
Q1 from review questions!
The three types of muscle tissue found in the human body are , , and . Which type is attached to the bones, enabling it to control body movement?
Smooth, cardiac, and skeletal.
The skeletal muscles are attached to the bone
Which two muscle types are striated?
cardiac and skeletal muscle
Which type of muscle tissue is controlled only by somatic motor neurons?
skeletal muscle
Arrange the following skeletal muscle components in order, from outermost to innermost: sarcolemma, connective tissue sheath, thick and thin filaments, myofibrils.
connective tissue –> sarcolemma —> myofibrils —> thick and thin filaments
The modified endoplasmic reticulum of skeletal muscle is called the . Its role is to sequester ions.
Sarcoplasmic reticulum; Ca+ ions
Which of the following statement(s) is (are) true about skeletal muscles?
a. They constitute about 60% of a person’s total body weight.
b. They position and move the skeleton.
c. The insertion of the muscle is more distal or mobile than the origin.
d. They are often paired into antagonistic muscle groups called flexors and extensors.
B, C, D all true
Flexor and extensor
The muscle is called a flexor is the centers of the connected bones are brought closer together when the muscle contracts. Flexion moves bones closer together. For ex: doing an arm curl, the radius and ulna move towards the humerus.
The muscle is an extensor if the bones are away from each other when the muscle contracts and the movement is called extension. Extension moves bones away from each other. For ex, when doing a push-up, the radius and ulna move away from the humerus.
T-tubules allow to move to the interior of the muscle fiber.
action potentials
List six proteins that make up the myofibrils. Which protein creates the power stroke for contraction?
Actin, myosin, troponin, tropomyosin, titin, and nebulin. Myosin produces the power stroke.
List the letters used to label the elements of a sarcomere. Which band has a Z disk in the middle? Which is the darkest band? Why? Which element forms the boundaries of a sarcomere? Name the line that divides the A band in half. What is the function of this line?
Z disk—ends of a sarcomere. I band—Z disk in the middle. A band (thick filaments)—darkest; H zone—lighter region of A band. M line divides A band in half; thick filaments link to each other.
Briefly explain the functions of titin and nebulin.
They keep actin and myosin in alignment. Titin helps stretched muscles return to resting length.
During contraction, the band remains a constant length. This band is composed primarily of molecules. Which components of the sarcomere approach each other during contraction?
A band; myosin. Z disks approach each other.
Explain the sliding filament theory of contraction.
Contraction occurs when thin and thick filaments slide past each other as myosin binds to actin, swivels, and pulls actin toward the center of the sarcomere.
Explain the roles of troponin, tropomyosin, and Ca2+ in skeletal muscle contraction.
Ca2+ binds to troponin, which repositions tropomyosin, uncovering actin’s myosin-binding sites.
Which neurotransmitter is released by somatic motor neurons?
Acetylcholine
What is the motor end plate, and what kinds of receptors are found there? Explain how neurotransmitter binding to these receptors creates an action potential.
The region of a muscle fiber where the synapse occurs. Contains ACh receptors. Influx of Na+ through ACh receptor-channels depolarizes muscle.
Match the following characteristics with the appropriate type(s) of muscle.
a. has the largest diameter
b. uses anaerobic metabolism, thus fatigues quickly
c. has the most blood vessels
d. has some myoglobin
e. is used for quick, fine movements
f. is also called red muscle
g. uses a combination of oxidative and glycolytic metabolism
h. has the most mitochondria
- fast-twitch glycolytic fibers
- fast-twitch oxidative-glycolytic fibers
- slow-twitch oxidative fibers
- a, b, e;
- d, f, g;
- c, d, f, h
A single contraction-relaxation cycle in a skeletal muscle fiber is known as a(n) .
twitch
List the steps of skeletal muscle contraction that require ATP.
ATP binding—myosin dissociates from actin. ATP hydrolysis— myosin head swings and binds to a new actin. Release of Pi initiates the power stroke.
The basic unit of contraction in an intact skeletal muscle is the . The force of contraction within a skeletal muscle is increased by additional motor units.
motor unit, recruitment
The two functional types of smooth muscle are and .
single-unit (visceral) and multi-unit
Make a map of muscle fiber structure using the following terms. Add terms if you like.
actin
Ca2+
cell
cell membrane
contractile protein
crossbridges
cytoplasm
elastic protein
glycogen
mitochondria
muscle fiber
myosin
nucleus
regulatory protein
sarcolemma
sarcoplasm
sarcoplasmic
titin
tropomyosin
troponin
t-tubule
use figs 12.3 to 12.6
How does an action potential in a muscle fiber trigger a Ca2+ signal inside the fiber?
Action potential activates DHP receptors that open SR Ca2+ channels.
Muscle fibers depend on a continuous supply of ATP. How do the fibers in the different types of muscle generate ATP?
Generate ATP by energy transfer from phosphocreatine. Oxidative fibers use oxygen to make ATP from glucose and fatty acids; glycolytic fibers get ATP primarily from anaerobic glycolysis.
Define muscle fatigue. Summarize factors that could play a role in its development. How can muscle fibers adapt to resist fatigue?
Fatigue—a reversible state in which a muscle can no longer generate or sustain the expected force. May involve changes in ion concentrations, depletion of nutrients, or excitation-contraction coupling. Increase size and number of mitochondria or increase blood supply.
Explain how you vary the strength and effort made by your muscles in picking up a pencil versus picking up a full gallon container of milk.
The body uses different types of motor units and recruits different numbers of motor units. Small movements use motor units with fewer muscle fibers; gross movements use motor units with more fibers.
Compare and contrast the following in skeletal and smooth muscle:
a. cellular anatomy
b. neural and chemical control of contraction
see tlb. 12.3
Arrange the following terms to create a map of skeletal muscle excitation, contraction, and relaxation. Terms may be used more than once. Add terms if you like.
acetylcholine
ACh receptor
actin
action potential
ADP
ATP
axon terminal
Ca2+
myosin
Na+
neuromuscular junction
Pi
power stroke
relaxation
rigor state
Ca2+-ATPase
calcium-release channels
contraction
crossbridge
DHP receptor
end-plate potential
exocytosis
motor end plate
sarcoplasmic reticulum
somatic motor neuron
tropomyosin
troponin
t-tubules
voltage-gated Ca2+ channels
use fig 12.8 to 12.10
What is the role of the sarcoplasmic reticulum in muscular contraction? How can smooth muscle contract when it has so little sarcoplasmic reticulum?
stores and releases Ca2+ on command. smooth muscle uses Ca2+ form the ECF.
Compare and contrast:
a. fast-twitch oxidative-glycolytic, fast-twitch glycolytic, and slow-twitch muscle fibers
b. a twitch and tetanus
c. action potentials in motor neurons and action potentials in skeletal muscles
d. temporal summation in motor neurons and summation in skeletal muscles
e. isotonic contraction and isometric contraction
f. slow-wave and pacemaker potentials
the source and role of
g. in skeletal and smooth muscle contraction
(a) Fast-twitch oxidative-glycolytic-smaller, some myoglobin, use both oxidative and glycolytic metabolism, more gatige-resistant. Fast-twitch glycolytic fibers-largest, rely primarily on anaerobic glycolysis, least fatigue-resistant. slow-twitch-develop tension more slowly, maintain tension longer, the most fatigue -resistant, depend rimarily on oxidative phosphorylation, more mitochondria. greater vascularity, large amounts of myoglobin, smallest in diameter: (b) Twitch-a single contraction-relaxation cycle. Tetanus-contraction with little to no relaxation. (c) Both result from inward Na+ current and outward K+ current through voltage-gated channels. Motor neuron action potential triggers ACh release. Muscle action potential triggers Ca2+ release from the sarcoplasmic reticulum. (d) Motor neuron temporal summation determines whether or not the neuron fires an action potential. Muscle cell summation increases force of contraction. (e) Isotonic contraction moves a load. Isometric contraction ceates tension without moving a load. (f) Slow-wave potentials-cycle of depolarization and repolarization in smooth muscle cells. pacemaker potentials-repetitive depolarizations to threshold in some smooth muscle and cardiac muscle. (g) skeletal muscle-sarcoplasmic reticulum. smooth muscle ECF and sarcoplasmic reticulum.
Explain the different factors that influence entry and release in smooth muscle fibers.
One way that scientists study muscles is to put them into a state of rigor by removing ATP. In this condition, actin and myosin are strongly linked but unable to move. On the basis of what you know about muscle contraction, predict what would happen to these muscles in a state of rigor if you (a) added ATP but no free calcium ions; (b) added ATP with a substantial concentration of calcium ions.
When curare, a South American Indian arrow poison, is placed on a nerve-muscle preparation, the muscle does not contract when the nerve is stimulated, even though neurotransmitter is still being released from the nerve. Provide every possible explanation you can think of for the action of curare.
On the basis of what you have learned about muscle fiber types and metabolism, predict what variations in structure you would find among these athletes:
a. a 7-foot, 2-inch-tall, 325-pound basketball player
b. a 5-foot, 10-inch-tall, 180-pound steer wrestler
c. a 5-foot, 7-inch-tall, 130-pound female figure skater
d. a 4-foot, 11-inch-tall, 89-pound female gymnast
