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