2 ' Muscle Physiology Flashcards
Muscular system is comprised of three types of muscle tissue:
Skeletal, cardiac, and smooth
Skeletal
Striated muscle attached to the skeleton used to facilitate movement by applying force to bones and joints via contractions
Cardiac
Involuntary, mononucleated, striated muscle found exclusively within the heart
Smooth
Non-striated muscle found within the “walls” of hollow organs such as the bladder, uterus, and GI tract
Signals initiated in the brain stimulate the nervous system, causing muscles to contract and produce tension
True
Motor information is carried via actin potentials from the central nervous system (CNS)
True
Action potential
Wave-like change in the electrical properties of a cell membrane that results from the difference in electrical charge between the inside and outside of the membrane and causes the muscle call to contract
Capillaries
Ting blood vessels that connect arteries and veins, forming an intricate network around body tissues in order to distribute oxygen and nutrients to the cells and remove waste substances
Myofibrils
Cylindrical structures containing the myofilaments actin (thin filament) and myosin (thick filament)
Surrounding myofibrils are a calcium-housing network called the sarcoplasmic reticulum (SR), tube-like structures that transfer signals called T-tubules, and mitochondria, which are used to produce energy
True
SR
A tubular network that surrounds each individual myofibril and acts as a storage site for calcium within the skeletal muscle
T-tubules
Tubules that pass in a transverse manner from the sarcolemma across a myofibril of striated muscle passing signals within the cell
Tension is created in a group of muscle fibers by initiation of the action potential
True
The action potential travels via an electrical current through the spinal cord and is transferred to the peripheral nervous system (PNS)
True
The current runs through outer levels of muscle tissue to very small nerve fibers called motor neurons which connect to the particular fibers to be contracted
True
Motor unit
Motor neuron and all the muscle fibers it innervates
Inside the muscle fiber, the following must occur to allow for a contraction (sliding filament theory):
5 actions
Action potent ion travels down the T-tubules and stimulates the SR
True
Calcium is released from the SR, acting as a key to unlock the bond between the thin contractile filament and troponin
True
Troponin molecule moves, rotating the tropomyosin molecule away from binding site
True
Myosin is free to attach to actin for in a cross-bridge
True
Adenosine triphosphate (ATP) is split at the myosin/actin attachment site and energy is released, allowing the muscle fiber to contract and produce force
True
A muscle fiber is either in a state of producing maximum tension or not productive any tension at all; this is known as the “all of none” principle
True
Motor units are stimulated within the desired muscle to produce movement
True
The greater the number of motor units stimulated, the more fibers recruited, producing more tension
True
Total skeletal muscle force dictates how many muscle fibers are recruited for the concentration
True
Two type of motor unit firing patterns:
Synchronized firing and Asynchronous firing
Synchronized firing
Employed during high-output demands involving fast-twitch fibers and warranting significant fiber recruitment m
Asynchronous firing
Employed during endurance activities involving slow-twitch fibers which conserve motor unit potential, allowing prolonged work
The ability to increase force production within a muscle through training is dependent on adaptations that occur to both:
Muscle fibers (size) and the nervous system (recruitment, firing rate, firing synchronicity)
Force production improvements can occur without the addition of new muscle due to efficiency changes related to motor unit recruitment
True
Inability to produce force, most notably due to intensity of exercise occurs in the CNS and PNS
True
Disrupts the motor units ability to produce force
True
As the rate of motor unit fatigue increases, performance proportionately declines
True
Rest interval or rest period
Period of time between repeated actions in an exercise; energy system specified and based on physical condition
Muscle cell recovery is dependent on the return of intracellular energy supply; circulatory-based, cellular by-product removal; and the delivery of O2
True
Recovery period is a Period of time between exercise bouts, during which muscle fibers will
Replenish their energy reserves, repair any damage resulting from the production of force, and fully return to normal pre-exertion levels
Two types of isotonic contractions involve lengthening or shortening of a working muscle
Eccentric contraction and Concentric contraction
Eccentric contraction
Muscle lengthens; negative work is produced; movement is decelerated
Concentric concentration
Muscle shortens; positive work is produced; movement is accelerated
Isometric contractions
Mostly used for stability; represent tension in the muscle that helps maintain position but does not cause acceleration or deceleration forces
Employed by stabilizing muscles to control movements and prevent undesirable actions
True
Type of muscle fiber recruited to produce a contraction depends on the amount of force needed
True
Three types of skeletal muscle fibers
Type IIb, type IIa and type I
Type IIb
High force-producing fibers, or face glycolytic fibers
Type IIa
Intermediate force-producing fibers, or fast oxidative/glycolytic fibers
Type I
Low force-producing fibers, or slow oxidative fibers
Fast-twitch fiber characteristics
Large diameter size, high force output but quick to fatigue (30-50g per motor unit), densely picked myofibrils, large glycogen reserves, preferentially recruited for high-power output activities, increases in size and strength when trained under conditions of short duration and high intensity and preferentially function using anaerobic metabolic systems
Slow-twitch fiber characteristics
50% smaller than fast-twitch fibers, produce low amounts of force (5g per motor unit), primarily use aerobic metabolic systems, better suited for endurance activities - fatigue-resistant, extensive capillary network and high mitochondrial density and higher amounts of myoglobin, increasing oxygen reserves in cells
Myoglobin
O2-transporting protein of muscle; resembles blood hemoglobin in function
Type IIa intermediate fiber characteristics
Used for activities requiring prolonged duration and/or elevated force, composition of both fast- and slow-twitch fiber characteristics, and adaptations support both anaerobic and aerobic activities
Genetically predetermined; training will not change concentrations of fibers within segments of the body
True
Postural muscles maintain a higher concentration of slow- twitch fibers
True
Soleus, deep muscles of the back, and the rectus abdominis must contract continuously to maintain upright posture and is not designed for rapid, high-force output; experience limited improvements in power/hypertrophh
True
Slow-twitch fibers do not convert to fast-twitch fibers (or vice versa), but muscle can become better suited to training stimulus due to the following changes:
Neural stimulation, capillary and mitochondrial density and enzyme concentration
Muscle tone
Some motor units in a muscle are always active even when the muscle is not contracting
Two primary proprioceptors used to manage the tonicity of muscle tissue
Muscle spindles and golgi tendon organs
Muscle spindles
Intrafusal fibers that lie parallel to normal muscle fibers which relay information to sensory neurons regarding changes in tissue length and tension
When rapidly stretched, they respond with a stretch reflex to initiate a concentration that limits an overstretch and potential damage to the muscle
True
Golgi tendon organs
Sensory receptors found within muscle tendons that communicate information to motor neurons regarding the presence of excessive tension that may cause damage
If tension in a muscle is too great, they send inhibitory signals to reduce motor neuron activity and thereby reduce the force of muscular contraction
True
