CHAPTER 08: MUSCLE PHYSIOLOGY Flashcards
A band
One of the dark bands that alternate with light (I) bands to create a striated appearance in a skeletal or cardiac muscle fiber when these fibers are viewed with a light microscope
actin
The contractile protein that forms the backbone of the thin filaments in muscle fibers
aerobic exercise
Exercise that can be supported by ATP formation accomplished by oxidative phosphorylation because adequate O2 is available to support the muscleUs modest energy demands; also called endurance-type exercise
alpha motor neuron
A motor neuron that innervates ordinary skeletal muscle fibers
anaerobic exercise
High-intensity exercise that can be supported by ATP formation accomplished by anaerobic glycolysis for brief periods of time when O2 delivery to a muscle is inadequate to support oxidative phosphorylation
atrophy
Decrease in mass of an organ
calmodulin
An intracellular Ca2 binding protein that, on activation by Ca2, induces a change in structure and function of another intracellular protein; especially important in smoothmuscle excitation-contraction coupling
cardiac muscle
The specialized muscle found only in the heart
contractile component
The sarcomere-containing myofibrils within a muscle fiber that are capable of shortening on excitation
contractile proteins
Myosin and actin, whose interaction brings about shortening (contraction) of a muscle fiber
cross bridges
The myosin moleculesU globular heads that protrude from a thick filament within a muscle fiber and interact with the actin molecules in the thin filaments to bring about shortening of the muscle fiber during contraction
end-plate potential (EPP)
The graded receptor potential that occurs at the motor end plate of a skeletal muscle fiber in response to binding with acetylcholine
excitation-contraction coupling
The series of events linking muscle excitation (the presence of an action potential) to muscle contraction (filament sliding and sarcomere shortening)
excitatory postsynaptic potential (EPSP)
A small depolarization of the postsynaptic membrane in response to neurotransmitter binding, thereby bringing the membrane closer to threshold
fatigue
Inability to maintain muscle tension at a given level despite sustained stimulation
functional syncytium
A group of smooth or cardiac muscle cells that are interconnected by gap junctions and function electrically and mechanically as a single unit
functional unit
The smallest component of an organ that can perform all the functions of the organ
gamma motor neuron
A motor neuron that innervates the fibers of a muscle-spindle receptor
glycolysis
A biochemical process that takes place in the cellUs cytosol and involves the breakdown of glucose into two pyruvic acid molecules
gradation of contraction
Variable magnitudes of tension produced in a single whole muscle
hyperplasia
An increase in the number of cells
hypertrophy
Increase in the size of an organ as a result of an increase in the size of its cells
I band
One of the light bands that alternate with dark (A) bands to create a striated appearance in a skeletal or cardiac muscle fiber when these fibers are viewed with a light microscope
isometric contraction
A muscle contraction in which the development of tension occurs at constant muscle length
isotonic contraction
A muscle contraction in which muscle tension remains constant as the muscle fiber changes length
lactic acid
An end product formed from pyruvic acid during the anaerobic process of glycolysis
lateral sacs
The expanded saclike regions of a muscle fiberUs sarcoplasmic reticulum; store and release calcium, which plays a key role in triggering muscle contraction
length-tension relationship
The relationship between the length of a muscle fiber at the onset of contraction and the tension the fiber can achieve on a subsequent tetanic contraction
motor activity
Movement of the body accomplished by contraction of skeletal muscles
motor unit
One motor neuron plus all the muscle fibers it innervates
motor unit recruitment
The progressive activation of a muscle fiberUs motor units to accomplish increasing gradations of contractile strength
multiunit smooth muscle
A smooth muscle mass that consists of multiple discrete units that function independently of each other and that must be separately stimulated by autonomic nerves to contract
muscle fiber
A single muscle cell, which is relatively long and cylindrical in shape
myofibril
A specialized intracellular structure of muscle cells that contains the contractile apparatus
myosin
The contractile protein that forms the thick filaments in muscle fibers
optimal length
The length before the onset of contraction of a muscle fiber at which maximal force can be developed on a subsequent tetanic contraction
oxidative phosphorylation
The entire sequence of mitochondrial biochemical reactions that uses oxygen to extract energy from the nutrients in food and transforms it into ATP, producing CO2 and H2O in the process
regulatory proteins
Troponin and tropomyosin, which play a role in regulating muscle contraction by either covering or exposing the sites of interaction between the contractile proteins
sarcomere
The functional unit of skeletal muscle; the area between two Z lines within a myofibril
sarcoplasmic reticulum
A fine meshwork of interconnected tubules that surrounds a muscle fiberUs myofibrils; contains expanded lateral sacs, which store calcium that is released into the cytosol in response to a local action potential
series-elastic component
The noncontractile portions of a skeletal muscle fiber, including the connective tissue and sarcoplasmic reticulum
single-unit smooth muscle
The most abundant type of smooth muscle; made up of muscle fibers that are interconnected by gap junctions so that they become excited and contract as a unit; also known as visceral smooth muscle
skeletal muscle
Striated muscle, which is attached to the skeleton and is responsible for movement of the bones in purposeful relation to one another; innervated by the somatic nervous system and under voluntary control
slow-wave potentials
Self-excitable activity of an excitable cell in which its membrane potential undergoes gradually alternating depolarizing and hyperpolarizing swings
smooth muscle
Involuntary muscle innervated by the autonomic nervous system and found in the walls of hollow organs and tubes
stretch reflex
A monosynaptic reflex in which an afferent neuron originating at a stretch-detecting receptor in a skeletal muscle terminates directly on the efferent neuron supplying the same muscle to cause it to contract and counteract the stretch
tension
The force produced during muscle contraction by shortening of the sarcomeres, resulting in stretching and tightening of the muscleUs elastic connective tissue and tendon, which transmit the tension to the bone to which the muscle is attached
tetanus
A smooth, maximal muscle contraction that occurs when the fiber is stimulated so rapidly that it does not have a chance to relax at all between stimuli
thick filaments
Specialized cytoskeletal structures within skeletal muscle that are made up of myosin molecules and interact with the thin filaments to accomplish shortening of the fiber during muscle contraction
thin filaments
Specialized cytoskeletal structures within skeletal muscle that are made up of actin, tropomyosin, and troponin molecules and interact with the thick filaments to accomplish shortening of the fiber during muscle contraction
transverse tubule (T tubule)
A perpendicular infolding of the surface membrane of a muscle fiber; rapidly spreads surface electric activity into the central portions of the muscle fiber
tropomyosin
One of the regulatory proteins found in the thin filaments of muscle fibers
troponin
One of the regulatory proteins found in the thin filaments of muscle fibers
twitch
A brief, weak contraction that occurs in response to a single action potential in a muscle fiber
twitch summation
The addition of two or more muscle twitches as a result of rapidly repetitive stimulation, resulting in greater tension in the fiber than that produced by a single action potential
Z line
A flattened disclike cytoskeletal protein that connects the thin filaments of two adjoining sarcomeres
