- acetylcholine (ACh)
- neurotransmitter that binds at a motor end-plate to trigger depolarization
- actin
- protein that makes up most of the thin myofilaments in a sarcomere muscle fiber
- action potential
- change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibers
- aerobic respiration
- production of ATP in the presence of oxygen
- angiogenesis
- formation of blood capillary networks
- aponeurosis
- broad, tendon-like sheet of connective tissue that attaches a skeletal muscle to another skeletal muscle or to a bone
- ATPase
- enzyme that hydrolyzes ATP to ADP
- atrophy
- loss of structural proteins from muscle fibers
- autorhythmicity
- heart’s ability to control its own contractions
- calmodulin
- regulatory protein that facilitates contraction in smooth muscles
- cardiac muscle
- striated muscle found in the heart; joined to one another at intercalated discs and under the regulation of pacemaker cells, which contract as one unit to pump blood through the circulatory system. Cardiac muscle is under involuntary control.
- concentric contraction
- muscle contraction that shortens the muscle to move a load
- contractility
- ability to shorten (contract) forcibly
- contraction phase
- twitch contraction phase when tension increases
- creatine phosphate
- phosphagen used to store energy from ATP and transfer it to muscle
- dense body
- sarcoplasmic structure that attaches to the sarcolemma and shortens the muscle as thin filaments slide past thick filaments
- depolarize
- to reduce the voltage difference between the inside and outside of a cell’s plasma membrane (the sarcolemma for a muscle fiber), making the inside less negative than at rest
- desmosome
- cell structure that anchors the ends of cardiac muscle fibers to allow contraction to occur
- eccentric contraction
- muscle contraction that lengthens the muscle as the tension is diminished
- elasticity
- ability to stretch and rebound
- endomysium
- loose, and well-hydrated connective tissue covering each muscle fiber in a skeletal muscle
- epimysium
- outer layer of connective tissue around a skeletal muscle
- excitability
- ability to undergo neural stimulation
- excitation-contraction coupling
- sequence of events from motor neuron signaling to a skeletal muscle fiber to contraction of the fiber’s sarcomeres
- extensibility
- ability to lengthen (extend)
- fascicle
- bundle of muscle fibers within a skeletal muscle
- fast glycolytic (FG)
- muscle fiber that primarily uses anaerobic glycolysis
- fast oxidative (FO)
- intermediate muscle fiber that is between slow oxidative and fast glycolytic fibers
- fibrosis
- replacement of muscle fibers by scar tissue
- glycolysis
- anaerobic breakdown of glucose to ATP
- graded muscle response
- modification of contraction strength
- hyperplasia
- process in which one cell splits to produce new cells
- hypertonia
- abnormally high muscle tone
- hypertrophy
- addition of structural proteins to muscle fibers
- hypotonia
- abnormally low muscle tone caused by the absence of low-level contractions
- intercalated disc
- part of the sarcolemma that connects cardiac tissue, and contains gap junctions and desmosomes
- isometric contraction
- muscle contraction that occurs with no change in muscle length
- isotonic contraction
- muscle contraction that involves changes in muscle length
- lactic acid
- product of anaerobic glycolysis
- latch-bridges
- subset of a cross-bridge in which actin and myosin remain locked together
- latent period
- the time when a twitch does not produce contraction
- motor end-plate
- sarcolemma of muscle fiber at the neuromuscular junction, with receptors for the neurotransmitter acetylcholine
- motor unit
- motor neuron and the group of muscle fibers it innervates
- muscle tension
- force generated by the contraction of the muscle; tension generated during isotonic contractions and isometric contractions
- muscle tone
- low levels of muscle contraction that occur when a muscle is not producing movement
- myoblast
- muscle-forming stem cell
- myofibril
- long, cylindrical organelle that runs parallel within the muscle fiber and contains the sarcomeres
- myogram
- instrument used to measure twitch tension
- myosin
- protein that makes up most of the thick cylindrical myofilament within a sarcomere muscle fiber
- myotube
- fusion of many myoblast cells
- neuromuscular junction (NMJ)
- synapse between the axon terminal of a motor neuron and the section of the membrane of a muscle fiber with receptors for the acetylcholine released by the terminal
- neurotransmitter
- signaling chemical released by nerve terminals that bind to and activate receptors on target cells
- oxygen debt
- amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction
- pacesetter cell
- cell that triggers action potentials in smooth muscle
- pericyte
- stem cell that regenerates smooth muscle cells
- perimysium
- connective tissue that bundles skeletal muscle fibers into fascicles within a skeletal muscle
- power stroke
- action of myosin pulling actin inward (toward the M line)
- pyruvic acid
- product of glycolysis that can be used in aerobic respiration or converted to lactic acid
- recruitment
- increase in the number of motor units involved in contraction
- relaxation phase
- period after twitch contraction when tension decreases
- sarcolemma
- plasma membrane of a skeletal muscle fiber
- sarcomere
- longitudinally, repeating functional unit of skeletal muscle, with all of the contractile and associated proteins involved in contraction
- sarcopenia
- age-related muscle atrophy
- sarcoplasm
- cytoplasm of a muscle cell
- sarcoplasmic reticulum (SR)
- specialized smooth endoplasmic reticulum, which stores, releases, and retrieves Ca++
- satellite cell
- stem cell that helps to repair muscle cells
- skeletal muscle
- striated, multinucleated muscle that requires signaling from the nervous system to trigger contraction; most skeletal muscles are referred to as voluntary muscles that move bones and produce movement
- slow oxidative (SO)
- muscle fiber that primarily uses aerobic respiration
- smooth muscle
- nonstriated, mononucleated muscle in the skin that is associated with hair follicles; assists in moving materials in the walls of internal organs, blood vessels, and internal passageways
- somites
- blocks of paraxial mesoderm cells
- stress-relaxation response
- relaxation of smooth muscle tissue after being stretched
- synaptic cleft
- space between a nerve (axon) terminal and a motor end-plate
- T-tubule
- projection of the sarcolemma into the interior of the cell
- tetanus
- a continuous fused contraction
- thick filament
- the thick myosin strands and their multiple heads projecting from the center of the sarcomere toward, but not all to way to, the Z-discs
- thin filament
- thin strands of actin and its troponin-tropomyosin complex projecting from the Z-discs toward the center of the sarcomere
- treppe
- stepwise increase in contraction tension
- triad
- the grouping of one T-tubule and two terminal cisternae
- tropomyosin
- regulatory protein that covers myosin-binding sites to prevent actin from binding to myosin
- troponin
- regulatory protein that binds to actin, tropomyosin, and calcium
- twitch
- single contraction produced by one action potential
- varicosity
- enlargement of neurons that release neurotransmitters into synaptic clefts
- visceral muscle
- smooth muscle found in the walls of visceral organs
- voltage-gated sodium channels
- membrane proteins that open sodium channels in response to a sufficient voltage change, and initiate and transmit the action potential as Na+ enters through the channel
- wave summation
- addition of successive neural stimuli to produce greater contraction