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63 terms

Muscle tissue

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myology
the scientific study of muscles
sphincter
ringlike band of smooth muscle that prevents outflow of the contents of a hollow organ
thermogenesis
heat production due to muscle contraction that helps maintain normal body temperature
excitability
the ability of muscle fibers to receive and respond to stimuli
contractility
the ability of cells or parts of cells to actively generate force to undergo shortening for movements
extensibility
the ability of muscle tissue to stretch when it is pulled
elasticity
the ability of tissue to return to its original shape after contraction or extension
muscle fibers
another name for muscles cells, due to their elongated shapes
fascia
a dense sheet or broad band of dense irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other body organs; holds muscles with similar functions together
epimysium
the outermost layer of connective tissue that encircles the entire muscle
perimysium
connective tissue layer that surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles
fascicle
a small bundle or cluster of muscle fibers
endomysium
a connective tissue layer that separates individual muscle fibers from one another
tendon
a cord of dense regular connective tissue composed of parallel bundles of collagen fibers that attach a muscle to a periosteum of a bone
aponeurosis
a tendon that resembles a broad, flat layer
hypertrophy
growth resulting in an enlargement of existing muscle fibers
hyperplasia
growth due to an increase in the number of muscle fibers
fibrosis
the replacement of muscle tissue by scar tissue
sarcolemma
the plasma membrane of a muscle cell
transverse (T) tubules
tiny, cylindrical invaginations of the sarcolemma of striated muscle fibers that conduct muscle action potentials toward the center of each muscle fiber
sarcoplasm
the cytoplasm of a muscle fiber
myoglobin
red-colored, iron-containing muscle protein that binds oxygen molecules that diffuse into the muscle fiber sarcoplasm from interstitial fluid
myofibrils
threadlike structures that extend longitudinally through a muscle fiber consisting mainly of thick filaments and thin filaments
sarcoplasmic reticulum (SR)
fluid-filled system of membranous sacs that encircle each myofibril; stores and releases calcium ions
muscular atrophy
a wasting away of muscles because of progressive loss of myofibrils due to disuse or denervation
filaments
the thin and thick proteins within myofibrils that are directly involved in the contractile process
sarcomere
the basic functional contractile unit of a myofibril
Z discs
narrow, plate-shaped regions of dense protein that separate one sarcomere from the next
A band
the darker middle part of the sarcomere which extends the entire length of the thick filaments
M line
supporting proteins that hold the thick filaments together in the middle of the sarcomere
myosin
the contractile protein that makes up the thick filaments of muscle fibers
actin
a contractile protein that is part thin filaments of muscle fibers
tropomyosin
one of two regulatory proteins that is part of the thin filament; covers the myosin-binding sites on actin
troponin
one of two regulatory proteins that is part of the thin filament; binds to calciumm ions and undergoes a shape change that moves tropomyosin away from the myosin-binding sites on actin
sliding filament model
the model that describes how skeletal muscle shortens during contraction due to the thin filaments sliding past the thick filaments
crossbridges
form when the myosin heads attach to actin during contraction
somatic motor neurons
the nerve cells that stimulate skeletal muscle fibers to contract
neuromuscular junction (NMJ)
the synapse between a somatic motor neuron and a skeletal muscle fiber
synapse
a region where communication occurs between two neurons, or between a neuron and a target cell
synaptic cleft
a small gap at the synapse that separates the two cells
neurotransmitter
chemicals that allow the first cell at a synapse to communicate with the second cell
synaptic vesicles
hundreds of membrane-enclosed sacs that are suspended in the cytosol within each synaptic end bulb
acetylcholine (ACh)
the neurotransmitter stored in synaptic vesicles that is released at the neuromuscular junction
motor end plate
the region of the muscle fiber sarcolemma opposite the synaptic end bulbs
creatine phosphate
an energy-rich molecule found only in muscle fibers that is synthesized when there is excess ATP
anaerobic cellular respiration
a series of ATP-producing reactions that do not require oxygen
aerobic cellular respiration
a series of oxygen-requiring reactions that produce ATP in mitochondria
muscle fatigue
the inability of a muscle to maintain force of contraction after prolonged activity
oxygen debt (recovery oxygen uptake)
refers to the added oxygen, over and above the resting oxygen consumption, that is taken into the body after exercise
motor unit
a somatic motor neuron plus all the skeletal muscle fibers it stimulates
myogram
a visual record of a muscle contraction
latent period
the brief delay that occurs between application of the stimulus and the beginning of contraction; the muscle action potential sweeps over the sarcolemma and calcium ions are released from the sarcoplasmic reticulum
contraction period
during this time, calcium ions bind to troponin, myosin-binding sites on actin are exposed, and crossbridges form
relaxation period
during this time, calcium ions are actively transported back into the sarcoplasmic reticulum, myosin-binding sites are covered by tropomyosin, myosin heads detach from actin, and tension in the muscle fiber decreases
refractory period
the time when a muscle fiber receives enough stimulation to contract that it temporarily loses its excitability and cannot respond for a time
muscle tone
a small amount of tautness or tension in the muscle due to weak, involuntary contractions of its motor units
isotonic contraction
the tension (force of contraction) developed by the muscle remains almost constant while the muscle changes its length; used for body movements and for moving objects
isometric contraction
occurs when the tension generated is not enough to exceed the resistance of the object to be moved, and the muscle does not change its length; holding a book steady using an outstretched arm
slow oxidative (SO) fibers
muscle fibers that are the smallest in diameter, the least powerful, appearing dark red due to large amounts of myoglobin and many blood capillaries; fatigue-resistant fibers that are adapted for maintaining posture and for aerobic, endurance-type activities like running a marathon
fast oxidative-glycolytic (FOG) fibers
muscle fibers that are intermediate in diameter, appearing dark red due to large amounts of myoglobin and many blood capillaries; used in walking and sprinting
fast glycolytic (FG) fibers
muscle fibers that are the largest in diameter and contain the most myofibrils; able to generate the most powerful contractions; low myoglobin content and few blood capillaries; adapted for intense anaerobic movements of short duration such as weight lifting
cardiac muscle fibers
the contractile cells of the heart
smooth muscle tone
a state of continued partial contraction that can sustain long-term tone in the GI tract and in the walls of blood vessels to maintain blood pressure