Chapter9 Flashcards
types of muscle tissue
- skeletal
- cardiac
- smooth
- Attached to bones and skin
- multinucleated, long, cylindrical cells
- Striated
- voluntary (i.e., conscious control)
skeletal muscle tissue
- Heart muscle
- Striated; intercalated disks (gap_ junctions)
- mononucleated_, branched cells
- Involuntary (i.e., conscious_ control)
cardiac muscle tissue
- In the walls of hollow organs, e.g., stomach , urinary bladder, and airways
- oblong nucleus, Spindle-shaped cells
- Not striated
- Involuntary (i.e., unconscious control)
smooth muscle tissue
- excitability (responsiveness or irritability): ability to receive and respond to stimuli
- contractibility : ability to shorten when stimulated
- extensibility : ability to be stretched
- elasticity : ability to recoil to resting length
special characteristics of muscle tissue
- Movement of bones or fluids (e.g., GI tract, blood)
- maintaining posture and body position
- Stabilizing joints
- Heat generation (especially skeletal muscle)
muscle functions
Each muscle is served by one artery , one nerve , and one or more veins
skeletal muscle
- epimysium : dense regular connective tissue surrounding entire muscle
- perimysium : fibrous connective tissue surrounding fascicles (groups of muscle fibers)
- endomysium : fine areolar connective tissue surrounding each muscle fiber
connective tissue sheaths of skeletal muscle
fibrous connective tissue surrounding fascicles (groups of muscle fibers)
perimysium (connective tissue sheath in skeletal muscle)
dense regular connective tissue surrounding entire muscle
epimysium (connective sheath of skeletal muscle)
fine areolar connective tissue surrounding each muscle fiber
endomysium (connective tissue sheath of skeletal muscle)
- ______—epimysium of muscle is fused to the periosteum of bone or perichondrium__ of cartilage
- ______—connective tissue wrappings extend beyond the muscle_ as a ropelike tendon or sheetlike aponeurosis
directly/ indirectly
- cylindrical_cell 10 to 100um in diameter, up to 30 cm long
- Many mitochondria [to generate force in skeletal muscle]
- Multiple peripheral nuclei [to generate myofibrils to develop proteins]
- Glycosomes for glycogen storage, myoglobin for O2 storage
- Also contain myofibrils, sarcoplasmic reticulum, and T tubules
microscopic anatomy of a skeletal muscle fiber
- contractile organelle of muscle fiber
- densely packed, rodlike elements
- ~80% of cell volume
- Exhibit striations: perfectly aligned repeating series of dark A bands and light I bands
myofibrils
- Network of smooth endoplasmic reticulum surrounding each myofibril
- Pairs of terminal cisternae form perpendicular cross channels
- Functions in the regulation of intracellular Ca2+ levels
sarcoplasmic reticulum
- Continuous with the sarcolemma
- penetrate the cell’s interior at each A band–I band junction
- Associate with the paired terminal cisternae to form triads that encircle each sarcomere
T(transverse) tubules
- _ _____ conduct impulses deep into muscle fiber
- Integral proteins protrude into the intermembrane space from T tubule and SR cisternae membranes
t tubules
t tubule proteins : ______ ______
voltage sensors
gated channels that regulate Ca2+ release from the cisternae
SR foot proteins
Shortening occurs when tension generated by cross bridges of the two contractile proteins: ____ and ____
actin and myosin
- Composed of the protein myosin
- Myosin heads contain:
- 2 smaller, light polypeptide chains form cross bridges
- Binding sites for actin of thin filaments
- Binding sites for ATP
- ATPase enzymes
ultrastructure of THICK filament
- Composed of the protein_ actin
- Composed of two regulatory proteins:
- Troponin (bind Ca+2)
- tropomyosin (cover crossbridge binding site
ultrastructure of THIN filament
- Smallest contractile unit (functional unit) of a muscle fiber
- The region of a myofibril_ between two successive Z discs
- Composed of thick and thin myofilaments made of contractile proteins
sacromere
- thick filaments: run the entire length of an A band
- Thin filaments : run the length of the I band and partway into the A band
- Z disc: coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another
- M line: line of protein myomesin_ that holds adjacent thick filaments together (structural protein)
features of sarcomere
In what state does thin and thick filaments overlap only slightly
relaxed state
during ______, myosin heads bind to actin , detach , and bind again, to propel the thin filaments toward the M line
contraction
As _ zones shorten and disappear, sarcomeres shorten, muscle cells shorten, and the whole muscle shortens
H
- activation : neural stimulation at aneuromuscular junction
- Excitation-contraction coupling:
- generation and propagation of an action potential along the sarcolemma
- final trigger: a brief rise in intracellular Ca2+ levels
Requirements for Skeletal Muscle Contraction
- skeletal muscles are stimulated by somatic motor neurons
- Axons of _motor__ neurons _travel_ from the central __nervous_ system via nerves to skeletal muscles
- Each axon forms several branches as it enters a muscle
- Each _axon_ ending forms a _neuromuscular__ junction with a single muscle_ fiber
events at the neuromuscular junction
- situated midway along the length of a muscle_fiber
- Axon terminal and muscle fiber are separated by a gel-filled space called the synaptic cleft
- synaptic vesicles of axon vesicles contain the neurotransmitter _acetylcholine (ACh)
- juntional folds of the sarcolemma contain ACh
neurmuscular junction
- nerve_ impulse arrives at axon _terminal__
- ACh is released and binds with _receptors__ on the sarcolemma_
- Electrical events lead to the generation of an action potential
events at neuromuscular junction
- ACh effects are quickly rteerminated_ by the enzyme acetylcholinesterase_
- Prevents continued muscle fiber contraction_ in the absence of additional stiumulation
destruction of acetylcholine
the 2 light polypeptide chains in a myosin molecules head link the thick and thin filaments together, forming __, and swivel around their point of attachment during contraction
cross bridges
Sequence of events_ by which _transmission__ of an AP along the sarcolemma leads to sliding of the myofilaments
Excitation-Contraction (E-C) Coupling
Latent period:
time__ when E-C coupling events occur
Time between AP initiation and the beginning of contraction
excitation contraction coupling LATENT PERIOD
- Continues as long as the Ca2+ signal_ and adequate _ATP_ are present
- cross_ bridge formation — high-energy myosin_ head attaches to thin filament
- Power stroke — _mysosin_ head pivots and pulls thin filament toward M line
cross bridge cycle
ATP attaches to myosin head and the cross bridge detaches
cross bridge detachment
energy from the hydrolysis of ATP cocks the myosin head into the high energy state
cocking of the myosin head
- no shortening; muscle tension increases but does not exceed the load
- once sufficient tension develops , tension remains relatively constant through rest of contractile period
isometric contraction
muscle shortens because muscle tension exceeds the load
isotonic contraction
- Same principles apply to contraction of a single fiber and a whole muscle
- contraction_produces tension , the force exerted on the load or object to be moved
- Contraction does not always shorten a muscle:
- isometric contraction: no shortening; muscle tension increases but does not exceed the load
- isotonic contraction: muscle shortens because muscle tension exceeds the load
4.Force and duration of contraction vary in response to stimuli of different frequencies and intensities
principles of muscle mechanics
a motor neuron and all (four to several hundred) muscle fibers it supplies
motor unit : the nerve muscle functional unit
____ motor units in muscles that control fine movements (fingers , eyes)
small
______ motor units in large weight-bearing muscles (thighs, hips)
large
- Muscle fibers from a ___ ___are spread throughout the muscle so that a single motor unit causes weak contraction of entire muscle
- Motor units in a muscle usually contract asynchronously ; helps prevent fatigue
motor unit
Response of a muscle to a single, brief threshold stimulus
simplest contraction observable in the lab (recorded as a myogram)
muscle twitch
- Latent period: events of excitation-contraction coupling
- Period of contraction: cross bridge formation; tension increases
- Period of relaxation : Ca2+ reentry into the SR; tension declines to zero
3 phases of a twitch
Different strength and duration of twitches are due to
variations in metabolic properties and enzymes btw muscles
- Variations in the degree of muscle contraction
- Required for proper control of skeletal movement
Responses are graded by:
- Changing the frequency of stimulation
- Changing the strength of the stimulus
graded muscle responses
a single stimulus results in a single contractile response- muscle twitch
response to change in stimulus frequency
Ca2+ release stimulates further contraction /further increase in stimulus frequency
temporal (wave) summation/ unfused (incomplete) tetanus
motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments
sequence of events for muscle contractions
funtional unit of a skeletal muscle is called
sarcomere
contractile units of skeletal muscle
myofibrils
surrounds the individual muscle cell?
endomysium
composed of myosin
thick filaments
During muscle contraction, myosin cross bridges attach to which active sites
actin filaments
What produces the striations of a skeletal muscle cell?
arrangement of myofilaments
The major function of the sarcoplasmic reticulum in muscle contraction is to ________.
regulate intracellular calcium concentration
What structure in skeletal muscle cells functions in calcium storage?
sarcoplasmic reticulum
Which muscle cells have the greatest ability to regenerate?
smooth
What is the role of tropomyosin in skeletal muscles?
Tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules.
When a muscle fiber _____, the I bands diminish in size, the H zones disappear, and the A bands move closer together but do not diminish in length.
contracts
The effect of a ______on the muscle cell membrane is to modify its ion permeability properties temporarily.
neurotransmitter
An increase in the calcium ion level in the sarcoplasm starts the sliding of the thin filaments. When the level of calcium ions declines, ___ ___
sliding stops
stimulus stength at which the first observable muscle contraction occurs
threshold stimulus
contraction force is precisely controlled by _______ , which brings more and more muscle fibers into action
recruitment (multiple motor unit summation)
- Constant, slightly contracted_ state of all muscles
- Due to spinal reflexes that activate groups of motor units alternately in response to input from stretch receptors in muscles
- Keeps muscles firm, healthy, and ready to respond
muscle tone
isotonic contractions are either ____ or _____
- concentric contractions—the muscle shortens and does work
- eccentric contractions—the muscle contracts as it lengthens
- The load is greater than the tension the muscle is able to develop
- tension_ increases to the muscle’s capacity, but the muscle neither shortens nor lengthens
isometric contractions
- Direct phosphorylation of ADP by creatine phosphate (CP)
- Anaerobic pathway (glycolysis )
- aerobic respiration
how ATP is regenerated by
glycolysis in cytosol, pyruvic acid, lactic acid released to blood
anaerobic pathway
this pathway :
- Produces 95% of ATP during rest and light to moderate exercise
- Fuels: stored glycogen , then bloodborne glucose, pyruvic acid from glycolysis , and free fatty acids
aerobic pathway
- physiological inability to contract
Occurs when:
- ionic imbalances (K+, Ca2+, Pi) interfere with E-C coupling
- Prolonged exercise damages the SR and inteferes with Ca2+ regulation and release
- Total lack of ATP occurs rarely, during states of continuous conraction , and causes contractures (continuous contractions )
muscle fatigue
- Extra O2 needed after exercise for:
- Replenishment of oxygen_ reserves, glycogen stores,ATP and CP reserves, Conversion of lactic acid to pyruvic acid, glucose, and glycogen
oxygen deficit
______ __ _____ is affected by:
number of muscle fibers stimulated (recruitment )
Relative size of the fibers—hypertrophy of cells increase strength
- Frequency of stimulation —increase frequency allows time for more effective transfer of tension to noncontractile components
- Length-tension relationship—muscles contract most strongly when muscle fibers are 80–120% of their normal resting length
force of contraction
velocity and duration of contraction influenced by…
muscle fiber type, load, recruitment
1.Speed of contraction : slow or fast, according to:
- speed at which myosin ATPases split ATP
- Pattern of electrical activity of the motor neurons
2.Metabolic pathways for ATP synthesis:
- Oxidative fibers—use aerobic pathways
- Glycolytic fibers—use anaerobic glycolysis
classification of muscle fiber according to these 2 characteristics
aerobic (endurance ) exercise leads to increased….
- muscle capillaries
- number of mitochondria
- myoglobin synthesis
- results in greater endurance, strength, resistance to fatigue
Resistance exercise (typically anaerobic) results in:
- Muscle hypertrophy (due to increase in fiber size)
- Increased mitochondria , myofilaments, glycogen stores, and connective tissue
- _______layer contracts; organ dilates and shortens
- _____ layer contracts_ ; organ constricts and elongates
longitudinal/ circular
_______ nerve fibers innervate smooth muscle at diffuse junctions
autonomic
______ are (bulbous swellings) of nerve fibers store and release neurotransmitters
varicosities
- Ratio of thick to thin filaments (1:13) is much lower than in skeletal muscle (1:2)
- thick filaments have heads along their entire length
- No troponin complex; protein calmodulin binds Ca2+
- Myofilaments are spirally arranged, causing smooth muscle to contract in a corkscrew manner
- Dense bodies: proteins that anchor noncontractile_ intermediate filaments to sarcolemma at regular intervals
mylofilaments in smooth muscle
- Slow, synchronized contractions
- Cells are electrically coupled by gap junctions
- Some cells are self-excitatory (depolarize without external stimuli); act as pacemakers for sheets of muscle
- Rate and intensity of contraction may be modified by neural and chemical stimuli
contraction of smooth muscle
- Stress-relaxation response:
- responds to stretch only briefly, then adapts to new length
- Retains ability to contract on demand
- enables organs such as the stomach and bladder to temporarily store contents
- Length and tension changes:
- Can contract when between half and twice its resting length
special features of smooth muscle contraction
- sheets contract rhymthmically as a unit (gap junctions)
- Often exhibit spontaneous action potentials
- Arranged in opposing sheets and exhibit stress-relaxation response
single unit visceral smooth muscle
- located in large airways, large arteries , arrector pili muscles, and iris of eye
- gap junctions are rare
- Arranged in motor units
- Graded contractions occur in response to neural stimuli
multiunit smooth muscle
in excitation contraction coupling the action potential is propagted down the _ ______ causing calcium to en released from the SR into the cytosol
t tubules
