Muscle
Events of skeletal muscle excitation-contraction coupling
1) AP is conducted along T-tubule membrane 2) DHP-receptor changes conformation in response to voltage change 3) Ryanodine receptor is pulled into an open conformation 4) Ca diffuses from SR into cytosol 5) Ca binds to troponin
The 4 steps of the cross-bridge cycle beginning in a resting cell, immediately after tropomyosin shifts to reveal the binding sites
1) Attachment of the cross-bridge to a thin filament 2) Movement of the cross-bridge, producing tension in the thin filament & dissociation of ADP & Pi from the cross-bridge 3) Detachment of the cross-bridge from the thin filament 4) Re-energizing the cross-bridge by hydrolysis of ATP
Events that occur after an increase in cytosolic Ca in a smooth muscle fiber
1) Ca binds to calmodulin 2) Ca-calmodulin complex binds to myosin light-chain kinase 3) Active myosin light-chain kinase uses ATP to phosphorylate myosin light chains in the globular head of myosin 4) Phosphorylation of myosin drives the cross-bridge away from the thick filament backbone, allowing it to bind to actin 5) Cross-bridges go thru repeated cycles of force generation if myosin light chains are phosphorylated
Steps of monosynaptic knee-jerk reflex
1) stretching of spindle fibers of muscle 2) distorting of central bag or chain region 3) stimulus of sensory neurons 4) APs travel to spinal cord via sensory neuron 5) somatic motor neuron stimulated 6) contraction of extrafusal fibers stimulated
Fibers containing myosin with high ATPase activity are called type ____ fibers.
2
Rocuronium
A long lasting, nondepolarizing NMJ blocking drug used during certain surgical procedures that blocks ACh from binding nAChRs
What is the motor end plate?
A specialized part of the sarcolemma within the NMJ
Organophosphate
A type of pesticide that inhibits AChesterase action resulting in skeletal muscle paralysis & death from asphyxiation
Chemical formula present at the state of a resting muscle
A+MxADPxPi
During muscle shortening, tension & stretch in the central region of an intrafusal fiber is maintained by _____.
APs in gamma motor neurons
How is the role of Ca different in the activation of smooth & skeletal muscle cells?
Activates contraction in smooth by binding to calmodulin, while in skeletal it activates by binding primarily to troponin
Reciprocal innervation =
Activation of neurons to 1 muscle with the simultaneous inhibitions of neurons to its antagonistic muscle
When cross-bridges cycle & a muscle shortens, what gets greater?
Amount of overlap b/w thick & thin filaments
Curare
An arrowhead poison that binds strongly to nAChR & blocks ACh from binding to the receptor
Comparing the role of ATP in smooth & skeletal muscle fiber contraction
An extra ATP must be hydrolyzed to phosphorylate myosin light-chains & activate contraction in smooth muscle, but otherwise ATP plays the same role in both types of muscle
What is the muscle or muscle group called that flexes a joint in relation to the muscle group that extends that joint?
Antagonist
Fast glycolytic or Type IIb fibers...
Are anaerobic & have a low myoglobin content
The general intention of any movement is determined by neurons that originate in the...
Areas of the brain involved in memory, emotions, & motivation, & the sensorimotor cortex
The decrease in size of a muscle that occurs due to prolonged inactivity is referred to as disuse _____.
Atrophy
Chemical formula present at the state of cross-bridges in rigor mortis
AxM
The following applies to cross-bridge heads...
Bind to & pull on actin & part of the myosin protein
Function of tropomyosin in skeletal muscle contractile regulation
Blocks myosin from binding to actin
Event that occurs at troponin during excitation-contraction coupling
Ca binds to this protein; causing shape change that moves tropomyosin
Some smooth muscles propagate membrane APs that activate contraction. In those cells, what type of ions provide the depolarizing current?
Calcium
The regulatory protein troponin is absent in smooth muscle, but tropomyosin is present, as is another protein called _____, which associates with the thin filaments & in some types of muscle may play a role in regulating contraction.
Caldesmon
In smooth muscle, Ca combines with the protein _____ which activates a kinase that phosphorylates the myosin light chains.
Calmodulin
In skeletal muscle, Ca binds to troponin, while in smooth muscle, the binding of Ca to _____ activates a signal cascade that results in phosphorylation of _____.
Calmodulin; myosin
A concentric contraction...
Can be an isotonic contraction; is a shortening contraction; involves a tension that's greater than the load
Extrafusal fibers
Category of skeletal muscle fibers that AREN'T part of the muscle spindle & which constitute the greatest mass & generate the force & movement of the muscle
Middle-level structures of the motor control hierarchy include the...
Cerebellum & thalamus, sensorimotor cortex, & basal nuclei & brainstem
What's the most abundant protein in the body?
Collagen
Middle-level neurons of the motor control hierarchy receive input from the...
Command neurons, brainstem & spinal cord interneurons, & vestibular apparatus & the eyes
The T-tubules...
Conduct action potentials & are continuous with the plasma membrane
Role of oxytocin in smooth muscle activity
Contracting agent
In a skeletal muscle isometric twitch, the time interval from the beginning of tension development to the peak tension is referred to as the ______ time.
Contraction
When the force-generating mechanism of a muscle is activated, it is called a ______.
Contraction
Synergistic muscles =
Contractions assist with the intended motion
Movements give rise to afferent input that...
Contributes to conscious perception of limb & body position & influences how a movement proceeds
Middle level functions
Creates motor programs that determine patterns of neural activity necessary for the actual movement; receives info directly from 2 other levels; includes the sensorimotor cortex, cerebellum, & brainstem; includes thalamus & parts of basal nuclei
What molecule can be used by muscle to recharge ADP into ATP during short intense bouts of exercise?
Creatine phosphate
Comparing the states of cross-bridges in resting smooth & skeletal muscle fibers
Cross-bridge heads in both types have ADP & Pi attached & are energized in preparation for a power stroke
Event that occurs at actin during excitation-contraction coupling
Cross-bridges bind to this protein, which generates contraction force
The progressive change in the size of a skeletal muscle caused by destruction of motor neurons that activate it is called _____ _____.
Denervation atrophy
The thin filaments in smooth muscle cells attach either to regions of the plasma membrane or to protein structures called ___ ____.
Dense bodies
The info determined by a motor program is transmitted via ______ to the level of the motor control hierarchy.
Descending pathways
Synergistic muscles
Different muscles which cause the same movement around a joint when contracting
Characteristics of single-unit smooth muscle
Display pacemaker activity; respond to stretch; many gap junctions
When cross-bridges cycle & a muscle shortens, what gets less?
Distance b/w Z-lines, width of the H-zone, & width of the I-bands
Exemplifies antagonistic muscle pairing
During sprinting, the quadriceps muscle group extends the knee and the hamstring muscle group flexes the knee; flexion of the arm by the biceps & extensions of the arm by the triceps
Correct statements about myosin
Each globular myosin head has a binding site for actin & 1 for ATP; each myosin head acts as a myosin ATPase enzyme; at rest, each globular myosin head is not attached to actin
What type of contraction is most likely due to muscle soreness & the inflammatory response?
Eccentric
Event that occurs at tropomyosin during excitation-contraction coupling
Elongated protein keeping cross-bridge binding sites blocked when cytosolic Ca is in low concentrations
Local level functions
Enacts the motor program in regards to specific joint angles & muscle tension generated; provides sensory afferent input about movements taking place; includes afferent neurons w/ their associated sensory receptors; includes levels of brainstem & spinal cord from which motor neurons exit
When the contraction of a muscle increases the angle b/w 2 articulated bones, it is called...
Extension
True or false: In the absence of ATP, cross-bridges will repetitively go through their cycle of binding, rotating, and unbinding from actin.
False
At lighter loads, the distance shortened is _____.
Farther
Succinylcholine
Fast acting (1 minute), short-lived (7-8 minutes) drug acts as an agonist to the ACh receptors & produces a depolarizing/desensitizing block similar to AChesterase inhibitors, thus immobilizing certain skeletal muscles during certain surgical procedures
Local level structure
Final common pathway out of the CNS
In smooth muscle... - Proliferation cannot occur thru mitosis - Cross-bridge cycle is faster than skeletal - Force generation depends on cross-bridge cycle - Range of optimal lengths is narrower than in skeletal - Cross-bridge cycle depends on actin phosphorylation
Force generation depends on cross-bridge cycle
Highest level functions
Forms complex plans related to one's intention to move; includes brain areas involved with memory & emotions; communicate w/ other levels via command neurons; includes sensorimotor cortex & areas involved with motivation
A sustained muscle contraction produced at higher action potential frequencies, with no force oscillations, is referred to as _____ _____.
Fused tetanus
What monitors whole-muscle tension?
Golgi tendon organ
What changes occur during concentric contraction of striated muscle sarcomeres?
H zone & I band get smaller; Z lines gets closer together; filament lengths are unchanged
The slowest contractions would occur at the _____ loads.
Heaviest
The myosin molecule is composed of 2 larger polypeptide ______ chains & 4 smaller _____ chains.
Heavy; light
Hormones that promote whole-muscle strength/growth
IGF-1 & androgens
Middle level of hierarchy receive...
Input from command neurons, afferent info from receptors in muscle, tendons, joints, skin, & vestibular apparatus & eyes
Local interneurons in spinal cord
Integrate central w/ local signaling Coordinate complex movements Local on/off switches
Characteristics of fast-oxidative-glycolytic (type IIa) fibers
Intermediate diameter, intermediate glycogen content, intermediate resistance to fatigue, high myoglobin, fast twitch rate
Muscle stretch
Intrafusal & extrafusal fibers elongated; stretch receptors fire at a higher frequency
Extrafusal fiber contraction
Intrafusal & extrafusal fibers shorten; stretch receptors become less & less active --> eventually signal disappears
Alpha-gamma coactivation
Intrafusal fibers elongate while extrafusal fibers shorten; prevents intrafusal muscle fibers from going completely slack during whole-muscle contraction; maintains afferent signaling during contraction
Titin is...
Is anchored into the Z disk; is bound to the thick filament; is responsible for elastic recoil of muscles after contraction
In skeletal muscle fibers, ATP...
Is used for Ca transport back to the SR; binding to myosin ATPase induces conformational changes that break the actin & myosin bond; is used by myosin ATPase to energize the myosin cross bridge
Creatine phosphate...
Is used to convert ADP into ATP
The shortening velocity is 0 when the load is = to the maximal _____ tension.
Isometric
What term describes a skeletal muscle contraction in which the muscle changes length while the load on the muscle remains constant?
Isotonic
What best defines the A bands in striated muscle?
It's the region that contains thick filaments
Characteristics of fast-glycolytic (type IIb)
Large diameter, high glycogen content, low resistance to fatigue, low myoglobin, fast twitch rate
A condition of smooth muscle in which persistent cytosolic Ca results in slow ATP hydrolysis & sustained tension is known as the _____ state.
Latch
Actions that require concentric contractions
Lifting your textbook off the desk & climbing up the stairs
The enzyme that dephosphorylates myosin & thus causes relaxation in smooth muscle cells is called myosin _____-_____ ______.
Light-chain phosphatase
The fastest contractions would occur at the _____ loads.
Lightest
The exact motor neurons to be activated for achieving a desired action are determined at the _____ level of the motor control hierarchy.
Local
What innervates motor neurons?
Local interneurons
At heavier loads, the latent period is _____.
Longer
What type of exercise is most likely to produce an increase in mitochondrial density in muscle fibers & an increase in the # of capillaries around the fibers?
Low intensity, long duration
The ____ ____ is a feature found at the center of a sarcomere, & is composed of protein filaments that interconnect neighboring thick filaments.
M line
Myosin...
Makes up the thick filament of the sarcomere, is a protein involved in muscle contraction
Intrafusal fibers
Modified skeletal muscle fibers w/n muscle spindle apparatus
The neurons whose axons innervate skeletal muscle fibers are known as ______ neurons.
Motor
Events that occur during a monosynaptic stretch reflex
Motor neuron stimulation; APs are conducted to spinal cord via afferent neurons; extrafusal muscle fibers contraction; stretching of spindle, distorting central region stimulating sensory neuron
What is it called when increasing # of motor units are activated, thus increasing the force generated?
Motor unit recruitment
Which of the following is NOT one of the four functions of ATP in skeletal muscle? - Energizing of the cross-bridges during splitting of ATP into ADP & Pi - Binding of ATP to myosin cross-bridges makes them dissociate from actin. - Generation of Na & K gradients by the Na/K -ATPase pump. - Movement of glucose from the extracellular fluid into the cytosol by Glucose/ATPase pumps. - Active transport of Ca from the cytosol into the SR by Ca-ATPase pumps.
Movement of glucose from the extracellular fluid into the cytosol by Glucose/ATPase pumps.
The action of the Ca ATPase pumps...
Moves Ca into the SR; allows the fiber to relax; moves Ca against its gradient
What monitors whole-muscle length?
Muscle spindle
The nervous systems receives info about the length of a muscle from the ______ ____ _____.
Muscle spindle apparatus
During embryonic development, skeletal muscle fibers are formed by the fusion of a # of undifferentiated, mononucleated cells known as _______.
Myoblasts
An oxygen-binding protein w/n skeletal muscle fibers known as ______ increases the rate of oxygen diffusion into the fiber & provides a small store of oxygen.
Myoglobin
Hormone that inhibits whole-muscle strength/growth
Myostatin
Which is NOT true about regulation of smooth muscle cells by autonomic neurons? The 2nd autonomic neuron releases NT onto smooth muscle. NTs are release from varicosities. Contractile activity can be increased or decreased, depending on which NT receptors are stimulated. NT receptors are found only at well-defined motor end plates.
NT receptors are found only at well-defined motor end plates.
The synapse at which activation of skeletal muscle fibers occurs is called the...
Neuromuscular junction
______ is a gas produced by epithelial cells & blood vessel endothelial cells that's one of the most common paracrine signals that induces relaxation of smooth muscle cells.
Nitric Oxide
The shortening velocity is maximal when there is ___ load.
No
The length at which skeletal muscle fibers develop the greatest isometric active tension is termed the _____ ______.
Optimal length
Which fiber classification identifies skeletal muscle fibers as having high capacity for manufacturing ATP aerobically?
Oxidative fibers
During moderate intensity exercise, most of the ATP used for muscle contraction is formed by...
Oxidative phosphorylation
Some smooth muscles have a membrane potential that spontaneously & rhythmically depolarizes to threshold & produces APs. This spontaneous depolarization toward the threshold voltage is known as a ____ ____.
Pacemaker potential
Stretch receptors are...
Peripheral ends of afferent neurons & wrap around intrafusal muscle fibers
Role of progesterone in smooth muscle activity
Prevents contraction
Oxidative phosphorylation characteristics
Produces ATP used during moderate, prolonged levels of muscular activity; requires oxygen; uses glycogen broken down into glucose during the first 5-10 minutes of moderate exercise; blood glucose & fatty acids become fuel after 10 min of exercise
Glycolysis characteristics
Produces a significant fraction of ATP during high-intensity exercise; lactic acid is a waste product; produces only small quantities of ATP for each metabolized glucose molecule; produces ATP from glucose quickly in the absence of oxygen
Role of NO in smooth muscle activity
Promotes relaxation of nervous & epithelial tissue
Sensory info regarding the position of the body in space & the location of its parts relative to one another is called ______.
Proprioception
Creatine phosphate characteristics
Rapid means of forming ATP during the first few seconds of muscle contraction; reaction is catalyzed by creatine kinase; very rapid, requiring only a single enzymatic reaction; allows time for the other 2 pathways to increase their ATP production
Oxidative muscle fibers containing large amounts of myoglobin are sometimes referred to as (red or white?) muscle fibers?
Red
Higher centers structure
Regions of the brain involved with memory, emotion, & motivation
Role of NE in smooth muscle activity
Relaxes airway muscles, contracts blood vessels
Stretch reflexes serve to...
Return a muscle that has changed length back to its original length
Event that occurs at sarcoplasmic reticulum during excitation-contraction coupling
Ryanodine receptor in its membrane allows Ca to flow into cytosol
Which is NOT true about slow-oxidative skeletal muscle fibers? - SO fibers have substantial glycogen stores - Have lots of mitochondria - Depend strongly on O2 to get ATP - Tend to be high in myoglobin - Use creatine phosphate for the 1st few seconds of activity
SO fibers have substantial glycogen stores
What do skeletal muscles contain that smooth muscles do not?
Sarcomeres
"Pacemaker" potentials
Self-generated oscillations w/o input from other things; can trigger APs w/ each wave
A muscle will ______ (shorten or lengthen?) if the tension it develops is greater than the load on it.
Shorten
At heavier loads, the duration of the movement of the load is ____.
Shorter
Smooth muscles that have numerous gap junctions & contract as 1 group are referred to as ____ ____ smooth muscles, while _____ smooth muscles have few if any gap junctions & require direct nerve stimulation
Single unit; multiunit
Term that refers to a type of smooth muscle in which cells are connected by gap junctions & undergo synchronous contractions
Single-unit
What type of muscle is multinucleate, with unbranched, striated fibers?
Skeletal muscle
Some smooth muscle cells have regular periodic fluctuations of membrane potential due to regular variations in depolarizing & repolarizing ion fluxes across the membranes. These fluctuations, which do not always bring the membrane to threshold, are called ____ ____.
Slow waves
Skeletal muscle fibers containing myosin with low ATPase activity are classified as _____, also called _____ fibers.
Slow-twitch; type 1
At heavier loads, the velocity of shortening is _____.
Slower
Characteristics of slow-oxidative (type I) fibers
Small diameter, low glycogen content, high resistance to fatigue, high myoglobin, slow twitch rate
True statements about smooth muscle structure
Smooth muscle thin filaments lack the regulatory protein troponin; there are no sarcomeres; the plateau of the length-active tension curve occupies a much broader range in lengths in smooth muscle than it does in skeletal muscle; smooth muscle cells have single nuclei & have the capacity to divide throughout the lifetime of an individual
In some smooth muscle cells, the cytosolic Ca concentration is sufficient to maintain a low level of basal cross-bridge activity in the absence of external stimuli. The resulting constant low level tension is referred to as...
Smooth muscle tone
Inputs that can activate contraction in the various types of smooth muscle cells
Spontaneous electrical activity in the plasma membrane of the muscle cell; stretch; NTs release by autonomic neurons; hormones
Characteristics of skeletal muscle
Striated & multinucleate
Muscle soreness resulting from extensive use following a period of relative inactivity is believed to be caused by what?
Structural damage to muscle cells & their membranes
True of both concentric & eccentric contraction
Tension develops in the muscle; muscle changes length; they are isotonic contractions
Which correctly describes the relationship b/w sarcomere length & active, isometric, tetanic tensions in skeletal muscle cells?
Tension is highest at intermediate lengths, & lower when the muscle fiber shortens or is stretched from that length
There is a plateau of tension in the curve relating skeletal muscle length to its maximum isometric tetanic tension. Which of the following best describes mechanisms delineating the lower & upper limits of this plateau?
Tension is maximum from the length where an H-zone first becomes apparent to the point at which the H-zone becomes so wide that some cross-bridges cannot reach thin filaments
Where is most of the Ca stored in a relaxed skeletal muscle fiber?
Terminal cisternae of SR
Middle level structure
Thalamus, basal nuclei, & sensorimotor cortex
What is most closely associated with the conformational change of the cross-bridge head that moves the thin filament?
The dissociation of ADP & Pi from the cross-bridge head
Why does the shortening velocity decrease as the load increases in an isotonic twitch contraction?
The increased load decreases the overall rate of ATP hydrolysis
False statements about smooth muscle structure
The mechanism of muscle shortening in smooth muscle involves shortening & widening of the thick & thin filaments; smooth muscle cells are typically 10-100 microns in length & several cm long; dense bodies found in smooth muscle play the same role as the thick filaments in skeletal muscle sarcomeres; the relative amounts of actin & myosin are exactly the same in smooth muscle as in skeletal muscle
Which correctly describes the mechanism of the change in active force generation when a skeletal muscle fiber is activated at progressively longer lengths, beginning from its resting length?
The reduction in overlap of thick & thin filaments allows fewer cross-bridges to attach, so active force declines
How does smooth muscle differ from skeletal muscle?
The thin filaments in smooth muscle cells are much longer; the myofilaments are not associated into myofibrils; smooth muscle does not have sarcomeres
Explanation for how a shortening contraction of muscle occurs
Thick & thin filaments slide past each other as cross-bridges cycle & the sarcomere shortens
The elastic protein _____ extends from the Z line to the M line & is linked to both the M line proteins & thick filaments.
Titin
Present in the I bands of skeletal muscle
Titin, actin, tropomyosin
How is ATP used during muscle contraction?
To break the bond b/w actin & myosin, to energize the myosin heads & put them into position, to fuel the pumps that move Ca back into the SR after contraction
What regulatory protein that's critical for the function of skeletal muscle is absent in thin filaments of smooth muscle?
Troponin
True or false: the latent period of an isotonic twitch contraction is longer than the latent period of an isometric twitch contraction.
True
When tropomyosin is removed from binding sites on actin, energized cross-bridges automatically bind to those sites. True/false
True
At low stimulation frequency, tension in a skeletal muscle fiber may oscillate as it partially relaxes b/w stimuli. This is called an____ ____.
Unfused tetanus
The swellings of postganglionic autonomic neurons that release NTs onto smooth muscle cells are referred to as...
Varicosities
Event that occurs at T-tubules during excitation-contraction coupling
Voltage-sensing protein in its membrane changes conformation during AP propagation
With reference to the load-velocity relationship in skeletal muscle fibers, under what conditions will the velocity of shortening be the greatest?
When the load on the fiber is 0
When cross-bridges cycle & a muscle shortens, what stays the same?
Width of the A-band & M-line
Stimulation of nociceptors in the skin of a limb activates flexor muscles & inhibits ipsilateral extensor muscles, a negative feedback loop that's a component of a reflex called the ______ reflex.
Withdrawal