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