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Flashcards in Skeletal and Smooth Muscle Deck (65)
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the properties of muscles are:
what do these mean

contractility-ability of a muscle to shorten w/ force
excitability-capacity of muscle to respond to stimulus
extensibility-muscle can be stretched to its normal resting length and beyond, to a limited degree
elasticity-ability of muscle to recoil to original resting length after stretched


skeletal, smooth, cardiac muscle
how many nuclei? wehre is it located?

skeletal-multiple nuclei peripherally located, voluntary and involunatry (refelx only)
smooth-single nucleus centrally located, involuntary, gap junctions in vesceral smooth muscle
cardiac-single nucleus centrally located, involuntary, intercalated discs


what is one of the most important roles of CT

to mechanically transmit the forces generated by contracting muscle cells to the bones to which they are attached


where to collagen fibers in tendons insert themselves

into complex infoldings of the sarcolemma of the muscle fibers


what do muscle fibers or cells develop from? how long?

100 microns x up to 30cm long


what are satellite cells

stem cells under basement membrane


what is a myofibril

cylindrical, filamentous, bundles that consist of an end to end chainlike arrangement of sarcomeres


what is a triad

1 on each side of T tubule at AI junction of skeletal muscle
-how Ca activates muscle contraction


what is the sarcoplasmic reticulum

smooth ER in muscle, surround myofibril


what are T tubules

deep invaginations of the sarcolemma
-uniform contraction of cells


in myofibril striations, what are the darker bands
what are the lighter bands?
which decompose light

A bands (anisotropic-decompose light into 2 rays in polarized light)
I bands (isotropic, dont alter polarized light)


what is a sarcomere

z line to z line
unit of muscle contraction


what is titan

protein, coiled at rest, prevent overstretching,
-heavy, largest protein known (MW 3~10^6)
-binds z line to m line
-spans half the length of a sarcomere
-acts as a framework that lines up the myosin and actin filaments and makes the contractility machinery of the sarcomere work


what is the z line
what is the m line

-point of attachment of actin filaments
-group of myosin filaments, point of achoring myosin


what does alpha actin do

anchors actin to z line


where does dystrophin reside

just inside the sarcolemma


connectin and titan are what?



actin myofilaments slide over myosin to shorten what?
what do not change lengths?
what is responsible for skeletal muscle contraction
when do sarcomeres lengthen?
sarcomers are in _____ so contractile force is additive

actin and myosin
shortening sarcomeres


which bands narrow during contraction
which band is unchanged

H and I
A band


what are thick filaments composed of
what are thin filaments composed of

actin (mainly), troponin, and tropomyosin


what are the 2 associated light chains myosin heads have
what are 2 important binding sites on head

essential and regulatory
actin-binding and atp-binding


what are tropomyosin and troponin complex associated w/?
waht does it regulate

regulates contraction in response to calcium


thin filaments are 2 entrwined strands of waht

macromolecular subunits of G-actin (globular) joined front to back to form F-actin (fiber)


what are the 3 subunits of troponin

C-binds calcium
T-attaches to tropomyosin


In the crossbridge cycle, it starts at rest (actin/myosin interaction weak), ATP is partially hydrolyzed wehre?
when activated, what happens

myosin head (in rest cocked position but not bound to actin filaments)
-interaction is stronger and crossbridges become firmly attached


initially, the crossbridge is at a right angle but rapidly shifts to 45, what supplies energy for this step? what form is it in?

an ATP bound to each crossbridge. this ATP is in partially broken down form


what must happen for the crossbridge cycle to detach

new molec of ATP must bind to myosin head and undergo partial hydrolysis
-cycle can then begin again


what happens at rest in the effect of filament overlap on force generation

what does short muscle equal? extend muscle?

optimal force can be produced by a muscle
sarcomere aligned best (minimal overlap of actin and myosin, therefore max room to move)

short=more overlap
extend=reduced tension bc reduced overlap


tests for heart attack include blood levels of what? how does that get into the blood?

troponin -can also occur w/ sig. aerobic exercise
when cardiac muscle breaks down


what is a motor endplate

a motor neuron synapses on the sarcolemma
-entire area has sig invaginations of the plasma membrane
-infoldings are lined w ACh receptors
-axons are meylinated by schwann cells


what is a motor unit

axon brances as it courses through muscle, and each of its terminal branches innervates a single muscle fiber.
one axon per muscle cell.


postsynaptic membrane is also called what?
what is its voltage change called?

endplate membrane
-its voltage change is called the endplate potential


acetylcholinesterase is located where?

synaptic cleft and postsynaptic membrane


action potential extends down T-tubules: what are the steps

1. depolarization causes L-type voltage sensors on T-tubule membrane to open ryanodine calcium channels in SR, allowing rapid release of Ca
2. calcium binds to troponin C subunit
3. calcium pump in SR takes Ca back up


what are t-tubules purpose

to bring stimulation/signal from motor unit deep inside a muscle cell so all sarcomeres can be contracted


what is membrane depolarization caused by

binding of ACh to the Ach (nicotonic) receptors in NMJ which causes an ionic shift (bc its an ionotropic receptor)


sarcoplasic reticulum is a significant storage site for what



what does botulinum toxin interfere w/
-curare binds tightly to acetylcholine receptors but does not open channel, leading to what

acetylchoine release (SNARE protein interference)


enhancement of neuromuscular transmission is done by

eserine, an ACh-esterase inhibitor, leaving ACh in the synaptic cleft longer, promoting muscle contraction


what does myasthenia gravis result from
what is a possible treatment

antibodies to the ACh receptor blocking binding of ACh to muscle receptors
-pt first present ptosis
-eserine is a possible treatment for MG, allowing more/longer period of ACh in synaptic cleft to compete w/ antibody ACh receptor binding


waht does a twitch result from

single action potential
-force low bc its brief


in temporal summation of twitches from indiv action potentials, what do skeletal muscles want to do?
if a second stimulus is given during relatation from the 1st, what happens?
when a second stimulus closely follows 1st, what happens?
if stimuli are given repeatedly and rapidly, the result is a sustained contraction called what?

temporally summate the force of contraction

additional force is developed

force and duration of twitch increases

tetanus-a form a temporal summation


what does organization of motor units allow of the msucle?

partial activation


if muscles adapted for fine and precise control, only a few muscle fibers are associated with what?

a total force of a muscle is determined by what?

as more motor units are activated, what happens..

a given motor unit

the number of motor units active at one time

force increases


what is isometric muscle contraction

what is isotonic muscle contraction

muscle prevented from shortening-pulls against attachments and develops force
-muscle is stimulated but length doesnt change
ex. martial arts and yoga

muscle can shorten and exert a constant force while doing so (work = load x dist)
-allows for muscle shortening with stimulation
ex. weight lifting


what are teh 3 muscle energy sources

creatine phophate
-during rest, stores energy to synthesize ATP
-when creatine is drained, use:

anaerobic respiration
-occurs in absense of oxygen and results in breakdown of glucose to yield ATP and lactic acid
aerobic respiratoin
-only in presense of oxygen, produces more ATP/energy than aerobic


what is slow twitch :
why is it red?
what kind of muscles here?
how is the crossbridge cycle?
what kind of diamter fibers?
engage in what kind of resp more efficeintly?
how is the ATPase breakdown?

dark meat, red bc of myoglobin (pigmented oxygen carrying muscle protein, oxygen reserve in muscle)
-endurance muscles
-crossbridge cycle is slower in these muscles
-posture muscles: those that are contracted all the time (ex most back muscles), fatigue resistant
-smaller diameter fibers
-engage in aerobic respiration more efficiently
-ATPase breakdown slow
-low glycogen


what is intermediate twitch muscle?
-what kind of diameter
-high what capacity?
-what kind of myoglobin?

fast oxidative- endurance in trained muscles
intermediate fiber diatmeter
high anaerobic capacity
intermediate myoglobin
fatigue resistant
high glycogen


what are fast switch muscles
what color mean
mit and capillaries?

fast glycolytic, rapid intense movemtns
large diameter
low myoglobin
few mit and capillaries
fatigue prone
high glycogen


what are the steps to muscle reflexes-withdrawal

1. arrival of stimulus and activation of receptor
2. activation of sensory neuron
3. info processing in CNS
4. activation of a motor neuron
5. response by effector


what are the pain receptors

pseudounipolar neuroons of the dorsal root ganglia


where is reflex circuitry in?

all w/in the spinal cord, very fast


what are the steps to a monosynaptic, deep tendon reflex (ex. knee jerk)

1. stretching of muscle stimulates muscle spindles
2. activation of sensory neuron
3. info processing at motor neuron
4.activation of motor neuron
5. contraction of muscle


wehre does the monosynpatic deep tendon reflex occur?
wehre do afferent nuerons synapse directly on?

L3/L4 level of spinal cord



waht do muscle spindles sense in deep tendon reflex?
what do they provide data about?
they are encapsulated muscle fibers w/ what?

rate of stretch
-data about muscle length and rate of stretch
-afferent neurons (intrafusal vs extrafusal fibers_


what are intrafusal fibers
what are extrafusal fibers

gamma motor neurons (travel efferently back to spindle to reset the set point) can innervate muscle as well but mostly the spindle

alpha motor neurons (std motor neuron in ant horn of spinal cord which innervates muscle at NMJ) aka LMN


what are the 2 types of sensors w/in the muscle spindle

nuclear chain fiber-measure static length (if nothing happens, send signal)
nuclear bag fiber-thicker, sends signal of a change, ending w/ the muscle, in which the spindle is located, contracting, dynamic


what is the golgi tendon organ handled by?
what does it provide information for?

about the amont of force being generated, not the rate of change


what are the types of smooth muscle

visceral or unitary-function as a unit via gap junctions so fibers dont need to stimulate many cells ex. syncitium (single cell w/ many nuclei)
multiunit-cells act as independent units,ex. pupillary constrictor


morphology-is it striated?
cell margins have what?
what is at the ends of central nucleus?
are tehre T tubules?
what is required to initiate contractions
what kind of intermediat efilaments
cells are coupled by what?

-not striated, fusiform (actin and myosin filaments overlap giving a dense body (sm muscle equiv of a z lin) where actin filaments are anchored
-NO bc cells are small
-calcium but diff from skeletal muscle
-thick, thin, and int filaments. thin and int filaments ass w/ dense bodies (analgous to Z line) noncontractile int filaments (desmin and vimentin)
-desmosome and gap junctions


in smooth muscle contraction, what does calcium enter through?
Ca release from SR by waht?
what is Ca restored by?
Na is taken outside of the cell via what? what does this allow?

-voltage and ligand gated channels
-IP3 and Ca itself
-active transport system in SR and plasma mem (Ca ATPase) and by Na-Ca exchange
-Na/K pump, allowing the Ca/Na exchange to get more Ca out of the cell


what is contraction mediated by?
what kind of regulation?
when calmodulin binds 4 Ca ions, it associates w/ what?
what does it need to proceed?

myosin filament proteins
myosin linked regulation: thin filaments lack troponin
-w/ myosin light chain kinase (MLCK) and light chains become phophorylated
-crossbridge cycle then proceeds


what is relaxation mediated by?
-dephohsphoylated mysoin has low affinity for what?

myosin light chain phosphatase (MLCP)
-actin, so cycle terminates


biochemical relaxation mechanisms have 2: both involving what?
binding of norepinephrine activates what? what does this result in?
what stimulates guanyly cyclase? what does tihs lead to? then promote? then lead?

2nd messengers
-adenylyl cyclase, resulting in formation of cAMP, which is a promoter of relaxtion
-NO, leads to activation of cGMP-dependent protein kinase and promotes the opening of calcium-activated K ion channels leading to hyperpolarization and relaxation


NO is thought to be what

autoregulatory factor responsible for keeping retinal capillaries patent