Flashcards in Skeletal and Smooth Muscle Deck (65)
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
which bands narrow during contraction
which band is unchanged
H and I
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
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)
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?
-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?
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
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
-during rest, stores energy to synthesize ATP
-when creatine is drained, use:
-occurs in absense of oxygen and results in breakdown of glucose to yield ATP and lactic acid
-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)
-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
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
what are fast switch muscles
what color mean
mit and capillaries?
fast glycolytic, rapid intense movemtns
few mit and capillaries
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?
-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