Phys: Muscle Physiology Flashcards
What is the reason for rigor mortis?
Due to loss of ATP
Skeletal muscle fibers range from _____ to _____ in diameter
10 to 80 micrometers
Each fiber is made up of…
Successively smaller subunits
The sarcolemma consists of a tru cell membrane called the ________ _____________
Plasma membrane
Each muscle fibers contains hundreds to thousands of ________
Myofibrils
Each myofibril is composed of about 1500 _______ filaments and about 3000 _______ filaments
Myosin, actin
Actin and myosin are large, polymerized protein molecules that are responsible for…
The actual muscle contraction
The myosin and actin filaments partially interdigitate and cause the myofibrils to have….
Alternate light and dark bands
Muscle fibers:
-single cells
-multinucleated
-surrounded by the sarcolemma
Myofibrils :
-contractile elements
-surrounded by sarcoplasm
___________ lie between myofibrils
Cellular organelles
_______ is the thin filament
Actin
_______ is the thick filament
Myosin
Sarcomere
Smallest contractile unit of muscle fiber
Actin _______ connects to the disc
Directly
Myosin is connected to the disc via ______
Titin (connectin)
One end of the titin molecules is _______ and attached to the Z disc. The other part of titin is tethered to ________
Elastic, myosin
In the relaxed state, the ends of actin filaments extending from two successive Z discs, ….
barely overlap one another
In the contracted state the actin filaments…
Are pulled inward among the myosin filaments so their ends overlap one another to maximum extent
Muscle contraction occurs by a..
Sliding filament mechanism
F-actin is a…
double stranded helix
F-actin is composed of…
Polymerized G-actin
What is bound to each G-actin?
ADP
What binds to the F-actin active sites?
Myosin heads
Tropomyosin covers the _____________ and prevents __________from binding
Active sites, myosin
Troponin has three subunits:
-I
-T
-C
Troponin subunit I binds ______
Actin
Troponin T subunits binds ________________
Tropomyosin
Troponin C subunits binds ____
Ca2+
What is required for muscle contraction
CALCIUM
The myosin filament is made up of 200 or more…
Individual myosin molecules
Protruding arms and heads of myosin are called:
Cross-bridges
Each cross-bridge is flexible at two points called ________
Hinges
2 hinges locations:
-where arm leaves body of myosin filament
-where head attaches to the arm
The hinged arms allow the heads to be either…
Extended far outward from the body of myosin filaments or brought close to the body
Walk-along theory steps:
- Myosin head attached to actin
- Myosin head releases (ATP bound)
- Myosin head “cocked” (ADP and Pi bound)
- Myosin head attaches to new site (ADP)
When myosin head is “cocked’ what is happening?
Head is extending perpendicularly toward the actin filament, but is not yet attached to the actin
Formation of cross-bridges is associated with…
Hydrolysis of ATP and generation of force
At rest, Tropomyosin…
Covers the myosin binding sites in actin, preventing myosin heads to bind
When Troponin-Tropomyosin complex binds with Ca2+…
The active sites on the actin filaments are uncovered and the myosin heads then bond with these sites
T-tubules are invaginations of the __________ filled with ___________
Sarcolemma, extracellular fluid
T-tubules penetrate the____________ and do what?
Muscle fiber, branch and form networks
T-tubules transmit APs…
Deep into the muscle fibers
Sarcoplasmic reticulum is made up of:
-terminal cisternae
-longitudinal tubules
Terminal cisternae form…
Junctional “feet” adjacent to the T-tubule membrane
Ca2+ is stored in the…
Sarcoplasmic reticulum
Dihydropyridine receptor (DHPR) is a _______________
Voltage receptor
DHPR opens the _____ channel on the ________________ and allows for _____ to diffuse into the sarcoplasm and initiate muscle contraction
CA2+, Sarcoplasmic reticulum, Ca2+
What is Ca2+ release channel called?
RyR
What transports Ca2+ to the sarcoplasmic reticulum from the sarcoplasm after the DHPR closes?
SERCA
Protein inside the reticulum that binds a lot of calcium:
Calsequestrin
The contractile force of skeletal muscle increases in a _______________ manner as a result of bindings _______ to __________
Ca2+ dependent manners, Ca2+ to Troponin C
At rest the Intracellular free calcium concentration is _____________, and after its release from the SR…
Less than 10 X 10 -7M, Intracellular free Ca2+ concentration increases
As load increases, the speed at which muscle can lift it __________
Decreases
As the load goes up, the contraction velocity goes ______
Down
Slower contraction gives more time for…
Cross bridges to form
Length-tension relation measures….
Tension developed during isometric contractions when the muscle is set to fixed lengths
Active tension __________ be measured directly
Cannot be
Passive tension (PT)
Tension required to extend a resting muscle by stretching the muscle to different lengths
Total tension (TT):
Active tension and passive combined. Tension developed when the muscle is stimulated to contract at different lengths
Active tension (AT):
-Different between TT and PT
-is proportional to the number of cross-bridges formed
Active tension falls away _____________ with increasing and decreasing length
Linearly
Normal length of sarcomere where there is maximum strength of contraction :
2.0 to 2.2 micrometer
Stress is used to compare _________ generated by different sized muscles
Tension
In skeletal muscle, maximal active stress is developed at…
Normal resting length
At longer and shorter lengths, stress ________
Declines
Cardiac muscle normally operates at lengths…
Below optimal length, so you can have more output
Motor unit is a…
Collection of muscle fibers innervated by a single motor neuron
Each motor neuron that leaves the spinal cord innervates multiple muscle fibers, with the number of fibers innervated depending on….
The type of muscle
Small muscles that react rapidly and must be exact have…
More nerve fibers for fewer muscle fibers
Large muscles that do not require fine control may have…
Several hundred muscle fibers in a motor unit
Force summation
Increase in contraction intensity has a result of the additive effect of individual twitch contractions
Multiple fiber summation:
-increase in the number of motor units contracting simultaneously
The size principle in muscle contraction:
Motor units are recruited from smallest to largest
Frequency summation:
Results from an increase in the frequency of contraction of a single motor unit
neuromuscular junction:
specialized synapse between a motor neuron and a muscle fiber
Neuromuscular junction occirs at a structure on the muscle fiber called the…
Motor end plate
Synaptic trough
Invagination in the motor end plate membrane
Synaptic cleft size and what it contains:
-20-30 mm wide
-large quantities of ACHe
Subneural clefts
-increases in surface area of postsynaptic membrane with ACh-gated channels at top and voltage gated Na+ channel in bottom
Ca2+ channels are localized around linear structures on the presynaptic membrane called _____________
Dense bars
In the region of dense bars,m what fuses with the membrane?
Vesicles
ACh receptors are located at ____ of subneural cleft
Top
Voltage gated Na+ channels are located in ____________ of subneural cleft
Bottom half
Acetylcholine-gated channels is a…
Cation channel that does not differentiate but there is a net movement of positive ions
Neuromuscular junction steps:
- Action potential travels down motor neuron to presynaptic terminal
- Depol. Of presynaptic term and Ca channel open and goes into terminal
- ACh is extruded into the synapse by exocytosis
- ACh binds to nictotinic receptors on motor end plate
- Channels for Na/K opened in motor end plate
- Depol. Of motor plate causes end plate potential and action potentials to be generated in adjacent muscle tissues
- ACh is degraded to choline and acetate by AChE and choline is taken back to presynaptic term on Na+ choline cotrasnporter and Hemicholinium blocks choline reuptake Rand depletes the presynaptic endings of ACh stores
*when ACh no longer bound, EPPs stops, action potentials stop, and contraction stops
At the motor end plate opening of the nicotinic ACh receptor channels produce an ______________
End plate potential
End plate potential will normally…
Initiate an AP if the current is significant to open voltage sodium channel
What terminates end plate potential process?
Acetylcholinesterase
Curariform drugs (D-turbocurarine) block _______ channels by competing for ACh binding site
nACh
Curariform drugs reduce ____________ of end-plate potential and therefore, __________
Amplitude, no AP
Curariform drugs paralyzes _________ muscles
Respiratory muscles
Botulinum toxin decreases the release of ____ from _________________
ACh from nerve terminals
Botulinum toxin has an _________ stimulus to initiate action potential
Insufficient
Botulinum toxin locally reduces…
Wrinkles
Botulinum toxin locally reduces…
Wrinkles
Botulinum toxin systemically ____________ respiratory muscles
Paralyzes
ACh-like drugs examples:
Methacholine, carbachol, nicotine
ACh-like drugs bind and activate ______________ACh receptors and are NOT destroyed by AChE
Nicotinic ACh receptors
ACh-like drugs act as ___________-
Agonists
Anti-AChE (neostigmine) blocks degradation of ______________
Acetylcholine
Anti-AChE prolong…
ACh effect contractions
Anti-AChE is used and is important in what condition?
Myasthenia gravis
Sarin is a nerve gas that is an ___________________poison that inhibits ______________ which raises ACh levels
Organophosphorus, acetylcholinesterase
Treatment for Sarin:
Pralidoxime and atropine, which reactivates acetylcholinesterase
Atropine blocks what receptors?
Muscarinic ACh receptors
Myasthenia gravis symptoms:
-weakness in skeletal muscle
-paralysis—lethal in extreme cases when respiratory muscles are involved
Myasthenia gravis is an autoimmune disease that is characterized by…
The presence of antibodies against the nicotinic ACh receptor which damages or destroys them
Myasthenia gravis causes weak _____________
End-plate potentials
Treatment of myasthenia gravis:
-ameliorated by anti-AChE
-increases amount of ACh in NMJ
-prednisone and other drugs to suppress immune system
-plasmapheresis (removal of antibodies)
Lambert-Eaton myasthenic syndrome (LEMS) symptoms:
-same symptoms as myasthenia gravis
-40% also have small lung cancer
-skeletal muscle weakness/paralysis
Cause of lambert-eaton myasthenic syndrome (LEMS) cause:
-autoimmune attack against voltage-gated calcium channels on the presynaptic motor nerve terminal
-weak end plate potential
Treatment for LEMS
-anti-AChE
-increases amount of ACh in NMJ
-chemotherapy w radiation therapy
-plasmapheresis is not effective
Smooth muscles are ______________cells with NO _____________
Mononucleate, striations
Location of smooth muscle:
-walls of hollow organs
-gut
-IRIS
-airways
-blood vessels
-urogenital system
2 groupings of smooth muscles:
-unitary or visceral
-multi unitary
Smooth muscle can operate over a large range of lengths with _________% shortening possible
60-75%
Smooth muscle can maintain force for________________via __________________
Long periods: hours, days, weeks, via latch state
Smooth muscle has ____ action potential
Ca2+
Smooth muscle has a poorly developed…
Sarcoplasmic reticulum
Exciatation in smooth muscles is transmitted by _____ action potential or _________________ into fiber.
Ca2+, dimple diffusion of Ca2+
Ca2+ can ALSO be released from the ___
SR
_____________in the terminal axons contain the neurotransmitter
Varicosities
Smooth muscle EC coupling is regulated by __________
Myosin …NOT ACTIN
In smooth muscle EC coupling the _________complex is absent
Troponin complex
What is similar in structure to Troponin in smooth muscles EC coupling?
Calmodulin
Myosin does not hydrolyze ATP in smooth muscles EC coupling unless it is _______________ on the regulatory light chain
Phosphorylated
What enzyme phosphorylates the light chain in smooth muscles EC coupling EC coupling?
Myosin light chain kinase (MLCK)
Why is the phosphorylation of the light chain in smooth muscles EC coupling Ca2+ sensitive?
MLCK is only active in the presence of calmodulin (small Ca binding protein)
Contraction of smooth muscles is initiated by…
Calcium from ECF or SR
In smooth muscle contraction, calcium binds to _____________
Calmodulin
In smooth uncle contraction, Ca-calmodulin-MLCK complex leads to the phosphorylation of the ______
MLC
MLC is apart of the __________________
Myosin head
In smooth muscle contraction, Phosphorylated myosin head binds to _______, and ____________ occurs immediately
Actin, power stroke
In smooth muscle relaxation, a second ATP is required to …
Release myosin head from actin
Smooth muscle contraction-relaxation cross bridge cycling requires both ________ and ________
MLCK and MLCP
Smooth muscle contraction-relaxation MLCP activity is regulates and can change Ca2+ _____________
Sensitivity
Calcium enters smooth muscles via:
-2nd messenger gated channels
-depolarization
-ligand gated channels
Calcium entering smooth muscle via 2nd messenger gated channels:
-hormones or neurotransmitters activate Gq receptors which make IP3
-opens Ca2+ channels on SR: IP3 gated channels and RYR
Calcium entering smooth muscle via depolarization:
-spread through gap junctions what open voltage gated channels on cell surface
-calcium can open RyR channels on SR to increase Ca more
Calcium entering smooth muscle via ligand gated channels:
-hormones or neurotransmitters open channels and let Ca2+ in
-calcium can open RyR channels on SR and can also open VGCCs
Two ways that smooth muscles can contract:
Topically and phasically
Phasic contractions in smooth muscles:
-like skeletal muscles
-single spike of Ca2+, single contraction, and relaxation
Tonic contractions in smooth muscles:
-single Ca2+ spike but maintained forces
-partially due to the “latch state” of smooth muscles myosin
Endothelial cells release:
NO - nitric oxide
Sildenafil (viagra)
-A phosphodiesterase-5 (PDE-5) inhibitor that is used to treat male sexual problems (ED)
-degradation cyclic GMP
