Chapter 12 - Muscle Physiology Flashcards
What are the three types of muscle?
- skeletal muscle
- smooth muscle
- cardiac muscle
How do the types of muscle differ from each other?
differ based on:
- appearance (shape, # nuclei, striations)
- control (voluntary/involuntary)
- function
Describe the characteristics of cardiac muscle
- branched
- striated
- uninucleated
- involuntary control
Describe the characteristics of skeletal muscle
- tubular
- striated
- multinucleated
- voluntary control
Describe the characteristics of smooth muscle
- spindle-shaped
- nonstriated
- uninucleated
- involuntary control
muscle tissue consists of _________ ______
muscle cells
What is an alternate name of “muscle cell”
muscle fiber
How would you describe the organization of skeletal muscle in general
tubes within a tube
Name the skeletal muscle organization from largest to smallest structure
- skeletal muscle
- muscle fascicle
- muscle fiber/cell
- myofibrils
- myofilaments
Name the different types of skeletal muscle coverings
- epimysium
- perimysium
- endomysium
Define epimysium, perimysium, and endomysium
epimysium: surrounds entire skeletal muscle
perimysium: surrounds the fascicle
endomysium: surrounds the fiber
What surrounds a skeletal muscle fiber (hint: not the endomysium)
sarcolemma (similar to cell membrane)
What structure of skeletal muscle is surrounded by a sarcolemma and contains the sarcoplasmic reticulum (SR)?
skeletal muscle fiber/cell
What is the function of the SR?
stores Ca2+
What is the function of the sarcolemma?
surrounds skeletal muscle fiber (similar to CM)
What is the infolding of the sarcolemma and is something an AP can travel down?
T tubule
What are myofilaments, what are 2 general types of myofilaments, and how are myofilaments arranged?
Smallest structural unit of skeletal muscle; contains sarcomeres
Two types of myofilaments:
Thick filament - myosin
Thin filament - actin (+2 others)
Arrangement:
Into a sarcomere that has dark and light patterns = striations
What structural unit of skeletal muscle is arranged into a sarcomere?
myofilaments
A sarcomere is ________ a cell
NOT
Define a sarcomere. Draw and label all of the different parts of a sarcomere
Basic contractile unit of skeletal muscle that consists of thick and thin myofilaments that have varying amounts of overlap = striations (IS NOT A CELL)
Myosin is a ______ filament, whereas actin is a _______ filament. Myosin and actin are considered _________
thick
thin
myofilaments
What is the reason that skeletal muscle has striations (what are striations due to)?
overlap between thick and thin myofilaments = striations
A sarcomeres ________ can vary. It can _______ or __________
length
shorten
elongate
What area does a sarcomere cover?
the distance between two adjacent
Z-discs
Name all the bands/discs/lines found in a sarcomere
MIZAH
- M line
- I band
- Z discs/line
- A band
- H band
Describe the M line of a sarcomere
helps hold down myosin
Describe the I band of a sarcomere
100% thin filament (actin); no overlap
Describe the Z discs/lines of a sarcomere
in center/bisects I band
Describe the A band of a sarcomere
contains entire length of myosin; varying amounts of overlap with actin
Describe the H band of a sarcomere
100% myosin and in center of A band; no overlap with actin
Name only the thin filaments that make up a sarcomere
actin
tropomyosin
troponin
What type of thin filament contains myosin binding sites?
actin
Define actin (thin filament) and function
thin, consists of 2 twisted strands of actin molecules
has myosin binding site
Define tropomyosin (thin filament) and function
long, fibrous protein, intertwined with actin filament
covers up myosin-binding sites of actin when muscle is relaxed
What thin filament covers up myosin-binding sites of actin when muscle is relaxed
tropomyosin
Define troponin (thin filament)
globular protein that sits on top of tropomyosin
contains Ca2+ binding sites (contraction)
What thin filament contains Ca2+ binding sites?
troponin
What does myosin consists of? (hint: what is its general structure)
Which part interacts with the thin filament?
myosin head
hinge
tail
What contains actin binding sites and ATP binding sites?
myosin head
What binding sites does myosin contain?
actin binding sites
ATP binding sites
What happens at the actin-binding site (on myosin)?
binds to actin
(both actin and myosin binding sites interact/bind to each other)
What happens at the ATP binding site (on myosin)?
catalyzes hydrolysis of ATP (ATP -> ADP + Pi)
When ATP is present on myosin, ______ between actin and myosin -> ___________
detachment
relaxation
When ADP is present on myosin, _______ between actin and myosin -> _________
attachment
contraction
Where would you specifically find a myosin-binding site, actin-binding site, and ATP-binding site?
Myosin binding site: actin
Actin binding site: myosin head
ATP binding site: myosin head
What is the sliding filament theory?
is the sliding between thick and thin myofilaments to change sarcomere size
When a muscle contracts, __________ __________
sarcomeres shorten
TRUE or FALSE: The H band contains the entire thick filament
False, it only has a portion of it that does not overlap with the thin filament
TRUE or FALSE: The I band contains only actin
True, I band contains 100% actin
TRUE or FALSE: Actin and myosin must bind to each other when the sarcomere shortens
True
TRUE or FALSE: The length of actin shortens, but the length of myosin does not change when a sarcomere shortens
False, neither actin nor myosin length change
What filament slides toward the M line
thin filament (actin)
Which part(s) of the sarcomere shorten or change in size when skeletal muscle contracts?
H and I band shorten (HI and BYE); Distance between M line and Z discs shorten
Neither ______ or ________ change in ________ during a muscle contraction
actin (thin)
myosin (thick)
length
Why is Ca2+ necessary for skeletal muscle contraction? (What is the function of Ca2+)
Ca2+ binds to troponin, which changes it shape and position of tropomyosin shifts to expose myosin binding sites on actin filaments
Define a “cross-bridge”
Attachment between myosin (head) and actin
TRUE or FALSE: During the power stroke, myosin moves toward the M-line/center of the sarcomere
False, actin is the filament that slides toward the M-line (myosin remains stationary)
Define a “power stroke” and what is the result of such an event? What step in the Sliding Filament Throy happened immediately before and immediately after the power stroke?
Power stroke happens when Pi falls off from the myosin head and moves laterally toward the tail
Before power stroke: Pi falls off
After power stroke: ADP falls off
Regarding the cross bridge, what happens when ATP is present on the myosin head?
Myosin head will detach from the myosin binding site on actin
What happens chemically and physically/mechanically to the myosin head when ATP gets hydrolyzed?
ATP is hydrolyzed into ADP + Pi to return the myosin head to its original position
What is the Ca2+ pump and when/why would it function/operate?
Ca2+ pump located on the SR and functions to move Ca2+ ions from “cytoplasm” (sarcoplasm) back into SR -> will allow for muscle relaxation
Define the NMJ. What is usually found in this space?
Neural Muscular Junction: Synapse between motor neuron and muscle cells
ACh (NT/Ligand/Chemical)+ AChE
How does the myosin head get repositioned once ADP and Pi fall off?
ATP will bind to ATP binding site and will be hydrolyzed into ADP and Pi. This reenergizes myosin head to return to its original position
Skeletal muscle cells can have _______
AP (action potentials)
What is the goal of excitation-contraction coupling in skeletal and cardiac muscle?
release Ca2+ from SR -> contraction
What are the functions of the nicotinic ACh receptor? (What does it act as?)
- ionotropic receptor for ACh
- LG-Na+ channel
What is the RMP for skeletal muscle cells?
-70mV to -95mV
The nicotinic ACh receptor requires binding of ______ ACh molecules
2
Regarding the skeletal muscle AP graph, label the following: RMP, threshold, peak of AP, initial depolarization,rapid depolarization, repolarization, hyperpolarization, VG-Na+ channel first opens, VG-Na+ channel first closes, VG-K+ channel first open, LG-ion channel first opens
check answer on review question doc
What is an EPP and how does it get generated?
End Plate potential is the initial depolarization (analogous to EPSP)
Is generated by the influx of Na+ through the opening of the nicotinic ACh receptor (LG-Na+ channel)
What is a T tubule, DHP receptor, and Ryanodine receptor? What is the relationship between these three things?
T tubule: infolding of sarcolemma
DHP receptor: VG-Ca+ channels
Ryanodine receptors: Ca2+ release channels on SR membrane
Between all of these, an AP will travel down the T tubule and activate the DHP receptor. It is coupled with the ryanodine receptor and it will also become activated.
Regarding skeletal muscle excitation-contraction couplings, what is meant by the phrase “calcium-induced, calcium released”?
An outside source of Ca2+ is needed to flow through the DHP receptor (into the cytoplasm) to induce the release of Ca2+ out of the SR via the Ryanodine receptor
Describe how the sliding filament theory works
- skeletal muscle fiber stimulated by motor neuron at the NMJ
series of interactions occur in prior to step 2
- Ca2+ released from SR and intracellular Ca2+ concentration increases
- Ca2+ binds to troponin and troponin changes shape
- the position of tropomyosin shifts to expose the myosin binding sites on actin
- If ADP + Pi is present on myosin head, it attaches to actin (known as cross bridge)
- Pi falls off from myosin head and moves laterally toward tail (power stroke)
- power stroke causes thin filament (actin) to slide along thick filament (myosin) and moves thin filament toward center of sarcomere
sarcomere shorten and whole skeletal muscle tissue contracts
- ADP falls off after power stroke -> ATP binding site now empty
- New ATP binds to myosin head -> detaches from actin
- ATP hydrolyzed into ADP + Pi -> reenergizes myosin head to return to original position
- Ca2+ transported back to SR via Ca2+ pump (for relaxation purposes)
What falls off AFTER power stroke?
ADP
What happened to the myosin head to cause it to perform the power stroke?
Pi fell off from the myosin head -> power stroke
How does the myosin head get reenergized to return to its original position?
ATP binds to empty ATP binding site on myosin head and hydrolyzed into ADP + Pi = reenergized to original position
What is the value of threshold for an AP of skeletal muscle cells?
-65mV
Explain excitation-contraction coupling in skeletal muscle
- AP reaches axon terminal of motor neuron (NT vesicles fuse as a result of influx of Ca2+ due to opening of VG Ca2+ channel)
- ACh released into NMJ
- ACh binds to nicotinic ACh receptor on sarcolemma of skeletal muscle cell
(receptor + channel) - Na+ diffused into skeletal muscle cell -> initial depolarization (EPP)
- Once EPP reach threshold (-65mv) -> VG-Na+ ch. open -> more Na+ diffuses in = skeletal muscle cell AP STARTS
- AP travels along sarcolemma down to the T tubules
- AP activated DHP receptors (VG-Ca2+ channels) on T tubules
- extracellular Ca2+ diffuses in -> intracellular Ca2+ increases
- activation of DHP receptor activates its coupled receptor, Ryanodine receptors (Ca2+ release channels) on SR membrane
- Ca2+ diffuses out of SR and into cytoplasm (process known as Ca2+ induced Ca2+ released mechanism)
- intracellular Ca2+ increases and initial Ca2+ triggers more Ryanodine receptors to open via positive feedback
- Ca2+ that was released from the SR (intracellular) will bind to troponin and initiates contraction (sliding filament theory)
CA2+ USED FOR CONTRACTION COMES FROM SR NOT EXTRACELLULARLY
What happens to skeletal muscle if the nicotinic ACh receptor is blocked? What happens if the VG-Ca2+ channels are blocked?
Both would lead to no contraction of skeletal muscle
(Na+ cannot flow through nicotinic ACh receptor to begin EPP and Ca2+ cannot flow through VG-Ca2+ channels to initiate Ca2+ induced, Ca2+ released mechanism -> no contraction)
VG-Ca2+ channels in skeletal muscle cells are also known as…
DHP receptors
What is Acetylcholinesterase, what is its function, and where is it present?
AChE is an enzyme that degrades ACh to decrease [ACh] at the NMJ -> relaxation
What are the ways in which skeletal muscle relaxes?
- ryanodine receptors inhibited via negative feedback (bc of high intracellular Ca2+) to stop release of Ca2+ via SR
- Ca2+ pump (on SR) pumps cytoplasmic Ca2+ back into SR
- use AChE (acetylcholinesterase) to clear out/degrade ACh at the NMJ
A __________ in Ca2+ in skeletal muscle will lead to relaxation
decrease
What is rigor mortis? (just define it)
rigidity or stiffness of the body after death that peaks at about 10-12 hours after death
What is rigor mortis caused by?
due to prolonged contraction (lots of Ca2+) of skeletal muscle because once someone has passed, no ATP is made, so the myosin head cannot detach from actin. Therefore, the cross-bridge cannot break and Ca2+ cannot be pumped back into SR (both require ATP). Body will remain in contracted state
What types of muscle(s) are controlled by the SNS (somatic NS) and ANS (autonomic NS)?
SNS - skeletal muscle
ANS - smooth and cardiac
Where is smooth muscle found in the body?
DRUBB
- digestive organs
- reproductive tracts
- urinary tracts
- bronchioles
- blood vessel walls
TRUE or FALSE: Smooth muscle have actin and myosin arranged into sarcomeres
False, thick and thin filaments in smooth muscle are NOT arranged into sarcomeres
Structurally, how is smooth muscle different from skeletal muscle
- Thin and Thick filaments are NOT arranged into sarcomeres
- Actin is attached to dense bodies (in skeletal muscle actin is attached to Z discs)
- No troponin (Ca2+ binds to Calmodulin instead -> Ca2+-Calmodulin complex)
- Few/no SRs
- Caveoles (shallow infoldings) instead of T tubules
- No NMJ
Because smooth muscle does not have troponin, what does Ca2+ bind to?
binds to calmodulin to form Ca2+-Calmodulin complex
Ca2+ from the __________ environment leads to contraction in smooth muscle
extracellular (comes from Ca2+ diffused from VG-Ca2+ channels)
Ca2+ from the __________ environment leads to contraction in skeletal muscle
intracellular (comes from the Ca2+ released from SR via RyR)
Why don’t you have an NMJ in smooth muscle?
because NT are released over a larger area from varicosities of autonomic neurons
If smooth muscle have very few SRs, then what is the source of Ca2+ needed for smooth muscle contraction? What does this Ca2+ bind to?
Extracellular Ca2+ (that diffuses in via VG-Ca2+ channels @ threshold)
Ca2+ binds to Calmodulin to form the Ca2+-Calmodulin complex
Define a varicosity
Axon-like swelling of autonomic neurons (ANS) that contain and release NTs
What pathways can stimulate smooth muscle?
neuronal pathways (by autonomic neurons)
endocrine pathways (by hormones)
What are the two types of stimulation in a neuronal pathway of smooth muscle?
- extrinsic stimulation
- intrinsic stimulation
Compare extrinsic stimulation and intrinsic stimulation for smooth muscle. Provide examples
extrinsic stimulation: stimulus originates outside smooth muscle tissue
-> ex: external stimulus -> CNS -> PNS -> ANS -> PANS and SANS -> effects tissue
intrinsic stimulation: stimulus originates within the body/tissue
-> ex: enteric nervous system (GI tract; has its own NS)
What are some examples of NT that are a part of smooth muscle extrinsic and intrinsic stimulation?
ACh
Epinephrine
Nitric Oxide (NO)
Know the RMP and threshold values for smooth muscle AP graph
RMP = -60mV
Threshold = -40mV
What structure is calmodulin analogous to in skeletal muscle?
troponin
In smooth muscle, what happens at the end of RMP?
LG-ion channels open to create graded depolarization/potential
What are graded potentials?
are the initial depolarization in smooth muscle
(EPP is the initial depolarization in skeletal muscle)
Regarding smooth muscle excitation-contraction coupling, list the enzymes that can lead to contraction, and which enzymes lead to relaxation. Also, for each of these enzymes, state if it is active/inactive and phosphorylated/dephosphorylated
CONTRACTION
- Ca2+-Calmodulin
- MLCK (active)
- MLC - phosphorylated
- Myosin Phosphatase - phosphorylated (inactive)
- Rho kinase (active)
RELAXATION
- MLCK - phosphorylated (inactive)
- MLC
- Myosin Phosphatase (active)
- Myosin Phosphatase Phosphatase (active)
- Rho kinase - phosphorylated (inactive)
- PKG (active)
Describe excitation-contraction coupling in smooth muscle
- RMP is at -60mV
- stimulation -> LG ion channels open -> graded potentials
- if threshold reached at -40mV, VG-Ca2+ channels open -> Ca2+ diffuse in -> sharp rise in Ca2+
- Ca2+ binds to calmodulin -> Ca2+-Calmodulin Complex formed
- Ca2+-Calmodulin dephosphorylates MLCK (inactive) -> MLCK (active)
- MLCK (active) phosphorylates MLC (“active”) -> cross-bridge attachment -> contractoin
How does smooth muscle relax?
myosin phosphatase (active) dephosphorylates MLC -> breaks cross bridge -> relaxation
TRUE or FAlSE: Cardiac muscle is striated
True, it contains sarcomeres similar to skeletal muscle
What types of muscle(s) contain sarcomeres?
skeletal and cardiac muscle
Define gap junctions
site at which cardiac muscle cells are connected (intercalated discs) and allows for traveling of AP from one cell to another
Define myocardium
a mass of cardiac muscle cells connected to each other via gap junctions
What type of muscle(s) does not need nerve stimulation to generate an AP?
cardiac muscle
Define a pacemaker
The region (SA node) at which an AP in cardiac muscle begins; located in right atrium
Why is heart rate able to increase or decrease?
it can be influenced by ANS (SANS-increase HR and PANS-decrease HR) and hormones
