Muscle Physiology Part 1 Flashcards
They are highly specialized for the 💡conversion of chemical energy to mechanical energy by using 💡ATP (adenosine triphosphate).
These are 💡excitable cells, which have the 💡capability to produce response.
MUSCLE CELLS
The capability of muscle cells to convert 💡chemical energy to mechanical.
NOTE: - It is a characteristic of 💡skeletal muscles which differs from nerve cells.
Contraction
MUSCLE CELLS has the capacity to transmit __ along the cell membrane.
Action potential
In muscle cells, force is generated by the interaction of (1) __, a process that requires transient elevation of __.
(1) actin and myosin molecules
2) intracellular Calcium (Ca++
Skeletal muscles will not contract unless __.
Stimulated by neurons
Smooth & cardiac muscle will contract without __ but their contraction can be influenced by the nervous system.
Nervous stimulation
PHYSIOLOGIC PROPERTIES OF SKELETAL MUSCLES
Irritability / Excitability Conductivity Contractility Authomaticity Rythmicity Unitary Multi-unit
It is the ability to 💡generate an action potential.
Irritability / Excitability
It is the ability to 💡transmit action potential along the cell membrane.
Conductivity
It is the ability to convert 💡chemical energy into a mechanical response.
Contractility
THREE MAJOR TYPES OF MUSCLES:
Skeletal
Cardiac
Smooth
It is the only type of muscle that is 💡not striated.
Smooth muscle
Location of skeletal muscle.
Begins and ends in a tendon
Location of cardiac muscle.
Heart
Location of smooth muscle.
Hollow organs, blood vessels, eyes
What is the shape of skeletal muscle?
Long, unbranched, cylindrical, multinucleated (nucleus located peripherally)
What is the shape of cardiac muscle?
Cylindrical, branched/bifurcation nucleated/ mononucleated (centrally)
What is the shape of smooth muscle?
Spindle-shape, mononucleated (usually centrally located)
Gap junction/ syncytial connections is 💡only absent with what type of muscle?
Skeletal muscle
💡Innervation for the muscle cells.
Skeletal muscle: Voluntary (CNS)
Smooth and cardiac muscles: Involuntary (ANS)
What is the function of skeletal muscle?
Locomotion, Work production, breathing
What is the function of cardiac muscle?
Biomechanical pump
What is the function of smooth muscle?
Peristalsis, GIT, GUT, Respiratory
Pace maker cells is 💡only absent with what type of muscle?
Skeletal muscle
It has the ability to 💡generate impulses even without stimulation.
Pacemaker Cells
Syncytial function once stimulates one cardiac muscle cell all will contract, function as one. (once the heart is formed during fetal life, it starts its activity all throughout life, doesn’t need stimulation because
of their pace makers)
True
Pacemaker cells syncytial function (unitary smooth muscle cells present in hollow organs)
True
Sarcomere is 💡only absent with what type of muscle?
Smooth Muscle
Z-line is 💡only absent with what type of muscle?
Smooth Muscle (Dense body)
Intermediate Filaments is 💡only present with what type of muscle?
Smooth Muscle (desmin and vimentin)
Regulation of Contraction in Skeletal Muscle
Thin filament regulated
Regulation of Contraction in Cardiac Muscle
Thin filament regulated
Regulation of Contraction in Smooth Muscle
Thick filament regulated
What is the 💡Source of Calcium in Skeletal Muscle
Sarcoplasmic Reticulum
What is the 💡Source of Calcium in Cardiac and Smooth Muscle
Sarcoplasmic Reticulum and ECF
Troponin is 💡only absent with what type of muscle?
Smooth Muscle (Calmodulin)
T-tubule (Sarcotubular system) is 💡only absent with what type of muscle?
Smooth Muscle (calveolae)
T-tubule of Skeletal muscle
Triad (A and I band) less developed
T-tubule of Cardiac Muscle
Diad (Z line) well
developed
💡Excitation Contraction Coupling of Skeletal muscle and Cardiac Muscle
Electrochemical Coupling
💡Excitation Contraction Coupling of Smooth Muscle
Pharmaco-mechanical Coupling
It is the ability to 💡produce an action potential even without stimulus
Authomaticity
It refers to the 💡regularity of impulse
Rythmicity
The only 💡one nerve but supplies several muscle fibers through gap junctions
Unitary
MUSCLES PRIMARY FUNCTIONS
Generate a 💡force or 💡movement in response to a physiologic stimulus by transducing 💡chemical or electrical stimuli into a 💡mechanical response triggered by a 💡rise in free cytosolic Ca++ concentration.
It surrounds the 💡whole skeletal muscle
Epimysium
It is a several 💡bundle inside the whole skeletal muscle
Fasciculus
It is a connective tissue that 💡covers fasciculi
Perimysium
These are 💡structures inside one fasciculus, 💡building block of skeletal muscle (💡structural and functional unit); innervated by the nerve.
Muscle fibers
It is connective tissue that 💡covers muscle fiber
Endomysium
It is is a specialized region of the tendon where the ends of the muscle fibers interdigitate with the tendon for the transmission of the force of contraction of the muscle to the tendon to effect movement of the skeleton (discussed later in this section).
Myotendinous junction
What will happen if epimysium, perimysium, and endomysium go out of the muscle.
It’ll thicken and become a tendon.
ORGANIZATIONS of Skeletal Muscle
Origin Insertion Point of attachment on the far side Distal Tendons (connective tissue) Connects muscle to a bone Flexor muscle Contraction decreases the angle of joint Extensor muscle Contraction increases the angle of joint
- 💡Point of attachment closest to the spine
- More proximal
Origin
At the ends of the muscle, the connective tissue layers come together to form a __, which 💡attaches the muscle to the skeleton.
Tendon
The connective tissue layers of the tendon are composed mainly of __, and they serve to 💡transmit movement of the actin and myosin molecules to the skeleton to effect movement.
The connective tissue layers also contribute to 💡passive tension of muscle and 💡prevent damage to the muscle fibers as a result of overstretching or contraction (or both).
Elastin and collagen
fibers
These are 💡structures inside a muscle fiber made up of 💡alternating actin and myosin filaments (thick and thin filaments).
They are 💡subdivided longitudinally into sarcomeres (2 um)
Myofibrils
💡Actin and myosin filaments in muscle fiber are collectively called?
They are 💡key molecular regulators of the contraction in cardiac and skeletal muscles.
Myofilaments
They are demarcated by 💡2 dark lines (Z lines) and represents a 💡repeating contractile unit in skeletal muscle.
Sarcomere
It contains 💡thin filaments composed of actin.
Located on 💡either side of the Z line
Light band
I band
It contains 💡thick filaments composed of myosin.
Located 💡between two I bands within a sarcomere.
There is an 💡overlapping of thick and thin filaments (dark area at the end)
A band
It 💡light area in the center of sarcomere (💡inside A band) that contains 💡myosin (thick) but no actin (thin) and is 💡divided centrally by M band.
H zone/band
It is evident in the 💡center of sarcomere; critical for 💡organization and alignment of thick filaments
It signifies the 💡polarity of arrangement of myosin molecule.
M line
It is the 💡division in between myofibrils
It is a two dark lines that demarcates sarcomere.
Z line
It 💡surrounds myofibril; 💡storage and release of Calcium.
Sarcoplasmic reticulum (smooth ER)
It is the 💡cell membrane in muscle fiber.
Sarcolemma
These are 💡invaginations of sarcolemma; extracellular network.
T tubules
These are 💡portion of SR nearest the T tubules; 💡site of Ca++ release; 💡critical for contraction of skeletal muscle.
Terminal cisternae
It is critical for 💡reaccumulating of Ca++ in the SR; for 💡relaxation of muscle.
SERCA (Sarcoplasmic Endoplasmic Reticulum Ca++ ATPase)
The thick myosin filaments are 💡tethered to the Z line by cytoskeletal protein called __.
It may also serve as a 💡mechanosensory and influence 💡gene expression and 💡protein degradation in a mechanical activity–dependent manner.
Titin
Different structure associated with cell membrane of muscle:
Muscle end plate
T-tubule
Synaptic fold in motor end plate
Terminal cistern.
It is an 💡area of sarcolemma in 💡contact with nerve that thickens.
Muscle end plate
An area where there is 💡invagination of sarcolemma; 💡transmission of action potential from membrane to fiber (in cardiac muscle this is where it transmits action potential)
T-tubule
It is important because on top of it is where 💡acetylcholine receptor is located which is a 💡ligand gated channel and on the folds is where 💡voltage gated channel is located.
Synaptic fold in motor end plate
As Sarcoplasmic Reticulum approaches T tubule, it enlarges/ dilates and forms the __.
Terminal cistern
SARCOTUBULAR SYSTEM is made up of?
T System and a Sarcoplasmic Reticulum
SARCOTUBULAR SYSTEM of Skeletal Muscle
It is made up of 1 T tubule & 2 terminal cisterns = TRIAD
SARCOTUBULAR SYSTEM of Cardiac Muscle
It has also sarcotubular system but only 1 T tubule and 1 Terminal cistern = DIAD
Why does Smooth Muscle do not contain SARCOTUBULAR SYSTEM?
Because it does not have T tubule (caveolae)
- Present in 💡T tubule
- In skeletal it acts as 💡voltage sensor which is activated by voltage changes like 💡depolarization, 💡action potential, and 💡local potential. (DHP is a 💡Calcium channel except in skeletal)
- In cardiac it acts as 💡Calcium channel, if activated (during action potential) it opens and Calcium gets inside.
- L-type voltage-gated Ca++ channel
DHPR (Dihydropyridine receptor)
- Present in 💡sarcoplasmic reticulum
- Between 💡terminal cisternae and T tubule
- Responsible for 💡calcium release from muscle contraction
**Both cardiac and skeletal, have this receptor and serves as 💡voltage-gated Calcium channel
RYR (Ryanodine receptor)
Muscle Relaxation:
Relaxation of smooth muscle occurs when (1)__ below a critical level as Ca++ is pumped out of the cell or into the sarcoplasmic reticulum. Ca++ is then released from (2)__ and (3)__ removes phosphate from the myosin light chain, causing (4)__ of the myosin head from the actin filament and (5)__ of the smooth muscle.
ADP, adenosine diphosphate; ATP, adenosine triphosphate; Na+, sodium; P, phosphate.
(1) calcium ion (Ca++) concentration decreases
(2) calmodulin (CaM)
(3) myosin phosphatase
(4) detachment
(5) relaxation
- Located in 💡lumen of cisternae
- 💡Regulates calcium release
- Allows Calcium to be stored at 💡high concentration to establish a favorable efflux when stimulated
- 💡Calcium buffer
Calsequestrin
It is a 💡SH3-cysteine rich domain 3 that 💡critical for coupling of the DHPR to the RYR during excitation contraction coupling in skeletal muscle SR.
It is is not present in cardiac muscle, which relies on Ca++ influx through the sarcolemma to initiate Ca++ release from the RYR instead of the direct coupling of the DHPR and the RYR in skeletal muscle.
Stac3
- It is located in the terminal cisternae that binds both 💡RYR and 💡calsequestrin
- 💡Increases buffering capacity at the site of Ca release by anchor calsequestrin near the RYR. (Ca buffer)
Triadin, Junctin
- Binds 💡 triadin in a calcium-dependent manner
- It raises the possibility that it has a role more important than serving simply as a Ca++ buffer.
Histidine Rich Calcium Binding Protein
💡Calcium Pump, responsible for 💡re-sequestration (uptake) of Calcium back to the SR (💡2 Calcium in for 💡1 ATP Hydrolyzed)
Sarcoplasmic Endoplasmic Reticulum Calcium ATPase (SERCA)
Protein that 💡transfers from sites of Ca++ uptake in the longitudinal tubules to sites of Ca++ release in the terminal cisternae.
!! The portion of the myofibril (or of the whole muscle fiber) that lies between two successive Z disks
Sarcolumenin
Muscle Contraction:
Intracellular calcium ion (Ca++) concentration increases when (1)__ through calcium channels in the cell membrane or is released from the (2)__. The Ca++ binds to (3)__ to form a Ca++-CaM complex, which then activates (4)__. The active MLCK phosphorylates the (5)__ leading to attachment of the myosin head with the actin filament and contraction of the smooth muscle.
ADP, adenosine diphosphate; ATP, adenosine triphosphate; P, phosphate.
(1) Ca++ enters the cell
(2) sarcoplasmic reticulum
(3) calmodulin (CaM)
(4) myosin light chain kinase (MLCK)
(5) myosin light chain
Structures inside sarcomere:
A Band (Dark Band) H Zone M band I Band (Light Band) M line
In 💡relax state, H zone is?
Wider
In 💡contracted state, H zone is?
Narrower
It is is made up of only one molecule known as 💡myosin (1 long tail and 2 myosin heads, tail to tail).
Thick filament
It is important because this is where enzyme 💡ATPase (hydrolyze ATP to ADP) is located.
This is also the 💡binding site.
Myosin heads aka cross bridges
Arrangement of 2 myosin molecule is __ which forms M band
Bipolar
Myosin heads aka cross bridges is anchored in __ via cytoskeleton protein called titin.
Z-line
Thin filament is made up of what 3 molecules?
- Actin
- Tropomyosin
- Troponin
Made up of 1 molecule of 💡Globular actin (G actin) but get several in the form of filament called 💡Filamentous actin (F actin)]
Only 💡1 line (G actin), 💡whole filament (F actin)
2 F actin filaments arrange 💡helically to form 1 filament
In one filament there is a 💡groove where tropomyosin (relaxing protein) is located
Actin
Responsible for 💡inhibition of contraction
There are 7 binding sites covered by 1 tropomyosin
Tropomyosin
Where does tropomyosin found?
Found in the groove of actin and bound to troponin
What is the function of Troponin in the skeletal muscle?
Regulatory protein
It is a troponin that binds with 💡Calcium
Troponin C
in every 💡1 molecule of trop C maximum of 💡4 calcium can bind
It is a troponin that binds with 💡Tropomyosin
Troponin T
It facilitate 💡inhibition of contraction by 💡inhibiting interaction of actin and myosin
Troponin I
What is the function of 💡Tropomyosin in the skeletal muscle?
Relaxing protein
What is the function of 💡Actin in the skeletal muscle?
Contractile protein
What is the function of 💡Myosin in the skeletal muscle?
Molecular motor protein
When skeletal muscle contract, thick filament moves (1)__ and H-zone (2)__, decreases until it disappears
(1) medially
(2) narrow
There are 6 thin filaments that surround 1 thick filament (HEXAGONAL ARRANGEMENT)
True
It 💡connects/aligns/anchors 2 tails of Myosin, forming the line at the center called 💡M line
Myomesin
It binds/anchor actin with Z line
Cap Z/ Alpha actinin
💡Largest protein in the body
💡Anchors thick filament to Z line
💡Senses changes in muscle tension
💡Tensor sensing protein
Made up of folded domains because it provides elasticity to the muscle during stretching.
Important in organization and alignment of thick filament
Serves as 💡mechanosensor and influence 💡gene expression and 💡protein degradation in a mechanical activity dependent manner
Titin
Disorder with Titin
Titinopathies
💡Control/regulate the 💡length of actin/thin filament.
Found along the 💡thin filament
Aided by 💡tropomodulin
💡Elongated cytoskeletal protein
Nebulin
It 💡initiates the length of actin filament
It is located at the end of the thin filament
Tropomodulin
It is a large protein (≈480 kDa) that consists of six different polypeptides with one pair of large heavy chains (≈200 kDa) and two pairs of light chains (≈20 kDa).
Myosin
It 💡covers binding site between myosin and actin
Each tropomyosin dimer extends across 7 actin molecules
Tropomyosin Relaxing Protein
It is formed when 💡heavy chains are wound together in an 💡α-helical configuration to form a 💡long rod-like segment, and the 💡N-terminal portions of each heavy chain.
It 💡extends away from the thick filament toward the actin thin filament and is the 💡portion of the molecule that can bind to actin.
It is able to 💡hydrolyze ATP, because the 💡ATPase activity is located here.
It requires the presence of essential light chains
Myosin head
These are two pairs of light chains are associated with the globular head.
Essential light chains
Regulatory light chains
It is a light chain that is crucial for the 💡ATPase activity of myosin.
Essential light chains
It is a light chain that can be phosphorylated by Ca ++/calmodulin-dependent myosin light chain protein kinase, which can influence the interaction of myosin with actin
Regulatory light chains
This proteins found in the thick filaments may also participate in the bipolar organization or packing of the thick filament (or both).
Myomesin and C protein
💡Connects actin filament to 💡dextroglycan which provides 💡strength for the muscle (ex. laminin)
Provides 💡structural link between subsarcolemmal cytoskeleton of the muscle and extracellular matrix
💡Stabilizes sarcolemma and hence prevents contraction induced injury
DYSTROPHIN GLYCOPROTEIN COMPLEX
Cross-Bridge Cycle.
In the relaxed state (state a), ATP is (1)__ (M • ADP • Pi). In the presence of elevated myoplasmic Ca++ (state b), (2)__. Hydrolysis of (3)__ is completed (state c) and causes a conformational change in the myosin molecule that pulls the actin filament toward the center of the sarcomere. A new ATP molecule binds to myosin and causes release of the (5)__ (state d). Partial hydrolysis of the newly bound ATP recocks the myosin head, which is now ready to bind again and again. If myoplasmic [Ca++] is still (6)__, the cycle repeats. If myoplasmic [Ca++] is low, (7)__ results.
(1) partially hydrolyzed
(2) myosin (M) binds to actin (A)
(3) ATP
(4) cross-bridge
(5) partial hydrolysis
(6) elevated
(7) relaxation
