Skeletal Muscle Flashcards
Titin
large elastic proteins that anchors myosin to Z lines-help stabilize the centering of MYOSIN in the sarcomere.
Nebulin
elongated INELASTIC protein that is attached to Zlines and assists in anchoring ACTIN to Z lines
alpha actinin
protein that bundles actin into parallel arrays and anchors actin to z lines
tropomodulin
protein that caps the free end of actin and regulates its length
myomesin
myosin-binding protein that holds myosin in register at the M line- forms several distinct stripes on either side of the M line
Desmin
intermediate filament that forms a lattice around the sarcomere at the level of Z lines-stabilizes myofibrils by attaching Z lines to one another and to the plasma membrane.
Dystrophin
Links laminin (residues in external lamina of muscle cell) .
what happens when there is an absence in Dystriopin?
Associated with progressive muscle weakness (Duchenes’s muscular dystrophy)
-encoded on X chromosome; affects primarily in males
Transverse Tubules in skeletal muscle
present at A-1 junction (2 per sarcomere)
sarcoplasmic reticulum. Function and features
- endoplasmic reticulum of muscle- generally lack ribosomes
- role is to release to calcium
- many calcium pumps
Specialized cisternae
form triads with T-tubles:TC+T+TC
What are the steps of sliding filament model
1.)excitation initiated by synapses (Ach)
2.)action potential propagates along sarcolemma and t tubules
3.)calcium released by terminal cisternae into sarcoplasma as a result of voltage-sensor proteins depolarizing and stimulating opening calcium channels in terminal cisternae
4)Calcium binds troponin-C,
5)Myosin/actin bind together weakly (binding has 2 effects..)
6)conformational change in myosin head, exposing ATP binding site-ATP BINDS TO MYOSIN
7)Binding releases myosin from actin
8)ATPase portion of myosin head cleave ATP
ATP-> ADP +Pi, myosin uses energy to recock for the next cycle
9)tropomyosin slides back over myosin/ actin binding site-troponin returns to its pre-contraction position
When calcium binds troponin what happens with myosin?
causing TnI to dissociate from actin molecules, allowing troponin complex uncover myosin-binding sites on the actin molecules
Myosin/ actin binding together weakly has What 2 effects ?
1) myosin affinity for actin increases
2) cocked myosin head moves actin along the thick filament, generating power stroke of muscle contraction- ADP is lost during this stage
Without ATP what happens?
actin and myosin will remain bound (rigor Mortis)
where is alpha motor neuronal axons located? what is its function?
ventral horn of spinal cord gray matter
- supply a muscle cell
- motor unit: alpha motor neurons and all the muscle cells it supples
- schwann cells
- motor end plate
How is Ach used in muscle?
Ach binds to Ach receptor muscles. This causes Na+ to open up, which causes the plasma membrane to be depolarized. this will cause voltage Ca2+ channels to open
neuromuscular spindle (aKA proprioceptor)
- SENSORY structure located in skeletal muscle
- detects degree of tension in the muscle
- sphindle consist of specialized muscle fibers, nuclear bag and nuclear chain fibers collectively
Extrafusal fibers
normal skeletal muscle fibers
-alpha motor innervation
Intrafusal fibers (muscle spindle)
contain nuclear bag fibers, nuclear chain, ,modified muscle cells
- modified muscle cell (part muscle can contract)
- part sensory receptor (sense length, tension, velocity/rate)
What is the difference between nuclear bag fibers and nuclear chain fibers?
Nuclear bag fibers are thicker: multinucleated region is expanded while nuclear chain fibers contain multiple nuclei in a row
What is a modified muscle cell?
- Part muscle (myofibrils can contract)
2. part sensory receptor (sense length, tension, velocity/rate)
primary afferent fibers
- detect length and rate of contraction
- ends are called Annulospiral Endings
- wrap both bag and chain fibers
secondary afferent fibers (length)
- flower spray endings
- mostly chain fibers
Gamma motor neurons
(are the efferent nerve fibers to intrafusal fibers)
- contain a gamma motor end plate
- innervate intrafusal fibers and regulate their tension; SENSITIViTY
- Motor portion: permits intrafusal fiber contraction-maintains length/tension relationship with extrafusal fibers
What makes the the cardiac muscle striated?
Due to myofilament arrangement similar to skeletal muscle.
Developing cardiac muscles don’t form what?
anatomical syncytium
To form long fibers, cardiac muscles are attached end to end by intercalated disks forming what?
functional syncytium
How does cardiac muscle differ from skeletal muscle in morphology?
-Nucleus: large with blunt ends; are centrally located
-More mitochondria and found within myofilaments
-fibers: often branch instead of straight fibers
T-tubles are at the Zline
-intercalated disks
-sarcoplasmic reticulum: less extensive
-terminal cisternae: much smaller than skeletal muscle
-t-tubles form dyads at Z-lines. T-tubules are much larger than those found in skeletal muscle-one T-tubule per sarcomere in cardiac muscle.
-calcium comes from outside the cell.
What is unique about smooth muscle compared to striated muscle?
slow in comparison and energy efficient
What type of stimuli induces smooth muscle contraction besides alteration of calcium muscle?
- hormones (oxytocine)
- nerve impulses
- stretch
What role does caveloe play in smooth muscle?
sequestering calcium-equivalent to t-tubules of striated muscle
What is the ratio of actin:myosin in smooth muscle and striated muscle?
smooth: 12:1
striated: 6:1
What can smooth muscle synthesize?
collagen and elastin
what are dense plaques?
pivot points for contraction
smooth muscle has no
troponin and tubles
Muscle fibers are composed of what?
myofibrils
myofibrils
longitudinally arranged bundles of thick and then myofilaments.
myofilament
actin and myosin filaments.
A band
contains actin and myosin filaments-defined by length of myosin. (constant length-does not change length)
I band
contains only actin (variable length)
H band
contains only myosin (variable in length)
M-line
myosin attachment line
Z-line
sarcomere boundary-actin attachment line. z-lines contain alpha actinin, proteins that anchors actin to z-lines
sarcomere
basic functional unit. portion of myofibril between 2 adjacent z lines
What are the components that make up actin
-G:actin (monomer)
-F:actin (polymer of G-actin. forms double helix
-tropomyosin: double helix of 2 polypeptides
-Troponin: (3 subunits)
Tn-C:binds calcium
Tn-I: inhibits actin/ myosin binding
Tn-T: binds troponin complex to tropomyosin
what are the myosin components
- heavy meromyosin (S-1 binds actin)
- light meromyosinbinds to other myosin molecules.
- myosin myofilament consists of multiple myosin molecules linked together.
What changes with contraction
H and I band (shorten) during contraction
A band remains the same
cell to cell cohesion made of what type of junctions in cardiac cells
fascia adherens
macula adherens
gap junctions
