MUSCLE Flashcards
what is the definition of muscle + what does it do
- a bundle of fibrous tissue that can contract to to produce movement
what are the 3 types of muscle
- striated - locomotion and posture - voluntary
- smooth - involuntary
- cardiac
what is the epimysium
a sheath of fibrous elastic tissue surrounding a muscle
what is the perimysium
a sheath of connective tissue surrounding a bundle of muscle fibres (fascicles)
what is the endomysium
connective tissue that surrounds each individual muscle fiber
how is muscle developed in embryos - first step
muscle pattern laid down
how is muscle developed in fetus
cells fuse and myofibril production
how is the way muscle produced changed in adults
the ability to make new muscle is reduced
what type of cells are skeletal muscle fibres made from + their general structure
- fused cells
- multinucleated
- 3 cell types
-sarcolemma
-sarcoplasm
-sarcoplasmic reticulum (SR)
-transverse tubular system (TT)
what is the structure of a sarcomere
unit of contraction of the myofibril
Z-line
either end of sarcomere
thin fiaments insertion
M-line
origin of thick filaments
A-band
overlap of thick and thin filaments
I-band
only thin filaments
what is the structure of myosin and the 2 types of light chains
head - actin binding
tail - 2 intertwined heavy chains
2 regulatory light chains - ATPase activity
2 alkali light chains - stabilize myosin head
hinge - movement of myosin head
what is the role of troponin on the actin filament
blocks myosin receptors
what is the role of troponin on the actin filament
controls tropomyosin position
what is the ‘triad’ made up from
2 cisternae and 1 T tubule
how are T tubules formed
plasma membrane invaginating into muscle fibre
how is contraction initiated - 5 steps , start from when motor nerve releases acetylcholine
motor nerve releases acetylcholine
action potential travels down T tubule
sarcoplasmic reticulum releases Ca++ into sarcoplasm
Ca++ activates troponin C
myofibril contracts
how is calcium released into the sarcoplasm
- AP activates T tubule voltage gated L-type Ca++ (DHP receptor)
- couple with ryanodine receptors on sarcoplasmic reticulum
- opens channels to release Ca++ into sarcoplasm
Ca++ released into myofibril activating troponin C and cross bridge cycling
what is a DHP receptor
dihydropyridine receptor,
- normally a voltage-dependent calcium channel
what is channel coupling
when CaV1.1 receptor DHP
- undergoes a conformational change
and leads to calcium being released from the SR store
what are the 3 troponin molecules and what do they bind to
- C - binds Ca++
- I - anchors complex to actin
- t - binds to tropomyosin
how is the cross bridge cycle initiated (sliding filament model basically)
- tropomyosin blocks myosin binding site
- Ca++ binds to troponin C causing a conformational change in the troponin complex
- troponin I moves away from actin filament
- Troponin T pushes tropomyosin away from myosin binding site on actin
- myosin head binds to actin
what is the cross bridge cycle in 5 stages
- atp binding
- atp hydrolysis
- cross bridge formation
- release of Pi from myosin
- adp release
in what position is myosin originally in at the start of the cross bridge cycle
myosin head is attached to actin filament bc of power stroke from previous cycle
how is ca2+ removed from the cytoplasm
-ca2+ pump at plasma membrane
-Na-Ca exchanger (NCX)
-Ca reuptake into Sr via Ca pump
when contracting, what does the amount of force generated depend on?
no. of active muscles
cross sectional area of muscle
initial resting length of muscle
rate at which muscle shortens
frequency of stimulation
what is the lenght-tension relationship in muscles a direct result of?
the cross bridge formation
and anatomy of thick + thin filaments
why are muscles elastic (what molecule)
titin - need to double check this lol
what is the force velocity relationship between muscles
as velocity increases force decreases
