Skeletal muscle Flashcards
Definition of terminal cistenae
Areas of sarcoplasmic reticulum of muscle cells surrounding T tubules, store Ca, release it when action potentials down T tubules
Types of muscle
Skeletal
Cardiac
Smooth
Properties of skeletal muscle
Large fibres, multinucleate cells
Striated
Properties of cardiac muscle
Small fibres, uninucleate
Striated
Joined in series by intercalated discs
Properties of smooth muscle
Small fibres
No striations
Describe the sarcoplasmic reticulum and T system
Arranged as repeating networks around myofibrils
Terminal cisterna, surround T tubules, store Ca2+ from ryanodine receptors and release when membrane depolarized
When membrane depolarized, voltage sensor proteins activated
T tubules and adjacent cistern form triad
Function of nebulin
Acts as a template for actin filaments
Function of titin
Extends from Z to M
During relaxation, generates passive tension through extension when sarcomere stretched
Functional stages of sarcomere, resting stage
Some interdigitation between actin and myosin
Functional stages of sarcomere, contracted stage
Increased interdigitation
Concentric contraction
Functional stages of sarcomere, stretched stage
No interdigitation
H and I bands are wide
A band always remains
Eccentric contraction
Innervation, initiation of contraction
Each muscle fibre needs to be innervated, electrically separated
Acetylcholine released from motor end plate, bind to voltage gated Na+ channels
Na+ channels open, Na+ enters cell
Depolarization spreads over membrane via T tubules
Voltage dependent Ca channels in T tubules open => Ryanodine receptors on SERCA open
Ca2+ released into sarcoplasm, binds to troponin complex, tropomyosin changes, myosin head can teach contract
Contraction cycle,
Detachment of myosin from actin
ATP binds to myosin => link between myosin and actin weakens => crossbridge detaches
Contraction cycle, recovery stroke
ATP => ADP and Pi
Myosin head moves backwards and binds to actin
Crossbridge forms
Contraction cycle, power stroke
Pi is released => initiates the power stroke
Actin is pulled towards the M line
ADP leftover is released
Effects of force generation in the contraction cycle
Increases binding affinity
Myosin head generates force, straighten up, forces thin filament=power stroke, sarcomere shortens
Comparison of action potential to the twitch
Action potential is considerably shorter than twitch time
Effects of summation of Ca2+
Frequency of twitch occurs at faster rate than Ca2+ can be removed
If Ca2+ not removed, muscle cannot relax fully between twitches
Increase in Ca2+, exposes more myosin binging sites on actin, increases cross bridges, increases tension
What happens when muscles relax
Ca2+ removed into sarcoplasmic reticulum by ATPase
Ca2+ conc decreases, released from troponin, tropomyosin to recover
Crossbridges release and muscle relaxes
Function of T1 oxidative fibres
Sustained cont
Posture
Function of T2A glycolytic/oxidative fibres
Phasic movements
Walking
Function of T2B glycolytic fibres
Phasic movements
Jumping, quick
Speed of development of max tension in T1 oxidative fibres
Slowest
Speed of development of max tension in T2A oxidative/glycolytic fibres
Medium
