L5: Physiology of Muscle Contraction Flashcards
how does troponin work
1) 4 calcium ions bind to troponin C
2) in heart TnC only binds to 3 Ca2+
3) causes troponin to change its conformation
4) Conformational changes in troponin shut off TNI
5) Tropomyosin-troponin leaves F-actin groove and unmasks the myosin binding site on actin
6) Next myosin heads make cross bridges cycling to actin
7) myosin breaks down Atp
8) myosin pulls thin filaments
what does the significance of the total TNI marker
Total TnI = marker for total muscle breakdown
what does the cardiac TNI signify
Cardiac TnI = marker for myocardial infarct
describe cross bridge cycling
contraction depends on the binding of myosin heads to thin filaments at specific sites
-In resting state of sarcomere, myosin heads are blocked from binding to actin by tropomyosin
this occupies the specific binding sites -( in F-actin double helical groovwe)
describe the relationship between force generation and sarcomere length (study slide 7)
-Increase in overlap of thick and thin filaments provide an increase in force
core memorisation of cross bridge cycling
1) myosin releases actin
2) myosin head cleaves ATP
3) Myosin head binds actin
4) power stroke performed
what occurs in rigor mortis
- Atp depleted after death
- muscle cell does not requester ca2+ into SR, so increase in cytosolic ca2+
- Ca2+ allows cross bridge cycle contraction until ATP and creatine P runs out
- w/O ATP- myosin stops just after power stroke, so actin still bound to myosin, and this ends when muscle tissue degrades in 3 days
Info on creatine
1- creatine found in muscle fibres
2- Phosphorylated to creatine phosphate
3- this is how energy is stored in the muscle
what occurs to creatine phosphate during cross cycling
When cross bridge cycling hydrolyses ATP to ADP + pi, creatine phosphate donates a high energy phosphate to ADP restoring it to ATP
ATP levels must be kept stable - buffering and regeneration
the reaction is catalysed both ways by creatine phosphokinase
difference between creatine and creatinine
Creatine is a small molecule that can accept high energy phosphate bonds from ATP
- creatine-phosphate is the above molecule after phosphate has been added to it
-creatinine is a diagnostic marker for kidney function
and is the breakdown product of creatine
what is CPK a biomarker for
Muscle destruction
detected by antibodies
describe the calcium gradients
there are 2 calcium gradients;
- extracellular vs cytosolic free calcium
- SR vs cytosolic free calcium
It is the efflux of calcium from the SR to the cytoplasm that provides most of the calcium
the depolarisation of muscle
1- ACh leads to muscle depolarisation
2- active nicotinic AChR leads to net inward current
3- depolarisation spread via T-tubules
4- local action potentials trigger calcium efflux from terminal cisternae across membrane of sarcoplasmic reticulum into fibre cytoplasm
describe E-C coupling
Ryanodine receptor (RyR)
in SR membrane releases ca2+ from SR triggered by voltage sensor on ca2+ channel
SERCA in SR membrane pumps ca2+ back into SR and requires ATP
what is the molecular basis of tetany
- single AP leads to calcium release from SR which leads to twitch
- Ca2+ ions are rapidly pumped back into SR leading to the end of twitch
- Frequent Aps lead to insufficient calcium resequestration and summation of contraction
study slide 16
how was it
what are the 2 main types of muscle fibres
1- slow twitch (type 1 red oxidative, small diam, )
high myoglobin, many mitochondria
2- fast twitch (type 2 white- non- oxidative wide diam lower myoglobin, increases energy from glycolysis
what are the differing properties of the fibres
- aerobic vs anaerobic
- faster calcium reuptake
- maximum tension produced
fatigue resistance
what are the basis of muscle fibre type
Slow -fast
type 1 2A 2X 2B
how are the fibre types distributed -ie
Soleus= 80% type 1 (slow), 20% type 2A
vastus lateralis = mixture of type 1 2A and 2X
study slide 20
how was it
what are the 3 types of muscle coordination
Motor Units
Recruitment & size principle
Tetany
Fusion of myocytes into long myofibres
define motor units
a single alpha motor neuron and all muscle fibres it innervates
functions as a single contractile unit of skeletal muscle
all muscle fibres in a single motor unit are of the same type
describe motor units in large muscles
-responsible for large muscle contractions that are powerful and synapse onto 1000 fibres
describe a small muscle motor unit
Mediate precision movement- synapse onto 2/3 muscle fibres
what does the type and function of the lower motor neuron determine
The muscle fibres
what is isometric contractile force generation
generates a variable force while length of muscle remains unchanged
isotonic force generation?
generates a constant force while the length of the muscle changes
describe the sequence for force generation in muscle fibre
stage 1 : isometric- force increases, joint doesn’t move, as muscle force - force increases -ie biceps and brachioradialis
stage 2: isotonic : force remains the same, arm moves, glass moves upward in response to force- overcoming gravitational and inertia forces keeping glass on table
glass starts to rise as muscles shorten and the elbow bends and force generated by the muscle is constant as glass moves
what are the types of muscular force generation
Concentric- force during contraction - tossing a ball into air
eccentric: force during muscle elongation - catching a ball
what controls force generation
proprioception
what is the recruitment size principle
As the initial contraction occurs, more and more motor units are recruited starting with smaller ones and progressively adding larger ones
allows fine graduation of force for small movements
until it becomes contraction=isotonic
what is the difference between upper and lower MND
LMND :
- weakness
- muscle atrophy
UPMND:
spasticity and hypertonia
describe and give an example of a stretch reflex
Patellar reflex which functions for posture and balance
it controls muscle length and increases muscle force
what fibres are in sensory organs
intrafusal fibres
what fibres ae in traction organs
Extrafusal fibres
what does a lack of patellars reflex cause
westphals sign
