Lecture 1- physiology of skeletal muscle contraction Flashcards
How many Ca2+ bind to troponin C (TnC)?
4
what does tropinin C mean?
C=calcium binding
How many TnC bind in the heart muscle?
3
What is the result of Ca binding to troponin?
TnC changes confirmation
What does the conformational change in TnC to TnI and what is the result of this?
shut off TnI
tropomysin-troponin leaves F actin groove and unmasks the myosin binding site on actin
Next myosin head make cross bridges to actin- this breaks down ATP and pulls thin filaments
what is total TnI marker of and what is the cardiac TnI marker of?
total TnI- marker for total muscle breakdown
Cardiac TnI- marker for myocardial infarct
what causes the increase in force generation?
Increased overlap with thin and thick filaments
Explain the process of rigor mortis?
ATP depleted after death
muscles do not resequester Ca2+ in SR >INCREASING cytosolic Ca2+
Ca2+ allows crossbridge cycle contraction until ATP&creatine-P run out
No ATP=myosin stops just after the power stroke with myosin head still bound to actin
when does rigor mortis end?
when muscle tissues degrade- 3 days after death
Where is creatine found?
muscle fibres
what is creatine phosphorylated to and what is the function of this?
creatine phosphate
energy storage in the muscle
how is the energy stored in the creatine molecule?
high energy phosphate bonds
How can creatine phosphate help to restore ATP levels?
donates high energy phosphate to ADP restoring it ATP
which enzyme catalyses the ATP buffering and regeneration reaction?
creatine phosphokinase (CPK)
what is the CPK marker of in muscles?
muscle destruction
what are the two Ca2+ gradients?
- Extracellular Vs Cytosolic free Ca2+
2. SR vs Cytosolic free Ca2+
what is the general role of Ca2+?
triggers contraction
where does the most of the Ca2+ come from?
efflux of Ca2+ from the SR to cytoplasm provides most of the Ca2+
what is the effect of depolarisation of Ca2+ conc?
INCREASED
What is the function of Ryanodine receptor (RyR)?
In SR RELEASES Ca2+ from SR
What is the release from RyR triggered by?
voltage sensor on Ca2+ channel
what is the role of the SERCA (Smooth endoplasmic Reticulum Calcium ATPase) and what else is required?
In SR memmbrane- SERCA pumps back Ca2+ into SR and required ATP
what does excitation and contraction coupling mean?
the molecular mechanism for how the depolarisation of the plasma membrane leads to the release of Ca2+ into the cytoplasm followed by contraction.
define a twitch and how does twitch end?
A single AP—–> Ca2+ release from SR—–> twitch
Ca2+ ions are rapidly pumped back into SR- end of twitch
Define Tetany?
frequent AP—->insufficent Ca2+ resquesteration —->summation of contraction
describe the two main types of muscle fibres and explain their properties?
SLOQ twitch- (type I- Red- oxidative small daim, has myoglobin and many mitochondria
FAST twitch- Type II- white, non-oxidative and wide diam)
Lower myoglobin and increased energy from glycolysis
Explain how else the fibre type differ?
- aerobic vs anaerobic
- faster Ca reuptake (fast)
- Max tension produced
- fatigue resistance (slow)
Explain the scale of muscle fibre types from slow (type I) to Fast (IIB)?
Type I -slow- sustained
IIA-
IIX
IIB- Fast- intermittent and precise
why does muscles contain mixture of fibre types composition?
depends on the action of the muscle
what does the proportion of muscle depend on?
physical fitness Inactive moderately active endurance athlete anaerobic athlete
Name three types of motor co-ordination?
- Motor units- recruitment &size principle
- Tetany
- Fusion of myocyte into long myofibres
Define a motor unit?
A single alpha motor neuron and all muscle fibres it innervates
explain how these motor units function and their fibre types?
function as a single contractile unit of skeletal muscle ALL fibres in the single motor unit are the same type- Slow exidative etc
In large muscles, a single motor neurone synapses with how many muscle fibres?
1000 fibres
In small muscle, a single motor neuron synapses with how many muscle fibres?
2-3 muscle fibres
what does type and function of the lower motor neuron determine?
muscle fibre
Define- Isometric and isotonic in terms of force generation?
Isometric-generates a variable force while length of the muscle remains unchanged (iso-same metric length)
ISotonic- generates a constant force while the length of muscle changes
what are the types of muscular force generation?
Concentric
Eccentric
Explain the concentric and eccentric force generation with an example?
Concentric- force during contraction- tossing a ball into the air
Eccentric- force during muscle elongation- braking a car
can both types of force generation occur in the same behaviour?
Yes
what controls the force generation and what does it depend on?
proprioception- controls the force generation based on length and stretch of the muscle
explain the difference between lower motor neuron disease Vs upper motor neuron disease?
LOWER-
weakness and muscle atrophy
UPPER-
Spasticity and hpertonic
What is the function of stretch reflex?
controls muscle length
increases muscle force
What does lack of patellar reflex mean?
Aka- westphal’s sign- may indicate damage to the femoral nerve
what type of the muscle fibres are part of the stretch reflex?
sensory muscle spindle fibres which detect stretch and length and proprioception
describe the location and properties of the spindle fibre?
spindle is parrallel to other muscle fibres
ipsilateral spinal reflex
monosynaptic
describe the muscle spindle fibre?
3-12 intrafusal fibres
spindle- regulates relationship between muscle length and muscle contractility
what is the role of gamma motor neurons?
increase sensitivity
what does the absence of the Westphal’s sign mean?
receptor damage
femoral nerve damage
peripheral nerver disease
Tendon Reflex function?
protects from overloading by decreasing the muscle force—–> dropping the load
Explain the properties of tendon reflex?
sensor Golgi tendon organ detects tension in series with muscle in tendon- near the border with muscle Disynaptic Ipsilateral spinal reflex
