Lecture 12 - Skeletal Muscle Performance and Plasticity Flashcards
what are the 3 types of muscle fibres?
type I fibres
type IIB fibres
type IIA fibres
what are the 3 key differences between the fibre types?
type of myosin expressed
oxidative vs glycolytic energy production
type of SERCA pump expressed
what is effect of the type of myosin expressed?
- determines fast or slow utilisation of ATP
- alters the speed of cross bridge cycling –> fast or slow speed of contraction
- fast or slow rate of utilisation of substrate for ATP generation –> fatigue prone or fatigue resistant
what is the effect of oxidative vs glycolytic energy production?
- high oxidative activity from mitochondria can generate ATP continuously using O2 and substrates from blood but only relatively slowly (also high myoglobin)
- high glycolytic activity can generate ATP quickly from muscle glycogen but stores are limited and deplete quickly
what is the effect of the type of SERCA pump expressed?
-faster or slower clearance of Ca2+ from the sarcoplasm into the sarcoplasmic reticulum (SR) –> faster or slower drop in tension
what are muscle fibre distribution based on?
based on function
where are fast twitch muscle fibres distributed?
distributed in muscles that aren’t often used but when they are used they are rapid power producing but susceptible to fatigue
what is an example of a muscle composed of fast twitch muscle fibres?
the biceps brachii
where are slow twitch muscle fibres distributed?
distributed in muscles that are low power and fatigue resistant as these muscles are used often
what is an example of a muscle composed of slow twitch muscle fibres?
the soleus
how does strength training effect skeletal muscle?
strength training generates more actin and myosin and this increases the diameter of muscle fibres which is called hypertrophy
what is hypertrophy in terms of skeletal muscle?
increase in the size of tissues by the increase of cell size that generates more actin-myosin interactions producing more force
how does endurance training effect skeletal muscle?
endurance training increases the oxidative capacity which increases the ability for sustained activity. This is because endurance training increases the number of mitochondria (more oxidative enzymes), increases capillaries + myoglobin, increases muscle stores of lipids and increases the ability of these lipids to be used directly from the blood
what do mitochondria produce in terms of enzymes?
oxidative enzymes
what is muscle contraction in terms of tension?
muscle contraction is the generation of tension
what is isotonic contraction?
contraction where force is held constant while the muscle length changes
what is isometric contraction?
contraction where length is held constant as the contraction does not require skeletal muscle shortening
what is an eccentric contraction?
contraction where force exceeds the force of the muscle resulting in muscle lengthening
what is a concentric contraction?
contraction where the force generated by the muscle is less than the muscle force at rest so the muscle begins to shorten
what determines the amount of force skeletal muscle can generate in different types of contractions?
changes based on the length of the muscle and speed of contraction
when is the length-tension relationship of skeletal muscle performed?
performed in an isometric contraction where skeletal muscle length is fixed at set points
what is the relationship between skeletal muscle recoil and the amount of force applied?
skeletal muscle wants to naturally recoil due to its elastic properties and the more force applied increases the desire to recoil
what is passive tension?
the longer muscle is stretched it means more force has been applied to stretch the muscle further
what is the relationship between passive tension and stretching a muscle?
as you stretch a muscle you can measure greater and greater passive tension due to the elastic component of muscle causing it to act like a rubberband
what is active tension?
when you electrically stimulate skeletal muscle resulting in a twitch
what determines the size of a skeletal muscle twitch?
the length of skeletal muscle
why does the active tension curve (graph) not go all the way down to zero?
because it is hard to get skeletal muscle shorter than its resting length
what is the relationship between normal resting length of skeletal muscle and force generated from a muscle twitch?
at normal resting length you can generate the peak amount of force in a muscle twitch
what is the active tension curve due to?
due to the amount of cross bridge interactions
what allows a high velocity of muscle shortening?
if there is no external weight when shortening the muscle allowing it to occur very quickly
what does speed or velocity of muscle shortening determine?
determines how much force can be generated by the number of cross bridges
how does the nervous system regulate muscle force?
regulates muscle force by controlling activity in ‘motor units’
what is a motor unit?
a motor neuron and all the muscle fibres it innervates
what are the properties of motor units?
- all muscle fibres in one motor unit are the same metabolic type (fast or slow ATPase)
- all fibres in a motor unit activate at once
what determines the maximum force generated from a motor unit?
the size of the motor unit which is determined from the size of the motor neuron cell body depending on the number of muscle fibres in one motor unit
what is the muscle force regulated by?
regulated by changing the rate of activity in each motor unit (rate modulation/ mechanical summation) or by changing the number of units that are active (recruitment
what is the order of motor unit recruitment?
the recruitment of motor units is ordered from smallest to largest
