Muscular Structure & Adaptation Flashcards
differences between slow (type I) and fast (type II) twitch fibres?
slow twitch fibres:
- slow maintained contraction
- fatigue resistant
- lots of mitochondria, vascularisation and myoglobin
- oxidative, more aerobic
fast twitch fibres:
- bigger, more powerful forces for shorter durations
- fatigue quickly
few mitochondria, little vascularisation - also called white muscle - and little myoglobin
- more anaerobic = subdivided into type IIx which is glycolytic and IIa which is glycolytic and oxidative mixed
explain the importance of myofibril proteins existing in isoforms for muscle adaptability
though vertebrae sarcomere structure is the same throughout, the different isoforms of myofibril proteins allows for functional tuning
different isoforms can adapt to different requirements for muscle function
examples of functional variability:
1. variable Ca sensitivity with troponin and tropomyosin isoforms
- the rate of ATP hydrolysis influenced by type I (slow)/ type II (fast) myosin heavy chain isoforms, expressed by the muscle twitch fibres
- fibre type composition of I and II varies for muscle to adapt to its function
what is a motor unit?
motor unit consists of a motor neurone and the bundle of muscle fibres within a muscle it innervates
motor units transmit signals from the nervous system to the muscle fibres - leads to contraction
what is a slow twitch muscle fibre?
muscle fibre that maintains slow contraction and is fatigue resistant. often called red muscle due to high vascularisation
what is fast twitch muscle?
muscle fibre that provides bigger, more powerful forces but for shorter durations and fatigues quickly. often called white muscle due to lack of vascularisation
explain how force generation by the muscle is controlled - relate this to the activity of individual motor units
- correlation between the size of motor neurones, motor units and the size and type of muscle fibres within the motor units
- summation and tetanus
larger motor neurones innervate larger motor units with more muscle fibres = greater force generation
recruitment of motor units is regulated by the nervous system to control force generation. for example, low-force tasks involve smaller motor units and neurones with few muscle fibres.
muscle fibre types influence the functional characteristics and force generation of the motor unit - slow and fast twitch. slow for finer motor control.
summation and tetanus affect force generation. slower motor units are recruited before fast motor units for a higher force generation. fast motor units require a higher firing rate.
what is temporal summation?
the additive effect of multiple stimuli causing repeated stimulation
how does temporal summation generate tetanus?
constant motor nerve stimulation causes a fusion of individual twitches which generates tetanus as sustained muscle contraction
rapidly delivered stimuli at a high frequency
what is tetanus?
sustained muscle contraction from a high frequency of nerve impulses delivered rapidly
how do complete and incomplete tetanus differ?
complete tetanus- the frequency of stimulation is high, and individual twitches fuse into a sustained contraction/ tetanus
incomplete tetanus - partial relaxation between contractions as the frequency of stimulation is high but not delivered as rapidly to completely fuse the individual contractions
how does skeletal muscle tone affect control of force generation?
neural input is important for generating muscle force - motor neurons stimulate muscle fibres for contraction
muscle tone is driven by muscle spindles and reflex arcs = regulate force generation by adjusting muscle length and triggering reflexive contractions
reflex arc pathway - muscle spindles act as sensory receptors that detect changes in muscle length, information through dorsal roots to the spinal cord, motor neurone sends signal for muscle contraction
constant low-level contraction in muscles, helps muscles maintain a state of readiness for force generation
what is myogenesis?
the process by which muscle tissue is formed
describe the process for myogenesis
paracrine factors induce the release of myogenic regulatory factors (MRFs) from mesodermal precursor cells
under influence of paracrine factors and MRFs, mesodermal cells commit to myogenic development - differentiate into myoblasts
myoblasts proliferate under influence of growth factors - form a pool of myoblasts as muscle precursor cells
myogenin expression induced - myoblasts stop proliferating and commit to terminal differentiation
myoblasts fuse together and form a large, multi-nucleated structure = myotubes
myotubes matures into functional muscle fibres
what is MRF?
myogenic regulatory factor
- group of transcription factors
- important in regulating commitment of mesodermal precursor cells to the myogenic lineage
what are satellite cells?
stem cells on the periphery of mature muscle cells
- activate in response to growth/ muscle tissue damage
- differentiate and contribute to muscle tissue repair and growth post-natally
