Skeletal Muscle Flashcards
(21 cards)
How are Z disks connected
Fine threads of intermediate filaments (desmin) via latitudinal and longitudinal strands
Costameres
Strengthened areas on the sarcolemma
Where do connections between sarcomeres end
Beyond the sarcolemma/muscle fibre membrane; they go to costameres on the sarcolemma which form rings around the fibre and reach out into the interstitial space
Titin
Protein that surrounds actin and myosin and is the main protector against overstretch
Sarcolemma
Muscle Fibre Membrane
Lumbrical Muscles
Muscles deep in the palm of the hand which tighten the grips of our fingers
Endomysium
Loose connective tissue surrounding each muscle fibre
Receives some force from desmin
Perimysium
Mixed connective tissue (dense or loose) separating groups of muscle fibres into fasicles
Epimysium
Loose connective tissue between connective tissue covering the muscle (Fascia) and muscle body
Motor End Plate
Synapse between nerve and muscle fibre; one synapse per fibre
How is SkM fibre AP generated (simply)
Motor End Plate stimulation (or electrical stimulation)
There are no gap junctions
Motor Unit
A motor neuron and the muscle fibres it innervates. Contains more than one muscle fibre but all fibres of one unit are of the same type
Difference between muscle fibre types/myosin isoforms
Type I are slow twitch and have higher oxidative capacity (more mitochondria), stain darker
Type IIa and IIX are fast twitch and have lower oxidative capacity better higher glycolytic capacity (anaerobic respiration)
Type I and IIX are extremes, IIA is like an intermediate
Which Fibre type/isoform has the highest resistance to fatigue
Type I (Slow-twitch)
Are all fibres in a given motor unit the same type/isoform?
Yes - being commanded by the same nerve, they do the same amount of work
Storage fuels in each muscle fibre type
I - Triglycerides
IIA - Triglycerides, Glycogen
IIX - Creatine Phosphate, Glycogen
**Lipids as fuel source for long distance, carbs (and creatine) for intense exercise
Describe size principle
As more force is needed, motor units are recruited in order according to their size with small units (type I) being recruited before bigger ones (type IIA then IIX) based on demand
Compare Type I vs Type II muscle distribution between a marathon runner and bodybuilder
Marathon - More type I and bigger, normal or even relatively small type II
Higher oxidative capacity (more mitochondria)
Bodybuilder - More type II and bigger, and also bigger than average type I (size principal)
Lower oxidative capacity due to more myofibrils packed into a fibre
Development of embryological skeletal muscle
Mononucleic precursor cells migrate into space where muscles form and multiply and align to fuse into muscle fibre precursors before starting to synthesise myofibril proteins
**DONT STRESS THIS YOU’LL DO MORE LATER (PROBABLY)
Satellite cells (muscle)
Stem cell reserve of muscles; most precursors had fused into fibres during embryological development but these did not
They stay closely apposed to a muscle fibre but do not fuse and can replace damaged muscle cells and fuse to form myofibrils as done to embryos
**Double arrow head is basement membrane
Look at this… that’s all
