Muscle microstructure and contraction Flashcards
smooth muscle is under —- control from the —— nervous system
involuntary
autonomic
cardiac muscle can contract ——- but is under the influence of the —— nervous system and —— ——
autonomously
autonomic
circulating chemicals
Skeletal muscles are under ——– control, usually attached to —– and —— to bring about ——-
voluntary (somatic nervous system)
bones
contract
movement
bundles of muscle fibres (myofibres)
fasicles
myofibres are made up of
myofibrils made up to myofilaments
connective tissue surrounding muscles
epimysium
connective tissue surrounding fasicles
perimysium
connective tissue surrounding myofibres adjacent to sarcolemma
endomysium
myofibres are covered by
sarcolemma (plasma membrane)
cytoplasm in a myofibre is called, and —– / —— are present
sarcoplasm
mitochondria myoglobin
function of t tubules
to carry impulse deep into center of myofibre, innervating all myofibrils
dense protein - —– separate sarcomeres !!!!!!!!!!!!!!!!!
Z - discs
Dark band
A band (thick - myosin) overlap of myosin and actin
Light band
I band ( thin - actin)
myosin has - globular heads
single tail formed by — ——-
2
a-helices
structure of actin
each molecule has a
filaments also contain
molecules twisted into helix
myosin binding site
troponin and tropomyosin
during contraction
I / A / H band
I - shorter
A - same
H - shorter / disappeared
middle of sarcomere is the
M - line
Initiation of muscle contraction
action potential propagates across sarcolemma and into t-tubules
Dihydropyridine (DHP) senses ΔV / changes conformational shape
opens ryanodine receptor
Ca2+ released from sarcoplasmic reticulum into sarcoplasm surrounding filaments
Ca2+ binds to troponin
tropomyosin moves
exposing myosin binding site on actin
charged myosin head binds to actin
binding and discharge of ADP causes myosin head to pivot POWER STROKE
ATP binding unbinds myosin head from actin filament
*while action potentials continue Ca2+ continuously actively transported into SR and pumped out.
motor unit
one motor nerve and all muscle fibres innervated by it
motor nerves can innervate ——- myofibres.
Myofibres can be innervated by —– —- nerve
multiple (avg 600)
only one
Slow motor unit, S type 1
smallest diameter cell body
small dendritic trees
thinnest axons
slowest conduction velocity
Fast, fatigue resistant motor unit
FR type IIA
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
Fast, fatiguable motor unit
FF type IIB
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
Slow type 1 muscle fibre Myoglobin content Colour Aerobic capacity Anaerobic capacity
High
thus Red
High
Low
Fast fatigue resistant muscle fibre FR type IIA Myoglobin content Colour Aerobic capacity Anaerobic capacity
High ish
thus pink
moderate
High ish
Fast fatiguable muscle fibre FF type IIB Myoglobin content Colour Aerobic capacity Anaerobic capacity
Low
thus white
low
High
Regulation of muscle force
recruitment - smaller units recruited first, if more force required more units recruited
Rate coding - slower units fire at lower frequency, rate increases force increases
Summation (rate coding)
units fire too fast to allow muscle to relax between arriving action potentials
if a fast and slow twitch muscle are cross innervated
the slow one becomes faster
the faster becomes slower
the motor neurone has some effect on the properties of the muscle fibres it innervates
Types of muscle contraction
isometric - hold / muscle stays same length whilst generating force
concentric - contraction
eccentric - controlled relaxation
Skeletal muscle structure
Three main types of muscle: smooth, cardiac and skeletal
Skeletal muscle is composed of myofibres, myofibrils and myofilaments
Skeletal muscle is striped and component parts are arranged in sarcomeres
Actin and myosin are proteins involved in contraction.
Muscle contraction
Ca2+ is released from sarcoplasmic reticulum
Ca2+ binding to troponin on actin causes change in tropomyosin revealing myosin binding site
crossbridges formed
POWERSTROKE causes contraction
ATP used for contraction and release
Motor units
name for neuron and all muscle fibres
3 main types (slow, fast fatigue resistant and fast fatiguable)
contraction of motor unit causes contraction of all fibres of unit
sizes vary
muscles have varying proportions of types of unit
units have different properties
recruitment and coding mechanisms for controlling contraction (force)
neuron has effect on fibre type (neurotrophic factors)
different types of contraction by skeletal muscles
Plasticity
motor units can change following training
typically type IIB to IIA
spinal cord injury and microgravity can cause shift from slow to fast
ageing causes loss of slow and fast, but predominantly fast
