Muscular contraction+microstructure Flashcards
How is smooth muscle controlled?
Involuntary control from ANS
How is cardiac muscle controlled?
Circulating chemicals and ANS
How is skeletal muscle controlled?
Voluntary control-To bring about movement
Label types of muscle fibres
Parallel
Fusiform
Triangular
Label types of muscle fibre
Unipennate
Bipennate
Multipennate
What is the present in the sarcoplasm?
Myoglobin
Mitochondria
What are myofibres composed of?
Myofilaments(Actin, myosin)
What is the Z-disc?
Actin base chain-separate sarcomeres
What is the H-zone?
Zone where only myosin is present
Diameter of a myofibril
1-2um
Do myofilaments and myofibrils extend along the whole length of the myfibres?
Myofilaments don’t
Myofibrils do
What is the A-band?
Whole length of actin chain
What is the I-band
Zone with only actin
What is the structure of a myosin filament?
2 globular heads
Single tail formed by 2 a-helices
-Several hundred form 1 filament
What 2 other molecules exist on the actin chain?
Troponin
Tropomyosin
What occurs to the H zone, I band and A-zone during contraction
H zone decreases/disappears
I band decreases
A band stays same
What enzyme breaks down ACh in an NM junction
Acetylcholine esterase
How is the ryanodine receptor opened?
Dihydropyridine (DHP) receptor in T-tubule membrane: senses ΔV & changes shape of the protein linked to ryanodine receptor
How do muscle contractions stop through Ca2+ removal?
Ca2+ is actively transported into the SR continuously while action potentials continue. ATP- driven pump (uptake rate < or = release rate).
For muscle contraction control, where are the upper and lower motor neurones?
Upper-brain
lower-Brainstem and spinal cord
Approximately how many neurones and muscle fibres do humans have?
Humans have approximately 420,000 motor neurons and 250 million skeletal muscle fibres.
Roughly how many muscle fibres does each motor neurone innervate/
600
What does stimulation of a motor unit lead to?
Contraction of all the muscles innervated by that motor neurone
What does this table show?
Huge variation in ratio of neurone to muscle fibres innervated
Characteristics of a Type I motor unit
Slow
smallest diameter cell bodies
small dendritic trees
thinnest axons
slowest conduction velocity
Characteristics of a Type IIa motor unit
Fast fatigue resistant
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
Characteristics of a Type IIb motor unit
Fast fatiguable
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
What method can tell you the variety in muscle fibre types?
ATPase staining method
How are motor units classified?
Tension generated
Speed of contraction
Fatiguability of the motor unit
Generally what order are motor units recruited in?
Slow
Fast fatigue resistant
Fast fatiguable
Outline the 2 methods by which motor unit activation is regulated?
Recruitment
Smaller motor units are recruited first, as more force is needed more(larger) units are recruited
-Allows for fine movement e.g writing
Rate coding
Slower units fire at a slower frequency
as firing speed increases, force generated increases
-Summation occurs when firing frequency is too fast for the muscle to relax in between contractions
2 functions of neurotrophic factors
Prevent neuronal death
Promote growth of neurons after injury
What occurs if a fast and slow twitch muscle are cross innervated?
The slow one becomes fast and vice versa
Label types of contraction
Isometric
Concentric
Eccentric
Outline how ageing affects the proportion of muscle fibre types?
Loss of type I and II fibres but also preferential loss of type II fibres. This results in a larger proportion of type I fibres in aged muscle (evidence from slower contraction times).
What most likely occurs to muscles in terms of type switching with training?
IIB to IIA
What can cause a shift from type I to type II muscle fibres?
Severe deconditioning
Spinal cord injury
Spaceflight micorgravity
