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Flashcards in Muscles Deck (36):
1

Sliding filament theory

A band constant, I bands shorten attached to Z disks
Myosin constant

2

ATPase cycle of myosin

Action potential -> calcium release from t tubule
Troponin C -> movement of tropomyosin and unblocking of myosin binding sites
Calcium drawn back after action potential stops
ATP binds to myosin -> head detachment
ATP hydrolysed, cocked state
Head swings, Weakly binds
Release of Pi -> power stroke and return to original angle
ADP release and repeat

3

Alpha actinin

Actin cross linking protein actin -> titin
Assists assembly of Z line

4

Tropomyosin

2 strand alpha helical coiled coil
Binds to 7 actin subunits
Modulates tropomyosin
Slows depolymerisation

5

Troponin C

One of 3 subunits
Ca binding to regulatory domain
Conformational change

6

Cap Z and tropomodulin

CapZ- + end of actin. Inhibits polymerisation.
Tropomodulin- caps - end of actin. Inhibits depolymerisation.

7

Nebulin

Binds up to 200 actin monomers
Z lines -> - ends
Regulates thin filament length

8

Titin

3.7MDa
Span I and A bands
Ends overlap in M line, continuous filament
Unfolds under tension and re folds
Force transmission through the sarcomere

9

Excitation contraction coupling

Action potential -> ACH release
ACH -> nACH -> depolarisation
Potential spreads from t tubules to change DHP receptor conformation
Calcium enters the cytoplasm as channels opened
Calcium binds to troponin

10

Sources of muscle fibre ATP

Creatine + ATP -> Phosphocreatine reversible
Citric acid cycle
Glycolysis

11

Length-tension relationship

Maximum tension = maximum cross bridges
Each sarcomere 10%, whole muscle 10%, 5-10nm/ATP

Tension depends on sarcomere length at start, frequency of action potentials

Speed- speed of calcium back into SE, fatigue resistance

12

Type 1 muscle fibre

Slow red muscle
Slow oxidative
Marathon runner
High motor unit size
Low ATPase
High myoglobin
High mitochondria
Small diameter

13

Type 2A

Intermediate (fast oxidative)
High myoglobin
High ATPase
Medium glycolytic enzymes

14

Type 2B

Fast white/ fast glycolytic
2-6 fibres per neuron
High ATPase
Low myoglobin
High glycolytic enzymes
Large diameter

15

Regulation of cardiac muscle contraction

Action potential
Voltage gated Ca open
Rise in intracellular Ca -> Ca release from SR
Ca binds to troponin allowing contraction

Ca dissociates from troponin
Ca pumped back into SR
Ca exchanged for Na across sarcolemma

16

Contraction of smooth muscle

Ca enters cell when channels open
Release of Ca from SR
Ca binds to calmodulin
Activates myosin light chain kinase
Phosphorylates myosin light chains
Activates myosin ATPase activity -> cross bridges

17

Relaxation of smooth muscle

Myosin phosphatase dephosphorylates light chains
Ca removed by SR and Ca/Na exchanger
Ca dissociates from calmodulin

18

Muscle spindles

Send information about muscle stretch to CNS
Connective tissue capsule with intrafusal fibres
Sensory nerve endings are stretch activated -> rapid fire
Action potentials for muscle tone

19

Muscle spindle reflex

Heavy load stretches the muscles and spindles causing contraction

20

Knee jerk reflex

Quadriceps contract in response to spindle activation
Inhibitory neuron Causes the hamstring to relax

21

Golgi tendon reflex

Muscle contraction activates sensory neurons
Synapse with inhibitory neurons which inhibit motor neurons
Muscle relaxation
Protects from heavy loads

22

Joint capsule proprioreceptors

1- small corpuscles
2- large corpuscles
3- resemble Golgi tendon organs
4- free nerve endings

23

Reflex movement

Simple and rapid
Sensory receptors
Knee jerk, cough
Minimal involvement of higher brain

24

Voluntary movement

Most complex, external stimuli
Integrated in cerebral cortex
Ascending and descending pathways

25

Rhythmic movements

Combination of voluntary and reflex
Initiation and termination requires cerebral cortex (walking)
Maintained by spinal cord (Central pattern generators)

26

Tetanus

Clostridium tetani
First affect jaw
Toxin is taken up and transport to spinal cord
Inhibits release of neurotransmitter from inhibitory neurons
Excessive excitation and spasm

27

Duchenne muscular dystrophy

X linked, recessive
Mutations in dystrophin
Actin filaments to extra cellular matrix
Muscle cells cannot withstand stress of contraction

28

Hypertrophy

Apical- apex
Septal- septum
Obstructive- septum which blocks flow to aorta
Thickening of walls
Mainly thick mutations, muscle builds to compensate

29

Hypertrophic cardiomyopathy

Excessively thick muscle
Disarray in myocytes

30

Dilated cardiomyopathy

Left ventricle stretched
Heart unable to pump strongly

31

Arrythmogenic right ventricular cardiomyopathy

Inherited
Damaged muscle replaced by scars and fat
Sudden death in the young

32

Inheritance patterns

Recessive effect- protein absent or completely dysfunctional
Haploinsufficincy- not expressed, 50% decrease in level
Dominant negative- poison peptide and can dominate phenotype

33

Arg403Gln mutation

B myosin heavy chain mutation
Most severe phenotype
50% die by 40

34

Restrictive cardiomyopathy

Ventricles stiffen
Back up of blood into the lungs and veins
Least common
Unknown cause, secondary cause, or metabolic
Following radiation after cancer
Genetic abnormalities as HCM

35

Distal arthrogryposis

Skeletal muscle disease
Contracture of hands and feet
Mild 1- only hands and feet, most common
Severe 2- contracture of face
Mutations in myosin, tropomyosin, troponin, myosin binding protein C

36

Organisation of skeletal muscle

Stem cells -> muscle cells
Sarcoplasmic reticulum is a modified ER wrapped around myofibrils
Concentrates and sequesters Ca2+
T tubules allow potentials from cell surface -> interior fibre