Muscles, contraction and movement Flashcards Preview

HUBS191 Human Movement and Sensation > Muscles, contraction and movement > Flashcards

Flashcards in Muscles, contraction and movement Deck (75)
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function of cardiac muscle

pumping of blood


function of smooth muscle

to control the movement of fluid e.g. blood, urine, digestion


function of skeletal muscle

to move, maintain posture, generate heat


structure of skeletal muscle

  1. Tendon attaches muscle to bone
  2. fascia
  3. muscle
  4. epimysium
  5. muscle bundle
  6. perimysium
  7. fascicle
  8. endomysium
  9. muscle cell aka muscle fibre aka myocyte
  10. sarcoplasmic reticulum and T tubule
  11. myofibrils
  12. sarcomere
  13. myofilaments



invagination of Extracellular space that allows the action potential to enter the myofibril and initiate the release of Ca2+



T-tubule sandwiched between two SR



plasma membrane of the muscle cell


sarcoplasmic reticulum

ER of a muscle cell and stores calcium



myofilament between to Z-disks= basal contractile unit


thin filament

actin, tropomyosin, troponin; Globular actin forms a double helix strand surround by two thin strands of tropomyosin


thick filament

myosin and myosin head


NMJ vs synapse

  • In healthy humans, there is no IPSP or EPSP
  • if an action potential reaches the NMJ it will cause contraction;
  • Should call the cleft the NMJ cleft rather than the synaptic clefts


3 steps of skeletal muscle contraction

excitation, contraction, relaxation


steps of excitation

  1. AP reaches end of motor neuron, which causes Ca2+ entry into nerve terminal
  2. Neuronal action potential Acetylcholine (Ach) released from the nerve terminal in synaptic vesicles
  3. Synaptic vesicles release Ach, which diffuses into the synaptic cleft
  4. Ach stimulates Ach-receptors on the adjacent muscle fibre, initiating an impulse in the muscle fibre
  5. Depolarisation of muscle sarcolemma, initiating an action potential
  6. Electro-chemical-electro coupling
  7. Action potential on the muscle fibre- always sufficient to reach threshold in healthy individuals


steps of contraction

  1. AP travels over sarcolemma and T-tubules very quickly, which triggers the release of Ca2+ ions from the adjacent sarcoplasmic reticulum almost simultaneously along the myofibril
  2. Large Ca2+ release from the internal Ca2+ store- ions diffuse to the myofilaments to trigger cross-bridge formation
  3. Cross-bridge formation of myofilaments
  4. Myosin head is in its energised state, with ATP bound
  5. Ca2+- troponin interaction exposes active site
  6. Actin-myosin interact as a cross-bridge
  7. Energised myosin head pulls the actin in a power-stroke


steps of relaxation

  1. No new AP- sarcolemma repolarises
  2. Ca2+ no longer bind to Troponin; ion re-uptake into internal Ca2+ store
  3. Troponin active sites are hidden
  4. Actin and myosin are still bound but not enough Ca2+ ions to initiate new cross-bridges
  5. ATP must bind for actin and myosin to uncouple cross-bridge


sliding filament model

  • When inactive the filaments are not over one another
  • When activated the myofibril shortens as the z-lines move closer
  • Myofilaments do not change length themselves


motor unit

one somatic Motor Neuron and Muscle Fibres innervated by its branches


energy sources for contraction

Anaerobic and anaerobic


features of anaerobic respiration

- short term - fast energy production - no O2 required - ATP, creatine phosphate, glycolysis


features of aerobic respiration

- long term - steady - slower energy production - O2 required - Oxidative phosphorylation


why is energy required for relaxation?

Ca2+ re-uptake into SR and uncoupling of crossbridges


types of muscle fibres

red, white and intermediate (myosin type IIa)


features of red muscle fibres and example

high myoglobin (myosin type I), high aerobic enzymes - soleus


features of white muscle fibres and example

low myoglobin (myosin type IIx), low aerobic enzymes - eye


function of red (myosin type I) fibres

slow rate interaction with actin; slow force production; slow energy consumption; sustained by aerobic metabolism


function of white (myosin type IIx) fibres

fast rate interaction with actin; fast force production; fast energy consumption; use anaerobic metabolism


what is a twitch

the smallest tension a muscle can produce - a single AP in a single motor unit


what is treppe

- repeated stimuli - sustained levels of SR Ca2+ = more contraction - actin and myosin become more sensitive to Ca2+ - more sensitive at higher temperatures


what is tetanus

- rapidly repeated stimuli - closely spaced twitches - heat increases sensitivity - mechanical summation due to high Ca2+ in SR