Lecture 5 - Exercising Muscles 1 Flashcards
three types of muscle tissue
Smooth muscle
- > involuntary, hollow organs
Cardiac muscles
- > involuntary, heart
Skeletal muscle
- > voluntary, skeleton
Parts of skeletal muscle
Entire muscle
- > epimysium
*consists of many bundles (fasciculi)
Fasciculi
- > surrounded by perimysium
*consists of individual muscle cells/fibres
Muscle fibres
- > surrounded by endomysium
*consists of myofibrils divided into sarcomeres
parts of the muscle fibre and what they do
Plasmalemma (cell membrane)
- > fused with tendon
- > conducts AP
- > maintains pH and transports nutrients
Satellite cells
- > muscle growth and development
- > responds to injury, immobilization and training
Sarcoplasm
- > cytoplasm of muscle cell
- > unique features: glycogen storage and myoglobin
Transvers Tubules
- > extensions of plasmalemma
- > carry AP deep into muscle fibre
Sarcoplasmic Reticulum (SA)
- > Ca storage
myofibrils vs sarcomeres
Myofibrils
Muscle - > fasciculi - > muscle fibre - > myofibril
*hundreds of thousands per muscle fibre
Sarcomere
- > basic contractile element of skeletal muscle
- > end to end for full myofibril length
components of a sarcomere
distinctive striped/striated appearance
A-bands
- > dark stripes
I-Bands
- > light stripes
H-Zone
- > middle of A-Band
M-Line
- > middle of H-zone
characteristics of actin and myosin
Actin (thin filament)
- > shows up lighter under microscope
- > I-Band contains only actin filaments
Myosin (thick filaments)
- > shows up darker
- > A-band contains both actin and myosin fil.
- > H-zone contains only myosin fil.
parts of myosin
*two intertwined filaments with globular heads*
Globular heads
- > protrude 360deg from thick filament axis
- > will interact with actin for contraction
Stabilized by tintin
composition of actin/thin filaments
composed of 3 proteins
Actin
- > contains myosin binding site
Tropomyosin
- > covers active site at rest
Troponin
- > anchored to actin, moves tropomyosin
*anchored at Z-disc and equally spaced out my tintin*
alpha motor neuron
innervate muscle fibres
motor unit
comprised of single alpha motor neuron and all fibres it innervates
- > more operating motor units = more contractile force
neuromuscular juntion
site of communication between neuron and muscle
- > consists of synapse between alpha motor neuron and the muscle fibre
explain excitation-contraction coupling (muscle fibre contraction)
- AP stars in brain
- AP arrives at axon termina, releases ACh
- Ach crosses synapse, binds to Ach receptors on plasmalemma
- AP travels down plasmalemma to T-Tubules
- This triggers Ca release from SR
- Ca eneables actin-myosin contraction
role of Ca in muscle fibres
When AP arrives at SR from T-Tubules
- > SR are sensitive to electric charge so this causes mass release of Ca into sarcoplasma
Ca binds to troponin on thin filament
- > tropomyosin-Ca complex moves tropomyosin
- > myosin binds to actin, causing contraction
described the relaxed state of a muscle contraction
- > no actin-myosin interaction at binding site
- > myofilaments overlap a bit
describe the contracted state of a muscle fibre
- > myosin head pulls actin towards sarcomere centre (powerstroke)
- > filament slide past each other
- > sarcomeres, myofibrils, muscle fibres all shorted
what happens when power stroke ends
- > myosin detaches from active site
- > myosin head rotates back to original position
- > myosin attaches to another active site farther down
*this process continues until Z dic reaches myosin filament OR AP stops and Ca gets pumped back into SR*
where does ATP bind to provide energy used in contraction
ATP binds to myosin head (ATPase on myosin head)
what happens when AP ends and electrical stimulation of SR stops?
Ca is pumped back into SR
- > stored until next AP arrives
Without Ca, Troponin and tropomyosin return to resting conformation
- > covers myosin-binding site and prevents A-M cross bridging
titin
the third myofilament
- > internal spring
- > keeps myosin aligned during contraction and stabilizes adjacent sarcomeres
