Muscles Flashcards
What are muscles?
Bundles of fibres wrapped in connective tissue sheaths
What are skeletal muscles?
Multi nucleated striated fibres that contain sarcomeres that are made in utero by myoblasts
How are skeletal muscles classified?
According to their speed and wether or not they are oxidative or glycosidic
What are oxidative fibres?
Red fibres that have a small diameter and contain many mitochondria, contain myoglobin and are more vascular
What are the benefits of being vascular?
Enhanced delivery of oxygen and nutrients
What is the function of myoglobin?
Enhances the delivery of oxygen
Where is mitochondria used?
Oxidative phosphorylation
What is the function of slow oxidative fibres?
Resistance of fatigue
What is the function of fast oxidative fibres?
Intermediate resistance of fatigue
What are glycolytic fibres?
White fibres with a large diameter and contain few mitochondria. They have a decreased blood supply but a high concentration of glycolytic enzymes and glycogen
What happens to fast glycolytic fibres
They fatigue quickly
What is fatigue?
Prevents a lot of ATP from being used in breaking/reforming cross bridges in order to sustain contractions
What causes fatigue?
Repeated muscle stimulation
What is tetanus?
State of extended contraction due to the summation of APs which prevents Ca from returning to the sarcoplasmic reticulum so tropomyosin remains in it’s unblocked state, so cross bridges are not broken
Why can Ca not re-enter the sarcoplasmic reticulum due to tetanus?
Tetanic tension > twitch tension
What is the process of recruitment?
As load increases, more motor fibres are needed to compensate so more muscles can be involved in the movement
What is an isotonic twitch?
Contraction with shortening length
What is another name for isotonic twitches?
Concentric
What is an isometric twitch?
Contraction with constant length
What is an eccentric twitch?
Contraction with increasing length
What is the process of excitation-coupling contraction?
Muscle fires APs, Ca ions are released from the SR, Ca ions bind to troponin on actin filaments, tropomyosin is removed, binding sites are exposed, myosin binds to actin, cross-bridges form, contraction occurs, Ca ions return to the SR, tropomyosin returns to its original shape, cross-bridges break, contraction ends
What does contraction cause?
Various changes in the sarcomere
What happens when filaments slide over each other?
A band and H zone decrease
What is the A band?
Myosin
What is the I band?
Actin
What is the H zone?
Space between opposite actin filaments
What is a Z line?
Dark line that separates each sarcomere
What is smooth muscle?
Involuntary, mono nucleated muscles that is supplied by the ANS and contains no striation but contains myosin and actin
How are myosin and actin arranged in smooth muscle?
Diagonally, anchored to membranes and cell structures by dense bodies
Where does smooth muscle exist?
Hollow organs
What are examples of hollow organs?
GI tract, bladder and airways
How do smooth muscles operate?
By forming cross-bridges between myosin and actin but by a different mechanism than skeletal muscle
What type of muscle can sustain contractions for longer?
Smooth muscle
Why is smooth muscle useful in BVs?
Smooth muscle can sustain contractions for longer so they can stay open for longer periods of time
How do contractions occur in smooth muscle?
APs released from muscle, Ca ions released from SR, Ca ions bind to calmodulin, calmodulin binds to light chain kinase, myosin to phosphorylated by ATP, cross-bridges form with actin, contraction occurs
How does relaxation occur in smooth muscle?
Myosin light chain phosphatase dephosphorlyates the cross bridges
