KIN 103 (Chp: 12) Flashcards
What happens durring a muscle contraction microscopically?
Contraction- filaments slide, sarcomeres shorten
Relaxation- calcium transported back into SR, filaments uncouple, sarcomeres lengthen
At what rate does tension occur?
Tension increases rapidly and dissipates slowly
How are contractions generated?
Contractions are generated by the summation of repetitive twitches of many muscle fibres (section 1.3).
What do amplitude and rate depend on in muscle fibers?
Amplitude and rate depend on muscle fiber type (section 1.2)
When do muscles need a steady supply of ATP
- Muscles require a steady supply of ATP
- during contractions for cross bridge movement and release
- during relaxation to pump Ca back into sarcoplasmic reticulum
- after contractions to restore and maintain balance of Na and K
Where does the ATP come from?
- There is only enough “free” ATP to produce 8 twitches
- The next source is high-energy phosphate bonds in phosphocreatine
- Next source is metabolism of carbohydrates (glucose)
Muscles at rest (ATP formation)
ATP (from metabolism) + creatine -> ADP + phosphocreatine
Working muscle (Use of ATP)
Phosphocreatine + ADP -> Creatine + ATP
Contraction Fatigue (Central fatigue can be caused by)
psychological factors, failure of control neurons in brain and spinal cord
Contraction fatigue (Peripheral fatigue can be caused by)
- extended submaximal exercise leads to depletion of glycogen stores
- short-duration maximal exertion leads to increased levels of Pi
- maximal exercise leads to ion imbalances
K leaves muscle fiber, leading to increased extracellular K altering the membrane potential
Skeletal muscle classification depends on
Mechanical: maximal shortening velocity (fast vs slow)
maximal force generating capacity
Metabolic: major pathway used to make ATP
Oxidative vs glycolytic
Three types of muscle fibers (slow oxidative)
Slow-oxidative (SO, type 1)
fatigue-resistant
slow, sustained movements (e.g. posture)
Three types of muscle fibers (fast oxidative)
Fast-oxidative-glycolytic (FOG, type IIa)
Three types of muscle fibers (fast glycolytic)
Fast-glycolytic (FG, type IIb)
fatigue rapidly
fast, powerful movements (e.g. a sprint)
What is important to remember about all three muscle types
Most skeletal muscles include all three types.
Slow oxidative (Metabolic properties?)
Slow-Oxidative fibers: get most of their ATP via oxidative phosphorylation
- lots of mitochondria
- strong blood supply and cells contain lots
of myoglobin giving them a dark red color
- smaller in diameter
Fast glycolytic (metabolic properties?)
Fast-Glycolytic fibers: get most of their ATP via anaerobic glycolysis
- few mitochondrion, lots of glycogen
- few blood vessels and little myoglobin (white appearance)
- larger diameter (more myofibrils=stronger)
Slow oxidative muscles (Mechanical properties)
Slow-oxidative skeletal muscle responds well to repetitive stimulation without becoming fatigued; muscles of body
posture are examples
Fast oxidative muscles (Mechanical properties)
Fast-oxidative skeletal muscle responds quickly to repetitive stimulation without becoming fatigued; muscles used in walking are examples.
Fast glycolytic muscles (Mechanical properties)
Fast-glycolytic skeletal muscle is used for quick bursts of strong activation, such as muscles used to jump or to run a short sprint.
Muscle twitches types (4 types)
Single twitches: single twitch
Summation: stimulations together that add
Unfused tetanus: enough apart for relaxing
Complete tetanus: no relaxation between