Whole Muscle Physiology Flashcards
Muscle twitch
A single, brief contraction and relaxation cycle in a muscle fiber
3 phases of muscle contraction
lag phase - the gap between stimulus and beginning of contraction
contraction phase
relaxation phase
Motor units
a single motor neuron and all the muscle fibers it innervates.
An action potential in the motor neuron > generates an action potential in each of the muscle fibers it innervates
Motor unit number
Muscle performing delicate and precise movements have many motor units
2 ways to increase the force of a contraction
Summation
Recruitment
Summation
increasing the force of contraction of muscle fibers within the muscle
Recruitment
increasing the number of muscle fibers contracting
Treppe
Increase in tension when a muscle is repeatedly contracted
Possibly explained by an increase in Ca2+ levels around myofibrils
It’s why athletes warm-up before their main exercise
Multiple-motor-unit summation
increased stimulus strength and increased number of contracting motor units
Force of contraction increases as more and more motor units are stimulated
Tetanus
A period of sustained muscle contraction
Incomplete tetanus
Muscle fibers partially relax between contractions
Complete tetanus
Muscle fibers produce action potentials so rapidly that no relaxation occurs
Multiple wave summation
The increased tension produced as a result of the increase in the frequency of the contractions
Active tension & muscle length
length of a muscle has a strong influence on amount of active tension it produces
Active tension curve
Length of muscle increases > active tension increase… to a point
If it stretches further than optimum length, active tension begins to decline
This is why weight lifters assume positions where muscles are stretched close to optimum length
Passive tension
tension applied when a muscle stretches but is not stimulated - like an elastic band. Exists due to muscle elasticity
Total tension
Sum of active and passive tension
Types of muscle contractions (4)
1) isometric - length of the muscle does not change, but the number of tension increases // posture
2) isotonic - the amount of tension produced by the muscle is constant but the length of muscle changes // waving or using a keyboard
3) concentric - isotonic contraction where the tension in muscle overcome opposing resistance, shortening the muscle // lifting a backpack from the floor to table
4) eccentric - isotonic contraction where tension is maintained in a muscle but opposing resistance causes the muscle to increase in length // slowly lowering a heavy weight
Slow-twitch muscle fibers (type 1)
contract more slowly Have a better-developed blood supply Have more mitochondria More fatigue resistant Respond slowly to nervous stimulation Break down ATP more slowly Have large amounts of myoglobin Functions - posture and endurance
Fast-twitch muscles (type 2)
Respond rapidly to nervous stimulation Break down ATP more rapidly than slow-titch Less-well-developed blood supply Fewer myoglobins Smaller mitochondria Large deposits of glycogen Fatigue quickly Functions - Rapid, intense movements of short duration
Glycogen
The stored form of glucose. Body relies on glycogen for sustained exercise
How can you increase the muscular strength and mass of fast-twitch muscles?
Weight lifting/ anaerobic exercise
How can you increase the vascularity of muscles and en the size of slow-twitch muscles
aerobic exercise
Can you convert a type 1 muscle fiber to a type 2 muscle fiber
No
Can you convert a type 2a muscle fiber to a type 2b muscle fiber
Yes
Anabolic steroids
Synthetic hormone taken to increase size and strength of muscles
Beyond increasing muscle size, what else improved strength in a trained person?
1) Nervous system can recruit a larger number of motor units simultaneously
2) Metabolic enzymes increase in hypertrophied muscles, making ATp production easier and nutrient absorption easier
