Neuromuscular System and Exercise Flashcards
What is the neuromuscular system
the interaction between the nervous system and the muscles.
What happens when there is a voluntary decision to move?
Efferent nerve impulses are sent
What is the basic functional unit of movement?
Motor neuron
What is in a motor unit?
Anterior motor neuron
Muscle fibers it innervates
What is a motor neuron?
Efferent nerve and is relatively large in diameter
leads to neuromuscular junstion
Myelinated thus provides fast conductivity
What is a motor units?
Includes the interface and muscle fiber
Site of acetylcholine release = change in NA2+ and K+ permeability
Initiating depolarization and contraction
How can we study motor units?
1) Electromyography (surface and intramuscular)
- Quality and quantity of electrical activity
2) Muscle biopsy
- Removal and analysis of a small portion of muscle
- Directly measures fibers
3) Force/Power Output Device
- Measures force, power, torque, angular velocity
4) Other imaging devices
What are the classifications of the 3 primary motor units?
Fast Fatiguable -high force -thickest -fatigue Fast fatigue resistance -fast -mod force -thick Slow twitch -low force -fatigue resistance
What is the nerve to muscle fibre ratio definition?
A single motor neuron and the number of muscle fibres stimulated
What is gross movement?
Muscles involved a higher muscle fiber to nerve ratio (gastroc 1:1776)
What is precise movement?
Fine movements have a lower muscle fiber to nerve ratio
eye 10:1
What is Hennman’s size principle?
Small neurons fire first
Need to be at or above 60% of MVC to recruit fast fatigue
What motor units are recruited first?
slow motor units for both power and endurance movements
-Slow have a lower recruitment threshold (depolarize quicker)
What accounts for force production during fast velocity exercise?
Fast fatigue and fast fatigue resistant
What are the fiber type classification?
Type I (Slow) Type IIa (FFR) Type II b/x (FF)
How are the muscle fibers classified?
By the myosin heavy chain(MHC)
Within each MU type the fibers can vary, how?
In their properties and they co-express different proportions of MHC that can change with training.
What are the four main points to distribution?
1) fiber type varies within multifunction muscles
2) Fiber type varies between different muscles
3) Variation of same muscle between two different people
4) Vary due to function of muscle
What are skeletal muscle contraction types?
Isotonic = same tension (lifting weight) Isokinetic = same velocity (cybex) Isometric = same measure (no movement)
What is a concentric action?
Shortening under tension
What is an eccentric action?
lengthening under tension
What is a static action?
tension within the muscle but no visible movement
How does muscle muscle tension vary?
1) Muscle length
2) Joint angle
3) Velocity of movement
4) Percent of fast twitch fibers
What is torque?
Work and torque are the same
It is a twisting force that tends to cause rotation
What effects do muscle length have on tension?
Max tension occurs near resting length of the muscle because of max overlap of myosin and actin cross bridge
What effects do joint angle have on tension?
Muscle tension is greatest some where in the middle of the ROM
What effect does velocity of a movement have on tension?
Isometric produce the greatest tension
MU Recruitment Times:
-Isometric more time for recruitment
-Fast contraction less time
What effect does the percent of fast twitch have on tension?
-Higher peak torque at most angular velocities with greater fast twitch fibers
What are neural factors influencing muscle tension?
1) Conscious CNS drive (Increase/decrease tension)
2) Muscle spindle respond to stretch pf muscle to increase tension
3) Golgi tendon organ and some ligaments respond to tension and cause reflexes
What is a muscle spindle?
Information about fiber length and tension.
Responds to stretch (counteracts stretch)
What is the Golgi tendon organ?
Activated by excessive muscle tension
Responds by reflex inhibition of muscle
Why does muscle force increase with increase in velocity
Greater CNS drive
Greater MU recruitment
Greater passive tension contribution from series and parallel elastic components
Muscle power increases with…
increase in concentric movement velocity up to 50% max shortening velocity
After ~50% PO decreases
Concentric peak torque is inversely related to
angular velocity
faster the movement less time for recruitment
Muscles with greatest % of FF will have…
greatest power/strength output at any given velocity
Larger muscle fibers, faster MN conduction velocity, greater Ca2+ release
