Neuromusculoskeletal Response to Exercise Flashcards
Two divisions of the nervous system
Peripheral and Central
Motor Unit
The anterior motor neuron and all of the muscle fibers innervated by it
Neuromuscular Junction
Interface between the end of a myelinated motor neuron and muscle fiber. Transmits impulse to initiate muscle action.
T tubule
Transmits action potential throughout muscle cell
Depolarization of T-tubule causes…
Ca2+ release from SR lateral sacs
Ca2+ binds to …. after its release from the SR
Troponin-tropomyosin in the actin filaments. Allows actin to bind with myosin
During muscle action, actin combines with….
myosin ATP-ase to split ATP with energy release. Tension from the energy release produces crossbridge movement
Myosin crossbridges are broken by…
ATP binding. Leads to sliding of thick and thin filaments, causing muscular shortening
Crossbridge activation continues when….
The concentration of Ca2+ remains high
When muscle stimulation ceases…
Ca2+ moves back into the SR’s lateral sacs through active transport
Ca2+ removal restores the….
inhibitory action of troponin-tropomyosin.
Four nerve fiber groups
A-alpha
A-Beta
A-Delta
C-nerve fibers
The thickness of a nerve fiber dictates…
The speed of neural transmission within the fiber
Phyiologic and mechanical properties that classify a motor unit
Twitch characteristics
Tension characteristics
Fatigability
Type IIb characteristics
Fast twitch
High Force
Fast Fatigue
Type IIa characteristics
Fast twitch
Moderate force
Fatigue resistant
Type I characteristics
Slow twitch
Low force
Fatigue Resistant
All or None principle
A stimulus strong enough to trigger an AP in the motor neuron activates all fibers in the motor unit
Temporal summation of APs
Superimposing one AP on another AP
Force of muscle action via
Increase motor unit recruitment
Increased frequency of motor unit discharge
Motor unit recruitment
As muscle force requirements increase, motor neurons with larger axons are recruited
Size principle
The orderly recruiment of specific motor units to produce a smooth muscle action; allows the CNS to fine tune activity
How long does it take to see changes in strength?
Gains can be seen after on session, but six weeks min for true strength
Early strength gains related to…
Neural adaptations starting in the CNS. Increased neural drive begins in motor cortex
Resistance training affect on Motor Unit activation
Increase in number of motor units recruited
Increase in motor unit firing rate
Increased potential for motor unit synchronization
Reduction in co-activation of antagonist muscle
Golgi Tendon Organs
Connect to extrafusal fibers near tendon’s junction to muscle
Detect difference in tension generated by active muscle
When stimulated, golgi tendon organs…
transmit signals to the spinal cord to elicit reflex inhibition of the muscles they supply
Resistance training decreases GTO inhibition
Central Fatigue
Alteration in brain neurotransmitter concentration which alter density of neural impulse to muscle
Decreased nerve impulse=
decreased force production
Low intensity training affect at NMJ
Muscle fiber diameter decreases while nerve terminal remains unchanged
High intensity training affect at NMJ
Dispersion of synapses increases. Nerve stimulates more fibers
Aerobic exercise improves
Cognitive function of older adults
Learning in children
Mood disorders
-anxiety and depression
Proposed mechanism for aerobic exercise effect on the CNS
Improved circulation to the brain
Increased amounts of Neurotrophins
neurotrophins
Brain derived neurotrophic factor
Insulin like growth factor
Fibroblast growth factor 2
BDNF
Instrumental in changing the brain, especially hippocampus
Easily regulated by physical activity
Primary differences between skeletal muscles fibers
Primary mechanism of ATP production
Type of motor neuron innervation
Type of myosin heavy chain expressed
Fast-twitch fiber characteristics
High capability for electrochemical transmission of AP
High myoisin ATPase activity
Rapid Ca2+ release and uptake
High rate of crossbridge turnover
Fast twitch fiber speed of shortening is…
Three to Five times faster than slow-twitch fibers
Fast twitch fibers rely on…
a well developed, short term glycolytic system for energy transfer
Type IIa fibers
Fast-oxidative-glycolytic fibers
Type IIb fibers
Possess the greatest anaerobic potential and most rapid shortening velocity
Slow Twitch Fiber characteristics
Low myosin ATPase activity
Slow calcium handling ability and shortening speed
Less well-developed glycolytic capacity than fast twitch fibers
Large and numerous mitochondria
Prolonged aerobic training causes
Larger and more numerous mitochondria; capillary density increase; Increase in oxidative enzymes; Endurance improvements at low power; selective hypertrophy
Adaptations to resistance training
Increase muscle strength and endurance; increase fiber size and amount of IIa fibers; Increase enzyme activity; Increase metabolic energy stores; Increase connective tissue integrity; Decreased body fat
Why does muscle hypertrophy?
Repeated muscle injury; particularly with repeated eccentric actions
Eccentric Contration disrupts
SR
T-system
Z disk
Damage to a single muscle fiber leads to..
Inflammation
Proliferation
Maturation
mRNA mediates the stimulation of
Myofibrillar protein synthesis; overcompensation of protein synthesis causes hypertrophy
Hyperplasia
Increased number of muscle fibers
Can we add muscle fibers?
Inconclusive; enlargement of existing fibers represents greatest change in cross sectional area
De training
Cessation of resistance exercise
Muscle fiber response to de training
Reductions in muscle strength
Reduction in Type II fiber area
Muscle fiber response to immobilization
Muscle atrophy can occur quickly; depends on fiber type and positioning
Normal maintenance of a muscle fiber is the product of..
Protein synthesis and protein degradation
Atrophy summary
Decreased fiber diameter
Decreased number of myofibrils
Decrease in intramuscular capillary density
Increase in fibrous and fatty tissue deposits in muscle
Muscle adaptations to stretch
Routine stretching may add sarcomeres in series at the muscle tendon junction
A-Alpha nerve
Largest diameter, fastest
A-Beta nerve
Medium diameter; medium speed
A-Delta nerve
Smaller diameter; slowest of myelinated fibers
C-nerve fiber
Smallest diameter, slowest conduction
