Neuromuscular System Flashcards
Explain the specific steps of the sliding filament theory
- Tight binding in the rigor state. Cross bridge at 45 degree angle
- ATP binds to the binding site on myosin. Myosin dissociates from actin
- ATPase hydrolyzes the ATP. ADP and P remain bound to myosin
- The myosin head swings over and binds weakly to a new actin molecule. Cross bridge at 90 degrees
- Release of P initiates the power stroke. The myosin head rotates on its hinge, pushing the actin filament past it
- At the end of the power stroke, the myosin head releases ADP and resumes the tightly bound rigor state
Motor unit anatomy
- Cell body houses the control center
- Axon extends from the cord and delivers an impulse to the muscle fibers it innervates
- Dendrites receive impulses through spinal cord connections and conduct them toward the cell of the body
- Nerve cells conduct impulses in one direction only down the axon away from the stimulation point
- All of a motor unit’s muscle fibers disperse over subregions of the muscle with other motor unit fibers
Muscle fiber types
Type I
- ~50% of fibers in an average muscle
- Peak tension in 110ms (slow twitch)
- Motor unit has smaller neuron, 300 fibers
Type IIa (~25% of fibers)
Type IIx (~25% of fibers)
*Type I vs Type II fibers have different types of myosin
Fiber type determinants
Genetic factors
- Determine which a-motor neurons innervate fibers
- Fibers differentiate based on a-motor neuron
Training factors
- Endurance vs strength training, detraining
- Can induce small (10%) change in fiber type
Aging
- Muscles lose type II motor units
Gradation of force
The force of muscle action varies from slight to maximal in one of two mechanisms:
- Increasing number of motor units recruited
- Increasing the frequency of motor unit discharge
How muscle fibers adapt to training
Type I
- High aerobic endurance
- Can maintain exercise for long periods
- require oxygen for ATP production
- Low-intensity aerobic exercise, daily activities
- Efficiently produce ATP from fat, carbohydrate
Type II in general
- Poor aerobic endurance, fatigue quickly
- Produce ATP anaerobically
Type IIa
- More force, faster fatigue than type I
- Short, high-intensity endurance events (1,600m run)
Type IIx
- Seldom used for everyday activities
- Short, explosive sprints (100m)
GTO’s and muscle spindles
Golgi tendon organs:
- Connect in series to skeletal muscle fibers and located in ligaments of joints to detect differences in muscle tension
- When activated by tension or stretch, golgi receptors transmit signals to cause reflex inhibition of the muscles they supply
- Protect muscles and its connective tissue harness from injury by sudden, excessive load or stretch
Muscle spindles:
- Provide mechano-sensory information about changes in muscle fiber length and tension
- Primarily respond to muscle stretch through reflex action by initiating a stronger muscle action to counteract the stretch
- More spindles exist in muscles that routinely perform complex movements
Size principle
Order of recruitment of motor units directly related to size of alpha-motor neuron
- Smallest (type I) motor units recruited first
- Midsize (type IIa) motor units recruited next
- Largest (type IIx) recruited last
Speed-force relationship and length-tension relationship and how they are involved in exercise
Speed-force (force-velocity):
- Concentric: maximal force development decreases at higher speeds
(Concentric muscle contraction = muscle shortening)
- Eccentric: maximal force development increases at higher speeds
(Eccentric muscle contraction = muscle lengthening)
Length-tension:
- Optimal sarcomere length = optimal overlap
- Too short or too stretched = little or no force develops
Hypertrophy vs. hyperplasia
Hypertrophy: Strength gains
- Increase in muscle size
- Facilitated by testosterone, a natural anabolic steroid hormone
Hyperplasia:
- Increase in number of muscle fibers
Stretch reflex and reciprocal inhibition (agonists and antagonists)
Stretch reflex:
- Muscle spindle responds to stretch
- Afferent nerve fiber that carries the sensory impulse from the spindle to the spinal cord
- Efferent spinal cord motor neuron that activates the stretched muscle fibers
Coactivation of agonists, antagonists:
- Normally antagonists oppose agonist force
- Agonist = stretched muscle
- Antagonist = opposite muscle inhibiting agonist so to not overstretch
Discuss the adaptations in muscle and other tissues to resistance training and the differences between genders or with age
After 3-6 months of resistance training:
- 25-100% strength gain
- Learn to more effectively produce force
- Learn to produce true maximal movement
- Young men experience greatest absolute gains vs young women, older men, children
- Women have the same ability to develop strength, however, cannot get as big as men due to different hormones
- Children can gain both strength and muscle mass with proper safeguards
- Resistance training helps restore age-related loss of muscle mass in elderly
