The Neuromuscular System and Exercise
The
Neuromuscular System
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Consists of:
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Nervous System
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Central Nervous System Brain and
Spinal Cord
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Peripheral Nervous System
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Somatic system excites muscle
activation
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Autonomic system excites or inhibits
muscle activation
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Sympathetic excites
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Parasympathetic inhibit or slow down
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Muscular System
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Skeletal
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Cardiac
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Smooth
The
Neuromuscular Connection
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Motor Unit
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Defined as the nerve + the muscle fibers that it
innervates
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The ratio of muscle fibers to nerve relates to
function
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Delicate, precise work requires a lower muscle fiber
number to nerve ratio, e.g. 10 muscle fibers to one nerve (eye muscles)
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Less complex movements require a higher muscle fiber
number to nerve ratio, e.g. 3000 muscle fibers to one nerve (leg muscles
The
Neuromuscular Junction
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Gap between the nerve ending and muscle fiber
Neuromuscular
Fatigue
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Fatigue may represent a disruption in the normal
function of one of these components:
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Central nervous system (brain and spinal cord)
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Peripheral nervous system (nerve itself)
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Neuromuscular junction
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Muscle fiber
Central Nervous System Fatigue
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Influenced by peripheral fatigue factors such as
lactic acid accumulation in muscle
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Influenced by ion disturbances in the blood
* in these cases,
the brain and spinal cord send inhibitory signals back to origins of fatigue
Nerve
fatigue
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Not likely that the nerve fatigues but is possible
since it requires nutrients to survive.
If lacking nutrients, it could slow in its function.
Neuromuscular Junction Fatigue
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It is possible that levels of acetylcholine could be
depleted resulting in fatigue.
Muscle
Fiber Fatigue
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Muscle fiber is most likely site of fatigue due to:
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Accumulation of lactic acid
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Prevents binding of calcium to troponin
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Makes it difficult for myosin to bind to actin fiber
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Depletion of ATP & PC stores
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Depletion of muscle glycogen
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Lack of O2 getting to the muscle
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Insufficient blood flow
Muscle
Types
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Skeletal
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Function is to create movement
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Cardiac
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Function is to pump blood for movement to occur
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Smooth
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Function is to constrict blood vessels to allow for
appropriate blood distribution, and move contents of internal organs
Skeletal
Muscle
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Structure
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Held together by connective tissue
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Epimysium completely surrounds muscle
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Perimysium surrounds bundles of muscle fibers (~150
fibers); bundles known as fasciculi
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Endomysium surround each muscle fiber
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Composition
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Contains ~ 75% water, 20% protein, 5%
other substances (minerals, fuel, enzymes, etc.)
Types
of Skeletal Muscle
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Fiber Types:
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Type I = slow-contracting
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Type II = fast-contracting
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Type IIA has both anaerobic and aerobic abilities
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Type IIB has primarily anaerobic ability
Comparison
of Fiber Types
Fiber Type Composition in Elite and Non-athletes
Can we change fiber types with training?
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Genetic code largely determines a persons predominant
fiber type.
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However, with specific training, one can improve
either their aerobic or anaerobic capacities to a certain level
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For example, a person with primarily fast-twitch fiber
muscles can improve their endurance to a certain level if they do long distance
running but will most likely not attain elite status as a marathon runner.