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Neuromuscular System

KIN 416 - Berry College - Dept. of Kinesiology

David Elmer

on 4 February 2016

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Transcript of Neuromuscular System

Resting membrane potential (-70mv) across cell membrane, due to ion concentration gradients (primarily Na+ and K+)
established by Na+/K+ ATPase pump
maintained by voltage-gated Na+ and K+ channels
gradual rise due to opening of slow Na+ channels
fast Na+ channels open
Na+ channels close
K+ channels open
K+ channels close
Na+/K+ ATPase restores gradient
Motor Unit
A motor neuron and all the muscle fibers that it innervates
the number of fibers in a motor unit is related to function
fine motor control = fewer fibers (23:1)
large muscles = more fibers (2000:1)
Size Principle of
Motorneuron Recruitment
smallest motor units in a muscle are recruited first
they also produce the least force
if more force is needed, then progressively larger motor units are recruited
Pros of this principle?
Myosin ATPase
Fiber types
How are they distinguished?
aerobic capacity
myosin ATPase activity
amount of contractile protein
maximum force production
speed of contraction
Type I
aka slow-twitch, slow-oxidative, slow fatigue-resistant
1. # of mitochondria
2. capillary density
3. amount of myoglobin
highest aerobic capacity
slowest myosin ATPase
least contractile protein
lowest force production
slowest speed of contraction
highest efficiency
* Greatest resistance to fatigue
Type IIa
aka intermediate fibers, fast fatigue-resistant
In the middle for everything!
aerobic capacity
myosin ATPase activity
amount of contractile protein
force production
speed of contraction
Type IIx
aka fast twitch, fast-glycolytic, fast fatiguable
lowest aerobic capacity
highest myosin ATPase activity
greatest amount of contractile protein
greatest force production
greatest speed of contraction
lowest efficiency
*Greatest force production and speed
tend to have more H form of LDH
tend to have more M form of LDH
Order of recruitment
Muscle twitch
Response to a single stimulation
can vary in force and speed according to fiber type
As stimulations are received with less time between them, twitches begin to summate
not enough time for fiber to fully relax
Summation eventually results in muscle tetanus
multiple twitches with fused peaks
contraction time, half relaxation time, force
Rate coding
muscles can alter their force production by increasing or decreasing their firing rate
up to 10x increase in force
very important when greater force is required from smaller muscles
Fiber type twitch characteristics
initially, recruitment is primary means of increased force production
rate coding becomes more important as you reach maximum force development
in general...
sustained, low force contractions
motor units will be cycled on and off so they can be given short breaks
only occurs at < 40% of maximal force
lengthening contractions
greater afferent feedback to type I and small type IIA fibers
lengthening contractions would activate the GTOs, but they would only be effective for inhibiting smaller, weaker fibers
results in preferential activation of bigger, more forceful motor units
some motor units are active during shortening but not during lengthening, and vice versa
sudden, corrective movements
type IIX motor units are sometimes
selectively activated
in the case of a sudden, corrective movement
e.g. extensor muscle in toes:
some motor units are not active during walking or running, only in rapid accelerations or changes of direction
1/2 relaxation time
peak rate of force development
peak relaxation rate
contraction time
(this is just a screenshot... go to the other prezi for details)
Neuromuscular System
muscle proprioceptors
detect changes in muscle pH, extracellular K+, O2, and CO2
specialized free nerve endings
muscle spindle
run parallel with muscle fibers
detect change in muscle length and static muscle length
higher density of muscle spindles in muscles with fine motor control
rapid stretch of muscle spindle results in reflex contraction
golgi tendon organs
located in the tendon
monitor muscular tension
high tension activates GTOs, resulting in inhibition of muscle contractions
provide info on metabolic rate
make use of
reflex arc
(spinal cord)
(muscle spindle)
electrical signal
Full transcript