Unit-1: Neuromuscular Aspect

of Movement-2

Contents of the lesson • All or none law

• Strength of Contraction

• Group Action of Muscles

• Reciprocal Innervation

• Muscular Fatigue

All or None Law • This law states that:

“ When a stimulus of minimum threshold is sent to

the motor unit then all the muscle fibers, within unit,

are recruited and contracted to their full extent.”

• Full response or No response.

All or None Law

Strength of Contraction Certain important terms to understand:

• Phasic Contraction:

Muscle’s response to a single stimulus of sufficient

magnitude.

• Twitch:

a single contraction of a muscle fiber in response to brief

threshold stimulation.

Strength of Contraction • Latent Period

Short Period of time b/w stimulation and tension

development. “ Reaction time of muscle fiber”

Strength of Contraction • Relaxation Period

the time during which the tension is removed from

the muscle fiber.

Strength of Contraction • Multiple Wave Summation

The summation of multiple stimuli and their tensions

from twitches when subsequent stimulus arrives before

the complete relaxation period in a muscle fiber.

Strength of Contraction • Tetany or Tetnus Contraction

A sustained contraction resulting from multiple wave

summation.

Strength of Contraction • Strength of Contraction = Tension generated.

• So, in terms of strength;

Fused tetany> Unfused Tetany> Multiple Wave summation> twitch

Strength of contraction

Group Action of Muscles • “Coordination among the contraction and activities

of motor muscles to effectively execute a motor

action. “

Gro

up

Act

ion

of

Mu

scle

Agonist: prime movers

Antagonist: contralateral muscle

Stabilizers

Synergist

Neutralizers

Reciprocal Innervation • Sherrington’s Law of Reciprocal Inhibition

• “For the initiation of any motor action, motor

neurons carry exciting impulse to agonist muscle

and inhibitory impulse to antagonist muscles.”

• Important for neuromuscular coordination and

delaying fatigue.

Muscle Fatigue • “ State of discomfort and decline in the efficiency

and functioning capacity of the muscle due to

prolonged or excessive exertion”

• “ Failure to execute voluntary contraction”

Causes of Muscle Fatigue • Lack of Na+ ion in the motor nerve.

• Decline in the release of AcH from Neuromuscular

Junction.

• Accumulation of Lactic Acid.

• Reduction in ATP-CP stores.

• Reduction in muscle glucose

• CNS fails to initiate and relay nerve impulse to the

muscle.

References • https://www.wikiwand.com/en/All-or-none_law

• http://www.unm.edu/~jimmy/muscle3_notes.htm

• Shaw,Dhananjoy. (1998).Biomechanics and

kinesiology of human

motion.Khelsahityapublication. Newdelhi

• Floyed ,R.T.(2009). manual of structural

kinesiology.,USA,ed.16. humankinetics

Doubts?

Topics to be revised for the next lesson

• Moment of Inertia

• Center of gravity and balance

• Levers and mechanical advantage

• Linear and angular Momentum

• Principle of conservation of Angular Momentum

• Motor Action and it’s Characteristics

• Fluid drag