SSEH1101 Study Guide - Final Guide: Maximum Force, Sarcomere, Extraocular Muscles
24 Jun 2018
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Single Motor Unit Contraction
1. The Motor Unit
a. A Motor Unit Comprises
i. Motor Neuron
ii. All attached muscle fibres
2. Recruitment
a. Small motor units produce precise movements
b. Large motor units produce gross movements
3. Muscle Tone
a. Asynchronous motor unit contraction causes a constant state of low-level tension
on the muscle.
Whole Muscle Contraction
3 Factors affect tension in the muscle
1. Frequency of Stimulation
a. Single Stimulus
b. Multiple Stimuli (treppe, temporal summation, incomplete tetanus, complete
tetanus, fatigue)
2. Number of Motor Units Contraction
a. Stimulation voltage is increase to recruit motor units
b. Sub threshold stimulus
c. Threshold stimulus
d. Recruitment
e. Maximal stimulus
3. Degree of Muscle Stretch
a. Unstretched muscle
b. Moderate stretched muscle
c. Overstretched muscle
The Motor Unit
While MUSCLE FIBRE is the basic structural unit of muscle, and contracts to its fullest extent
when stimulated.. The muscle fibre does not act as an independent unitt
→ The basic functional unit of muscle is known as MOTOR UNIT
→ Each motor unit consists of an a MOTOR NEURON plus all the muscle fibres it innovates
Depending on region of body, a MOTOR NEURON may innovate:
1. Only a few muscle fibres
a. Eye muscles = 3 fibres/a MN
b. Fine control of movements
2. Many muscle fibres
a. Vasti muscles = 150 fibres/a MN
b. Gross control of movements
Size of muscle plays a role to stimulate fibres and reach full tension development
Force Production
1. Temporal Summation
a. Force production is affected by the firing rate of the a MN
b. As rate of firing increases, so also does the tension developed in the attached
muscle fibres as well as the whole muscle
2. Motor Unit Recruitment
a. Stronger stimuli cause multiple motor unit recruitment
b. Red or Slow Twitch (ST) Fibres tend to be recruited first, followed by Fast Twitch
Fibres (FT) which require higher threshold voltages
c. After a point, all muscle fibres are recruited and no further increases in tension
are possible
3. The Length of the Muscle
a. Force production is affected by the length of muscle at any given movement
b. This is determined by the number of cross bridge links that can be made within
each sarcomere and gives rise to the Length - Tension Relationship
Maximum Force Production → Strength a muscle bulk (cross-sectional area). However,
strength may increase without change to muscle bulk (particularly at the start of a new training
regime)
→ It has been proposed that these early improvements in strength are due to:
1. Changes in the involvement of motor units (tug of war analogy)
2. Decrease contraction of antagonist muscles (muscles that oppose the action of the
prime mover)
3. Disinhibition of the agonist (body’s protective mechanism)
Document Summary
Single motor unit contraction: the motor unit, a motor unit comprises, motor neuron ii. All attached muscle fibres: recruitment, small motor units produce precise movements, large motor units produce gross movements, muscle tone, asynchronous motor unit contraction causes a constant state of low-level tension on the muscle. While muscle fibre is the basic structural unit of muscle, and contracts to its fullest extent when stimulated The muscle fibre does not act as an independent unitt. The basic functional unit of muscle is known as motor unit. Each motor unit consists of an a motor neuron plus all the muscle fibres it innovates. Depending on region of body, a motor neuron may innovate: only a few muscle fibres, eye muscles = 3 fibres/a mn, fine control of movements, many muscle fibres, vasti muscles = 150 fibres/a mn, gross control of movements. Size of muscle plays a role to stimulate fibres and reach full tension development.
