HES 202 EXAM QUESTIONS AND ANSWERS LATEST
UPDATE
motor unit size principle
motor units are recruited in order from small to large
Functional consequences of size principle
Simplifies the task of modulating force not necessary for higher centres to select
specific combinations of MUs
Functional consequences of size principle 2
Ensures a smooth increase in force production
Functional consequences of size principle 3
Minimizes fatigue as slow twitch, fatigue-resistant muscle fibres are activated first
RECRUITMENT - FAST CONTRACTIONS
Recruitment threshold can change within a motor unit
Order across motor units remains consistent
MOTOR UNIT - RATE CODING
Force-frequency curve Sigmoidal relationship
Firing rate match
contractile speed
MOTOR UNIT - FORCE CONTROL 1
Increase the number of motor units (recruitment)
MOTOR UNIT - FORCE CONTROL 2
Increase rate of firing of individual motor units (rate coding)
Force control. How am I able to maintain a steady contraction if my MUs are only
firing/discharging at 8 Hz?
Each motor unit produces partially fused tetanus; because units fire asynchronously
with each other, the net force is smooth
EMG - Indwelling
Somewhat invasive, but single cells
MOTOR UNIT - RECRUITMENT RANGE
Upper limit of recruitment varies between muscles
Adductor Pollicis - 30%
MVC Biceps Brachii - 80%
MVCSoleus - >95% MVC
Divergence:
a single neuron synapses on multiple
Convergence:
multiple neurons "converge" on fewer neurons
Extrafusal:
skeletal muscle fibre
Intrafusal
muscle spindle
afferent
to
UPDATE
motor unit size principle
motor units are recruited in order from small to large
Functional consequences of size principle
Simplifies the task of modulating force not necessary for higher centres to select
specific combinations of MUs
Functional consequences of size principle 2
Ensures a smooth increase in force production
Functional consequences of size principle 3
Minimizes fatigue as slow twitch, fatigue-resistant muscle fibres are activated first
RECRUITMENT - FAST CONTRACTIONS
Recruitment threshold can change within a motor unit
Order across motor units remains consistent
MOTOR UNIT - RATE CODING
Force-frequency curve Sigmoidal relationship
Firing rate match
contractile speed
MOTOR UNIT - FORCE CONTROL 1
Increase the number of motor units (recruitment)
MOTOR UNIT - FORCE CONTROL 2
Increase rate of firing of individual motor units (rate coding)
Force control. How am I able to maintain a steady contraction if my MUs are only
firing/discharging at 8 Hz?
Each motor unit produces partially fused tetanus; because units fire asynchronously
with each other, the net force is smooth
EMG - Indwelling
Somewhat invasive, but single cells
MOTOR UNIT - RECRUITMENT RANGE
Upper limit of recruitment varies between muscles
Adductor Pollicis - 30%
MVC Biceps Brachii - 80%
MVCSoleus - >95% MVC
Divergence:
a single neuron synapses on multiple
Convergence:
multiple neurons "converge" on fewer neurons
Extrafusal:
skeletal muscle fibre
Intrafusal
muscle spindle
afferent
to
