Midterm 1 - Unit 1 Lecture 3 Flashcards
what is a motor unit
an individual motor neuron and all of the muscle fibers that it innervates
what is innervation ratio
The number of fibers innervated by a motor unit
what is a small motor unit innervation ratio
2
what is a large motor unit innervation ratio
5
The number of muscle fibers innervated will vary depending upon the muscle. True or false
true
how many muscle fibres are innervated by the Gastrocnemius
up to 2000 fibres
how many muscle fibres are innervated by the eye muslces
as few as 5 fibers
the more muscle fibers innervated the ___________
greater force produced
the fewer muscle fibers innervated ____________
the less force produced, but allows for greater accuracy
firing rate of motor neuron is proportional ________
the force generated
how is size of the MU is related to force
bigger MU produce more force than smaller ones (because of more muscle fibres)
smaller MU are easier to control for fine movement
why does response to synaptic input depend on size of motor neuron. Provide an example
Due to surface area and axon diameter
smaller motor neurons with smaller surface areas
Larger EPSP
Slower conduction velocity
Fewer muscle fibers
why does response to synaptic input depend on size of motor neuron
Due to surface area and axon diameter
During muscle contraction which MUs are recruited first
small MUs are recruited before large ones
what is the size principle
when small MUs are recruited before large ones, because it allows gradation of muscle force
how would we increase force
Increase the number of active motor units
Increase the firing rate of active motor units
The level of force where the last motor unit is recruited is different between muscles. True or false. Provide an example
true. Hand muscle has all motor units recruited at 60% max slow contraction(therefore in order to increase force you would then have to increase the firing rate); 85% in biceps
what is a motor neuron pool
all the individual motor neurons innervating a single muscle
Ratio of motor neurons to muscle fibres affects the precision of control. True or flase
true
where are the Motor neurons innervating one muscle located
clustered in the spinal cord
how much do motor neuron pools spread out
Can extend 1 to 4 spinal segments
what are the two types of muscle fibres
Extrafusal muscle fibres
Intrafusal muscle fibres
what are extrafusal muscle fibres
Regular muscle fibres
Contraction of these fibres allow for movement
innervated by alpha motor neurons
Movers
what are intrafusal muscle fibres
Fewer of them;located deep within most skeletal muscles along side extrafusal muscle fibres
4-7 in group and wrapped in capsule separating them from the rest of the muscle: groups are called Muscle spindles
Sensors
what is a key difference between intrafusal and extrafusal muscle fibres
Change in length just like the extrafusal muscle fibres, but do NOT generate force
they detect changes in muscle length
specialized for proprioception which informs us about how our body is positioned or moving in space
what are the two types of motor neurons
Alpha (α) motor neurons
Gamma (γ) motor neurons
what are alpha motor neurons
innervate extrafusal muscle fibers
control muscle contraction
what are Gamma (γ) motor neurons
innervate muscle spindles (intrafusal muscle fibres)
controls the sensitivity of muscle spindles
what are Symptoms of Alpha Motor Neuron Injury
Muscle Weakness – loss of strength
Fasciculations – uncontrolled muscle twitch
Atrophy - loss of muscle mass
Hyporeflexia – decreased reflexes
Hypotonia – lack of passive resistance
