Midterm 1 - Unit 1 Lecture 3

Question 1

what is a motor unit

Answer 1

an individual motor neuron and all of the muscle fibers that it innervates

Question 2

what is innervation ratio

Answer 2

The number of fibers innervated by a motor unit

Question 3

what is a small motor unit innervation ratio

Answer 3

2

Question 4

what is a large motor unit innervation ratio

Answer 4

5

Question 5

The number of muscle fibers innervated will vary depending upon the muscle. True or false

Answer 5

true

Question 6

how many muscle fibres are innervated by the Gastrocnemius

Answer 6

up to 2000 fibres

Question 7

how many muscle fibres are innervated by the eye muslces

Answer 7

as few as 5 fibers

Question 8

the more muscle fibers innervated the ___________

Answer 8

greater force produced

Question 9

the fewer muscle fibers innervated ____________

Answer 9

the less force produced, but allows for greater accuracy

Question 10

firing rate of motor neuron is proportional ________

Answer 10

the force generated

Question 11

how is size of the MU is related to force

Answer 11

bigger MU produce more force than smaller ones (because of more muscle fibres)
smaller MU are easier to control for fine movement

Question 12

why does response to synaptic input depend on size of motor neuron. Provide an example

Answer 12

Due to surface area and axon diameter
smaller motor neurons with smaller surface areas
Larger EPSP
Slower conduction velocity
Fewer muscle fibers

Question 12

why does response to synaptic input depend on size of motor neuron

Answer 12

Due to surface area and axon diameter

Question 13

During muscle contraction which MUs are recruited first

Answer 13

small MUs are recruited before large ones

Question 14

what is the size principle

Answer 14

when small MUs are recruited before large ones, because it allows gradation of muscle force

Question 15

how would we increase force

Answer 15

Increase the number of active motor units
Increase the firing rate of active motor units

Question 16

The level of force where the last motor unit is recruited is different between muscles. True or false. Provide an example

Answer 16

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

Question 17

what is a motor neuron pool

Answer 17

all the individual motor neurons innervating a single muscle

Question 18

Ratio of motor neurons to muscle fibres affects the precision of control. True or flase

Answer 18

true

Question 19

where are the Motor neurons innervating one muscle located

Answer 19

clustered in the spinal cord

Question 20

how much do motor neuron pools spread out

Answer 20

Can extend 1 to 4 spinal segments

Question 21

what are the two types of muscle fibres

Answer 21

Extrafusal muscle fibres
Intrafusal muscle fibres

Question 22

what are extrafusal muscle fibres

Answer 22

Regular muscle fibres
Contraction of these fibres allow for movement
innervated by alpha motor neurons
Movers

Question 23

what are intrafusal muscle fibres

Answer 23

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

Question 24

what is a key difference between intrafusal and extrafusal muscle fibres

Answer 24

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

Question 25

what are the two types of motor neurons

Answer 25

Alpha (α) motor neurons
Gamma (γ) motor neurons

Question 26

what are alpha motor neurons

Answer 26

innervate extrafusal muscle fibers
control muscle contraction

Question 27

what are Gamma (γ) motor neurons

Answer 27

innervate muscle spindles (intrafusal muscle fibres)
controls the sensitivity of muscle spindles

Question 28

what are Symptoms of Alpha Motor Neuron Injury

Answer 28

Muscle Weakness – loss of strength
Fasciculations – uncontrolled muscle twitch
Atrophy - loss of muscle mass
Hyporeflexia – decreased reflexes
Hypotonia – lack of passive resistance