Human Morph Lab NMJ / EMG

Describe the Fiber cross-sectional area of the following skeletal muscle fiber: Slow Oxidative (SO) Fibers (Type I Fibers).

small

Describe the Fiber cross-sectional area of the following skeletal muscle fiber: Fast Oxidative (FO) Fibers (Type IIa Fibers).

medium

Describe the Fiber cross-sectional area of the following skeletal muscle fiber: Fast Glycolytic (FG) Fibers (Type IIb Fibers).

large

Describe the order of recruitment of the following skeletal muscle fiber: Slow Oxidative (SO) Fibers (Type I Fibers).

first

Describe the order of recruitment of the following skeletal muscle fiber: Fast Oxidative (FO) Fibers (Type IIa Fibers)

second

Describe the order of recruitment of the following skeletal muscle fiber: Fast Glycolytic (FG) Fibers (Type IIb Fibers).

third

Describe the resistance to fatigue of the following skeletal muscle fiber: Fast Oxidative (FO) Fibers (Type IIa Fibers).

medium

Describe the resistance to fatigue of the following skeletal muscle fiber: Slow Oxidative (SO) Fibers (Type I Fibers).

large

Describe the resistance to fatigue of the following skeletal muscle fiber: Fast Glycolytic (FG) Fibers (Type IIb Fibers).

small

Describe the size of motor units of the following skeletal muscle fiber: Fast Glycolytic (FG) Fibers (Type IIb Fibers).

large

Describe the size of motor units of the following skeletal muscle fiber: Slow Oxidative (SO) Fibers (Type I Fibers).

small

Describe the size of motor units of the following skeletal muscle fiber: Fast Oxidative (FO) Fibers (Type IIa Fibers).

medium

Describe the speed of contraction of the following skeletal muscle fiber: Slow Oxidative (SO) Fibers (Type I Fibers).

slow

Describe the speed of contraction of the following skeletal muscle fiber: Fast Oxidative (FO) Fibers (Type IIa Fibers) and Fast Glycolytic (FG) Fibers (Type IIb Fibers).

fast

Describe the twitch speed and force of the following skeletal muscle fiber: Slow Oxidative (SO) Fibers (Type I Fibers).

slow and small

Describe the twitch speed and force of the following skeletal muscle fiber: Fast Oxidative (FO) Fibers (Type IIa Fibers).

fast and medium

Describe the twitch speed and force of the following skeletal muscle fiber: Fast Glycolytic (FG) Fibers (Type IIb Fibers).

fast and large

What is each skeletal muscle fiber innervated by?

somatic motor neuron

What is a motor unit?

a single motor neuron and all muscle fibers innervated by that motor neuron

The point of interaction between an axonal branch and an individual skeletal muscle fiber is called?

a neuromuscular junction

Each neuromuscular junction is composed of?

• an oval-shaped synaptic knob of a motor neuron

• a motor end plate of a skeletal muscle fiber

• A synaptic cleft

True or false: the skeletal muscle fibers within a motor unit are of the same type.

true

What do small motor units consist of?

Slow Oxidative (SO) Fibers

• recruited first

What do medium motor units consist of?

Fast Oxidative (FO) Fibers

What do large motor units consist of?

Fast Glycolytic (FG) Fibers

The strength of a muscle contraction is related to?

the number of motor units in the muscle that are activated during the same time period

The strength of a striated muscle contraction is directly proportional to?

the amount of electrical activity in the muscle

the area under the graph of the absolute integral of the EMG is linearly proportional to?

the strength of the muscle contraction

Is there a linear relationship between the absolute integral under EMG signals and the absolute integral under the muscle contraction?

yes, positive

Do muscle fibers have a refractory period like nerve fibers?

yes bc both generate action potentials

Does the amplitude of the EMG signal and the force of contraction, as measured by the absolute integrals, increase because a finite number of fibers are firing more often, or because more fibers are recruited to fire as the intensity of signals in the motor neurons increases, or a combination of these two?

combination of both as the intensity of motor neuron signals increases, the amplitude of the EMG signal and the force of muscle contraction generally increase

How do you think the firing rate of motor neurons changes during a maximal contraction compared to a minimal contraction?

max: motor neurons fire at a higher frequency = larger EMG signal and a greater force of contraction

min: motor neurons fire at a relatively low frequency = small EMG signal and a low force of contraction

Why is the relationship between EMG amplitude and muscle force not always perfectly linear? What factors could influence this?

because electrical activity in a muscle does not translate directly into an equal increase in mechanical force

• Motor unit recruitment

• Firing frequency

• Muscle length and contraction type

Describe muscle.

made up of dascicles (bundles) of muscle fibers, which consists of myofibrils (contractile proteins)

Describe the formation of an electrical signal in the process of muscle work in an electromyogram.

1) after the arrival of a nerve impulse to the MU, the membrane of the muscle fiber is depolarized (within 0.5 ms)

2) depolarization process spreads to both sides of the muscle cell at a speed of 2-6 m/s.

3) The electrodes located in this field record the voltage (electric potential) of muscle fibers

What happens if the electrodes are placed along the muscle fibers?

the electrical signal of the fibers will be bipolar in shape and the sign of the first wave will depend on the location of the electrode with respect to the fibers

What does the absolute integral measure?

the area under a curve