Skeletal Muscle: Electromyography Lab

Question 1

Skeletal muscle is ensheathed in a tough connective tissue called___________

Answer 1

epimysium

Question 2

fascicles

Answer 2

bundles of muscle fibers

Question 3

Each muscle is made up of many ________ that are ensheathed in a connect _______ _________.

Answer 3

fascicles, tissue perimysium

Question 4

what does connect tissue perimysium do?

Answer 4

allow for passage for vasculature and nerves

Question 5

what does each fascicle consist of?

Answer 5

many muscle fibers that are ensheathed by connective tissue endomysium.

Question 6

what does connective tissue at each level help with?

Answer 6

To distribute force, resist tensile force and maintain shape of muscle

Question 7

Each skeletal muscle fiber is a __________ _________ surrounded by ___________ which contains __________ and many myofibrils.

Answer 7

multi nucleated syncytium, sarcolemma, sarcoplasm

Question 8

multi nucleated syncytium

Answer 8

fusion of multiple cells

Question 9

sarcolemma

Answer 9

plasma membrane

Question 10

sarcoplasm

Answer 10

cytoplasm

Question 11

myofibril

Answer 11

chain of sarcomeres

Question 12

What is the function unit of contraction?

Answer 12

sarcomere

Question 13

why are skeletal muscle fibers considered striated?

Answer 13

because of the striped appearance of sarcomeres under the microscope

Question 14

what causes the striped appearance under the microscope when looking at a muscle fiber?

Answer 14

the highly organized alternating pattern of A bands and I bands

Question 15

what are A bands and I bands produced by?

Answer 15

actin and myosin myofilaments

Question 16

Z-line (disc)

Answer 16

sarcomere boundary

Question 17

A-band

Answer 17

region of myosin with some actin overlap

Question 18

I-band

Answer 18

region of only actin

Question 19

H-zone

Answer 19

region of only myosin

Question 20

Skeletal muscle is under _________ control and is innervated by _______ _______.

Answer 20

voluntary, motor neurons

Question 21

neuromuscular junction

Answer 21

chemical synapse between motor neuron and a muscle fiber

Question 22

what does Acetylcholine released from the motor neuron do?

Answer 22

it diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors

Question 23

After acetylcholine binds to nicotinic acetylcholine receptors, what happens next?

Answer 23

This binding brings out end-plate potentials which triggers action potentials in the muscle fiber

Question 24

what does action potentials in the muscle fibers cause?

Answer 24

causes the release of Ca2+ from the sarcoplasmic reticulum (storage site) which allows myosin to bind with actin
forming a cross-bridge.

Question 25

list the steps of action potentials in muscle fibers

Answer 25

• release of Ca2+ from the sarcoplasmic reticulum which allows myosin to bind with actin forming a cross-bridge.
• Myosin then pulls actin towards the center of the sarcomere.
• The sliding of actin over myosin causes each sarcomere to shorten
• This occurs simultaneously in all the sarcomeres of a muscle fiber and generates a muscle contraction.

Question 26

sliding filament theory of contraction

Answer 26

The sliding of actin over myosin to generate force

Question 27

During contraction, the sliding of actin over the myosin causing the I band, H zone, and ultimately the entire sarcomere to?

Answer 27

shorten, whereas the A band remain the same length.

Question 28

T/F: Although the axon of the motor neuron branches multiple times (as collateral branches) to innervate multiple muscle fibers, each muscle fiber in a muscle is innervated by one, and only one, motor neuron.

Answer 28

TRUE

Question 29

Motor unit

Answer 29

A motor neuron and all the muscle fibers it innervates

Question 30

The number of muscle fibers controlled by a single motor neuron can vary from?

Answer 30

5 to more than 500

Question 31

what is an example of a motor neuron that uses 5 muscles fibers?

Answer 31

fine motor control of muscles of the fingers

Question 32

what is an example of a motor neuron that uses 500 muscles fibers?

Answer 32

gross control of the quadriceps

Question 33

T/F: Groups of motor units work together to coordinate
the contraction of a single muscle.

Answer 33

true

Question 34

motor pool

Answer 34

All the motor units of a specific muscle.

Question 35

The degree of contraction (and the force generated) is mediated by the central nervous system via 2 mechanisms, what are they?

Answer 35

• Multiple motor unit summation (= recruitment)
• Temporal summation (= wave summation)

Question 36

Multiple motor unit summation (= recruitment)

Answer 36

increasing the contractile force of a muscle by increasing the number of motor units within a muscle.

Question 37

Temporal summation (= wave summation)

Answer 37

increasing the contractile force of a muscle by increasing action potential frequency of individual motor units

Question 38

The strength of a muscle contraction is proportional to?

Answer 38

The load placed on the muscle.

Question 39

When an increase in strength is required to perform a task, the force of muscle contraction can be increased by?

Answer 39

• increasing the number of motor units being activated
• increasing the stimulation of those active motor units

Question 40

T/F: During rest, muscle is in a constant state of slight tension (tonus) that serves to maintain the muscle is a state of readiness.

Answer 40

True

Question 41

tonus

Answer 41

state of slight tension

Question 42

what is tonus produced by?

Answer 42

produced by alternate periodic activation of a small number of motor units via innervation of CNS motor neurons

Question 43

T/F: The propagation of action potentials by motor neurons and muscle fibers during contraction generates voltage differences (mV) in the overlying skin that can be
detected through surface electromyography.

Answer 43

TRUE

Question 44

what can electromyography be used for?

Answer 44

used to examine the electrical activity of muscle during varying degrees of contraction

Question 45

What is the subsequent recording of an electromyography known as?

Answer 45

electromyogram (EMG)