Muscle Physiology

Question 1

Muscle responsible for creating movement (The Prime Mover).
Is the contracting muscle

Answer 1

Agonist

Question 2

Opposes movement of prime mover and controls speed of movement.
Is relaxed when prime mover is contracted.

Answer 2

Antagonist

Question 3

The smallest contractile unit of muscle fiber

Answer 3

Sarcomere

Question 4

What does a Sarcomere consist of?
Where does it measure from?

Answer 4

Consists of thick myosin filaments and thin actin filaments

It measures from Z disc to Z disc

Question 5

How does the myosin heads bind to the Actin?

Answer 5

1. It requires Ca2+ ions to be released.
2. Ca2+ binds to troponin and mechanically deforms it
3. That causes the tropomyosin to change position resulting in myosin binding site on the actin to be exposed.
4. Once bind site is exposed, myosin head binds to actin

Question 6

Contraction of Skeletal Muscle Cell. What does each of the following components of the skeletal muscle do during contraction?

1. I Bands
2. Z-Lines
3. A Bands
4. H- Zones
5. Filaments (myosin & actin)

Answer 6

1. I-Bands - shorten
2. Z-lines move closer together
3. A Bands move closer together
4. H-Zones shorten
5. Remain unchanged in length

Question 7

ATP ——>

Answer 7

ADP+Pi

Question 8

ADP+Pi ——>

Answer 8

ATP

Question 9

What is Pi?

Answer 9

Inorganic phosphate -

Question 10

What molecule provides the energy for the power stroke?

Answer 10

ATP

Question 11

What is required at the end of the power stroke in order to detach the cross bridge?

Answer 11

A new ATP molecule that binds to the Myosin head

Question 12

What causes Rigor Mortis?

Answer 12

The lack of ATP. If no ATP binds to myosin head then, myosin head cannot detach from actin=stuck - rigor mortis

Question 13

A single power stroke can shorten muscle by how much?

Answer 13

1% of its resting length

Question 14

Why must the power stroke be repeated many times?

Answer 14

because muscle can shorten up to 60% and a single power stroke shortens muscle by 1% only. need to stroke it more!

Question 15

What is called when an electrical event is transformed to a chemical event in order to transmit an AP to the Sarcolemma?

Answer 15

Neuromuscular Junction

Question 16

1. Which N.T. is released and where does it release from?
2. Where does the N.T release into?
3. What is required to stimulate the release of this N.T?

Answer 16

1. Acetylcholine - releases from Somatic Motor exonal endings
2. ACh releases into the neuromuscular junction (synaptic cleft)
3. Entry of Ca2+ ions into the axonal ending

Question 17

What does ACh do once it is released into the neuromuscular junction?

Is it a chemical or electrical action?

Answer 17

It opens chemically gated Na+ channels on the sarcolemma.

It is the chemical event of the neuromuscular junction

Question 18

What kind of gated channels on the sarcolemma does ACh open?

Answer 18

Chemically gated Na+ gated channels

Question 19

What kind of receptors are on the chemically gated Na+ channels in which ACh binds to?
Where are they located?

Answer 19

Cholinergic and nicotinic receptors
They are located on the sarcolemma

Question 20

1. Na+ ion diffuse inward along the sarcolemma on what kind of gradient?
2. What does it reproduce?

Answer 20

1. Electrochemical gradient
2. Another action potential

Question 21

When does excitation contraction coupling occur?

Answer 21

During the Latent Period

Question 22

1. What is the period of AP initiation to the beginning of mechanical activity?
2. How long does it last?
3. What occurs during this period?

Answer 22

1. The Latent Period
2. 1-2 ms
3. AP & Excitation Contraction Coupling.

Question 23

What is required for power stroke cycle to be repeated?

Answer 23

Ca2+ must stay bound to troponin

Question 24

What happens if the ACh receptors close?

Answer 24

AP’s stop as no Na+ is present to trigger the DHP to open the RyR1 channel on the Sarcoplasmic reticulum, therefore Ca2+ levels drop and cant bind to troponin.

Question 25

What happens if Ca2+ is disassociates from troponin?

Answer 25

troponin shifts back to original position, resulting in tropomyosin covering back up the binding site on the actin for the myosin head

Question 26

What kind of gates allow Na+ to enter be brought to threshold along the sarcolemma?

Answer 26

Voltage gated sodium channels

Question 27

Where is the Ca2+ released from after the DHP channel triggers the RyR1 channels to open?

Answer 27

Ca2+ is released from the Terminal Cisternae of the Sarcoplasmic Reticulum

Question 28

What kind of channels are the RyR1 channels

Answer 28

calcium channels

Question 29

What causes the Excitation contraction coupling sequence to be repeated?

Answer 29

1. the arrival of a new nerve impulse

Question 30

What happens if nerve impulses are delivered rapidly?

Answer 30

Ca2+ levels in the cell remain high, muscles don't completely relax, contraction is sustained.

Question 31

A somatic motor neuron and all the muscle fibers it supplies is called what?

Answer 31

A motor unit

Question 32

What happens when a somatic motor neuron is activated?

Answer 32

All the muscle fibers it innervates are stimulated in an "all or none" contraction

Question 33

Where on the muscle cell does each branching axonal ending of a motor neuron innervate the cell

Answer 33

At approx the middle of the muscle fiber

Question 34

Why does stimulation of a motor unit cause a weak contraction of the entire muscle?

Answer 34

Because they are spread out through the muscle and not clustered together

Question 35

What is the innervation ratio for fine motor control units? Give an example of a fine motor unit

Answer 35

1. Ratio is 1 neuron: 25 fibers (1:25) 2. eye muscle,

Question 36

What is the innervation ratio for large motor units? Give an example and what kind of control is it called?

Answer 36

Ratio: 1: 2000 (1 neuron to 2k fibers) 2. Quadriceps; for gross, powerful control

Question 37

Term for a single muscle fiber quickly contracting and relaxing in response to a single electrical pulse. Its an all or nothing deal and can only be seen on a myogram.

Answer 37

Twitch

Question 38

What are the 3 phases of muscle twitch and explain each

Answer 38

1. Latent Phase: stimulus delivered > muscle tension increases but no response seen on myogram (2-4 ms) 2. Contraction: cross bridges is active and muscle shortens (10 - 100 ms) 3. Relaxation: Re-entry of Ca2+ back to SR. Muscle tension returns to zero.

Question 39

What is the partial contraction in which a single muscle cell response to a stimulation in an "all or none" fashion

Answer 39

Graded contraction

Question 40

Which type of fiber can only twitch and cannot produce a sustained contraction?

Answer 40

Isolated Fiber.

Question 41

What is used to records twitch and the response of an isolated fiber?

Answer 41

A myogram

Question 42

How are muscle motor unit firings initially synchronized to gain strength/force?

Answer 42

At first they are asynchronized (not synchronized) but eventually they become more synchronized and coordinated in their force production

Question 43

The addition of individual twitches 92 successive firings) is called what?

Answer 43

Wave Summation

Question 44

Re: wave summation, which nerve impulse is stronger if 2 identical nerve impulses are delivered to the muscle in rapid succession? the 1st or 2nd?

Answer 44

The 2nd

Question 45

Re; Wave Summation, why is the first contraction weaker than the successive contractions? (3 reasons)

Answer 45

1. There is more Ca2+ available now 2. Slack in the system taken up by 1st impulse 3. increased heat increases enzyme activity

Question 46

What is theory that the 1st contraction is less strong than successive contractions? (Hint: Stair case effect, more Ca2+ available, slack in system, heat makes enzymes faster)

Answer 46

The Treppe Effect

Question 47

Describe Muscle Tone and its functions:

Answer 47

1. Muscle is in a constant slightly contracted state (slight tension) 2. Function: maintain posture, stabilize joints 3. Small # of motor units are in this slight contracted state 4. It's a neuromuscular function; not actual "toning" of muscle 5. motor units are highly asynchronous and respond to nerve impulses from higher motor centers in brain and spinal cord

Question 48

What is Motor Unit Summation? What is Maximal Stimulus:

Answer 48

Asynchronous unit summation to control force of contraction When all muscle motor units are activated from smaller first, then to larger

Question 49

Why does muscle need ATP?

Answer 49

1. Its the immediate energy source for muscle contraction (cross bridge action) 2. ATP is the ONLY energy source for SKELETAL MUSCLE; so it must be regenerated quickly.

Question 50

How much ATP does muscle contain?

Answer 50

4-6 seconds worth/approx 10 twitches