Muscle Physiology Flashcards
Muscle responsible for creating movement (The Prime Mover).
Is the contracting muscle
Agonist
Opposes movement of prime mover and controls speed of movement.
Is relaxed when prime mover is contracted.
Antagonist
The smallest contractile unit of muscle fiber
Sarcomere
What does a Sarcomere consist of?
Where does it measure from?
Consists of thick myosin filaments and thin actin filaments
It measures from Z disc to Z disc
How does the myosin heads bind to the Actin?
- It requires Ca2+ ions to be released.
- Ca2+ binds to troponin and mechanically deforms it
- That causes the tropomyosin to change position resulting in myosin binding site on the actin to be exposed.
- Once bind site is exposed, myosin head binds to actin
Contraction of Skeletal Muscle Cell. What does each of the following components of the skeletal muscle do during contraction?
- I Bands
- Z-Lines
- A Bands
- H- Zones
- Filaments (myosin & actin)
- I-Bands - shorten
- Z-lines move closer together
- A Bands move closer together
- H-Zones shorten
- Remain unchanged in length
ATP ——>
ADP+Pi
ADP+Pi ——>
ATP
What is Pi?
Inorganic phosphate -
What molecule provides the energy for the power stroke?
ATP
What is required at the end of the power stroke in order to detach the cross bridge?
A new ATP molecule that binds to the Myosin head
What causes Rigor Mortis?
The lack of ATP. If no ATP binds to myosin head then, myosin head cannot detach from actin=stuck - rigor mortis
A single power stroke can shorten muscle by how much?
1% of its resting length
Why must the power stroke be repeated many times?
because muscle can shorten up to 60% and a single power stroke shortens muscle by 1% only. need to stroke it more!
What is called when an electrical event is transformed to a chemical event in order to transmit an AP to the Sarcolemma?
Neuromuscular Junction
- Which N.T. is released and where does it release from?
- Where does the N.T release into?
- What is required to stimulate the release of this N.T?
- Acetylcholine - releases from Somatic Motor exonal endings
- ACh releases into the neuromuscular junction (synaptic cleft)
- Entry of Ca2+ ions into the axonal ending
What does ACh do once it is released into the neuromuscular junction?
Is it a chemical or electrical action?
It opens chemically gated Na+ channels on the sarcolemma.
It is the chemical event of the neuromuscular junction
What kind of gated channels on the sarcolemma does ACh open?
Chemically gated Na+ gated channels
What kind of receptors are on the chemically gated Na+ channels in which ACh binds to?
Where are they located?
Cholinergic and nicotinic receptors
They are located on the sarcolemma
- Na+ ion diffuse inward along the sarcolemma on what kind of gradient?
- What does it reproduce?
- Electrochemical gradient
- Another action potential
When does excitation contraction coupling occur?
During the Latent Period
- What is the period of AP initiation to the beginning of mechanical activity?
- How long does it last?
- What occurs during this period?
- The Latent Period
- 1-2 ms
- AP & Excitation Contraction Coupling.
What is required for power stroke cycle to be repeated?
Ca2+ must stay bound to troponin
What happens if the ACh receptors close?
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.
What happens if Ca2+ is disassociates from troponin?
troponin shifts back to original position, resulting in tropomyosin covering back up the binding site on the actin for the myosin head
What kind of gates allow Na+ to enter be brought to threshold along the sarcolemma?
Voltage gated sodium channels
Where is the Ca2+ released from after the DHP channel triggers the RyR1 channels to open?
Ca2+ is released from the Terminal Cisternae of the Sarcoplasmic Reticulum
What kind of channels are the RyR1 channels
calcium channels
What causes the Excitation contraction coupling sequence to be repeated?
- the arrival of a new nerve impulse
What happens if nerve impulses are delivered rapidly?
Ca2+ levels in the cell remain high, muscles don’t completely relax, contraction is sustained.
A somatic motor neuron and all the muscle fibers it supplies is called what?
A motor unit
What happens when a somatic motor neuron is activated?
All the muscle fibers it innervates are stimulated in an “all or none” contraction
Where on the muscle cell does each branching axonal ending of a motor neuron innervate the cell
At approx the middle of the muscle fiber
Why does stimulation of a motor unit cause a weak contraction of the entire muscle?
Because they are spread out through the muscle and not clustered together
What is the innervation ratio for fine motor control units?
Give an example of a fine motor unit
- Ratio is 1 neuron: 25 fibers (1:25)
- eye muscle,
What is the innervation ratio for large motor units?
Give an example and what kind of control is it called?
Ratio: 1: 2000 (1 neuron to 2k fibers)
- Quadriceps; for gross, powerful control
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.
Twitch
What are the 3 phases of muscle twitch and explain each
- Latent Phase: stimulus delivered > muscle tension increases but no response seen on myogram (2-4 ms)
- Contraction: cross bridges is active and muscle shortens (10 - 100 ms)
- Relaxation: Re-entry of Ca2+ back to SR. Muscle tension returns to zero.
What is the partial contraction in which a single muscle cell response to a stimulation in an “all or none” fashion
Graded contraction
Which type of fiber can only twitch and cannot produce a sustained contraction?
Isolated Fiber.
What is used to records twitch and the response of an isolated fiber?
A myogram
How are muscle motor unit firings initially synchronized to gain strength/force?
At first they are asynchronized (not synchronized) but eventually they become more synchronized and coordinated in their force production
The addition of individual twitches 92 successive firings) is called what?
Wave Summation
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?
The 2nd
Re; Wave Summation, why is the first contraction weaker than the successive contractions? (3 reasons)
- There is more Ca2+ available now
- Slack in the system taken up by 1st impulse
- increased heat increases enzyme activity
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)
The Treppe Effect
Describe Muscle Tone and its functions:
- Muscle is in a constant slightly contracted state (slight tension)
- Function: maintain posture, stabilize joints
- Small # of motor units are in this slight contracted state
- It’s a neuromuscular function; not actual “toning” of muscle
- motor units are highly asynchronous and respond to nerve impulses from higher motor centers in brain and spinal cord
What is Motor Unit Summation?
What is Maximal Stimulus:
Asynchronous unit summation to control force of contraction
When all muscle motor units are activated from smaller first, then to larger
Why does muscle need ATP?
- Its the immediate energy source for muscle contraction (cross bridge action)
- ATP is the ONLY energy source for SKELETAL MUSCLE; so it must be regenerated quickly.
How much ATP does muscle contain?
4-6 seconds worth/approx 10 twitches
