Post on 26-Jan-2016
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Skeletal Muscle ContractionAdrian LuiKinesiology – OTHSMrs. Coe
About Me
OTHS Graduate
University of Waterloo – Kinesiology (BSc.)
Brock University – Muscle Physiology (MSc.)
University of Canterbury – Secondary Education (Grad. Dip)
Ask me anything!
In Two Periods…
1. Motor Neurons• Passing the
message from brain to muscle
2. Excitation Coupling• “Interpreting” the
signal
3. Sliding Filament Theory• Physical
contraction
Muscle Anatomy
Muscle Anatomy
OUTSIDE
Muscle Belly
Epimyesium - The prefix means “outside” (epi)
Fasciculus
“Perimyesium” - The prefix means “around” (peri)
Muscle Fibre
“Epimyesium” - The prefix means “Inside” (endo)
SARCOLEMMA
The Motor Unit – Squeeze Game
p. 35
The Motor UnitSends from the neuron body to the muscle fibres
(AP) depolarizes (travels down) the axon hillock as it hops over the myelinated sheathes
AP’s: All or None
Once an electrical signal fires, ALL muscle fibres associated with the motor neuron WILL contract
A single motor unit may stimulate anywhere between to muscle fibres
Neuromuscular Junction
• AP depolarizes to the axon terminal
• The electrical signal causes a release of chemicals (neurotransmitters):
Neuromuscular Junction
Acetylcholine (Ach) crosses the and attaches to the Ach receptors on the motor end plate of the muscle fibre
This in turn sends another electrical signal within the muscle fibre
T - Tubules
• The electrical signal from the motor end plate travels to the T-Tubules and causes a physical reaction at the
Down the T-Tubules
AP causes the release of calcium from the
__________________ (SR)
• Calcium (Ca2+) travels from an area of high concentration to low concentration
• Ca2+ the major signaling messenger for muscle contraction
Review1. Message sent from brain (CNS) to spinal
cord and then to the limb (PNS).
2. Message (action potential) travels from the cell body of a neuron, down its axon to the axon terminal.
3. Acetylcholine (Ach) is released from the axon terminal where it binds to receptors found on the motor end plate of the muscle fibre.
4. The receptors initiate another action potential down the T-Tubules and causes the release of calcium from the sarcoplasmic reticulum.
Ca2+ is release …
Ca2+ interacts with Myofibrils (Myosin & Actin)
Sliding Filament Theory
Sliding Filament Theory
Originally, it was thought that myosin would curl up in and physically shorten when muscle is contracted
This was disproved when the width of the A Band (myosin) ___________ change during contraction
It was discovered that Myosin and Actin ___________ over each other during contraction
MyosinAlso known as: _________
Golf Clubs (Drivers) bundled together with heads facing outward
Has a binding site for: _________
Does most of the work in the “power stroke”
Actin
Also known as: __________
Globules arrange like a winding chain
Is associated with Troponin and Tropomyosin
Is the ______________ for the power stroke
ATP Binds…
ATP binds to myosin head
Myosin binds to actin in a “_________” position
ATP = ADP + Pi
ATP is broken down and _________ is released causing a _________________ where myosin slides past actin
ADP and Pi are released from the myosin head
Another ATP binds …
A fresh ATP binds as the myosin dissociates (weakly binds) with Actin
It’s ready to go again!
But where does Ca2+ come in?
Troponin and Tropomysoin
_____________ Ca2+ bound to troponin, Tropomyosin BLOCKS myosin from binding onto actin
Therefore, Ca2+ needs to be present and binds to troponin
Troponin and Tropomysoin
With Ca2+ bound to ___________ , _____________ slides out of the way to allow actin / myosin interaction
How do stop Contraction?
Sarcoplasmic (endo) Recticulum Calcium ATPase (SERCA)
SERCA pumps Ca2+ back into the SR against a concentration gradient
Therefore requires energy
Concentric vs Eccentric
Concentric = shortening WHILE creating force
Eccentric = lengthening WHILE creating force
How do we create force then?
The ____________ of actin / myosin interactions (or crossbridges formed)