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)