ANATOMY

Unit 4 Notes:Sliding Filament

Theory

(1) Muscle Contraction

• Sliding Filaments = Muscle Contraction

• The Basic Steps:

1- Message sent

2- Neurotransmitter

3- Depolarization

4- Calcium + Troponin = Actin Exposed

5- Actin + Myosin (Contraction)

(2) Neuron to Muscle

• Cause:– Conscious decision to move– Homeostatic response

• Nervous System Sends a Message to the Effector Organ:– Neurotransmitter released (ACh, acetylcholine)– ACh binds to sarcolemma of muscle fiber– ACh initiates opening of sodium-potassium

channels

(3) Depolarization of the Muscle

• Cause: – Binding of ACh to sodium-potassium channels– Opening of channels + Movement of Na-K+

across sarcolemma

• Involves the Movement of Charges:– More Na+ moves in, Than K+ moves out– Imbalance of charges electrical current

(action potential)

(4) The Release of Calcium

• Cause: Depolarization

• Action Potential across the Sarcoplasmic Reticulum causes the release of Calcium:– Ca+ released from membrane of sarcoplasmic

reticulum.– Ca+ binds with troponin:

• Troponin-Tropomyosion conformation changes

• Troponin & Tropomyosin no longer cover Actin• Actin is exposed

(5) Myosin interacts with Actin:

• Cause:– Troponin & Tropomyosin unveils Actin– Actin exposed

• Myosin releases Inorganic Phosphate + ADP– Pi + ADP = ATP– Myosin changes conformation– Myosin binds to Actin– Myosin and Actin slide towards each other – WE HAVE A CONTRACTION! WOO WOO!

(6) Relaxation

• ATP binds back with myosin…–Myosin detaches and moves away from

Actin

–Troponin & Tropomyosin cover up Actin

–Ca+ moves back into Sarcoplasmic Reticulum

–Repolarization Sarcolemma stable again

(7) Why is it called the Sliding Filament Theory?

• Movement of myofilaments causes contraction

• Myosin grabs actin & SLIDES them towards the center

(1-2) Depolarization of Sarcolemma & Generation of Action Potential

(3) Calcium Ions released from Sarcoplasmic Reticulum

(4-6) Calcium binds to troponin, tropomyosin moves, actin exposed

(7-8) Myosin attaches to actin, Myosin moves actin, ATP released

(9) Calcium removed by active transport

(10) Everything moves back & contraction done!