Muscle Tissue Cont.

Physiology

Chapter 10

Contraction of Skeletal Muscle = The Sliding Filament Mechanism

• thin and thick filaments slide past each other to shorten each sarcomere and thus each myofibril

• the cumulative effect is to shorten the muscle http://www.lab.anhb.uwa.edu.au/mb140/

CorePages/Muscle/Muscle.htm#SKELETAL

Skeletal Muscle InnervationThe Neuromuscular

Junction: • where neurons communicate

with the muscle fibers • point of communication is a

small gap = synapse• the chemical that travels

across the synapse = neurotransmitter (acetylcholine - ACh)

Steps of Skeletal Muscle Contraction

1. Neurotransmitter ACh is released from the neuron; binds to its receptor on the sarcolemma, and causes the sodium channels to open

  ha5lf0909ab_a.jpg

Steps of Skeletal Muscle Contraction

2. As Na+ ions flow in, an action potential begins

action potential = the spread of depolarization

3. ACh removed by enzyme acetylcholinesterase

 

Steps of Skeletal Muscle Contraction   4. Action potential causes

release of Ca++ ions 5. Ca++ binds to troponin,

causing tropomyosin to move out of its blocking position

6. Contraction: myosin forms cross bridges to actin, muscle shortens, ATP is used

 

Steps of Skeletal Muscle Contraction  

7. Ca++ ions are reabsorbed

8. Myosin binds to new ATP

9. Troponin-tropomyosin complex returns to normal position

10. Contraction ends; muscle returns to its resting length

STUDY FIG. 10.11 p. 317

Skeletal Muscle Contraction = Sliding Filament Theory

The Contraction Cycle Animation

http://www.sci.sdsu.edu/movies/actin_myosin_gif.html

Rigor Mortis

• When death occurs, Ca++ ions leak and cause some contraction of the muscles = stiffness

• Without ATP, cross-bridges cannot detach

• Lasts ~24 hours, then lysosomal enzymes break down myofilaments

To help you memorize muscles, check out:

• http://msjensen.education.umn.edu/webanatomy/

University of Minnesota, WebAnatomy

• With your laptop, check out: www.gwc.maricopa.edu/class/bio201/muscle/mustut.htm