Muscle Contraction
Biomed Academy Body Systems
Draw and label a sarcomere. Include: z-­‐lines, actin 5ilaments, myosin 5ilaments with heads, light bands, dark bands
Use available resources to explain how skeletal muscle contracts. Include in your explanation:
nerve impulse, acetylcholine, calcium ions, sarcoplasmic reticulum, actin, myosin, actin-­‐myosin crossbridges, sliding 5ilaments, ATP, troponin complex, tropomyosin
A.P. Biology
Lecture Notes
Sensory Reception: Taste, Smell, Muscle Contraction
Taste and Smell-Direct chemoreception. Chemicals bond to specific receptors in
neuron cell membranes causing changes in membrane permeability that creates
action potential.
A brief discussion of skeletal systems
1. hydrostatic skeletons-planaria, worms
2. exoskeleton-grasshoppers, crayfish
3. endoskeleton-mammals, birds, fish etc.
A brief discussion of muscular system
1. Muscles work against some type of skeleton. They only PULL and therefore
work in antagonistic pairs.
2. Vertebrate skeletal muscle anatomy (fig. 49.26)
a. the muscle
b. the muscle fiber
c. the myofibril containing many sarcomeres (the contracting unit)
d. the sarcomere consisting of actin, myosin, tropomyosin,
and troponin
3. Muscle contraction mechanism
a. stimulated by action potential of motor neuron. The axon of these
neurons releases acetylcholine (THE neurotransmitter).
b. this causes depolarization deep within the muscle cells
c. at rest, the myosin binding sites on the actin are blocked by protein
(tropomyosin) and troponin complex
d. sarcoplasmic reticulum of muscle cell becomes depolarized and
releases store of Ca+2 ions.
e. the Ca +2 binds to troponin causing thin filaments to change shape
and expose binding sites.
f. crossbridges form between the actin and myosin and slide past one
another using ATP energy....this is muscle contraction.
g. contraction is terminated when sarcoplasmic reticulum “pumps” Ca+2
out of cytoplasm. As Ca+2 levels decrease, the tropomyosintroponin complex again blocks binding sites.