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Chapter 12

Chapter 12 notes

Biological Sciences
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Chapter 12- Muscles
-muscle generate motion force and heat
-there are 3 types of muscle; skeletal cardiac and smooth muscle. Skeletal and cardiac
muscle are striated muscles
-skeletal muscles are controlled by somatic motor neurons. Cardiac muscle and smooth
muscle are controlled by autonomic innervation, paracrines, and hormones. Some smooth
and cardiac muscles are autorhhthmic and contrast spontaneously
Skeletal Muscle
-skeletal muscles are usually attached to bones by tendons. The origin is the end of the
muscle attached closest to the trunk or to the more stationary bone. The insertion is the
more distal or mobile attachment
-at a flexible joint, muscle contraction moves the skeleton. Flexors bring bones closer
together; extensors move bones away from each other. Flexor- extensory pairs are
examples of antagonistic muscle groups
-a skeletal muscle is a collection of muscle fibers, large cells with many nuclei
-T-tubules allow action potentials to move rapidly into the interior of the fiber and release
calcium from the sarcoplasmic reticulum
-Myofibrils are intracellular bundles of contractile and elastic proteins. Thick filaments are
made of myosin. Thin filaments are made mostly of actin. Titin and nebulin hold thick
and thin filaments in position.
-Myosin binds to actin, creating crossbridges between the thick and thin filaments
-One sarcromere is composed of 2 Z disks and the filaments between them. A sarcromere
is divided into I bands (thin fimlaments only) and an A band that runs the length of a
thick filament, and a central H zone occupied by thick filaments only. The M line and Z
disks represent attachment sites for myosin and actin
-The force created by a contracting muscle is called muscle tension. The load is a weight
or force that opposes contraction of a muscle
-The sliding filament theory or contraction states that during contraction, overlapping
thick and thin filaments slide past each other in an energy dependant manner as a result of
actin myosin cross bridge movement
-In relaxed muscle, tropomyosin partially blocks the myosin binding site on actin. To
initiate concentration Ca binds to troponin. This unblocks the myosin binding sites and
allows myosin to complete its power stroke.
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