Transcript Anatomy chapter 8 (Muscular System)

•There are three different types of muscles:
•Smooth muscle tissue has no striations
(lines) and is not generally under conscious
control.
•Generates force but acts very slowly.
•Skeletal muscle tissue has striations and is
under conscious control.
•Generates significant force and can respond
very quickly.
•Cardiac muscle tissue is similar to skeletal
muscles, but contains intercallated discs,
which help synchronize the heartbeat.
Muscles are made up of a hierarchy of
smaller and smaller units.
•Skeletal muscles are made of fibers that
run the length of the muscle.
•Each fiber is a single cell with many
nuclei.
•The fibers consist of smaller myofibrils
•Each myofibril is made up of thin filaments
(actin + tropomyosin + troponin) and thick
filaments (myosin)
•The myofibril is divided into groups of thin and
thick filaments called a sarcomere.
•Each sarcomere is separated by Z-lines.
This sarcomere consists of several sections
•Z-line - the borders of the sarcomere
•I-band - area near Z-lines where there
are only thin filaments.
•A-band - region that corresponds to
the length of the thick filaments. Part is
dark, part is light.
•H-zone - only thick filaments
Muscle Contraction
•Contraction takes place according to the
sliding filament model.
•Neither the thick filaments nor the thin
filaments change length.
•They slide past each other
•Sarcomere shortens (Z-lines come closer
together).
•This contraction will occur when a myosin
breaks down an ATP molecule to change its
shape to its high energy conformation.
The myosin holds on to the ADP + P
•The myosin head will bind to an actin
filament.
•The myosin then releases the ADP + P and
relaxes into its low energy state.
•Since it is still attached to the actin, this
results in a force on the actin.
•Another ATP molecule binds to the myosin
changing it to its low energy conformation.
•Repeat
•This process is regulated by Calcium ion
(Ca+2) levels in the muscle cell cytoplasm.
•A signal is sent to the muscle cell by a
neuron through the use of Acetylcholine.
•This signal causes the Sarcoplasmic
reticulum to release Ca+2 ions.
•The Ca+2 ions bind to troponin molecule that is
part of the thin filament.
•This binding causes the troponin to change
shape which causes the tropomyosin to move.
•When the tropomyosin moves, myosin binding
sites on the actin are uncovered.
•This allows the myosin to bind to the actin.
•When the Ca+2 ions are in low concentration, the
troponin molecule changes shape again and
moves the tropomyosin back to its original
position.
Major Muscles
•Muscles tend to come in pairs called flexors and
extensors
•Flexors decrease the angle between two bones
•Extensors increase the angle between two bones
•Ex: Biceps brachii flexes the elbow while the
triceps brachii extends it.