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MUSCULAR SYSTEM
(pp. 813-817)
I. Purpose
The primary function of the muscular system is to produce _movement________. The contraction of
muscle tissue requires _ATP__, so muscles are constantly carrying out _cellular respiration____
and require a large number of _mitochondria___.
II. Description
A. Muscle Fibers
Individual muscle cells are called muscle _fibers_______. All humans have the _same___
number of fibers. Muscle bulk occurs because of _thickening____________ of muscle fibers,
not an increase in the number of muscle cells.
B. Muscle Types
1. Skeletal Muscle - _Voluntary___, _striated___ muscle cells that fuse together to form a
_multinucleated_________ muscle fiber. Muscle fibers are arranged end-to-end to produce
strong contractions. If the oxygen supply to muscle cells is depleted, they can switch to
_lactic acid fermentation____ for energy production.
2. Cardiac Muscle - _Involuntary_____, _striated___ muscle cells found only in the
_heart____, with each cell having its own nucleus. Cardiac muscle cells are arranged in chains
that lattice together. When the muscle contracts, the entire lattice of cells
contracts together producing a powerful contraction.
3. Smooth Muscle - _Involuntary__, _smooth____ muscle cells. Smooth muscle contractions
are slow and prolonged. Found in the _digestive tract, blood vessels, urinary bladder___
C. Muscle Contraction
Each muscle fiber contains thousands of contracting units called _sarcomeres_________.
Sarcomeres are made up of two types of protein filaments:
1. Actin - _Thin______filaments that form the border of each sarcomere.
2. Myosin - _Thick____ filaments found in the _middle____ of the sarcomere.
Actin and myosin overlap to produce the _striated____ pattern seen in _skeletal_______
and _cardiac______ muscle. When a muscle contracts, the actin and myosin filaments slide
over each other and the sarcomere _contracts________. Every sarcomere within a
single muscle fiber contracts as a unit, thereby shortening the entire _fiber_____. The
number of fibers that can contract at one time determine an individual’s _strength_. The length of
the contraction time is known as _endurance_.
III. Skeletal Muscle
A. Anatomy - Skeletal muscles are attached to bones by tough bands of tissue called _tendons_.
Every muscle has at least 2 tendons, each attached to a different bone:
1. Origin – Muscle attachment site(s) that __does not move____
2. Insertion – Bone that is _moved by the contraction_____________. For example,
the _biceps brachii__________ has _tendons_________________ attaching it to the
_scapula____ and _radius_____. The origin is the _scapula___ and the insertion is the
_radius_____.
B. Movement - Skeletal muscles attached to the bones of the _appendicular_____ skeleton work in
opposing pairs.
1. Flexor – muscle that causes limb to _bend___ at _joint_.
2. Extensor – muscle that causes limb to _straighten_____ at _joint_____. For example,
contraction of the biceps brachii _bends____ the arm so it acts as a _flexor____, while
contraction of the triceps brachii _straightens_____ the arm so it is the _extensor___.