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Lecture 22

BSC 215 Lecture 22: Types of Muscles

Biological Sciences
Course Code
BSC 215
Jason Pienaar

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Types of Muscles
Muscle enables complex movements that are either voluntaryunder
conscious controlsuch as turning the pages of this book, or involuntary,
such as the contraction of the heart or the peristalsis in the gut. To
understand how muscle accomplishes these various activities, you need to
know the physiology behind a muscle contraction. This requires a detailed
knowledge of the muscle's microscopic anatomy. Of course, muscle
contractions will not take place without adequate nervous stimulation or a
sufficient supply of ATP, the muscles' fuel. ATP is obtained via cellular
respiration, which is accomplished by several different metabolic pathways.
There are three types of muscles:
Skeletal muscles are attached mainly to the skeletal bones but some are
also attached to other structures (such as the eyes for eye movement)
and causes movements of the body. Skeletal muscle is also called
striated muscle, because of its banding pattern when viewed under a
microscope (for clarification, see cardiac muscle below), or voluntary
muscle (because muscle contractions can be consciously controlled).
Cardiac muscle is responsible for the rhythmic contractions of the heart.
Cardiac muscle is involuntaryit generates its own stimuli to initiate a
muscle contraction. While cardiac muscle also consists of striations,
the main characteristic (to differentiate these striations from skeletal
muscle) is the presence of intercalated disks.
Smooth muscle lines the walls of hollow organs. For example, it lines the
walls of blood vessels and of the digestive tract, where it serves to
advance the movement of substances. A smooth muscle contraction is
relatively slow and involuntary.
Muscle Metabolism
In order for muscles to contract, ATP must be available in the muscle fiber. ATP is available
from the following sources:
Within the muscle fiber. ATP available within the muscle fiber can maintain
muscle contraction for several seconds.
Creatine phosphate. Creatine phosphate, a highenergy molecule stored in
muscle cells, transfers its highenergy phosphate group to ADP to form ATP. The
creatine phosphate in muscle cells is able to generate enough ATP to maintain
muscle contraction for about 15 seconds.
Glucose stored within the cell. Glucose within the cell is stored in the
carbohydrate glycogen. Through the metabolic process of glycogenolysis,
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