Muscular System
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I. Introduction to the Muscular
System
A.
Functions of Muscular System
1. Skeletal muscle tissue forms skeletal
muscles, organs that also contain connective
tissue, nerves and blood vessels.
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2. The muscular system includes
approximately 700 skeletal muscles.
3. There are five functions of the muscular
system they are:
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a.
Produce movement
b.
Maintain posture and body position
c.
Support soft tissue
d.
Guard entrance and exits
e. Maintain body temperature
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B. Anatomy of Skeletal Muscles
1.
There are three types of muscles in the
body: smooth, cardiac and skeletal, all differ in
structure and function. All muscle tissues
posses some basic characteristics and
properties.
2. Irritability- Muscle tissue receives and
responds to a stimulus from a nerve impulse.
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Smooth Muscle
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Skeletal muscle
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Cardiac Muscle
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3. Contractility- Muscle tissue responds to a
stimulus by contracting, or shortening its length.
4. Extensibility- after muscles has contracted or
shortened they go back to their regular length.
5. Elasticity, A muscle tissue has an innate tension
that causes it to assume a desired shape regardless
of how it might be stretched.
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C. Development of Skeletal Muscles
1.
The formation of the muscular system
begins about 4 weeks of embryonic
development. The beginning cells are called
myobasts.
2. It is not certain when skeletal muscles are
able to move but by the 17th week the fetal
movements- quickening are strong enough for
the mother to feel.
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D. Attachment
1.
Skeletal muscles are usually long and narrow,
span a joint, and are attached to a bone at either end
by a tendon.
2.
As the muscle contracts, one of the bones
moves relative to the other joint.
3. The more fixed, or stationary, attachment is
designated as the origin of a muscle, whereas the
movable end is its insertion.
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4. The fleshy, thickened portion of a muscle is
referred to as its belly, or gaster.
5. Usually the belly of a muscle is located on
the proximal bone that is to be moved.
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6. The joint is spanned by a tendon from the
muscle
7. A tendon is toughened, dense fibrous
connective tissue that connects a muscle to
the periosteum of a bone.
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II. Muscle Mechanics
A.
The individual muscle cells in muscle tissue are tied
together and surrounded by connective tissue.
1. 1. When muscle cells contract they pull producing
tension.
2. Tension applied to an object tends to pull the
object to the tension.
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3. Resistance is a passive force that opposes the
movement.
4. Compression, or a push applied to an object,
tends to force the object away from the source of
compression.
5. Muscles that contract together and are
coordinated in accomplishing a particular movement
are said to be synergistic.
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6. Antagonistic muscles perform opposite
functions and are generally located on the
opposite sides of the limb.
7. Example-Biceps contract together (flex)
and the triceps extend (relaxes)
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8. An entire skeletal muscle contract when its
components muscle fibers are stimulated.
Two things determine the amount of tension
produced in the skeletal muscle as a whole.
-The frequency of stimulation
-The number of muscle fibers activated
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B. The frequency of Muscle Fiber
stimulation
1. A twitch is a single stimulus contractionrelaxation sequence in a muscle fiber.
2. The latent period begins at stimulation
and typically lasts about 2msec. No tension is
produced by the muscle fiber.
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3. The contraction phase, tension rises to a
peak. Maximum tension is reached roughly
15msec after stimulation.
4. During relaxation phase, muscle tension
falls to resting levels. This phase continues
for about 25msec.
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III. The Energetics of Muscular
Activity
A. Muscle contraction requires large amounts of
energy. Example- an active skeletal muscle fiber
may require 600 TRILLION ATP molecules
EACH second!
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1. The primary function of ATP is the transfer of
energy from one location to another, not the longterm storage of energy.
2. At rest, a skeletal muscle fiber produces more
ATP than it needs.
3.
Under these conditions, ATP transfers energy to
creatine.
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4. The energy transfer creates another highenergy compound, creatine phosphate (CP)
C. Glycolysis and ATP generation-SEE
HANDOUT and BOARD!!!
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B. Muscle Fatigue
1.
A skeletal muscle fiber is said to be
fatigued when it can no longer contract
despite continued neural stimulation.
2. Muscle fatigue is caused by the exhaustion
of energy reserves or builds up of lactic acid.
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Boston Marathon
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3. If muscle contraction uses ATP at or below
the maximum rate of mitochondria ATP
generation, the muscle fiber can function
aerobically.
4. Fatigue will NOT occur until glycogen and
other reserves such as lipids and amino acids
are depleted.
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5. This type of fatigue affects the muscles of
long-distance athletes, such as marathon
runners, after hours of exertion.
6. When a muscle produces a sudden,
intense burst of activity, the ATP is provided by
glycolysis.
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7. After a relatively short time (seconds to
minutes) the rising lactic acids levels lower the
tissue pH and the muscle can no longer
function normally.
8. Athletes running sprints have this type of
fatigue
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C. The Recovery Period
1. During the recovery period, conditions inside the
muscle are returned to normal pre-exertion levels.
2. The muscle’s metabolic activity focuses on the
removal of lactic acid and the replacement of
intracellular energy reserves, and the body as a
while loses the heat generated during intense
muscular contraction.
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3. The reaction that converts pyruvic acid is freely
reversible.
4. During the recovery period, when lactic acid
concentration is high, the lactic acid is converted
back to pyruvic acid.
5. This pyruvic acid can be used 1- to synthesize
glucose and 2- to generate ATP through
mitochondrial activity.
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6. During the recovery period, the body’s
oxygen demand remains above normal resting
levels.
7. The additional oxygen required during the
recovery period to restore the normal preexertion levels is called an oxygen debt.
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8. Liver cells consume most of the extra
oxygen, as they produce ATP for the
conversion of lactic acid back to glucose, and
by muscle cells as they restore their reserves
of ATP.
9. While the oxygen debt is being repaid,
breathing rate and depth are increased. This
is why you continue to breath heavy after
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exercising.
D. Muscle Performance
1. Muscle performance can be considered
in terms of power, the maximum amount of
tension produced by a particular muscle or
muscle groups.
2. Endurance the amount of time for which
the individual can perform a particular activity.
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3. Two major factors determine the
performance capabilities of particular skeletal
muscle 1- types of muscle fibers and 2physical conditioning or training.
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E. Types of skeletal muscle fibers
1.
There are two types of fibers- fast and slow.
2. Most of the skeletal muscle fibers in the body
are fast fibers because they can contract in
0.10 seconds or less following stimulation.
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3. Slow fibers take three times longer to
contract; however, they can continue
contracting for extended periods after a fast
muscle would have become fatigued.
4. Three specializations related to the
availability of oxygen and their uses make this
possible 1- oxygen supply 2- oxygen storage
3- oxygen use.
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F. Physical conditioning
1. Physical conditioning and training
schedules enables athletes to improve both
power and endurance.
2. Anaerobic endurance is the length of time
muscle contractions can be supported by
Glycolysis and existing energy of ATP.
Example- 50-yard dash.
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3. Athletes training to develop anaerobic
endurance perform frequent, brief, intensive
workouts.
4. The net effect is an enlargement, or
hypertrophy of the stimulated muscle as seen
in weight lifters or body builders.
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5. Aerobic endurance is the length of time a
muscle can continue to contract while being
supported by mitochondrial activities.
6. Aerobic endurance is determined by the
availability of substrates for aerobic
metabolism from the breakdown of
carbohydrates, lipids or amino acids.
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IV. Cardiac and Smooth muscle
tissues
A.
Cardiac muscle tissue
1. Cardiac muscle cells are relatively small and
usually have a single, centrally placed nucleus.
Cardiac muscle tissue is found only in the heart.
2. Cardiac muscle tissue contrast WITHOUT
stimulation-automatic. Pacemaker cells normally
determine the timing of contractions.
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3. Cardiac muscle cell contractions last
roughly 10 times as long as those of skeletal
muscle fibers.
4. Cardiac muscle cells rely on aerobic
metabolism for the energy needed to continue
to contract.
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B. Smooth Muscle tissue
1. Smooth muscle tissue is found within almost
every organ.
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V. Anatomy of the Muscular System
A.
The muscular system includes all of the skeletal
muscles that can be controlled voluntarily.
B. Each muscle begins at an origin, ends at an
insertion, and contract to produce a specific
action.
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1. The origin end remains stationary while the
insertion moves.
2. When muscles contract, they may produce
flexion, extension, adduction, abduction, protraction,
retraction, elevation, depression, rotation,
circumduction, pronation, supination, inversion or
eversion.
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3. Actions of muscles may be described in
two ways- 1- actions in terms of bone affected
(flexion of the forearm). 2- describes muscle
action in terms of joint involvement. (Flexion
at elbow)
4. Muscles can be described by their primary
actions:
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a. Prime mover or agonist: chiefly responsible for
producing a particular movement.
b. Antagonists- Muscles whose actions oppose the
movement produced by another muscle.
c. Synergist- A muscle that helps the prime mover to
work efficiently. May provide additional pull near the
insertion or stabilize the point of origin.
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5. Fixators are synergists that stabilize the
origin of a prime mover by preventing
movement at another joint.
C. Naming of skeletal muscles.
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1. The human body has approximately 700
muscles, which all have names.
2. The names of muscles give clues to the
locations of the muscles.
3. The first part of man names indicates the
origin and the second part the insertion of the
muscle.
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VI. The Axial Muscles
A. The axial muscles fall into four logical groups based
on location function or both.
1. The muscles of the head and neck. These
muscles are responsible for facial expression,
chewing and swallowing.
2. The muscles of the spine. These include flexors
and extensors of the head, neck and spinal column.
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3. Muscles of the trunk. Form the muscular
walls of the thoracic and abdominopelvic
cavities.
4. Muscles of the pelvic floor. Extend
between the sacrum and pelvic girdle.
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VII. The appendicular Muslces
A. Includes the muscles of the shoulders and
upper limbs and the muscles of the pelvic girdle
and lower limbs.
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A. Aging and the Muscular system
1. Skeletal muscles become smaller in diameter.
2. Skeletal muscles become less elastic.
3. The tolerance for exercise decreases.
4. The ability to recover from muscular injuries
decrease.
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B. Integration with other systems.
1. To operate at maximum efficiency, the
muscular system must be supported by many
other systems. Such as the cardiac system,
respiratory, Integumentary, nervous and
endocrine system.
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IX. Clinical considerations
A.
Problems with the muscular system.
1. Muscular Dystrophy is an inherited
disease, which cause progressive muscular
weakness and deterioration.
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1. When death occurs, circulation ceases
and the skeletal muscles are deprived of
oxygen. Causing stiffness of the muscles.
2. A hernia develops when an organ
protrudes through an abnormal opening in the
surrounding cavity wall.
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Umbilical hernia
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Epigastric hernia
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The End
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