Muscular System Notes
*Human body has over 650 different muscles
*Muscles make up 40-50% of your total body weight
*Muscular System has Three Main Responsibilities
1. Body Movements
2. Body Form and Shape, Maintaining Posture
3. Body Heat, to maintain body temperature
*Muscular System has Three Types of Muscles
1. Skeletal --- Striated --- Voluntary
2. Smooth --- Visceral --- Involuntary
3. Cardiac --- Found only in the HEART --- Involuntary
Characteristics of all Muscles
1. Contractibility --- Muscle shortens or contracts
2. Excitability or Irritability --- Ability to respond to certain stimuli
By producing electrical signals called Action Potentials (Impulses)
Muscle Attachments and Functions
Muscles must be attached to bones for leverage in order to have
something to pull against. Muscles only pull, never push.
TENDONS hold bones to muscles at the joints.
Origin --- Part attached to a fixed structure or bone, moves the least
Amount during a contraction
Insertion --- Part attached to a moveable structure or bone, moves the
most during contractions
Belly --- Central Body of a Muscle
Prime Mover --- Produces movement in a single direction
Antagonist --- Opposite direction movement of a Prime Mover
Biceps – Front of the arm Flexor
“ORIGIN” – Attached to the Scapula and Humerus. These bones
stay stationary when contracting
“Insertion” – Attached to the Radius this bone moves during a
contraction
Triceps – Antagonist when the Bicep is working
Synergists – Set of muscle groups that help to steady a movement or
stabilize joint activity
Skeletal Muscle --- Attached to the Bones
This is voluntary because it contains nerves under voluntary control.
Each muscle cell is known as a muscle fiber. The Cell membrane is
Called the SARCOLEMMA and the cytoplasm is called SARCOPLASM.
*Fleshy Body Part
*Contract Quickly, Fatigues Easily, Lacks the ability to contract for long
periods of time.
*Blinking the eyes, talking, breathing, dancing, eating and writing are all
types of skeletal muscle movements
Smooth Muscle --- Called this because they have no distinct marking
or striations
*Unattached to bones
*Act Slowly
*Do not Tire Easily
*Can Remain Contracted for a long time
*Not under conscious control --- Involuntary
*Actions are controlled by the Autonomic Nervous System
*Smooth muscles are found in the walls of the Internal Organs, including
The stomach, intestines, uterus, and blood vessels
Cardiac Muscle --- Cells are striated, branched, and Involuntary
*Cells are joined by membranes of adjacent cells are fused at places
Called INTERCALATED DISCS
*Won’t permit independent cell contractions
*Requires a continuous supply of oxygen to function. If oxygen is cut
off for as little as 30 seconds then cells will begin to die.
Sphincter or Dilator Muscle --- Muscles in the openings between the
esophagus and stomach and intestines. Found in the walls of the
anus, urethra, and mouth. They open and close to control passages.
Sources of Energy and Heat
Human Beings usually maintain their body temperature within a
narrow range (98.6 – 99.8 degrees)
ATP --- Adenosine Triphosphate is the major source of energy that is
stored inside the muscles. This a quick energy source that
burns off fast and used in an emergency situation.
Lactic Acid --- This is a by-product during this process that causes cramps
Contraction of Skeletal Muscles--- Occurs as a result of two major events
1. Myoneural Stimulation
2. Contraction of Muscle Proteins
Muscle Fatigue --- Caused by accumulation of lactic acid in the muscle
because of a lack of oxygen in the blood. When muscles contract
without oxygen it is called (ANAEROBIC)
Oxygen Debt --- The amount of oxygen needed to take in to change the
lactic acid back into glucose to be used by the muscle cells
Muscle Tone --- Muscles should always be slightly contracted and ready
to pull.
Isotonic Contractions --- When muscles contract and shorten
Isometric Contractions --- Tension in a muscle increases but it doesn’t
Shorten
Atrophy --- Failing to exercise muscles so they become weak or flaccid.
This may cause muscles to shrink from lack of use
Hypertrophy --- Over exercising, muscles will become enlarged. The size
of the muscle fibers become enlarged
Naming of Skeletal Muscles
1.
2.
3.
4.
Location
Size
Direction
Number of Origins
5. Number of Insertions
6. Actions
7. Shape