The Muscular System
SAP2. Students will analyze the interdependence of the integumentary,
skeletal, and muscular systems as these relate to the protection, support and
movement of the human body.
Explain how the skeletal structures provide support and protection for tissues, and
function together with the muscular system to make movements possible.
Types of Muscular Tissue
• Muscular tissue makes up 40% - 50% of the total body weight.
• Skeletal muscle – attached to bones and moves parts of the skeleton.
It is striated (has light and dark bands). It can contract and relax by
conscious control (voluntary).
• Cardiac muscle – found only in the heart. It is also striated. It is
involuntary
• Smooth muscle – located in walls of internal structures (blood vessels,
airways, the stomach the intestines). It helps control digestion, blood
pressure regulation. It is nonstriated and involuntary.
Functions of the Muscular Tissue
1. Producing body movements – walking, running
2. Stabilizing body positions – sitting, standing, holding the
head upright
3. Regulating organ volume – sphincters prevent outflow of
the contents of a hollow organ: storage of urine, food in
the stomach,
Functions of the Muscular Tissue
4. Moving substances within the body – cardiac muscle
contractions pumps blood through the body, contraction and
relaxation of muscle in blood vessels regulate blood flow
5. Producing heat – as muscles contract they produce heat that is
used to maintain a normal body temperature (homeostasis).
Involuntary contractions (shivering) can help warm the body by
increasing rate of heat production.
Skeletal Muscle Tissue
• Perimysium – Surrounds bundles of 10 – 100 muscle
fibers call fascicles
• Endomysium – wraps around each individual muscle
fiber
• Tendon- cord of dense connective tissue composed of
bundles of collagen fibers. They attach muscle to bone.
Skeletal Muscle (pg. 174)
Quiz
Yourself
Histology (study of the microscopic structure
of tissues)
• Muscle fibers are arranged parallel to each other. Each fiber is covered by a
membrane called the sarcolemma.
• The muscle fibers cytoplasm is called sarcoplasm which has many
mitochondria that produce large amounts of ATP when a muscle contracts.
• Throughout the sarcoplasm is sarcoplasmic reticulum which are tubules
that stores calcium ions which are required for muscle contraction.
Myoglobin (a red pigment) is also in the sarcoplasm and it stores oxygen to
be used by the mitochondria to generate ATP.
Muscular Atrophy
• Is a wasting away of muscle. The muscle fibers
decrease in size because of loss of myofibrils.
• How does it happen? People who are bedridden,
limbs that have been in casts
Muscular hypertrophy
• Is an increase in muscle fiber diameter due to the
production of more myofibrils, mitochondria,
sarcoplasmic reticulum, etc.
• It results from forceful, repetitive activity such as strength
training. Since they contain more myofibrils they are
capable of contractions that are more forceful.
Botulinum Toxin
• It blocks the release of acetylcholine (ACh) at the neuromuscular
junction.
• It is used as a medicine.
• Helps patients with crossed eyes and uncontrollable blinking
• Cosmetic treatment to relax muscles that cause facial wrinkles
(Botox)
• Stops back pain due to spasms in the lumbar region
Rigor Mortis
• When a person dies, Ca begins to leak out of the
sarcoplasmic reticulum and binds to troponin, causing the
filaments to slide. ATP production has ceased so the
crossbridges cannot detach from actin. The resulting
stiffness of the muscles is rigor mortis, rigidity of death.
It begins 3-4 hours after death and lasts for about 24
hours.
Muscle Tone
• Even when a muscle is not contracting, a small number of motor units are
involuntarily activated to produce a sustained contraction of their muscle
fibers. To sustain muscle tone small groups of motor units are alternately
active and inactive in a constantly shifting pattern. This keeps skeletal
muscles firm but does not produce movement.
• Example: the tone of muscles in the back of the neck keeps the head upright
and prevents it from slumping forward.
• Therefore, tone is established by neurons in the brain and spinal cord that
excite the muscles neurons.
Energy for Contraction
• Muscles must have ATP and Calcium to contract
• As muscles become more active more ATP is needed.
• The ATP inside the muscle fibers is only enough to power a contraction for
a few seconds!
• If exercise is continued it must synthesize more ATP. It comes from 3
sources.
Energy for Contraction
• 1. Creatine phosphate which comes from excess ATP. It is an energy-rich
molecule that is unique to muscle fibers. A phosphate from ATP is
transferred to creatine (a small amino acie-like molecule that is synthesized in
the liver, kidneys and pancreas and comes from milk, red meat and fish)
forming creatine phosphate and ADP. It provides about 15 seconds of
energy. Read blue box on pg 182-183
• 2. Anaerobic cellular respiration – without the use of oxygen…..Through
the conversion of creatine phosphate and glycolysis (from ATP) it can
provide energy for about 30 to 40 seconds of maximal muscle activity
Energy for Contraction
• 3. Aerobic cellular respiration – oxygen requiring reactions that produce
ATP in mitochondria. Muscle fibers get oxygen from the blood and from
myoglobin (which is a protein found in the sarcoplasm)
• Aerobic respiration yields much more ATP!!!!!
Muscle Fatigue
• The inability for a muscle to contract forcefully after prolonged activity.
• A big factor in fatigue is a decline in the Ca level in the sarcoplasm, a
depletion of creatine phosphate, insufficient oxygen, build up of lactic acid
and ADP, and failure of nerve impulses
Cardiac Muscle
• Skeletal muscle contracts when stimulated by a nerve impulse
• Cardiac muscle fibers act as a pacemaker to initiate each cardiac contraction.
The built in rhythm is called autorhythmicity. Several hormones and
neurotransmitters can increase or decrease heart rate by speeding or slowing
the hearts pacemaker.
• Beats about 75 times per minute.
• The mitochondria in cardiac fibers are larger and more numerous than
skeletal muscle.
Aging
• At about 30 years old……humans begin a slow progressive loss of skeletal
muscle mass that is replace by connective tissue and adipose tissue (fat)
• Due to……….decline in physical activity!
• In addition….there is a decrease in muscle reflexes and flexibility.
• So we need to stay active!!!!! Aerobic activities and strength training !!!!!!
Muscles producing movement
• As we saw in the chicken wing…..muscles are not directly attached to bones.
They are attached by tendons. When a muscle contracts it pulls one bone
toward another. The 2 bones don’t move equally. One is held at almost its
original position called the origin. The other end is attached by a tendon to
the movable bone called the insertion. Think of bending your arm. The
humerus is the point of origin. The radius and ulna are the point of
insertion. Look at Figure 8.12 on pg 189
Stretching
• Read the Focus on Wellness on pg 190
• When does tissue stretch the best?
• How do you increase flexibility?
Neuromuscular disease
• When skeletal muscle function is abnormal due to disease or damage of
components of a motor unit, somatic motor neurons and neuromuscular
junctions or muscle fibers.
Duchenne muscular dystrophy
• The most common form of muscular dystrophy (muscle destroying disease –
progressive degeneration of muscle fibers).
• Strikes boys (because it is on the X chromosome…males only have one)
• By 12 they are unable to walk.
• By 20 – 30 respiratory/cardiac failure which eventually causes death
Fibromyalgia
• A painful disorder that usually appears at 25-50 years of age
• Mostly women
• A striking pain that results from pressure at specific “striking points”.
Myalgia
• Pain in or associated with muscles
Myositis
• Inflammation of muscle fibers/cells.