Download Muscular System

Muscular System
--”mus” means little mouse
--Called this because contraction of muscle
looks like a mouse under the skin
4 functions of muscle:
1. Movement- ex. Move arm,
smile
2. Generate heat
3. Maintain posture
4. Stabilize joints
Characteristics that allow
muscle to function:
1. Contractibility- shortens with force
2. Excitability- Responds to a stimulus by
a nerve
3. Extendable- Can be stretched back to
the resting position and slightly beyond
(ex. Calf muscle)
4. Recoilable- elastic- go to the original
resting place after being stretched
Components of muscle
Fibers- cells that make up
muscle
-They are elongated and
are in bundles
-They look and function
like fibers that make up a
cable
Muscle either functions automatically or
we have it make it work
1. Voluntary muscle- must volunteer it to
work - you control it - Ex. Walking
muscles
2. Involuntary muscle- works
automatically without you having to tell it
to – Ex. heart
Muscles are divided into 3
groups:
1. Skeletal muscle- voluntary
2. Smooth muscle- involuntary
3. Cardiac muscle- involuntary
1
2
3
I. Skeletal Muscle:
• Makes up to 40% of our
body weight on average
• Attaches to the skeleton
(bone)
• Contracts rapidly but tires
quickly (ex. Running)
Skeletal muscle fibers (cells) have the
following characteristics:
1.
2.
3.
4.
Striated- appear to be striped/banded
Multinucleated- more than 1 nucleus
Long
Voluntary- must tell to work
Structure of skeletal muscle:
• Endomysium- delicate
sheath that surrounds each
cell
• Perimysium- sheath that
surrounds several fibers
• (surrounds each bundle of
cells)
• Fascicle- bundle of fibers
• Epimycium- sheath around
several fascicles
– Covers entire muscle
– Connects muscle to
tendons which connect
to bone
Functions of tendon
1. Anchor muscle
2. Provide durability- stronger
than muscle
3. Conserve space- more of
these can pass through
joints than muscle
Get prepared for this one!
II. Smooth muscle:
--No striations-appears smooth
--Involuntary
--Found in the wall of hollow organs like stomach
--Has 1 nucleus
--Has slow contractions but last a long time
(steady)
Functions of smooth muscle
-Propel substances along digestive tract
III. Cardiac muscle:
--Found only in heart
--Involuntary, striated and arranged in spiral
--Cells branch and are joined together by
interculated disc
--Has sustained contractions at a fairly steady rate
(lasts a long time)
When these contractions stop-death occurs
How muscle accomplishes its
functions:
1. Produce movement- skeletal muscle is the
only muscle that causes locomotion (move
from 1 place to another)
-cardiac and smooth muscle- work to
circulate blood
-smooth muscle- forces fluids and other
substances through channels
(ex. Food, urine)
2. Maintain posture- skeletal muscle constantly
makes adjustments to maintain the body erect
against gravity
Muscle function Contd.
3. Stabilize joints- skeletal muscles pull on
bone which stabilizes the joints
-tendons work with muscle to do this
4. Generate heat- as all muscle contracts,
chemical reactions are occurring that
release heat (ATP powers contractions-as
it is broken down it releases heat energy)
ex. As exercise, burn ATP so temp. rises
Skeletal Muscle: (over 600 of these)
•
•
•
•
Anatomy of skeletal muscle
fibers
Each skeletal muscle fiber has
bands
Each skeletal muscle fiber has
organelles called myofibrils
Myofibrils are made of units
called sarcomeres (extends
from 1 striation to another)
Contraction occurs within the
sarcomeres
Sarcomeres are made of 2 types of
filaments
1. Myosin- Thick
filament that
extends entire
length
2. Actin- Thin
filament
What causes these striations (sarcomeres) in
muscle to contract/shorten?
• When a muscle is resting, the outside of it
has a positive charge and the inside has
a positive charge
• The difference between the charges inside
and outside the cell is called the resting
membrane potential
• An electrical current is sent by the nerve
causing the charges to differ which
produces a contraction
Parts needed for a contraction:
• A nerve cell (neuron) stimulates muscle cell by
an electrical current called and action potential
• 1 nerve cell may stimulate several muscle fibers
• 1 neuron plus the fibers it stimulates is called a
motor unit
• The junction where the neuron joins the muscle
is called the neuromuscular junction
Energy for muscle contractions comes from ATP
(adenosine triphosphate) adenosine plus 3
phosphates:
There are 3 ways ATP is made:
1. Creatine phosphate- this substance in muscles
gives ADP (adenosine diphosphate) a
phosphate to make ATP
-This is the substance you get from
supplements
-Quick energy for muscle contraction
-Each ATP made depletes in 20 seconds
ADP + P  ATP
2. Aerobic respiration- requires oxygen and burns
glucose to make ATP (1 glucose makes 36 ATP)
C6H12O6  CO2 + H2O + 36 ATP
3. Anaerobic respiration- Uses no oxygen but it
requires a lot of glucose to make ATP. It is much
less efficient
-If you contract muscle faster than glucose and
oxygen can be made in muscle, lactic acid is
made. This causes the muscle fatigue and
soreness, burning
C6H12O6  pyruvic acid + 2 ATP
What caused fatigue (the muscles to not
want to contract)?
Strenuous muscle contraction in exercise
Result: won’t contract even when stimulated
Ex. Weight lifter, marathon runners
Ideally, the muscle needs a good blood supply with
a lot of oxygen. When contracted too fast to get
enough oxygen, the muscle produces lactic acid
instead of the needed ATP.
No ATP= no contraction
In most cases, we don’t exercise to the
extreme. Usually, we can breath heavy
and replace oxygen and ATP
True fatigue- complete stopping of
contractions-rarely occurs except in
marathon runners
2 types of muscle contractions:
1. Isotonic contraction- muscles shorten
Ex. Bending of knee
2. Isometric contraction- a resistance occurs
so no shortening can occur
Ex. Weight lifting
What causes muscle tone?
-As muscles are used a lot, some fibers will
contract constantly (ex. Tight calf muscle)
Causes the muscles to be toned
-The less you exercise, the less the muscle
is used so the less it contracts (flabby)
Effects of accidents on muscle:
-If nerves to muscles are damaged, all fibers
will relax because no signal is sent to
stimulate them
-Has no tone, called flacid
ex. Damaged nerve to legs causes
paralysis
Role of exercise in muscles:
-Increases strength,
size, endurance of
muscle
2 Kinds of Exercise:
1.
Aerobic exercise- called endurance exercise
Ex. Biking, jogging, aerobics
-results in stronger, more flexible muscle that
resists fatigue
Why? The muscle’s blood supply increases in
each cell causing more mitochondria to
form. Mitochondria are the place ATP is
made.
More ATP-more energy for muscle contraction
-Muscles don’t increase much in size
2. Resistance exercise- strength training
-Results in larger muscles because the
muscle is made to contract against as much
force possible
Ex. Heavy weights
-Fibers (muscles) enlarge because they make
more filaments to become stronger
*It is best to use both programs
Areas of a joint where muscle
attaches:
Origin- Attaches to less movable part of bone
Insertion- Attaches to the more movable part of
bone
5 major movements of muscle:
1. Flexion- Decreases the angle-2 bones get
closer Ex. Bend elbow
2. Extension- Increases the angle-increase
distance
Ex. Straighten leg
3. Abduction- Move a limb away from midline
of body
Ex. Lift out arm
4. Adduction- Move limb toward body
Ex. Fold knees toward stomach
5. Rotation- Occurs at ball and socket joint
Ex. Swing arm