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Chapter 6
The Muscular System
• The essential function of a muscle is to
shorten or contract
• As a result of this ability, muscles are
responsible for almost all body
movement and can be viewed as the
“machines of the body”
Overview of Muscle
Tissues
Muscle Types - Three
1. Skeletal
2. Cardiac
3. Smooth
The 3 Types of Muscle Tissue
differ in:
• Cell structure
• Body location
• How they are stimulated to contract
The three types of muscle
tissue are similar because:
1. All muscle cells are elongated – called
muscle fibers
2. The ability of muscle to shorten or
contract depends on 2 types of
myofilaments (part of the cytoskeleton)
Skeletal Muscle
1. Fibers are packaged into skeletal
muscles that attach to the skeleton
2. Cigar-shaped
3. Multinucleate (many nuclei)
4. Largest of the muscle fibers
5. Striated muscle (appear striped)
6. Voluntary muscle (conscious
control)
7. Form smoother contours of the
body
Key words to think of for
skeletal muscle:
• Skeletal, striated, voluntary
• Skeletal muscles are very fragile,
but they are capable of exerting
tremendous power.
• They are able to do this because:
thousands of fibers are bundled
together with connective tissue –
these bundles are then bundled
together
Tendons
• Attach muscle to bone
Figure 09.02
Functions of the tendons
1. Anchor muscles
2. Provide durability and conserve
space
3. Crossover bony projections
Smooth Muscle
• No striations
• Involuntary
• Found in the walls of hollow
digestive organs
• Propels substances along a definite
path
•
•
•
•
Spindle shaped
Single nucleus
Arranged in sheets or layers
Muscle contraction is slow and
sustained
Key words:
• Visceral, non-striated, involuntary
Cardiac Muscle
1. Found only the heart
2. Striated and involuntary
Key Words:
• Cardiac
• Striated
• involuntary
Muscle Functions
• Muscles play four important roles in
the body.
1. Produce movement
• Moves the body
2. Maintain posture
• Allow you to remain in an erect or
seated posture despite gravity
3. Stabilize Joints
• Muscle tendons are extremely
important in reinforcing and
stabilizing joints
4. Generating Heat
• Heat is a by product of muscle
activity
• ATP used as power – ¾ escapes as
heat
Microscopic Anatomy of
Skeletal Muscles
• Skeletal muscle contains both actin and
mysosin filaments
• The overlapping pattern of thick and thin
filaments is responsible for the light and
dark bands seen in skeletal striated muscle
• The thick filaments are made up of a
protein called myosin
• The thin filaments are made of a protein
called actin.
• Sarcomere: contractile unit
Skeletal Muscle
Activity
The 2 special functional
properties of muscles:
1. Irritability – ability to receive and
respond to a stimuli
2. Contractility – ability to shorten with
adequate stimuli
•
Skeletal muscles must be stimulated by
nerve impulses to contract.
Motor Unit
• One neuron (nerve cell) and all the
skeletal muscles it stimulates
Figure 09.09
How a muscle contracts
• A nerve impulse reaches the end of
the nerve a neurotransmitter is
released.
• The neurotransmitter that
stimulates skeletal muscle is
acetylcholine (Ach)
• When enough acetylcholine is
released, sodium ions (Na+) will
rush into the muscle.
• This rush of ions creates an
electrical current known as the
action potential.
• The action potential travels over
the entire muscle causing it to
contract.
The events that return a muscle
to its resting state:
1. Diffusion of K+ (potassium) out of
the cell
2. Activation of the Na+/K+ pump
The Sliding Filament Theory
• Muscle fibers contract when the
sarcomere shortens.
• The sarcomere shortens when the
actin fibers slide past the myosin
filaments
• Myosin moves the actin.
• The sliding filament theory refers to
the movement of actin in relation to
myosin.
• ATP supplies the energy for muscle
contraction.
• Myosin filaments do all the work.
The actin filaments just sit there.
Figure 09.04
• Myosin filaments breakdown ATP
and have crossbridges that pull the
actin filaments toward the center of
the sarcomere.
Contraction of
Skeletal Muscle as a
whole
Figure 09.06
Graded Responses
• Different degrees of shortening
• Different numbers of muscles contract
Graded muscle contractions can
be produced in two ways:
1. By changing the speed of muscle
stimulation
2. By changing the number of muscle
cells being stimulated
Providing Energy for
Muscle Contraction
1. Direct phosphorylation of
ADP by creatine phosphate (CP)
• CP gives a phosphate to ADP to make
ATP
• ATP is regenerated in a fraction of a
second
• CP supplied energy used in 20 seconds
2. Aerobic Respiration – ATP is
made by aerobic respiration
• 1 glucose – 36 ATP
• Fairly slow – needs continuous
Adenosine Triphosphate
supply of oxygen
3. Anaerobic Respiration and
Lactic Acid Formation
• No oxygen
• 2 ATP per glucose
• Lactic acid is made and builds up in
muscles
• 5X faster than aerobic
• 30-40 seconds of strenuous
exercise
• Problems: needs lots of glucose
– Small amount of ATP produced
per glucose
– Lactic acid
3. Anaerobic Respiration and
Lactic Acid Formation
• No oxygen
• 2 ATP per glucose
• Lactic acid is made and builds up in
muscles
• 5X faster than aerobic
• 30-40 seconds of strenuous
exercise
• Problems: needs lots of glucose
– Small amount of ATP produced
per glucose
– Lactic acid
Muscle Fatigue and
Oxygen Debt
Muscle Fatigue
• Occurs when muscles are exercised
strenuously
Fatigued
• When a muscle is unable to
contract even though it is being
stimulated
Oxygen Debt
• The volume of oxygen needed after
exercise to get rid of the lactic acid
formed during exercise
• The major factor that effects the
work that a muscle can do and how
long it can do work without
becoming fatigued is:
• How good the blood supply is
When muscles lack oxygen:
1. Lactic acid builds up
2. Muscles also run out of ATP
So lack of ATP and lactic acid build up
cause a muscle to stop contracting
The Two Types of
Muscle Contractions
Isotonic contractions
• When the force of the muscle
contraction is greater than the
force that is resisting the
contraction
• Ex. Weight is lifted
Isometric Contractions
• When the resistance to the
contraction is equal to the force
generated in the muscle tissue
(muscle do not contract or only a
little)
• Pulling on a stationary bar
Effect of Exercise on
Muscles
• Muscle inactivity always leads to:
muscle weakening and wasting
away
• Regular exercise increases muscle:
size, strength and endurance
Atrophy
• Diminish in size and become weaker
• result of no exercise
Hypertrophy
• Increase in size and strength
• Result of exercise
• Anabolic steroids are sometimes
taken by athletes to promote
muscle growth
Undesirable effects of anabolic
steroid use:
•
•
•
•
•
Cardiovascular disease
Liver and kidney dysfunction
Impotency
Sterility
Increase in rash behavior “roid
rage”
Slow Twitch Muscle Fibers Legs
• Steadier tug
• More endurance
• Aerobic energy production – tire
when fuel is gone
• Sports useful in: long distance
running, biking, jogging, swimming
• Color: dark
• Many mitochondria, dense capillary
beds which draw more blood and
oxygen
Fast Twitch Muscle Fibers Breasts
• Anaerobic – tire quick because of
lactic acid build up
• Designed for strength
• Explosions of energy
• Sports useful in: sprinting, weight
lifting
• Color: white
• Few mitochondria, few blood cells
Aerobic or Endurance Excercise
• Stronger more flexible muscles with
greater resistance to fatigue
• Blood supply increases as cells form
more mitochondria and store more
oxygen
Body Benefits
1. Overall body metabolism is more
efficient
2. Improves digestion
3. Skeleton stronger
4. Heart pumps more blood with each
beat
5. Fat deposits cleared
6. Lungs are more efficient at gas
exchange
Resistance or Isometric
Exercise
• A few minutes every other day
• Muscles increase in size because
muscle cells increase in size (not
increase in number of cells)
• Amount of reinforcing connective
tissue also increases
Types of Muscles
• Muscles cannot push. They can only
pull.
• So most body movements are a result
of the activity of pairs or teams of
muscles acting together or against
each other
• Muscle groups are arranged on the
skeleton so that whatever one muscle
can do, another group of muscles can
do in reverse
Naming Skeletal
Muscles
Skeletal muscles are given
names based on:
1.
2.
3.
4.
Size – gluteus maximus
Shape – deltoid
Location
Direction of fibers – rectus – up
and down – transverse – horizontal
5. Number of attachments – biceps –
2 attachments
6. Action
Figure 09.22
Figure 09.23
Figure 09.24
Figure 09.25a
Figure 09.27b
Figure 09.27c
Figure 09.27d
Figure 09.28
Figure 09.29d
Figure 09.31b
Figure 09.34
Figure 09.35a
Figure 09.37a
Figure 09.37b
Figure 09.37c
Figure 09.38c
Figure 09.39a
Figure 09.39a
Figure 09.39b
Figure 09.40
The End