2. Muscle System Functions
Provides voluntary
movement of body
Enables breathing,
blinking, and smiling
Allows you to hop,
skip, jump, or do
push-ups
Maintains posture
Produces heat
3. Functions Continued
Provides movement of
internal organs
Moves food through
digestive tract
Enables bladder control
Causes involuntary actions
Reflex actions
Adjusts opening of pupils
Causes hair to stand on
end ( )
4. Properties of Muscles
Excitability: capacity of muscle to respond to
a stimulus
Contractility: ability of a muscle to shorten
and generate pulling force
Extensibility: muscle can be stretched back to
its original length
Elasticity: ability of muscle to recoil to original
resting length after stretched
5. Muscle Tissue
Characteristics
Is made up of
contractile fibers
Provides movement
Controlled by the
nervous system
Voluntary-
consciously
controlled
Involuntary- not
under conscious
control
Cardiac
Skeletal
Smooth
6. Red vs white muscle fibers
a.Red (slow) fibers- greater number of mitochondria
- contain high concentration of myoglobin
-react at a slow rate; do not undergo fatigue even with
sustained contraction
- ex. Postural muscles which are opposed to gravity
b. White (fast) fibers-contain little myoglobin/mitochon
- react rapidly and undergo anaerobic respiration
-generate force quickly but not for long durations
-ex. Fingers and eye movements ( darting motions)
c. Intermediate fibers- postural muscles that are capable of
rapid contraction at times
- ex. Calf muscle-supports leg but also capable of running,
walking, jumping
8. Nerve and Blood Vessel
Supply
Motor neurons
stimulate muscle fibers to contract
Neuron axons branch so that each muscle fiber (muscle
cell) is innervated
Form a neuromuscular junction (= myoneural junction)
Capillary beds surround muscle fibers
Muscles require large amts of energy
Extensive vascular network delivers necessary oxygen
and nutrients and carries away metabolic waste
produced by muscle fibers
10. Types of Muscle Tissue
There are
three main
types of
muscle tissue
Skeletal
(striated)
Cardiac
(heart)
Smooth
(visceral)
11. Types of Muscle cont.
Skeletal
Attached to bones
Makes up 40% of body weight
Responsible for locomotion, facial
expressions, posture, respiratory movements,
other types of body movement
Voluntary in action; controlled by somatic
motor neurons
Skeletal
12. Smooth Muscle
In the walls of hollow organs, blood vessels,
eye, glands, uterus, skin
Some functions: propel urine, mix food in
digestive tract, dilating/constricting pupils,
regulating blood flow,
In some locations, autorhythmic
Controlled involuntarily by
endocrine and autonomic
nervous systems
Smooth
13. Heart: major source of movement of
blood
Autorhythmic
Controlled involuntarily by endocrine
and autonomic nervous systems
Cardiac Muscle
Cardiac
14. Comparison of Muscle Types
Muscle Type Cardiac
Function
Movement of
bone
Walls of internal
organs + in skinLocation
Attached to
bone
Heart
SmoothSkeletal
Striated- light
and dark bands
Many nuclei
Striated
One or two
nuclei
Characteristics
Non-striated
One nucleus
(visceral)
Long + slender Branching
Shape Spindle shape
Control Mode
Beating of heart
Involuntary Involuntary
Movement of
internal organs
Voluntary
15. Sarcomere
Myofibril
Contain two
types of protein
filaments
Actin and
Myosin
Z disc- point of
anchor of actin
Sarcomere-
functional unit
of a myofibril,
region
between Z
discs
Thin Filaments
Actin
Molecule
Thick Filaments
Myosin Molecule
Z Disc
Sarcomere
17. Myosin (Thick) Myofilament
Many elongated myosin molecules shaped like golf clubs.
Single filament contains roughly 300 myosin molecules
Molecule consists of two heavy myosin molecules wound
together to form a rod portion lying parallel to the myosin
myofilament and two heads that extend laterally.
18. Myosin Filaments cont
Myosin heads
1. Can bind to active sites on the actin molecules
to form cross-bridges. (Actin binding site)
2. Attached to the rod portion by a hinge region
that can bend and straighten during
contraction.
3. Have ATPase activity: activity that breaks down
adenosine triphosphate (ATP), releasing
energy. Part of the energy is used to bend the
hinge region of the myosin molecule during
contraction
19. Actin (Thin) Myofilaments
1. F (fibrous) actin
2. Tropomyosin
3. Troponin
Two strands of fibrous (F)
actin form a double helix
elongating the myofilament;
attached at either end at
sarcomere.
Composed of G actin
monomers each of which
has a myosin-binding site
Actin site can bind
myosin during muscle
contraction.
• composed of 3 major proteins
20. Actin Filaments cont
Tropomyosin: an elongated protein
winds along the groove of the F
actin double helix.
Troponin is composed of three
subunits:
Tn-A : binds to actin
Tn-T :binds to tropomyosin,
Tn-C :binds to calcium ions.
22. Mechanics of a Muscle
Contraction
What stimulates a muscle to
contract?
Your nervous system
What cells are involved?
Muscle cells and a motor neuron
Motor neuron sends
impulse to muscle cells
One neuron will form
synapses with many
muscle cells
What is this called?
A motor unit
Let’s take a look under
the microscope.…A motor unit
23. A motor unit is a motor neuron and all
the muscle fibers it supplies
The number of muscle fibers per motor
unit can vary from a few (4-6) to
hundreds (1200-1500)
Muscles that control fine movements
(fingers, eyes) have small motor units
Large weight-bearing muscles (thighs,
hips) have large motor units
28. Sarcoplasmic Reticulum
(SR)
SR is an elaborate, smooth endoplasmic reticulum
runs longitudinally and surrounds each myofibril
Form chambers called terminal cisternae on either side
of the T-tubules
A single T-tubule and the 2 terminal cisternae form
a triad
SR stores Ca++ when muscle not is contracting
When stimulated, calcium released into sarcoplasm
SR membrane has Ca++ pumps that function to pump
Ca++ out of the sarcoplasm back into the SR after
contraction
30. Mechanics of a Muscle
Contraction
Where does stimulation occur?
Neuromuscular junction
How do motor neurons
communicate with
muscle cells?
Neurotransmitters (typically
acetylcholine) carry
impulse signal across the gap
What happens when a
muscle cell is stimulated?
Calcium ions are released into the muscle cell
Myofibrils are
surrounded by
calcium-
containing
sarcoplasmic
reticulum.
Neurotransmitters
31. Mechanics of a Muscle
Contraction
What do calcium ions do?
Cause interaction between actin and myosin
How do actin and myosin interact?
Actin filaments slide over the myosin filaments.
What model explains this?
Sliding Filament Model
32. What causes actin to slide over
myosin?
The head of myosin connects
to actin and pivots.
What is this connection called?
cross-bridge
The binding of the myosin heads
throughout the sarcomere occurs
asynchronously…
some myosin heads are
binding while other heads are
releasing the actin filaments.
33. Role of Calcium Ions in Contraction
When muscle is relaxed, attachment sites for
myosin heads are physically blocked by
tropomyosin.
In order to contract a muscle, troponin
must move tropomyosin.
Complex regulated calcium ion
concentration.
Muscle fibers store Ca++ in
sarcoplasmic reticulum.
35. Mechanics of a Muscle
Contraction
What provides the energy to swivel the head of
myosin? _____
How exactly does the sliding filament model work?
In the sliding filament model of muscle contraction, the
(thin) actin filaments
[red] (that are attached
to the Z-line) slide (are
actually pulled) inward
along the (thick)
myosin filaments
[blue], and the
sarcomere (measured
from one Z line to the
next) is shortened.
ATP
36. Mechanics of a Muscle
Contraction
When each sarcomere becomes shorter it
causes each myofibril to become shorter.
When each
myofibril becomes
shorter it causes
the muscle fibers
to become shorter
When each
muscle fiber
shortens the
overall muscle
contracts.
Sarcomere
42. Electrical changes during
muscular contraction
•Depolarization- Na+ moves inside (+)
•Repolarization- (-) charge
•Absolute refractory period- depolarized
membrane, a 2nd stimulus is ineffective ( no
response)
•Relative refractory period- during repolarization,
stronger stimulus can cause a response
44. Mechanical changes- tension
develops when filaments attempt to slide
past each other
Isotonic contraction- ‘same tension’
- results in shortening of muscle but tension
remains the same
- filaments are successful in sliding
- moved through a distance
-ex. Walking, lifting an object, bending knee,
smiling
Types of Muscle Contraction
45. Isometric contraction- ‘same length’
- contraction without shortening
-increased tension due to exertion against an
immovable object
-not successful in sliding
-Ex. Posture, holding an object, standing
still, opposing gravity
47. Mechanical changes cont
Muscle twitch- response after application of
threshold stimulus
-single, brief, jerky contraction
Summation- stimuli applied in succession
-cells do not get chance to relax between stimuli
-can be summed up
48. Tetanus- application of stimuli in rapid
succession
-no period of relation between them
-contraction bec sustained and prolonged
-may dev tension 4x as during a single twitch
Treppe( staircase effect)- stimuli applied at
slower rate than tetanus
-increased fusion of twitches
-individual contraction gradually becomes
stronger for a short time though stimulus
strength is unchanged
54. Sources of energy for
muscular contraction
Ca2++ and myosin cause ATP breakdown
Creatine phosphate- from excess ATP
-stored in muscles
Glycogen breakdown through anaerobic
respiration
-only for short-term energy
production
55. Tone- state of partial contraction which gives
muscles a certain firmness
Plasticity- in smooth muscles only
-ability to stretch w/o developing
lasting increase in tension
- dev resistance to stretching at first
-later tension decreases and muscle
adjusts to new length
-in hollow visceral organs like urinary
bladder, stomach, small intestines
56. Control of a Muscle
Contraction
How long does a muscle cell
remain contracted?
Until the release of acetylcholine
stops.
How strongly does a muscle fiber contract?
To it’s fullest extent.
All-or-none response
So what controls the
strength of a contraction?
Number of muscle cells recruited
To get a stronger contraction, more
cells are stimulated
A single cell can’t contract harder
57. Muscle Disorders
A strain is an injury to a muscle or
tendon, and is often caused by
overuse, force, or stretching.
Injured area
experiences:
pain and
soreness
swelling
warmth, bruising,
or redness
difficulty using or
moving the
injured area in a
normal manner
Strain
58. Muscle Disorders
R.I.C.E.
Rest: Stop all activities which
cause pain.
Ice: Helps reduce swelling.
Never ice more than 10-15 min.
at a time. Protect the skin.
Compression: Wrap the strained
area to reduce swelling.
Elevation: Keep the strained area as
close to the level of the heart as is
conveniently possible to keep blood
from pooling in the injured area.
Treatment for Muscle Injuries
59. Muscle Disorders
Muscle spasm- when A muscle (or even a few
fibers of a muscle) involuntarily contract
Muscle cramp- involuntarily + forcibly
contracted muscle that does not relax
A forceful + sustained spasm
CrampsSpasms
Can last anywhere from a few
seconds to a quarter of an hour
Caused by strain or injury
Muscle feels tied up in knots
60. Muscle Disorders
Tetanus is a preventable disease through vaccination
Caused by bacteria that enters the body
through the skin
Found in soil, dust and manure
Toxin bacteria produces interferes with nerve
transmission to your muscles and causes
them to seize up in painful spasms.
Tetanus typically starts in the jaw and muscles
of the face, quickly spreading to the arms and legs.
“Lockjaw”
Difficulty swallowing
Intestines often seize up
Bladder fails to empty
Asphyxiation
Cardiac arrest
Tetanus
61. Muscle Disorders
Produced naturally by the body to support such functions as
fighting stress and promoting growth and development
Referred to as roids, juice, hype, weight trainers, gym candy,
arnolds, stackers, or pumpers
People use steroid pills, gels, creams, or injections to improve their
sports performance or the way they look.
Anabolic steroids cause many different types of problems
types of problems
premature balding or hair loss
dizziness
mood swings
problems sleeping
nausea and vomiting
high blood pressure
aching joints
urinary problems
shortening of final adult height
increased risk of heart disease,
stroke, and some cancers
Anabolic Steroids
62. Muscle Disorders
People with cerebral palsy
may have difficulty walking. They may
also have trouble with tasks such as
writing or using scissors.
Some people with cerebral palsy have
other medical conditions, including
seizure disorders or mental
impairment.
Cerebral palsy happens when the
areas of the brain that control
movement and posture do not develop
correctly or get damaged.
Cerebral Palsy
63. Muscle Disorders
A genetic condition that describes over 20
genetic and hereditary muscle diseases.
Characterized by progressive skeletal muscle
weakness, defects in muscle proteins, and the
death of muscle cells and tissue.
In some cases, cardiac and smooth muscles
are affected.
Progressive Muscular Wasting (weakness)
Poor Balance and Frequent Falls
Walking Difficulty + Waddling Gait
Limited Range of Movement
Scoliosis (curvature of the spine)
Inability to Walk
Muscle Atrophy and Drooping Eyelids
Muscular Dystrophy
Principal symptoms:
64. chronic autoimmune neuromuscular disease characterized
by varying degrees of weakness of the skeletal muscles
Caused by a defect in the transmission of nerve impulses
at the neuromuscular junction
Antibodies (produced by the body's own immune system)
block, alter, or destroy the receptors for acetylcholine at the
neuromuscular junction which prevents the muscle
contraction from occurring.
Myasthenia
Gravis
65. Certain muscles such as those that control
eye and eyelid movement, facial expression,
chewing, talking, and swallowing are often
involved. The muscles that control
breathing and neck and limb movements
may also be affected.
Patients initially complain of drooping eye
lids that get worse as the day goes on; they
develop double vision, difficulty talking, and
difficulty chewing.
66. Rigor mortis- stiffness of skeletal
muscles after death
Myosin-actin crossbridges are still intact or in
a state of midcontraction at the time of death
Crossbridges left attached due to depletion of
ATP
Bonds not broken-rigid muscles
Rigor mortis disappears as the body
decomposes