ANATOMY & PHYSIOLOGY OF MUSCULAR SYSTEM.ppt

Mr. V. Atputhavadivel
Nursing Educator
College of Nursing
Batticaloa,
Sri Lanka.

Muscular System
• The muscular system
consists of all the muscles
of the body.
• These make up
approximately 42% of total
body weight, and are
composed of long, slender
cells known as fibers.
• The fibers are different
lengths and vary in color
from white to deep red.

Each muscle consists of a
group of fibers held
together by connective
tissue, and enclosed in a
fibrous sheath or fascia.
Muscular System

Types of Muscle
Muscles cause movement, help to maintain posture,
and produce heat.
There are 3 types, classified according to function
and appearance:

Types of muscle…
Fast, white muscle fibers contract rapidly, have
poor blood supply, operate without oxygen, and tire
quickly.
Slow, red muscle fibers contract more slowly, have
better blood supplies, operate with oxygen, and do
not tire as easily. They are used in ongoing
movements, such as maintaining posture.

Types of muscle…
Smooth muscle lines most hollow organs of the
body, such as the intestines, stomach, and uterus.
They help move substances through tubular areas
such as blood vessels and the small intestines,
contracting automatically and rhythmically.

Types of muscle…
Smooth muscles contract slower than skeletal
muscles, but can remain contracted longer, and are
not as dependent on oxygen.
They are stimulated by electrical impulses or
hormones, and use carbohydrates for energy.

Types of muscle…
They are stimulated to contract by electrical
impulses sent out from small clumps of specialized
tissue in the heart, the sinoatrial and
atrioventricular node.
The cardiac muscle
or myocardium are
striated like
skeletal muscles,
but are smaller and
shorter.

Skeletal Muscles
Human body contains over 400 skeletal muscles
⚫ 40-50% of total body weight
Functions of skeletal muscle
• Body movement (Locomotion)
• Maintenance of posture
• Respiration
• Diaphragmand intercostal contractions
• Communication (Verbal and Facial)
• Constrictionof organs and vessels
• Peristalsis of intestinal tract
• Pupils
• Productionof body heat (Thermogenesis)

Characteristics of Skeletal Muscle
Most are attached by tendons to bones
Cells are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by
connective tissue = great force, but tires
easily

Structure of Skeletal Muscle
⚫Composed of muscle cells
(fibers), connective tissue,
blood vessels, nerves
⚫Fibers are long, cylindrical,
and multinucleated
⚫Muscles 1 mm- 4 cm in
length
9

 Endomysium –
around single
muscle fiber
 Perimysium –
around a
fascicle
(bundle) of
fibers

 Epimysium –
covers the
entire skeletal
muscle
 Fascia – on the
outside of the
epimysium

 Epimysium blends into a connective
tissue attachment
Tendon – cord-like structure
Aponeuroses – sheet-like structure
 Sites of muscle attachment
Bones
Cartilages
Connective tissue coverings

Structure of Skeletal Muscle Fiber:
Terms
⚫Sarcolemma = Cell membrane
⚫Sarcoplasm = Cytoplasm
⚫Sarcoplasmic Reticulum =
Endoplasmic Reticulum
⚫Sarcosomes = Mitochontria

Structure of Skeletal Muscle Fiber
 Cells are multinucleate
 Nuclei are just beneath the sarcolemma

Structure of Skeletal Muscle Fiber …
 Sarcolemma – specialized plasma
membrane
 Sarcoplasmic reticulum – specialized
smooth endoplasmic reticulum

Structure of Skeletal Muscle Fiber …
 Myofibril
Bundles of myofilaments
Myofibrils are aligned to give clear bands
I band =
light band
A band =
dark band

Structure of Skeletal Muscle Fiber…
 Sarcomere
Contractile unit of a muscle fiber

 Organization of the sarcomere
Thick filaments = myosin filaments
Composed of the protein myosin
Has ATPase enzymes

 Organization of the sarcomere
Thin filaments = actin filaments
Composed of the protein actin

 Myosin filaments have heads
(extensions, or cross bridges)
 Myosin and
actin are overlap

Properties of Skeletal Muscle cells
or fibers
 Irritability – ability to receive and
respond to a stimulus
 Contractility – ability to shorten when an
adequate stimulus is received

Nerve Stimulus to Muscles
 Skeletal
muscles must
be stimulated
by a nerve to
contract (motor
neruron)
 Motor unit
One neuron
Muscle cells
stimulated by
that neuron

Neuromuscular Junctions
 Neuromuscular junctions – association site
of nerve and muscle

Neuromuscular Junctions..
 Synaptic cleft – gap between nerve and
muscle
Nerve and muscle do not make contact
Area between nerve and muscle is filled with
interstitial fluid

Transmission of Nerve Impulse to
Muscle
 Neurotransmitter – chemical released
by nerve upon arrival of nerve impulse
The neurotransmitter for skeletal muscle is
acetylcholine
 Neurotransmitter attaches to receptors
on the sarcolemma
 Sarcolemma becomes permeable to
sodium (Na+)

Transmission of Nerve Impulse to
Muscle
 Sodium move into the cell, generates an
action potential
 Once started, muscle contraction cannot
be stopped

The Sliding Filament Theory of
Muscle Contraction
 Activation by nerve
causes myosin
heads
(crossbridges) to
attach to binding
sites on the thin
filament
 Myosin heads then
bind to the next site
of the thin filament

The Sliding Filament Theory of
Muscle Contraction
 This continued
action causes a
sliding of the myosin
along the actin
 The result is that the
muscle is shortened
(contracted)

Contraction of a Skeletal Muscle
 Muscle fiber contraction is “all or none”
 Within a skeletal muscle, not all fibers
may be stimulated during the same
interval
 Different combinations of muscle fiber
contractions may give differing
responses
 Graded responses – different degrees
of skeletal muscle shortening, rapid
stimulus = constant contraction or
tetanus

Muscle Response to Strong Stimuli
 Muscle force depends upon the number
of fibers stimulated
 More fibers contracting results in
greater muscle tension
 Muscles can continue to contract unless
they run out of energy

Energy for Muscle Contraction
 Initially, muscles used stored ATP for
energy
Bonds of ATP are broken to release energy
Only 4-6 seconds worth of ATP is stored by
muscles
 After this initial time, other pathways
must be utilized to produce ATP

 Direct phosphorylation
 Muscle cells contain creatine
phosphate (CP)
 CP is a high-energy
molecule
 After ATP is depleted, ADP is
left
 CP transfers energy to ADP,
to regenerate ATP
 CP supplies are exhausted in
about 20 seconds

 Anaerobic glycolysis
Reaction that breaks
down glucose without
oxygen
Glucose is broken down
to pyruvic acid to
produce some ATP
Pyruvic acid is
converted to lactic acid

 Anaerobic glycolysis
(continued)
This reaction is not as
efficient, but is fast
Huge amounts of
glucose are needed
Lactic acid produces
muscle fatigue

 Aerobic Respiration
Series of metabolic
pathways that occur in
the mitochondria
Glucose is broken down
to carbon dioxide and
water, releasing energy
This is a slower reaction
that requires continuous
oxygen

Muscle Fatigue and Oxygen Debt
 When a muscle is fatigued, it is unable to
contract
 The common reason for muscle fatigue is
oxygen debt (deficit)
Oxygen must be “repaid” to tissue to remove
oxygen debt
Oxygen is required to get rid of accumulated
lactic acid
 Increasing acidity (from lactic acid) and lack
of ATP causes the muscle to contract less

Types of Muscle Contractions
 Isotonic contractions
Myofilaments are able to slide past each
other during contractions
The muscle shortens
 Isometric contractions
Tension in the muscles increases
The muscle is unable to shorten

Muscle Tone
 Some fibers are contracted even in a
relaxed muscle
 Different fibers contract at different
times to provide muscle tone
 The process of stimulating various
fibers is under involuntary control

Muscles and Body Movements
 Movement is
attained due to
a muscle
moving an
attached bone

Muscles and Body Movements
 Muscles are
attached to at
least two points
Origin –
attachment to a
moveable bone
Insertion –
attachment to an
immovable bone

Effects of Exercise on Muscle
 Results of increased muscle use
Increase in muscle size
Increase in muscle strength
Increase in muscle efficiency
Muscle becomes more fatigue resistant

Types of Ordinary Body Movements
 Flexion – decreases angle of joint and
brings two bones closer together
 Extension- opposite of flexion
 Rotation- movement of a bone in
longitudinal axis, shaking head “no”
 Abduction/Adduction (see slides)
 Circumduction (see slides)

Left: Abduction
– moving the leg
away from the
midline
Above –
Adduction-
moving toward
the midline
Right:
Circumduction: cone-
shaped movement,
proximal end doesn’t
move, while distal end
moves in a circle.

Types of Muscles
 Prime mover – muscle with the major
responsibility for a certain movement
 Antagonist – muscle that opposes or
reverses a prime mover
 Synergist – muscle that aids a prime
mover in a movement and helps prevent
rotation

Naming of Skeletal Muscles
 Direction of muscle fibers
Example: rectus (straight)
 Relative size of the muscle
Example: maximus (largest)

 Location of the muscle
Example: many muscles are named
for bones (e.g., temporalis)
 Number of origins
Example: triceps (three heads)

 Location of the muscles origin and
insertion
Example: sterno (on the sternum)
 Shape of the muscle
Example: deltoid (triangular)
 Action of the muscle
Example: flexor and extensor (flexes or
extends a bone)

Muscles of the face
•There are many muscles involved in changing facial
expression and with movement of the lower jaw
during chewing and speaking.
•Only the main muscles are described here. (Except
where indicated the muscles are present in pairs,
one on each side)

Muscles of the face…
1. Occipitofrontalis (unpaired)
• This consists of a posterior muscular part over the
occipital bone (occipitalis), an anterior part over the
frontal bone (frontalis) and an extensive flat tendon or
aponeurosis that stretches over the dome of the skull
and joins the two muscular parts. It raises the eyebrows.

2. Levator palpebrae superioris
• This muscle extends from the posterior part of the
orbital cavity to the upper eyelid. It raises the eyelid.

3. Orbicularis oculi
•This muscle surrounds the eye, eyelid and
orbital cavity. It closes the eye and when
strongly contracted ‘screws up’ the eyes.

4. Buccinator
•This flat muscle of the cheek draws the cheeks
in towards the teeth in chewing and in forcible
expulsion of air from the mouth (‘the
trumpeter’s muscle’).

5. Orbicularis oris
(unpaired)
•This muscle surrounds
the mouth and blends
with the muscles of the
cheeks. It closes the lips
and, when strongly
contracted, shapes the
mouth for whistling.

6. Masseter
•This is a broad muscle, extending from the zygomatic
arch to the angle of the jaw. In chewing it draws the
mandible up to the maxilla, closing the jaw, and
exerts considerable pressure on the food.

Muscles of the face……….
7. Temporalis
•This muscle covers the squamous part of the
temporal bone. It passes behind the zygomatic
arch to be inserted into the coronoid process of
the mandible. It closes the mouth and assists with
chewing.

Muscles of the face……….
8. Pterygoid
•This muscle extends from the sphenoid bone to the
mandible. It closes the mouth and pulls the lower
jaw forward.

Muscles of the neck
There are many muscles in the neck, but only the
two largest are considered here
•Sternocleidomastoid
•Trapezius

Sternocleidomastoid
•This muscle arises from the manubrium of the
sternum and the clavicle and extends upwards to
the mastoid process of the temporal bone.

Sternocleidomastoid
•It assists in turning the head
from side to side. When the
muscle on one side contracts
it draws the head towards the
shoulder.
•When both contract at the
same time they flex the
cervical vertebrae or draw the
sternum and clavicles
upwards when the head is
maintained in a fixed position,
e.g. in forced respiration.

Trapezius
•This muscle covers the shoulder and the back of the neck.

Trapezius
•The upper attachment is
to the occipital
protuberance, the medial
attachment is to the
transverse processes of
the cervical and thoracic
vertebrae and the lateral
attachment is to the
clavicle and to the spinous
and acromion processes of
the scapula.

Trapezius
•It pulls the head backwards, squares the shoulders and
controls the movements of the scapula when the
shoulder joint is in use.

Muscles of the back
•There are six pairs of large muscles in the back, in
addition to those forming the posterior abdominal wall.
•The arrangement of these muscles is the same on each
side of the vertebral column.
They are:
• Trapezius
• Latissimus dorsi
• Teres major
• Psoas
• Quadratus lumborum
• Sacrospinalis.

Teres major
•This originates from the
inferior angle of the
scapula and is inserted
into the humerus just
below the shoulder
joint.
•It extends, adducts and
medially rotates the
arm

Psoas
•This arises from the
transverse processes and
bodies of the lumbar
vertebrae.
•It passes across the flat
part of the ilium and
behind the inguinal
ligament to be inserted
into the femur.
•Together with the iliacus
it flexes the hip joint

Latissimus dorsi
• This arises from the posterior
part of the iliac crest and
the spinous processes of the
lumbar and lower thoracic
vertebrae.
• It passes upwards across the
back then under the arm to
be inserted into the bicipital
groove of the humerus.
• It adducts, medially rotates
and extends the arm.

Quadratus lumborum
•This muscle originates from the iliac crest, then it passes
upwards, parallel and close to the vertebral column and it
is inserted into the 12th rib.

Quadratus lumborum
•Together the two
muscles fix the
lower rib during
respiration and
cause extension of
the vertebral
column (bending
backwards).
•If one muscle
contracts it causes
lateral flexion of the
lumbar region of
the vertebral
column.

Sacrospinalis (erector spinae)
•This is a group of muscles lying between the spinous and
transverse processes of the vertebrae.
•They originate from the sacrum and are finally inserted into
the occipital bone.
•Their contraction
causes extension
of the vertebral
column.

Muscles of the abdominal wall
Five pairs of muscles form the abdominal wall.
From the surface inwards they are:
• Rectus abdominis
• External oblique
• Internal oblique
• Transversus abdominis
• Quadratus lumborum

Muscles of the abdominal wall ……
•The anterior abdominal
wall is divided
longitudinally by a very
strong midline
tendinous cord, the
linea alba (meaning
‘white cord’).
•Which extends from
the xiphoid process of
the sternum to the
symphysis pubis.

Muscles of the abdominal wall …………..
Rectus Abdominis
•This is the most superficial muscle. It is broad and flat,
originating from the transverse part of the pubic bone then
passing upwards to be inserted into the lower ribs and the
xiphoid process of the sternum. Medially the two muscles
are attached to the linea alba.

External oblique
•This muscle extends from the lower ribs downwards and
forward to be inserted into the iliac crest and, by an
aponeurosis, to the linea alba.

Internal oblique
•This muscle lies deep to the external oblique.

Internal oblique
•Its fibres arise from the iliac crest and by a broad band of
fascia from the spinous processes of the lumbar
vertebrae.
•The fibres pass upwards towards the midline to be
inserted into the lower ribs and, by an aponeurosis, into
the linea alba.

Transversus abdominis
•This is the deepest muscle of the abdominal wall.
•The fibres arise from the iliac crest and the lumbar vertebrae
and pass across the abdominal wall to be inserted into the
linea alba by an aponeurosis.

Functions of Pair Abdominal Muscles
•The main function of these paired muscles is to form the
strong muscular anterior wall of the abdominal cavity.
•When the muscles contract together they:
• compress the abdominal organs
• flex the vertebral column in the lumbar region
•Contraction of the muscles on one side only bends the
trunk towards that side.
•Contraction of the oblique muscles on one side rotates the
trunk.

Inguinal canal
•This canal is 2.5 to 4 cm long
and passes obliquely
through the abdominal wall.
•It runs parallel to and
immediately in front of the
transversalis fascia and part
of the inguinal ligament.

Inguinal canal
•In the male it
contains the
sperniatic cord and in
the female, the
round ligament.
• Inguinal hernia –
Herniotomy & Repair

Muscles of the pelvic floor
The pelvic floor is divided into two halves that unite along
the midline..
The muscles are:
•Levator ani –
•Coccygeus -

Muscles of the pelvic floor……
Fj caHj;jpj;jir

Levator ani
•A pair of broad flat muscles, forming the anterior part of
the pelvic floor.
•They originate from the inner surface of the true pelvis
and unite in the midline.
•Together they form a sling that supports the pelvic organs.

Coccygeus
•This is a paired triangular sheet of muscle situated
behind the levator ani.
•They originate from the medial surface of the ischium
and are inserted into the sacrum and coccyx.
•They complete the formation of the pelvic floor, which is
perforated in the male by the urethra and anus, and in
the female by the urethra, vagina and anus.

Functions of Pelvic Floor
•supports the organs of the pelvis and maintains
continence, i.e. it resists raised intrapelvic pressure
during micturition and defaecation.

Muscles of the Shoulder and Upper
Limb
• These muscles stabilise the association between the
appendicular and axial skeletons at the pectoral girdle, and
stabilise and allow movement of the shoulders and upper
arms.

Limb …
1. Coracobrachialis
2. Deltoid
3. Pectoralis major
4. Biceps
5. Brachialis
6. Triceps
7. Brachioradialis
8. Pronator quadratus

Limb …
09. Pronator teres
10. Supinator
11. Flexor carpi radialis
12. Flexor carpi ulnaris
13. Extensor carpi radialis longus and brevis
14. Extensor carpi ulnaris
15. Palmarus longus
16.Extensor digitorum

Limb .…

Muscles of the shoulder and upper limb ……………….
1. Coracobrachialis

Muscles of the shoulder and upper limb ……………….
2. Deltoid
 Deltoid forms the fleshy and rounded contour of
the shoulder and the main function is movement
of the arm.

2. Deltoid…
•The injection site is in the
middle of the deltoid muscle,
about 2.5 to 5 cm (1 to 2
inches) below the acromion
process.
•To locate this area, lay three
fingers across the deltoid
muscle and below the acromion
process.
•The injection site is generally
three finger widths below, in the
middle of the muscle.

Muscles of the shoulder and upper limb …………..
3. Pectoralis major
•This lies on the anterior
thoracic wall.

Origin:
– Medial half of the clavicle
– The sternum.
– Upper six costal cartilage.
Insertion:
•Lateral lip of bicipital groove of
the humerus.
Action:
– Adduction, flexion and medial
rotation of the arm.
– Climbing.
•It is an accessory muscle of
inspiration.
Nerve Supply:
•Medial and lateral pectoral
nerves.

4. Biceps Brachii
• This lies on the
anterior aspect of
the upper arm.

Muscles of the shoulder and upper limb ……
5. Brachialis
 This lies on the
anterior aspect
of the upper
arm deep to
the biceps.
 It is the main
flexor of the
elbow joint.

6. Triceps
 This lies on the posterior aspect of the humerus.
 It helps to stabilise the shoulder joint, assists in adduction
of the arm and extends the elbow joint.

7. Brachioradialis
•The brachioradialis spans the elbow joint, originating
on the distal end of the humerus and inserts on the
lateral epicondyle of the radius.
•When it contracts, it flexes the elbow joint.

8. Pronator teres
•This lies obliquely across the upper third of the front
of the forearm.

9. Pronator quadratus
• This square-shaped muscle is the main muscle causing
pronation of the hand and has attachments on the lower
sections of both the radius and the ulna.

10. Supinator
This lies obliquely across
the posterior and lateral
aspects of the forearm.
• It rotates the radioulnar
joints- supination.
• It lies deep to the muscles

11. Flexor carpi radialis
This lies on the anterior
surface of the forearm.

12. Flexor carpi ulnaris
•This lies on the medial
aspect of the forearm.

13. Extensor carpi
radialis longus and
brevis
• These lie on the
posterior aspect of the
forearm.

14. Extensor carpi ulnaris
• This lies on the posterior
surface of the forearm.
• It originates from the lateral
epicondyle of the humerus and
is inserted into the fifth
metacarpal bone.
• It extends and adducts the
wrist.

15. Palmarus longus

16. Extensor
digitorum

In the wrist, it divides into four
tendons, one for each finger

Muscles of the hip and lower limb
•The biggest muscles of the body are found here.
•Their function is largely in weight bearing, body
weight in walking, running and as shock absorbers.

Muscles
of the
hip and
lower
limb

Muscles of the hip and lower limb
1. Psoas
2. Iliacus
3. Quadriceps femoris
4. Obturators
5. Gluteals
6. Sartorius
7. Adductor group
8. Hamstrings
9. Gastrocnemius
10. Anterior tibialis
11. Soleus

Muscles of the hip and lower limb …………
Psoas

Muscles of the hip and lower limb …………
Iliacus
•This lies in the iliac
fossa of the innominate
bone.
•Origin - iliac crest
•Insertion - lesser
trochanter of the femur.
•Action - the combined
action of the iliacus and
psoas flexes the hip
joint.

Muscles of the hip and lower limb ………..

Quadriceps femoris
• The rectus femoris originates
from the ilium and the three
vasti from the upper end of
the femur.
• Together they inserted into
the tibia by the patellar
tendon.
• Only the rectus femoris flexes
the hip joint.
• Together, the group acts as a
very strong extensor of the
knee joint.

Obturators
•The obturators, deep muscles
of the buttock.
•Origins - rim of the obturator
foramen of the pelvis
•Insert - proximal femur.
•Their main function lies in
lateral rotation at the hip joint.

Gluteals
• These consist of the gluteus maximus, medius and
minimus.
• These together form the fleshy part of the buttock.

Sartorius
•This is the longest
muscle in the body
and crosses both the
hip and knee joints.

Adductor group
• This lies on the medial aspect of the thigh.
•They originate from the pubic bone and are inserted
into the linea aspera of the femur.
•They adduct and medially rotate the thigh.

Hamstrings
• These lie on the posterior
aspect of the thigh.
• Origin - ischium
• Insertion -upper end of the
tibia.
• They are the biceps femoris,
semimembranosus and
semitendinosus muscles.
• They flex the knee joint.

Gastrocnemius
•This forms the bulk of the calf of the leg.
•It arises by two heads, one from each condyle of the
femur
•Inserted calcaneus by the calcanean tendon (Achilles
tendon).
•Action - flexion at the knee and plantar flexion (rising
onto the ball of the foot) at the ankle.

Gastrocnemius..
•It arises by two heads,
one from each condyle
of the femur
•Inserted calcaneus by
the calcanean tendon
(Achilles tendon).
•Action - flexion at the
knee and plantar flexion
(rising onto the ball of
the foot) at the ankle.

Anterior tibialis
•Originates - upper
end of the tibia,
•Inserted into the
middle cuneiform
bone by a long
tendon.
•It is associated with
dorsiflexion of the
foot.

Soleus
•This is one of the main muscles of the calf of the leg,
lying immediately deep to the gastrocnemius.
•It originates from the upper parts of the fibula and the
tibia.
•Its tendon joins that of the gastrocnemius so that
they have a common insertion into the calcaneus by
the calcanean (Achilles) tendon.
•It causes plantarflexion at the ankle and helps to
stabilise the joint when standing.

Muscles of Respiration
• Chest expansion
during inspiration –
muscles activities
• Normal quit
breathing –
intercostal muscles
and diaphragm
• During difficult or
deep breathing –
assisted by muscles
of the neck,
shoulder, abdominal.

Intercostal muscles
• 12 pairs of rib
forming 11 pairs of
intercostals space
• 11 pairs intercostals
space occupy by 2
layers of
intercostals muscles
• External and
internal intercostals
muscles

External intercostal muscle
These extend downwards and forwards from the lower
border of the rib above to the upper border of the rib
below.

Internal intercostal muscle
These extend downwards and backwards from the
lower border of the rib above to the upper border of the
rib below.

Diaphragm
•The diaphragm is a dome-shaped muscular structure
separating the thoracic and abdominal cavities.
•It forms the floor of the thoracic cavity and the roof of
the abdominal cavity.

Disease of muscle
Myasthenia gravis
• Auto immune disease
•Unknown origin
•Antibodies – produced bind and block
acetylcholine ( neuro transmitter)
•Muscle weakness - ptosis or diplopia
•Affects more women than male

Disease of muscle…..
•Muscular dystrophies
Muscular dystrophies are a group of muscle diseases
caused by mutations in a person's genes. Over time,
muscle weakness decreases mobility, making
everyday tasks difficult.
•Crush syndrome
Crush syndrome is the systemic manifestation of
muscular tissue lysis (rhabdomyolysis) resulting from
a continuous and prolonged pressure.

ANATOMY & PHYSIOLOGY OF MUSCULAR SYSTEM.ppt

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to ANATOMY & PHYSIOLOGY OF MUSCULAR SYSTEM.ppt

Similar to ANATOMY & PHYSIOLOGY OF MUSCULAR SYSTEM.ppt (20)

Recently uploaded

Recently uploaded (20)

ANATOMY & PHYSIOLOGY OF MUSCULAR SYSTEM.ppt