Pcc - Bio 231 - Lecture Midterm 2 - Chapter 10

Front 1

Isometric contraction:

Back 1

• The muscle develops tension but not shorten

Front 2

Isotonic contraction:

Back 2

• The tension developed by the muscle remains constant while the
muscle shorten.

Front 3

A fascia

Back 3

– sheet or broad band of fibrous connective tissue that supports and
surrounds muscles and other organs of the body.

Front 4

Superficial fascia

Back 4

– Separates muscle from skin.
– Composed of areolar connective tissue, and adipose tissue ( store TG,
insulating layer reduces heat loss, protects muscle from physical
trauma).
– Provides a pathway for nerves, blood vessels, lymphatic vessels to
enter and exit muscles.

Front 5

Deep fascia

Back 5

– Dense irregular connective tissue holds the muscles with similar
functions together.
– Allows free movement of muscles, carries nerves, blood vessels,
lymphatic vessels, and fill spaces between muscles.
– Three connective tissue layers extend from the deep fascia into the
muscle ( epimysium, perimysium, endomysium).

Front 6

Epimysium

Back 6

– Dense irregular connective
tissue
– the outermost layer encircling
the whole muscle
– Separates the muscle from
surrounding tissues and organs
– Connected to the deep fascia

Front 7

Perimysium

Back 7

– Dense irregular connective
tissue
– Surrounds groups of individual
muscle fibers, separating them
into bundles called fascicles.
– Contains blood vessels and
nerves

Front 8

Endomysium

Back 8

– Thin sheath of areolar connective
tissue penetrating the interior of
each fascicle separating individual
muscle fibers from one another.
– Contains
• capillary networks that supply
blood to muscle fibers
• satellite cells, embryonic stem
cells that function in the repair
of damaged muscle
• Nerve fibers that control the
muscle
• All three layers are continuous with the
connective tissue that attaches skeletal
muscles to other structures such as
bone or other muscle
• All three connective tissue layers may
extend beyond the muscle fiber to form
a tendon (or aponeurosis) that attaches
the muscle to the periosteum of a bone.

Front 9

Somatic motor neurons

Back 9

– A threadlike axon, wrapped with myelin
– extend from the brain or spinal cord to a group of skeletal muscle
fibers
– The axon branches and extends to different skeletal muscle fibers.
– Neuromuscular junction:
• the structural and functional site of communication between neuron
and muscle.

Front 10

Satellite cells

Back 10

– Some myoblasts in mature muscle retain the capacity
to fuse with one another or with damaged muscle
fibers to regenerate muscle fibers.

Front 11

Sarcolemma

Back 11

– Muscle plasma membrane
– Has transmembrane potential

Front 12

T tubules

Back 12

– Invagination of the Sarcolemma, tunnel in from the surface to the center of the
muscle fiber
– Open to the outside of the fiber, Filled with interstitial fluid
• Muscle action potential propagates along the Sarcolemma and the T tubules,
excite the muscle fiber almost the same instant.

Front 13

Sarcoplasma

Back 13

– Muscle cell cytoplasm
– Contains glycogen, myoglobin ( protein found only in muscles, carries oxygen),
mitochondria lie in rows close to the contracted proteins that use ATP.

Front 14

Myofibrils

Back 14

– Striated contractile fibrils
– 2 <m in diameter
– extend the entire length of the
muscle fibers.
– Responsible for skeletal muscle
contraction
– Anchored to the inner surface of
the sarcolemma
– Consist of
• bundle of myofilaments ( thin,
and thick)

Front 15

Sarcoplasmic Reticulum

Back 15

– Membranous sac encircles each
myofibrils
– Has dilated end sacs called
terminal cisterns which a butt T
tubules
– Store Calcium ions
– Triad:
• T tubule and

Front 16

Sarcomeres

Back 16

• The basic functional unit of
myofibril
• separated by Z discs.
• A sarcomere contains;
– Thick and thin filaments
– Proteins stabilize the
position of the thick and
thin filaments
– Proteins regulate the
interaction of thin and
thick filaments
• The interaction between thin
and thick filaments is
responsible for the muscle
contraction
• Filaments
– Do not extend the entire
length of the muscle fiber
– Thick and thin filaments
overlap one another to create
striation. ( 2 thin : 1 thick)

Front 17

A band

Back 17

– The dark middle area of the
sarcomere
– Extends the entire length of
the thick filament
– Towards the end is a zone of
overlap where thick and thin
filaments lie side by side
– Contain three subdivisions

Front 18

I band

Back 18

– Contain the rest of the thin
filaments, but not thick
filaments
– Z disc passes through the
center of the I-band

Front 19

Z line

Back 19

– marks the boundary between
adjacent sarcomere
– Contains protein actins that
interconnect thin filaments of
adjacent sarcomere

Front 20

H zone

Back 20

– Narrow, in the center of the A band
– Contains thick but not thin filaments in resting sarcomere

Front 21

M line

Back 21

– Supporting proteins hold the thick filaments together at the
center of the edge zone

Front 22

Zone of overlap

Back 22

– Thin filaments situated between the thick filaments
– Each thick filament is surrounded by six thin filaments

Front 23

Muscle proteins

Back 23

• Myofibrils built from three proteins:
1. Contractile protein:
• Generate force when contracted
• Proteins are myosin and actin
2. Regulatory protein: part of the thin filament.
• Tropomyosin:
• covers the myosin-binding site in relaxed muscles, blocking
myosin
• Troponin:
• holds tropomyosin in place
3. Structure proteins
• Contribute to the alignment, stability, elasticity, extensibility of
myofibrils.
• Proteins are titin, myomesin, dystrophin

Front 24

Myosin

Back 24

– 10-12 nm thick, and 1.6
<m long
– In skeletal muscle, 300
myosin molecules form a
single thick filament.
– Myosin has a tail points
toward the M line, and
lie parallel to each other
forming a shaft
– Head has two subunits
project toward the
surrounding thin
filaments
• There are no myosin
heads in the H zone

Front 25

Actin

Back 25

– 5-6 nm thick, and 1<m long
– Consist of four proteins
• F actin
– Twisted strand composed of two 300-400 globular protein G actin
– G actin contains the active site that binds to myosin
• Nebulin
– Long strand extends a long F actin between G actin
– Holds F actin together
• Tropomyosin
– Double strand protein covers seven active sites on G actin and prevents
actin-myosin interaction
– Bound to troponin
• Troponin
– Three globular subunits
» One binds to tropomyosin making troponin-tropomyosin complex
» One binds to G actin holding

Front 26

Muscle proteins

Back 26

• Titin:
– Huge size, span half the sarcomere ( Z to M line).
– Anchors thick filaments to Z disc and M line.
– Extends the length of the thick filament and then continues across the I
band to the Z line on each side
– The portion within the I band is elastic and will recoil after stretching
• Myomesin
– Structural protein form the M line
– Binds to Titin and connects adjacent thick filament to one another
• Dystrophin :
– Links thin filaments of the sarcomere to integral membrane proteins that
will attach to connective tissue matrix
reinforce Sarcolemma
help
transmit tension to tendons.

Front 27

Contraction

Back 27

• Myofibrils get shorter
• The H zones and the I
bands get smaller
• Overlap zone gets
larger
• Z lines move closer
• The width of the A
band remains constant

Front 28

Sliding fliament mechanism

Back 28

• Myosin heads attach to thin
filaments pulling it toward
the M line
• Thin filaments slide inward
and meet at the center of a
sarcomere
• Z discs come closer together
• Sarcomere shortens which
shorten the whole muscle
fiber and the entire muscle
• The Length of individual
thick and thin filaments do
not change

Front 29

Excitation contraction coupling

Back 29

• Calcium stored in SR
• Action potential opens calcium
release channels in the SR
• Calcium released into the cytosol
around thick and thin filaments
• calcium binds Troponin which
moves Troponin-Tropomyosin
complex away from myosinbinding
site on actin
• myosin heads bind to actin and the
contraction cycle begins .
• Relaxation
– SR contains calcium active
transport pumps that move
calcium from the cytosol into
SR and bind it to calsequestrin
– Ca concentration in the
cytosol will decrease
– Troponin-Tropomyosin
complex covers myosin
binding sites, and the muscle
fiber relaxes

Front 30

The contraction cycle

Back 30

1. ATP hydrolysis:
– myosin head
includes ATPbinding
pocket
and ATPase
– Hydrolysis
energizes myosin
heads
– the products of
hydrolysis, ADP
and a phosphate
group, are
attached to the
myosin head
2. Attachment of
myosin to acting to
form crossbridges.
– The energized
myosin heads
attach to myosinbinding
site on
the actin
– The phosphate
group released
1. Power stroke:
– The release of
phosphate
group triggers a
power stroke
– the pocket on
the myosin
head opens and
the myosin
head rotates and
releases ADP,
sliding the thin
filament toward
the M line.
2. Detachment of
myosin from actin:
– the myosin
binds another
ATP at the
ATP-binding
pocket

myosin heads
detach from
actin