Module 6- Part 1

Front 1

Three types of muscle tissue

Back 1

•Smooth

•Cardiac

•Skeletal

Front 2

Smooth Muscle

Back 2

•In the walls of organs

•Not striated

•Involuntary

Front 3

Skeletal Muscle

Back 3

•Attached to bones and skin

•Striated

•Voluntary

Front 4

Cardiac Muscle

Back 4

•Found only in the heart

•Striated

•involuntary

Front 5

Properties of Muscle Tissue

Back 5

•Excitability

•Contractility

•Extensibility

•Elasticity

Front 6

Excitability

Back 6

Responds to chemicals released from nerve cells

Front 7

Contractility

Back 7

Ability to shorten and generate force

Front 8

Extensibility

Back 8

Ability to be stretched without damaging the tissue

Front 9

Elasticity

Back 9

Ability to return to original shape after being stretched

Front 10

Muscle Functions

Back 10

•Movement of bones or fluids

•Maintaining posture and body position

•Stabilizing joints

•Heat generation (esp. Skeletal muscle)

Front 11

Connective tissue sheaths

Back 11

•Endomysium

•Perimysium

•Epimysium

Front 12

Endomysium

Back 12

The innermost sheath consisting of areolar connective tissue surrounds individual muscle fibers

Front 13

Perimysium

Back 13

A fibrous connective tissue surrounding groups of muscle fibers called fascicles

Front 14

Epimysium

Back 14

The outermost sheath called Epimysium wraps around the whole muscle and helps transfer the force generated by contraction of the muscle onto bones or skin. It consists of dense irregular connective tissue.

Front 15

Skeletal Muscle: Attachments

Back 15

Muscles attach:

•Directly- Epimysium of muscle is fused to the periosteum of bone of perichondrium of cartilage

•Indirectly- Connective tissue wrappings extend beyond the muscle as a rope like tendon or sheet like aponeurosis

Front 16

Profile of a skeletal muscle fiber

Back 16

•Long cells- fibers not visible without a Microscope

•Multi nucleated

•Sarcolemma- plasma membrane of the muscle

•Sarcoplasm- muscle cytoplasm

•Sarcoplasmic reticulum- muscle endoplasmic reticulum

•Mitochondria- Many to make ATP

•Glycosomes- For glycogen storage, myoglobin for O2 storage

Front 17

What sets muscle tissue apart?

Back 17

•It's ability to convert chemical energy into mechanical

•The structures that are designed to do just that are rod like structures called myofibrils that make up ~80% of the cell volume

Front 18

Sarcomere

Back 18

Smallest contractile or functional until of a muscle fiber is a sarcomere. It is defined as the region of a myofibril between two successive z discs. It is composed of thick and thin myofilaments.

Front 19

Muscle Hierarchy (Big-Small)

Back 19

1. Muscles

2. Fascicles

3. Muscle Fibers (cells)

4. Myofibrils (hundreds to thousands in a single muscle fiber)

5. Sarcomeres

6. Myofilaments (thick and thin)

Front 20

Sarcomere

Back 20

I band- LIGHT

A band- DARK

Front 21

Z Disc

Back 21

Coin shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another

Front 22

Thick filament

Back 22

Runs the entire length of the A band

Front 23

M line

Back 23

Line of protein that holds adjacent thick filaments together

Front 24

H zone

Back 24

Lighter mid-region where filaments do not overlap

Front 25

Thin filament

Back 25

Runs the entire length of the I band and partway into the A band

Front 26

Sarcoplasmic Reticulum

Back 26

•Network of smooth endoplasmic reticulum surrounding each Myofibril

•Pairs of terminal cisternae form perpendicular cross channels

•Functions in the regulation of intercellular Ca2+ levels

Front 27

Intercellular calcium turns muscle contraction on and off

Back 27

Where does this calcium come from?

•Terminal cisternae of Sarcoplasmic reticulum

Front 28

T Tubules

Back 28

•the Sarcolemma dips down as T tubules (Transverse tubules) at the A-I band junction

•The T Tubules associate with the paired terminal cisternae to form triads that encircle each sarcomere

Front 29

The Sarcolemma dips down as t tubules at the A-I band junction. The t tubules contain voltage sensors that open gated SR foot proteins which release Ca2+ and start contraction

Back 29

Back (Definition)

Front 30

Once calcium is released it binds to troponin, tropomyosin moves and this exposes myosin binding sites on the actin

Back 30

Front 31

Muscle contraction

Back 31

•The generation of force

•Sarcomeres contract when the thick and thin myofilaments slide over each other

Front 32

Sliding Filament model of contraction

Back 32

•In the relaxed state, thin and thick filaments overlap only slightly

•During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the m line

•As H zones shorten and disappear, Sarcomeres shorten, muscle cells shorten and the whole muscle shortens

Front 33

Requirements for skeletal muscle contraction

Back 33

•Skeletal muscle cells do not contract without a signal from their motor neuron in the central nervous system

•Activation- neural stimulation at a neuromuscular junction

•Excitation-contraction coupling:

•Generation and propagation of an action potential along the Sarcolemma

•Final trigger: A Brief rise in intracellular CA2+ levels

Front 34

Activation

Back 34

•Axons of motor neurons travel from the central nervous system via Nerves to skeletal muscles

•Each axon forms several branches as it enters a muscle

•Each axon ending forms a neuromuscular junction with a single muscle fiber

Front 35

Activation

Back 35

•Axons of motor neurons travel from the central nervous system via Nerves to skeletal muscles

•Each axon forms several branches as it enters a muscle

•Each axon ending forms a neuromuscular junction with a single muscle fiber

Front 36

Neuromuscular

Back 36

•Situated midway along the length of a muscle fibers

•Axon terminal and muscle fiber are separated by a gel-filled space called the synaptic cleft

•Synaptic vesicles- of axon terminal contain the neurotransmitter acetylcholine (ACh)

•Junctional folds of the Sarcolemma contain ACh receptors

Front 37

Events at the neuromuscular junction

Back 37

•Nerve impulse arrives at axon terminal

•ACh is released and binds with receptors on the Sarcolemma

•Electrical events lead to the generation of an action potential

•ACh effects are quickly terminated by the enzyme Acetylcholinesterase

•Prevents continued muscle fiber contraction in the absence of additional stimulation

Front 38

Events in generation of an action potential: 1. Local depolarization

Back 38

Front 39

Events in generation of an action potential: 2. Generation and propagation of an action potential

Back 39

Front 40

Events in generation of an action potential: 3. Repolarization

Back 40

Front 41

Excitation-Contraction (E-C) Coupling

Back 41

• sequence of events by which transmission of an AP along the sarcolemma leads to sliding of the myofilaments

• latent period: Time when EC coupling events occur

• Time between AP initiation and the beginning of contraction

• AP is propagated along sarcomere to T tubules

•Voltage sensitive proteins stimulate Ca2+ release from SR

• Ca2+ is necessary for contraction

Front 42

Cross bridge cycle

Back 42

• Crossbridge formation-high-energy myosin head attaches to thin filament

• working (power) stroke- myosin head pivots and pulls thin filament toward M line

• Crossbridge detachment: ATP attaches to myosin head and the cross bridge detaches

•"Cocking" of the myosin head- energy from hydrolysis of ATP cocks the myosin head into the high energy state

• continues as long as the calcium signal and adequate ATP are present