Chapter 10: Muscle Tissue. Muscle Tissue A primary tissue type, divided into : Cardiac muscle Smooth muscle Skeletal muscle Attached to bones Allows us.

Chapter 10:Muscle Tissue

Muscle Tissue

•A primary tissue type, divided into:• Cardiac muscle• Smooth muscle• Skeletal muscle• Attached to bones• Allows us to move• Contains CT, nerves and blood vessels

Functions of Skeletal Muscles

1.

2.

3.

4.

5.

CT Organization – 3 layers

Surrounds entire muscle Separates muscle from

surrounding tissues Connected to deep fascia

1. Epimysium

1. Perimysium Divides the skeletal

muscle into a series of compartments

Each compartment contains a bundle of muscle fibers:

1. Endomysium

Surrounds individual skeletal muscle fibers

Interconnects adjacent muscle fibers

Satellite Cells -

At the end of a muscle: All 3 layers come

together to form a:

Both attach skeletal muscles to bones

Tendon fibers extend into the bone matrix

Microanatomy of Skeletal Muscle Fibers

• Skeletal muscle cells are called fibers• Enormous• Multinucleate• Myoblasts fuse during development to form

individual skeletal muscle fibers

Microanatomy of Skeletal Muscle Fibers

• Sarcolemma – cell membrane of muscle fiber▫ Surround sarcoplasm▫ Change in the

transmembrane potential is the start of a contraction

• Transverse Tubules – continuous with sarcolemma and extends into the sarcoplasm▫ form passageways through

muscle fibers▫ Filled with extracellular

fluid▫ Action potentials

Microanatomy of Skeletal Muscle Fibers

• Myofibrils – cylindrical structures encircled by T tubules▫ As long as the cell▫ Made of myofilaments

Thin filaments - actin Thick filaments – myosin

▫ Responsible for muscle fiber contraction

▫ Mitochondria and glycogen

Microanatomy of Skeletal Muscle Fibers

• Sarcoplasmic Reticulum – similar to ER of other cells▫ Forms network around each

myofibril

• Terminal cisternae – expanded chambers of SR on either side of a T tubule▫ Ca+2 ions storage

• Triad – pair of terminal cisternae plus a T tubule▫ Separate fluids

Microanatomy of Skeletal Muscle Fibers

• Sarcomere – repeating contractile units that make up myofibrils▫ Smallest functional unit in muscle fibers▫ Muscle contraction▫ Made up of: thick and thin filaments, stabilizing proteins and

regulating proteins▫ Striated

Microanatomy of Skeletal Muscle Fibers

• A bands – dark bands at center of sarcomere▫ Thick filaments (myosin)▫ Contains:

M line – center of A band, connects each thick filament together

H zone – lighter region on either side of M line, contains thick filaments

Zone of overlap – thick and thin filaments overlap one another

Microanatomy of Skeletal Muscle Fibers

• I bands – light bands on both sides of A band▫ Thin filaments (actin) ▫ Contains:

Z lines – boundary between adjacent sarcomeres

Titin – protein that aligns thick and thin filaments

▫Extends from thick filaments

Level 1: Skeletal Muscle

Level 2: Muscle Fascicle

Level 3: Muscle Fiber

Level 4: Myofibril

Level 5: Sarcomere

Muscle Contraction• Sliding Filament Theory

▫ Caused by interactions of thick and thin filaments▫ Triggered by free Ca2+ in sarcoplasm

Muscle Contraction• Thin Filaments – made of 4 proteins:

▫ F actin – 2 twisted strands of G actin, contain active sites for the binding of myosin

▫ Nebulin – holds 2 strands of G actin together▫ Tropomyosin – covers G actin active sites to prevent

actin/myosin interactions▫ Troponin – holds tropomyosin to G actin AND contains a site

for the binding of Ca2+

Holds until Ca2+ binds to the active site Contraction can only occur if position changes

Muscle Contraction• Thick Filaments – consist of a pair of myosin subunits

wrapped around each other▫ Tail – binds to other myosin molecules▫ Head – 2 subunits, project towards nearest thin filament

▫ During muscle contractions myosin heads pivot towards thin filaments, forming cross-bridges with G actin active sites

Muscle Contraction

• Sliding Filament Theory▫ Thin filaments slide

towards M line – shortening

▫ A band remains the same, but the Z lines move closer together

Muscle Contraction• Neuromuscular Junction - NMJ

▫ Where the action potential starts▫ Each branch ends at a synaptic terminal, which contains

mitochondria and Acetylcholine Neurotransmitter that alters the permeability of the sarcolemma

Muscle Contraction• Synaptic cleft –

• Motor end plate –

▫ Both contain AChE – breaks down Ach

• Action potential travels along the nerve axon and ends at the synaptic terminal, which changes the permeability

• ACh is released

Muscle Contraction• ACh diffuses across the synaptic cleft

and binds to ACh receptors on motor end plate

• Increase in membrane permeability to sodium ions that rush into the sarcoplasm

▫ Keeps going until AChE removes all ACh

• Travels along sarcolemma to T tubules and leads to excitation-contraction coupling -▫ Action potential leads to contraction▫ Triads release Ca2+

▫ Triggers muscle contractions

Muscle Contraction at Sarcomere

1. Exposure of active sites▫ Calcium ions bind to

troponin, changing its position and shifting tropomyosin away from active sites

2. Attachment of cross-bridges▫ Myosin heads bind to

active sites

Muscle Contraction at Sarcomere

3. Pivoting▫ Power stroke

4. Detachment of cross-bridges▫ ATP binds to myosin head,

link is broken▫ Attach to another active site

Muscle Contraction at Sarcomere

Muscle Contraction

at Sarcomere

5. Reactivation of myosin▫ ATP to ADP and phosphate▫ Cycle is repeated

• All sarcomeres contract at the same time

• Contraction duration depends on:

▫ Duration of neural stimulus▫ Amount of free Ca2+ ions

in sarcoplasm▫ Availability of ATP

Muscle Contraction• 1. At NMJ, ACh is released and

binds to receptors on sarcolemma

• 2. Change in transmembrane potential results in action potential that spreads across entire surface of cell and T tubules

• 3. SR releases stored calcium ions, increasing Ca2+ around sarcomeres

• 4. Calcium ions bind to troponin, which exposes active sites on thin filaments and cross-bridges form

• 5. Contraction begins as repeated cycles of cross-bridge formation and detachment happen

Muscle Contraction

• 6. ACh is broken down by AChE and action potential ends

• 7. SR reabsorbs calcium ions and concentration in sarcoplasm decreases

• 8. Active sites are re-covered

• 9. Contraction ends

• 10. Muscle relaxation – sarcomeres remain uncontracted

Rigor Mortis

• Stop in blood circulation causes skeletal muscles to be deprived of oxygen and nutrients –

• SR becomes unable to pump calcium ions out of sarcoplasm

• Extra calcium ions trigger a sustained contraction▫ Cross-bridges form, but cannot detach

• Lasts 15-25 hours after death

2 Types of Muscle Tension• Isotonic Contraction

▫ Skeletal muscle changes length resulting in motion▫ If muscle tension > resistance: muscle shortens (concentric

contraction)▫ If muscle tension < resistance: muscle lengthens (eccentric

contraction)

2 Types of Muscle Contraction

• Isometric Contraction▫ Muscle develops tension, but does not shorten

Resistance and Speed of Contraction • Inversely related• The heavier the resistance on a muscle:

▫ the longer it takes for shortening to begin▫ the less the muscle will shorten

Muscle Relaxation

• After contraction, a muscle fiber returns to resting length by:▫ Elastic forces

The pull of elastic elements (tendons and ligaments) Expands the sarcomeres to resting length

▫ Opposing muscle contractions Reverse the direction of the original motion The work of opposing skeletal muscle pairs

▫ Gravity Can take the place of opposing muscle contraction to

return a muscle to its resting state

ATP and Muscle Contraction• Muscle contraction uses a lot of ATP • Muscles store enough energy to start contraction, but

must manufacture more ATP▫ Generates ATP at the same rate that it is used

• ATP and CP ▫ ATP – active energy model (aerobic and anaerobic)▫ Creatine Phosphate (CP) – storage molecule for excess

ATP in resting muscle

▫ ATP – 2 seconds▫ CP – 15 seconds▫ Glycogen – 130 seconds (anaerobic) and 40 mins (aerobic)▫ Fats

ATP and Muscle Contraction •At rest:

▫Cells use fatty acids to create CP, ATP and glycogen – rebuilding their storages (beta oxidation)

•Moderate Activity:▫Cells use fatty acids or glucose and oxygen to

produce ATP (aerobic respiration) Muscle wont fatigue until all energy is used up Marathon runners

•Peak Activity▫Cells use oxygen faster than it is supplied

Aerobic resp only provides 1/3 of needed ATP Anaerobic resp provides the rest – lactic acid

Muscle Metabolism

Muscle Fatigue• When muscles can no longer perform a required

activity, they are fatigued• Results of Muscle Fatigue:

Depletion of metabolic reserves Damage to sarcolemma and SR Low pH (lactic acid) Muscle exhaustion and pain

• The Recovery Period The time required after exertion for muscles to return to

normal Oxygen becomes available Mitochondrial activity resumes

Muscle Fatigue

• The Cori Cycle The removal and recycling of lactic acid by the liver Liver converts lactic acid to pyruvic acid Glucose is released to recharge muscle glycogen reserves

Oxygen Debt – after exercise: Body needs more oxygen than usual to normalize metabolic activityHeavy breathing

3 Types of Skeletal Fibers • Fast Fibers:

▫ Contract quickly▫ High CP▫ Large diameter, huge glycogen reserves and few

mitochondria▫ Strong contractions, but fatigue quickly▫ White meat – chicken breast

• Slow Fibers▫ Slow to contract and slow to fatigue▫ Low CP▫ Small diameter, but a lot of mitochondria▫ High oxygen supply▫ Contain myoglobin (red pigment, binds to oxygen)▫ Dark meat – chicken legs

3 Types of Muscle Fibers• Intermediate Fibers

▫ Mid-sized▫ Low myoglobin▫ More capillaries than fast fibers, slower to fatigue▫ Table 10-3, page 298 ▫ Human Muscles

• Muscle Hypertrophy - muscle Growth from heavy training▫ increases diameter of

muscle fibers▫ increases number of

myofibrils▫ increases mitochondria,

glycogen reserves

• Muscle Atrophy – lack of muscle activity▫ Reduced in muscle size,

tone and power

Physical Conditioning

• Anaerobic Endurance ▫ Uses fast fibers, fatigues quickly with strenuous

activities 50 m dash, weightlifting

▫ Improved by frequent, brief, intensive workouts – interval training

• Aerobic Endurance – supported by mitochondria▫ Prolonged activity – uses a lot of oxygen and

nutrients Marathon running

▫ Improved by repetitive and cardiovascular training

Cardiac Muscle Tissue

• Striated tissue• Smaller cells with single nucleus• Short T-tubules and sarcoplasm

▫No triads or terminal cisternae• All aerobic

▫High in myoglobin and mitochondria

• Intercalated discs

Smooth Muscle• Blood vessels, reproductive and digestive systems, etc• Different arrangement of actin and myosin• Non-striated

Characteristics of Skeletal, Cardiac, and Smooth Muscle