Muscle Tissue

Muscles makeup how much of our body mass?

Nearly half

Muscles convert chemical energy into

Mechanical energy for movement

What are the 5 main muscle properties?

-Electrical excitability

-Conductivity

-Contractility

-Extensibility

-Elasticity

Since muscles have conductivity, what does this mean?

They can conduct electrical currents in the body

Extensibility gives muscles the ability to

Stretch without damage

The ability for muscles to return to their original shape after contraction or extension is...

Elasticity

What are the 6 main characteristics of skeletal muscle?

-Form muscular system

-Attached to skeleton

-Striated

-Voluntary

-Multinuclear

-Stimulated by nerve impulses

What are the 6 main functions of skeletal muscle?

-Speech

-Voluntary movement

-Maintain posture

-Control body openings (ie. mouth)

-Body temperature regulation

-Blood sugar levels

What are the 5 main smooth muscle characteristics?

-Found in internal organs

-Involuntary

-Non-striated

-1 nucleus

-Excited by nerve stimuli AND self-excitable

What are the 4 main functions of smooth muscle?

-Movement for internal organs

-Control blood flow & blood pressure

-Act as valves (sphincters)

-Piloerection (skin)

What are the 9 main distinct things to remember about cardiac muscle?

-Has cardiocytes

-Produce blood flow

-Involuntary

-Intercalated discs

-Striated

-1 nucleus

-Cells connected laterally

-Self-excitable

-Has own pacemaker

What type of muscle forms the muscular system?

Skeletal muscle

Skeletal muscle has _______ tissue and _______ ________

Nerve tissue and blood supply

Fascicles are...

Bundles of muscle fibers

The Epimysium is...

The membrane around the ENTIRE muscle

The Perimysium is...

The membrane around the Fascicles

The Endomysium is...

The membrane that surrounds the muscle fibers

How are muscle fibers arranged?

In parallel bundles called fascicles

The sarcolemma is...

The plasma membrane of the skeletal muscle fiber

Sarcoplasmic reticulum has...

Ca2+ ions

Transverse tubules (t-tubules)...

Carry impulses for contraction (like electrical wiring!)

Sarcomeres are...

Contractile units

Sarcomeres make up...

Myofibrils

The sarcoplasmic reticulum (SR) is...

A network of membranous channels surrounding each myofibril

Sarcoplasmic Reticulum (SR) stores...

Calcium

What are terminal cisternae?

Expanded ends on either side of a transverse tubule (found in SR)

What is a triad?

2 terminal cisternae + 1 transverse tubule in between

Myofibrils make up (are found within)

Muscle fibers

Myofibrils are made of...

Bundles of thick and thin myofilaments

What are the end to end contractile units that make up myofibrils called?

Sarcomeres!

What are the lines that separate one sarcomere from the next?

Z-lines

What bands are between Z bands and appear light?

I bands

A bands appear _______ and _______________ thick and thin myofilaments

dark; overlap

M lines are _____ ______ __________ of sarcomeres

in the middle

In relaxed sarcomeres, H bands only have ________ filaments

thick

When thin (actin) myofilaments slide along thick (myosin) myofilaments toward the middle of each sarcomere...

a muscle contraction occurs

What happens to Z-lines during muscle contraction?

They're pulled toward the middle of the sarcomere

During contraction, all sarcomeres ________

Shorten

During contraction, all myofibrils ________

Shorten

Thick myofilaments are arranged _____ to _____

Tail to tail (heads face in both directions)

Thick myofilaments are made of _______ myosin molecules and have _______ heads

300 ; flexible

Thin myofilaments are mostly ______

Actin

In thin myofilaments, actin is wrapped by thin filaments of _______________

Tropomyosin

The troponin complex is made of...

Globular protein of 3 subunits

What 2 things does Dystrophin do?

-Attaches peripheral actin to endomysium via linking proteins

-Transfers force of sarcomere contraction to endomysium, then to tendon

Muscle dystrophy is caused by...

Lack of dystrophin

When a sarcomere contracts, the I bands and H bands get smaller. True or False?

True

When a sarcomere contracts, the A band gets smaller. True or False?

False

What are the 4 things needed for muscle contraction?

-Nerve impulses to release calcium

-Calcium for binding myosin heads to actin

-ATP

-Anaerobic and Aerobic respiration to produce ATP

What make up nerves?

Axons

Nerve impulses travel down...

T-tubules

What is the nerve transmitter released from synaptic knobs?

Acetylcholine (ACH)

What energizes and cocks myosin heads?

ATP

Nerve impulses release...

Calcium

What are the strands of protein that cover actin active sites called?

Tropomyosin

The sarcomere can't contract until calcium...

Uncovers actin active sites

Sarcomere contraction is also called...

Excitation-Contraction Coupling

How many steps of Excitation-Contraction Coupling are there?

6

What is in Step 1 of sarcomere contraction?

The Myosin heads are energized & cocked, but the actin active sites are still covered by tropomyosin (there's no Ca2+ available)

What is in Step 2 of sarcomere contraction?

The binding sites become uncovered as nerve impulses spread down t-tubules and Ca2+ is released from SR and bonded to the Troponin complex. Troponin flexes and pulls tropomyosin off actin active sites

What happens in Step 3 of sarcomere contraction?

The Myosin heads bind to actin & a CROSS-BRIDGE is formed

What happens in Step 4 of sarcomere contraction?

The Myosin heads pivot (flex), pulling thin myofilaments from each end of sarcomere to the middle

What happens in Step 5 of sarcomere contraction?

Cross-Bridge detachment as ATP is added and makes the myosin heads release their grip with actin

If Ca2+ can be thought of as glue for the binding, then ________ can be thought of as the opposite of glue.

ATP

What happens in Step 6 of sarcomere contraction?

Myosin reactivation (repeating until full contraction)

-The ATP that was just added becomes hydrolyzed and re-energizes the myosin heads causes them to re-cock and bind to next actin active sites

What 4 things happen causing sarcomere contraction to stop (relax)?

-Nerve impulses stop

-Ca2+ gets pumped back into SR

-Troponin complex unflexes, allowing tropomyosin to cover the actin sites again

-Repeating cycle stops bc cross-bridge can't be formed anymore

What composes a motor unit?

A motor neuron and the many skeletal muscle fibers it stimulates

Motor neurons branch into...

Several motor nerve endings

A motor neuron can stimulate many ____________ __________ fibers simultaneously

Skeletal muscle

How many muscle fibers are found in a motor unit?

10-100s

Heavier items require a greater number of _________ _________ to pickup

Motor units

A single rapid contraction is called a...

Muscle twitch

Desired muscle contractions require (2)...

-Sustained, relatively smooth contractions

-Ability to increase contraction strength

Myograms are...

Recordings of muscle twitches

Do twitches have increasing strengths?

Yes

Low frequency stimuli produce...

Identical twitches

Higher frequency stimuli produce...

Temporal (wave) summation

Temporal (wave) summation is how many stimuli per sec?

20-40 stimuli per sec

Incomplete tetanus is...

Only partial relaxation between stimuli

Fluttering is found in Complete tetanus. True or False?

False. Fluttering is found in incomplete tetanus

Complete tetanus is...

No relaxation between stimuli

______________ makes muscle contraction stronger

Tetanus

The more motor units recruited, the ___________ the contraction

Stronger

Fewer and smaller motor units are used when...

Minimal contraction strength is required

More larger motor units are used when...

Maximum strength is required

Individual motor units _________, meaning they can't keep contracting without resting to recover

Fatigue

During longer periods of sustained contraction...

Not all motor units contract at the same time

When some motor units are contracting while others are relaxing & recovering, this is called...

Asynchronous contraction

Contractions are sustained and made stronger by... (2)

Temporal Summation & Motor unit recruitment

What is Temporal summation?

Varying degrees of stimulus frequency which doesn't allow muscle to relax

What are the benefits of muscles always being partially contracted (muscle tone)?

-Posture maintenance

-Better muscle coordination

-Readies muscle for faster action when needed

-Prevents muscle atrophy

Isotonic (literally) means...

Equal tension

Iso=

equal

What are the 2 types of Isotonic muscle contraction?

Concentric & Eccentric

Isotonic muscle contractions are used for...

Body movements and moving objects

When a muscle shortens and pulls on another structure to produce movement and reduce the angle at a joint, this is...

Concentric Isotonic Contraction

When tension exerted by myosin cross-bridges resists movement of a load and slows the lengthening process, this is...

Eccentric Isotonic Contraction

Pulling a dumbbell UP is

Concentric

Slowly bringing a dumbbell down is

Eccentric

Angle getting bigger at joint is

Eccentric