PLTW HBS Muscles

sarcomere

basic contractile unit of a muscle fiber

myofilaments

composed of thick and thin filaments

mitochondria

dispersed through muscle fibers

sarcoplasmic reticulum

network of tubes that run paralell to the myofilaments

transverse tubules

run perpendicular to the filaments

sarcolemma

surrounds muscle fiber

what are the thick filaments

myosin

what are the thin filaments

actin

z line

boundary between sarcomeres

what are the two different types of myofilaments

myosin and actin

what is a sarcomere defined as

the region betweeen two z-lines

where does muscle contraction start

in the brain, where a signal is sent to the motor neuron

what do vesicles contain

the neurotransmitter acetylcholine

where does acetylcholine reach

the receptors

what is the gap between the neuron and muscle fiber called

synapse

where does the impulse travel down

the sarcolemma

the impulse travels into the transverse tubules where is causes…

calcium to be released from the sarcoplasmic reticulum

calcium binds to the actin and causes it to change shape so that it can interact with…

myosin

the change in shape allows myosin heads to form…

cross bridges bettwen the actin and myosin

energy from ATP is used to create a…

“power stroke” between the two filaments. the actin filament slides inward and shortens, or contracts, the whole muscle

the motor unit consists of

muscle fibers and a motor neuron

what neurotransmitter causes a muscle contraction

:acetylcholine

what substance causes the actin to change shape

calcium

how does myosin and actin interact with each other

actin changes shape due to calcium

what substance provides the energy for muscle contraction

ATP

where is calcium released from

:sarcoplasmic reticulum

REMEMBER THIS ORDER

1. Signal travels down the motor neuron

2. calcium released for sarcoplasm

3. actin changes shape

4. cross bridges form

5. ATP creates a power stroke, shortening actin filament

what is troponin

troponin is a protein on thin muscle filaments. it promotes muscle contraction

what is tropomyosin

tropomyosin is a protein on thin muscle filaments. it blocks muscle contraction

what happens inside your muscle when you get a muscle cramp

msucles tighten without voluntary input from the brain, which signals pain receptors. in the cells, muscle fibers contract in response to impulses generated by lower motor neurons

bone

where tendon attaches

tendon

where muscle attaches to bone

myofibril/muscle cell

contains actin and myosin

endomysium

contains group of muscle cells

fasicle

surrounds groups of endomysium

perimysium

contains groups of fasicles

epimysium

surrounds whole muscle

what are the seven characteristics of muscle naming

shape, size, fiber direction, location, number of origins, action of muscles, origin + insertion

size example

gluteus maximus and gluteus minimus

location example

frontalis and temporalis

shape example

trapezius and rhomboid

direction example

orbicularius oculi and transverse abdominus

action example

flexor and extensor

origin + insertion example

sterno and brachii

number of insertions example

biceps and triceps

what are the muscle rules

1. muscles must have at least two attachments and must cross at least one joint

2. muscles always “pull” and get shorter

3. the attachment that moves is known as the “insertion” and the attachment that remains stationary is known as the “origin”

4. muscles that decrease the angle between ventral surfaces of the body are known as flexors. muscles that increase the angle between ventral surfaces of the body are known as extensors

5. muscles work in opposing pairs

6. muscle striations (stripes) point to the attachments andshow direction of pull

striations

muscle tissue where the contractile fibrils form stripes under the microscope

voluntary

muscle that you voluntarily move (ex. arm)

involuntary

muscle that moves involuntarily (ex. heart)

tendon

cord of strong, flexible tissue that connects muscle to bones

is skeletal muscle…

striated Y

voluntary Y

where is it?: throughout body

what is the function?: allows for voluntary movement

is smooth muscle…

striated N

voluntary N

where is it?: liver, stomach, pancreasm intestines

what is the function?: digestion, etc

is cardiac muscle…

striated Y

voluntary N

where is it?: heart

what is the function?: moves blood throughout body

where does ATP work best

in a salt solution, which allows it to use the salt ions

what is ATP

ATP is energy

pectoralis major

insertion: top of scapula

origin: sternum

action: adducts, medially rotates, and transversally adducts arm at glenohumeral joint

pectoralis minor

insertion: top of humerus

origin: between the 3, 4, and 5 ribs

action: stabilization, depression, abduction, or protraction, interanl rotation and downward rotation of the scapula (ex. pitching, swimming)

what does a grade two tear mean

moderate tear to affected muscle. this tear results in pain, loss of strength and movement, and a long recovery time

movements that cause this: lifting, athletics, holding things

what treatment options are available for a grade two tear

most commonly physical therapy, or surgery

brachiallis

two origins, one insertion, bottom of humerus

triceps

one origin, one insertion, back bottom of humerus

how is it that the entire muscle shortens during a contraction but the actin and myosin in the sarcomere never shorten themselves?

actin and myosin filaments themselves do not shorten, the sliding motion between them during contraction leads to the shortening of the sarcomeres and, consequently, the entire muscle.

Sliding Filament Theory

Actin and myosin do not shorten themselves. Instead, they slide past each other. When a muscle contracts, myosin heads bind to actin filaments, forming cross-bridges. The myosin heads then pull the actin filaments toward the center of the sarcomere.

order of sliding filament theory

1. A nerve impulse travels down the axon to the neuromuscular junction on a muscle cell. (The neuromuscular junction is the point where the axons of the nerve meet with the muscle cell.)

2. The neurotransmitter (acetylcholine) is released from the axon ending.

3. The acetylcholine travels across the synapse and binds to receptors on the sarcolemma (muscle cell membrane), which causes the depolarization of the sarcolemma by opening ion channels and allowing Na+ ions into the muscle cell.

4. Na+ ions diffuse into the muscle fiber and depolarization continues. This creates a wave of action potential (electrical current) across the sarcolemma.

5. The action potential travels across the sarcolemma and down the T-tubules, which triggers the sarcoplasmic reticulum to release Ca+ ions.

6. Ca+ ions bind with troponin, which moves the tropomyosin and opens up the myosin binding sites on the actin.

7. Myosin is now ready to bind with the actin and form cross bridges, which begins the contraction process. In order to contract, ATP binds to the myosin.

8. The myosin heads then change their shape and pull the actin filaments inward. The ADP and P are released, and the myosin heads return to a low energy position.

9. ATP is then hydrolyzed (broken down) to ADP and P, which gives the myosin the energy to move its head to the high energy position.

10. Actin and myosin bind together to form a cross bridge.