Second muscles (beginning of quiz 10/15)

Sarcomere

extends from one Z disc to another Z disc

Thin filaments attach to

Z discs

Thick filaments location

center of sarcomere and ends overlap with thin filament

M-line location and purpose

in the middle of the sarcomere and holds the thick filament in place

Titin attaches

the thick filament to the Z discs

Sections of sarcomere

H-zone, I-band, A-band

H-zone

center of sarcomere when there is no overlap between thick and thin filament (includes M-line and thick filament

I-band

ends of sarcomere where there is only thin filament

A-band

contains entire thick filament and some overlap with thin filament

During contraction, the sarcomere

shortens

H-zone during contraction

shortens

I-band during contraction

shortens

A-band during contraction

remains the same

Motor unit

a single motor neuron and all of the muscle fibers it innervates

Neuromuscular junction

connection between axon of motor neuron and the sarcolemma of the muscle fiber

Muscle contraction steps

1. motor neuron releases acelycholine (ACh) into neuromuscular junction

2. acetylcholine (ACh) binds to receptor on sarcalemma of muscle fiber

3. this causes Na+ channels to open on the sarcolemma

4. Na enters cell, sarcolemma depdarizes

5. an action potential travels along the sarcolemma

6. an even acetylcholine is broken down by acetylcholinesterase (happens while gen action potential)

7. the action potential travels down transverse tubules

8. this causes the sarcoplasmic reticulum to release Ca into the sarcoplasm

9. Ca+ diffuses into myofibrils

10. Ca+ binds to troponin on thin filament

11. Troponin pulls the tropomyosin off of the myosin head biding sites on actin

12. prior to this, ATP has bound which causes the myosin head to tilt towards the actin

13. myosin head binds to actin

14. myosin head pivots toward center of the sarcomere which pulls actin towards the center of the sarcomere

15. a new ATP binds to myosin head causing it to release actin

16. this allows the myosin head to bind to a new site on actin and continue to shorten the sarcomere

17. This continues to happen along as there is acetylcholine at the neuromuscular junction

Acetylcholine in muscle contraction

released by motor neuron, into neuromuscular junction, binds to receptor of muscle fiber, opens Na+ channels

acetylcholinesterase role in muscle ocntraction

breaks down extra acytlecholine

Ca+ role in muscle contraction

action potential causes release from sarcoplasmic reticulum into the sarcoplasm, diffuses into myofibrils, binds to troponin on thin filament

Troponin role in muscle contraction

pulls the tropomyosin off of the myosin head biding sites on actin

ATP role in muscle contraction

causes the myosin head to tilt towards the actin, binds to myosin head causing it to release actin

Myosin head role in muscle contraction

binds to actin, pivots toward center of the sarcomere which pulls actin towards the center of the sarcomere