1. The Muscular System

2. Characteristics of Muscle Tissue
Contractility- the ability to shorten and thicken
Excitability – ability of muscle tissue to receive and respond to stimuli
Extensibility – ability of the muscle to stretch
Elasticity – the ability of the muscle tissue to return to its original shape after contraction

3. 3 Types of Muscle Tissue:
Smooth – located in walls of hollow internal structures, non-striated, involuntary
Skeletal – attached mostly to bone, striated, voluntary
Cardiac – found in the heart, striated, involuntary

4. Anatomy of Skeletal Muscle
Key Terms:
Muscle fiber – muscle cell
Epimysium – conn. tissue surrounding entire muscle
Perimysium – conn. tissue surrounding fascicles
Fascicle – bundle of muscle fibers (cells)
Endomysium – conn. tissue surrounding individual fibers

5. Skeletal Muscle Cells Muscle cell = muscle fiber
Contains many nuclei and mitochondria
Each muscle fiber contains many myofibrils – threadlike protein filaments – 2 types:
Myosin – thick filaments
Actin – thin filaments
Organization of these produces striations charac. of skeletal muscle tissue

6. Sarcomere Key Terms: actin (thin filaments) myosin (thick filaments)
A band – dark band made up of thick filaments
M line – dark line in center of A band
I band – light band made up of thin filaments
Z line – mark boundary between sarcomeres

7. Sarcomere: the functional contractile unit of muscle

9. Sliding Filament Theory
Myosin – protein strands with globular parts called cross-bridges
Actin – protein strands with binding sites where myosin cross-bridges can attach; binding site protected by troponin and tropomyosin
Ca+ moves troponin and tropomyosin out of the way so cross bridges can bind.
Cross-bridges (myosin) bind to actin and produce a powerstroke (myosin cross-bridges pull actin toward H zone)
ATP releases the myosin. IT DOES NOT PRODUCE THE POWERSTROKE
Cross-bridges release and attach to new binding site on actin, and whole process begins again; will continue as long as calcium and ATP are available

10. 5 steps to muscle contraction
Ca+ is released in large amounts
Ca+ moves troponin and tropmyosin out of way of myosin (so it can grab actin)
Myosin grabs actin and pulls it in 1 step
ATP causes myosin to release actin
Steps 3 & 4 are repeated until;
A. muscle can no longer contract any further.
B. nerve impulse ends causing muscle relaxation.

11. 3 Steps from nerves to muscles
Nerve impulse comes from brain to activate muscle
At the end of the nerve Acetylcholine is released into gap between muscle and nerve (neuromuscular junction).
Acetylcholine causes the release of Ca+

12. Summary of Muscle Contraction

13. 6 Steps of Muscle Relaxation
Nerve impulse stops
Acetylcholine is no longer released at neuromuscular junction
Calcium ions are removed
Without Ca+ Troponin and tropomyosin go back to blocking myosin from grabbing actin.
ATP causes linkage between myosin and actin to break
Muscle fibers relax

14. Rigor Mortis
When a person dies they release Ca+ causing their muscle to contract.
This also causes the use of ATP
However, the body is no longer producing ATP so the myosin cross bridges can not release.
This causes the muscles to stay contracted and the body to feel stiff.

15. Energy Sources for Contraction
ATP supplies the energy for muscle fiber contraction, which lasts only a few seconds. ATP must be regenerated continuously if the contraction is to continue.
There are 3 pathways in which ATP is regenerated:
1. Creatine phosphate, found in muscle fibers, stores energy that can be used to synthesize ATP from ADP and phosphate (uses no oxygen); runs out fast

16. Cont:
2. Aerobic Respiration: glucose is broken down to supply ATP (oxygen is required).
Yields 36 ATP
3. Anaerobic Respiration – glucose is broken down not in the presence of Oxygen
This yields 2 ATP.