The Muscular System
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 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
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
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
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
Sarcomere:
the functional
contractile unit of
muscle
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
5 steps to muscle contraction
1. Ca+ is released in large amounts
2. Ca+ moves troponin and tropmyosin out
of way of myosin (so it can grab actin)
3. Myosin grabs actin and pulls it in 1 step
4. ATP causes myosin to release actin
5. Steps 3 & 4 are repeated until;
A. muscle can no longer contract any
further.
B. nerve impulse ends causing muscle
relaxation.
3 Steps from nerves to muscles
1. Nerve impulse comes from brain
to activate muscle
2. At the end of the nerve
Acetylcholine is released into gap
between muscle and nerve
(neuromuscular junction).
3. Acetylcholine causes the release
of Ca+
Summary of
Muscle
Contraction
6 Steps of Muscle Relaxation
1. Nerve impulse stops
2. Acetylcholine is no longer released at
neuromuscular junction
3. Calcium ions are removed
4. Without Ca+ Troponin and tropomyosin
go back to blocking myosin from
grabbing actin.
5. ATP causes linkage between myosin
and actin to break
6. Muscle fibers relax
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.
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
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.