Download Muscles and Muscle Tissue

Chapter 7-1
THE MUSCULAR SYSTEM
A. OVERVIEW
1.
2.
3.
Makes up about half the body’s mass
Prefix myo-, mys-, or sarco = muscle
3 types
a.
Skeletal
1)
Longest muscle cells
2)
Have striations
3)
voluntary
4) Cover skeleton
5) Contract rapidly
6) Tires quickly and needs rest
7) Can have a lot of power
b. Cardiac
1) Only in the heart
2) Striated
3) Involuntary
c. Smooth
1) Hollow organs
a) Stomach
b) Respiratory passages
c) Urinary bladder
2) Push fluids through body
3) Involuntary
4. Characteristics
a. Excitability – receive and respond to stimuli
b. Contractility – ability to shorten forcibly
c. Extensibility – ability to be stretched
d. Elasticity – recoil after being stretched
5. Functions
a. Producing movement
b. Maintain posture
c. Stabilizing joints
d. Generate heat
e. Protecting organs
B. SKELETAL MUSCLE
1.
Gross Anatomy
a.
Nerve and blood supply
1)
Each muscle – 1 nerve,
artery, and 1 or more veins
2)
Exit and enter by center of muscle and branch
throughout the rest
3) Nerve ending controls activity
4) Contracting uses tons of energy – need
continuous delivery of O2 and nutrients
5) Lots of waste after contraction – taken out by
capillaries
b. Connective tissue sheaths
1) Keep bulging muscles from bursting
2) Inside to outside
a) Endomysium – surrounds each muscle fiber
b) Perimysium – surrounds fascicles (bundles of fibers)
c) Epimysium – Surrounds entire muscle
3) Continuous w/tendons which attach to bone
4) Helps move bones
PARTS OF MUSCLE
2. Microscopic anatomy
a. Sarcolemma – plasma membrane of a muscle
b. Sarcoplasm – cytoplasm of muscle cell
1) Has more myoglobin – pigment that transports oxygen
2) More glycosomes – store glycogen
c. Zones of muscle
1) Each myofibril has zones
a) A band is at the center – length of thick filament
b) I band is distance b/w A bands
c) Z disc – middle of I band
d) M line – middle of thick filament
2) Thick filaments
a) Aka – myosin
b) Smooth in the middle
c) Heads on the outsides
d) Heads attach to thin filaments
i. attachments called crossbridges
ii. Thin filaments – actin
d. Sliding filament model
1) Myosin’s cross bridges are force generating sites
2) Shortening occurs when tension on cross bridge is greater
than the opposing force
3) Contraction ends when:
a) Cross bridges become inactive
b) Tension generated declines – relaxing muscle
4) Theory states
a) Nervous system sends signal
b) Ca is transferred to cells via t tubules
- cut transversely over myofilament
c) Myosin heads latch onto actin
d) Impossible w/o Ca ions
e) Sliding begins – power stroke
f) Cross bridges are formed and broken several times during
contraction
i. Acts like a ratchet
ii. Sends actin toward center of sarcomere
- Sarcomere - 1 Z disc to next Z disc
iii. Myosin heads take turns with contractions
g) Muscle cells shorten
h) I bands shorten – Z disc is pulled towards myosin
i) Ca leaves and muscle relaxes
j) All-or-none response
i. Need enough to over come threshold
ii. More stimulus doesn’t make muscle respond more
iii. Length of contraction changes, not strength
 How
could this fit into lifting cars?
Maybe all the cross bridges move at
once….maybe more cross bridges are used
at one time

http://www.cnn.com/2012/08/01/us/virginia-daughter-saves-dad/
 Muscle
Contractions

http://www.youtube.com/watch?v=NRzJjx3ANuE&feature=related

http://www.youtube.com/watch?v=WVuW560nRII
3. NEUROMUSCULAR JUNCTION (PG 172)
a.
Each muscle fiber is connected to a motor neuron
b.
Connected to brain or spinal cord
c.
Muscles contract when stimulated by neuron
d.
Neuromuscular junction – site where never meets
muscle
1) Forms a motor end plate
2) Has lots of mitochondria
3) Membrane has lots of folds
e. Neuron is branched – going to many fibers
f. Branches go to synaptic clefts (depression in fibers)
g. Nerve fibers
1) Have a lot of mitochondria
2) Have lots of synaptic vesicles
a) Store chemicals
b) Chemicals called neurotransmitters
c) Specifically acetylcholine
h. Impulse releases neurotransmitters
i. Neurotransmitters flood muscle via transverse tubules (t
tubules)
j. Cause contraction over entire muscle
4. WARM UPS FOR ATHLETES
a.
Muscle after long rest - Contractions half as strong as
those that happen later (in response to stimuli of same
strength)
b.
Treppe – staircase pattern
c. More Ca = more cross bridges
d. As muscles generate heat
1) Enzymes are more efficient
2) Muscle is more pliable
e. Causes slightly stronger contractions w/each successive
stimulus (during starting phase of activity)
5. Muscle Tone
a. Relaxed muscles are almost always slightly contracted
b. Keeps muscles firm, healthy, and ready to respond
c. Helps with posture
6. Lactic acid
a. Energy source during anaerobic conditions
1) Long, intense muscle use
2) Sprints
b. Most diffuses in 30min
c. Accumulation gives muscle fatigue and soreness
7. Effect of exercise on muscles
a. Actively using muscle
1) Increase in size and strength
2) More efficient
3) Fatigue resistant
b. Inactivity ALWAYS
1) Leads to muscle weakness
2) Muscle atrophy
C. MUSCLE WASTING
1.
Muscle strength decreases 50% by 80yrs old
a.
This causes them to fall more
b.
Ties in w/osteoporosis
c.
ELEDERLY NEED TO EXERCISE – increases muscle
2. Muscular dystrophy
a. Muscles weaken with more use
b. 1860 was discovered
c. Multiple types
d. Duchenne Muscular Dystrophy (DMD)
1) Most common
2) Most severe
3) 15 – 51 for life span
e. Signs/symptoms
1) Poor balance
2) Drooping eyelids
3) Inability to walk
4) Waddling gait
5) Breathing difficulties
6) Muscle spasms
7) Others
f. No cure
g. Inherited
D. FUN FACTS
1.
Rigor Mortis
a.
Partial contraction of muscles
b.
Myosin and actin have cross bridges
c.
Doesn’t relax until muscle starts to decompose
d.
72 hrs +
2. 17 muscles to smile and 42 to frown
3. Eye muscles are the busiest – move about 100,000 times a
day
4. Muscles can only pull – can’t push
5. Biggest muscle of the body – gluteus maximus
6. Goose bumps are because of muscles
7. 40% of body weight is muscles