Transcript Muscle Notes

Smooth - no striations, involuntary
visceral organs
Skeletal - striated, voluntary,
tires easily, powerful
Cardiac - striated, involuntary
intercalated disks
Endomysium - connective tissue that surrounds the
muscle fibers
Perimysium - fibrous membrane that forms a bundle of
fibers called fascicles
Epimysium - covers the entire muscle and blends into
the strong cord-like tendons
Fascia – connective tissue that surrounds the muscle just
outside the epimysium and tendon
Fig 10-3 p281
Muscle Functions
1. Movement and regulation of body fluids
(heart- blood, bladder- urine)
2. Maintains posture
3. Stabilizes joints
4. Generates heat
Microscopic Anatomy of Skeletal Muscle
Cell membrane
cytoplasm
Long ribbon like
Organelles made up of
myofilaments
p313 Box 11-1
Microscopic Anatomy of Skeletal Muscle
Give
striped
appearance
I band - (light)
A band - (dark)
Z line - midpoint in the
I band
H zone - portion of A band
where thick and thin
filaments don’t overlap
myosin
actin
Sarcomere - tiny contractile units in myofibrils of skeletal muscle
between the Z lines.
I. Myofilaments
-Thick filaments p315 Fig 11-4
Myosin filaments - made mostly of the protein myosin
and also contain ATPase enzymes
*Make up the length of the Dark A band
Myosin heads - small projections or cross bridges that
link the thick and thin filaments together
during contraction
-Thin Filaments p315 Fig 11-4
Actin filaments - contain actin (contractile protein) and
regulatory proteins (tropomyosin and
troponin)that prevent myosin head
from binding to actin.
Skeletal Muscle Activity
p316 Fig 11-5
Motor unit - a motor neuron and the skeletal muscle cells it
stimulates
Neuromuscular junction
-nerve muscle connection
Synaptic cleft
- gap between nerve
endings and muscle cells
Skeletal Muscle Activity
What Happens During Muscle Contraction?????
1. Nerve impulse reaches axon terminal
and a neurotransmitter acetylcholine
ACh is released across synapse
2. ACh attaches to receptors on
membrane of muscle (sarcolemma)
3. Causes sarcolemma to become
permeable to Na+ ions
4. This creates an action potential or
electrical current that travels the cell
to cause it to contract
Skeletal Muscle Activity
p317 Fig 11-7
What Happens During Muscle Contraction?????
5. SR releases Ca+ into the
sarcoplasm where it binds to troponin
causing the tropomyosin molecules
to shift exposing the active sites
on actin.
6. Myosin heads bind to actin
causing the actin and myosin
filaments to slide (ATP)
7. Muscle fibers shorten as it
contracts
Pearson Muscle Contraction
SR - membraneous channels that
surround each myofibril, and store
Ca+ and release on demand.
Skeletal Muscle Activity
What Happens During Muscle Relaxation?????
1. Cholinesterase breaks down ACh
2. Ca+ ions diffuse back into SR and tropomyosin returns to
its original position.
3. Actin and Myosin filaments are broken and slide apart
4. Muscle relaxes
Energy Sources for Muscle Contraction
ATP must be regenerated continuously b/c muscles store
only 4-6 seconds worth of ATP
1) Creatine Phosphate (CP) - CP & ADP result in a transfer
of a phosphate group to make ATP
2) Aerobic respiration - 1 glucose
36 ATP
*slow and requires continuous O2 and nutrients
3) Anaerobic - glycolysis
*lactic acid buildup
2 ATP w/out O2
Oxygen Debt – is the amt of extra oxygen required by muscle
tissue to convert accumulated lactic acid to
glucose in the liver and to restore supplies of
ATP and creatine phosphate following vigorous
exercise.
Muscle Fatigue - is due to the accumulation of lactic
acid and can cause the muscle to lose its ability
to contract (exhaustion produced by strenuous
activity)
The Muscle Response - Contraction
Threshold stimulus - is the minimal stimulus needed to
elicit a muscular contraction
All or None Response - when a muscle fiber contracts it
always contracts to the fullest
extent
Muscle Twitch
Myogram is a recording of a muscle contraction
•Latent period - time between when the stimulus is applied
and when it responds
•Period of contraction
•Period of relaxation
Sustained Contraction - when a muscle is unable to
complete relaxation period before
next stimulus
•Response to rapid series of stimuli
•Tetanic contraction is forceful and sustained, and has partial
or lacks partial relaxation (smooth)
•Tonic contraction is responsible for muscle tone (response
to nerve impulses from spinal cord sending continual, partial
stimuli). Responsible for posture.
*If sustained contraction is lost body will collapse
(loss of consciousness)
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