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The muscular system How skeletal muscle works A few words about cardiac and smooth muscle Organization of skeletal muscl

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The muscular system How skeletal muscle works A few words about cardiac and smooth muscle Organization of skeletal muscle The major muscle groups. The skeletal muscle cell: the muscle fiber May be as long as the muscle itself Several nuclei and many mitochondria

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Presentation Transcript
slide1

The muscular system

How skeletal muscle works

A few words about cardiac and smooth muscle

Organization of skeletal muscle

The major muscle groups

slide3

The skeletal muscle cell: the muscle fiber

May be as long as the muscle itself

Several nuclei and many mitochondria

Extensive sarcoplasmic reticulum

Striations due to actin and myosin filaments

(myofibrils)

slide5

Sarcomere- functional unit

(note “sarco” prefix)

During muscle contraction these shorten

Characteristic patterns seen: I, A, H bands,

etc.

slide8

How does a muscle fiber contract?

“sliding filament” model

Myosin filaments contain cross-bridges

pulling actin shortens sarcomere

Requirement for ATP and calcium

Action triggered by acetylcholine

Stopped by breakdown of the enzyme

(see p. 178)

slide10

Sources for ATP?

Respiration (aerobic and anaerobic)

anaerobic when oxygen runs out

pyruvate is converted to lactic acid

fatigue

lactic acid is carried in blood to liver,

and converted back to glucose

Creatine phosphate

Myoglobin

Heat produced in process; helps sustain

body temperature

slide11

Responses of single muscle fiber

threshold stimulus

if this is achieved, muscle will contract

fully (all-or-none)

Slow fibers- weak contraction, resist fatigue

contain more blood flow,mitochondria

aerobic exercise enhances development

Fast fibers- strong contraction, fatigue easily

anaerobic exercise will increase number

of filaments in a cell (not more cells)

slide12

A muscle fiber can be stimulated many times

(summation) so that it cannot relax between

twitches

Tetany- sustained contraction

More than one motor unit can be stimulated, too

for sustained muscle work

Muscle tone- some contraction is sustained

slide13

Smooth muscle contains actin and myosin

filaments; arranged differently from

skeletal muscle

Regulated differently- calmodulin

Multiunit- separate fibers

iris, blood vessel walls

Visceral (internal organs)

stimulus is transmitted from one cell

to another

Rhythmicity- pattern of contractions

self-activated

slide14

Smooth muscle contraction controlled by

acetylcholine and norepinephrine

Neurotransmitters stimulate different organs,

have different effects

Smooth muscle fibers can sustain longer

contraction and use less ATP; also

can stretch

What sorts of movements are seen in these

organs?

slide15

Cardiac muscle

striated, involuntary muscle

Cells are short and branched

Calcium channels regulate flux of calcium

twitches last longer than in skeletal

muscles

Intercalated discs connect one cell to another;

help with rapid transmission of signals

slide16

Entire structure (heart muscle) contracts

as a unit

Is also self-stimulatory and rhythmic

Activity begins in a specific region of the

heart and spreads over the entire

structure

We’ll talk about the pattern and regulation

later!

Complarison of the 3 types of muscle p. 185