chapter 9 the muscular system
DESCRIPTION
Chapter 9 The Muscular System. Skeletal Muscle Structure. Tendon – connect muscle to bone Fascia – outermost covering; covers entire muscle & continuous w/tendon; separates muscle from adjacent muscles Aponeuroses - connect muscle to muscle. Skeletal Muscle Structure. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 9The Muscular System
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Skeletal Muscle Structure
Tendon – connect muscle to bone
Fascia – outermost covering; covers entire muscle & continuous w/tendon; separates muscle from adjacent muscles
Aponeuroses- connect muscle tomuscle
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Skeletal Muscle Structure
Coverings: Epimysium – covers entire muscle
(under fascia) Perimysium – covers
muscle bundle (fascicle) Endomysium –
covers each fiber (cell) Sarcolemma – cell
membrane
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Skeletal Muscle Structure – Cont.
Sarcoplasmic reticulum (SR) channels for transport Myofibrils – threads that compose muscle fibers;
contain protein filaments:1. actin – thin2. myosin – thick
Skeletal Muscle Structure
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Skeletal Muscle Structure
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Muscle Fiber (muscle cell)
Cisternae of SR – enlarged portions
Transverse tubules (T-tubules) – important in muscle contraction
Sarcoplasm – cytoplasm
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Breakdown of Skeletal Muscle
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Parts of a Sarcomere (functional unit of a muscle)
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Parts of a Sarcomere
•Z lines – end points• M line – middle• I band – on either side of Z line; actin filaments only• H zone – on either side of M line; myosin filaments only• A band – overlapping actin & myosin filaments
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Parts of a Sarcomere
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Neuromuscular Junction – junction b/t motor neuron & muscle
Motor neuron – carries impulse from brain or spinal cord to muscle
Motor end plate – end of muscle fiber; many nuclei & mitochon-dria located here
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Neuromuscular Junction
Neurotransmitters (ntm) chemicals that help carry impulses
Motor unit – 1 motorneuron & fibers thatit stimulates
Synaptic vesicles – store neurotransmitter; most common – acetylcholine (ACh)
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Electron Micrograph Neuromuscular Junction
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Neuromuscular Junction Animation
Neuromuscular Junction Animation
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4 Proteins in Muscle Cells:
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Troponin & Tropomyosin
4 proteins are found in muscle cells: actin, myosin, troponin & tropomyosin
troponin – appear as globules; providea binding site for Ca+²
tropomyosin – appear as ribbons; cover the myosincross-bridgebinding sites in a relaxed muscle
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Sliding Filament Theory (How Muscles Contract)
• Muscle fiber stimulated by release of ACh from synaptic vesicles of neuron
• ACh causes impulse to travel to muscle cell membrane
• Transverse tubules (T-tubules) carry impulse deep into muscle fibers
• Sarcoplasmic reticulum releases Ca ions (Ca²+)
• Ca²+ bind to troponin, tropomyosin moves, exposing binding sites on actin filaments
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Sliding Filament Theory (How Muscles Contract )
• Linkages form b/t actin & myosin
• Actin filaments move inward, shortening the sarcomere
• Muscle fiber relaxes when Ca²+ are transported back to S.R.
• The enzyme cholinesterase (or AChesterase) decomposes ACh
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Sliding Filament Theory
Relaxed muscle – binding sites on actin are covered by tropomyosin
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Sliding Filament Theory
Ca²+ binds to troponin Tropomyosin
slides out of the way Myosin binds to actin &
pulls inward Sarcomeres
shorten & muscle contracts
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Sliding Filament Theory
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Energy for Muscle Contraction
ATP (adenosine triphosphate) provides the energy for muscle contraction
When ATP is converted to ADP (adenosine diphosphate) by losing the last phosphate, energy is released.
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Energy for Muscle Contraction • Cells depend on cellular respiration of glucose to synthesize ATP
•An additional source is creatine phosphate
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Energy for Muscle Contraction
Creatine phosphate stores excess energy
Can be used to convert ADP back into ATP
Anaerobic respiration (in the absence of O2) provides few ATP’s, while aerobic resp. (in the presence of O2) provides many ATP’s
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Creatine Phosphate
High amts. of ATP - ATP is used to Low amts. of ATP – CP is used synthesize CP, which stores energy to resynthesize ATP.for later use.
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Importance of Myoglobin l.a. carried by blood to liver; liver can convert l.a. to glucose, but requires ATP (ATP being used for muscle contraction)
myoglobin – stores O2
in muscle cells; gives muscle its red color
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Aerobic vs. Anaerobic Respiration
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Aerobic vs. Anaerobic Respiration
Carried by blood to liver; liver can convert l.a. to glucose, but requires ATP (ATP being used for muscle contraction)
Imp. b/c blood supplyduring muscle contr. may decrease
As l.a. accumulates, O2 debt occurs
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•Strenuous exercise leads to O2 deficiency & lactic acid buildup
•ATP provides energy for muscle contraction
•Amt. of O2 needed to convert accumulated l.a. to glucose & restore ATP levels = O2 debt
•L.A. accumulation leads to muscle fatigue b/c pH of muscle cell is lowered & muscle cannot contract
Oxygen Debt
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•Muscle cramp – fatigued muscle has lack of ATP needed to move Ca+² back into S.R.; cross bridges not broken
•Rigor mortis – takes up to 72 hrs. to occur; sarcolemma becomes more permeable to Ca+² & ATP levels insufficient
Muscle Cramp
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Myogram
•Pattern or graph of a muscle contraction•A single contraction is called a muscle twitch•3 parts:•Latent (lag) phase – brief pd. of delay b/t when the stimulus is applied & actual contraction occurs•Contraction•Relaxation – return to original state
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Patterns of Contraction a) Muscle Twitch –
single contraction b) Staircase Effect
many stimuli closelyspaced w/completerelaxation in b/t; each contraction generate incr. force
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Patterns of Contraction c) Summation – when
the 2nd stimulus occursduring the relaxationpd. of 1st contr.; the2nd contr. generatesmore force
d) Tetany – when twitches fuse into 1 sustained contr.
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Muscle Facts If a muscle is stimulated twice in quick
succession, it may not respond the 2nd time – called refractory period
Threshold – the minimum stimulus needed to cause a contraction
All-or-none – increasing the strength of the stimulation does NOT incr. the degree of contraction (a muscle contracts completely or not at all)
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More Facts Incr. stimulation from motor neurons
causes a greater # of motor units to contract & vice versa
Called recruitment of motor units Incr. the rate of stimulation also incr.
the degree of contraction Muscle tone – a sustained contraction
caused by nerve impulses from s.c. to a small # of muscle fibers in the back, neck, etc.; maintains posture
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Origin & Insertion
Origin – end of musclethat attaches to stationary bone
Insertion – end of musclethat attaches to movingbone
During contr., insertion is pulled toward origin
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Muscle Functions in Groups
Prime mover – responsible for most of the movement (ex.- biceps)
Synergist – aids the prime mover
Antagonist – resists the prime mover & causes
movement in the opposite direction (ex. - triceps)
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Structural Differences of 3 Types of Muscle
Skeletal Muscle
Smooth Muscle
Cardiac Muscle
Cells elongated w/multiple nuclei/cell
Cells spindle-shaped w/1 nucleus/cell
Cells branching w/1 nucleus/cell
T-tubules present
No T-tubules T-tubules lg.; releases lg.
amts. of Ca++; can contract longer (Ca channel blockers)
Striated/voluntary
Non-striated/invol.
Striated/invol.
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Functional Differences of 3 Types of Muscle
Skeletal Muscle Smooth Muscle Cardiac MuscleNeeds nerve impulse
for contractionDisplays rhythmicity
& cells stimulates each other (as in
peristalsis)
Displays rhythmicity & self-excitation
Ca+² binds to troponin
Ca+² binds to calmodulin
Ca+² binds to troponin
Not affected by hormones
Hormones may affect contraction
Hormones may affect rate of contr.
Contracts & relaxes rapidly
Slower to contract but can maintain
contraction longer
Contracts & relaxes at a certain rate
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Functional Differences - Continued
Skeletal Muscle
Smooth Muscle
Cardiac Muscle
Not affected by stretching
Stretching of fibers may
stimulate contr.(ex.-stomach)
Remains in a refractory pd.
until contraction ends (tetany won’t occur)
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Fast Twitch vs. Slow Twitch Muscle
Fast Twitch Slow Twitch
Contracts quickly, tires easily (sprinter)
Contracts slowly, tires slowly (long
distance)
Fewer mitochondria More mitochondria
Less myoglobin More myoglobin
White muscle Red muscle
Composes smaller muscles (eyes,
hands, etc.)
Composes lg. muscles (legs, back,
etc.)
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Levers• Parts of a lever:
wt., force, pivot3 types of levers:
• 1st class – W-P-F(seesaw/scissors)
• 2nd class – P-W-F(wheelbarrow)
• 3rd class – W-F-P(forceps)
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Bones & Muscles as Levers
• Forearm bends – 3rd class lever (biceps attaches at a pt. on the radius below the elbow joint)
• Forearm straightens - 1st class lever ((triceps attaches at a pt. on the ulna above the elbow joint)
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Bones & Muscles as Levers
Standing on tip-toe – 2nd class lever(P-W-F)