Chapter 9 The Muscular System
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Chapter 9The Muscular System
Skeletal Muscle Structure
Tendon –
Fascia – outermost covering; covers entire muscle & continuous w/tendon; separates muscle from adjacent muscles
Skeletal Muscle Structure
Coverings: Epimysium – covers entire muscle
(under fascia) Perimysium –
Endomysium – covers each fiber (cell)
Sarcolemma-
Skeletal Muscle Structure – Cont.
Sarcoplasmic reticulum (SR) channels for transport Myofibrils – threads that compose muscle fibers;
contain protein filaments:1. actin –2. myosin –
Skeletal Muscle Structure
Skeletal Muscle Structure
Muscle Fiber (muscle cell)
Cisternae of SR – enlarged portions
Transverse tubules (T-tubules) –
Sarcoplasm – cytoplasm
Breakdown of Skeletal Muscle
Parts of a Sarcomere (functional unit of a muscle)
Parts of a Sarcomere
•Z lines – end points• M line –• I band – on either side of Z line; actin filaments only• H zone –
•A band – overlapping actin & myosin filaments
Parts of a Sarcomere
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
Neuromuscular Junction
Neurotransmitters (ntm) chemicals that help carry impulses
Motor unit
Synaptic vesicles – store neurotransmitter; most common – acetylcholine (ACh)
Electron Micrograph Neuromuscular Junction
4 Proteins in Muscle Cells:
Troponin & Tropomyosin
4 proteins are found in muscle cells: actin, myosin, troponin & tropomyosin
troponin –
tropomyosin – appear as ribbons; cover the myosincross-bridgebinding sites in a relaxed muscle
Sliding Filament Theory (How Muscles Contract)
• Muscle fiber stimulated by release of ACh from synaptic vesicles of neuron
•
• Transverse tubules (T-tubules) carry impulse deep into muscle fibers
•
• Ca²+ bind to troponin, tropomyosin moves, exposing binding sites on actin filaments
Sliding Filament Theory (How Muscles Contract )
• Linkages form b/t actin & myosin
•
• Muscle fiber relaxes when Ca²+ are transported back to S.R.
• The enzyme cholinesterase (or AChesterase) decomposes ACh
Sliding Filament Theory
Relaxed muscle –
Sliding Filament Theory
Ca²+ binds to troponin Tropomyosin
slides out of the way
Sarcomeres shorten & muscle contracts
Sliding Filament Theory
Energy for Muscle Contraction
ATP (adenosine triphosphate)
When ATP is converted to ADP (adenosine diphosphate) by losing the last phosphate, energy is released.
Energy for Muscle Contraction • Cells depend on cellular respiration of glucose to synthesize ATP
•An additional source is creatine phosphate
Energy for Muscle Contraction
Creatine phosphate stores excess energy
Anaerobic respiration (in the absence of O2) provides few ATP’s, while aerobic resp. (in the presence of O2) provides many ATP’s
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.
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 –
Aerobic vs. Anaerobic Respiration
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
•Strenuous exercise leads to O2 deficiency & lactic acid buildup
•
•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
•Muscle cramp –
•Rigor mortis – takes up to 72 hrs. to occur; sarcolemma becomes more permeable to Ca+² & ATP levels insufficient
Muscle Cramp
Myogram
•Pattern or graph of a muscle contraction•A single contraction is called a muscle twitch•3 parts:•Latent (lag) phase –
•Contraction•Relaxation –
Patterns of Contraction a) Muscle Twitch –
single contraction b) Staircase Effect
Patterns of Contraction c) Summation – when
the 2nd stimulus occursduring the relaxationpd. of 1st contr.; the2nd contr. generatesmore force
d) Tetany-
Muscle Facts If a muscle is stimulated twice in quick
succession, it may not respond the 2nd time – called refractory period
Threshold –
All-or-none – increasing the strength of the stimulation does NOT incr. the degree of contraction (a muscle contracts completely or not at all)
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 –
Origin & Insertion
Origin –
Insertion – end of musclethat attaches to movingbone
During contr., insertion is pulled toward origin
Muscle Functions in Groups
Prime mover – responsible for most of the movement (ex.- biceps)
Synergist –
Antagonist – resists the prime mover & causes movement in the opposite direction (ex. - triceps)
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
No T-tubules T-tubules lg.; releases lg.
amts. of Ca++; can contract longer (Ca channel blockers)
Striated/voluntary
Striated/invol.
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)
Ca+² binds to calmodulin
Ca+² binds to troponin
Not affected by hormones
Slower to contract but can maintain
contraction longer
Contracts & relaxes at a certain rate
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)
Fast Twitch vs. Slow Twitch Muscle
Fast Twitch Slow Twitch
Contracts slowly, tires slowly (long
distance)
Fewer mitochondria
Less myoglobin More myoglobin
Red muscle
Composes smaller muscles (eyes,
hands, etc.)
Levers• Parts of a lever:
wt., force, pivot3 types of levers:
• 1st class –
• 2nd class – P-W-F(wheelbarrow)
• 3rd class –
•
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)
Bones & Muscles as Levers
Standing on tip-toe – 2nd class lever(P-W-F)
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