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)