Chpt. 49 Muscles & Motor Locomotion Why Do We Need All That ATP?

Function of Muscles: To convert chemical energy of ATP into mechanical work, To get around… To get your food To digest your food To pump your heart so that oxygen can get to that mitochondria

1) Cardiac rapid contraction 2) Skeletal rapid contraction 3) Smooth slow sustained contraction Types of Muscle Tissue:

voluntary, striated involuntary, striated auto-rhythmic involuntary, non-striated evolved first multi-nucleated digestive system arteries, veins heart moves bone

As a side … Insect flight muscles contract more rapidly than ANY OTHER 1,000 contractions/second Highest metabolic rate Contain more mitochondria than any other tissue HOW get oxygen???

HOW DO WE MOVE THESE 206 BONES?

SKELETAL MUSCLE

skeletal muscles move bones by pulling …not pushing, therefore they come in antagonistic pairs:

So in other words, in order to flex, you must contract your flexor muscles… and in order to, relax, you must contract the antagonistic muscle flexorextensor flexor vs. extensor

Extensor (quadracep) Notice the TENDON connects the muscle to the bone. One bone is pulled towards another bone upon contraction.

Vertebrate Skeletal Muscle Structure: tendon skeletal muscle muscle fiber (cell) myofilaments myofibrils plasma membrane nuclei composed of smaller & smaller & smaller units

Vertebrate Skeletal Muscle each muscle fiber = one long, cylindrical, multinucleated cell

Vertebrate Skeletal Muscle Muscle fiber cells composed of: bundles of myofibrils (threadlike structures) Bundle of fibers

Myofibrils are basically parallel “contractile units”

Myofibrils consist of even smaller structures: thick filaments thin filaments

myofibrils have a regular arrangement regular arrangement

sarcomere = basic unit of a myofibril - hundreds are connected end to end & make up the myofibril

sarcomeres are made of these proteins: thick filaments thin filaments

Thin filaments: actin Complex (bunch) of proteins: –braid of actin molecules & tropomyosin fibers tropomyosin fibers secured with troponin complex these are proteins

Thick filaments: myosin Single protein –myosin molecule long protein with globular head bundle of myosin proteins: globular heads aligned

Thick & thin filaments MyosinMyosin tails aligned together & heads pointed away from center of sarcomere

sarcomere = basic unit of a myofibril - hundreds are connected end to end & make up the myofibril

SARCOMER E

making up the sarcomere… Z-lines = the borders of the sarcomere (actin)

at rest, the thick myosin & thin actin filaments in the sarcomere do not overlap completely:

area inwhich only thick myosin filaments = H zone

Area inwhich only thin actin filaments = I band

Area in which both: thin actin filaments & thick myosin filaments = A band

More muscle anatomy: SARCOLEMMA = plasma membrane

More muscle anatomy: T tubule = inward extension of the plasma membrane

More muscle anatomy: mitochondrion = ohh, there are plenty!

More muscle anatomy: sarcoplasmic reticulum = another name for endoplasmic reticulum

How does the Muscle Contract?

Sliding Filament Model

Motor Unit (Usually hundreds of muscle fibers)

NEUROMUSCULAR JUNCTION

NEUROTRANSMITTOR ~ ACETYLCHOLINE released as action potential moves to synaptic terminal of muscle fiber

The acetylcholine causes the action potential to continue in the muscle fiber

The action potential spreads into T-Tubules (invaginations in the membrane of the muscle fibers)

The a.p. opens Ca +2 channels in the sarcoplasmic reticulum (e.r.)

The special type of smooth endoplasmic reticulum found in smooth and striated muscle fibers whose function is to store and release calcium ions.

Ca +2 flows & binds to a protein in the actin filament

Sliding Filament Model At rest myosin binding sites are blocked (with trypomyosin) Thin actin filament has myosin binding sites…

Sliding Filament Model Thin actin filament has myosin binding sites… myosin binding sites are opened when Ca +2 binds to the troponin. (Ca +2 is released as a result of acetylcholein rushing through the T-tubules)

Sliding Filament Model At rest, myosin head is bound to an ATP -- ATP

Sliding Filament Model when Ca +2 floods into the cell, Myosin head hydrolyzes (breaks) ATP to ADP and P --.

Sliding Filament Model Myosin binds to Actin --        this forms a cross-bridge When this occurs, the myosin head changes shape and releases the ADP + P

Sliding Filament Model the myosin head changes shape and releases the ADP + P

Sliding Filament Model The thin actin filament is pulled toward the center of the sarcomere…

Sliding Filament Model

cross-bridge broken when ATP binds back to the myosin head ATP

3 2 Cleaving ATP  ADP + P allows myosin head to bind to actin filament ATP form cross bridge ADP release cross bridge shorten sarcomere 1 4 ADP expelled

What is the Stimulus that causes muscle to contract?

Synapse with Neuron & Muscle Synaptic Terminal of neuron releases acetylcholine

Synapse with Neuron & Muscle Ca++ released Binding sites on actin are now exposed. Myosin head now binds to the actin

Synapse with Neuron & Muscle ATP Muscles do not relax until the Ca ++ is pumped back into the sarcoplasmic reticulum

Put it all together… 1 ATP Action potential travels a.p, travels through T-Tubules Ca +2 released & binds to troponin complex Cross bridge formed Ca +2 depleates; cross bridge broken/ ATP back on myosin head Ca +2 pumped back into s.r. / ATP required Acetylcholine released

Put it all together… 1 ATP

Muscle limits: Muscle fatigue –lack of sugar lack of ATP to restore Ca 2+ gradient –low O 2 lactic acidcauses pH drop which interferes with protein function –synaptic fatigue loss of acetylcholine Muscle cramps –build up of lactic acid –ATP depletion –ion imbalance massage or stretching increases circulation

Rigor mortis So why are dead people “stiffs”? –no life, no breathing –no breathing, no O 2 –no O 2, no aerobic respiration –no aerobic respiration, no ATP –no ATP, no Ca 2+ pumps –Ca 2+ stays in muscle cytoplasm –muscle fibers continually contract tetany or rigor mortis –eventually tissues breakdown & relax measurement for time of death

Money for Beauty What is Botox? –Toxin derived from Closteridium botulinum –blocks the release of acetylcholine –Muscles relax… which takes away the wrinkle

*The transmission of an impulse from a nerve to the surface of a resting muscle initiates a contraction in that muscle. Biochemical and biophysical studies of muscle tissue have resulted in an explanation for muscle contraction known as the sliding-filament theory. a. Describe the chemical changes that occur when a nerve impulse is transmitted to the surface of a resting muscle cell. b. Describe the internal structure of a muscle fiber as revealed by electron microscopy. c. On the basis of this structure, explain the sliding- filament theory.

*7. Discuss the mechanism by which a muscle cell contracts or a nerve cell transmits an impulse. Include in your discussion the relationship between cell structure and function.

Action potential causes Ca 2+ release from SR –Ca 2+ binds to troponin Troponin moves tropomyosin uncovering myosin binding site on actin Myosin binds actin –uses ATP to "ratchet" each time –releases, "unratchets" & binds to next actin Myosin pulls actin chain along Sarcomere shortens –Z discs move closer together Whole fiber shortens  contraction! Ca 2+ pumps restore Ca 2+ to SR  relaxation! –pumps use ATP ATP