AP Biology

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AP Biology

Muscles

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Introduction

• In order for the bones to move. Muscles must ___________.

• There are three types of muscles:

– Smooth/Involuntary: digestive system, blood vessels, internal organs.

– Cardiac: heart

– Voluntary/Striated/Skeletal: controlled by somatic

nervous system…on skeleton.

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Arrangement

• Muscles: connective tissue and muscles

• Muscle fiber: precise arrangement of proteins.

• A collection of muscle fibers: Fasciculi.

• A single muscle fiber: Myofibril. A muscle cell is made up of a number of myofibrils.

• Blood vessels and nerves run through the

fibers and the whole muscle is surrounded by

Fascia.

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More

• Fascia is connective tissue made up of collagen and

elastin. The fascia will form the tendons (connect muscle to bone).

• Two types of tendons:

– Insertion: move

– Origin: doesn’t move…anchor.

• Muscles will shorten when they contract. As they shorten,

they will pull on the tendons, the origins will anchor the

muscle, the insertion will pull on the bone. As the muscle

pulls, the bone will move around the joint and move.

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More and more

• Since muscles will only contract, the bone needs to be moved back to the original position.

Muscles work in pairs: Antagonists.

• These move the bone in opposite directions.

– E.g.: bicep brachii and tricep brachii. Pectoralis major and Latissimus dorsi

• Muscles only contract and relax.

• How do muscles get shorter (contract)?

• Great question

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Ultrastructure of muscle

• We are looking at skeletal muscles.

• Sarcolemma, neuromuscular jxn, Glycogen and fat molecules, T tubules, sarcoplasmic reticulum,

mitochondria.

• Protein: actin and myosin.

• Proteins form a banding pattern: Z line, A band (actin and myosin), I band (actin alone), H zone (myosin

alone)

• Sarcomere: between the Z lines. Basic unit of

contraction.

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Myosin and Actin

• Myosin: made up of smaller proteins: head and tail (Nike swoosh). On head: ATP, tails are fused together. About 350 myosin proteins make up the myosin band.

• Actin: has myosin binding site.

• Myosin bent. When ATP hydrolyzes, The energy

changes myosin shape. Myosin can straighten

out and grab the actin (on the myosin binding

sites). Forms a Cross-Bridge.

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Myosin and Actin, 2

• After grabbing the myosin binding sites, the energy is used up, so the myosin reverts to low energy state.

• Pulls on the actin. Actin slides, so that the Z lines get closer together or the sarcomere shortens.

• A new ATP binds on the myosin head.

• 5 X per second.

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Tropomyosin and Troponin Complex

• When a muscle is at rest, tropomyosin (TM) blocks the myosin binding sites on actin. The Troponin Complex (TC) will hold TM in place.

• Ca

²⁺

from the Sarcoplasmic Reticulum (SR) will bind to the TC, which changes shape. It can’t hold the TM in place anymore. Once the

mysoin binding sites are exposed, the ATP on

the myosin head hydrolyzes.

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Steps to muscle contraction

• 1) The motor cortex in your brain sends an

impulse down to the motor neuron to a specific muscle.

• 2) The motor neuron will stimulate the sarcolemma at the neuromuscular jxn.

• 3) The impulse is transmitted down the muscle fiber by the T tubule.

• 4) The impulse from the T tubule will stimulate

the SR to release Ca

²⁺

.

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More steps

• 5) The Ca

²⁺

will bind to the TC. The TC changes shape and can’t hold the TM in place.

• 6) The myosin binding sites are exposed. The ATP on the myosin head hydrolyzes.

• 7) The myosin changes shape and binds to the actin at the myosin binding site.

• 8) The myosin reverts back to the low energy

state and pulls on the actin.

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More Steps

• 9) The actin filaments slide closer together.

• 10) ATP reattaches to the myosin head.

• 11) The Ca2+ flows back into the SR by active transport.

• 12) The TC shape changes, can hold TM in place and they myosin binding sites are blocked.

• 5 X per second.

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Rigor Mortis

• No more ATP available. No more myosin moving, no more Ca

²⁺

back into the SR.

• Muscles stay contracted.

• Bacteria will break cross links, eventually.

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2 types of muscle contractions

• Isotonic: muscle contracts, the bone moves.

– Excessive exercise and lifting weight can tear the myosin heads. You will cause tissue damage,

inflammatory response, pain receptors are

sensitized, you have DOMS (delayed onset muscle soreness). Your body will undergo protein

synthesis to produce more myosin and actin,

muscle will get thicker…more myosin heads can

pull on more actin to lift the heavier weight.

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Second type of muscle contraction

• Isometric: contract muscle and the bone doesn’t move.

• Driving your car. Work muscles.

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Skeletal muscles and Fxns

• Head and Neck:

– Frontalis: lifts eyebrows

– Obicularis Oculi: wink/blink

– Zygomaticus: lifts the corner of the mouth – Obicularis Oris: closes lips/kiss

– Sternocleidomastoid: turns head side to side

– Trapezius: shrug

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Skeletal muscles and Fxns, 2

• Back and Front:

– Latissimus Dorsi: pulls on humerus, back and down

– Deltoids (anterior, posterior, medial): pulls on humerus, up.

– Pectoralis major: pulls on humerus, front (across chest)

– External obliques: flex side ways.

– Rectus abdominis: sit up

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Skeletal muscles and Fxns, 3

• Arms and hands:

– Bicep Brachii: flex forearm

– Tricep Brachii: extends formearm – Flexor carpi: flexes hand

– Extensor carpi: extends hand – Flexor digitorum: flexes fingers

– Extensor digitorum: extends fingers

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Skeletal muscles and Fxns, 4

• Legs:

– Satorius: cross legs

– Quadricep femoris group (4 muscles): extends lower leg

– Hamstring group: extends leg (hamstring pull) – Gluteus maximus: extends thigh

– Gluteus medius: moves legs out.

– Adductor longus: moves legs in

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Skeletal muscle and Fxn, 5

• Lower leg and feet:

– Gastrocnemius: extends foot

– Tibialis anterior: flexes foot (shin splits. I’ll solve that problem…forever).

– Flexor digitorum longus: flexes toes

– Extensor digitorum longus: extends toes.

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Role of Energy

• Need ATP for muscle contraction

• ATP is produced by the mitochondria.

• You need oxygen to produce ATP. You will

produce 38 molecules of ATP per molecule of glucose with oxygen.

• Oxygen is carried by the blood and enters the cell.

• Without oxygen, you produce ATP anaerobically

and don’t use the mitochondria.

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Then what happens

• Without oxygen, the cells produce 2 ATP

molecules per glucose. That’s not enough to stay alive.

• With this production of 2 ATP, you will

produce lactic acid…this causes the muscles to burn. Other organisms produce ethanol…