Biol 105 VI. Energy source for muscle contraction Lecture … 105... · · 2014-10-11Energy source for muscle contraction ... Muscular System Remember there were different types

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The Muscular System

Biol 105Lecture 12Chapter 6

Copyright © 2009 Pearson Education, Inc.

Outline

I. Characteristics of musclesII. Three types of musclesIII. Functions of musclesIV. Structure of skeletal musclesV. Mechanics of muscle contractionVI. Energy source for muscle contraction


Muscular System

Remember there were different types of muscles: cardiac, smooth and skeletal.

All muscle cells are elongated and therefore are called muscle fibers.

All muscle tissues contract.

Muscles contain muscle cells (called muscle fibers), connective tissue, blood vessels, and nerves


1. Smooth muscle

2. Cardiac muscle

3. Skeletal muscle

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Types of Muscles


Smooth muscles are involuntary muscles found in the walls of many internal organs (digestive tract, respiratory system, blood vessels).

Function to aid in the function of other organs

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Smooth muscle


Cardiac muscles are involuntary muscles found only in the heart wall.

Functions by contracting to force blood from the heart into the arteries

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Cardiac muscle

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Skeletal muscle are voluntary muscles attached to the skeleton.

Usually work in pairs

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Skeletal muscle

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Skeletal Muscles Work in Pairs

Most skeletal muscles are antangonistic pairs.

One muscle contracts, the other relaxes

Muscles are attached to the bone by tendons

Skeletal Muscles are usually attached to two bones on opposite sides of a joint



The origin of the muscle is attached to the bone that remains stationary during movement

The insertion is attached to the bone that moves

Bones act as levers in working with skeletal muscles to produce movement



Figure 6.1a

(a) Flexion

The relaxed tricepsis stretched.

The biceps contracts and pulls the forearm up, flexing the arm.

Origin of muscle:attachment of muscle to less moveable bone

Insertion of muscle:attachment of muscle to more moveable bone

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Functions of Skeletal Muscles

1. Support the body – maintain our posture2. Movement of bones, and other tissues3. Help maintain a constant body temperature

– generates heat4. Helps move blood through the veins and

lymphatic fluid through the lymphatic vessels

5. Help to protect vital organs and stabilize joints


Structure of Skeletal Muscles

Muscles are covered by connective tissue called fascia.

A muscle contains bundles of skeletal muscle fibers (muscle cells), the bundles are called fascicles. These bundles are covered by connective tissue.

Blood vessels and nerves are between the fascicles.


Structure of Skeletal Muscles

Figure 6.3a–b(b) A light micrograph of a longitudinal view of skeletal muscle cells

Skeletal muscle consists of many bundles of muscle cells.

A muscle cellconsists of manymyofibrils.

A bundle of muscle cells is called a fascicle.

(a) A section of askeletal muscle

The striped (striated) appearance of a skeletal muscle cell is due to the regular arrangement of myofilaments.


Sarcomeres

Figure 6.3b–c

(b) A light micrograph of a longitudinal view of skeletal muscle cells

(c) A diagram and electron micrograph of a myofibril

Z line

One sarcomere

The striped (striated) appearance of a skeletal muscle cell is due to the regular arrangement of myofilaments.


Muscle Cells

Muscle cells are long cells called muscle fibers.

The muscle fiber is composed of long thin myofibrils

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a. T tubule b. Sarcoplasmic reticulumc. myofibril

d. Z linee. sarcomere f. sarcolemma


Muscle Cells cont

Myofibrils are bundles of myofilaments that contracts.

Myofilaments are made of actin and myosin filaments.

When muscle fibers are stimulated to contract, myofilaments slide past one another, causing sarcomeres to shorten.


Muscle Cell Components

Muscle cells (muscle fibers) have many of the same components as typical cells have but some of their components have different names



Sarcolemma – plasma membrane (cell membrane)

Sarcoplasm – similar to cytoplasm, contains large amount of stored glycogen and myoglobin.

Myoglobin is an oxygen binding protein similar to hemoglobin, but found only in muscles

Sarcoplasmic reticulum – similar to endoplasmic reticulum, one of its functions is to store Ca2+



Muscle cells (muscle fibers) also have unique features:

Multiple nuclei

Transverse tubules (T tubules) – extensions of the sarcolemma that come into contact with the sarcoplasmic reticulum.

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Muscle Contraction

The small myofibrils that make up the muscle fiber (muscle cell) contain two types of myofilaments: actin and myosin filaments

Sarcomere is the name for the structural unit of these myofilaments

The sarcomere goes between two dark lines = Z lines. The Z lines are protein sheets where the actin filaments attach


Sarcomeres

Figure 6.3c–d

(c) A diagram andelectron micrographof a myofibril

(d) A sarcomere, the contractile unit of a skeletal muscle, contains actin and myosin myofilaments.

Z line

Z line

Z line

Actin

Myosin

One sarcomere

One sarcomere


The two myofilaments are:

Actin filaments: thin filaments that formed by two intertwining strands of the protein actin.

Myosin filaments: Thick filaments of the protein myosin shaped like a golf club, with a round “head”.

Myofilaments – actin and myosin


The myosin heads can bind and detach from the thin actin filament. When bound it creates cross-bridges.

When the muscle is stimulated, these filaments slide past each other, making the sarcomere to shorten

Myofilaments – actin and myosin


Muscle Contraction cont

A neuron signals the muscle to contract

The myosin heads attach to the actin then pull the actin toward the center of the sarcomere

Then the myosin heads detach


Sarcomeres

Figure 6.4

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Neuromuscular Junction

Figure 6.7 (1 of 2)


Steps of Muscle Contraction

1. Action potentials are transmitted through the neurons.

2. At the end of the neurons neurotransmitters are released

3. Neurotransmitters bind to receptor on the sarcolemma



4. The receptors are ion channels that open

5. An action potential travels through the T tubules

6. The action potential goes to the sarcoplasmic reticulum

7. The sarcoplasmic reticulum releases Ca2+.



8. The calcium binds to the troponin on the actin filament

9. This opens up binding site for the myosin to attach

10. Now the myosin binds to the actin

11. ATP is needed for the myosin to slide past the actin


Sarcomeres

Figure 6.6 (1 of 2)

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Sarcomeres

Figure 6.6 (2 of 2)


Tropomyosin-troponin complex

The tropomyosin-troponin complex is attached to the actin filament.

Calcium binds to the troponin, causing a shift in the complex, opening the sites for myosin to attach.


ATP is needed for the myofilaments to slide past each other


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ATP

ATP is the currency. Like money in the bank.

The bonds between the phosphate groups are high energy bonds


The Energy Source

Muscle contractions take a lot of energy in the form of ATP.

Muscles get their ATP from three sources:

1. The breakdown of creatine phosphate 2. Cellular respiration 3. Fermentation


1. Creatine Phosphate

Creatine phosphate regenerates ADP to make ATP

This gives quick energy for a few seconds (up to 30 sec)

Only 1 ATP is produced per creatine phosphate

Oxygen is not needed.

When a muscle is resting, the ATP in turn regenerates creatine phosphate.


2. Cellular Respiration

In the mitochondria, glucose is broken down to produce ATP.

Remember that oxygen is needed on the electron transport chain to produce the ATP.

Carbon dioxide is produced as a waste product during the Krebs cycle step in cellular respiration

Can provide energy for hours. Produces 36 ATP per glucose molecule Can use glucose as well as fatty acids and amino

acids for energy source


3. Fermentation

This is when the cell only uses glycolysis, and glucose is broken down to lactic acid.

Since the Krebs cycle and the electron transport chain is skipped, no oxygen is required.

No CO2 is produced as a waste produce but lactic acid is produced

Can provide energy for 30 – 60 sec 2 ATP produced per glucose molecule

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ATP Comes from Many Sources

Figure 6.10 Copyright © 2009 Pearson Education, Inc.


Figure 6.10 (1 of 2)

6 seconds 10 seconds 30–40 seconds

ATP stored in muscles

ATP formed from creatine phosphate and ADP

ATP generated from glycogen stored in muscles and broken down to form glucose

Oxygen limited• Glucose oxidized

to lactic acid



Figure 6.10 (2 of 2)

End of exercise After prolonged exercise

ATP generated from glycogen stored in muscles and broken down to form glucose

Oxygen debt paid back

Breathe heavily to deliver oxygen• Lactic acid used to produce ATP• Creatine phosphate restored• Oxygen restored to myoglobin• Glycogen reserves restored

Oxygen present• Heart beats faster to deliveroxygen more quickly

• Myoglobin releases oxygen


CP breakdown

Cellular Respiration

Fermentation

Requires O2 No Yes No

Produces CO2

No Yes No

# ATP produced

1 36 2

Duration 30 sec Hours 30-60 sec


Important Concepts

Read Chapter 10 for next lecture

What are the three types of muscles, where are they found, are they under vol. or invol control

What are the functions of skeletal, cardiac and smooth muscles

How do skeletal muscles work in pairs?

What is the structure and the components of a muscle, and of a muscle cell (muscle fiber) and the functions of the muscle cell components.


Important Concepts

What is the function of tendons?

What stimulates a muscle to contract

Be able to describe the steps of how the message is transmitted from the neuron to the myofilaments

What is the role of Ca2+.

What happens when the message is received by the myofilaments?

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Important Concepts

What are the components of the muscle fibers, their functions, be able to identify them in an illustration, including: myofibrils, sarcomeres, Z lines, the myofilaments - actin and myosin filaments, cross-bridges, sarcolemma, sarcoplasm, sarcoplasmic reticulum, T-tubules

What are the components and the function of the tropomyosin-troponin complex


Important Concepts

What are the three energy sources for muscle contraction, which require oxygen, which produce carbon dioxide, how many ATP are produced, how long can it provide energy


Definitions

muscle fibers, Myoglobin, fascia, fascicles, myofibrils, sarcomere, involuntary, voluntary, origin, insertion

Biol 105 VI. Energy source for muscle contraction Lecture … 105... · · 2014-10-11Energy source for muscle contraction ... Muscular System Remember there were different types

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