The Muscular System - Napa Valley College · Muscular System Recall there are different types of...
Transcript of The Muscular System - Napa Valley College · Muscular System Recall there are different types of...
The Muscular System
Biology 105 Lecture 12 Chapter 6
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Outline
I. Characteristics of muscles II. Three types of muscles III. Functions of muscles IV. Structure of skeletal muscles V. Mechanics of muscle contraction VI. Energy source for muscle contraction
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Muscular System
Recall there are different types of muscles: smooth, cardiac, and skeletal.
All muscle cells are elongated, and therefore are called muscle fibers.
All muscle tissues contract.
Muscles contain muscle fibers, connective tissue, blood vessels, and nerves.
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Smooth muscles are involuntary muscles found in the walls of many internal organs (digestive tract, respiratory system, blood vessels).
They aid in the function of other organs.
Smooth Muscle
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Cardiac muscles are involuntary muscles found only in the heart wall.
They function by contracting, which forces blood from the heart into the arteries.
Cardiac Muscle
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Skeletal muscles are voluntary muscles attached to the skeleton.
They usually work in pairs.
Skeletal Muscle
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Skeletal Muscles Work in Pairs
Most skeletal muscles work in antagonistic pairs: One muscle contracts, while 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.
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Skeletal Muscles Work in Pairs
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.
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Skeletal Muscles Work in Pairs
Figure 6.1a
(a) Flexion
The relaxed triceps is 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 posture 2. Movement of bones and other tissues 3. Help maintain a constant body temperature –
generate heat 4. Help move blood through the veins and
lymphatic fluid through the lymphatic vessels 5. Help to protect vital organs and stabilize
joints
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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.
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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 cell consists of many myofibrils.
A bundle of muscle cells is called a fascicle.
(a) A section of a skeletal muscle
The striped (striated) appearance of a skeletal muscle cell is due to the regular arrangement of myofilaments.
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Muscle Cell Components
Muscle cells (muscle fibers) have many of the same components as typical cells, but some of their components have different names… Sarcolemma – plasma membrane (cell
membrane).
Sarcoplasm – similar to cytoplasm, and contains large amounts 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, and functions as a Ca2+ store.
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Muscle Cell Components
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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a. T tubule b. Sarcoplasmic reticulum c. myofibril
d. Z line e. sarcomere f. sarcolemma
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Muscle Cells (Fibers)
The muscle fiber is composed of long, thin myofibrils.
Myofibrils are bundles of myofilaments that contract: There are two types of myofilaments: actin and
myosin.
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Muscle Contraction
A sarcomere is the name for the structural unit of these myofilaments.
When you look at the myofibril, the sarcomere lies between two dark lines called Z lines: The Z lines are protein sheets where the actin
filaments attach.
When muscle fibers are stimulated to contract, myofilaments slide past one another, causing sarcomeres to shorten.
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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.
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Sarcomeres
Figure 6.3c–d
(c) A diagram and electron micrograph of 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
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The two myofilaments are:
Actin filaments: thin filaments that are formed by two intertwining strands of the protein actin.
Myosin filaments: thick filaments of the protein myosin that are shaped like a golf club with a round “head”.
The myosin heads can bind and detach from the thin actin filament. When bound, they create cross-bridges.
Myofilaments – Actin and Myosin
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Muscle Contraction
A neuron signals the muscle to contract.
The myosin heads attach to the actin, and then pull the actin toward the center of the sarcomere.
The myosin heads detach.
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Sarcomeres Shorten During Muscle Contraction
Figure 6.4
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Steps of Muscle Contraction
1. Action potentials are transmitted through the neurons.
2. At the end of the neurons, neurotransmitters are released into the synaptic cleft.
3. Neurotransmitters bind to receptors on the sarcolemma.
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Neuromuscular Junction
Figure 6.7 (1 of 2)
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Steps of Muscle Contraction
4. These receptors are ion channels that open.
5. An action potential travels through the T tubules of the muscle fiber.
6. The action potential goes to the sarcoplasmic reticulum.
7. The sarcoplasmic reticulum releases Ca2+.
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Steps of Muscle Contraction
8. The calcium binds to the troponin on the actin filament.
9. This uncovers the 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.
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Sarcomeres
Figure 6.6 (1 of 2)
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Sarcomeres
Figure 6.6 (2 of 2)
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Tropomyosin-Troponin Complex
The tropomyosin-troponin complex is attached to the actin filament.
Calcium binds to the troponin, causing a shift in the complex, which opens the sites for myosin to attach.
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A bundle of muscle cells is called a:
33% 33% 33% 1. Fascicle 2. Fascia 3. Muscle fiber
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What is the oxygen-binding protein found only in muscles?
Myo
sin A
ctin
Hem
oglobin
Myo
globin
25% 25%25%25%1. Myosin 2. Actin 3. Hemoglobin 4. Myoglobin
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Which ion is required for the myofilaments to bind to each other?
Potassiu
m
Calc
ium
Chlorid
e
Sodium
25% 25%25%25%1. Potassium 2. Calcium 3. Chloride 4. Sodium
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Where is the calcium stored?
Nucle
us
Sarcolem
ma
Sarcoplas
mic ret
iculum
33% 33%33%1. Nucleus 2. Sarcolemma 3. Sarcoplasmic
reticulum
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ATP is needed for the myofilaments to slide past each other
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ATP
ATP is the energy currency – like money in the bank!
The bonds between the phosphate groups are high energy bonds.
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The Energy Sources
Muscle contractions take a lot of energy in the form of ATP.
Muscles get their ATP from three sources: 1. Breakdown of creatine phosphate 2. Cellular respiration 3. Fermentation
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1. Creatine Phosphate
Creatine phosphate regenerates ADP to make ATP.
This gives quick energy for a few seconds (up to 30 seconds).
Only 1 ATP is produced per creatine phosphate.
Oxygen is not needed.
When a muscle is resting, the ATP in turn regenerates creatine phosphate.
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2. Cellular Respiration
In the mitochondria, glucose is broken down to produce ATP.
Remember that oxygen is needed for the electron transport chain to produce ATP.
Carbon dioxide is produced as a waste product during the Krebs Cycle of 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 the energy source.
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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 are skipped, no oxygen is required.
No CO2 is produced as a waste product, but lactic acid is produced.
Can provide energy for 30 – 60 seconds. Only 2 ATP produced per glucose molecule.
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ATP Comes from Many Sources
Figure 6.10
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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
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Which energy source would a long-distance runner mainly use on a run that lasted for hours?
Fermen
tation
Cell
ular re
spira
tion
Crea
tine P
hosp
hate
25% 25%25%25% 1. Fermentation 2. Cellular respiration 3. Creatine phosphate
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Which energy source would a sprinter use in the first 5 seconds of the race?
Fermen
tation
Cell
ular re
spira
tion
Crea
tine P
hosp
hate
25% 25%25%25% 1. Fermentation 2. Cellular respiration 3. Creatine phosphate
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Important Concepts
Read Chapter 6
What are the three types of muscles? Where are they found, and are they under voluntary or involuntary control?
What are the functions of skeletal, cardiac, and smooth muscles?
How do skeletal muscles work in pairs?
What is the function of tendons?
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Important Concepts
What is the overall structure of a muscle? What are the components of a muscle, and of a muscle cell (muscle fiber)? What are the functions of the muscle fiber components?
You should be able to identify the muscle fiber components in an illustration, including: myofibrils, sarcomeres, Z lines, myofilaments (actin and myosin filaments), cross-bridges, sarcolemma, sarcoplasm, sarcoplasmic reticulum, T tubules
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Important Concepts
What stimulates a muscle to contract?
You should 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?
What are the components and the function of the tropomyosin-troponin complex?
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Important Concepts
What are the three energy sources used for muscle contraction? Which of these require oxygen and which produce carbon dioxide? How many ATP are produced, and how long can each energy source provide energy?
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Definitions
Muscle fiber, myoglobin, fascia, fascicle, myofibril, sarcomere, involuntary, voluntary, origin, insertion