The Muscular System - Napa Valley College · Muscular System § Remember there were different types...

The Muscular System

Biol 105 Chapter 6

Copyright © 2009 Pearson Education, Inc.

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


Muscular System

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

§  All muscle cells are elongated and contain many protein fibers and therefore are called muscle fibers. (muscle cell = muscle fiber)

§  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

11-2

Types of Muscles


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

§  Aid in the function of other organs.

11-2

Smooth Muscle


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

§  Function by contracting to force blood from the heart into the arteries.

11-2

Cardiac Muscle


§  Skeletal muscle are voluntary muscles attached to the skeleton.

§  Usually work in pairs.

11-2

Skeletal Muscle


Skeletal Muscles Work in Pairs

§  Most skeletal muscles are found in antagonistic pairs.

§  When 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 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


Functions of Skeletal Muscles

1.  Support the body – maintain our posture. 2.  Movement of bones and other tissues. 3.  Help maintain a constant body temperature

– generates heat. 4.  Helps move blood through the veins and

lymphatic fluid through the lymphatic vessels.

5.  Help to protect vital organs. 6.  Stabilize joints.


Smooth muscles are under this kind of control

Voluntary

Invo

luntar

y

50%50%1.  Voluntary 2.  Involuntary


Smooth muscles are found in

The hea

rt

Diges

tive t

ract

Atta

ched

to bo

nes

33% 33%33%1.  The heart 2.  Digestive tract 3.  Attached to bones


Muscle Cells (Muscle Fibers)

§  Bundles of myofilaments are the contractile portion of a muscle fiber.

§  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 Cells (Muscle Fibers)

§  Long, thin bundles of myofilaments are called Myofibrils.

§  Muscle cells are long cells packed with myofibrils and are therefore called muscle fibers.


Structure of Skeletal Muscles

§  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.

§  Muscles are covered by connective tissue called fascia.


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.

A myofibril consists of many 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.


A bundle of muscle cells is called a:

Fascic

les

Fascia

Musc

le Fiber

33% 33%33%1.  Fascicle 2.  Fascia 3.  Muscle Fiber


Muscle Cell Components

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


Muscle Cell Components §  Sarcolemma – plasma membrane (cell

membrane).

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

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


Muscle Cell Components §  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.

§  Myoglobin - an oxygen binding protein similar to hemoglobin, but found only in muscles.

§  Sarcomeres – the contractile units of a muscle fiber.


a. T tubule b. Sarcoplasmic reticulum c. myofibril

d. Z line e. sarcomere f. sarcolemma


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 stretches between two dark lines called Z lines. The Z lines are protein sheets where the actin filaments attach.


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


§  The two myofilaments are:

§  Actin filaments: thin filaments that form 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 they create cross-bridges.

§  When the muscle is stimulated, these filaments slide past each other, causing the sarcomere to shorten. This action is called a power stroke.

Myofilaments – Actin and Myosin


Muscle Contraction cont…

§  A neuron signals the muscle to contract.

§  The myosin heads attach to the actin (cross bridge formation) then pull the actin toward the center of the sarcomere (power stroke).

§  Then the myosin heads detach.


Sarcomeres

Figure 6.4


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 the neurotransmitter Acetylcholine is released.

3.  Acetylcholine binds to its receptor on the sarcolemma.



4.  The receptors are ion channels that open and allow Na+ to enter the cell triggering an action potential.

5.  The action potential travels down the T-tubules.

6.  The action potential reaches the sarcoplasmic reticulum.

7.  The sarcoplasmic reticulum releases Ca2+.



8.  The calcium binds to the troponin on the actin filament, causing tropomyosin to move.

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.


Troponin-Tropomyosin 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.


Sarcomeres

Figure 6.6 (1 of 2)


Sarcomeres

Figure 6.6 (2 of 2)


ATP is needed for the myofilaments to slide past each other


What is the an 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


What 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


Where is the calcium stored?

Nucle

us

Sarcolem

ma

Sarcoplas

mic ret

iculum

33% 33%33%1.  Nucleus 2.  Sarcolemma 3.  Sarcoplasmic

reticulum


ATP

§  ATP is the currency. Like money in your pocket.

§  The bonds between the phosphate groups are high energy bonds.


The Energy Source

§  Muscle contractions use a lot of energy in the form of ATP.

§  Muscles get their ATP from three sources:

§  1. The breakdown of Creatine Phosphate §  2. Anaerobic Fermentation §  3. Cellular Respiration


1. Creatine Phosphate

§  Creatine phosphate regenerates ADP to make ATP.

§  This gives quick energy for a few seconds (up to ~10 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. Anaerobic 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.


3. Aerobic Cellular Respiration

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

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

§  Carbon dioxide is produced as a waste product during the Citric Acid Cycle and Transition Rxn steps 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.


ATP Comes from Many Sources

Figure 6.10



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 deliver oxygen 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


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.  Aerobic Cellular

Respiration 3.  Creatine

Phosphate


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


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?


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

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