the muscular system - napa valley collegenapavalley.edu › people › aross › documents ›...

The Muscular System

Biol 105

Lecture 12

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 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

11-2

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

11-2

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

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 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 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 and stabilize

joints


Smooth muscles are under this kind of control

1. Voluntary

2. Involuntary


Smooth muscles are found in

1. The heart

2. Digestive tract

3. Attached to bones


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 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.


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:

1. Fascicles

2. Fascia

3. Muscle Fibers


Muscle Cells

Muscle cells are long cells called muscle

fibers.

The muscle fiber is composed of long thin

myofibrils


a. T tubule b. Sarcoplasmic reticulum

c. 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.


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 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 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


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)


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


What is the an oxygen binding protein found only

in muscles?

1. Myosin

2. Actin

3. Hemoglobin

4. Myoglobin


What ion is required for the myofilaments to bind

to each other?

1. Potassium

2. Calcium

3. Chloride

4. Sodium


Where is the calcium stored?

1. Nucleus

2. Sarcolemma

3. Sarcoplasmic

reticulum


a. T tubule b. Sarcoplasmic reticulum

c. myofibril

d. Z linee. sarcomere f. sarcolemma


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


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?

1. Fermentation


3. Creatine

Phosphate


Which energy source would a sprinter use in the

first 5 seconds of the race?

1. Fermentation


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

the muscular system - napa valley collegenapavalley.edu › people › aross › documents ›...

Documents