An Introduction to Human Biology (Muscles)

7/30/2019 An Introduction to Human Biology (Muscles)

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Muscles


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Muscles

Muscle is one of our 4 tissue types and

muscle tissue combined with nerves,blood vessels, and various connective

tissues is what makes up those muscle

organs that are familiar to us. Muscles are quite complex and as well

find out, they are a marvel of both

biology and physics.


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Muscle Functions

1. Production of Movement

Movement of body parts and of theenvironment

Movement of blood through the heart andthe circulatory vessels.

Movement of lymph through the lymphaticvessels

Movement of food (and, subsequently, foodwaste) through the GI tract

Movement of bile out of the gallbladder and

into the digestive tract Movement of urine through the urinary tract

Movement of semen through the malereproductive tract and female reproductivetract

Movement of a newborn through the birth


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Muscle Functions

2. Maintenanceof posture Muscle contraction is constantly

allowing us to remain upright.

The muscles of your neck are

keeping your head up right now.

As you stand, your leg muscles

keep you on two feet.

3. Thermogenesis

Generation of heat. Occurs via

shivering an involuntary

contraction of skeletal muscle.


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Muscle

Functions

4. Stabilizationof joints Muscles keep the

tendons that cross the

joint nice and taut. This

does a wonderful job ofmaintaining the integrity

of the joint.

All the things muscles do fall under one of these 4 categories


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3 Types of Muscle Tissue


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Characteristics of Muscle Tissue

1. Excitability

The ability to receive and respond to a

stimulus

The response is the generation of an

electrical impulse that travels along the

plasma membrane of the muscle cell.


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Characteristics of Muscle Tissue

2. Contractility

The ability to shorten forcibly when adequately

stimulated.

This is the defining property of muscle tissue.3. Extensibility

The ability to be stretched

4. Elasticity

The ability to recoil and resume original length after

being stretched.


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Skeletal Muscle the organ

Skeletal muscle organsare dominated bymuscle tissue but alsocontain nervous,

vascular and assortedconnective tissues

The whole muscle is

surrounded by a layer ofdense irregularconnective tissue knownas the epimysium


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Skeletal Muscle

the organ

Epimysium surrounds severalbundles known as fascicles

Each fascicle is a bundle of

super-long skeletal muscle cells(muscle fibers), surrounded bya layer of dense irregular CTcalled the perimysium(peri=around)

Each muscle cell extends thelength of the whole muscleorgan and is surrounded by afine layer of loose connectivetissue, the endomysium

The epi-, peri-, andendomysium are all continuouswith one another


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In this photomicrograph, you should notice: the epimysium on the

left, the multiple fascicles, the translucent perimysium partitioning

them , and the multiple muscle fibers making up the fascicles.


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Skeletal Muscle

Blood & Nerve

Supply

Each skeletal muscle is

typically supplied byone nerve, an artery

and one or more veins.

They all enter/exit viathe connective tissue

coverings and branch

extensively.


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Skeletal Muscle Attachments

Most span joints and are attached to bones. The attachment of the muscle to the immoveable bone

in a joint is its origin, while the attachment to themoveable bone is its insertion.


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Indirect attachments

are typical. The

muscle CT extends

and forms either a

cordlike structure (a

tendon) or a

sheetlike structure

(aponeurosis) whichattaches to the

periosteum or

perichondrium.

Muscle attachments may

be direct or indirect.

Direct attachments are less

common. The epimysium is

fused to a periosteum or a

perichondrium.


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Skeletal Muscle

Microanatomy

Each skeletal muscle cell is known

as a skeletal muscle fiber becausethey are so long. Their diameter can be up to 100um and their length can

be as long as 30cm.

Theyre so large because a single skeletal muscle cell

results from the fusion of hundreds of embryonicprecursor cells called myoblasts.

A cell made from the fusion of many others is known as asyncytium.

Each skeletal muscle fiber will have multiple nuclei.


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Myofibrils

Each muscle fiber contains rodlike structures called

myofibrils that extend the length of the cell. They arebasically long bundles of protein structures calledmyofilaments and their actions give muscle the ability tocontract.

The myofilaments are classified as thick filaments andthin filaments.


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Myofilaments

2 types of myofilaments (thick & thin) make upmyofibrils.

Thick myofilaments are made the protein myosin

A single myosin protein

resembles 2 golf clubswhose shafts have been

twisted about one another

About 300 of these

myosin molecules are

joined together to form a

single thick filament


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Each thin filament is made up of 3 different types

of protein: actin, tropomyosin, and troponin.

Each thin filament consists of a long helical doublestrand. This strand is a polymer that resembles a string

of beads. Each bead is the globular protein actin. On

each actin subunit, there is a myosin binding site.

Loosely wrapped around the actin helix and covering the

myosin binding site is the filamentous protein,

tropomyosin.

Bound to both the actin and the tropomyosin is a trio of

proteins collectively known as troponin.


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Note the relationship between the thin and thick filaments


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Muscle Contraction:

The Sliding Filament Hypothesis

Place your right palm on the back of your left hand. Nowslide your right palm toward your left elbow. What happened to the distance between your elbows?

It got shorter!

This is how muscle contraction occurs.

The thin filaments slide over the thick filaments. This pulls the Zdiscs closer together. When all the sarcomeres in a fiber do this,the entire fiber gets shorter which pulls on the endomysium,perimysium, epimysium and attached tendon and then pulls on thebone. Voila, we have movement.

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An Introduction to Human Biology (Muscles)