The Muscular System Notes

The Muscular System

The Muscular System 

The Muscular System 

Muscles

Muscles make up almost half the weight of the body

there are 650 different muscles in the human body

the size of your muscles is influenced by how much you use them. this is why speed skaters have large leg muscles

Individual elongated muscle cells can be up to 12 inches, or 30 centimetres, in length

at about the age of 40, the number and diameter of muscle fibers begin to decrease, and by age 80, up to 50 percent of the muscle mass may be lost. exercise and good nutrition help to minimize this loss.

muscle is a general term for all contractile tissue.

Functions of Muscular Tissue

Like nervous tissue, muscles are excitable or “irritable”

they can respond to a stimulus

Unlike nerves, however, muscles are also:

Contractible (they can shorten in length)

Extensible (they can extend or stretch)

Elastic (they can return to their original shape)

Types of Muscular Tissue

Types of Muscular Tissue

Muscle

Location

Function

Appearance

Control

Skeletal

skeleton

movement,
heat, posture

striated, multi-nucleated (eccentric), fibers
parallel

voluntary

Cardiac

heart

pump blood
continuously

striated, one central nucleus

involuntary

Visceral

(smooth
muscle)

G.I. tract,
uterus, eye, blood vessels

Peristalsis,
blood pressure, pupil size, erects hairs

no
striations
, one central
nucleus

involuntary

 

 

 

 

 

 

 

 

 

 

 

 

The Muscular System

Skeletal muscle is the only organ of the muscular system

Skeletal muscle is composed of skeletal muscle tissue and also contains nervous tissue, blood vessels and connective tissue

Half of the body’s weight is muscle tissue

Skeletal muscle = 40% in males, 32% in females

Cardiac muscle = 10%

Skeletal muscle fibers (cells) are arranged into bundles called fascicles
Fascicles are bound by connective tissue

Connective Tissue Coverings

Deep fascia – Surrounds entire skeletal muscle and extends beyond its length
                      Surrounds an individual skeletal muscle, separating it from other muscles
                      Fascia may extend beyond the ends of the muscle to become a tendon
                      Fascia may connect muscle to muscle and is called an aponeurosis
Epimysium – Closely surrounds skeletal muscle, binds fascicles together
Perimysium – Surrounds each fascicle
Endomysium – Surrounds each muscle fiber (cell)

Characteristics of Skeletal Muscle Tissue

Long, thin contractile fibers that are Striated
Striations due to arrangement of thick and thin filaments
Under voluntary control
Attached to the bones of the skeleton by tendons
Allow for movement, facial expressions, breathing, swallowing, writing, talking and singing, posture, heat production, joint stability

Skeletal Muscle Arrangement

A single muscle cell is a muscle fiber
Fibers are made up of myofibrils
Myofibrils are made up of thick and thin filaments
 
Sarcolemma – muscle cell membrane
Sarcoplasm – muscle cell  cytoplasm
Skeletal Muscle Arrangement

Skeletal Muscle Cells

Myofibrils are striated
Striations due to arrangement of thick and thin filaments
Seen as alternating areas of light and dark bands
The length of each myofibril is divided into repeating units called sarcomeres
A sarcomere is the functional unit of skeletal muscle

Sarcomere Arrangement

Sarcomere Arrangement

Sarcomere Structure

Sarcomere exists from Z-line to Z-line
A-Band is dark middle band- Overlapping think and thin filaments
I-Band – ends of A-Band, thin filaments only
Z-line is in the middle if the I-Band
Myosin filaments are held to the Z-line by titin proteins

Microscopic anatomy of a skeletal muscle fiber

Microscopic anatomy of a skeletal muscle fiber

Thick Filament Structure

Composed of many myosin molecules
Each myosin molecule has a tail region and 2 globular heads (crossbridges)
Thick Filament Structure

Thin Filament Structure

Thin Filament Structure
Composed of actin protein
2 strands of globular actin molecules twisted into a helix
Actin filaments have binding sites for myosin cross bridges
Tropomyosin protein spirals around actin helix
Troponin protein (3 subunits) is attached to actin and holds tropomyosin in place
Call this the troponin-tropomyosin complex

Specialized Organelles of Skeletal Muscle

Sarcoplasmic Reticulum (SR) – a type of ER

Surrounds each myofibril, running parallel to it
Stores calcium, when stimulated, calcium diffuses into sarcoplasm

Transverse Tubules (TT) 

Extends into sarcoplasm as invaginations continuous with sarcolemma
T tubules run between cisternae of SR
Filled with extracellular fluid
Cisternae of SR and TT form a triad near where thick and thin filaments overlap

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