the muscular system - napavalley.edunapavalley.edu/people/briddell/documents/bio 105... · the...

© 2014 Pearson Education, Inc.

Lecture Presentation

Anne Gasc

Hawaii Pacific University and

University of Hawaii–Honolulu Community College

BIOLOGY OF HUMANSConcepts, Applications, and Issues

Fifth Edition

Judith Goodenough Betty McGuire

6The Muscular System


The Muscular System

OUTLINE:

Function and Characteristics of Muscles

Skeletal Muscles Working in Pairs

Contraction of Muscles

Voluntary Movement

Energy for Muscle Contraction

Slow-Twitch and Fast-Twitch Muscle Cells

Building Muscle



All muscles are

Excitable (they respond to stimuli)

Contractile (they can shorten)

Extensible (they can stretch)

Elastic (they can return to their original length after

being shortened or stretched)

Three types of muscle

Skeletal

Cardiac

Smooth



Skeletal muscles are voluntary muscles responsible

for

Moving our body

Maintaining posture

Supporting internal organs

Pushing against veins and lymphatic vessels to move

blood and lymph along

Generating heat


Skeletal Muscles Working in Pairs

The body has more than 600 skeletal muscles

Synergistic muscles

Muscles that must contract at the same time to cause

movement

Antagonistic muscles

Movement is produced when one muscle of the pair

contracts and the other relaxes

Example: the biceps muscle and triceps muscle of the

upper arm


Figure 6.1 Skeletal muscle.


Figure 6.2 Some major muscles of the body.


Damage to Skeletal Muscles or Tendons

Most of the major muscles we use for locomotion, manipulation, and other voluntary movements are attached to bones

Tendon

Band of connective tissue that attaches a muscle to a bone

Origin of a muscle

The end attached to the bone that remains relatively stationary during movement

Insertion of a muscle

The end attached to the bone that moves



Tendinitis

Condition of having an inflamed tendon

Caused by overuse, misuse, or age

Healing is slow because tendons have a poor blood

supply

Most effective treatment is rest



Muscle pull

Also called a muscle strain or tear

Caused by overstretching that damages the muscle or

tendon

Treatment includes ice to reduce swelling and

keeping the muscle stretched



An entire, intact muscle is formed from individual

muscle fibers grouped in increasingly larger bundles,

each wrapped in a connective tissue sheath

Fascicle: a bundle of muscle cells

A skeletal muscle has many fascicles

Each fascicle is surrounded by its own connective

tissue sheath

The connective tissue sheaths of fascicles merge at

the ends of muscles to form tendons that attach the

muscle to bone



A muscle cell a muscle fiber

When skeletal muscle cells are viewed under a

microscope, they have distinct bands called

striations formed by the arrangement of myofibrils

within the cell

Myofibrils are specialized bundles of proteins

Each myofibril contains two types of myofilaments

Myosin (thick) filaments

Actin (thin) filaments are more numerous



Each myofibril has tens of thousands of contractile

units, called sarcomeres. The ends of each

sarcomere are marked by dark protein bands called

Z lines. Within each sarcomere the actin and myosin

filaments are specifically arranged

One end of each actin filament is attached to a Z line

Myosin filaments lie in the middle of the sarcomere,

and their ends partially overlap with surrounding actin

filaments. The degree of overlap increases when the

muscle contracts


Figure 6.3 The structure of a skeletal muscle.



Muscle contraction occurs at the molecular level

According to the sliding filament model, a muscle

contracts when actin filaments slide past myosin

filaments, shortening the sarcomere

Myosin molecules are shaped like two-headed golf

clubs. The club-shaped myosin heads are key to

moving actin filaments



The myosin head, also known as a cross-bridge,

attaches to a nearby actin filament

Then the head bends and swivels, pulling the actin

filament toward the midline of the sarcomere

The myosin head disengages from the actin filament

The movements of myosin require ATP

The cycle begins again


Figure 6.4 When a muscle contracts, actin filaments slide past

myosin filaments.



Muscle contraction is controlled by the availability of

calcium ions

Muscle cells contain the proteins troponin and

tropomyosin

The troponin-tropomyosin complex and calcium ions

regulate muscle contraction at the actin-myosin

binding sites



When a muscle is relaxed, the troponin-tropomyosin

complex covers the actin-myosin binding sites

Muscle contraction occurs when calcium ions bind to

troponin, causing it to change shape

This change in shape moves tropomyosin, exposing

the actin-myosin binding sites


Figure 6.5 Calcium ions initiate muscle contraction.


Calcium Ions and Regulatory Proteins

Calcium ions are stored in the sarcoplasmic

reticulum, a form of smooth endoplasmic reticulum

found in muscle cells

Transverse tubules (T tubules)

Pockets in the plasma membrane of a muscle cell

Carry signals from motor neurons deep into the

muscle cell to every sarcomere


Calcium Ions and Regulatory Proteins

Rigor mortis

Muscle contraction will occur as long as ATP is

present

Without ATP, cross-bridges cannot be broken

Within 3 to 4 hours after death, the muscles become

stiff rigor mortis

Actin and myosin gradually break down and muscles

relax again after 2 to 3 days


Role of Nerves

Neuromuscular junction

Junction between the tip of a motor neuron and a

skeletal muscle cell

A nerve impulse travels down a motor neuron to the

neuromuscular junction, where it causes the release

of acetylcholine (a neurotransmitter) from the motor

neuron

Acetylcholine diffuses across a small gap and binds

to receptors on the plasma membrane of the muscle

cell


Role of Nerves

The acetylcholine causes changes in the

permeability of the muscle cell, resulting in an

electrochemical message similar to a nerve impulse

The message travels along the plasma membrane

into the T tubules and then to the sarcoplasmic

reticulum, releasing calcium ions for muscle

contraction


Role of Nerves

Web Activity: Muscle Structure and Function


Figure 6.6 Neuromuscular junction.


Muscular Dystrophy (MD)

A group of inherited conditions in which muscles

weaken: if too many calcium ions enter a muscle

cell, proteins may be destroyed, eventually causing

the cell to die; on a large scale, muscles weaken

Duchenne muscular dystrophy

One of the most common forms

The gene for production of the protein dystrophin is

defective

Lack of dystrophin allows excess calcium ions to enter

muscle cells, eventually killing the cells


Voluntary Movement

Motor unit: a motor neuron and all the muscle cells it

stimulates

All the muscle cells in a given motor unit contract

together

The number of muscle cells in a motor unit is highly

variable

Muscles responsible for precise movements have

fewer muscle cells in each motor unit than do muscles

responsible for less precise movements

On average, there are 150 muscle cells in a motor unit


Figure 6.7 A motor unit.


Motor Units and Recruitment

Increasing the number of motor units that are

stimulated increases the strength of muscle

contraction. This process, performed by the nervous

system, is called recruitment.

Muscle twitch

Contraction of a muscle in response to a single

stimulus

Twitches are very brief and typically not part of normal

movements

If a second stimulus is received before the muscle is

fully relaxed, the second twitch will be stronger than the

first, due to summation


Muscle Twitches, Summation, and Tetanus

A sustained, powerful contraction caused by very

frequent stimuli

Fatigue sets in when a muscle is unable to contract

even when stimulated

Changing the frequency of stimulation is another

way to vary the contraction of muscles


Figure 6.8 Muscle contraction shown graphically.


Energy for Muscle Contraction

Muscle contraction requires an enormous amount of

energy

ATP for muscle contraction comes from many

sources, typically used in sequence

ATP stored in muscle cells

Creatine phosphate stored in muscle cells

Anaerobic metabolic pathways

Aerobic respiration


Figure 6.9 Energy sources for muscle contraction.



Slow-twitch muscle cells

Contract slowly, with great endurance

Abundant mitochondria

Packed with myoglobin (oxygen-binding pigment)

Dark, reddish appearance

Myoglobin

Rich blood supply



Fast-twitch muscle cells

Contract rapidly and powerfully but with much less

endurance

Can make and break cross-bridge attachments more

rapidly

Have more actin and myosin

Rely on anaerobic metabolic pathways to generate

ATP and therefore tire quickly


Figure 6.10 Slow- and fast-twitch muscle cells.


Building Muscle

Aerobic exercise

Enough oxygen is delivered to the muscles to keep

them going for long periods

Increases endurance and coordination

Promotes development of new blood vessels

Increases the number of mitochondria

Typically does not increase size of muscles

Examples: walking, jogging, swimming


Building Muscle

Resistance exercise

Builds strength

Muscles increase in size when they are repeatedly

made to exert more than 75% of their maximum force

Increases in muscle size reflect increases in the

diameter of existing muscle cells

Example: weight lifting


Building Muscle

| From Star to Suspicion:

Did Cycling Champ Use Steroids?

steroids.mov

steroids.mov


You Should Now Be Able To:

Describe the function and characteristics of muscles

Know how muscles contract and explain voluntary

movement, muscle twitch, tetanus and rigor mortis

Describe the possible damage to skeletal muscles or

tendons

Describe where the energy comes from for muscle

contraction

Understand the difference between slow-twitch and

fast-twitch muscle cells, how to build muscle, and

the risks associated with the use of steroids

the muscular system - napavalley.edunapavalley.edu/people/briddell/documents/bio 105... · the...

Documents