Muscular System
Chapter 8
Introduction
• All movements require muscles
• They are specialized cells that use chemical energy
to contract
• They provide muscle tone, propel body fluids and
food, generate the heartbeat and distribute heat
• Three types: skeletal, smooth and cardiac
• We will just talk about skeletal this chapter
http://t1.gstatic.com/images?q=tbn:ANd9GcRBgTwo0pCWijCpU1047_hoBesy-Wf8REPi0R4jROH1aRnGTyu4
Structure of a Skeletal Muscle
• It is composed of skeletal muscle tissue,
nervous tissue, blood, and connective
tissue
•
Muscles > Fascicles > Muscle fiber (cells) > Myofibrils > Thick and thin filaments
Structure of Skeletal muscle:
Connective tissue coverings
• A muscle is covered by layers of fibrous
connective tissue called a fascia
• It may project longer than the muscle and
form a tendon by connecting to the bone
• Sometimes they form aponeuroses which
are sheets that connect to adjacent
muscles
http://www.guwsmedical.info/blood-vessels/images/4518_264_558-aponeuroses.jpg
• All parts of a skeletal muscle are enclosed
in layers of connective tissue which form a
network
• Epimyseum > perimyseum > fasicles >
endomyseum
• All of those are connective tissues
Structure of Skeletal Muscle:
Skeletal Muscle Fibers
• SMF is a single cell that contracts in
response to stimulation and then relaxes
when stimulation ends (may extend full
length of muscle)
• The sacroplasm (cytoplasm) contains
many threadlike myofibrils that lie parallel
to one another
SMF & Myofibril
http://211.174.114.20/catalog/2011%5C2011_08/actinx2.jpg
• Myofibrils aid in muscle contraction and
contain 2 types of protein filaments:
– Myosin- thick muscle filaments
– Actin- thin muscle filaments
• These alternating bands cause the
striations
http://www.sport-fitness-advisor.com/images/actin_myosin.jpg
• 2 main parts to striations:
– I bands are composed of actin (thin/light) directly attached to z
lines
– A bands are composed of myosin (thick/dark) that overlap the
thin filaments
• In the center of the A band is the H zone which is a central
region that has the M line inside
• The segment of a myofibril that extends from one z line to the next is
called a sacromere
http://site.motifolio.com/images/Arrangement-of-myofilaments-in-the-sarcomere-relaxed-state-9111135.png
http://apbrwww5.apsu.edu/thompsonj/Anatomy%20&%20Physiology/2010/2010%20Exam%20Reviews/Exam%203%20Review/09-03bc_skelemusfi_1.jpg
• Sacroplasmic reticulum – Membranous
network of channels and tubules (similar to
ER)
• Transverse tubules – Membranous
channel that extends inward from a
muscle fiber membrane and passes
through the fiber
• These two structures activate muscle
contraction when fiber is stimulated
Neuromuscular Junction
• Each SMF connects to an axon from a
nerve cell, called a motor neuron
• Muscle fiber contracts only when
stimulated by neuron
• Neuromuscular junction – connection
between the motor neuron and muscle
fiber
http://www.biologycorner.com/anatomy/muscles/muscle_images/neuromuscular_junction.jpg
• The muscle fiber forms a motor end plate
• The end of the motor neuron has many
vesicles that contain chemicals called
neurotransmitter (acetocholine)
• A nerve impulse travels to the neuron
which releases some of the
neurotransmitters into the gap which
stimulates the muscle fiber to contract
http://4.bp.blogspot.com/-gmzOZ8xvH1w/UF7d_9n7P8I/AAAAAAAAACE/FDmkFYMAEnY/s1600/neuromuscular-junction.jpg
Motor Units
• One motor neuron may connect to many
muscle fibers because they are branched
• When one impulse is sent it stimulates all
of the muscle fibers that the motor neuron
is connected to
• A motor neuron and the muscle fibers that
is controls make up a motor unit
Motor Unit
http://staff.fcps.net/cverdecc/adv%20a&p/notes/muscle%20unit/contration%20of%20motor/contra36.jpg
Muscle contraction
animation
http://classconnection.s3.amazonaws.com/1517/flashcards/715536/jpg/picture1.jpg
Contraction video
http://blazerstrength.com/wp-content/uploads/2012/07/atpadpcp.jpg
http://jeb.biologists.org/content/207/20/3441/F2.large.jpg
http://click4biology.info/c4b/3/images/3.7/summary.gif
http://legacy.owensboro.kctcs.edu/gcaplan/anat/images/Image370.gif
http://www.pef.uni-lj.si/eprolab/comlab/sttop/sttop-bm/figures/Myogram%20-%20contractions%2001.gif
http://classes.midlandstech.edu/carterp/Courses/bio210/chap09/Slide29.JPG