Class notes

Chapter 10 - Muscular System

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Course
HLSC 120 - Anatomy (HLSC120)

Institution
University Of Alberta (UofA)

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HLSC 120 – Human Anatomy
Chapter 10: Muscular System
made up of over 700 skeletal muscles
Myology – study of muscles  Deep fascia – visceral / muscular fascia; ensheathes these 3 connective tissue
Muscular tissue accounts for 40-50% of total body mass. layers; expansive sheet of dense irregular connective tissue that separates
PROPERTIES OF MUSCLE TISSUE individual muscles, binds together muscles w/ similar functions, forms sheaths
 Excitability - electrical excitability / irritability; responsiveness to a certain to help distribute nerves, blood vessels, and lymphatic vessels, fill spaces b/w
stimulus muscles
 Contractility –creates tension w/n the cell (contraction) w/c may cause the cell o Superficial fascia – subcutaneous layer / hypodermis; composed of
to shorten w/c results in either a pull on bones of the skeleton or the areolar connective tissue and adipose connective tissue that separates
movement of specific body parts muscle from skin; underneath is where the deep fascia is found
 Extensibility – ability to extend in length in response to the contraction of MUSCLE ATTACHMENTS
opposing muscle cells  Tendon – at the ends of a muscle, connective tissue layers merge to form a
 Elasticity – ability of the contracted muscle cell to recoil to its resting length fibrous tendon; connects the muscle to the bone, skin, or another muscle; have
when the applied tension is removed thick, cordlike structure; forms an aponeurosis
SKELETAL MUSCLE TISSUE o Aponeuroses – a flat sheet-like fibrous-membrane that aids in the
 composed of 4 types of tissue: epithelial, connective, muscle, nervous connection to the bone
 striated and usually attached to one or more bones Upon contraction, one of the bones moves while the other bone usually remains
 often referred to as muscle fibers fixed.
FUNCTIONS OF SKELETAL MUSCLE TISSUE  Origin – less movable attachment of a muscle; typically lies proximal to the
 Responsible for producing body movements insertion
 Stabilizing body positions / maintains posture  Insertion – more movable attachment of the muscle; pulled toward the origin
 Storage and movement of materials (i.e. nutrients, glycogen, fats) BLOOD VESSELS AND NERVES
 Producing heat / temperature regulation extensive network extends through both the epimysium and perimysium
 Expressions of emotions  Blood vessels – deliver to the muscle fibers both nutrients and oxygen needed
 Support and protection of organs for the production of ATP; remove waste products produced by the muscle
STRUCTURE OF A SKELETAL MUSCLE TISSUE fibers
CONNECTIVE TISSUE COVERINGS  Somatic nervous system – allows the voluntary movements of the skeletal
 Endomysium – innermost connective tissue layer; delicate, areolar tissue layer; muscles
surrounds each muscle fiber; has reticular fibers to help bind together  Motor neurons – stimulate muscle contraction; innervate muscle fibers w/n the
neighboring muscle fibers and support capillaries near these fibers muscle; has an axon
 Perimysium – surrounds the fascicles; its dense irregular connective tissue o Axon – long extension; nerve fiber; transmits a nerve impulse to a
sheath contains extensive arrays of blood vessels and nerves that branch to muscle fiber; travels through the epimysium and perimysium and
supply each individual fascicle enters the endomysium where it sends a nerve impulse to an
o Fascicles – bundles of muscle fibers individual muscle fiber
 Epimysium – layer of dense irregular connective tissue; surrounds the entire o Neuromuscular junction – junction b/w the axon and the muscle fiber
skeletal muscle itself

, MICROSCOPIC ANATOMY filament resembling a string of beads; each spherical
 Skeletal muscles are multinucleated. molecule has a binding site for:
o Myoblasts – groups of embryonic cells; fuse to form single skeletal  myosin – protein that makes up thick filaments
muscle fibers wherein each myoblast nucleus contributes to the  tropomyosin - regulatory protein; resembles a shorter,
eventual total number of nuclei thinner, twisted filament that covers small sections of the
o Satellite cells – embryonic-like cells that remain in adult skeletal actin strands
muscle tissue; may be stimulated to differentiate and assist in the  troponin – regulatory protein; attach to actin to anchor the
repair and regeneration of a muscle if a skeletal muscle is injured troponin in place; attach to tropomyosin to hold it in place
 Sarcolemma – plasma membrane of a skeletal muscle over the surface of the actin
 Sarcoplasm – cytoplasm of the muscle fiber o thick filaments – 2x as large as thin filaments (11nm); assembled form
 Mitochondria – contains approx 300 mitochondria per muscle fiber since the bundles of the protein myosin
fibers have a great demand for energy  myosin – consists of 2 strands, each has a free, globular head
 Lysosomes and other organelles are also present. and an attached, elongated tail; myosin molecules are
 2 main structures unique to muscle fibers: oriented on either end of the thick filament; myosin heads
o T-tubules – transverse tubules; deep invaginations of the sarcolemma are also referred to as
that extend into the sarcoplasm of skeletal muscle fibers as a network  crossbridges – bec during a contraction they bind
of narrow membrane tubules; helps stimulate and coordinate muscle thick filaments to thin filaments, thus forming a
contractions bridge between them
o Sacroplasmic reticulum (SR) – internal membrane complex; similar to Striated appearance of the skeletal muscle is due to size and density differences bw
smooth ER; reservoir for calcium ions needed to initiate muscle thick and thin filaments.
contraction  A bands – dark bands; contain the entire thick filament
 Terminal cisternae – blind sacs of sarcoplasmic reticulum;  I bands – lighter than A bands; contain thin filaments only
pairs immediately adjacent to each T-tubule; reservoirs of  H zone – light, central region in A band
calcium ions; interact w/ T-tubulues during muscle o when muscle fiber is relaxed – no thin filaments are present
contraction o at maximal contraction – thin filaments are pulled into this zone, H
 Triad – structure formed by 2 terminal cisternae and the zone disappears
centrally placed T-tubule  M line – thin protein meshwork structure in the center of the H zone of a
MYOFIBRILS AND MYOFILAMENTS relaxed fiber; serves as an attachment site for thick filaments; keeps the thick
 Myofibrils – long cylindrical structures in the sarcoplasm; 1-2 micrometers in filaments aligned during contraction and relaxation events
diameter; extends the length of the entire muscle fiber; consists myofilaments  Z disc / Z line – thin protein structure in the center of the I band; serves as an
o During contraction – shorten as their component proteins change attachment site for thin filament ends; circular but only the edge is visible so it
position; causes the fiber to shorten looks like a line
 Myofilaments – short bundles; may take many successive groupings of o Connectins – z-disc proteins; anchor and interconnect the thin
myofilaments to run the entire length of the myofibril; classifications: filament ends at either end of a sacromere
o thin filaments – 5-6 nm in diameter; composed of actin o Titin – elastic proteins; attach thin and thick filaments and M-line
 actin – 2 strands of protein twisted around each other to proteins to the z-disc to maintain their organization and order
form a helical shape; in each helical strand, many small, ORGANIZATION OF A SACROMERE
spherical molecules connect to teach other to form a long sacromere – functional contractile unit of a skeletal muscle fiber; defined as one

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