June 16, 2023 • 27 mins
This is the last chapter of the book!
This textbook is designed specifically for Kansas State's Biology 198 Class. The course is taught using the studio approach and based on active learning. The studio manual contains all of the learning objectives for each class period and is the record of all student activities. Hence, this textbook is more of a reference tool while the studio manual is the learning tool.
Authors: Robert Bear, David Rintoul, Bruce Snyder, Martha Smith-Caldas, Christopher Herren, and Eva Horne
Kansas State University Libraries
New Prairie Press
Bear, Robert; Rintoul, David; Snyder, Bruce; Smith-Caldas, Martha; Herren, Christopher; and Horne, Eva, "Principles of Biology" (2016). Open Access Textbooks. 1. https://newprairiepress.org/textbooks/1
The textbook was originally published and is also available to download at http://cnx.org/contents/db89c8f8-a27c-4685-ad2a-19d11a2a7e2e@24.1.It is licensed under a Creative Commons Attribution License 4.0 license.
This textbook is designed specifically for Kansas State's Biology 198 Class. The course is taught using the studio approach and based on active learning. The studio manual contains all of the learning objectives for each class period and is the record of all student activities. Hence, this textbook is more of a reference tool while the studio manual is the learning tool.
Authors: Robert Bear, David Rintoul, Bruce Snyder, Martha Smith-Caldas, Christopher Herren, and Eva Horne
Kansas State University Libraries
New Prairie Press
Bear, Robert; Rintoul, David; Snyder, Bruce; Smith-Caldas, Martha; Herren, Christopher; and Horne, Eva, "Principles of Biology" (2016). Open Access Textbooks. 1. https://newprairiepress.org/textbooks/1
The textbook was originally published and is also available to download at http://cnx.org/contents/db89c8f8-a27c-4685-ad2a-19d11a2a7e2e@24.1.It is licensed under a Creative Commons Attribution License 4.0 license.
Mark as Played
Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
(00:00):
Welcome to Principles of Biology. Thisbook was written by the Open Alternative Textbook
Initiative at Kansas State University and isbeing released as a podcast and distributed under
the terms of the Creative Commons AttributionLicense. Today's episode is Chapter twenty nine
point one musculo Skeletal system. Allhyperlinks, images and sources can be found
(00:22):
at the link to the book.In the description of all the constituents of
the human body, bone is thehardest, the driest, the earthiest,
and the coldest, And excepting onlythe teeth, it is devoid of sensation.
God, the great creator of allthings, formed its substance to this
specification with good reason, intending itto be like a foundation for the whole
(00:43):
body. For at the fabric ofthe human body, bones perform the same
function as de walls and beams andhouses, pulls in tents and keels,
and ribs and boats. Andreas Visalius, Flemish anatomist into Humani's Corporus Fabrica,
fifteen forty three. As the Saliusrecognized long ago, the muscular and skeletal
systems provide support to the body andallow for a wide range of movement.
(01:06):
The bones of the skeletal system protectthe body's internal organs and support the weight
of the body. The muscles ofthe muscular system can tract and pull on
the bones, allowing for movements asdiverse as standing, walking, running,
and grasping items. Injury or diseaseaffecting the musculo skeletal system can be very
debilitating in humans. The most commonmusculoskeletal diseases worldwide are caused by malnutrition.
(01:33):
Ailments that affect the joints are alsowidespread, such as arthritis, which can
make movement difficult and in advanced casescompletely impair mobility. Types of skeletal systems.
A skeletal system is necessary to supportthe body, protect internal organs,
and allow for the movement of anorganism. There are three different skeleton designs
(01:53):
that fulfill these functions, hydrostatic skeleton, exoskeleton, and endoskeleton. Hydrostatic skeleton
a hydrostatic skeleton is a skeleton formedby a fluid filled compartment within the body
called the salum. The organs ofthe salum are supported by the aqueous fluid,
which also resists external compression. Thiscompartment is under hydrostatic pressure because of
(02:17):
the fluid and supports the other organsof the organism. This type of skeletal
system is found in soft bodied animalssuch as sea anemones, earthworms, Nyderia,
and other invertebrates. Figure photo showsa white sea star with red bumps
along the tops and tips of itsarms. The skeleton of the red knobbed
(02:38):
seastar Pretoristerlnchia is an example of ahydrostatic skeleton. Credit a mod of forty
four slash Wikimedia Commons. Movement ina hydrostatic skeleton is provided by muscles that
surround the sealum. The muscles ina hydrostatic skeleton contract to change the shape
of the salum. The pressure ofthe fluid in the salum produces movement.
(03:00):
For example, earthworms move by wavesof muscular contractions of the skeletal muscle of
the body. Wall. Hydrostatic skeletoncalled peristalsis which alternately shorten and lengthen the
body. Lengthening the body extends theanterior end of the organism. Most organisms
have a mechanism to fix themselves inthe substrate. Shortening the muscles then draws
(03:22):
the posterior portion of the body forward. Although a hydrostatic skeleton is well suited
to invertebrate organisms such as earthworms andsome aquatic organisms, It is not an
efficient skeleton for terrestrial animals. Exoskeletonan exoskeleton is a chinness external skeleton that
consists of a hard encasement on thesurface of an organism. For example,
(03:45):
the shells of crabs and insects areexoskeletons. Figure. This skeleton type provides
defense against predators, supports the body, and allows for movement through the contraction
of attached muscles. As with endoskeletonssee below, muscles must cross a joint
inside the exoskeleton. Shortening of themuscle thus changes the relationship of the two
(04:06):
segments of the exoskeleton. Arthropods suchas crabs and lobsters have exoskeletons that consist
of thirty to fifty percent keton,a polysaccharide derivative of glucose that is a
strong but flexible material. Keton issecreted by the epidermal cells. The exoskeleton
is further strengthened by the addition ofcalcium carbonate and organisms such as the lobster.
(04:30):
Because the exoskeleton is a cellular,arthropods must periodically shed their exoskeletons as
they grow, because the exoskeleton doesnot grow as the organism grows. Photo
shows a crab with orange legs anda black body crawling on a tree.
Muscles attached to the exoskeleton of thehalloween crab Jeckosinus quadratus allow it to move.
(04:51):
Endoskeleton. An endoskeleton is a skeletonthat consists of hard, mineralized structures
located within the soft tissue of organisms. The bones of vertebrates are composed of
tissues and mineralized tissues. Endoskeletons providesupport for the body, protect internal organs,
and allow for movement through contraction ofmuscles attached to the skeleton. Photo
(05:15):
shows a human skeleton riding a buckinghorse skeleton. The skeletons of humans and
horses are examples of endoskeletons. CreditRoss Murphy as an example. The human
skeleton is an endoskeleton that consists oftwo hundred and six bones in the adult.
It has five main functions, providingsupport to the body, storing minerals
(05:36):
and lipids, producing blood cells,protecting internal organs, and allowing for movement.
The skeletal system invertebrates is divided intothe axial skeleton, which consists of
the skull, vertebral column, andrib cage, and the appendicular skeleton,
which consists of the shoulders, limbbones, the pectoral girdle and the pelvic
(05:56):
girdle. Main divisions of the vertebrateskeleton on a human skeleton. The parts
of the axial skeleton are highlighted.The axial skeleton of humans consists of the
bones of the skull, ossicles ofthe middle ear, highway bone, vertebra
column, and rib cage. Creditmodification of work by Marianna Ruiz Viarel.
(06:17):
Illustration shows the appendicular skeleton, whichconsists of arms, legs, shoulder bones,
and the pelvic girdle. The humanappendicular skeleton is composed of the bones
of the pectoral limbs, arm,forearm, hand, the pelvic limbs,
thigh, leg, foot, thepectoral girdle, and the pelvic girdle.
Credit modification of work by Marianna Ruisviaraal. Evolution of body design for locomotion
(06:44):
on land. The transition of vertebratesfrom fish ancestors to land dwelling animals required
a number of changes in body design, since movement on land poses challenges that
are different from those posed by movementin water. Water provides a certain amount
of lift, which is on land, so mussels are needed to provide that
lift on land. It also providesa medium to push against, and many
(07:06):
fish use lateral undulations to push againstthe water and generate forward movement. Air
does not provide the same resistance,and so lateral undulations on land would not
produce much movement forward. As certainfish began to move on to land,
they retained their lateral undulation form oflocomotion. However, instead of pushing against
(07:28):
water, their fins became points ofcontact with the ground and the lateral undulations
became rotations about those points of contact. The lack of buoyancy provided by water
led to increased ossification of the bonesand strengthening of the mussels, as well
as providing selective pressure that resulted inchanges in arrangement of the wrist bones of
these early tetrapods. The effect ofgravity also led to changes in the axial
(07:50):
skeleton, since rotations around the contactpoints with the ground caused new torsional strains
on the vertebra column. A firmermore also fied vertebral column became common in
land animals because it reduces the strainand also provides strength to support the weight
of the body. In later tetrapods, the vertebrie began allowing for vertical rather
(08:11):
than lateral flexing. The vertebrae ofthe neck also evolved to allow movement of
the head independently of the body,a range of motion not found in fish.
In early terrestrial tetrapods, link thelimbs were splayed out to the side,
reflecting the position of the fins intheir fishy ancestors. This resulted in
a form of motion that was similarto performing push ups while walking, which
(08:33):
requires large muscles to move the limbstoward the midline. This is not an
efficient form of locomotion, and selectivepressure soon led to a configuration where the
limbs were placed underneath the body sothat each stripe requires less energy to move
the animal forward. The rotation aroundthe point of contact became a motion that
is more like a pendulum when thelimbs are underneath the body, producing a
(08:56):
stripe that was much more efficient formovement over land. Additional changes were required
in the appendicular skeleton to accommodate thenew ranges of motion that were enabled by
that limb placement muscles. Muscle cellsare specialized for contraction. Muscles allow for
emotions such as walking, and theyalso facilitate bodily processes such as respiration and
(09:18):
digestion. The body contains three typesof muscle tissue, skeletal muscle, cardiac
muscle, and smooth muscle. FigureThe skeletal muscle cells are long and arranged
in parallel bands that give the appearanceof striations. Each cell has a multiple
nuclei. Smooth muscle cells have nostriations and only one nuclei pre cell.
(09:41):
Cardiac muscles are striated but have onlyone nucleus. The body contains three types
of muscle tissue, skeletal muscle,smooth muscle, and cardiac muscle. Visualized
here using light microscopy. Smooth musclecells are short, tapered at each end
and have only one plump nucleus ineach Cardiac muscle cells are branched and striated
(10:03):
but short. The cytoplasm may branch, and they have one nucleus in the
center of the cell. Credit modificationof work by NZI NIH scale bar data
from Matt Russell Skeletal muscle tissue forms. Skeletal muscles which attached to bones or
skin, and control locomotion in anymovement that can be consciously controlled. Because
(10:24):
it can be controlled by thought,skeletal muscle is also called voluntary muscle.
Skeletal muscles are long and cylindrical inappearance. When viewed under a microscope,
skeletal muscle tissue has a striped orstriated appearance. The striations are caused by
the regular arrangement of contractile proteins actinand myocin. Actin is a globular contractile
(10:46):
protein that interacts with myocin from musclecontraction. Skeletal muscle cells form by fusion
of many muscle cells called myoblasts,and thus of multiple nuclei present in a
single cell. Smooth muscle tissue occursin the walls of hollow organs such as
the intestines, stomach, and urinarybladder, and around passages such as the
(11:07):
respiratory tract and blood vessels. Smoothmuscle has no striations, is not under
voluntary control as only one nucleus purcellis tapered at both ends, and is
also called involuntary muscle. Cardiac muscletissue is only found in the heart and
cardiac contractions pump blood throughout the bodyand maintain blood pressure. Like skeletal muscle,
(11:28):
cardiac muscle is striated, but unlikeskeletal muscle, cardiac muscle cannot be
consciously controlled and is called involuntary muscle. It has one nucleus. Purcell is
branched and is distinguished by the presenceof intercolated disks. Intercolated discs are ion
permeable junctions between individual cardiac muscle cells, which allow for synchronized contractions of the
(11:50):
various regions of the heart. Skeletalmuscle fiber structure. Each skeletal muscle fiber
is a skeletal muscle cell. Thesecells are incredibly large, with diameters of
up to one hundred m and lengthsof up to thirty centimeters. The plasma
membrane of a skeletal muscle fiber iscalled the sarcilemma. The sarcilemma is the
(12:13):
site of action potential conduction, whichtriggers muscle contraction. Within each muscle fiber
are myofibrils, long cylindrical structures thatlie parallel to the muscle fiber. Myofibrils
run the entire length of the musclefiber, and because they are only approximately
one point two m in diameter,hundreds to thousands can be found inside one
(12:33):
muscle fiber. They attach to thesarcilemma at their ends, so that as
myofibrils shorten, the entire muscle cellcontracts. Figure illustration shows a long tubular
skeletal muscle cell that runs the lengthof a muscle fiber. Bundles of fibers
called myofibrils run the length of thecell. The myiofibrils have a banded appearance.
(12:56):
A skeletal muscle cell is surrounded bya plasma membrane called the sarcolemma,
with a cytoplasm called the sarcoplasm.A muscle fiber is composed of many fibrils
packaged into orderly units. The striatedappearance of skeletal muscle tissue is a result
of repeating bands of the proteinsactin andmyacin that are present along the length of
myofibrils. Darkie bands and light eyebandsrepeat along myafibrils, and the alignment of
(13:22):
myafibrils in the cell causes the entirecell to appear striated or banded. Each
eyband has a dense line running verticallythrough the middle, called a Z disc
or Z line. The z disksmark the border of units called sarkimares,
which are the functional units of skeletalmuscle. One sarkimare is the space between
two consecutive Z discs and contains oneentire A band and two house of an
(13:45):
eyeband one on either side of theA band. A myiafibril is composed of
many sarkimares running along its length,and as the sarkimares individually contract, the
maafibrils and muscle cells shorten. Figureillustration shows part of a tubular myofibril,
which consists of many sarcimares. Zigzagging lines called Z lines, run perpendicular
(14:07):
to the fiber. Each sarcimare startsat one Z line and ends at the
next. A straight perpendicular line calledan M line, exists halfway between each
Z line. Thick filaments extend outfrom the M lines parallel to the length
of the myofibril. Thin filaments extendfrom the Z lines and extend into the
(14:28):
space between the thick filaments. Asarkimare is the region from one Z line
to the next C line. Manysarkimares are present in a myofibril, resulting
in the striation pattern characteristic of skeletalmuscle. Myofibrils are composed of smaller structures
called myofilaments. There are two maintypes of filaments, thick filaments and thin
(14:50):
filaments. Each has different compositions andlocations. Thick filaments occur only in the
A band of a myofibral. Thinfilam moments attached to a protein and the
Z disc called alphactinin, and occuracross the entire length of the iband and
part way into the A band.The region at which thick and thin filaments
overlap has a dense appearance as thereis little space between the filaments. Thin
(15:15):
filaments do not extend all the wayinto the A bands, leaving a central
region of the A band that onlycontains thick filaments. This central region of
the A band looks slightly lighter thanthe rest of the A band and is
called the H zone. The middleof the H zone has a vertical line
called the M line, at whichaccessory proteins hold together thick filaments. Both
(15:35):
the Z disc and the M linehold myofilaments in place to maintain the structural
arrangement and layering of the myofibril.Myofibrils are connected to each other by intermediate
or desmin filaments that attached to theZ disk. Thick and thin filaments are
themselves composed of proteins. Thick filamentsare primarily composed of the protein miacin.
(15:58):
The tail of a myacin molecule connectswith other myacin molecules to form the central
region of a thick filament near theM line, whereas the heads aligne on
either side of the thick filament wherethe thin filaments overlap. The primary component
of thin filaments is the actin protein. Two other components of the thin filament
are tropomyacin and tropinin. Actin hasbinding sites for myacin attachment. Strands of
(16:23):
tropomycin block the binding sites and preventactin myycin interactions when the muscles are at
rest. Troponin consists of three globularsubunits. One subunit binds to tropomyacin,
one subunit binds to actin, andone subunit bind c A two plus ions
sliding filament model of contraction for amuscle cell to contract, The sarcimare must
(16:48):
shorten. However, individual thick andthin filaments. The components of sarcimeres do
not shorten. Instead, they slideby one another, causing the sarcimare to
shorten while the filaments remain the samelength. The sliding filament theory of muscle
contraction was developed to explain the differencesobserved in the lengths of the named bands
on the sarkimare at different degrees ofmuscle contraction and relaxation. The mechanism of
(17:12):
contraction is the binding of mycin toactin forming cross bridges that generate filament movement.
Figure Part of the illustration shows arelaxed muscle fiber. Two zig zagging
Z lines extend from top to bottom. Thin actin filaments extend left and right
from each Z line. Between thez lines is a vertical M line.
(17:36):
Thick mycin filaments extend left and rightfrom the M line. The thick and
thin filaments partially overlap. The Aband represents the length that the thick filaments
extend from both sides of the Mline. The I band represents the part
of the thin filaments that does notoverlap with the thick filaments. Part beach
shows a contracted muscle fiber. Inthe contract fiber, the thick and thin
(18:00):
filaments completely overlap. The A bandis the same length as an uncontracted muscle,
but the iband has shrunken to thewidth of the Z line. When
a a sarkimare b contracts, theZ lines move closer together and the iband
gets smaller. The A band staysthe same width, and at full contraction,
(18:21):
the thin filaments overlap. When asarkimare shortens, some regions shorten,
whereas others stay the same length.A sarkimare is defined as the distance between
two consecutive Z discs or Z lines. When a muscle contracts, the distance
between the Z disks is reduced.The H zone, the central region of
the A zone, contains only thickfilaments and is shortened during contraction. The
(18:45):
iband contains only thin filaments and alsoshortens. The A band does not shorten.
It remains the same length, butA bands of different sarkimeres move closer
together during contraction, eventually disappearing.Thin film elements are pulled by the thick
filaments towards the center of the sarcimareuntil the Z discs approach the thick filaments.
(19:06):
The zone of overlap in which thinfilaments and thick filaments occupy the same
area increases as the thin filaments moveinward. ATP and muscle contraction. The
motion of muscle shortening occurs as myiacinheads bind to actin and pull the actin
inwards. This action requires energy,which is provided by ATP. Myasin binds
(19:27):
to actin at a binding site onthe globular actin protein. Myiasin has another
binding site for ATP and acts asan enzyme to convert ATP to ADP,
releasing an inorganic phosphate molecule and energy. The energy can be harnessed to promote
contraction via the sliding filament mechanism describedabove. ATP binding causes myosin to release
(19:51):
actin, allowing actin and myacin todetach from each other. After this happens,
the newly bound ATP is converted toADP and inorganic phosphate PI. The
enzyme at the binding site on myosinis called ATPAS. The energy released during
ATP hydrolysis changes the angle of themyiasin head into a copped position. The
(20:12):
myiasin head is then in a positionfor further movement, possessing potential energy,
but ADP and PIE are still attached. If actin binding sites are covered and
unavailable, the myiosin will remain inthe high energy configuration, with ADP hydrolyzed
but still attached. If the actinbinding sites are uncovered, a cross bridge
(20:32):
will form. That is, themyiasin head spans the distance between the actin
and myosin molecules Pi is then released, allowing myosin to expend the stored energy.
As a conformational change, the myiosinhead moves toward the M line,
pulling the actin along with it.As the actin is pulled, the filaments
move approximately ten nanometers towards the Mline. This movement is called the power
(20:56):
stroke as it is the step atwhich forces produced. As the actin is
pulled toward the m line, thesarkimere shortens and the muscle contracts. When
the myiasin head is cocked, itcontains energy and is in a high energy
configuration. This energy is expended asthe myiacin head moves through the power stroke.
At the end of the power stroke, the myiasin head is in a
(21:18):
low energy position. After the powerstroke ADP is released. However, the
CrossBridge formed is still in place andactin and myacin are bound together. ADP
can then attach to myacin, whichallows the CrossBridge cycle to start again and
further muscle contraction can occur. Figureillustration shows two actin filaments coiled with tropomyacin
(21:41):
in a helix sitting beside a myiasinfilament. Each actin filament is made of
round actin subunits linked in a chain. A bulbous myiacin head with ADP and
pie attached sticks up from the myosinfilament. The contraction cycle begins when calcium
binds to the actin filament, allowingthe mya and head to from a cross
bridge. During the power stroke,the myacin headbands and ADP and phosphate are
(22:06):
released. As a result, theactin filament moves relative to the myosin filament.
A new molecule of ATP binds tothe myacin head, causing it to
detach. The ATP hydrolyzes to ADPand pie, returning the myocin head to
the cop position. The CrossBridge musclecontraction cycle, which is triggered by c
(22:26):
A two plus binding to The actinactive site is shown. With each contraction
cycle, actin moves relative to myocin, and the thick and thin filament slide
past each other. Regulatory proteins.When a muscle is in a resting state,
actin and myocin are separated to keepactin from binding to the active site
(22:47):
on myosin. Regulatory proteins block themolecular binding sites. Tropomyacin blocks myyocin binding
sites on actin molecules, preventing CrossBridgeformation and preventing contraction in a muscle without
nervous input. Tropinin binds to tropomyacinand helps to position it on the actin
molecule. It also binds calcium ions. To enable a muscle contraction, tropomyacin
(23:11):
must change conformation, uncovering the myisinbinding site on an actin molecule and allowing
cross bridge formation. This can onlyhappen in the presence of calcium, which
is kept at extremely low concentrations inthe sarcoplasm. If present, calciumyens bind
to tropinin, causing conformational changes introponin that allow tropomyacin to move away from
(23:33):
the myiocin binding sites on actin.Once the tropomyacin is removed, a cross
bridge can form between actin and myacin, triggering contraction. CrossBridge cycling continues until
c A two plus ions and ADPare no longer available in tropomyacin again covers
the binding sites on actin. Excitationcontraction coupling. Excitation contraction coupling is the
(23:56):
link transduction between the action potentill generatedin the sarcilemma and the start of a
muscle contraction. The trigger for calciumrelease from the sarcoplasmic reticulum into the sarcoplasm
is a neural signal. Each skeletalmuscle fiber is controlled by a motor neuron,
which conducts signals from the brain orspinal cord to the muscle. The
(24:18):
area of the sarca lemma on themuscle fiber that interacts with the neuron is
called the motor end plate. Theend of the neurons axon is called the
synaptic terminal, and it does notactually contact the motor end plate. A
small space called the synaptic cleft separatesthe synaptic terminal from the motor end plate.
Electrical signals travel along the neuron's axon, which branches through the muscle and
(24:41):
connects to individual muscle fibers at aneuromuscular junction. This junction is functionally similar
to a synapse between two nerve cells, allowing a signal from the nerve cell
to initiate an action potential in themuscle plasma membrane. The action potential in
the muscle cell causes C A plusplus to be released from intracellular stores.
This elevated calcium concentration triggers the bindingof actin and miacin atp hyrolysis, and
(25:07):
all of the other steps in contractionthat are outlined above. The neurotransmitter released
at the neuromuscular junction in most animalsis acetylcholine. It is released from the
nerve call ending and binds to receptorson the muscle cell plasma membrane figure.
These receptors act as sodium channels whenacetyl coline is bound to them. The
influx of sodium depolarizes the muscle cell, triggering an action potential in a similar
(25:33):
fashion to the action potential found innerve cells. The acetyl coline is rapidly
degraded in the neuromuscular junction by anenzyme called acetylcholinesterase. Various natural toxins,
such as the corrari used on poisonarrows by South American indigenous tribes, and
synthetic toxins, including nerve gases andinsecticides, target the components of the neuromuscular
(25:55):
junction, including both the receptor andthe acetylcholinesterase. The deadly nerve gas known
as serin irreversibly inhibits acetyl coolinesterase.What effect would serin have on muscle contraction
and how does that effect lead todeath? There are four steps in the
start of a muscle contraction. Stepone, acetyl coline, released from synaptic
(26:17):
vesicles in the axon terminal, bindsto receptors on the muscle cell plasma membrane.
Step two, an action potential isinitiated that travels down the t tubule.
Step three, calcium ions are releasedfrom the sarcoplasmic reticulum in response to
the change in voltage. Step four, calciumyons bind to tropinin exposing active sites
(26:38):
on actin. Cross bridge formation occurs, and muscles contract. Three additional steps
are part of the end of amuscle contraction. Step five, acetyl coline
is removed from the synaptic cleft byacetyl coolinesterase. Step six, calciumyons are
transported back into the sarcoplasmic reticulum.Step seven, tropomycin covers active sites on
(27:03):
actin preventing cross bridge formation, sothe muscle contraction ends acetylcholine effects at the
neuromuscular junction. The depolarization of themuscle plasma membrane releases calcium from the sarcoplasmic
reticulum and initiates contraction of the muscle. This podcast will be released episodically and
(27:25):
follow the sections of the text bookin the description. For a deeper understanding,
we encourage you review the text versionof this work voice by voicemaker Dotayne.
This was produced by Brandon Casturo asa creative Common Sense production.
Welcome to Principles of Biology. Thisbook was written by the Open Alternative Textbook
Initiative at Kansas State University and isbeing released as a podcast and distributed under
the terms of the Creative Commons AttributionLicense. Today's episode is Chapter twenty nine
point one musculo Skeletal system. Allhyperlinks, images and sources can be found
(00:22):
at the link to the book.In the description of all the constituents of
the human body, bone is thehardest, the driest, the earthiest,
and the coldest, And excepting onlythe teeth, it is devoid of sensation.
God, the great creator of allthings, formed its substance to this
specification with good reason, intending itto be like a foundation for the whole
(00:43):
body. For at the fabric ofthe human body, bones perform the same
function as de walls and beams andhouses, pulls in tents and keels,
and ribs and boats. Andreas Visalius, Flemish anatomist into Humani's Corporus Fabrica,
fifteen forty three. As the Saliusrecognized long ago, the muscular and skeletal
systems provide support to the body andallow for a wide range of movement.
(01:06):
The bones of the skeletal system protectthe body's internal organs and support the weight
of the body. The muscles ofthe muscular system can tract and pull on
the bones, allowing for movements asdiverse as standing, walking, running,
and grasping items. Injury or diseaseaffecting the musculo skeletal system can be very
debilitating in humans. The most commonmusculoskeletal diseases worldwide are caused by malnutrition.
(01:33):
Ailments that affect the joints are alsowidespread, such as arthritis, which can
make movement difficult and in advanced casescompletely impair mobility. Types of skeletal systems.
A skeletal system is necessary to supportthe body, protect internal organs,
and allow for the movement of anorganism. There are three different skeleton designs
(01:53):
that fulfill these functions, hydrostatic skeleton, exoskeleton, and endoskeleton. Hydrostatic skeleton
a hydrostatic skeleton is a skeleton formedby a fluid filled compartment within the body
called the salum. The organs ofthe salum are supported by the aqueous fluid,
which also resists external compression. Thiscompartment is under hydrostatic pressure because of
(02:17):
the fluid and supports the other organsof the organism. This type of skeletal
system is found in soft bodied animalssuch as sea anemones, earthworms, Nyderia,
and other invertebrates. Figure photo showsa white sea star with red bumps
along the tops and tips of itsarms. The skeleton of the red knobbed
(02:38):
seastar Pretoristerlnchia is an example of ahydrostatic skeleton. Credit a mod of forty
four slash Wikimedia Commons. Movement ina hydrostatic skeleton is provided by muscles that
surround the sealum. The muscles ina hydrostatic skeleton contract to change the shape
of the salum. The pressure ofthe fluid in the salum produces movement.
(03:00):
For example, earthworms move by wavesof muscular contractions of the skeletal muscle of
the body. Wall. Hydrostatic skeletoncalled peristalsis which alternately shorten and lengthen the
body. Lengthening the body extends theanterior end of the organism. Most organisms
have a mechanism to fix themselves inthe substrate. Shortening the muscles then draws
(03:22):
the posterior portion of the body forward. Although a hydrostatic skeleton is well suited
to invertebrate organisms such as earthworms andsome aquatic organisms, It is not an
efficient skeleton for terrestrial animals. Exoskeletonan exoskeleton is a chinness external skeleton that
consists of a hard encasement on thesurface of an organism. For example,
(03:45):
the shells of crabs and insects areexoskeletons. Figure. This skeleton type provides
defense against predators, supports the body, and allows for movement through the contraction
of attached muscles. As with endoskeletonssee below, muscles must cross a joint
inside the exoskeleton. Shortening of themuscle thus changes the relationship of the two
(04:06):
segments of the exoskeleton. Arthropods suchas crabs and lobsters have exoskeletons that consist
of thirty to fifty percent keton,a polysaccharide derivative of glucose that is a
strong but flexible material. Keton issecreted by the epidermal cells. The exoskeleton
is further strengthened by the addition ofcalcium carbonate and organisms such as the lobster.
(04:30):
Because the exoskeleton is a cellular,arthropods must periodically shed their exoskeletons as
they grow, because the exoskeleton doesnot grow as the organism grows. Photo
shows a crab with orange legs anda black body crawling on a tree.
Muscles attached to the exoskeleton of thehalloween crab Jeckosinus quadratus allow it to move.
(04:51):
Endoskeleton. An endoskeleton is a skeletonthat consists of hard, mineralized structures
located within the soft tissue of organisms. The bones of vertebrates are composed of
tissues and mineralized tissues. Endoskeletons providesupport for the body, protect internal organs,
and allow for movement through contraction ofmuscles attached to the skeleton. Photo
(05:15):
shows a human skeleton riding a buckinghorse skeleton. The skeletons of humans and
horses are examples of endoskeletons. CreditRoss Murphy as an example. The human
skeleton is an endoskeleton that consists oftwo hundred and six bones in the adult.
It has five main functions, providingsupport to the body, storing minerals
(05:36):
and lipids, producing blood cells,protecting internal organs, and allowing for movement.
The skeletal system invertebrates is divided intothe axial skeleton, which consists of
the skull, vertebral column, andrib cage, and the appendicular skeleton,
which consists of the shoulders, limbbones, the pectoral girdle and the pelvic
(05:56):
girdle. Main divisions of the vertebrateskeleton on a human skeleton. The parts
of the axial skeleton are highlighted.The axial skeleton of humans consists of the
bones of the skull, ossicles ofthe middle ear, highway bone, vertebra
column, and rib cage. Creditmodification of work by Marianna Ruiz Viarel.
(06:17):
Illustration shows the appendicular skeleton, whichconsists of arms, legs, shoulder bones,
and the pelvic girdle. The humanappendicular skeleton is composed of the bones
of the pectoral limbs, arm,forearm, hand, the pelvic limbs,
thigh, leg, foot, thepectoral girdle, and the pelvic girdle.
Credit modification of work by Marianna Ruisviaraal. Evolution of body design for locomotion
(06:44):
on land. The transition of vertebratesfrom fish ancestors to land dwelling animals required
a number of changes in body design, since movement on land poses challenges that
are different from those posed by movementin water. Water provides a certain amount
of lift, which is on land, so mussels are needed to provide that
lift on land. It also providesa medium to push against, and many
(07:06):
fish use lateral undulations to push againstthe water and generate forward movement. Air
does not provide the same resistance,and so lateral undulations on land would not
produce much movement forward. As certainfish began to move on to land,
they retained their lateral undulation form oflocomotion. However, instead of pushing against
(07:28):
water, their fins became points ofcontact with the ground and the lateral undulations
became rotations about those points of contact. The lack of buoyancy provided by water
led to increased ossification of the bonesand strengthening of the mussels, as well
as providing selective pressure that resulted inchanges in arrangement of the wrist bones of
these early tetrapods. The effect ofgravity also led to changes in the axial
(07:50):
skeleton, since rotations around the contactpoints with the ground caused new torsional strains
on the vertebra column. A firmermore also fied vertebral column became common in
land animals because it reduces the strainand also provides strength to support the weight
of the body. In later tetrapods, the vertebrie began allowing for vertical rather
(08:11):
than lateral flexing. The vertebrae ofthe neck also evolved to allow movement of
the head independently of the body,a range of motion not found in fish.
In early terrestrial tetrapods, link thelimbs were splayed out to the side,
reflecting the position of the fins intheir fishy ancestors. This resulted in
a form of motion that was similarto performing push ups while walking, which
(08:33):
requires large muscles to move the limbstoward the midline. This is not an
efficient form of locomotion, and selectivepressure soon led to a configuration where the
limbs were placed underneath the body sothat each stripe requires less energy to move
the animal forward. The rotation aroundthe point of contact became a motion that
is more like a pendulum when thelimbs are underneath the body, producing a
(08:56):
stripe that was much more efficient formovement over land. Additional changes were required
in the appendicular skeleton to accommodate thenew ranges of motion that were enabled by
that limb placement muscles. Muscle cellsare specialized for contraction. Muscles allow for
emotions such as walking, and theyalso facilitate bodily processes such as respiration and
(09:18):
digestion. The body contains three typesof muscle tissue, skeletal muscle, cardiac
muscle, and smooth muscle. FigureThe skeletal muscle cells are long and arranged
in parallel bands that give the appearanceof striations. Each cell has a multiple
nuclei. Smooth muscle cells have nostriations and only one nuclei pre cell.
(09:41):
Cardiac muscles are striated but have onlyone nucleus. The body contains three types
of muscle tissue, skeletal muscle,smooth muscle, and cardiac muscle. Visualized
here using light microscopy. Smooth musclecells are short, tapered at each end
and have only one plump nucleus ineach Cardiac muscle cells are branched and striated
(10:03):
but short. The cytoplasm may branch, and they have one nucleus in the
center of the cell. Credit modificationof work by NZI NIH scale bar data
from Matt Russell Skeletal muscle tissue forms. Skeletal muscles which attached to bones or
skin, and control locomotion in anymovement that can be consciously controlled. Because
(10:24):
it can be controlled by thought,skeletal muscle is also called voluntary muscle.
Skeletal muscles are long and cylindrical inappearance. When viewed under a microscope,
skeletal muscle tissue has a striped orstriated appearance. The striations are caused by
the regular arrangement of contractile proteins actinand myocin. Actin is a globular contractile
(10:46):
protein that interacts with myocin from musclecontraction. Skeletal muscle cells form by fusion
of many muscle cells called myoblasts,and thus of multiple nuclei present in a
single cell. Smooth muscle tissue occursin the walls of hollow organs such as
the intestines, stomach, and urinarybladder, and around passages such as the
(11:07):
respiratory tract and blood vessels. Smoothmuscle has no striations, is not under
voluntary control as only one nucleus purcellis tapered at both ends, and is
also called involuntary muscle. Cardiac muscletissue is only found in the heart and
cardiac contractions pump blood throughout the bodyand maintain blood pressure. Like skeletal muscle,
(11:28):
cardiac muscle is striated, but unlikeskeletal muscle, cardiac muscle cannot be
consciously controlled and is called involuntary muscle. It has one nucleus. Purcell is
branched and is distinguished by the presenceof intercolated disks. Intercolated discs are ion
permeable junctions between individual cardiac muscle cells, which allow for synchronized contractions of the
(11:50):
various regions of the heart. Skeletalmuscle fiber structure. Each skeletal muscle fiber
is a skeletal muscle cell. Thesecells are incredibly large, with diameters of
up to one hundred m and lengthsof up to thirty centimeters. The plasma
membrane of a skeletal muscle fiber iscalled the sarcilemma. The sarcilemma is the
(12:13):
site of action potential conduction, whichtriggers muscle contraction. Within each muscle fiber
are myofibrils, long cylindrical structures thatlie parallel to the muscle fiber. Myofibrils
run the entire length of the musclefiber, and because they are only approximately
one point two m in diameter,hundreds to thousands can be found inside one
(12:33):
muscle fiber. They attach to thesarcilemma at their ends, so that as
myofibrils shorten, the entire muscle cellcontracts. Figure illustration shows a long tubular
skeletal muscle cell that runs the lengthof a muscle fiber. Bundles of fibers
called myofibrils run the length of thecell. The myiofibrils have a banded appearance.
(12:56):
A skeletal muscle cell is surrounded bya plasma membrane called the sarcolemma,
with a cytoplasm called the sarcoplasm.A muscle fiber is composed of many fibrils
packaged into orderly units. The striatedappearance of skeletal muscle tissue is a result
of repeating bands of the proteinsactin andmyacin that are present along the length of
myofibrils. Darkie bands and light eyebandsrepeat along myafibrils, and the alignment of
(13:22):
myafibrils in the cell causes the entirecell to appear striated or banded. Each
eyband has a dense line running verticallythrough the middle, called a Z disc
or Z line. The z disksmark the border of units called sarkimares,
which are the functional units of skeletalmuscle. One sarkimare is the space between
two consecutive Z discs and contains oneentire A band and two house of an
(13:45):
eyeband one on either side of theA band. A myiafibril is composed of
many sarkimares running along its length,and as the sarkimares individually contract, the
maafibrils and muscle cells shorten. Figureillustration shows part of a tubular myofibril,
which consists of many sarcimares. Zigzagging lines called Z lines, run perpendicular
(14:07):
to the fiber. Each sarcimare startsat one Z line and ends at the
next. A straight perpendicular line calledan M line, exists halfway between each
Z line. Thick filaments extend outfrom the M lines parallel to the length
of the myofibril. Thin filaments extendfrom the Z lines and extend into the
(14:28):
space between the thick filaments. Asarkimare is the region from one Z line
to the next C line. Manysarkimares are present in a myofibril, resulting
in the striation pattern characteristic of skeletalmuscle. Myofibrils are composed of smaller structures
called myofilaments. There are two maintypes of filaments, thick filaments and thin
(14:50):
filaments. Each has different compositions andlocations. Thick filaments occur only in the
A band of a myofibral. Thinfilam moments attached to a protein and the
Z disc called alphactinin, and occuracross the entire length of the iband and
part way into the A band.The region at which thick and thin filaments
overlap has a dense appearance as thereis little space between the filaments. Thin
(15:15):
filaments do not extend all the wayinto the A bands, leaving a central
region of the A band that onlycontains thick filaments. This central region of
the A band looks slightly lighter thanthe rest of the A band and is
called the H zone. The middleof the H zone has a vertical line
called the M line, at whichaccessory proteins hold together thick filaments. Both
(15:35):
the Z disc and the M linehold myofilaments in place to maintain the structural
arrangement and layering of the myofibril.Myofibrils are connected to each other by intermediate
or desmin filaments that attached to theZ disk. Thick and thin filaments are
themselves composed of proteins. Thick filamentsare primarily composed of the protein miacin.
(15:58):
The tail of a myacin molecule connectswith other myacin molecules to form the central
region of a thick filament near theM line, whereas the heads aligne on
either side of the thick filament wherethe thin filaments overlap. The primary component
of thin filaments is the actin protein. Two other components of the thin filament
are tropomyacin and tropinin. Actin hasbinding sites for myacin attachment. Strands of
(16:23):
tropomycin block the binding sites and preventactin myycin interactions when the muscles are at
rest. Troponin consists of three globularsubunits. One subunit binds to tropomyacin,
one subunit binds to actin, andone subunit bind c A two plus ions
sliding filament model of contraction for amuscle cell to contract, The sarcimare must
(16:48):
shorten. However, individual thick andthin filaments. The components of sarcimeres do
not shorten. Instead, they slideby one another, causing the sarcimare to
shorten while the filaments remain the samelength. The sliding filament theory of muscle
contraction was developed to explain the differencesobserved in the lengths of the named bands
on the sarkimare at different degrees ofmuscle contraction and relaxation. The mechanism of
(17:12):
contraction is the binding of mycin toactin forming cross bridges that generate filament movement.
Figure Part of the illustration shows arelaxed muscle fiber. Two zig zagging
Z lines extend from top to bottom. Thin actin filaments extend left and right
from each Z line. Between thez lines is a vertical M line.
(17:36):
Thick mycin filaments extend left and rightfrom the M line. The thick and
thin filaments partially overlap. The Aband represents the length that the thick filaments
extend from both sides of the Mline. The I band represents the part
of the thin filaments that does notoverlap with the thick filaments. Part beach
shows a contracted muscle fiber. Inthe contract fiber, the thick and thin
(18:00):
filaments completely overlap. The A bandis the same length as an uncontracted muscle,
but the iband has shrunken to thewidth of the Z line. When
a a sarkimare b contracts, theZ lines move closer together and the iband
gets smaller. The A band staysthe same width, and at full contraction,
(18:21):
the thin filaments overlap. When asarkimare shortens, some regions shorten,
whereas others stay the same length.A sarkimare is defined as the distance between
two consecutive Z discs or Z lines. When a muscle contracts, the distance
between the Z disks is reduced.The H zone, the central region of
the A zone, contains only thickfilaments and is shortened during contraction. The
(18:45):
iband contains only thin filaments and alsoshortens. The A band does not shorten.
It remains the same length, butA bands of different sarkimeres move closer
together during contraction, eventually disappearing.Thin film elements are pulled by the thick
filaments towards the center of the sarcimareuntil the Z discs approach the thick filaments.
(19:06):
The zone of overlap in which thinfilaments and thick filaments occupy the same
area increases as the thin filaments moveinward. ATP and muscle contraction. The
motion of muscle shortening occurs as myiacinheads bind to actin and pull the actin
inwards. This action requires energy,which is provided by ATP. Myasin binds
(19:27):
to actin at a binding site onthe globular actin protein. Myiasin has another
binding site for ATP and acts asan enzyme to convert ATP to ADP,
releasing an inorganic phosphate molecule and energy. The energy can be harnessed to promote
contraction via the sliding filament mechanism describedabove. ATP binding causes myosin to release
(19:51):
actin, allowing actin and myacin todetach from each other. After this happens,
the newly bound ATP is converted toADP and inorganic phosphate PI. The
enzyme at the binding site on myosinis called ATPAS. The energy released during
ATP hydrolysis changes the angle of themyiasin head into a copped position. The
(20:12):
myiasin head is then in a positionfor further movement, possessing potential energy,
but ADP and PIE are still attached. If actin binding sites are covered and
unavailable, the myiosin will remain inthe high energy configuration, with ADP hydrolyzed
but still attached. If the actinbinding sites are uncovered, a cross bridge
(20:32):
will form. That is, themyiasin head spans the distance between the actin
and myosin molecules Pi is then released, allowing myosin to expend the stored energy.
As a conformational change, the myiosinhead moves toward the M line,
pulling the actin along with it.As the actin is pulled, the filaments
move approximately ten nanometers towards the Mline. This movement is called the power
(20:56):
stroke as it is the step atwhich forces produced. As the actin is
pulled toward the m line, thesarkimere shortens and the muscle contracts. When
the myiasin head is cocked, itcontains energy and is in a high energy
configuration. This energy is expended asthe myiacin head moves through the power stroke.
At the end of the power stroke, the myiasin head is in a
(21:18):
low energy position. After the powerstroke ADP is released. However, the
CrossBridge formed is still in place andactin and myacin are bound together. ADP
can then attach to myacin, whichallows the CrossBridge cycle to start again and
further muscle contraction can occur. Figureillustration shows two actin filaments coiled with tropomyacin
(21:41):
in a helix sitting beside a myiasinfilament. Each actin filament is made of
round actin subunits linked in a chain. A bulbous myiacin head with ADP and
pie attached sticks up from the myosinfilament. The contraction cycle begins when calcium
binds to the actin filament, allowingthe mya and head to from a cross
bridge. During the power stroke,the myacin headbands and ADP and phosphate are
(22:06):
released. As a result, theactin filament moves relative to the myosin filament.
A new molecule of ATP binds tothe myacin head, causing it to
detach. The ATP hydrolyzes to ADPand pie, returning the myocin head to
the cop position. The CrossBridge musclecontraction cycle, which is triggered by c
(22:26):
A two plus binding to The actinactive site is shown. With each contraction
cycle, actin moves relative to myocin, and the thick and thin filament slide
past each other. Regulatory proteins.When a muscle is in a resting state,
actin and myocin are separated to keepactin from binding to the active site
(22:47):
on myosin. Regulatory proteins block themolecular binding sites. Tropomyacin blocks myyocin binding
sites on actin molecules, preventing CrossBridgeformation and preventing contraction in a muscle without
nervous input. Tropinin binds to tropomyacinand helps to position it on the actin
molecule. It also binds calcium ions. To enable a muscle contraction, tropomyacin
(23:11):
must change conformation, uncovering the myisinbinding site on an actin molecule and allowing
cross bridge formation. This can onlyhappen in the presence of calcium, which
is kept at extremely low concentrations inthe sarcoplasm. If present, calciumyens bind
to tropinin, causing conformational changes introponin that allow tropomyacin to move away from
(23:33):
the myiocin binding sites on actin.Once the tropomyacin is removed, a cross
bridge can form between actin and myacin, triggering contraction. CrossBridge cycling continues until
c A two plus ions and ADPare no longer available in tropomyacin again covers
the binding sites on actin. Excitationcontraction coupling. Excitation contraction coupling is the
(23:56):
link transduction between the action potentill generatedin the sarcilemma and the start of a
muscle contraction. The trigger for calciumrelease from the sarcoplasmic reticulum into the sarcoplasm
is a neural signal. Each skeletalmuscle fiber is controlled by a motor neuron,
which conducts signals from the brain orspinal cord to the muscle. The
(24:18):
area of the sarca lemma on themuscle fiber that interacts with the neuron is
called the motor end plate. Theend of the neurons axon is called the
synaptic terminal, and it does notactually contact the motor end plate. A
small space called the synaptic cleft separatesthe synaptic terminal from the motor end plate.
Electrical signals travel along the neuron's axon, which branches through the muscle and
(24:41):
connects to individual muscle fibers at aneuromuscular junction. This junction is functionally similar
to a synapse between two nerve cells, allowing a signal from the nerve cell
to initiate an action potential in themuscle plasma membrane. The action potential in
the muscle cell causes C A plusplus to be released from intracellular stores.
This elevated calcium concentration triggers the bindingof actin and miacin atp hyrolysis, and
(25:07):
all of the other steps in contractionthat are outlined above. The neurotransmitter released
at the neuromuscular junction in most animalsis acetylcholine. It is released from the
nerve call ending and binds to receptorson the muscle cell plasma membrane figure.
These receptors act as sodium channels whenacetyl coline is bound to them. The
influx of sodium depolarizes the muscle cell, triggering an action potential in a similar
(25:33):
fashion to the action potential found innerve cells. The acetyl coline is rapidly
degraded in the neuromuscular junction by anenzyme called acetylcholinesterase. Various natural toxins,
such as the corrari used on poisonarrows by South American indigenous tribes, and
synthetic toxins, including nerve gases andinsecticides, target the components of the neuromuscular
(25:55):
junction, including both the receptor andthe acetylcholinesterase. The deadly nerve gas known
as serin irreversibly inhibits acetyl coolinesterase.What effect would serin have on muscle contraction
and how does that effect lead todeath? There are four steps in the
start of a muscle contraction. Stepone, acetyl coline, released from synaptic
(26:17):
vesicles in the axon terminal, bindsto receptors on the muscle cell plasma membrane.
Step two, an action potential isinitiated that travels down the t tubule.
Step three, calcium ions are releasedfrom the sarcoplasmic reticulum in response to
the change in voltage. Step four, calciumyons bind to tropinin exposing active sites
(26:38):
on actin. Cross bridge formation occurs, and muscles contract. Three additional steps
are part of the end of amuscle contraction. Step five, acetyl coline
is removed from the synaptic cleft byacetyl coolinesterase. Step six, calciumyons are
transported back into the sarcoplasmic reticulum.Step seven, tropomycin covers active sites on
(27:03):
actin preventing cross bridge formation, sothe muscle contraction ends acetylcholine effects at the
neuromuscular junction. The depolarization of themuscle plasma membrane releases calcium from the sarcoplasmic
reticulum and initiates contraction of the muscle. This podcast will be released episodically and
(27:25):
follow the sections of the text bookin the description. For a deeper understanding,
we encourage you review the text versionof this work voice by voicemaker Dotayne.
This was produced by Brandon Casturo asa creative Common Sense production.
Popular Podcasts
Stuff You Should Know
If you've ever wanted to know about champagne, satanism, the Stonewall Uprising, chaos theory, LSD, El Nino, true crime and Rosa Parks, then look no further. Josh and Chuck have you covered.
Dateline NBC
Current and classic episodes, featuring compelling true-crime mysteries, powerful documentaries and in-depth investigations. Follow now to get the latest episodes of Dateline NBC completely free, or subscribe to Dateline Premium for ad-free listening and exclusive bonus content: DatelinePremium.com
The Bobby Bones Show
Listen to 'The Bobby Bones Show' by downloading the daily full replay.