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Exam 2 Histology Notes - Dr. Mays
Histology (BIOL 4003)
Auburn University
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Exam 2 Histology Notes Module 5- Muscle Muscle-Introducion All muscle has cells that are opimized for contracility o All of these cells come from the mesoderm o Difereniate by process of cell lengthening o Contain myoibrillar proteins: Acin and myosin What is muscle? o Sarcoplasm - cytoplasm of muscle cells o Sarcoplasmic reiculum - smooth ER of muscle cells Serves as site of calcium storage and release during contracility o Sarcolemma – Plasmalemma (cell membrane) of muscle cells The sarcolemma in skeletal and cardiac muscle will form tubular projecions called transverse tubules that will extend into the sarcoplasm and be associated with the SR o Myoiber – a single muscle cell o In skeletal and cardiac only: Sarcomere: contracile unit Myoibril/myoilament: a string of sarcomeres Sarcosome: specialized long mitochondria Muscle terms: o Epimysium- thick collagenous connecive issue that surrounds large bundles of muscle There are several fascicles within the epimysium o Fascicle- bundles of muscle cells surrounded by their own connecive issue (the perimysium) o Perimysium- connecive issue surrounding the fascicles o Endomysium- coninuous with the perimysium and forms this very thin layer around each individual muscle iber Innermost layer Skeletal muscle o Striated muscle o Composed of muscle ibers Each muscle iber is a long cylindrical mulinucleated cell The nuclei will be present at the edge just under the sarcolemma The nuclei are elongated o Diameters range from 10-100 micrometers o The iber can be many cenimeters long o Can be found in the tongue, diaphragm, eyes, and upper esophagus o Signals are all or nothing Exam 2 Histology Notes Module 5- Muscle Muscle-Introducion All muscle has cells that are opimized for contracility o All of these cells come from the mesoderm o Difereniate by process of cell lengthening o Contain myoibrillar proteins: Acin and myosin What is muscle? o Sarcoplasm - cytoplasm of muscle cells o Sarcoplasmic reiculum - smooth ER of muscle cells Serves as site of calcium storage and release during contracility o Sarcolemma – Plasmalemma (cell membrane) of muscle cells The sarcolemma in skeletal and cardiac muscle will form tubular projecions called transverse tubules that will extend into the sarcoplasm and be associated with the SR o Myoiber – a single muscle cell o In skeletal and cardiac only: Sarcomere: contracile unit Myoibril/myoilament: a string of sarcomeres Sarcosome: specialized long mitochondria Muscle terms: o Epimysium- thick collagenous connecive issue that surrounds large bundles of muscle There are several fascicles within the epimysium o Fascicle- bundles of muscle cells surrounded by their own connecive issue (the perimysium) o Perimysium- connecive issue surrounding the fascicles o Endomysium- coninuous with the perimysium and forms this very thin layer around each individual muscle iber Innermost layer Skeletal muscle o Striated muscle o Composed of muscle ibers Each muscle iber is a long cylindrical mulinucleated cell The nuclei will be present at the edge just under the sarcolemma The nuclei are elongated o Diameters range from 10-100 micrometers o The iber can be many cenimeters long o Can be found in the tongue, diaphragm, eyes, and upper esophagus o Signals are all or nothing In order for skeletal muscle to funcion, it must contain a well-developed sarcoplasmic reiculum Contains organized sarcomeres We oten see it called striated muscle because of this organizaion o Embryologically, these ibers come from mesenchymal myoblasts which will fuse to form myotubes that contain muliple nuclei They will difereniate into striated muscle ibers Some of the cells will remain undifereniated These are called muscle satellite cells that are muscle progenitor cells that could become muscle cells later o Skeletal muscles typically respond to increased load by increasing iber size (called hypertrophy) o If there is a need for regeneraion, satellite cells could difereniate into muscle ibers o In this type of issue, regeneraion is limited Speciic pictures of skeletal muscle: o a) Epimysium at outer edge staining dark red, the endomysium around each muscle iber, and the perimysium dividing the fascicles o b) Special stain for laminin that shows the external laminae of the muscle ibers surrounded by the endomysium The brown is where the external laminae is o c) Myotendenous juncion- the connecive issue is coninuous with this tendon as we go into the muscle Diagram of T-tubules o This is a diagram of just one muscle cell Myoibrils o The sarcoplasmic reiculum contains pumps and other proteins for calcium sequestraion This surrounds the myoibrils in the network o T-tubules are extensions of the sarcolemma that are associated in a triad with two terminal cisternae of the SR The T-tubules will funcion in organizing contracion o Exam 2 Histology Notes Module 5- Muscle Muscle-Introducion All muscle has cells that are opimized for contracility o All of these cells come from the mesoderm o Difereniate by process of cell lengthening o Contain myoibrillar proteins: Acin and myosin What is muscle? o Sarcoplasm - cytoplasm of muscle cells o Sarcoplasmic reiculum - smooth ER of muscle cells Serves as site of calcium storage and release during contracility o Sarcolemma – Plasmalemma (cell membrane) of muscle cells The sarcolemma in skeletal and cardiac muscle will form tubular projecions called transverse tubules that will extend into the sarcoplasm and be associated with the SR o Myoiber – a single muscle cell o In skeletal and cardiac only: Sarcomere: contracile unit Myoibril/myoilament: a string of sarcomeres Sarcosome: specialized long mitochondria Muscle terms: o Epimysium- thick collagenous connecive issue that surrounds large bundles of muscle There are several fascicles within the epimysium o Fascicle- bundles of muscle cells surrounded by their own connecive issue (the perimysium) o Perimysium- connecive issue surrounding the fascicles o Endomysium- coninuous with the perimysium and forms this very thin layer around each individual muscle iber Innermost layer Skeletal muscle o Striated muscle o Composed of muscle ibers Each muscle iber is a long cylindrical mulinucleated cell The nuclei will be present at the edge just under the sarcolemma The nuclei are elongated o Diameters range from 10-100 micrometers o The iber can be many cenimeters long o Can be found in the tongue, diaphragm, eyes, and upper esophagus o Signals are all or nothing In order for skeletal muscle to funcion, it must contain a well-developed sarcoplasmic reiculum Contains organized sarcomeres We oten see it called striated muscle because of this organizaion o Embryologically, these ibers come from mesenchymal myoblasts which will fuse to form myotubes that contain muliple nuclei They will difereniate into striated muscle ibers Some of the cells will remain undifereniated These are called muscle satellite cells that are muscle progenitor cells that could become muscle cells later o Skeletal muscles typically respond to increased load by increasing iber size (called hypertrophy) o If there is a need for regeneraion, satellite cells could difereniate into muscle ibers o In this type of issue, regeneraion is limited Speciic pictures of skeletal muscle: o a) Epimysium at outer edge staining dark red, the endomysium around each muscle iber, and the perimysium dividing the fascicles o b) Special stain for laminin that shows the external laminae of the muscle ibers surrounded by the endomysium The brown is where the external laminae is o c) Myotendenous juncion- the connecive issue is coninuous with this tendon as we go into the muscle Diagram of T-tubules o This is a diagram of just one muscle cell Myoibrils o The sarcoplasmic reiculum contains pumps and other proteins for calcium sequestraion This surrounds the myoibrils in the network o T-tubules are extensions of the sarcolemma that are associated in a triad with two terminal cisternae of the SR The T-tubules will funcion in organizing contracion o The triad will allow for depolarizaion of the sarcolemma and the T-tubule to afect the sarcoplasmic reiculum and trigger the release of calcium ions into the cytoplasm that will iniiate contracion The triad is very important in iniiaing contracion Blood vessels in muscle o Due to the need for oxygen, sugar, calcium, blood low is very important for muscle cells Muscle- Striaions in Skeletal Muscle Organizaion: o The sarcoplasm is extremely organized with long cylinders of ilament bundles called myoibrils running parallel to the iber axis o At lower magniicaion you can see the dark and light alternaing secions The A band- the dark band Anisotropic Birefringent in polarized light The I band- the light band Isotropic Doesn’t alter polarized light In the center of the I band there is one dark line called the Z disk o A sarcomere is measured from Z disk to Z disk o Approximately 2 micrometers long o The dark and light bands are due to the thick and thin myoilaments made of myosin (thick) and F-acin (thin) Myosin The thick myosin ilaments are 1 micrometers long and 15 nm wide Large and composed of two idenical heavy chains and two pairs of light chains Exam 2 Histology Notes Module 5- Muscle Muscle-Introducion All muscle has cells that are opimized for contracility o All of these cells come from the mesoderm o Difereniate by process of cell lengthening o Contain myoibrillar proteins: Acin and myosin What is muscle? o Sarcoplasm - cytoplasm of muscle cells o Sarcoplasmic reiculum - smooth ER of muscle cells Serves as site of calcium storage and release during contracility o Sarcolemma – Plasmalemma (cell membrane) of muscle cells The sarcolemma in skeletal and cardiac muscle will form tubular projecions called transverse tubules that will extend into the sarcoplasm and be associated with the SR o Myoiber – a single muscle cell o In skeletal and cardiac only: Sarcomere: contracile unit Myoibril/myoilament: a string of sarcomeres Sarcosome: specialized long mitochondria Muscle terms: o Epimysium- thick collagenous connecive issue that surrounds large bundles of muscle There are several fascicles within the epimysium o Fascicle- bundles of muscle cells surrounded by their own connecive issue (the perimysium) o Perimysium- connecive issue surrounding the fascicles o Endomysium- coninuous with the perimysium and forms this very thin layer around each individual muscle iber Innermost layer Skeletal muscle o Striated muscle o Composed of muscle ibers Each muscle iber is a long cylindrical mulinucleated cell The nuclei will be present at the edge just under the sarcolemma The nuclei are elongated o Diameters range from 10-100 micrometers o The iber can be many cenimeters long o Can be found in the tongue, diaphragm, eyes, and upper esophagus o Signals are all or nothing In order for skeletal muscle to funcion, it must contain a well-developed sarcoplasmic reiculum Contains organized sarcomeres We oten see it called striated muscle because of this organizaion o Embryologically, these ibers come from mesenchymal myoblasts which will fuse to form myotubes that contain muliple nuclei They will difereniate into striated muscle ibers Some of the cells will remain undifereniated These are called muscle satellite cells that are muscle progenitor cells that could become muscle cells later o Skeletal muscles typically respond to increased load by increasing iber size (called hypertrophy) o If there is a need for regeneraion, satellite cells could difereniate into muscle ibers o In this type of issue, regeneraion is limited Speciic pictures of skeletal muscle: o a) Epimysium at outer edge staining dark red, the endomysium around each muscle iber, and the perimysium dividing the fascicles o b) Special stain for laminin that shows the external laminae of the muscle ibers surrounded by the endomysium The brown is where the external laminae is o c) Myotendenous juncion- the connecive issue is coninuous with this tendon as we go into the muscle Diagram of T-tubules o This is a diagram of just one muscle cell Myoibrils o The sarcoplasmic reiculum contains pumps and other proteins for calcium sequestraion This surrounds the myoibrils in the network o T-tubules are extensions of the sarcolemma that are associated in a triad with two terminal cisternae of the SR The T-tubules will funcion in organizing contracion o The triad will allow for depolarizaion of the sarcolemma and the T-tubule to afect the sarcoplasmic reiculum and trigger the release of calcium ions into the cytoplasm that will iniiate contracion The triad is very important in iniiaing contracion Blood vessels in muscle o Due to the need for oxygen, sugar, calcium, blood low is very important for muscle cells Muscle- Striaions in Skeletal Muscle Organizaion: o The sarcoplasm is extremely organized with long cylinders of ilament bundles called myoibrils running parallel to the iber axis o At lower magniicaion you can see the dark and light alternaing secions The A band- the dark band Anisotropic Birefringent in polarized light The I band- the light band Isotropic Doesn’t alter polarized light In the center of the I band there is one dark line called the Z disk o A sarcomere is measured from Z disk to Z disk o Approximately 2 micrometers long o The dark and light bands are due to the thick and thin myoilaments made of myosin (thick) and F-acin (thin) Myosin The thick myosin ilaments are 1 micrometers long and 15 nm wide Large and composed of two idenical heavy chains and two pairs of light chains The heavy chains are rod-like motor proteins that are twisted together forming twisted myosin tails The projecions at the end of each heavy chain contain four light chains and form the myosin heads o The heads will bind to the thin ilaments of acin to form cross bridges between the thick and the thin ilaments and ATP o Acin o The thin ilament is helical and contains binding sites for the myosin heads on each G-acin molecule There are two associated proteins: o Tropomyosin is located in the groove of the twisted acin strands o Troponin is made up of three subunits One binds to tropomyosin, one binds to calcium, and one regulates the interacion between acin and myosin Other important structures: The H zone contains only thick ilaments and lies in the center of the A band The M line is in the center of the H zone The M line has some other molecules that are involved in cross-linking and stabilizing those myosin ilaments Contains the myosin binding protein called myomesin o Myomesin- protein that forms the cross bridges that are helping stabilize the myosin ilaments and keep them in place Contains protein kinase that catalyzes the transfer of phosphate groups from phosphocreaine (high energy storage molecules that can supply ATP from ADP for contracion) Tiin ilament- lies between the thin ilaments of acin, helping with stabilizaion Exam 2 Histology Notes Module 5- Muscle Muscle-Introducion All muscle has cells that are opimized for contracility o All of these cells come from the mesoderm o Difereniate by process of cell lengthening o Contain myoibrillar proteins: Acin and myosin What is muscle? o Sarcoplasm - cytoplasm of muscle cells o Sarcoplasmic reiculum - smooth ER of muscle cells Serves as site of calcium storage and release during contracility o Sarcolemma – Plasmalemma (cell membrane) of muscle cells The sarcolemma in skeletal and cardiac muscle will form tubular projecions called transverse tubules that will extend into the sarcoplasm and be associated with the SR o Myoiber – a single muscle cell o In skeletal and cardiac only: Sarcomere: contracile unit Myoibril/myoilament: a string of sarcomeres Sarcosome: specialized long mitochondria Muscle terms: o Epimysium- thick collagenous connecive issue that surrounds large bundles of muscle There are several fascicles within the epimysium o Fascicle- bundles of muscle cells surrounded by their own connecive issue (the perimysium) o Perimysium- connecive issue surrounding the fascicles o Endomysium- coninuous with the perimysium and forms this very thin layer around each individual muscle iber Innermost layer Skeletal muscle o Striated muscle o Composed of muscle ibers Each muscle iber is a long cylindrical mulinucleated cell The nuclei will be present at the edge just under the sarcolemma The nuclei are elongated o Diameters range from 10-100 micrometers o The iber can be many cenimeters long o Can be found in the tongue, diaphragm, eyes, and upper esophagus o Signals are all or nothing In order for skeletal muscle to funcion, it must contain a well-developed sarcoplasmic reiculum Contains organized sarcomeres We oten see it called striated muscle because of this organizaion o Embryologically, these ibers come from mesenchymal myoblasts which will fuse to form myotubes that contain muliple nuclei They will difereniate into striated muscle ibers Some of the cells will remain undifereniated These are called muscle satellite cells that are muscle progenitor cells that could become muscle cells later o Skeletal muscles typically respond to increased load by increasing iber size (called hypertrophy) o If there is a need for regeneraion, satellite cells could difereniate into muscle ibers o In this type of issue, regeneraion is limited Speciic pictures of skeletal muscle: o a) Epimysium at outer edge staining dark red, the endomysium around each muscle iber, and the perimysium dividing the fascicles o b) Special stain for laminin that shows the external laminae of the muscle ibers surrounded by the endomysium The brown is where the external laminae is o c) Myotendenous juncion- the connecive issue is coninuous with this tendon as we go into the muscle Diagram of T-tubules o This is a diagram of just one muscle cell Myoibrils o The sarcoplasmic reiculum contains pumps and other proteins for calcium sequestraion This surrounds the myoibrils in the network o T-tubules are extensions of the sarcolemma that are associated in a triad with two terminal cisternae of the SR The T-tubules will funcion in organizing contracion o The triad will allow for depolarizaion of the sarcolemma and the T-tubule to afect the sarcoplasmic reiculum and trigger the release of calcium ions into the cytoplasm that will iniiate contracion The triad is very important in iniiaing contracion Blood vessels in muscle o Due to the need for oxygen, sugar, calcium, blood low is very important for muscle cells Muscle- Striaions in Skeletal Muscle Organizaion: o The sarcoplasm is extremely organized with long cylinders of ilament bundles called myoibrils running parallel to the iber axis o At lower magniicaion you can see the dark and light alternaing secions The A band- the dark band Anisotropic Birefringent in polarized light The I band- the light band Isotropic Doesn’t alter polarized light In the center of the I band there is one dark line called the Z disk o A sarcomere is measured from Z disk to Z disk o Approximately 2 micrometers long o The dark and light bands are due to the thick and thin myoilaments made of myosin (thick) and F-acin (thin) Myosin The thick myosin ilaments are 1 micrometers long and 15 nm wide Large and composed of two idenical heavy chains and two pairs of light chains The heavy chains are rod-like motor proteins that are twisted together forming twisted myosin tails The projecions at the end of each heavy chain contain four light chains and form the myosin heads o The heads will bind to the thin ilaments of acin to form cross bridges between the thick and the thin ilaments and ATP o Acin o The thin ilament is helical and contains binding sites for the myosin heads on each G-acin molecule There are two associated proteins: o Tropomyosin is located in the groove of the twisted acin strands o Troponin is made up of three subunits One binds to tropomyosin, one binds to calcium, and one regulates the interacion between acin and myosin Other important structures: The H zone contains only thick ilaments and lies in the center of the A band The M line is in the center of the H zone The M line has some other molecules that are involved in cross-linking and stabilizing those myosin ilaments Contains the myosin binding protein called myomesin o Myomesin- protein that forms the cross bridges that are helping stabilize the myosin ilaments and keep them in place Contains protein kinase that catalyzes the transfer of phosphate groups from phosphocreaine (high energy storage molecules that can supply ATP from ADP for contracion) Tiin ilament- lies between the thin ilaments of acin, helping with stabilizaion Accessory protein found within the I band Largest protein in the body Provides a scafold and elasic properies that support the thick ilaments and connect them to the Z disk Allows the thick ilaments not to sag in between the thin ilaments Connecin- found in the Z disk, which helps to stabilize and bind those acin ilaments in place Neuromuscular juncion (Book goes into much more detail) o Contracion is induced by the neuromuscular juncion The acion potenial is transmited along the t-tubules to terminal cisternae that cause the SR to release calcium o Steps of muscle contracion: (1) Nerve impulse triggers acetylcholine release into the synapic clet at the motor end plate. Acetylcholine will bind to Ach receptors in the motor end plate of the NMJ, which iniiates an impulse in the sarcolemma of the muscle iber. (2) The impulse will travel quickly along the sarcolemma and therefore along the t-tubules. From there it will go to the sarcoplasmic reiculum where the calcium ions can then be released from the terminal cisternae of the SR and those calcium ions can be released into the sarcoplasm. (3) The calcium ions bind to troponin, which will change shape and move the tropomyosin and expose the acive sites on the acin where myosin can bind to form those cross-bridges. Myosin will atach to the acin. (4) The myosin heads, which are bound to acin at the acive site, will pivot. This moves the thin ilament towards the Z Exam 2 Histology Notes Module 5- Muscle Muscle-Introducion All muscle has cells that are opimized for contracility o All of these cells come from the mesoderm o Difereniate by process of cell lengthening o Contain myoibrillar proteins: Acin and myosin What is muscle? o Sarcoplasm - cytoplasm of muscle cells o Sarcoplasmic reiculum - smooth ER of muscle cells Serves as site of calcium storage and release during contracility o Sarcolemma – Plasmalemma (cell membrane) of muscle cells The sarcolemma in skeletal and cardiac muscle will form tubular projecions called transverse tubules that will extend into the sarcoplasm and be associated with the SR o Myoiber – a single muscle cell o In skeletal and cardiac only: Sarcomere: contracile unit Myoibril/myoilament: a string of sarcomeres Sarcosome: specialized long mitochondria Muscle terms: o Epimysium- thick collagenous connecive issue that surrounds large bundles of muscle There are several fascicles within the epimysium o Fascicle- bundles of muscle cells surrounded by their own connecive issue (the perimysium) o Perimysium- connecive issue surrounding the fascicles o Endomysium- coninuous with the perimysium and forms this very thin layer around each individual muscle iber Innermost layer Skeletal muscle o Striated muscle o Composed of muscle ibers Each muscle iber is a long cylindrical mulinucleated cell The nuclei will be present at the edge just under the sarcolemma The nuclei are elongated o Diameters range from 10-100 micrometers o The iber can be many cenimeters long o Can be found in the tongue, diaphragm, eyes, and upper esophagus o Signals are all or nothing In order for skeletal muscle to funcion, it must contain a well-developed sarcoplasmic reiculum Contains organized sarcomeres We oten see it called striated muscle because of this organizaion o Embryologically, these ibers come from mesenchymal myoblasts which will fuse to form myotubes that contain muliple nuclei They will difereniate into striated muscle ibers Some of the cells will remain undifereniated These are called muscle satellite cells that are muscle progenitor cells that could become muscle cells later o Skeletal muscles typically respond to increased load by increasing iber size (called hypertrophy) o If there is a need for regeneraion, satellite cells could difereniate into muscle ibers o In this type of issue, regeneraion is limited Speciic pictures of skeletal muscle: o a) Epimysium at outer edge staining dark red, the endomysium around each muscle iber, and the perimysium dividing the fascicles o b) Special stain for laminin that shows the external laminae of the muscle ibers surrounded by the endomysium The brown is where the external laminae is o c) Myotendenous juncion- the connecive issue is coninuous with this tendon as we go into the muscle Diagram of T-tubules o This is a diagram of just one muscle cell Myoibrils o The sarcoplasmic reiculum contains pumps and other proteins for calcium sequestraion This surrounds the myoibrils in the network o T-tubules are extensions of the sarcolemma that are associated in a triad with two terminal cisternae of the SR The T-tubules will funcion in organizing contracion o The triad will allow for depolarizaion of the sarcolemma and the T-tubule to afect the sarcoplasmic reiculum and trigger the release of calcium ions into the cytoplasm that will iniiate contracion The triad is very important in iniiaing contracion Blood vessels in muscle o Due to the need for oxygen, sugar, calcium, blood low is very important for muscle cells Muscle- Striaions in Skeletal Muscle Organizaion: o The sarcoplasm is extremely organized with long cylinders of ilament bundles called myoibrils running parallel to the iber axis o At lower magniicaion you can see the dark and light alternaing secions The A band- the dark band Anisotropic Birefringent in polarized light The I band- the light band Isotropic Doesn’t alter polarized light In the center of the I band there is one dark line called the Z disk o A sarcomere is measured from Z disk to Z disk o Approximately 2 micrometers long o The dark and light bands are due to the thick and thin myoilaments made of myosin (thick) and F-acin (thin) Myosin The thick myosin ilaments are 1 micrometers long and 15 nm wide Large and composed of two idenical heavy chains and two pairs of light chains The heavy chains are rod-like motor proteins that are twisted together forming twisted myosin tails The projecions at the end of each heavy chain contain four light chains and form the myosin heads o The heads will bind to the thin ilaments of acin to form cross bridges between the thick and the thin ilaments and ATP o Acin o The thin ilament is helical and contains binding sites for the myosin heads on each G-acin molecule There are two associated proteins: o Tropomyosin is located in the groove of the twisted acin strands o Troponin is made up of three subunits One binds to tropomyosin, one binds to calcium, and one regulates the interacion between acin and myosin Other important structures: The H zone contains only thick ilaments and lies in the center of the A band The M line is in the center of the H zone The M line has some other molecules that are involved in cross-linking and stabilizing those myosin ilaments Contains the myosin binding protein called myomesin o Myomesin- protein that forms the cross bridges that are helping stabilize the myosin ilaments and keep them in place Contains protein kinase that catalyzes the transfer of phosphate groups from phosphocreaine (high energy storage molecules that can supply ATP from ADP for contracion) Tiin ilament- lies between the thin ilaments of acin, helping with stabilizaion Accessory protein found within the I band Largest protein in the body Provides a scafold and elasic properies that support the thick ilaments and connect them to the Z disk Allows the thick ilaments not to sag in between the thin ilaments Connecin- found in the Z disk, which helps to stabilize and bind those acin ilaments in place Neuromuscular juncion (Book goes into much more detail) o Contracion is induced by the neuromuscular juncion The acion potenial is transmited along the t-tubules to terminal cisternae that cause the SR to release calcium o Steps of muscle contracion: (1) Nerve impulse triggers acetylcholine release into the synapic clet at the motor end plate. Acetylcholine will bind to Ach receptors in the motor end plate of the NMJ, which iniiates an impulse in the sarcolemma of the muscle iber. (2) The impulse will travel quickly along the sarcolemma and therefore along the t-tubules. From there it will go to the sarcoplasmic reiculum where the calcium ions can then be released from the terminal cisternae of the SR and those calcium ions can be released into the sarcoplasm. (3) The calcium ions bind to troponin, which will change shape and move the tropomyosin and expose the acive sites on the acin where myosin can bind to form those cross-bridges. Myosin will atach to the acin. (4) The myosin heads, which are bound to acin at the acive site, will pivot. This moves the thin ilament towards the Z disk. ATP binds those myosin heads and it is broken down to ADP and phosphate. The myosin heads will then detach from the thin ilament. They return to their original posiion before they pivoted. This cycle will repeat and slide the thick and thin ilaments past each other and as this happens the sarcomere shortens and the muscle contracts. This will happen unil there is no more calcium to bind to the troponin. So the calcium binding to the troponin is the key to geing those myosin heads to bind to the binding sites on acin and then pivot (5) Once there is no more calcium, the acive sites won’t be exposed and the atachment to acive site won’t happen. When the impulse to contract stops, the calcium ions are moved via acive transport more quickly back into the SR. The tropomyosin will cover up the acive sites again. Filaments return to their relaxed state o Rigormortous is when the absence of ATP results in the acin-myosin cross bridges remaining stable, resuling in rigidity. The muscles are coninuously tense. o Innervaion of the neuromuscular juncion- Depending on the muscle, the innervaion may be very broad or very speciic In large muscles that perform coarse movement, the axon from a motor neuron may form motor end plates with 100 or more muscle cells. One axon could branch into all these diferent neuromuscular juncions. In cases where there is ine control, a single motor neuron may innervate 1 muscle iber Things like wriing, muscles in your ingers Muscle: Spindles and Tendons Sensory receptors Proprioceptors o Muscle spindles- Stretch receptors The spindle is surrounded by a thin capsule of perimysium that is modiied and it contains some thin muscle ibers illed with nuclei called intrafusal muscle ibers These intrafusal ibers will have more nuclei then a normal iber Sensory axons seen in the green will penetrate each muscle spindle then wrap around those intrafusal ibers When the ibers surrounding them, the extrafusal ibers, change length the movement is detected by the sensory nerves which relay the informaion to the spinal chord The feedback allows for relexes that are complex and for opposing muscle acivity to be coordinate Such as walking o Golgi Tendon Organs: Encloses the sensory axons that penetrate the collagen bundles at the Myotendenous juncion It is smaller This organ can detect changes in tension in the tendon that are caused by muscle contracion If the tension becomes excessive, this can actually inhibit motor nerve acivity Can help regulate the amount of efort required for paricular acion Types of muscle ibers: o Slow oxidaive: Slow contracions, long periods, no faigue Exam 2 Histology Notes Module 5- Muscle Muscle-Introducion All muscle has cells that are opimized for contracility o All of these cells come from the mesoderm o Difereniate by process of cell lengthening o Contain myoibrillar proteins: Acin and myosin What is muscle? o Sarcoplasm - cytoplasm of muscle cells o Sarcoplasmic reiculum - smooth ER of muscle cells Serves as site of calcium storage and release during contracility o Sarcolemma – Plasmalemma (cell membrane) of muscle cells The sarcolemma in skeletal and cardiac muscle will form tubular projecions called transverse tubules that will extend into the sarcoplasm and be associated with the SR o Myoiber – a single muscle cell o In skeletal and cardiac only: Sarcomere: contracile unit Myoibril/myoilament: a string of sarcomeres Sarcosome: specialized long mitochondria Muscle terms: o Epimysium- thick collagenous connecive issue that surrounds large bundles of muscle There are several fascicles within the epimysium o Fascicle- bundles of muscle cells surrounded by their own connecive issue (the perimysium) o Perimysium- connecive issue surrounding the fascicles o Endomysium- coninuous with the perimysium and forms this very thin layer around each individual muscle iber Innermost layer Skeletal muscle o Striated muscle o Composed of muscle ibers Each muscle iber is a long cylindrical mulinucleated cell The nuclei will be present at the edge just under the sarcolemma The nuclei are elongated o Diameters range from 10-100 micrometers o The iber can be many cenimeters long o Can be found in the tongue, diaphragm, eyes, and upper esophagus o Signals are all or nothing In order for skeletal muscle to funcion, it must contain a well-developed sarcoplasmic reiculum Contains organized sarcomeres We oten see it called striated muscle because of this organizaion o Embryologically, these ibers come from mesenchymal myoblasts which will fuse to form myotubes that contain muliple nuclei They will difereniate into striated muscle ibers Some of the cells will remain undifereniated These are called muscle satellite cells that are muscle progenitor cells that could become muscle cells later o Skeletal muscles typically respond to increased load by increasing iber size (called hypertrophy) o If there is a need for regeneraion, satellite cells could difereniate into muscle ibers o In this type of issue, regeneraion is limited Speciic pictures of skeletal muscle: o a) Epimysium at outer edge staining dark red, the endomysium around each muscle iber, and the perimysium dividing the fascicles o b) Special stain for laminin that shows the external laminae of the muscle ibers surrounded by the endomysium The brown is where the external laminae is o c) Myotendenous juncion- the connecive issue is coninuous with this tendon as we go into the muscle Diagram of T-tubules o This is a diagram of just one muscle cell Myoibrils o The sarcoplasmic reiculum contains pumps and other proteins for calcium sequestraion This surrounds the myoibrils in the network o T-tubules are extensions of the sarcolemma that are associated in a triad with two terminal cisternae of the SR The T-tubules will funcion in organizing contracion o The triad will allow for depolarizaion of the sarcolemma and the T-tubule to afect the sarcoplasmic reiculum and trigger the release of calcium ions into the cytoplasm that will iniiate contracion The triad is very important in iniiaing contracion Blood vessels in muscle o Due to the need for oxygen, sugar, calcium, blood low is very important for muscle cells Muscle- Striaions in Skeletal Muscle Organizaion: o The sarcoplasm is extremely organized with long cylinders of ilament bundles called myoibrils running parallel to the iber axis o At lower magniicaion you can see the dark and light alternaing secions The A band- the dark band Anisotropic Birefringent in polarized light The I band- the light band Isotropic Doesn’t alter polarized light In the center of the I band there is one dark line called the Z disk o A sarcomere is measured from Z disk to Z disk o Approximately 2 micrometers long o The dark and light bands are due to the thick and thin myoilaments made of myosin (thick) and F-acin (thin) Myosin The thick myosin ilaments are 1 micrometers long and 15 nm wide Large and composed of two idenical heavy chains and two pairs of light chains The heavy chains are rod-like motor proteins that are twisted together forming twisted myosin tails The projecions at the end of each heavy chain contain four light chains and form the myosin heads o The heads will bind to the thin ilaments of acin to form cross bridges between the thick and the thin ilaments and ATP o Acin o The thin ilament is helical and contains binding sites for the myosin heads on each G-acin molecule There are two associated proteins: o Tropomyosin is located in the groove of the twisted acin strands o Troponin is made up of three subunits One binds to tropomyosin, one binds to calcium, and one regulates the interacion between acin and myosin Other important structures: The H zone contains only thick ilaments and lies in the center of the A band The M line is in the center of the H zone The M line has some other molecules that are involved in cross-linking and stabilizing those myosin ilaments Contains the myosin binding protein called myomesin o Myomesin- protein that forms the cross bridges that are helping stabilize the myosin ilaments and keep them in place Contains protein kinase that catalyzes the transfer of phosphate groups from phosphocreaine (high energy storage molecules that can supply ATP from ADP for contracion) Tiin ilament- lies between the thin ilaments of acin, helping with stabilizaion Accessory protein found within the I band Largest protein in the body Provides a scafold and elasic properies that support the thick ilaments and connect them to the Z disk Allows the thick ilaments not to sag in between the thin ilaments Connecin- found in the Z disk, which helps to stabilize and bind those acin ilaments in place Neuromuscular juncion (Book goes into much more detail) o Contracion is induced by the neuromuscular juncion The acion potenial is transmited along the t-tubules to terminal cisternae that cause the SR to release calcium o Steps of muscle contracion: (1) Nerve impulse triggers acetylcholine release into the synapic clet at the motor end plate. Acetylcholine will bind to Ach receptors in the motor end plate of the NMJ, which iniiates an impulse in the sarcolemma of the muscle iber. (2) The impulse will travel quickly along the sarcolemma and therefore along the t-tubules. From there it will go to the sarcoplasmic reiculum where the calcium ions can then be released from the terminal cisternae of the SR and those calcium ions can be released into the sarcoplasm. (3) The calcium ions bind to troponin, which will change shape and move the tropomyosin and expose the acive sites on the acin where myosin can bind to form those cross-bridges. Myosin will atach to the acin. (4) The myosin heads, which are bound to acin at the acive site, will pivot. This moves the thin ilament towards the Z disk. ATP binds those myosin heads and it is broken down to ADP and phosphate. The myosin heads will then detach from the thin ilament. They return to their original posiion before they pivoted. This cycle will repeat and slide the thick and thin ilaments past each other and as this happens the sarcomere shortens and the muscle contracts. This will happen unil there is no more calcium to bind to the troponin. So the calcium binding to the troponin is the key to geing those myosin heads to bind to the binding sites on acin and then pivot (5) Once there is no more calcium, the acive sites won’t be exposed and the atachment to acive site won’t happen. When the impulse to contract stops, the calcium ions are moved via acive transport more quickly back into the SR. The tropomyosin will cover up the acive sites again. Filaments return to their relaxed state o Rigormortous is when the absence of ATP results in the acin-myosin cross bridges remaining stable, resuling in rigidity. The muscles are coninuously tense. o Innervaion of the neuromuscular juncion- Depending on the muscle, the innervaion may be very broad or very speciic In large muscles that perform coarse movement, the axon from a motor neuron may form motor end plates with 100 or more muscle cells. One axon could branch into all these diferent neuromuscular juncions. In cases where there is ine control, a single motor neuron may innervate 1 muscle iber Things like wriing, muscles in your ingers Muscle: Spindles and Tendons Sensory receptors Proprioceptors o Muscle spindles- Stretch receptors The spindle is surrounded by a thin capsule of perimysium that is modiied and it contains some thin muscle ibers illed with nuclei called intrafusal muscle ibers These intrafusal ibers will have more nuclei then a normal iber Sensory axons seen in the green will penetrate each muscle spindle then wrap around those intrafusal ibers When the ibers surrounding them, the extrafusal ibers, change length the movement is detected by the sensory nerves which relay the informaion to the spinal chord The feedback allows for relexes that are complex and for opposing muscle acivity to be coordinate Such as walking o Golgi Tendon Organs: Encloses the sensory axons that penetrate the collagen bundles at the Myotendenous juncion It is smaller This organ can detect changes in tension in the tendon that are caused by muscle contracion If the tension becomes excessive, this can actually inhibit motor nerve acivity Can help regulate the amount of efort required for paricular acion Types of muscle ibers: o Slow oxidaive: Slow contracions, long periods, no faigue Many mitochondria, capillaries, myoglobin (which stores oxygen) Myoglobin is similar to hemoglobin in that it stores oxygen but it is found in the muscle Fresh issue of this is dark or red in color Remember that oxidaive phosphorylaion is using oxygen and it’s happening in the mitochondria Stain darker Fast glycolyic: Rapid, short-term contracion, rapid faigue Few mitochondria, few capillaries and depend on anaerobic metabolism (so no myoglobin) Lacic acid is produced Glycolysis does not require oxygen and it will produce less ATP Stain lighter Fast oxidaive-glycolyic: Intermediate between slow oxidaive and fast oxidaive-glycolyic o o Cardiac Muscle: Characterisics of cardiac muscle: o Heart o Tends to have smaller cells: 10-20μm diameter 50-100 μm long o Central nuclei Tend to be located centrally within the cell and then nearby you may have t-tubules located in diads (instead of triads seen in skeletal muscle) at the Z disk Exam 2 Histology Notes Module 5- Muscle Muscle-Introducion All muscle has cells that are opimized for contracility o All of these cells come from the mesoderm o Difereniate by process of cell lengthening o Contain myoibrillar proteins: Acin and myosin What is muscle? o Sarcoplasm - cytoplasm of muscle cells o Sarcoplasmic reiculum - smooth ER of muscle cells Serves as site of calcium storage and release during contracility o Sarcolemma – Plasmalemma (cell membrane) of muscle cells The sarcolemma in skeletal and cardiac muscle will form tubular projecions called transverse tubules that will extend into the sarcoplasm and be associated with the SR o Myoiber – a single muscle cell o In skeletal and cardiac only: Sarcomere: contracile unit Myoibril/myoilament: a string of sarcomeres Sarcosome: specialized long mitochondria Muscle terms: o Epimysium- thick collagenous connecive issue that surrounds large bundles of muscle There are several fascicles within the epimysium o Fascicle- bundles of muscle cells surrounded by their own connecive issue (the perimysium) o Perimysium- connecive issue surrounding the fascicles o Endomysium- coninuous with the perimysium and forms this very thin layer around each individual muscle iber Innermost layer Skeletal muscle o Striated muscle o Composed of muscle ibers Each muscle iber is a long cylindrical mulinucleated cell The nuclei will be present at the edge just under the sarcolemma The nuclei are elongated o Diameters range from 10-100 micrometers o The iber can be many cenimeters long o Can be found in the tongue, diaphragm, eyes, and upper esophagus o Signals are all or nothing In order for skeletal muscle to funcion, it must contain a well-developed sarcoplasmic reiculum Contains organized sarcomeres We oten see it called striated muscle because of this organizaion o Embryologically, these ibers come from mesenchymal myoblasts which will fuse to form myotubes that contain muliple nuclei They will difereniate into striated muscle ibers Some of the cells will remain undifereniated These are called muscle satellite cells that are muscle progenitor cells that could become muscle cells later o Skeletal muscles typically respond to increased load by increasing iber size (called hypertrophy) o If there is a need for regeneraion, satellite cells could difereniate into muscle ibers o In this type of issue, regeneraion is limited Speciic pictures of skeletal muscle: o a) Epimysium at outer edge staining dark red, the endomysium around each muscle iber, and the perimysium dividing the fascicles o b) Special stain for laminin that shows the external laminae of the muscle ibers surrounded by the endomysium The brown is where the external laminae is o c) Myotendenous juncion- the connecive issue is coninuous with this tendon as we go into the muscle Diagram of T-tubules o This is a diagram of just one muscle cell Myoibrils o The sarcoplasmic reiculum contains pumps and other proteins for calcium sequestraion This surrounds the myoibrils in the network o T-tubules are extensions of the sarcolemma that are associated in a triad with two terminal cisternae of the SR The T-tubules will funcion in organizing contracion o The triad will allow for depolarizaion of the sarcolemma and the T-tubule to afect the sarcoplasmic reiculum and trigger the release of calcium ions into the cytoplasm that will iniiate contracion The triad is very important in iniiaing contracion Blood vessels in muscle o Due to the need for oxygen, sugar, calcium, blood low is very important for muscle cells Muscle- Striaions in Skeletal Muscle Organizaion: o The sarcoplasm is extremely organized with long cylinders of ilament bundles called myoibrils running parallel to the iber axis o At lower magniicaion you can see the dark and light alternaing secions The A band- the dark band Anisotropic Birefringent in polarized light The I band- the light band Isotropic Doesn’t alter polarized light In the center of the I band there is one dark line called the Z disk o A sarcomere is measured from Z disk to Z disk o Approximately 2 micrometers long o The dark and light bands are due to the thick and thin myoilaments made of myosin (thick) and F-acin (thin) Myosin The thick myosin ilaments are 1 micrometers long and 15 nm wide Large and composed of two idenical heavy chains and two pairs of light chains The heavy chains are rod-like motor proteins that are twisted together forming twisted myosin tails The projecions at the end of each heavy chain contain four light chains and form the myosin heads o The heads will bind to the thin ilaments of acin to form cross bridges between the thick and the thin ilaments and ATP o Acin o The thin ilament is helical and contains binding sites for the myosin heads on each G-acin molecule There are two associated proteins: o Tropomyosin is located in the groove of the twisted acin strands o Troponin is made up of three subunits One binds to tropomyosin, one binds to calcium, and one regulates the interacion between acin and myosin Other important structures: The H zone contains only thick ilaments and lies in the center of the A band The M line is in the center of the H zone The M line has some other molecules that are involved in cross-linking and stabilizing those myosin ilaments Contains the myosin binding protein called myomesin o Myomesin- protein that forms the cross bridges that are helping stabilize the myosin ilaments and keep them in place Contains protein kinase that catalyzes the transfer of phosphate groups from phosphocreaine (high energy storage molecules that can supply ATP from ADP for contracion) Tiin ilament- lies between the thin ilaments of acin, helping with stabilizaion Accessory protein found within the I band Largest protein in the body Provides a scafold and elasic properies that support the thick ilaments and connect them to the Z disk Allows the thick ilaments not to sag in between the thin ilaments Connecin- found in the Z disk, which helps to stabilize and bind those acin ilaments in place Neuromuscular juncion (Book goes into much more detail) o Contracion is induced by the neuromuscular juncion The acion potenial is transmited along the t-tubules to terminal cisternae that cause the SR to release calcium o Steps of muscle contracion: (1) Nerve impulse triggers acetylcholine release into the synapic clet at the motor end plate. Acetylcholine will bind to Ach receptors in the motor end plate of the NMJ, which iniiates an impulse in the sarcolemma of the muscle iber. (2) The impulse will travel quickly along the sarcolemma and therefore along the t-tubules. From there it will go to the sarcoplasmic reiculum where the calcium ions can then be released from the terminal cisternae of the SR and those calcium ions can be released into the sarcoplasm. (3) The calcium ions bind to troponin, which will change shape and move the tropomyosin and expose the acive sites on the acin where myosin can bind to form those cross-bridges. Myosin will atach to the acin. (4) The myosin heads, which are bound to acin at the acive site, will pivot. This moves the thin ilament towards the Z disk. ATP binds those myosin heads and it is broken down to ADP and phosphate. The myosin heads will then detach from the thin ilament. They return to their original posiion before they pivoted. This cycle will repeat and slide the thick and thin ilaments past each other and as this happens the sarcomere shortens and the muscle contracts. This will happen unil there is no more calcium to bind to the troponin. So the calcium binding to the troponin is the key to geing those myosin heads to bind to the binding sites on acin and then pivot (5) Once there is no more calcium, the acive sites won’t be exposed and the atachment to acive site won’t happen. When the impulse to contract stops, the calcium ions are moved via acive transport more quickly back into the SR. The tropomyosin will cover up the acive sites again. Filaments return to their relaxed state o Rigormortous is when the absence of ATP results in the acin-myosin cross bridges remaining stable, resuling in rigidity. The muscles are coninuously tense. o Innervaion of the neuromuscular juncion- Depending on the muscle, the innervaion may be very broad or very speciic In large muscles that perform coarse movement, the axon from a motor neuron may form motor end plates with 100 or more muscle cells. One axon could branch into all these diferent neuromuscular juncions. In cases where there is ine control, a single motor neuron may innervate 1 muscle iber Things like wriing, muscles in your ingers Muscle: Spindles and Tendons Sensory receptors Proprioceptors o Muscle spindles- Stretch receptors The spindle is surrounded by a thin capsule of perimysium that is modiied and it contains some thin muscle ibers illed with nuclei called intrafusal muscle ibers These intrafusal ibers will have more nuclei then a normal iber Sensory axons seen in the green will penetrate each muscle spindle then wrap around those intrafusal ibers When the ibers surrounding them, the extrafusal ibers, change length the movement is detected by the sensory nerves which relay the informaion to the spinal chord The feedback allows for relexes that are complex and for opposing muscle acivity to be coordinate Such as walking o Golgi Tendon Organs: Encloses the sensory axons that penetrate the collagen bundles at the Myotendenous juncion It is smaller This organ can detect changes in tension in the tendon that are caused by muscle contracion If the tension becomes excessive, this can actually inhibit motor nerve acivity Can help regulate the amount of efort required for paricular acion Types of muscle ibers: o Slow oxidaive: Slow contracions, long periods, no faigue Many mitochondria, capillaries, myoglobin (which stores oxygen) Myoglobin is similar to hemoglobin in that it stores oxygen but it is found in the muscle Fresh issue of this is dark or red in color Remember that oxidaive phosphorylaion is using oxygen and it’s happening in the mitochondria Stain darker Fast glycolyic: Rapid, short-term contracion, rapid faigue Few mitochondria, few capillaries and depend on anaerobic metabolism (so no myoglobin) Lacic acid is produced Glycolysis does not require oxygen and it will produce less ATP Stain lighter Fast oxidaive-glycolyic: Intermediate between slow oxidaive and fast oxidaive-glycolyic o o Cardiac Muscle: Characterisics of cardiac muscle: o Heart o Tends to have smaller cells: 10-20μm diameter 50-100 μm long o Central nuclei Tend to be located centrally within the cell and then nearby you may have t-tubules located in diads (instead of triads seen in skeletal muscle) at the Z disk o o o o o o o o o o Branching Involuntary Autonomic Striaions Contracions similar to skeletal Less developed sarcoplasmic reiculum Only one small terminal cisternae Usually easy to idenify Branching Central nuclei Intercalated disks Over ime, cardiac cells can accumulate lipofuscin due to aging Wear and tear pigment Granules tend to accumulate in the right atrium of the heart They container a precursor to a hormone called atrialnatrieureic factor Smooth muscle: Characterisics: o Autonomic/involuntary o Small 0-10 micrometers in diameter 50-200 micrometers long o Central nuclei o No striaions o Uses calmodulin instead of troponin o Instead of t-tubules, there are caveolae o Found in blood vessels, digesive and respiratory tracts, the uterus, bladder, and other organs o Fusiform shape- tapered at the ends o Contract in a coordinated fashion that moves the contents of the tract down the digesive tract, called peristalsis o There are two layers in the digesive tract: Innercircular layer- Encircles the digesive tract Exam 2 Histology Notes Module 5- Muscle Muscle-Introducion All muscle has cells that are opimized for contracility o All of these cells come from the mesoderm o Difereniate by process of cell lengthening o Contain myoibrillar proteins: Acin and myosin What is muscle? o Sarcoplasm - cytoplasm of muscle cells o Sarcoplasmic reiculum - smooth ER of muscle cells Serves as site of calcium storage and release during contracility o Sarcolemma – Plasmalemma (cell membrane) of muscle cells The sarcolemma in skeletal and cardiac muscle will form tubular projecions called transverse tubules that will extend into the sarcoplasm and be associated with the SR o Myoiber – a single muscle cell o In skeletal and cardiac only: Sarcomere: contracile unit Myoibril/myoilament: a string of sarcomeres Sarcosome: specialized long mitochondria Muscle terms: o Epimysium- thick collagenous connecive issue that surrounds large bundles of muscle There are several fascicles within the epimysium o Fascicle- bundles of muscle cells surrounded by their own connecive issue (the perimysium) o Perimysium- connecive issue surrounding the fascicles o Endomysium- coninuous with the perimysium and forms this very thin layer around each individual muscle iber Innermost layer Skeletal muscle o Striated muscle o Composed of muscle ibers Each muscle iber is a long cylindrical mulinucleated cell The nuclei will be present at the edge just under the sarcolemma The nuclei are elongated o Diameters range from 10-100 micrometers o The iber can be many cenimeters long o Can be found in the tongue, diaphragm, eyes, and upper esophagus o Signals are all or nothing In order for skeletal muscle to funcion, it must contain a well-developed sarcoplasmic reiculum Contains organized sarcomeres We oten see it called striated muscle because of this organizaion o Embryologically, these ibers come from mesenchymal myoblasts which will fuse to form myotubes that contain muliple nuclei They will difereniate into striated muscle ibers Some of the cells will remain undifereniated These are called muscle satellite cells that are muscle progenitor cells that could become muscle cells later o Skeletal muscles typically respond to increased load by increasing iber size (called hypertrophy) o If there is a need for regeneraion, satellite cells could difereniate into muscle ibers o In this type of issue, regeneraion is limited Speciic pictures of skeletal muscle: o a) Epimysium at outer edge staining dark red, the endomysium around each muscle iber, and the perimysium dividing the fascicles o b) Special stain for laminin that shows the external laminae of the muscle ibers surrounded by the endomysium The brown is where the external laminae is o c) Myotendenous juncion- the connecive issue is coninuous with this tendon as we go into the muscle Diagram of T-tubules o This is a diagram of just one muscle cell Myoibrils o The sarcoplasmic reiculum contains pumps and other proteins for calcium sequestraion This surrounds the myoibrils in the network o T-tubules are extensions of the sarcolemma that are associated in a triad with two terminal cisternae of the SR The T-tubules will funcion in organizing contracion o The triad will allow for depolarizaion of the sarcolemma and the T-tubule to afect the sarcoplasmic reiculum and trigger the release of calcium ions into the cytoplasm that will iniiate contracion The triad is very important in iniiaing contracion Blood vessels in muscle o Due to the need for oxygen, sugar, calcium, blood low is very important for muscle cells Muscle- Striaions in Skeletal Muscle Organizaion: o The sarcoplasm is extremely organized with long cylinders of ilament bundles called myoibrils running parallel to the iber axis o At lower magniicaion you can see the dark and light alternaing secions The A band- the dark band Anisotropic Birefringent in polarized light The I band- the light band Isotropic Doesn’t alter polarized light In the center of the I band there is one dark line called the Z disk o A sarcomere is measured from Z disk to Z disk o Approximately 2 micrometers long o The dark and light bands are due to the thick and thin myoilaments made of myosin (thick) and F-acin (thin) Myosin The thick myosin ilaments are 1 micrometers long and 15 nm wide Large and composed of two idenical heavy chains and two pairs of light chains The heavy chains are rod-like motor proteins that are twisted together forming twisted myosin tails The projecions at the end of each heavy chain contain four light chains and form the myosin heads o The heads will bind to the thin ilaments of acin to form cross bridges between the thick and the thin ilaments and ATP o Acin o The thin ilament is helical and contains binding sites for the myosin heads on each G-acin molecule There are two associated proteins: o Tropomyosin is located in the groove of the twisted acin strands o Troponin is made up of three subunits One binds to tropomyosin, one binds to calcium, and one regulates the interacion between acin and myosin Other important structures: The H zone contains only thick ilaments and lies in the center of the A band The M line is in the center of the H zone The M line has some other molecules that are involved in cross-linking and stabilizing those myosin ilaments Contains the myosin binding protein called myomesin o Myomesin- protein that forms the cross bridges that are helping stabilize the myosin ilaments and keep them in place Contains protein kinase that catalyzes the transfer of phosphate groups from phosphocreaine (high energy storage molecules that can supply ATP from ADP for contracion) Tiin ilament- lies between the thin ilaments of acin, helping with stabilizaion Accessory protein found within the I band Largest protein in the body Provides a scafold and elasic properies that support the thick ilaments and connect them to the Z disk Allows the thick ilaments not to sag in between the thin ilaments Connecin- found in the Z disk, which helps to stabilize and bind those acin ilaments in place Neuromuscular juncion (Book goes into much more detail) o Contracion is induced by the neuromuscular juncion The acion potenial is transmited along the t-tubules to terminal cisternae that cause the SR to release calcium o Steps of muscle contracion: (1) Nerve impulse triggers acetylcholine release into the synapic clet at the motor end plate. Acetylcholine will bind to Ach receptors in the motor end plate of the NMJ, which iniiates an impulse in the sarcolemma of the muscle iber. (2) The impulse will travel quickly along the sarcolemma and therefore along the t-tubules. From there it will go to the sarcoplasmic reiculum where the calcium ions can then be released from the terminal cisternae of the SR and those calcium ions can be released into the sarcoplasm. (3) The calcium ions bind to troponin, which will change shape and move the tropomyosin and expose the acive sites on the acin where myosin can bind to form those cross-bridges. Myosin will atach to the acin. (4) The myosin heads, which are bound to acin at the acive site, will pivot. This moves the thin ilament towards the Z disk. ATP binds those myosin heads and it is broken down to ADP and phosphate. The myosin heads will then detach from the thin ilament. They return to their original posiion before they pivoted. This cycle will repeat and slide the thick and thin ilaments past each other and as this happens the sarcomere shortens and the muscle contracts. This will happen unil there is no more calcium to bind to the troponin. So the calcium binding to the troponin is the key to geing those myosin heads to bind to the binding sites on acin and then pivot (5) Once there is no more calcium, the acive sites won’t be exposed and the atachment to acive site won’t happen. When the impulse to contract stops, the calcium ions are moved via acive transport more quickly back into the SR. The tropomyosin will cover up the acive sites again. Filaments return to their relaxed state o Rigormortous is when the absence of ATP results in the acin-myosin cross bridges remaining stable, resuling in rigidity. The muscles are coninuously tense. o Innervaion of the neuromuscular juncion- Depending on the muscle, the innervaion may be very broad or very speciic In large muscles that perform coarse movement, the axon from a motor neuron may form motor end plates with 100 or more muscle cells. One axon could branch into all these diferent neuromuscular juncions. In cases where there is ine control, a single motor neuron may innervate 1 muscle iber Things like wriing, muscles in your ingers Muscle: Spindles and Tendons Sensory receptors Proprioceptors o Muscle spindles- Stretch receptors The spindle is surrounded by a thin capsule of per
Exam 2 Histology Notes - Dr. Mays
Course: Histology (BIOL 4003)
University: Auburn University
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