09-30-2011, 05:12 PM
Another confusing concept is SKELETAL MUSCLE STRUCTURE : lets nail it down,
To begin with,
MYOCYTE(Myofiber/muscle fiber ) is made of BUNCH OF MYOFIBRILS(1micrometer diameter), each myofibril is made of bunch of MYOFILAMENTS (actin, myosin, titin etc) organised as repeated sections of contractile units called SARCOMERES.
Details,,
MUSCLE FIBRE / MYOFIBER / MYOCYTE
PLASMA MEMBRANE of a myofiber/myocyte is called SARCOLEMMA
CYTOPLASM of MYOCYTE/myofiber is called SARCOPLASM
NUCLEI are found pressed against sarcolemma.
BETWEEN MYOFIBRILS are mitochondria.
NO ENDOPLASMIC RETICULUM, instead it has SARCOPLASMIC RETICULUM which surrounds myofibrils and holds the reserve of CALCIUM needed for MUSCLE CONTRACTION.
DILATED SACS of sarcoplasmic reticulum are called TERMINAL CISTERNAE. they cross muscle fiber from side to side.
IN BETWEEN TWO TERMINAL CISTERNAE there are TUBULAR INFOLDINGS called TRANSVERSE TUBULES or called T-TUBULES. They are the PATHWAY FOR ACTION POTENTIAL to signal sarcoplasmic reticulum to release calcium that brings the process of contraction by interaction of actin and myosin and troponin etc myofilaments.
TRIAD = TWO TERMINAL CISTERNAE + T-TUBULE.
BASIC UNIT (STRUCTURAL ) of MUSCLE = MYOFIBRIL.
CONTRACTILE UNIT OF THE MUSCLE = SARCOMERE
MYOFIBRIL is 1micrometer in diameter by definition. EACH MYOCYTE contains bunch of myofibrils. EACH MYOFIBRIL contains repeated sections of SARCOMERES formed by the organisation of MYOFILAMENTS ( actin, myosin, titin and other structural elements )
SARCOMERES UNDER ELECTRON MICROSCOPE:
IN SARCOMERE we see MYOFILAMENTS and STRUCTURAL PROTEINS ELEMENTS interaction, some in action and some helping them by holding the ones in action. SARCOMERIC STRUCTURAL PROTEINS like TITIN, NEBULIN, TELETHONIN, ALPHA ACTININ, CALPAIN-3, OBSCURIN, MYOSIN BINDING PROTEIN-C, CALMODULIN-1, MVRF-1 are of importance.
What is a sarcomere?
SINGLE SARCOMERE contains two Z LINES.
TITIN is called GAINT POLYPEPTIDE of the BODY. It is organised in multiple folds, some interact with various protein elements at various parts of sarcomere (described below) to help maintain the intact structure of sarcomere. Its size is 3816 kDA, its very huge. Its N-TERMINAL is associated with I-BAND, and C-TERMINAL is associated with A-BAND.
TITIN interacts with following SARCOMERIC PROTEIN structural elements at following areas of sarcomere,
at
Z-LINE with TELETHONIN, ALPHA ACTININ
I- BAND with CALPAIN-3, OBSCURIN
M-LINE with MYOSIN BINDING PROTEIN C, CALMODULIN-1
we see
DARK ZONE and PALE ZONE alternating with each other in EM, how to identify,,
DARK ZONE ( areas where MYOSIN and ACTIN interact) AND
PALE ZONE ( areas where ACTIN IS NOT OVERLAPPED/ has no interaction, with MYOSIN )
TWO LINES called Z-LINE and M-LINE
THREE BANDS called I-BAND, A-BAND, H-BAND (in the order from Z line towards M line)
Z lines (from the German "Zwischenscheibe", the disc in between the I bands) are made of Z disks, which contains ACTIN myofilaments coiled with NEBULIN (600-900kDa ). Other structural elements that keeps them intact are TELETHONIN(TCAP), ALPHA ACTININ(ACTN). identified as DARK LINE in white/pale area under EM. From Z LINE actin myofilaments extend/span towards the myosin myofilaments.
M line - (MYOMESIN, an endline protein is present along with M line protein ) is the MIDDLE of a sarcomere, its the PROMINENT CENTER DARKEST LINE AMONG DARK AREA under EM. MYOSIN filaments OVER LAP HERE AND ARE BOUND. It is also marks the center of A-band and H-band.
I-BAND (ISORTOPIC BAND ) is the area covering either side of Z line, its the area where there is NO INTERACTION or NO OVERLAPPING between ACTIN and MYOSIN. Another important point is that I-BAND DECREASES IN SIZE DURING CONTRACTION.
A-BAND (ANISOTROPIC BAND ) is the ENTIRE DARK ZONE. It has H-band ( the paler area within the A-band ) and also M-line in it. This A-BAND represents the area where THERE IS INTERACTION OF ACTIN with MYOSIN.
H-BAND is the pallor area in A-BAND ( H means HELLER meaning BRIGHTER in german ). The middle of H-band contains M-line.
Note:
I, A, H are the names given based on the properties of these areas under polarizing microscope.
THE BAND that decreases/changes in SIZE/length is I-BAND
A-BAND and H-BAND are FIXED, they DONT CHANGE in SIZE/length.
Clinical aspect based questions on this concept, please contribute
To begin with,
MYOCYTE(Myofiber/muscle fiber ) is made of BUNCH OF MYOFIBRILS(1micrometer diameter), each myofibril is made of bunch of MYOFILAMENTS (actin, myosin, titin etc) organised as repeated sections of contractile units called SARCOMERES.
Details,,
MUSCLE FIBRE / MYOFIBER / MYOCYTE
PLASMA MEMBRANE of a myofiber/myocyte is called SARCOLEMMA
CYTOPLASM of MYOCYTE/myofiber is called SARCOPLASM
NUCLEI are found pressed against sarcolemma.
BETWEEN MYOFIBRILS are mitochondria.
NO ENDOPLASMIC RETICULUM, instead it has SARCOPLASMIC RETICULUM which surrounds myofibrils and holds the reserve of CALCIUM needed for MUSCLE CONTRACTION.
DILATED SACS of sarcoplasmic reticulum are called TERMINAL CISTERNAE. they cross muscle fiber from side to side.
IN BETWEEN TWO TERMINAL CISTERNAE there are TUBULAR INFOLDINGS called TRANSVERSE TUBULES or called T-TUBULES. They are the PATHWAY FOR ACTION POTENTIAL to signal sarcoplasmic reticulum to release calcium that brings the process of contraction by interaction of actin and myosin and troponin etc myofilaments.
TRIAD = TWO TERMINAL CISTERNAE + T-TUBULE.
BASIC UNIT (STRUCTURAL ) of MUSCLE = MYOFIBRIL.
CONTRACTILE UNIT OF THE MUSCLE = SARCOMERE
MYOFIBRIL is 1micrometer in diameter by definition. EACH MYOCYTE contains bunch of myofibrils. EACH MYOFIBRIL contains repeated sections of SARCOMERES formed by the organisation of MYOFILAMENTS ( actin, myosin, titin and other structural elements )
SARCOMERES UNDER ELECTRON MICROSCOPE:
IN SARCOMERE we see MYOFILAMENTS and STRUCTURAL PROTEINS ELEMENTS interaction, some in action and some helping them by holding the ones in action. SARCOMERIC STRUCTURAL PROTEINS like TITIN, NEBULIN, TELETHONIN, ALPHA ACTININ, CALPAIN-3, OBSCURIN, MYOSIN BINDING PROTEIN-C, CALMODULIN-1, MVRF-1 are of importance.
What is a sarcomere?
SINGLE SARCOMERE contains two Z LINES.
TITIN is called GAINT POLYPEPTIDE of the BODY. It is organised in multiple folds, some interact with various protein elements at various parts of sarcomere (described below) to help maintain the intact structure of sarcomere. Its size is 3816 kDA, its very huge. Its N-TERMINAL is associated with I-BAND, and C-TERMINAL is associated with A-BAND.
TITIN interacts with following SARCOMERIC PROTEIN structural elements at following areas of sarcomere,
at
Z-LINE with TELETHONIN, ALPHA ACTININ
I- BAND with CALPAIN-3, OBSCURIN
M-LINE with MYOSIN BINDING PROTEIN C, CALMODULIN-1
we see
DARK ZONE and PALE ZONE alternating with each other in EM, how to identify,,
DARK ZONE ( areas where MYOSIN and ACTIN interact) AND
PALE ZONE ( areas where ACTIN IS NOT OVERLAPPED/ has no interaction, with MYOSIN )
TWO LINES called Z-LINE and M-LINE
THREE BANDS called I-BAND, A-BAND, H-BAND (in the order from Z line towards M line)
Z lines (from the German "Zwischenscheibe", the disc in between the I bands) are made of Z disks, which contains ACTIN myofilaments coiled with NEBULIN (600-900kDa ). Other structural elements that keeps them intact are TELETHONIN(TCAP), ALPHA ACTININ(ACTN). identified as DARK LINE in white/pale area under EM. From Z LINE actin myofilaments extend/span towards the myosin myofilaments.
M line - (MYOMESIN, an endline protein is present along with M line protein ) is the MIDDLE of a sarcomere, its the PROMINENT CENTER DARKEST LINE AMONG DARK AREA under EM. MYOSIN filaments OVER LAP HERE AND ARE BOUND. It is also marks the center of A-band and H-band.
I-BAND (ISORTOPIC BAND ) is the area covering either side of Z line, its the area where there is NO INTERACTION or NO OVERLAPPING between ACTIN and MYOSIN. Another important point is that I-BAND DECREASES IN SIZE DURING CONTRACTION.
A-BAND (ANISOTROPIC BAND ) is the ENTIRE DARK ZONE. It has H-band ( the paler area within the A-band ) and also M-line in it. This A-BAND represents the area where THERE IS INTERACTION OF ACTIN with MYOSIN.
H-BAND is the pallor area in A-BAND ( H means HELLER meaning BRIGHTER in german ). The middle of H-band contains M-line.
Note:
I, A, H are the names given based on the properties of these areas under polarizing microscope.
THE BAND that decreases/changes in SIZE/length is I-BAND
A-BAND and H-BAND are FIXED, they DONT CHANGE in SIZE/length.
Clinical aspect based questions on this concept, please contribute
