FISIOLOGI OTOT I

Oleh : dr. Ermin Rachmawati

Lokasi

Striation

Kontrol

fungsi

1. Pergerakan tubuh2. Maintenance of posture3. Respirasi4. Produksi panas tubuh5. Komunikasi6. Konstriksi organ atau pembuluh darah7. Denyut jantung

1. Skeletal muscle, as its name implies, is the muscle attached to the skeleton

2. It is also called striated muscle3. The contraction of skeletal muscle is under voluntary

control.

1. excitability - responds to stimuli (e.g., nervous impulses)

2. contractility - able to shorten in length

3. extensibility - stretches when pulled

4. elasticity - tends to return to original shape & length after contraction or extension

•Membran sel dari muscle fiber•Menjalarkan impuls dan mempertahankan membran potensial•sarcolemma mempunyai lubang yang nantinya disana menjadi tempat bagi T tubule untuk berinvaginasi

•cytoplasm of a muscle cell •contains the usual subcellular elements• along with the Golgi apparatus, abundant myofibrils, a modified endoplasmic reticulum known as the sarcoplasmic reticulum (SR), myoglobin and mitochondria. •Transverse (T)-tubules invaginate the sarcolemma, allowing impulses to penetrate the cell and activate the SR.

NOTE :1. Inervasi

saraf motorik bermielin bercabang di dalam jaringan ikat perimisium, dimana saraf menghasilkan beberapa cabang terminal

2. Motor endplatePada tempat inervasi kehilangan selubung mielin dan membentuk bagian terminal melebar dinamakan motor endplate

1. Terjadi potensial aksi di membran presinaps

2. Saluran bergebsng untuk Ca2+ terbuka

3. Transmitter Asetilkolin dilepaskan dari vesikel

4. Transmitter berikatan dengan reseptor di membran postsinaps

5. Mempengaruhi kondisi ionik tubuh

6. Na influx tjd depolarisasi

1. Ca berikatan dengan troponin yang menyebabkan kompleks troponin tropomiosin terbuka

2. Kepala crossbridge akan tertarik oleh bagian aktif dari filamen aktin

3. Kepala crossbridge melekat pada filamen aktin

4. Terjadi power stroke

5. Kepala miosin terlepas kembali ke posisi tegak lurus dan berikatan dengan filamen aktin lainnya,kemudian terjadi power stroke berikutnya

(Pemiringan kepala crossbridge

disebut POWER STROKE)

Cara Penggunaan ATP untuk keperluan energi pada saat kontraksi1. ATP dihidrolisis oleh ATP-ase miosin , ADP dan

Pi tetap melekat di miosin, energi tersimpan di crossbridge

2. Ketika Ca berikatan dengan troponin, filamen aktin menjadi aktif dan mengikat miosin

3. Terjadi power stroke, sehingga ADP dan Pi dilepaskan

4. Hubungan antara aktin dan miosin terputus sewaktu molekul ATP baru berikatan dengan crossbridge dan mengakibatkan kepala miosin kembali ke posisi tegak lurus

Sumber energi otot rangka

1. Kreatin phospat2. Fosforilasi oksidatif3. Glikolisis

Characteristic of Skeletal Muscle Fiber Types berdasar perbedaan hidrolisis dan sintesa ATP

Characteristics Slow-twitch high-oxidative (Type I)

Fast-twitch Low-oxidative (Type IIa)

Low-oxidative (Type IIx)

Fiber diameter Smallest Intermediate Largest

Myoglobin content High Intermediate Low

Mitochondria Many Intermediate Few

Capillaries Many Intermediate Few

Metabolism High aerobic capacity Intermediate aerobic capacity

Low aerobic capacity

Fatigue Resistant Resistant Fast

Rate of ATP breakdown by ATPase in myosin

Slow Fast Fast

Location where fibers are numerous

Generally postural muscles and more in lower than upper limbs

Can predominates in lower limbs (sprinters)

Upper limbs (more in upper than lower limbs, more in legs

Functions Endurance activities and posture

Endurance activities in endurance trained muscles

Rapid, intense movements of short duration

Otot keseluruhan adalah sekelompok sel otot yang disatukan oleh jaringan konektif dan melekat pada tulang melalui tendon

Motor unit : semua serabut (sel otot) yang dipersyarafi oleh satu serabut syaraf

SINGLE MUSCLE TWITCH (KEDUTAN) : potensial aksi di tiap sel otot

Untuk menghasilkan gradasi tegangan seluruh otot, 2 faktor yang berpengaruh

1. Jumlah sel otot yang berkontraksi2. Tegangan sel otot yang berkontraksi

Untuk menimbulkan gerakan otot yang kuat diperlukan adanya sumasi yaitu penjumlahan dari muscle twitch,

Dengan penambahan motor unit yang berkontraksi secara serentak ( multiple motor unit summation/spatial summation)

Dengan meningkatkan frekuensi rangsangan pada motor unit (Wave summation )

Subthreshold stimulus (no motor unit respond)

Threshold stimulus (one

motor unit responds)

Submaximal stimuli (increasing numbers of motor units respond)

Supramaximal stimuli (all motor units respond)

Multiple Motor Unit Summation

Multiple – wave summation ……..

1

23

4 5

Multiple – Wave Summation

Multiple – wave summation caused by stimuli of increased frequency (1 – 5): complete relaxation between stimuli (1), incomplete tetanus – partial relaxation between stimuli (2–4), and complete tetanus – no relaxation between stimuli (5) Trepe ……………..

Trepe

Stimuli of constant strength

Trepe

When a rested muscle is stimulated repeatedly with maximal stimuli at a frequency the allows complete relaxation between stimuli, the second contraction produces a slightly greater tension than the first, and the third contraction produces a greater tension than the second. After a few contractions, the tension produced by all contraction is equal

TEXT book: Guyton and Hall; Fisiologi

Kedokteran Ganong Sherwood; From Cell to System Tortora Grabowsky

Muscle contraction1. Because skeletal muscle is voluntary muscle, contraction requires a nervous impulse. So, step 1 in contraction is when the

impulse is transferred from a neuron to the SARCOLEMMA of a muscle cell. 2. The impulse travels along the SARCOLEMMA and down to the T-tubules. From the T-TUBULES, the impulse passes to the

SARCOPLASMIC RETICULUM. 3. As the impulse travels along the Sarcoplasmic Reticulum (SR), the calcium gates in the membrane of the SR open. As a result,

CALCIUM diffuses out of the SR and among the myofilaments. 4. Calcium fills the binding sites in the TROPONIN muscles. As noted previously, this alters the shape and position of the

TROPONIN which in turn causes movement of the attached TROPOMYOSIN molecule. 5. Movement of TROPOMYOSIN permits the MYOSIN HEAD to contact ACTIN. 6. Contact with ACTIN cause the MYOSIN HEAD to swivel. 7. During the swivel, the MYOSIN HEAD is firmly attached to ACTIN. So, when the HEAD swivels it pulls the ACTIN (and,

therefore, the entire thin myofilament) forward. (Obviously, one MYOSIN HEAD cannot pull the entire thin myofilament. Many MYOSIN HEADS are swivelling simultaneously, or nearly so, and their collective efforts are enough to pull the entire thin myofilament).

8. At the end of the swivel, ATP fits into the binding site on the cross-bridge & this breaks the bond between the cross-bridge (myosin) and actin. The MYOSIN HEAD then swivels back. As it swivels back, the ATP breaks down to ADP & P and the cross-bridge again binds to an actin molecule.

9. As a result, the HEAD is once again bound firmly to ACTIN. However, because the HEAD was not attached to actin when it swivelled back, the HEAD will bind to a different ACTIN molecule (i.e., one further back on the thin myofilament). Once the HEAD is attached to ACTIN, the cross-bridge again swivels, SO STEP 7 IS REPEATED. As long as calcium is present (attached to TROPONIN), steps 7 through 9 will continue. And, as they do, the thin myofilament is being "pulled" by the MYOSIN HEADS of the thick myofilament. Thus, the THICK & THIN myofilaments are actually sliding past each other. As this occurs, the distance between the Z-lines of the sarcomere decreases. As sarcomeres get shorter, the myofibril, of course, gets shorter. And, obviously, the muscle fibers (and entire muscle) get shorter. Skeletal muscle relaxes when the nervous impulse stops. No impulse means that the membrane of the SARCOPLASMIC RETICULUM is no longer permeable to calcium (i.e., no impulse means that the CALCIUM GATES close). So, calcium no longer diffuses out. The CALCIUM PUMP in the membrane will now transport the calcium back into the SR. As this occurs, calcium ions leave the binding sites on the TOPONIN MOLECULES. Without calcium, TROPONIN returns to its original shape and position as does the attached TROPOMYOSIN. This means that TROPOMYOSIN is now back in position, in contact with the MYOSIN HEAD. So, the MYOSIN head is no longer in contact with ACTIN and, therefore, the muscle stops contracting (i.e., relaxes).