Lecture Five Flashcards
(38 cards)
What is the primary function of the Muscular System?
Produce movement in the body
What are the other functions of the Muscular System?
- Constriction of organs and vessels
- Cardiac contraction
- Respiration
- Postural maintenance
- Body heat production
What are the types of muscle?
Skeletal, smooth, cardiac
What are the functional classification of muscles?
Voluntary= skeletal Involuntary= cardiac & smooth
What are the is the histological classification of muscles?
Striated= cardiac & skeletal Non-striated= smooth
What is the Sarcolemma (Plasmalemma), composed of, what does it fuse to, what does it assist and what does it transport??
- Cell membrane is composed of the sarcolemma and basement membrane.
- Fuses with tendon which connects muscle to bone.
- Assists with the transmission of action potentials along the muscle.
- Transports metabolites in and out of cell.
What is the Sarcoplasmic Reticulum and what does to store?
- Specialised smooth endoplasmic reticulum in skeletal muscle, network of tubules run along and around myofibrils.
- Storage site of calcium
What is the transverse tubules?
- Extensions of the plasmalemma that pass laterally through the cell
- Allow action potentials to be transmitted into the myofibrils
What are other organelles of the skeletal muscle?
- Sarcoplasm
- Mitochondria
- Nucleus
- Multi-nucleated
- Myofibrils
- Myofilaments
What are the Myofibrils?
-Complex organelle composed of bundles of myofilaments.
What is the Sarcomere?
-Contractile unit of muscle.
o Z-line to Z-line
-Striation of myofibrils reflects overlapping of thick and thin filaments
-M-line: Myosin attachment
-Titin enables the muscle to stretch and recoil
What is myosin?
-Thick filaments are bundles of Myosin molecules
-Each globular ‘head’ of the myosin has:
o Myosin ATPase site
o Actin binding site
What is actin?
-Thin filaments are paired chains of actin molecules each with a myosin binding site.
What are the binding sites covered with in the sliding filament theory?
-At rest the binding sites are covered by the regulatory proteins
o Troponin
o Tropomyosin
What is the role of calcium in the sliding filament theory?
-At rest, myosin and actin are unable to bind due to Troponin and Tropomyosin.
o Tropomyosin covers the binding sites on actin
o Troponin holds Tropomyosin in place
-Troponin is the ‘lock’ that keeps binding sites inaccessible
-Calcium is the ‘key’
-Ca2+ is stored in the Sarcoplasmic Reticulum
-Upon release it spreads out in the sarcoplasm and binds to Troponin
o Troponin initiates contraction process by moving Tropomyosin away to expose the Myosin binding sites on actin.
What does calcium do to troponin in an excited sliding filament?
-Ca2+ binds to Troponin
o Changes shape exposing the binding sites by moving Tropomyosin aside
o Cross bridging occurs = attachment of Myosin to Actin
What are the stages in the sliding filament theory?
- Exposure of Active Sites
- Calcium is released
- Calcium makes it way to troponin which is then unlocked
- Pulls tropomyosin to uncover the myosin binding sites on actin. - Cross-bridge Formation
- When myosin binds to binding sites on actin - Power Stroke
- Energy stored in the myosin head if used to cause the power stroke. - Cross-bridge Release
- An ATP molecule binds to each head & causes detachment - ATP to ADP and P
- A chemical reaction causes the P to detach from ATP - Recovery Stroke
- Myosin head returns to resting position= energy stored in head.
What happens if calcium is still attached to troponin?
-If calcium is still attached to troponin the cycle starts again
-Repeated cycles of cross-bridge binding and power stroking ‘walks’ the cross bridges along the actin filaments pulling these inward
o Towards M-Line
-Overlap of the filaments increases and sarcomeres shorten
What is the role of ATP?
-Muscle action is an active process; therefore, it requires energy in the form of ATP.
o Myosin contains a binding site for ATP.
o In a relaxed state, the energised myosin heads are cocked back with ADP + Pi attached.
What happens in the power stroke in terms of ATP?
-Pi and ENERGY is released causing myosin head to pivot, pulling actin in towards centre of sarcomere; ADP is released from myosin.
What happens in the cross bridge stroke in terms of ATP?
-A new ATP binds to myosin head to release it from actin
What happens in the recovery stroke in terms of ATP?
-ATP is broken down by myosin ATPase to form ADP + Pi + energy to re-energise and re-position the head of myosin.
What happens to the sarcomere without ATP?
-Myosin and actin remain bound
-In rigor mortis, the muscles stiffen because there is no ATP to release the bond.
-When neural muscle stimulation ceases:
o Ca2+ actively transported back into the sarcoplasmic reticulum using ATP
o Tropomyosin will cover binding sites on actin
-Muscle relaxation requires energy supply by ATP
What are the functions that require ATP within a muscle?
- Power Stroke
- Release of myosin from actin after power stroke
- Transporting calcium back to sarcoplasmic reticulum
