W6: Muscle Contaction: Biochemical Events Flashcards
What is a single muscle cell?
Myocyte
What composes myofibrils?
Myofilaments (actin and myosin)
What forms a muscle fibre (myocyte)
Many myofibrils will collect to form a muscle fibre or myocyte.
What forms a fascicle?
Many muscle fibres/myocytes
What forms a muscle?
Fasciculi
What forms striations or non-striations?
The arrangement of actin and myosin. The sarcomere bands and lines for striations in skeletal muscle.
Tissue sheaths of skeletal muscle
Endomysium = tissue sheath enveloping a muscle fibre Perimysium = tissue sheath enveloping a fascicle Epimysium = tissue sheath enveloping all fascicles of a muscle
How does the neurovascular bundle run in a muscle?
The neurovascular muscle of any muscle runs in between and in parallel with muscle fascicles.
Muscle muscle fibre arrangement (from outside to inside) in smooth muscle GIT
Longitudinal muscle layer
Circular muscle layer
Longitudinal muscularis mucosae
Properties of a skeletal muscle fibre
Skeletal myocytes are tubular and multinucleated (nuclei in the periphery)
What is a sarcomere?
The functional unit of a muscle. Distance between 2 adjacent Z-lines. Repeated throughout the muscle.
What happens when the sarcomere shortens?
As the sarcomere shortens, the muscle contracts. Produces force.
What happens to the sarcomere bands and lines when the muscle contracts?
Z-lines come closer together
I bands shorten
H-zone shortens
A-bands stay the same length
What is the sarcomere made from?
Thick myosin filaments and thin actin filaments which overlap to produce a darkness
Overlapping of actin and myosin in a stretched (relaxed) muscle?
A stretched muscle has reduced overlapping of actin and myosin filaments. Thus reduced muscle strength because few cross-bridges can form between the actin and myosin. Pic at min 28:30
Overlapping of actin and myosin in a full contracted/shortened muscle
A full contracted muscle with lots of overlap between actin and myosin has a reduced potential for cross-bridges to form again, so there is low for production from the muscle. Pic at min 28:30
Properties of myosin
An individual myosin molecule has a rod-like structure from which 2 heads protrude. Each thick filament consists of many myosin molecules whose heads protrude at opposite ends of the filament. (29:30)
Properties of actin
Forms a helix. Tropomyosin molecules coil around the actin helix, reinforcing it. Troponin is attached to each tropomyosin molecule. Has a binding site for myosin which is blocked by the tropomyosin. Min 31.
How are actin and myosin arranged in a sarcomere?
In the centre of the sarcomere, the thick filaments are devoid of myosin heads. The myosin heads extend towards the actin filaments in regions of potential overlap.
What does the troponin complex consist of?
TnI, TnC, TNT. TnC plays a critical part in unlocking the binding sites on actin to make it available to the myosin heads.
The sliding filament model CHECK THIS WITH A TEXTBOOK
- Ca2+ released from the SR cause the tropomyosin molecule (undergoes a conformational change) to pull away from the binding sites on the actin molecule
- Myosin head now attached to the binding site on the actin filament and form cross-bridges.
- Head of myosin changes angle, moving the actin filament along as it does so. ATP is hydrolysed and produces the power stroke. The ADP molecule is released.
- ATP fixes to myosin head, causing it to detach from the actin filament.
- Hydrolysis of ATP to ADP by myosin provides energy for the myosin head to return to its normal position.
- Head of myosin reattaches to a binding site further along the actin filament and the cycle is repeated.
What is used as a marker for cardiac ischaemia?
Troponin (I and T) are released from ischaemic cardiac muscle within an hour. Smallest changes in blood troponin levels are indicative of cardiac muscle damage (quantity is not proportional to degree of damage tho).
