W6: Muscle Contaction: Biochemical Events

Question 1

What is a single muscle cell?

Answer 1

Myocyte

Question 2

What composes myofibrils?

Answer 2

Myofilaments (actin and myosin)

Question 3

What forms a muscle fibre (myocyte)

Answer 3

Many myofibrils will collect to form a muscle fibre or myocyte.

Question 4

What forms a fascicle?

Answer 4

Many muscle fibres/myocytes

Question 5

What forms a muscle?

Answer 5

Fasciculi

Question 6

What forms striations or non-striations?

Answer 6

The arrangement of actin and myosin. The sarcomere bands and lines for striations in skeletal muscle.

Question 7

Tissue sheaths of skeletal muscle

Answer 7

Endomysium = tissue sheath enveloping a muscle fibre
Perimysium = tissue sheath enveloping a fascicle
Epimysium = tissue sheath enveloping all fascicles of a muscle

Question 8

How does the neurovascular bundle run in a muscle?

Answer 8

The neurovascular muscle of any muscle runs in between and in parallel with muscle fascicles.

Question 9

Muscle muscle fibre arrangement (from outside to inside) in smooth muscle GIT

Answer 9

Longitudinal muscle layer
Circular muscle layer
Longitudinal muscularis mucosae

Question 10

Properties of a skeletal muscle fibre

Answer 10

Skeletal myocytes are tubular and multinucleated (nuclei in the periphery)

Question 11

What is a sarcomere?

Answer 11

The functional unit of a muscle. Distance between 2 adjacent Z-lines. Repeated throughout the muscle.

Question 12

What happens when the sarcomere shortens?

Answer 12

As the sarcomere shortens, the muscle contracts. Produces force.

Question 13

What happens to the sarcomere bands and lines when the muscle contracts?

Answer 13

Z-lines come closer together
I bands shorten
H-zone shortens
A-bands stay the same length

Question 14

What is the sarcomere made from?

Answer 14

Thick myosin filaments and thin actin filaments which overlap to produce a darkness

Question 15

Overlapping of actin and myosin in a stretched (relaxed) muscle?

Answer 15

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

Question 16

Overlapping of actin and myosin in a full contracted/shortened muscle

Answer 16

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

Question 17

Properties of myosin

Answer 17

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)

Question 18

Properties of actin

Answer 18

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.

Question 19

How are actin and myosin arranged in a sarcomere?

Answer 19

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.

Question 20

What does the troponin complex consist of?

Answer 20

TnI, TnC, TNT. TnC plays a critical part in unlocking the binding sites on actin to make it available to the myosin heads.

Question 21

The sliding filament model CHECK THIS WITH A TEXTBOOK

Answer 21

1. Ca2+ released from the SR cause the tropomyosin molecule (undergoes a conformational change) to pull away from the binding sites on the actin molecule
2. Myosin head now attached to the binding site on the actin filament and form cross-bridges.
3. 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.
4. ATP fixes to myosin head, causing it to detach from the actin filament.
5. Hydrolysis of ATP to ADP by myosin provides energy for the myosin head to return to its normal position.
6. Head of myosin reattaches to a binding site further along the actin filament and the cycle is repeated.

Question 22

What is used as a marker for cardiac ischaemia?

Answer 22

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).