Muscular system

Describe a sarcomere

A contractile unit, a segment of myofibril extending from one z line to the next (z lines - attachment points for sarcomeres).

How do sarcomeres function in a muscle cell?

Myosin and actin drive contraction. Myosin has heads to pull actin, powered by ATP. Myosin binds actin when stimulated and sarcomere shortens so muscle contracts.

Compare isotonic and isometric contraction

Isotonic: Muscle shortens while maintaining a constant force, movement occurs. E.g - lifting up arm/pencil, squats.

Isometric: Force is generated, muscle doesn’t shorten, no movement. E.g - holding something heavy while standing still, doing a plank

Compare slow vs fast twitch muscle fibers

Slow - contract slowly, make ATP as needed by aerobic metabolism, many mitochondria, used for endurance activities, well-supplied with blood vessels, store very little glycogen.

Fast - Contract fast, rapidly breakdown ATP, fewer mitochondria, capable of anaerobic respiration, used for brief high intensity workouts, store a lot of glycogen

Why do muscles contain both fast and slow twitch fibers?

A mix allows versatility, you can walk long distances without tiring (slow) or sprint suddenly (fast). The ratio varies by muscle function and genetics - endurance athletes have more slow and speed athletes have more fast.

List unique features of cardiac muscle and why their important to its function

Gap junctions - Allow cells to electrically stimulate the next one

Intercalated discs - ensure synchronization, heart pumps as one unit

Autorythmic - can contract without nerve stimulation

List unique features of smooth muscle and why their important to its function

Gap junctions - allow cells to activate each other

Can stretch and still contract - uterus, bladder

Non-striated - Allow for greater flexibility and sustained contraction (moving food along gut)

Describe 2 diseases of the muscular system

Muscular dystrophy - Genetic disease, extra Ca+ is leaked into cells which activates enzymes that destroy muscle proteins. Causes muscle weakening and wasting.

Muscle cramps - often caused by dehydration or ion imbalances.