Body Systems: Musculatory System (Sliding Filament Theory)

Question 1

Microstructures:

Answer 1

•sarcolemma:
-muscle fibre cell membrane.
•Sarcoplasm:
-cytoplasm of muscle fibre.
•sarcoplasmic reticulum:
-storage sites for calcium.
-surrounds myofibrils.
•myofibrils:
-threadlike strands within muscle fibres.
-actin = thin filament.
-myosin = thick filament.
•further divisions of myofibrils:
-Z-line.
-A-band.
-I-band.
-H-zone.

Question 2

Functions of skeletal muscles:

Answer 2

•supports the body: contraction of skeletal muscles opposes the force of gravity and allows us to stand and remain upright.
•makes bones move: movement of arms and legs, and eyes, facial expressions, and breathing.
•maintain constant body temperature: causes ATP to break down which releases heat.
•protect internal organs and stabilize joints: pads the bones that protect the organs and holds bones together.

Question 3

Components of actin filament:

Answer 3

•tropomyosin: long protein filament that blocks the myosin head binding sites.
•troponin: another protein attached to tropomyosin.
-both found on the actin filament.

Question 4

Muscle components:

Answer 4

-muscle contraction involve the action of two myofilaments: actin and myosin.
-1. Actin myofilaments: composed of globular actin proteins.
-2. Myosin filaments: composed of myosin molecules.

Question 5

Sliding filament theory:

Answer 5

-theory that helps scientists explain how muscle contraction occurs.
-thick and thin filaments do not change length.
-thick (myosin) is stationary (non moving), but thin (actin) slides closer together to shorten sarcomere.
••
-how muscle contraction occurs.
-Z-lines move closer together.
-sarcomere shortens.
-actin filaments slide over myosin filaments.
-actin and myosin filaments do not change shape.
-the energy for muscle contraction comes from ATP.

Question 6

(Sliding filament theory) step 1: cross bridge: (Could be step 2)

Answer 6

•myosin head bind to the actin filament.

Question 7

(Sliding filament theory) step 2: power stroke:

Answer 7

•myosin head preforms power stroke.
•ADP + pi detach.
•both Z-lines move towards the centre and contraction occurs.

Question 8

(Sliding filament theory) step 3: detachment:

Answer 8

•ATP binds to the myosin head.
•myosin detaches from actin.
•powered by ATP.
•tropomyosin blocks myosin binding sites on actin.

Question 9

(Sliding filament theory) step 4: hydrolysis:
(Could be step 1)

Answer 9

•brain sends signal to release Ca2+ from the sarcoplasmic reticulum.
•Ca2+ binds to troponin repositioning tropomyosin and exposing myosin binding sites on actin.
•ATP is split into ADP + pi + energy.
•myosin head goes into “ready” position.

Question 10

(Sliding filament theory) full:

Answer 10

•step 1 (or 2): myosin head bind to the actin filament.
•step 2: myosin head preforms power stroke.
•ADP + pi detach.
•both Z-lines move towards the centre and contraction occurs.
•step 3: ATP binds to the myosin head.
•myosin detaches from actin.
•powered by ATP.
•tropomyosin blocks myosin binding sites on actin.
•step 4 (or 1): brain sends signal to release Ca2+ from the sarcoplasmic reticulum.
•Ca2+ binds to troponin repositioning tropomyosin and exposing myosin binding sites on actin.
•ATP is split into ADP + pi + energy.
•myosin head goes into “ready” position.

Question 11

Energy for muscle contraction:

Answer 11

•ATP that is produced for strenuous exercise lasts only a few seconds.
•the muscle then acquires new ATP in 3 different ways, depending on the availability of oxygen:
••breakdown of creatine phosphate (anaerobic).
-used first to acquire ATP before it enters the mitochondria.
••aerobic cellular respiration.
-can only occur if oxygen is available.
••lactic acid fermentation (anaerobic).
-if exercise is so vigorous that oxygen cannot be delivered fast enough to the working muscles.
-causes an oxygen deficit.

Question 12

Creatine phosphate (from liver):

Answer 12

-high-energy compound that builds up when muscle is resting.
-it is the fastest way to make ATP available to muscles.
-provides enough energy for about 8 seconds of intense activity, and then it is spent.
-supplies a phosphate to ADP.
-a way to get ATP before O2 enters mitochondria.
-can take artificial creatine phosphate to help build muscles.

Question 13

Aerobic cellular respiration:

Answer 13

-takes place in the mitochondria.
-provides most of the muscles ATP.
-glycogen and fats are stored in muscle cells to be used to produce ATP when oxygen is available.
-produces CO2 and heat as waste.

Question 14

Lactic acid fermentation:

Answer 14

-supplies ATP in the absence of oxygen.
-produces lactate.
-accumulation of lactate/acid in the sarcoplasm.
-causes cramping and fatigue to set in.
-results in oxygen deficit.

Question 15

Muscle fatigue:

Answer 15

-lack of energy and build up of waste in muscles.
-oxygen debt: when energy demand exceeds ATP supply, lactic acid accumulates.
-causes muscle pain and is associated with fatigue.
-muscles become acidic—> fail to contract.
-rapid breathing after exercise is designed to repay oxygen debt.

Question 16

Rigor mortis:

Answer 16

-moments up to 60 hours after death.
-ATP production ceases and skeletal muscle becomes fixed—body stiff as a board.
-cross-bridges fail to detach.

Question 17

Summary: (musculatory system):

Answer 17

-splitting of ATP (hydrolysis) provides energy for muscle contraction.
-ATP allows myosin head to detach and muscle returns to relaxed state.
-Ca2+ released from SR during contraction.
-creatine phosphate regenerates ATP.