MUSCULOSKELETAL SYSTEM II

Question 1

Most energy required for muscle contraction is used for?

Answer 1

Walk along/ sliding filament mechanism.

Question 2

Small amount of energy is required for muscle contraction is used for what?

Answer 2

A. Calcium reuptake (from sarcoplasm to SR stores)
B. Na+/K+ ATPase pump located along muscle fibers for maintenance of appropriate environment for AP propagation along the muscle fibers.

Question 3

The ATP concentration in muscle fibers is equal to what?

Answer 3

= TO 4 millimolar which is enough to maintain full contraction for 1-2 secs.

Question 4

ATP split to ?

Answer 4

ADP to produce energy for contracting muscle fibers

Question 5

ADP is phosphorylated to what?

Answer 5

To form new ATP, happens within secs to allow the continuation of the muscle contraction

Question 6

List 3 sources of energy for muscle contraction

Answer 6

A. Phosphocreatine (creatine + phosphate- CP) a high energy molecule
B. Glycolysis of Glycogen: Previously stored in muscle cells.
C. Oxidative metabolism: aerobic process

Question 7

When ATP react with Creatine what are 2 products

Answer 7

1. ADP
2. Phosphocreatine

Question 8

Phosphocreatine get cleaved to produce what?

Answer 8

Free energy

Question 9

The reaction of CP+ ADP produces which products and uses which enzyme

Answer 9

ATP
Creatine
The creatine kinase is the enzyme used.

Question 10

Rapidly breakdown of glycogen produces which three products

Answer 10

1. ATP
2. LATIC ACID
   3.PYRUVIC ACID

Question 11

Muscle contraction can be sustained up to how long?

Answer 11

1 minute

Question 12

ATP can be used to re-inform which compound?

Answer 12

Phosphocreatine

Question 13

Over 95% of ATP utilized by muscles for sustained, long-term contraction
is derived from?

Answer 13

Oxidative metabolism

Question 14

The single skeletal muscle twitch lasts for how long?

Answer 14

25 to 200 ms depending on a type of a muslce.

Question 15

Each twitch is elicited by a single what?

Answer 15

AP

Question 16

Duration of a single twitch is long compared to the?

Answer 16

Duration of exciting AP

Question 17

The muscle twitch occurs in 3 phase name those phases and explain them.

Answer 17

A. Latent phase
Begin of stimulation (excitation) (2ms)
B. Contraction phase
Ca2+ binds with troponin C
Cross bridges form
Increase in tension.
exposure of active site
last for about 15ms
C. Relaxation Phase
Ca2+ decreases
Decreases in tension to rest.
Cross bridges detach.
last for about 25ms

Question 18

Due to difference in duration of twitch and AP it is possible to initiates what?

Answer 18

Initiates a 2nd AP before 1st muscle contraction ends.

Question 19

2nd AP stimulates what? explain

Answer 19

A twitch over the residual tension of the 1st twitch. Greater isometric tension than the 1st twitch= summation

Question 20

When multiple AP occurs close enough in time, what will summate?
Increases what?

Answer 20

Multiple twitches will summate
Increased in tension

Question 21

The higher the frequency of AP the higher?

Answer 21

Tension- frequency summation

Question 22

What is tetanus?

Answer 22

State at which individual twitches are not distinguishable from each other

Question 23

What happen when a stimulation is greatly increased?

Answer 23

Individual twitches occur close together in time.
Become fused
causes muscle tension remain at a steady plateau

Question 24

Each motor neurons leaving the spinal cord innervates a single muscle.
True or FALSE

Answer 24

False because Each motoneuron leaving spinal cord innervates multiple muscle
fibres

Question 25

What is the motor unit

Answer 25

all muscle fibers innervated by a single nerve fiber

Question 26

What is a Motor unit recruitment?

Answer 26

sequential activation of the motor unit to perform a designated task.

Question 27

What leads to muscle fatigue

Answer 27

prolonged and strong contraction of muscle

Question 28

Muscle fatigue is an inability of what?

Answer 28

The inability of contractile and metabolic process of muscle fibers to continue supply the work output.

Question 29

During muscle fatigue, there is a low blood supply. explain how?

Answer 29

Interruption of blood flow through a contracting muscle→ almost complete muscle fatigue within 1 or 2 minutes due to lack nutrient and oxygen supply

Question 30

In marathon runners the muscle fatigue occurs when?

Answer 30

occurs with a rate of muscle glycogen depletion.

Question 31

In sprinters what is the primary source of energy?

Answer 31

Glycolysis

Question 32

what happen in sprinters after few minutes or seconds of intense activity muscle

Answer 32

Lactic acid and its dissociation increases PH decreases Muscle activity decreases Rapid fatigue

Question 33

Analysis of lever system in the body depends on the knowledge of?

Answer 33

A. The point of muscle insertion 2. The distance between fulcrum and lever 3. The length of the lever 4. The position of the lever

Question 34

Explain the following terns Motor-end-plate Synaptic gutter/trough Synaptic cleft/space Subneural clelft

Answer 34

* A specialized region of the sarcolemma that invaginate closest to the presynaptic nerve terminal = motor-end-plate. * Synaptic gutter/trough= invagination membrane * Synaptic space/cleft= space between the terminal and the fibre membrane. * Subneural clefts= numerous smaller folds greatly increase the surface area at which neurotransmitter can act. * In axon terminal, there are many mitochondria which produce ATP used for excitatory neurotransmitter, ACh.

Question 35

Explain the secretion of acetylcholine by the nerve terminals

Answer 35

* Upon the arrival of AP at the NMJ, ACh are released from the synaptic terminal vesicles into synaptic cleft. * On the membrane of the motor neuron, are voltage-gated calcium channels, activated by the change in electrical potential in the neuronal membrane (presynaptic membrane)→ Ca2+ influx. * Ca2+ is believed to activate Ca2+ -calmodulin dependent protein kinase, which phosphorylates synapsin proteins which anchor ACh vesicles from the cytoskeleton and allow them to move to active zone of the presynaptic neural membrane adjacent to the voltage-gated Ca2+ channels. * Synaptic vesicles dock at release sites, fuse with the neural membrane, and empty their ACh into the synaptic space by the process of exocytosis.

Question 36

Acetylcholine Opens Ion Channels on Postsynaptic Membranes, explain.

Answer 36

ACh bind to ACh-gated Na+ channels (nicotinic receptors) located on postsynaptic membrane (at subneural clefts) → allow influx of Na+ ions → cause graded, depolarized end-plate potential (50 to 75 mV). * End-plate potential great enough to increase membrane potential to threshold → lead to activation of voltage-gated Na+ channels located near the end-plate → trigger an AP → propagates along the sarcolemma. * AP propagates along sarcolemma into the interior of the muscle fibres through Ttubules

Question 37

explain the Destruction of the Released Acetylcholine by Acetylcholinesterase:

Answer 37

* ACh in the synaptic cleft continues activating nicotinic receptors as long as it still persist in the synaptic space. * Acetylcholinesterase (ACh-E) rapidly deactivate ACh→ decline ACh levels in the synaptic cleft * Some ACh molecules diffuse out of the synaptic cleft.

Question 38

Action Potential in Skeletal Muscle 1. Resting membrane potential = 2. Duration of an AP = 3. Velocity of conduction =

Answer 38

1. -80 to -90 mV 2. 1 to 5 ms 3. 3 to 5 m/s

Question 39

Action Potential Spread to the Interior of the Muscle Fibre, explain

Answer 39

* AP generated from NMJ, propagates along the sarcolemma into transverse-tubule (Ttubule). * AP in T-tubule activates Ca2+ release from the SR. * Release of Ca2+ → muscle contraction = excitation-contraction coupling

Question 40

T tubules runs transvers to ?

Answer 40

Myofibrils

Question 41

Along the length of t tubules at terminals what are found

Answer 41

2 terminal cisternae

Question 42

Inside the SR, is a protein that can bind more Ca2+, name of the protein

Answer 42

Calsequestrin.

Question 43

Combination of T-tubule and 2 terminal cisternae is called?

Answer 43

= triad/triad junction.

Question 44

L type Ca2+ channel is also known as ?

Answer 44

DHP receptor

Question 45

explain what happen when the AP arrives in T- Tubules until contraction of a muscle

Answer 45

AP arrives in T-tubules & activates L-type Ca2+ channels (also know as DHP receptors) to open. * L-type Ca2+ channels are physically coupled with SR Ca2+-release channels (RYR1) → lead to Ca2+ release from the SR into the sarcoplasm. * Ca2+ binds to troponin-C → gets activated, conformational change, displaces tropomyosin→ troponin-tropomyosin complex inhibition→ exposure of active sites on F-actin (actin filament activation) → initiate muscle contraction.