Muscle contraction

Question 1

There are three types of muscle:

Answer 1

skeletal, cardiac, smooth
Skeletal muscle is controlled by the somatic nervous system. Cardiac and smooth are influenced by the autonomic nervous system
cardiac and smooth are striated - Striation is due to organisation of contractile proteins in the cell

Question 2

myofibrils

Answer 2

Each muscle cell contains many parallel myofibrils

Question 3

Skeletal muscle activity

Answer 3

Controlled by somatic motor neurons located in spinal cord & brainstem. “Motor unit” = one motor neuron plus the muscle cells it targets

Question 4

The neuromuscular junction

Answer 4

• A type of chemical synapse.
• Ach acts on nicotinic receptors to produce an “end plate potential”
• Voltage-gated Na+ channels start in the adjacent membrane.
• The “end plate potential” always triggers an AP in the muscle cell.

Question 5

Neuromuscular junction process

Answer 5

acetylcholine released by axon of motor neuron crosses cleft and binds to receptors/channels on motor end plate > enters T tubule > triggers Ca++ release from sarcoplasmic reticulum into skeletal muscle cell

Question 6

Sarcoplasmic reticulum

Answer 6

Sarcoplasmic reticulum sits next to myofibrils

Question 7

The sarcomere

Answer 7

The sarcomere is the basic contractile unit in skeletal muscle
thin myofilament - Actin
Thick myofilament - Myosin
Ca++ triggers actin/myosin interaction, actin filaments slide over thick filaments towards centre and sarcomere shortens

• without ATP can’t have contraction

Question 8

Calcium ions triggering actin and myosin interaction resulting in POWER STROKE.

Answer 8

• The sequence of events that results in the excitation contraction coupling is:

1. Action potential enters the T-tubule
2. AP then activates the sarcoplasmic reticulum to release Ca2+
3. Ca2+ binds to troponin
4. Troponin-Ca2+ complex pulls the tropomyosin exposing the binding sites on actin
5. Myosin heads bind to actin and with the release of Pi from ADP, Myosin head bends resulting in the power stroke
6. New ATP binds to Myosin head releasing the bond between Myosin and Actin
7. Ca2+ is pumped back into the SR

Question 9

The key element of actin/myosin interaction is “crossbridge cycling”

Answer 9

actin molecules in thin myofilament and myosin cross bridge > binding Myosin cross bridge to actin molecule > power stroke cross bridge bends, pulling thin myofilament inwards

• Requires constant supply of ATP for muscle contraction
• 6 actin fillaments, 6 myosin fillaments

Question 10

Excitation-contraction coupling in skeletal muscle

Answer 10

• Action potential in motor neuron
• Release of ACh at the neuromuscular junction
• ACh action at nicotinic receptors triggers an
end-plate potential
• AP initiated in skeletal muscle membrane
• AP enters T-tubules
• Ca++ release from sarcoplasmic reticulum • Ca++ triggers crossbridge cycling
• Sarcomeres shorten
• Muscle contracts

Question 11

Cellular structure affects skeletal muscle function

Answer 11

At resting muscle length, no relationship btwn actin or pyosin (100%)

at 170%, full lengthening
at 60%, full shortening

Question 12

golgi tendon organ

Answer 12

golgi tendon organ acts as relief valve when to much tension is developed on muscles, prevents damage from happening
* If muscle stretched > fires a lot of AP

Question 13

knee jerk reflex

Answer 13

reflex stimuatles in the spinal cord > the motor neurons to the extensor muscle > inhibits the motor neurons to the flexor muscles

Question 14

Production of ATP in skeletal muscle

Answer 14

get from brake down from glucose via glycolysis - 2

- 36 from oxidative phosphorylaction and 1 creatine phosphate

Question 15

slow twitch muscles

Answer 15

The ATP required for slow-twitch fiber contraction is generated through aerobic respiration (glycolysis and Krebs cycle

Question 16

fast twitch muscles

Answer 16

Rely on anaerobic respiration (glycolysis alone) to produce two molecules of ATP per molecule of glucose.