L3 - Neuromuscular Junction & Skeletal Muscle

Question 1

is skeletal muscle stimulated and regulated by the somatic or autonomic nervous system?

Answer 1

somatic nervous system

Question 2

what occurs at the neuromuscular junction?

Answer 2

the neurone synapses with skeletal muscle

Question 3

T/F the neurones that supply skeletal muscle are myelinated

Answer 3

TRUE - the neurones that supply skeletal muscle are myelinated

Question 4

where do neurones (alpha motor neurones/lower motor neurones) originate?

Answer 4

spinal cord

Question 5

what is released from the ends of these neurones into synaptic cleft?

Answer 5

neurotranmitter ACh

Question 6

what is synaptic cleft?

Answer 6

tiny gap between the end of the neurone and the muscle cell

Question 7

how does ACh cause a muscle action potential?

Answer 7

by binding to receptors on the motor end plate of the muscle

Question 8

what breaks down ACh after nerve action potentials cease?

Answer 8

enzyme anticholinesterases (AChE)

Question 9

give 4 examples of alterations of the NMJ

Answer 9

1. decreased numbers of functioning ACh receptors
2. decreased release of ACh - impaired synaptic transmission
3. decreased interaction between ACh and receptor
4. widespread therapeutic manipulation in anesthesia

Question 10

give an example of red muscle fibres

Answer 10

leg and back muscles

Question 11

does red or white muscle have more myoglobin and mitochondria?

Answer 11

red - myoglobin +++ (stores O2) and mitochondria +++ (ATP+++ for aerobic metabolism)

Question 12

which type of muscle fibre uses glycolic metabolism and which uses aerobic metabolism?

Answer 12

red - aerobic
white - glycolic

Question 13

T/F red muscle fibres fatigue faster than white muscle fibres

Answer 13

FALSE - red muscle fibres are fatigue resistant, white muscle fibres fatigue rapidly

Question 14

give an example of white muscle fibre

Answer 14

eye muscles

Question 15

what makes up myofibril?

Answer 15

proteins actin and myosin

Question 16

what does the sarcoplasmic reticulum store?

Answer 16

calcium

Question 17

what is a sarcomere?

Answer 17

arranged myofilaments of actin and myosin - extending from one Z disc to another (striated appearance)

Question 18

how does the contraction/relaxation cycle begin? (step1)

Answer 18

nerve impulse arrives at axon terminal of motor neuron and triggers release of ACh

Question 19

what does ACh do to trigger action potential? (step2)

Answer 19

ACh diffuses across synaptic cleft, binds to its receptors in the motor end plate - triggers AP

Question 20

what destroys ACh and why? (step3)

Answer 20

acetylcholinesterase destroys ACh so that another AP cannot occur unless more ACh is released from the motor neuron

Question 21

muscle AP travelling along transverse tubules does what? (step4)

Answer 21

opens Ca2+ release channels in the sarcoplasmic reticulum membrane, which allows calcium ions to flood into the sarcoplasm

Question 22

what does Ca2+ bind to? (step5)

Answer 22

Ca2+ binds to troponin on the thin filament, exposing the binding sites for myosin

Question 23

explain contraction (step6)

Answer 23

power strokes use ATP, myosin heads bind to actin, swivel and release, thin filaments are pulled toward centre of sarcomere

Question 24

what happens when Ca2+ release channels close? (step7)

Answer 24

Ca2+ active transport pumps use ATP to restore low level of Ca2+ in sarcoplasm

Question 25

what blocks the myosin binding sites on actin? (step8)

Answer 25

troponin-tropomyosin complex slides back into position
muscle relaxes!

Question 26

give 3 sources of ATP

Answer 26

1. creatine phosphate
2. anaerobic metabolism - glycolysis - but excessive anaerobic metabolism leads to build up of lactic acid
3. aerobic metabolism - and oxygen binding protein myoglobin