015 spl: muscle

Question 1

what muscle type is voluntary (somatic)?

Answer 1

• skeletal

Question 2

what muscle types are involuntary (autonomic)?

Answer 2

• cardiac, smooth

Question 3

what muscle types are striated?

Answer 3

• skeletal and cardiac

Question 4

which muscle types are myogenic?

Answer 4

• cardiac, smooth

Question 5

which muscle types are regulated by adrenaline?

Answer 5

• cardiac, smooth

Question 6

what does a sarcomere length, relative tension graph show?

Answer 6

• sliding filament theory
• sarcomere shortens and filaments overlap as contraction happens
• peak tension occurs a medium sarcomere length (partially overlapping)
• hill shape curve

Question 7

describe the graph for force of skeletal muscle against shortening velocity

Answer 7

• lengthening action = eccentric contraction = negative shortening velocity (lengthening), highest force
• isometric contraction = y intercept = 0 shortening velocity (same length), middle force
• shortening action = concentric contraction = postive shortening velocity, low force

Question 8

how long does it take for an intrinsic hand muscle to contract compared to a leg muscle?

Answer 8

• hand = 10-20ms
• leg = 50-200ms

Question 9

rank in order of increasing motor unit size:
gluteal muscles, extraocular muscles, intrinsic hand muscles, thigh muscles

Answer 9

1. extraocular muscles
2. intrinsic hand muscles
3. gluteal muscles
4. thigh muscles

Question 10

how is the distribution of slow and fast twitch fibres altered within a muscle following denervation and subsequent reinnervation?

Answer 10

• mature muscle fibres are innervated by a single axon, but if this is lost then nearby undamaged axons sprout to form new contacts with the denervated fibre
• initially there may be multiple innervations and then selected and eliminated like fetus
  -1 axon xan come

Question 11

how is the distribution of slow and fast twitch fibres altered within a muscle following denervation and subsequent reinnervation?

Answer 11

• mature muscle fibres are innervated by a single axon, but if this is lost then nearby undamaged axons sprout to form new contacts with the denervated fibre
• initially there may be multiple innervations and then selected and eliminated like fetus
  -1 axon can come to dominate an area of muscle after a long period of denervation causing grouping rather than random rearrangment
• the muscle fibres will assume the characteristics of the motorneurone which innervates them

Question 12

describe the sequence of events within a skeletal muscle fibre from an action potential to the myofibril generating a force

Answer 12

1. AP originate in cell body and move along axon and depolarise nerve terminal
2. Ca ions flow into nerve terminal causing ACh release into synapse
3. ACh diffuses across synapse and binds to ACh receptors on post-synpatic muscle membrane
4. this causes Na ion channels to open and an ions flow into muscle causing depolarisation (EPP)
5. when EPP reaches threshold, AP is generated going down T-tubules in muscle
6. AP causes release of Ca from sarcoplasmic reticulum
7. Ca binds to troponin and reveals actin-myosin binding sites
8. actin-myosin cross-bridges form and contraction occurs

Question 13

what are the 2 ways muscle increases force of contraction?

Answer 13

• increasing rate of motor units (rate coding)
• recruit additional motor units (recruitment)