Lecture 1 - Functional properties of skeletal muscle 1

Question 1

What are the events at a Neuromuscular Junction?

Answer 1

Opening of voltage gated Ca2+ channels and entry of Ca2+ to the terminal button of a motor neuron

Ca2+ triggers the release of ACh

ACh diffuses across the cleft and binds with receptors on the motor end plate

opening of cation channels (Na in, K out)

End-plate potential results, intiates an AP that propagates throughout the fibre

ACh destroyed by acetylcholinesterase - terminates the response

Question 2

What is muscles structure

Answer 2

made up of bundles (fascicles of fibres)

each fibre is made up of many fibrils

the myofibrils appear striaged because of the alternating dark and light bands in register

Question 3

What is sarcomere

Answer 3

.A sarcomere (Greek sarx “flesh”, meros “part”) is the basic unit of a muscle. Muscles are composed of tubular muscle cells (myocytes or myofibers), which are formed in a process known as myogenesis. Muscle cells are composed of tubular myofibrils. Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as dark and light bands. Sarcomeres are composed of long, fibrous proteins that slide past each other when the muscles contract and relax.

Question 4

What is the z-line

Answer 4

Actin molecules are bound to the Z line, which forms the borders of the sarcomere. Other bands appear when the sarcomere is relaxed.

Question 5

What is myosin /actin

Answer 5

Two of the important proteins are myosin, which forms the thick filament, and actin, which forms the thin filament. Myosin has a long, fibrous tail and a globular head, which binds to actin. The myosin head also binds to ATP, which is the source of energy for muscle movement. Myosin can only bind to actin when the binding sites on actin are exposed by calcium ions.

Question 6

What is the sarcoplasmic reticulum

Answer 6

Internal storage site of Ca2+

The sarcoplasmic reticulum is smooth ER found in myocytes. The sarcoplasmic reticulum contains large stores of calcium, which it sequesters and then releases when the muscle cell is stimulated. It plays a major role in excitation-contraction coupling.

Question 7

myofibrils occupy ___ of the fibre volume

Answer 7

80%

Question 8

__s to ____s of myofibrils exist in each fibre

Answer 8

100s to 1000s of myofibrils exist in each fibre

Question 9

myofibrils are approximately ____ in diameter

Answer 9

1-2um

Question 10

The nuclei of mitochondria in healthy muscle are located…

Answer 10

to the perihpery

will be in the centre in injured or regenerating muscle

Question 11

What does titin do?

Answer 11

Provides elasticity and stabilises myosin

Question 12

What are the two binding sites of Myosin

Answer 12

Actin bindings site

ATPase site

Question 13

What is the contraction mechanism:

Answer 13

Calcium binds to troponin

Cooperative conformational changes take place in troponin-tropomyosin system

The inhibition of actin and myosin interaction is released

Crossbridges of myosin filaments are attached to actin filaments

Tension is exerted, and/or the muscle shortens by the sliding filament mechanism

Question 14

Fibre length is rarely the same as ______ length

Answer 14

muscle

Question 15

most fibres insert ______ into the tendon - resembles a feather arrangement - called “pinnation” or “pennation

Answer 15

obliquely

allows more fibres to be packed in which increases the effective muscle cross-sectional area (CSA)

Question 16

Fusiform arrangement of muscle fibres is where they

Answer 16

run the full length (bicep)

Question 17

Unipennate/bipennate arragement is where

Answer 17

fibres some in towards a single tendon

Question 18

What is force production proportional to?

Answer 18

muscle CSA

gives rise to architectual specialisation - muscles are designed for a specific functoin

Question 19

Miometric =

Answer 19

Shortening, concentric

Question 20

Pliometric =

Answer 20

lengthening, eccentric

Question 21

The heavier the load, the …

Answer 21

slower the lift

Question 22

There is a latent period where muscle is contracting isometrically until sufficient _____ has been produced to equal the load

Answer 22

There is a latent period where muscle is contracting isometrically until sufficient tension has been produced to equal the load

Question 23

Not only is the rate of shortening reduced for heavy loads the …

Answer 23

amount of shortening is also decreased

Question 24

V(max) is related to…

Answer 24

muscle fibre type distribution and muscle architecture

Question 25

Power =

Answer 25

load x velocity

success in many sports is dependent upon maximal power output

Question 26

After the power stroke of the crossbridge that casues the sliding of the thin filaments, what happens next in contraction?

Answer 26

The bind ing of ATP to the crossbridge, which results in the crossbridge disconnecting from actin

The hydrolysis of ATP, which leads to the re-energising and re=positioning of the crossbridge

Cessation of AP - reuptake of Ca2+ into Sacroplasmic reticulum

relaxation

Question 27

Which receptor detects the AP that is propagated down into the muscle by the t-tubule?

Answer 27

DHP receptor

this then signals to the SR to release Ca2+

Question 28

What is a motor unit?

Answer 28

a motor neuron and all the muscle fibres that it innervates

Question 29

What is the optimum musle length?

Answer 29

length at which maximum twitch is recorded

Question 30

What is summation

Answer 30

staircase effect whereby twitch responses “add or “sum” together in response to repeated electrical stimulation (relates to the recruitment of motor units or the frequency-force relationship)

Question 31

What is tetanus?

Answer 31

the muscle response following stimualtion of a frequency sufficient to cause fusion

Question 32

What is the maximum isometric force?

Answer 32

maximum tetanic force response taken from the plateau of the freq-force relationship