Lecture 1 - Functional properties of skeletal muscle 1 Flashcards
What are the events at a Neuromuscular Junction?
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
What is muscles structure
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
What is sarcomere
.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.
What is the z-line
Actin molecules are bound to the Z line, which forms the borders of the sarcomere. Other bands appear when the sarcomere is relaxed.
What is myosin /actin
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.
What is the sarcoplasmic reticulum
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.
myofibrils occupy ___ of the fibre volume
80%
__s to ____s of myofibrils exist in each fibre
100s to 1000s of myofibrils exist in each fibre
myofibrils are approximately ____ in diameter
1-2um
The nuclei of mitochondria in healthy muscle are located…
to the perihpery
will be in the centre in injured or regenerating muscle
What does titin do?
Provides elasticity and stabilises myosin
What are the two binding sites of Myosin
Actin bindings site
ATPase site
What is the contraction mechanism:
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
Fibre length is rarely the same as ______ length
muscle
most fibres insert ______ into the tendon - resembles a feather arrangement - called “pinnation” or “pennation
obliquely
allows more fibres to be packed in which increases the effective muscle cross-sectional area (CSA)
Fusiform arrangement of muscle fibres is where they
run the full length (bicep)
Unipennate/bipennate arragement is where
fibres some in towards a single tendon
What is force production proportional to?
muscle CSA
gives rise to architectual specialisation - muscles are designed for a specific functoin
Miometric =
Shortening, concentric
Pliometric =
lengthening, eccentric
The heavier the load, the …
slower the lift
There is a latent period where muscle is contracting isometrically until sufficient _____ has been produced to equal the load
There is a latent period where muscle is contracting isometrically until sufficient tension has been produced to equal the load
Not only is the rate of shortening reduced for heavy loads the …
amount of shortening is also decreased
V(max) is related to…
muscle fibre type distribution and muscle architecture
Power =
load x velocity
success in many sports is dependent upon maximal power output
After the power stroke of the crossbridge that casues the sliding of the thin filaments, what happens next in contraction?
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
Which receptor detects the AP that is propagated down into the muscle by the t-tubule?
DHP receptor
this then signals to the SR to release Ca2+
What is a motor unit?
a motor neuron and all the muscle fibres that it innervates
What is the optimum musle length?
length at which maximum twitch is recorded
What is summation
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)
What is tetanus?
the muscle response following stimualtion of a frequency sufficient to cause fusion
What is the maximum isometric force?
maximum tetanic force response taken from the plateau of the freq-force relationship
