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 the structure of muscle tissue
muscle tissue is made up of bundles (fibers that make up fascicles)
each fiber is made up of many fibrils
the myofibrils appear striated because of the alternating dark and light bands
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 fiber 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)