Myofibrils
specialized contractile organelles of the muscle cell
Contain a lot of sarcomeres arranged in series
Sarcoplasmic reticulum
fluid filled tubes and sacs running along and surrounding each myofibril- they store and release calcium into the cells
sarcomeres
the functional unit of a myofibril of contraction
2 Contractile proteins?
actin and myosin
actin
makes up the thin filaments
Myosin
Makes up the thick filaments
Neuromuscular Junction
axon terminals that form a junction with the sarcolemma of a number of different muscle cells
Does the axon terminal or sarcolemma ever touch?
no
The Sliding filament mechanism
- once the signal reaches the muscle fibers, it crosses the synaptic cleft
- the signal is then continued by the muscle fibres and spreads out across the sarcolemma
- it then travels down the transverse tubules and stimulates the sarcoplasmic reticulum to release calcium.
- the calcium allows the myosin of the thick filament to with the actin of the thin filament.
- the myosin pulls the actin/thin filaments together
- it disengages and starts the cycle again
- this ratcheting of the filaments uses ATP
- with repetition, it shortens the sarcomere, the myofibril, the muscle fibre, the muscle
- when the aps stop, the sarcoplasmic reticulum pumps calcium back inside (this uses ATP)
- without sufficient calcium, the thick filaments cannot continue their ratcheting of the thin filaments
- tension generation stops
Creatine Phosphate
- a molecule that’s stores high amounts of energy in its chemical bonds
- PCr is split by an enzyme, the energy released is used to reform ATP.
- this happens very fast therefore PCr is the first source of energy used when muscle contraction begins
- Provides energy for 3-15 seconds of maximal contraction
- no oxygen needed
- no lactic acid produced (hence anaerobic alactic)
Anaerobic Glycolysis
- when muscle activity is continued over time PCr is depleted so glucose is used to restore the ATP
- broken down into 2 molecules of pyruvic acid and 2-3 ATP
- no oxygen, pyruvic acid does not go into the mitochondria it is converted into lactic acid
- the lactic acid diffuses out into the blood
- capable of producing energy for 30-40seconds
Aerobic Cellular respiration
this pathway is active when you are able to get oxygen in to the cells.
- oxygen is delivered from disusing in the blood or delivered by myoglobin.
- in the presence of oxygen, pyruvic acid enters the mitochondria and in a series of reactions that use oxygen, produces much more ATP (much more than glycolysis)
- carbohydrates, fats and proteins can be used in this process to make ATP
What are the three types of skeletal muscle fibers?
- Slow Oxidative.
- Fast Oxidative
- Fast Glycolytic
Isotonic
muscle contraction through a range against a resistance that is not changing
Concentric
A shortening contraction
Eccentric
A lengthening contraction
Isometric
Muscle contraction in which the length of the muscle does not visibly change
Flaccidity
A lack of tine from the nerve being damaged or cut.
Hypertrophy
Increase in muscle size
Atrophy
Decrease in Muscle size
Satellite cells
- undifferentiated muscle cells
- actively involved in muscle repair and regeneration
- capacity is limited
Epimysium
Connective tissue component
Surrounds the entire muscle
Perimysium
Surrounds the fascicles
connective tissue component
Endomysium
Surrounds the muscle fibers
