Mar 14 Muscle 2 Flashcards
A sarcomere is the functional region of a?
The sarcomere contains?
When a muscle contracts, it?
A sarcomere is the functional region of a myofibril contained between two Z-lines (or disks).
The sarcomere contains thin filaments (ACTIN) and thick filaments (MYOSIN).
When a muscle contracts, it shortens. At the microscopic level, the sarcomere shortens but NOT all parts shorten. Basically, actin filaments slide past each other… And thus the I band and H-zone shrink in size but the A band stays the same length…
How do Actin and Myosin “slide” past each other?
(2 things)
This process requires?
How do Actin and Myosin “slide” past each other?
During contraction, myosin heads attach to actin filaments, forming cross-bridges.
- The myosin heads then “walk” along the actin filaments, pulling them towards the center of the sarcomere (this is called Cross-Bridge Cycling)
This process requires some additional very important proteins in the sarcomere, called TROPOMYOSIN and TROPONIN and it requires the mineral (cation) calcium (Ca2+)
Tropomyosin acts as a?
Troponin (_____) acts as a?
Tropomyosin acts as a “blocker” for the
myosin binding location on actin.
Troponin (a protein complex) acts as a
binding site for Ca2+
what is “telling the muscles to contract?
(6 pathways from Motor Neuron)
what is “telling the muscles to contract?
motor Neuron -> Dendrites (Collect signals) -> Axonz (Passes signals) -> Myelin -> Neuromuscular Junction -> Muscle fiber
Neuromuscular Junction
(4 steps)
Neuromuscular Junction
Action potential Arrives
Vescicles release neurotransmitters (Acetylcholine)
Action potential continues to travel down T tubule via sarcolemma
Calcium Released by sarcoplasmic reticulum
Steps to the Sliding Filament Theory
1) (2 things)
Steps to the Sliding Filament Theory
1) When a nerve signal reaches the muscle cell, calcium is released from the sarcoplasmic reticulum surrounding the myofibrils. Calcium binds to troponin and causes a conformational change in the tropomyosin molecule which shift in position to expose the binding sites (dark green) of the actin proteins
Steps to the Sliding Filament Theory
2:
3:
2: The myosin heads bind to the binding sites of the actin proteins, to form a cross-bridge as the inorganic phosphate is released.
3: ADP is released which causes initiation of the power stroke, where the thin filament gets pulled closer toward the midline of a sarcomere (toward the M line).
Steps to the Sliding Filament Theory
4: (2 things)
4: An ATP molecule binds to the myosin head causing the separation of the actin-myosin cross-bridge. The ATP is subsequently hydrolyzed to ADP and inorganic Phosphate (step 1) and the energy transferred from the ATP to the myosin head causes it to “cock” back like the trigger of a gun.
Only living things produce ATP… When you die ATP:
And all your muscle are stiffened (called _____) because you need:
Only living things produce ATP… When you die ATP eventually drops to zero and all your muscle are stiffened (called Rigor mortis) because you need fresh ATP to move from step 3 to step 4 which is necessary for the breakdown of actin-myosin filaments in the muscle fibers.
Muscle Contractions, twitch summation and maximal force production (tetanus)
(2 things)
- With more neural stimulation, greater muscle forces are produced, and less muscle relaxation occurs.
- As greater stimulation more muscle fibres are activated and eventually they develop complete fusion (called tetanus)
Motor Units and Muscle Fibre Types
A motor unit is?
It consists of?
It acts as?
Each motor unit?
A motor unit is the fundamental unit of skeletal muscle movement.
It consists of a single motor neuron and all the muscle fibers it innervates.
It acts as the final output of the central nervous system for controlling muscle contractions.
Each motor unit innervates several muscle fibres of the same fibre type (i.e., “slow” or “fast” muscle fibre that appear as red or white, respectively.
