Mar 14 Muscle 2 Flashcards
A sarcomere is:
The sarcomere contains:
When a muscle contracts, which part gets shorter?
- A sarcomere is a part of a myofibril contained between two Z-lines (or disks).
- The sarcomere contains thin filaments (ACTIN) and thick filaments (MYOSIN).
- When a muscle contracts, the sarcomere gets shorter, but not all parts of it change size. The actin filaments slide past the myosin filaments. As a result, the I band and H zone get smaller, but the A band stays the same length.
Cross-bridge cycling:
Two important proteins:
During muscle contraction, myosin heads attach to actin filaments to form cross-bridges. The myosin heads then “walk” along the actin, pulling it toward the center of the sarcomere.
It requires two important proteins—tropomyosin and troponin—as well as the mineral (cation) calcium (Ca²⁺) to happen.
Tropomyosin:
Troponin:
- Tropomyosin acts as a “blocker” for the myosin binding location on actin.
- Troponin (a protein complex) acts as a binding site for Ca2+
Telling muscles to contract
(6 pathways from Motor Neuron)
Motor Neuron – Starts the signal.
Dendrites – Collect signals from the brain/spinal cord.
Axon – Carries the electrical signal down the neuron.
Myelin Sheath – Speeds up the signal along the axon.
Neuromuscular Junction – The connection between the neuron and the muscle.
Muscle Fiber – Receives the signal and begins to contract.
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
Step 1:
Steps to the Sliding Filament Theory
1)When a nerve signal reaches the muscle cell, calcium is released from the sarcoplasmic reticulum (which surrounds the myofibrils). The calcium binds to troponin, causing tropomyosin to shift. This shift exposes the binding sites on the actin filaments, allowing muscle contraction to begin.
Steps to the Sliding Filament Theory
2:
3:
2) The myosin heads bind to the exposed binding sites on the actin filaments, forming a cross-bridge. This happens as inorganic phosphate (Pi) is released.
3) ADP is then released, triggering the power stroke. During this stroke, the myosin head pulls the thin (actin) filament toward the center of the sarcomere, closer to the M line.
Steps to the Sliding Filament Theory
4:
4) A new ATP molecule binds to the myosin head, causing the myosin to detach from the actin—breaking the cross-bridge. The ATP is then hydrolyzed into ADP and inorganic phosphate (Pi), and the energy released is used to “re-cock” the myosin head, getting it ready for another cycle.
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)
- More neural stimulation = greater muscle forces are produced, and less muscle relaxation occurs.
- 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.
