Flashcards in 15CHAPTER 11: MUSCLE TISSUES Deck (102)
What are contractile proteins and what do they do?
Actin and myosin, shortens muscle fibers
What are regulatory proteins and what do they do?
Troponin and tropomyosin, acts like a switch
What is dystrophin?
A protein that links actin to cell membrane = endomysium
What happens what there is a lack of dystrophin?
Muscular dystrophy (genetic disorder)
What are the different kinds of striations?
A-band (dark), I-band (light), H-band, Z-disc, and sarcomeres.
What are A-bands composed of?
Entire thick filament + portion of thin filament
What are I-bands composed of?
Portion of thin filament, adjacent to Z disc
What are H-bands composed of?
Thick filament only (middle of A-band)
What are sarcomeres composed of?
Distance from one Z disc to the next; contractile unit of a muscle fiber
What are Z-bands composed of?
Anchorage for thin filaments and elastic filaments
What is a motor unit and # fibers innervated by 1 motor neuron depends?
One nerve fiber + all the muscle fibers it innervates, depends on function of muscle
What is a neuromuscular junction?
Functional connection between a nerve fiber and a muscle cell
What happens at the synaptic knob in the neuromuscular junction?
–neurotransmitter (Ach) is released travels across synaptic cleft
–Ach receptors on sarcolemma accepts neurotransmitter
–after a sequence of events, muscle contracts
What does it mean when cells are electrically excitable?
Plasma membranes exhibit voltage changes in response to stimulation
What is membrane potential (MP)?
The electrical charge in a cell relative to outside the cell
What kind of MP does most cells have?
Inside: proteins-, nucleic acids-, K+
Outside: Na+, Cl-
What is resting membrane potential (RMP) and what maintains it?
Difference in charge across the membrane, maintained by Na/K pump
What opens ion gates in plasma membrane?
When do voltage-gated ion channels open?
Open when the MP reaches a critical level (threshold)
When do ligand-gated ion channels open?
Open when a chemical messenger binds; e.g. acetylcholine
What happens during depolarization?
Na+ ion gates open, Na+ rushes into cell causing a positive MP
What happens during repolarization?
K+ ion gates open, K+ rushes into cell causing a negative MP
What is an action potential (AP)?
Quick up-and-down voltage shifts
What are the steps of Excitation of muscle by nerve (steps 1-5)?
1. Arrival of nerve signal
2. Acetylcholine is released
3. Binding of Ach to receptor
4. Opening of ligand-gated ion channel
5. Opening of voltage-gated ion channel
What are the 4 actions involved with behavior of skeletal muscle fibers?
1) Excitation = nerve action potentials lead to action potentials in muscle fiber
2) Excitation-contraction coupling = action potentials on the sarcolemma activate myofilaments
3) Contraction = shortening of muscle fiber
4) Relaxation = return to resting length
What are the steps of Excitation-contraction coupling (steps 6-9)?
6. Action potentials propagated
7. Calcium released from terminal cisternae
8. Binding of calcium to troponin
9. Shifting of tropomyosin; exposure of active sties on actin
What are the steps of Contraction (steps 10-13)?
10. Hydrolysis of ATP; activation and cocking of myosin head
11 Formation of myosin-actin cross-bridge
12. Power stroke; sliding of thin filament over thick filament
13. Binding of new ATP; breaking of cross-bridge
What are the steps of Relaxation (steps 14-18)?
14. Cessation of nervous stimulation and ACh release
15. ACh breakdown by AChE
16. Reabsorption of calcium ions by sarcoplasmic reticulum, ATP needed
17. Loss of calcium ions from troponin
18. Return of tropomyosin to position blocking active sites of actin
When do muscles return to resting length?
- When CT components stretch it out to resting length
- When contraction of antagonist lengthens it