Chapter 9 Muscle Tissue Part 2 Flashcards
Which of the following proteins make up the think filament in a sarcomere?
A. Actin
B. Titin
C. Myoglobin
D. Myosin
D. Myosin
What is the motor unit of the muscle? (Pathway showing two motor units (red and purple). Muscles cells with branched motor neuron.)
- Each muscle must be excited by a branch of a motor neuron (muscle cells DO NOT excite each other)
- A neuron branches about 200 times, so about 200 muscle cells are excited together this is defined as a motor unit
- As few as 3 muscle cells can be excited or as many as 1000
- Most muscle has many motor units that are not activated at the same time
What is the function of the Neuromuscular Junction?
- Axon of motor neurons forms a synapse with a muscle cell
- Motor plate is the region of synapse the muscle cell
- Acetylcholine (ACh) is the released neurotransmitter
- Released upon action potential
- ACh ligand-gated channels (receptor proteins) are located in the sarcolemma
- Acetylcholinesterase (AChE) enzyme is also in sarcolemma
- Breaks down extra ACh
Which of the following is required for release of acetylcholine from the presynaptic cell?
A. Myosin
B. Acetylcholine esterase
C. Calcium
D. Sarcolemma
D. Sarcolemma
What are the four stages for Muscle Contraction?
- Excitation
- Communication between the neuron and muscle cell
- Leads to excitation of muscle cell
- Excitation-contraction coupling
- Conversion of action potential in muscle cell to activation of proteins in the sarcomere
- Contraction
- Muscles develop tension and may shorten
- Sliding filament theory
- Relaxation
- Return of muscle cells to resting length
What does the Stage of Excitation consits of (steps 1-2)?
Action potential from motor neurons reaches end of axon
Voltage-gated calcium channels open
Calcium enters the neuron and causes synaptic vesicles to release acetylcholine (Ach)
What does the stage of Excitation consists of (Steps 3-4)?
ACh binds to receptors in the of motor plate
Receptors are ligand-gated, non-specific cation channels
Non-specific allows diffusion of both sodium and potassium
Sodium rushes into the cell depolarization
Potassium leaves the cell repolarization
Net result is depolarization
More sodium enters than potassium leaves
Called an end-plate potential (EPP)
What do the stages of Excitation conssts of (step 5)?
Depolarization from EPP causes muscle cell to reach threshold leading to action potential
Involves same voltage-gated channels as neurons
What is the function of the sarcoplasmic reticulum?
A. Store potassium ions
B. Store calcium ions
C. Store sodium ions
D. Store ATP
B. Stores Calcium ions
What do the stages of excitation-contraction coupling consists of (steps 6-7)
- Action potential travels across sarcolemma and DOWN T-tubules*
- Voltage-gated Na+ channels in T-tubules are physically linked to Ca+ ion channels in the sarcoplasmic reticulum
- Action potential triggers Na+ channels to open, SR calcium channels also open
- Calcium enters the cytoplasm of the muscle cell
- *T-Tubles do not coninue or is not continuous, Action Potentials will not connect to ER
Excitation-Contraction Coupling (steps 8 and 9)
What is the role of troponin?
A. Binds to calcium to expose active sites on thin filaments
B. Binds to sodium to expose active sites on thin filaments
C. Directly covers the active sites on thin filaments
D. Bind to the myosin heads
A. Bind to Calcium to expose active sites on thin filaments
What do the stages of Contraction consist of (steps 10 and 11)?
- Myosin hydrolyzes an ATP molecule
- Produces ADP + P
- Activates the myosin head in an extended position
- Myosin binds to the actin active site
- Forms a cross-bridge between actin and myosin
- ADP + P are still bound to myosin
What are the stages of Contraction (step 12-13)?
- Interaction of cross-bridge causes release of ADP and P
- Causes myosin head to flex
- Thin filament slide past the thick
- Another ATP molecule must bind myosin to release head
- Immediately hydrolyzes ATP and extends head of myosin
- Some heads are always bound to prevent slippage
- Thin and thick filaments do not become shorter, just slide past each other SLIDING FILAMENT THEORY
What do the stages of relaxation consist of (Steps 14-15)?
- Action potentials in axon cease
- No more acetylcholine (Ach) is released from the neuron
- Acetylcholinesterase (AchE) breaks down remaining acetylcholine
- Enzymatic reaction
- Breakdown products are transported back to neuron and recycled
- No EPP (or action potentials) are produced in the muscle membrane
What does the stage relaxtion consist of (step 16)?
- Active transport needed to pump calcium back into SR
- Active transport uses more ATP!!
What do the stages of relaxtion consist of (steps 17-18)?
- Binding of ATP to myosin causes dissociation from actin
- Troponin-tropomyosin complex covers active sites
- Due to lack of calcium
- Myosin cannot bind
- Stops the production or maintenance of tension
- Sarcomere returns to resting length
- Muscle cells return to its resting length
- Complete cycle is called a muscle twitch
What are the Strength of Contractions - Recruitment?
- Muscle contraction can vary in strength
- Total muscle contraction = Sum of individual muscle cell contraction
- Stronger impulse from brain cause more neurons to fire action potentials
- Results in more motor units contracting
- Stronger contraction
- Process is called RECRUITMENT
