Flashcards in Chapter 10 Deck (91)
What are action potentials?
are brief, temporary changes in the membrane potential of a cell from a resting negative value to a value, and then back to its resting negative value.
Action potentials are generated by
opening gated ion channels in the plasma membrane.
two types of gated channels are?
What do ligand gated channels open in response to?
The presence of certain chemicals called ligand
What do voltage gated channels open in response to?
In resone to changes in the membrane potential across the plasma membrane
What is depolarization?
A stage in action potential. In response to stimulus, voltage gated sodium ion channels open, and sodium ions enter the cell, making membrane potential less negative (rises to +30 mlV)
What is repolarization?
A step in action potential that is triggered by the closing of the voltage gated sodium ion channel. Simultaneously, the voltage gated potassium channel opens, letting potassium out of the cell, and repolarizing the cell to its -85mlV charge.
The NMJ (neuromuscular junction) is where a single motor neuron communicates with many ............ fibers. What is another name for the NMJ?
What are chemicals that trigger changes in a target tissue when released allowing for cell to cell communication?
What is the neurotransmitter released from a motor neuron stimulates a muscle fiber?
What are the three components of the neuromuscular junction?
1. The axon terminal
2. The synaptic cleft
3. The motor end plate
What is the ligand that opens the gates that allow sodium to diffuse into the cell?
What are the three faces of muscle contraction?
Excitation phase, Excitation contraction coupling, and the contraction phase
Summarize how the excitation phase begins
An action potential arrives at the axon terminal. The synaptic vesicles release acetylcholine into the synaptic cleft. Acetylcholine binds to the ligand gated ion channels in the motor end plate.
What is an end plate potential?
It is a local depolarization in the area of the motor end plate.
How is an end plate potential accomplished?
Entry of sodium ions into the myocyte depolarizes the sarcolemma locally which produces an end plate potential.
How is a functional muscle contraction produced?
Multiple end plate potential’s must be generated
Which enzyme rapidly degrades acetylcholine In the synaptic cleft
And end plate potential leads to the opening of voltage gated...........channels in the sarcolemma surrounding the motor end plate, which triggers an action potential
Action potentials propagate down the ........ , which signals to terminal cisternae to open voltage gated calcium ion channels releasing calcium ions into the cytosol
How does the contraction phase begin?
Calcium ions bind to troponin. The tropomyosin moves and the active sites of actin are exposed. When the active site of actin are exposed the myosin heads are able to bind tightly to them this is known as cross bridging
When is a myosin head cocked?
When The ATP that was bound to it is hydrolyzed
What does the myosin head bind to once it is cocked?
What is a power stroke? What promotes it?
When the myosin pivots and pulls the actin toward the center of the sarcomere. It is promoted by the removal of ADP and phosphate
What is required for the cross bridge cycle to repeat?
ATP must break the attachment of myosin to Actin
Muscle relaxation occurs in two separate steps. First, Motor neuron action potentials stop signaling for the release of .......... from axon terminals. Any acetylcholine left in the synaptic cleft is rapidly degraded by the enzyme ........... Since acetylcholine can no longer bind to the motor end plate, the end plate potential stop as ligand gated .............. channels close.
How does repolarization occur?
The Acetylcholine degrades into substances that can’t stimulate the muscle. Without stimulation the gated ion channels close on the end plate
How do the positions of troponin and tropomyosin change in the absence of calcium ions, and how does this make the muscle relax?
Troponin returns to its original position pushing tropomyosin back to where it blocks the active sites of the actin, which prevents myosin heads from binding to it.
The main immediate energy is stored as ..............in the muscle fiber and is rapidly consumed during muscle contraction.