Anatomy Exam 2
If TTX blocks the voltage-gated sodium channels in the squid giant axon, which cation flows into the cell and carries the (early) inward current?
Sodium
Normally, sodium and potassium leakage channels differ because __________.
Sodium ions diffuse through leakage channels into the cell, but potassium ions diffuse through leakage channels out of the cell
Items more prevalent in IF
Sodium, chloride
T/F the sodium-potassium pump is involved in establishing the RMP
TRUE
Which of the following statements about the resting membrane potential is TRUE?
The exterior of the cell has a net positive charge and the interior has a net negative charge
With the trend in mind, predict the amount of isotonic contraction with the weight of 300 grams.
The muscle would not shortening, because the isometric contraction could not overcome such a heavy weight.
T/F T-tubules are invaginations of the sarcolemma of a muscle cell
True
T/F The sequence of crossbridge formation and myofilament movement will be repeated as long as calcium ions are present
True
T/F the nerve impulse is an electrical current that travels along dendrites or axons.
True
T/F the sodium-potassium pump is involved in establishing the resting membrane potential.
True
During crossbridge cyclin, tension is created by...
a change in the shape of the myosin head.
According to your data, a single contraction produced maximum tension when the muscle was held at...
about 28 mm
Maximum tension is achieved when the muscle is at resting length. According to your data, the resting length of the muscle was:
about 28 mm
Keeping the membrane potential at 0 mV will...
allow current to flow. open voltage-gated sodium channels. open voltage-gated potassium channels
The bond between the actin and myosin head is broken when...
an ATP molecule binds to the myosin head
According to the sliding filament theory for skeletal muscle contraction, a shortening of the sarcomere is produced by...
an increase in the amount of overlap between the thick and thin filaments
Maximum tension is produced in a skeletal muscle fiber when it is...
at resting length
During an action potential, voltage-gated sodium channels open...
before voltage-gated potassium channels
At what weight did you record a maximum amount of muscle shortening?
between 20 to 60 grams
In the intact frog, muscles are held close to their resting length so that maximum tension can be achieved. Excessive shortening and lengthening of the muscle is prevented by:
bones and joints
If a drug was developed that interfered with the proper functioning of the microtubules found within the axons of neurons, how would you expect this to impact axonal transport processes?
both anterograde and retrograde transport processes would cease
At the synaptic knob, voltage-gated ______ channels open, thereby stimulating the synaptic vesicles to release their neurotransmitters by exocytosis
calcium
Substances that cause facilitation of a neuron ______.
cause the neuron to fire that may not under the same circumstances in the absence of the facilitator
Tendons...
connect a skeletal muscle to a bone
If maximum tension indicates that the thick and thin filaments are set at optimal overlap to produce a maximum number of crossbridges, further stretching of the muscle will...
decrease the amount of thick and thin filament overlap
Since the tension produced by a contracting muscle fiber depends upon the number of crossbridges between the thick and thin filaments, stretching the muscle beyond 28 mm:
decreases the amount of overlap and decreases the amount of tension produced by a single contraction.
During an action potential, the cell membrane...
depolarizes and becomes positive
The maximum amount of work done by the weight 120 grams. When compared with the response for a lighter weight like 40 grams, the response for the 120 gram weight...
displayed less shortening, had a longer latency period
Action potentials occur ______.
in the unmyelinated regions of an axon
If the amount of tension produced by the muscle depends upon the number of crossbridges, according to your data the number of crossbridges...
increase as the muscle was lengthened to about 28 mm
Initially, you applied a shock to the shortened muscle and measured the tension. You then stretched the muscle and repeated the experiment. After repeating the amount of tension...
increase as the muscle was stretched to about 28 mm
The duration of the latency period...
increases with weight. because more crossbridges must cycle to move a heavier weight, the latency period is increased with increasing weight.
When voltage-gated sodium channels are open, sodium flows ______ the neuron making the inside of the cell more _____.
into; positive
Which of the following best describes the role of Ca2+ in muscle contraction?
it binds to troponin, moving tropomyosin, so that myosin heads can bind to actin.
The giant squid axon is used in this experiment because...
it can accommodate the voltage clamp apparatus. it is large enough to place a wire along its length to measure membrane potential. It is large enough to place a wire along its length to apply current across the membrane.
Membrane depolarization produces an action potential because...
it opens voltage-gated channels in the membrane.
increasing the weight increased the latency period because...
it takes time to build up tension in the muscle and tendon to overcome the weight. Because it takes more crossbridge cycling to overcome a heavier weight, the latency period is extended in duration
When K+ diffuses out of the cell, the cell becomes _____ depolarized
less
When Na+ diffuses into the cell, the cell becomes _____ depolarized.
more
Depolarization occurs because...
more Na+ diffuse into the cell than K+ diffuse out of it
Depolarization occurs because....
more sodium ions diffuse into the cell than potassium ions diffuse out of it.
K+ diffusing out of the cell has a _____ feedback effect on the initial polarization
negative
Assume in a laboratory you were able to isolate a neuron and remove the Acetylcholine receptors from the postsynaptic membrane. The substance ______ would no longer cause facilitation of this neuron
nicotine
The voltage-gated Na+ channels _____ when the cell membrane reaches threshold level as a result of a stimulus
open
The latency period is the time...
period between stimulation and the shortening of the skeletal muscle. The latency period is the delay between stimulation and contraction
Na+ diffusing into the cell causes more Na+ gates to open, which is a _____ feedback loop
positive
Graded potentials are produced within ______ segment of a neuron
receptive
______ the time between signals sent from the same presynaptic terminal increases the strength of the graded potential. This is an example of ______ summation
reducing; temporal
The following information best describes the _____ phase of an action potential. -a membrane potential reading of +10 mV -inactivated voltage-gated sodium channels -open voltage-gated potassium channels
repolarization
The distance from one Z disk to the next Z disk is called a(n)
sarcomere
which current was abolished when TEA is injected into the axon?
the (later) outward current.
Voltage-gated potassium channels close because...
the membrane repolarizes back to resting
In this experiment, immediately after the latency period has passed...
the muscle contracted isotonically and lifted the weight.
In this experiment, when the muscle is stretched what happens to the length of the muscle fibers?
the muscle fibers get longer
During the latency period...
the muscle was contracting isometrically. The latency period is the time when an isometric muscle contraction builds tension in the tendon.
During contraction of a muscle, calcium ions bind to...
the troponin molecule
All of the following are filamentous proteins EXCEPT...
troponin
Indicate the summative effect that brings the initial segment closest to threshold.
two EPSPs in proximity to each other
Arrange the following in the proper order in which they occur at the postsynaptic side of a neuromuscular junction: 1) Action potential is propagated over the muscle cell membrane 2) depolarization of the postsynaptic membrane 3) sodium ions move into muscle cell
3, 2, 1
The area of the muscle fiber where the actin and myosin myofilaments overlap is the...
A band
Energy is released when...
ATP is broken down into ADP and phosphate
At what length do you think this muscle would be able to lift the heaviest weight?
About 28 mm.
At resting membrane potential, which of the following statements about the voltage-gated sodium ion (Na+) channels is true?
Activation gates are closed and inactivation gates are open
The enzyme choline acetyltransferase catalyzes the reaction between acetyl-CoA and choline resulting in the formation of the neurotransmitter acetylcholine. This enzyme is produced within the cell body of neurons, but the synthesis of acetyl choline occurs within the axon terminals. Which statement best describes the axonal transport mechanism associated with this process?
Choline acetyltransferase is transported in the anterograde direction
T/F The voltage-gated potassium channels close before the membrane potential is brought back to its resting level.
False
T/F in a relaxed muscle, the ends of the actin filaments overlap.
False
T/F receptors that bind the neurotransmitter at the postsynaptic cell membrane are voltage-gated.
False
During depolarization, which of the following statements about voltage-gated ion channels is TRUE?
Na+ gates open before K+ gates
Items more prevalent in Cytosol
Phosphate, Negatively charged proteins, potassium
If TEA blocks voltage-gated potassium channels in the squid giant axon, which cations flow out of the cell and carry the (later) outward current?
Potassium
The voltage clamp will apply equally and opposite current to keep the membrane potential at...
0 MV
The maximum amount of work done by the contracting muscle was observed when the muscle was lifting...
120 grams
During contraction, the actin myofilaments slide toward the...
H zone
In this lab, an electrical shock stimulates the muscle, which contracts and lifts the weight. The distance the weight is lifted is measured using...
a displacement transducer. In this case, a displacement is used to measure the distance the weight is lifted.
The primary neurotransmitter at the neuromuscular junction is...
acetylcholine
If acetylcholinesterase became mutated and nonfunctional, what would be the immediate result?
acetylcholine would build up in the synaptic cleft.
The original line tracing (now gray) consists of...
an initial inward current (in the yellow area) and then an outward current (in the green area)
A resting membrane potential of -70 mV indicates that the _____.
charges lining the inside of the plasma membrane are negative compared to the charges lining the outside
The voltage-gated Na+ channels _____ when the cell reaches +30 mV
close
The voltage clamp used in this experiment is used to measure...
currents that flow across the membrane
Demyelinating diseases cause a(n) ______ in the conduction velocity of action potentials.
decrease
Graded potentials result from the opening of ______.
ligand-gated channels
Depolarization occurs because...
more Na+ diffuse into the cell than K+ diffuse out of it.
An inhibitory postsynaptic potential results from the opening of ______.
potassium and/or chloride channels
Repolarization occurs because...
potassium ions continue to diffuse out of the cell after the inactivation gates of the voltage-gated sodium ion channels begin to close
Suppose that a new virus is discovered that specifically infects motor neurons. Assume that this virus enters neurons in conjunction with choline molecules. Once inside the cell, the virus enters the nucleus and replicates. Which direction describes the axonal transport route taken by this virus?
retrograde transport
An action potential causes calcium ions to diffuse from the _____ into the _____.
sarcoplasmic reticulum; sarcoplasm
Voltage-gated sodium channels close quickly after they open because...
sodium channels inherently close soon after they open
Look at your graph and determine the relationship between the amount of muscle shortening and weight.
the amount of muscle shortening generally decreases as weight increases.
The amount of work done by a skeletal muscle is...
the distance the weight is lifted multiplied by the weight. By definition work = force times distance
The application of TTX to the solution bathing the axon changed the line tracing by abolishing...
the initial inward current
Click on the "Latency Period" button in the journal. What is the effect of increasing the weight on the latency period?
the latency period increased as the weight was increased. The duration of the latency period and the amount of weight are directly correlated.
Since fibers are composed of a series of sarcomeres laid down next to one another, then what happens to the length of the sarcomeres when muscle fibers are stretched?
the sarcomere gets longer
In the sarcomere of skeletal muscle, myosin is found in...
the thick filaments
In the sarcomere of skeletal muscle, actin is found in...
the thin filaments
If demyelination occurs, why don't action potentials occur at regions of the axon that were previously myelinated?
these regions lack the appropriate concentration of voltage-gated sodium channels
before initiating the voltage clamp, the membrane potential of the giant squid axon was resting at a present value of...
-60 mV
What is the relationship between work and weight
the work done by the contraction increased to a maximum value and then decreased.
