16 .Action potentials are generated along a neuron because __________.
A.of cytoplasmic streaming within the neuron
B.depolarization of the membrane at one point causes an increase of permeability to sodium at the next point
C.they are pulled along by positive-negative attraction
D.the neuron cytoskeleton conducts electricity as long as an ion gradient is maintained by the sodium-potassium pump
E.of all of these factors
17 .Which one of the following statements about the transmission across a typical chemical synapse is NOT true?
A.Neurotransmitter molecules are stored in vesicles in the synaptic knobs.
B.Action potentials trigger chemical changes that make the neurotransmitter vesicles fuse with the plasma membrane of the sending neuron.
C.Vesicles containing neurotransmitter molecules diffuse to the receiving neuron's plasma membrane.
D.Neurotransmitter molecules bind to receptors in the receiving neuron's plasma membrane.
E.The binding of neurotransmitter molecules to receptors transmits an impulse across a synapse.
18 .How are neurons structurally adapted to chemically transmit impulses to neighboring neurons?
A.Synaptic knobs contain neurotransmitter substances within synaptic vesicles.
B.They have numerous nodes of Ranvier.
C.They have numerous dendrites.
D.They have Schwann cells that surround axons.
E.None of the above is correct.
a b c
16. The correct answer is B. Depolarization of the membrane at one point causes an increase of permeability to sodium at the next point.
To understand this concept, you need to know about the process of generating action potentials. Action potentials are electrical signals that allow neurons to communicate with each other. They are generated along the length of a neuron.
Within a neuron, information is transmitted via changes in electrical potential across the neuron's membrane. These changes in potential are caused by the movement of charged ions, such as sodium and potassium, across the membrane.
The process of generating an action potential begins with a stimulus that causes the membrane of a neuron to depolarize. Depolarization means that the inside of the neuron becomes less negative relative to the outside. This depolarization opens voltage-gated sodium channels in the membrane, allowing sodium ions to flow into the neuron.
As sodium ions flow into the neuron, the positive charge they carry causes the membrane at that point to depolarize further. This depolarization triggers the opening of sodium channels at the next point, and the process continues down the length of the neuron, resulting in the propagation of the action potential.
Therefore, the correct answer is B because the depolarization of the membrane at one point causes an increase in sodium permeability at the next point, allowing the action potential to propagate along the neuron.
17. The correct answer is C. Vesicles containing neurotransmitter molecules diffuse to the receiving neuron's plasma membrane.
To understand this, let's go through the typical process of transmission across a chemical synapse. A chemical synapse is the junction between two neurons where one neuron (the sending neuron) communicates with another neuron (the receiving neuron) by transmitting chemical signals.
When an action potential reaches the end of the sending neuron, it triggers the release of neurotransmitter molecules from vesicles within the synaptic knobs of the sending neuron. The neurotransmitter molecules are stored in these vesicles.
The neurotransmitter molecules are then released into the synaptic cleft, which is the small gap between the sending neuron and the receiving neuron. The molecules diffuse across the synaptic cleft and bind to specific receptors on the plasma membrane of the receiving neuron.
This binding of neurotransmitter molecules to receptors in the receiving neuron's plasma membrane initiates a series of chemical reactions, which generates a new electrical signal, allowing the impulse to be transmitted across the synapse.
Therefore, the incorrect statement is C. Vesicles containing neurotransmitter molecules do not diffuse to the receiving neuron's plasma membrane. Instead, the neurotransmitter molecules are released into the synaptic cleft and diffuse across it to bind to receptors on the receiving neuron's plasma membrane.
18. The correct answer is A. Synaptic knobs contain neurotransmitter substances within synaptic vesicles.
Neurons are structurally adapted to chemically transmit impulses to neighboring neurons through a structure called a synapse. A synapse is the junction between two neurons where the transmission of signals occurs.
At the end of a neuron, there is a specialized structure called the synaptic knob (also known as the presynaptic terminal or axon terminal). The synaptic knob contains small sacs called synaptic vesicles, which store neurotransmitter substances.
When an action potential reaches the synaptic knob, it triggers the release of neurotransmitter molecules from these synaptic vesicles into the synaptic cleft (the small space between the sending neuron and the receiving neuron).
The neurotransmitter molecules are then able to bind to specific receptors on the plasma membrane of the receiving neuron, initiating the transmission of the impulse.
Therefore, the correct answer is A. Synaptic knobs contain neurotransmitter substances within synaptic vesicles.