Chapter 11: Chemical Synapse

What condition will increase the diffusion of molecules, such as neurotransmitters?

an increased in the amount of neurotransmitter exocytized by the presynaptic axon. Increased differences in concentrations, or increased gradients, will increase diffusion.

List the correct sequence at the chemical synapse.

1. Action potential sweeps down presynaptic axon 2. Calcium channels open in axon terminal. 3. Synaptic vesicles fuse and exocytize neurotransmitter 4. Diffusion of neurotransmitter into extracellular fluid separating two neuron's membranes 5. Graded potential at postsynaptic membrane

Arrange the parts in order, from left to right, of a successful direct depolarization path within one neuron.

Dendrite > Cell body > Axon hillock > Axon > Presynaptic terminal Incoming messages to the dendrites or cell body pass through neuroplasm to the axon hillock. If a threshold stimulus value is reached at the axon hillock, depolarization passes down the axon to the presynaptic terminal containing synaptic vesicles.

Which of the following choices best represents synaptic transmission?

presynaptic axon to synapse to dendrite or postsynaptic cell body Synaptic transmission uses a synapse and, therefore, two cells. Incoming messages are dendritic or somatic; outgoing messages are axonal.

Predict the possible effect of a drug that totally blocs the neurotransmitter receptor on the postsynaptic membrane. For example, curare is a neurotoxin used by South American cultures. The primary effect of curare is that acetycholine, a major neuromuscular neurotransmitter, cannot bind at its receptor because curare is blocking it. Predict the possible effects of curare on the postsynaptic membrane and muscle.

Local graded potential and action potential transmission is blocked, and there is no response by the postsynaptic cell, the muscle. No ion channel or graded potential can be initiated; there is no subsequent action potential.

Which statement best describes exocytosis?

Membrane organelles fuse with the membrane and release contents out of the cell. The rise in intracellular Ca+2 binding with receptor proteins triggers the synaptic vesicles to fuse with the membrane and release contents out of the cell.

When an action potential arrives at the end of the axon terminal, a series of events take place that result in the release of neurotransmitter from the presynaptic axon. Select the answer that correctly describes the primary stimulus for vesicles to move toward the cell membrane and eventually release their contents.

Voltage-gated membrane channels open, and Ca+2 enters the cytoplasm, increasing intracellular calcium. Calcium enters the cytoplasm as a result of changes in the gated channel protein, increasing cytoplasmic content of Ca+2.

If the membrane of a postsynaptic dendrite is setting up a graded potential, what must have happened after neurotransmitter was released by the presynaptic terminal?

bound at postsynaptic receptors to open postsynaptic ion channels. Diffusion carries the transmitter from higher to lower concentration. The transmitter binds to a receptor on the postsynaptic membrane and effects a cascade of events, resulting in the opening of ion channels. These lead to graded potentials, which may set up an action potential.

Which of the following best characterizes depolarization?

small, consecutive steps of Na+ penetration into the axon along its length. The direction of flow for the Na+ ion is from the extracellular fluid into the cytoplasm (ICF). This occurs in small, consecutive steps.