Intro | Presynaptic Neuron | Postsynaptic Neuron | Terminal Button | Axon | Neural Impulse | Synaptic Vesicles | Neurotransmitter Molecules | Cell Membrane | Transmitter does not fit at receptor | Transmitter fits receptor | Receptor Sites | Synaptic Cleft
Part 1: Image-Mapped Tutorial
Part 2: Matching Self-Test
Part 3: Multiple-Choice Self-Test
Figure 3 illustrates the site where information is conveyed from one neuron to the next. At this junction, called the synapse, chemicals are used to transmit the electrical neuronal impulse. The structures and substances involved in synaptic transmission are identified and described.
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Four primary factors control whether an impulse will be generated on a neuron. At any given moment, a neuron may be under the influence of input from thousands of other neurons. Any combination of synapses on a given neuron may be active at any given time, and the rate of this activity at the synaptic level may vary. Whether or not threshold is reached, and an action potential generated, is dependent upon the spatial (i.e., multiple impulses from several neurons at the same time) and temporal (i.e., several impulses from one neuron over time) summation of all inputs at a given moment. In addition, the summation of excitatory and inhibitory influences will modulate the outcome. Synapses that are located closer to the axon hillock, where all input on a neuron is summated, have a greater influence on the outcome. Some neurons have a spontaneous firing rate that is independent of synaptic input. Incoming excitatory and inhibitory synaptic activity will adjust the spontaneous firing rate up or down, respectively. Temporal and spatial summation of synaptic input on a neuron underlies the integration of information from diverse sources. The convergence of input and comparison of this input at the neuronal level is the foundation of decision-making. The "decisions" of many neurons forming a network and acting in concert underlie the types of decisions that guide our behaviors.
Synapses are referred to as axodendritic, axosomatic, or axoaxonic depending on the structures forming the pre- and postsynaptic membranes.
| Suggestions for further study |
Dunant, Y, Israel, M. (1985, April). The release of acetylcholine. Scientific American, 252(4), 58-66.
Kalil, R.E. (1989, December). Synapse formation in the developing brain. Scientific American, 261(6), 76-79, 82-85.
Keynes, R.D. (1979, March). Ion channels in the nerve-cell membrane, Scientific American, 240(3), 126-132, 134-135.
Llinas, R.R. (1982, October). Calcium in synaptic transmission, Scientific American, 247(4), 56-65.
Nathanson, J.A., Greengard, P. (1977, August). "Second messengers" in the brain, Scientific American, 237(2), 109-119.
Rennie, J. (1990, January). Nervous excitement, Scientific American, 262(1), 21.
Satir, B. (1975, October). The final steps in secretion. Scientific American, 233(4), 29-37.
Snyder, S.H. (1985, October). The molecular basis of communication between cells, Scientific American, 253(4), 132-141.
http://www.sfn.org/briefings/nmda.html
(NMDA Receptors)
from Society for Neuroscience - Brain Briefings, 1994.
NMDA receptor blockers and the prevention of neuronal damage due to
stroke, epilepsy, Huntington's Disease, and AIDS.