Neuronal Synapses

Chemical synapses

-make up majority of synapses in NS -more efficient than electrical synapses because they convert electrical signals into chemical signals so no signal strength is lost. -undirectional

Effects of neurotransmitter when synaptic transmission occurs:

-some diffuse away from synaptic cleft in ECF -can be broken down by enzymes -some are reabsorbed into presynaptic neuron by a process called reuptake.

Events of Chemical Synapse:

1. an action potential in presynaptic neuron triggers voltage-gated calcium ion channels in axon terminal to open. 2. influx of calcium ions causes synaptic vesicles to release neurotransmitters into synaptic cleft. 3. neurotransmitters bind to receptors on postsynaptic neuron. 4. ion channels open, leading to a local potential and possibly an action potential if threshold is reached.

Reuptake

Neurotransmitters are reabsorbed into a presynaptic neuron.

Neurotransmitter receptors

bind to neurotransmitter secreted from presynaptic neuron that has diffused across synaptic cleft.

Transmission is bidirectional

either neuron can be pre or postsynaptic depending on which direction current is flowing between them.

Synaptic vesicles

filled with chemical messengers(neurotransmitters) that transmit signals from presynaptic to postsynaptic neurons are found at chemical synapses.

Spatial summation

involves simultaneous release of neurotransmitters from axon terminals of many presynaptic neurons.

Postsynaptic potentials

local potentials found in membranes of postsynaptic neuron.

Excitatory postsynaptic potential

membrane potential of postsynaptic neuron moves closer to threshold; caused by a small local depolarization.

Inhibitory postsynaptic potential

membrane potential of postsynaptic neuron moves farther away from threshold; caused by a small local hyperpolarization.

Synapse

neuron meeting its target cell(usually a neuron); can be either electrical or chemical.

Postsynaptic neuron

neuron receiving message from presynaptic neuron at its cell body, axon, or dendrites.

Presynaptic neuron

neuron sending message from its axon terminals.

Temporal summation

neurotransmitter is released repeatedly from axon terminal of a single presynaptic neuron; each local potential is short-lived so they must be gathered quickly to reach threshold and create action potential.

Electrical synapse

occurs between cells that are electrically coupled via gap junctions. -found in outside areas of brain responsible for programmed, automatic behaviors such as breathing. -flow directly from axoplasm of one neuron to next. -directional

Transmission is nearly instantaneous

only delay is time it takes presynaptic neuron to depolarize; much faster than chemical synapses.

Summation

phenomenon whereby all input form several postsynaptic potentials are added together to effect membrane potential at trigger zone.

Neural integration

process in which postsynaptic neuron integrates all incoming information into a single effect.

Synaptic cleft

small ECF-filled space; seperates presynaptic and postsynaptic neurons; found in chemical synapses; gap functions connect neurons in electrical synapses.

Axoaxonic synapse

synapse between axon of one neuron and axon of another neuron.

Axosomatic synapse

synapse between axon of one neuron and cell body of another neuron.

Axodendrite synapse

synapse between axon of one neuron and dendrite of another neuron.

Synaptic delay

time gap between arrival of action potential at axon terminal and effect on postsynaptic membrane.

Synaptic transmission

transfer of chemical or electrical signals between neurons at a synapse; fundamental process for most functions of nervous system.