anatomy 14.7

Interneurons

Billions of interneurons within the CNS that group into complex patterns called neural circuits.

Neural circuits

Groups of neurons arranged in specific patterns through which nerve impulses are conducted and distributed.

Alternate names for neural circuits

Neuronal pathways or pools.

Classification of neural circuits

Neural circuits are classified based on their function, not their anatomy.

Types of neural circuits

Converging, diverging, reverberating, and parallel-after-discharge circuits.

Location of neural circuits

Neural circuits may be localized to one specific CNS region or distributed across several CNS regions.

Input and output of neural circuits

All neural circuits have a restricted number of input sources and output destinations.

Converging circuit

Nerve impulses from several presynaptic neurons converge on a single postsynaptic neuron.

Basic pattern of a converging circuit

Many inputs lead to one output.

Example of a converging circuit

Multiple sensory neurons synapse on neurons in the salivary nuclei of the brainstem, resulting in saliva production.

Stimuli for saliva production in converging circuit

Smelling food, seeing that it is dinnertime, hearing food preparation, or seeing pictures of food.

Diverging circuit

One presynaptic neuron spreads information to several postsynaptic neurons.

What a diverging circuit can connect

One neuron can spread information to several neurons, or one circuit can spread information to multiple circuits.

Basic pattern of a diverging circuit

One or few inputs lead to many outputs.

Example of a diverging circuit

Activation of a few neurons in the motor cortex can excite thousands of muscle fibers in a muscle.

Difference between converging and diverging circuits

Converging circuits bring multiple inputs to one output, while diverging circuits spread one or a few inputs to multiple outputs.

Reverberating circuit

A circuit that uses feedback to produce repeated, cyclical stimulation.

Reverberation in a neural circuit

Repeated or cyclical stimulation of the circuit.

Functioning of a reverberating circuit after activation

Feedback repeatedly stimulates the circuit.

What can stop a reverberating circuit

Inhibitory stimuli or synaptic fatigue.

Synaptic fatigue

A temporary inability of the presynaptic cell to meet the demands of synaptic transmission because of insufficient neurotransmitter production.

Function maintained by a reverberating circuit during sleep

Continued breathing.

Parallel-after-discharge circuit

Several neurons or neural circuits process the same information simultaneously.

Beginning of a parallel-after-discharge circuit

One presynaptic neuron stimulates different groups of neurons.

Pathways in a parallel-after-discharge circuit

Each pathway carries the impulse along a separate route that ultimately synapses with a common postsynaptic cell.

Function associated with parallel-after-discharge circuits

Higher-order thinking.

Example of parallel-after-discharge circuit function

Performing precise mathematical calculations.

ALS

Amyotrophic lateral sclerosis, also called Lou Gehrig disease or Charcot disease.

Degeneration in ALS

The somatic motor system, involving neurons in both the brain and spinal cord.

Difference between diverging and reverberating circuits

Diverging circuits spread information to multiple outputs, while reverberating circuits use feedback to repeatedly stimulate the same circuit.