Neurons: structural class and circuits

Neurons are structurally classified according to?

the number of processes extending from the cell to the body 

Multipolar neurons structure

several dendrites and one axon

Multipolar neurons are located in:

the brain and spinal cord (interneurons)

most motor (efferent) neurons are MP

Bipolar neurons structure

two processes coming off, one main dendrite and one axon

Bipolar neurons location

retina of the eye, inner ear, and olfactory are of the brain

Unipolar neurons structure

are sensory neurons, cell body is between the axon and dendrite that are brought together and fuse into a single process that divide into two branches from the cell body 

Unipolar neurons location

cell body is located outside CNS in dorsal root ganglia

often found in sensory division, relays info from a region of the body to the CNS 

What are neural circuits?

neurons organized into complicated networks, each is a functional group or neurons that process a specific kind of info 

Simple series circuit

• output?

presynaptic neuron stimulates a single postsynaptic neuron (knee-jerk reflex)

Diverging circuit 

• output?

nerve impulse from single presynaptic neuron causes stimulation of (several) increasing number of postsynaptic neurons 

• one input and many outputs, amplifying the signal

Diverging circuit use

sympathetic mass activation

Converging circuit

• output?

several presynaptic neurons synapse with a single postsynaptic neuron (receives several impulses from different sources)

• inputs from many sources are converged into one output

Converging circuit usage

vision (many photoreceptors and bipolar cells communicate with 1 ganglion cell)

Reverberating circuit

• output?

presynaptic cell causes postsynaptic cell to transmit impulses through the circuit again and again 

• output neuron sends feedback to the input neuron, creating a loop that sustains the signal over tim

Reverberating circuit usage

short: breathing and short term memory

long: waking up, sleeping 

Parallel after-discharge circuit

• output?

single presynaptic cell stimulates a group of neurons, which each synapse with a common post synaptic cell

• input splits and then reconverges, creating a burst of output impulses

Parallel after-discharge circuit usage

involved with precise activities like mathematical equations