12.6: Neural Integration

Neural Integration

The ability to process, store, and recall information and use it to make decisions; chemical synapses allow for decision making; the more synapses, the slower the process but the faster you can carry out an action; based on postsynaptic potentials occurring in a cell receiving chemical signals

Excitatory Postsynaptic Potential (EPSP)

A voltage change (partially depolarization) of a post synaptic neuron or muscle cell in response to a neurotransmitter, making it more likely to reach threshold; usually results from Na+ flowing into cell; ex: glutamate and asparte produce action potential in brain cells; if EPSP > IPSP = fire

Inhibitory Postsynaptic Potential (IPSP)

Hyperpolarization of a post synaptic neuron in response to a neurotransmitter, making it less likely to reach threshold and fire; results either from Cl- into cell or K+ out of cell; ex: glycine and GABA ; if IPSP > EPSP = not fire

Summation

The process of adding up post synaptic potential and responding to their net effect; about 30 EPSPs are needed to reach threshold of fire (each is about 0.5 mV and lasts about 15- 20 msec.)

Temporal Summation

A single synapse generates EPSPs at such short time intervals that each is generated before the previous one decays, adding up overtime, the threshold is met and fires; deals with time

Spatial Summation

EPSPs from several different synapses add up to threshold at axon hillock and fires; deals with location

Facilitation

A process in which one neuron enhances the effect of another one; (spatial summation facilitate one another)

Presynaptic Inhibition

Occurs when one presynaptic neuron suppresses another one; function is to reduce or halt unwanted synaptic transmission; when signal is received, inhibitory neuron releases the inhibitory neurotransmitter (GABA), prevents Ca+ gated channels of neuron “S” from opening and does not release neurotransmitter

Neural Coding

The way in which the neurons system converts information to a meaningful patter of action potential (or sensory coding-sense organs); interpreting and carrying on quantitative and qualitative information via action potential

Qualitative Information

Encoded in terms of which neurons are firing; type of stimulus

Quantitative Information

Information about the intensity of a stimulus; weak stimuli only activate sensitive “low threshold” neurons and causes neurons to fire action potentials at slower rate while strong stimuli activates less sensitive “high threshold” neurons and causes higher firing frequency

Neural Pools

Large ensembles of neurons, each of which consists of “tons” of interneurons concerned with a particular body function; information comes to a neuronal pool via 1 input neurons, these neurons then branch and synapse with numerous interneurons in the pool, they then either form multiple synapses with a single postsynapse cell or form less synapses with a single postsynapse cell; can produce EPSPs at all points of contact with that cell and through spatial summation, make it fire more easily

Discharge Zone

An input neuron acting alone can make the postsynapse cells fire; unction is that it can stimulate those neurons to fire only with assistance of other input neurons or facilitates the other input neurons

Facilitated Zone

Cannot act alone to fire, has to work with the other interneurons in the zone to fire

Diverging Circuit

One nerve fiber branches and synapses with several post synaptic cells and then further synapse with more neurons; function is to send out the same message to numerous “receivers”

Converging Circuit

Input from many different nerve fibers is funneled to one neuron or neuronal pool; function is to take information from numerous different areas, organs, and/or systems and can better respond to the cumulative stimuli

Reverberating Circuits

neurons stimulate each other in a linear sequence, but one or more of the later neuron sends an axon collateral back to beginning, restimulating and starting process over again, function is short-term memory and possible uncontrolled “storms” of neuronal activity (ex: epilepsy); feed back system

Parallel After-Discharge Circuits

An input neuron diverges to stimulate several chains of neurons, each chain has a different number of synapses, they all reconverge on a single output neuron but each with varying delays (arrive at output at different times), output neuron continues to fire until all input is “used” (after discharge); no feedback synapse

Memory and Synaptic Plasticity

The physical basis of a memory is a pathway through the brain; new synapses have formed or existing synapses have been added, taken away or modified to make transmission easier

Synaptic Plasticity

The ability of synapses to change

Synaptic Potentiation

The process of making transmission easier

Immediate Memory

The ability to hold something in mind for just a few seconds; possible reverberating circuits; essential for reading ability

Short-Term Memory (STM)

Lasts from a few seconds to a few hours and is limited to a few bits of information; quickly forgotten; possible reverberating circuits or facilitation (via tetanic stimulation) or post-tetanic potentiation

Working Memory

A form of STM that allows us to hold an idea in mind long enough to carry out an action; reverberating circuits

Tetanic Stimulation

Rapid arrival of repetitive signals at a synapse may foster very brief memories; causes Ca++ accumulation and makes postsynaptic cell more likely to fire

Posttetanic Potentiation

Memory’s lasting longer; appears to be involved in jogging your memory from a few hours ago; Ca++ level in axon terminal stays elevated; little stimulation needed to recover memory

Long-Term Memory (LTM)

Lasts up to a lifetime and is less limited than STM in the amount of information it can store

Declarative (explicit) Memory

Type of LTM; the retention of events and facts that you can put into words; must think to remember these, can verbally explain it to someone

Procedural (implicit) Memory

Reflexive or unconscious memory; recalling without knowing/trying; includes motor skill and emotional memories

Long-Term Potentiation (LTP)

Involves NMDA receptors on dendritic spines of pyramidal neurons (helps create memories in your brain); when NMDA receptors bind to glutamate and receive tetanic stimuli, they allow Ca++ to enter the cell; Ca++ acts as a second messenger causing more NMDA receptors to be produced, and synthesizing proteins concerned with physically remodeling a synapse