Sensory Receptors, Neuronal Circuits for Processing Information (lec7) Save Groups

What is a neuronal pool?

A group of interconnected neurons that processes signals in a unique way, forming the foundation for functional differences in various brain areas.

What is the role of input neurons in a neuronal pool?

Input neurons branch to form thousands of terminals that synapse with various neurons in the pool, allowing for multiple connections.

What is an excitatory/suprathreshold stimulus?

A signal from input neurons that is sufficient to elicit an action potential in the output neuron.

What is a subthreshold stimulus?

A signal that increases the membrane potential in the output neuron but is not sufficient to elicit an action potential.

What are the three zones of activation in neuronal pools?

Discharge zone (triggers action potentials), facilitated zone (receives excitatory input but does not trigger action potentials), and inhibitory zone (receives inhibitory input).

What is divergence in neuronal pools?

When a small number of weak signals entering the neuronal pool lead to excitation of many neurons leaving the pool.

What is amplifying divergence?

An input signal spreads to an increasing number of neurons as it passes through successive neurons in its path.

What is convergence in neuronal pools?

Signals from multiple inputs unite to excite a single neuron.

What is a reciprocal inhibition circuit?

A circuit where an incoming signal causes an excitatory signal in one direction and a simultaneous inhibitory signal in another direction.

What is afterdischarge?

Neural firing that lasts longer than the incoming signal, functioning to increase the duration of the signal.

What are reverberatory (oscillatory) circuits?

Circuits that use positive feedback to repeatedly send a signal, important for rhythmical output signals.

What is continuous signal output in neuronal pools?

When a pool of neurons continuously produces signals even in the absence of input.

What is synaptic fatigue?

The progressive weakening of synaptic transmission due to prolonged or intense excitation stimuli.

What is synaptic sensitivity?

How readily a synapse transmits signals, influenced by neurotransmitter availability and receptor proteins.

What mechanisms stabilize neuronal circuits?

Inhibitory circuits, inhibitory feedback circuits, widespread inhibition, and synaptic fatigue.

What is the significance of synaptic after-discharges?

They prolong the firing of an output neuron due to sustained elevation of membrane potential from long-acting neurotransmitters.

How do reverberatory circuits affect timing?

They control the timing of rhythmic events by repeatedly sending signals through positive feedback.

What is the role of inhibitory feedback circuits?

They prevent self-re-excitation in neuronal circuits, helping to stabilize activity.

What is the function of the thalamus in neuronal processing?

It acts as a relay station for sensory and motor signals to the cerebral cortex.

What happens during an epileptic seizure?

Uncontrolled bursts of electrical activity spread through the brain due to uncontrolled reverberating signals.

What is the difference between short-term and long-term control of synaptic sensitivity?

Short-term control relates to neurotransmitter availability, while long-term control relates to the number of receptor proteins at the synapse.

What are the types of inputs to a neuronal pool?

Excitatory/suprathreshold stimulus and subthreshold stimulus.

What is the discharge zone in a neuronal pool?

The area where all neurons receive sufficient input to trigger action potentials.

What is the facilitated zone in a neuronal pool?

The area where neurons receive excitatory input but not enough to elicit action potentials.

What is the inhibitory zone in a neuronal pool?

The area where neurons receive inhibitory input, impeding the formation of action potentials.

What is a reverberatory (oscillatory) circuit?

A circuit where positive feedback within the neuronal circuit feeds back to re-excite the input of the same circuit.

What are mechanisms to stabilize neuronal circuits?

Inhibitory circuits, inhibitory feedback circuits, widespread inhibition, and synaptic fatigue.

What is the ASIA Impairment Scale?

A scale used to classify the severity of spinal cord injuries.

What are the types of spinal cord injuries?

Complete injuries and incomplete injuries, including anterior cord syndrome, posterior cord syndrome, central cord syndrome, and Brown-Sequard syndrome.

What are common causes of death after spinal cord injury?

Respiratory diseases, infections, cancer, hypertension, and other heart diseases.

What rehabilitation technologies are available for spinal cord injury patients?

Powered wheelchairs, exoskeletons, FES biking, and brain-computer interfaces.

What is the role of inhibitory circuits in the brain?

They prevent excessive spread of signals and help stabilize neuronal circuits.

What is the function of long-acting neurotransmitters in afterdischarge?

They prolong the firing of an output neuron by maintaining elevated membrane potential.

What is the significance of reverberatory circuits in rhythmic activities?

They control the timing of rhythmic events such as breathing and walking.

What happens during a complete spinal cord injury?

It results in loss of all motor and sensory functions below the injury site.

What is the role of the thalamus in neuronal circuits?

It acts as a relay station for sensory and motor signals to the cerebral cortex.

What is the impact of synaptic overuse on sensitivity?

It leads to a decrease in sensitivity due to the depletion of neurotransmitters or vesicles.

What is the difference between convergence from a single source and convergence from multiple sources?

Convergence from a single source involves multiple terminals from one fiber, while convergence from multiple sources involves summation from different pathways.

Neuronal Pool (Neural Circuit)

A functional group of interconnected neurons that processes signals in a unique way to perform a specific function.

Discharge Zone (of a Pool)

The area where neurons receive sufficient (suprathreshold) input to trigger action potentials.

Facilitated Zone (of a Pool)

The area where neurons receive excitatory (subthreshold) input, increasing their membrane potential but not enough to trigger an action potential.

Inhibitory Zone (of a Pool)

The area where neurons receive inhibitory input, impeding the formation of action potentials.

Function of Neuronal Pools

Relaying signals (routing) via divergence, convergence, and reciprocal inhibition, and prolonging signals (timing) via after-discharges and reverberatory circuits.

Divergence

When a small number of weak signals entering a pool excite a large number of neurons leaving the pool.

Amplifying Divergence

An input signal spreads to an increasing number of neurons as it passes through successive neurons in its path.

Divergence into Multiple Tracts

Information is transmitted simultaneously in two or more separate directions when it leaves the pool.

Convergence

Signals from multiple inputs unite to excite a single neuron.

Convergence from a Single Source

Multiple terminals from one incoming fiber tract terminate on the same neuron.

Convergence from Multiple Sources

Summation of information from multiple, separate neural pathways to control the activation of a single neuron.

Reciprocal Inhibition Circuit

An incoming signal causes an excitatory signal in one direction and a simultaneous inhibitory signal in another direction (via an inhibitory interneuron).

Function of Reciprocal Inhibition

Essential for coordinating antagonistic pairs of muscles (e.g., relaxing the hamstring while contracting the quadriceps in the knee jerk reflex) and preventing overactivity in the brain.

Afterdischarge

Neural firing (action potentials) that lasts longer than the incoming signal that caused it.

Synaptic After-Discharge Mechanism

Prolonged firing due to prolonged elevation of membrane potential caused by long-acting neurotransmitters (like neuropeptides) acting on metabotropic receptors.

Reverberatory (Oscillatory) Circuit Mechanism

Positive feedback within the neuronal circuit feeds back to re-excite the input of the same circuit, causing repetitive discharge.

Function of Reverberatory Circuits

Repeatedly send a signal; control the timing of a rhythmic event (e.g., breathing, walking).

Types of Reverberatory Circuits

Simplest, Delayed, and Circuits with parallel fibers.

Continuous Signal Output

When a pool of neurons continuously produces signals, even in the absence of input.

Continuous Intrinsic Neuronal Discharge

A mechanism of continuous output where neurons spontaneously discharge because their resting membrane potential is naturally above the threshold.

Role of Firing Rate in Continuous Output

Excitatory input increases the continuous firing rate, and inhibitory input decreases it; input signals only modify (like a carrier wave) the continuous output, they do not cause it.

Stabilizing Circuits

Inhibitory Circuits: Local and widespread inhibitory feedback circuits (e.g., in the basal ganglia) that prevent excessive spread or self-re-excitation of signals.

Stabilizing Circuits

Synaptic Fatigue: The mechanism where synaptic transmission becomes progressively weaker with intense or prolonged excitation, temporarily halting signal flow.

Short-Term Control of Synaptic Sensitivity

Related to the availability and replenishment of neurotransmitters and synaptic vesicles (sensitivity decreases with overuse and increases with rest).

Long-Term Control of Synaptic Sensitivity

Related to the number of receptor proteins at the synapse (overuse causes receptor removal/inactivation, increasing sensitivity requires fewer receptors being degraded).