What are reflexes?
Automatic muscular responses to stimuli
Reflexes are studied to understand how the nervous system responds to various stimuli.
In a leg flexion reflex, what is the sequence of neuron activation?
- Sensory neuron excites a second neuron
- Second neuron excites a motor neuron
- Motor neuron excites a muscle
This sequence illustrates how reflex actions occur in response to stimuli.
What is the circuit from sensory neuron to muscle response called?
Reflex arc
The reflex arc is essential for understanding how reflexes function in the nervous system.
True or false: A reflex requires communication between neurons.
TRUE
Cajal demonstrated that if one neuron is separate from another, communication is necessary for reflex actions.
What is temporal summation?
Cumulative effect of repeated stimuli within a brief time
Sherrington found that rapid repeated stimuli can combine to exceed the threshold of excitation in a neuron.
Who discovered the phenomenon of temporal summation?
Sherrington
He observed that a single stimulus might not evoke a reflex, but multiple rapid stimuli could.
What is the role of the presynaptic neuron?
Delivers transmission
It is the neuron that sends the signal to the postsynaptic neuron.
What is the role of the postsynaptic neuron?
Receives transmission
It is the neuron that receives the signal from the presynaptic neuron.
What happens to subthreshold excitation in the postsynaptic neuron over time?
It decays
However, it can combine with subsequent excitations if they occur quickly.
What is an excitatory postsynaptic potential (EPSP)?
Graded depolarization resulting from sodium ions flow
EPSPs can lead to action potentials if the threshold is reached.
What occurs if an EPSP does not reach the threshold?
The depolarization decays quickly
This means the neuron does not fire an action potential.
What is the difference between graded potentials and action potentials?
Graded potentials may be excitatory or inhibitory; action potentials are always depolarizations
Graded potentials can lead to EPSPs or IPSPs.
What is the property of spatial summation in synapses?
Summation over space
Synaptic inputs from separate locations combine their effects on a neuron.
Who discovered the concept of spatial summation?
Sherrington
He conducted experiments to demonstrate how synaptic inputs combine.
In Sherrington’s experiment, what was the result of pinching two points at once?
Produced a reflex
Neither pinch alone produced a reflex, but together they did.
What did Sherrington conclude about the activation of sensory neurons?
Pinching two points activated separate sensory neurons
Their axons converged onto one neuron in the spinal cord.
What happens when excitation from sensory axons does not reach the threshold?
No action potential is produced
A combination of excitations exceeding the threshold is necessary for an action potential.
Fill in the blank: A combination of excitations from sensory axons can exceed the _______ and produce an action potential.
threshold
This is crucial for the generation of an action potential in the neuron.
What does an inhibitory postsynaptic potential (IPSP) do?
- Increases the negative charge within the postsynaptic cell
- Moves the cell farther from the threshold
- Decreases the probability of an action potential
An IPSP resembles an EPSP but has opposite effects on the postsynaptic membrane.
Fill in the blank: An IPSP occurs when synaptic input selectively opens the gates for _______ ions to leave the cell or for chloride ions to enter the cell.
potassium
This movement carries a positive charge away from the cell.
