synapses_after action potential

Synapses

• Instructor: Ana Navarro Ceban, Ph.D.

Key Concepts to Understand for Exam

• EPSP (Excitatory Post-Synaptic Potential)

• IPSP (Inhibitory Post-Synaptic Potential)

• Temporal and Spatial Summation of Electrical Signals

• Spontaneous Firing Rate

• Synchronization

Historical Context

• Charles Scott Sherrington

  • Awarded the Nobel Prize in 1932 for work in neurophysiology.

Properties of Reflexes (as observed by Sherrington)

• Synaptic Delay: Reflexes occur more slowly than direct conduction along axons due to synaptic delays.

• Spatial Summation: Multiple weak stimuli, presented closely in time or space, can produce a stronger reflex than a single stimulus.

• Inhibitory Synapses: When one muscle group is excited, an opposing muscle group is relaxed.

Synaptic Delay

• Action Potential Speed: Approximately 40 m/s in sensory and motor axons. Reflex arcs conduct slower, at about 15 m/s due to synaptic delays.

• Sherrington was instrumental in introducing the term synapse.

Graded Potentials

• Definition: Graded potentials can be either depolarizations (excitatory) or hyperpolarizations (inhibitory).

• Visual Representation: Membrane Potential (mV)

  • +30 mV: Depolarization

  • -55 mV: Transition point

  • -70 mV: Resting potential

  • Hyperpolarization occurs after the action potential.

  • Key Types:

    • EPSP (Excitatory Post-Synaptic Potential)

    • IPSP (Inhibitory Post-Synaptic Potential)

Excitatory Synapses

• EPSP Defined: A temporary graded depolarization of the postsynaptic membrane due to sodium ions entering the cell, making action potentials more likely.

Inhibitory Synapses

• IPSP Defined: A temporary graded hyperpolarization of the postsynaptic membrane caused by potassium exiting the cell or chloride entering, making action potentials less likely.

Spatial Summation

• Definition: The combined effect of synaptic inputs from different locations that depolarize the neuron; important for the timing of stimuli.

Temporal Summation

• Definition: Cumulative effects of repeated stimuli within a short time frame can combine to produce an action potential, even if the original post-synaptic signal diminishes over time.

• Both spatial and temporal summation can occur simultaneously.

Spontaneous Firing Rate

• Characteristic: Periodic action potentials occur in the absence of synaptic input; this ongoing activity is significant for perception.

• The perception of stimuli may depend on spontaneous activity levels, which influence action potential frequency through EPSPs and IPSPs.

Neural Synchronization

• Definition: The synchronization of brain waves across different regions indicates coordinated neural communication, leading to oscillations.