Summation: EPSPs have to be summated to reach threshold. Types

1- Temporal (Time): rapid repetitive stimuli originating from ONE presynaptic neuron

2- Spatial (Space): multiple simultaneous stimuli from MANY presynaptic neurons

N.B. IPSP can be summated

3. Grand Post-Synaptic Potential (GPSP): sum of all EPSPs and IPSPs (neuron receives thousands of presynaptic inputs)

possible outcomes:

1. EPSPs = IPSPs → postsynaptic membrane potential will remain at resting level.

2. EPSPs < IPSPs → postsynaptic away from threshold and membrane inhibited

3. EPSPs > IPSPs → postsynaptic neuron doesn’t reach threshold →membrane is facilitated or in an excitatory state.

Example: micturition reflex is influenced by many signals but the response will vary:

a- Sensory signals from receptors in urinary bladder.

b- Facilitatory and Inhibitory signals from brain stem.

c- Voluntary control from the cerebral cortex.

Review: Physiology for 2nd year medical students Sensory