Synapses

Synapses

1. Simple reflex arc- the circuit from sensory neuron to muscle response. Doesn't need input from the brain (bypases the CNS). Slower than conduction along an axon and never faster than 15m per second. When one set of muscles become excited, another becomes relaxed.

   • Temporal summation- repeated stimuli within a brief time have a cummalative effect.
   • Spatial summation- synapses have the property of summation of space. Synaptic inputs from separate locations combine their effects on a neuron.
     • ensures that a sensory stimulus stimulates neurons enough to activate them
   • Excitary postsynaptic potentials (EPSP)- a graded depolarization and it results from a flow of sodium ions into the neuron.
     • If an EPSP doesn't cause the cell to reach it's threshold, the depolarization decays quickly.
     • If the ESPS occurs twice, the second will add to it producing temporal summation (increased action potential)
   • Inhibitory postsynaptic potentials (IPSP)- occurs when synpatic input selectively opens gates for potassium ions to leave the cell for chloride ions to enter the cell.
     • Produces a temporty hyperpolarization of a membrane (decreased action potential)