1-07 The Concept of the Synapse

1. Reflexes are relatively slow. Compared to the conduction of an action potential along an axon, which has a velocity around 40 meters/second, the speed of conduction through a reflex arc is only about 15 meters/second.

2. Reflexes are cumulative. They have temporal summation, which means that being exposed to several weak stimuli at slightly different times increases the intensity of the reflex arc. They also have spatial summation, so that the inputs originating from different locations add together to increase their effect on a neuron.

3. Reflexes can be inhibitory. A reflex arc can produce relaxation of certain muscles at the same time that it stimulates the contraction of other muscles.

The electrochemical signal that crosses the synapse can have an excitatory effect on the postsynaptic neuron, producing a graded depolarization of the neuron’s membrane (EPSP), or it can have an inhibitory effect, resulting in the temporary hyperpolarization of the membrane (IPSP).

A specialized gap between neurons in which chemical messengers called neurotransmitters are released and then migrate to receptor sites where they deliver their electrochemical signals

An automatic muscular response to a stimulus

The circuit by which a signal is delivered from a sensory neuron to a muscle via an interneuron and motor neuron; the reflex arc can produce an automatic response by bypassing the brain

The cumulative effect of repeated stimuli over a brief period of time

The cumulative effect of inputs originating in different areas of the body

The neuron that receives the electrochemical signal being delivered across the synapse

The neuron that delivers the electrochemical signal across the synapse

The graded depolarization of the membrane in the postsynaptic neuron

The temporary hyperpolarization of the membrane in the postsynaptic neuron

The baseline rate at which the postsynaptic neuron produces action potentials, even without synaptic input