chapter 4.3

Question 1

Whether or not a neuron fires depends on

Answer 1

the balance between the excitatory and inhibitory signals reaching its axon.

Question 2

axon hillock

Answer 2

once believed that actions potentials were generated here; the conical structure at the junction between the cell body and the axon.

Question 3

axon initial segment

Answer 3

where actions potentials are generated; adjacent to the axon hillock.

Question 4

threshold of excitation

Answer 4

usually about -65 mV.

Question 5

an action potential is generated.

Answer 5

If the sum of the depolarizations and the hyperpolarizations reaching the axon initial segment is sufficient to depolarize the membrane to the threshold of excitation

Question 6

Action potential (AP)

Answer 6

massive but momentary – lasting for 1 millisecond – reversal of the membrane potential from about -70 to about +50 mV. Not graded responses; their magnitude is not related in any way to the intensity of the stimuli that elicit them.

Question 7

All-or-none responses

Answer 7

APs either occur to their full extent or do not occur at all.

Question 8

Spatial summation

Answer 8

summation of EPSPs and IPSPs.

Question 9

Temporal summation

Answer 9

postsynaptic potentials produced in rapid succession at the same synapse sum to form a greater signal.

Question 10

Location of a synapse on a neuron’s receptive membrane is assumed to be an important factor in determining

Answer 10

its potential to influence the neuron’s firing. Because EPSPs and IPSPs are transmitted decrementally, synapses near the axon trigger zone have been assumed to have the most influence on the firing of the neuron. Although, some neurons have a mechanism for amplifying dendritic signals that originate far from their axon initial segments.

Question 11

Integration

Answer 11

adding or combing the number of individual signals into one overall signal. Neurons integrate incoming signals over space and over time.