Chapter 4.4: Electrical and Chemical Synapses

Question 1

Synapse

Answer 1

Junction between excitable cell and target cell.

Question 2

axon terminal synapse

Answer 2

pre synaptic terminal terminates at the axon terminal.

Question 3

axonal varicosities

Answer 3

pre syn terminal ends along unmyelinated axons in specialized compartments (bulges)

Question 4

en passent synapse

Answer 4

one neuron joins another but not at the axon terminal

Question 5

dendritic spine synapse

Answer 5

small bulge in dendrite that receives input from a single axon.

Question 6

dendrodendritic synapse

Answer 6

dendrite to dendrite

Question 7

axoaxonic synapse

Answer 7

axon terminal to axon hillock

Question 8

axodendritic synapse

Answer 8

axon terminal to dendrite. most common

Question 9

axosomatic synapse

Answer 9

axon terminal to soma

Question 10

2 mechanisms of info flow from synapses

Answer 10

1) electrical (DIRECT): rapid AP flow between adjacent cells by using GAP JUNCTIONS. seen in cardiac muscles at the intercalated disks
2) Chemical (INDIRECT): 2 cells are not directly connected to one another. Can occur Neuron to neuron or neuron to muscle. the gap is too large for gap junction electical signalling, and the neurons use chemical messengers to communicate instead.

Question 11

Limitations to electrical info flow across synapse

Answer 11

1) the post synaptic cells must be very close together in order for connexins to form gap junctions
2) communication in BOTH DIRECTIONS COULD HAPPEN
3) single type of communications; just exerts a change of membrane potential. there is noneuro transmitter release.

Question 12

advantages to chemical indirect info flow across a synapse

Answer 12

1) they are a UNIDIRECTIONAL method of info propagation because the NTs only travel on direction
2) allows for multiple types of communication; can cause depolarization or hyperpolarization.

Question 13

2 Types of inhibition

Answer 13

1) post synaptic inhibition

2) presynaptic inhibition

Question 14

post synaptic inhibition

Answer 14

inhibition at the POST syn cell by the presyn cell. Usually because a neurotransmitter opens hyperpolarizing channels in the post syn cell.

Question 15

Presynaptic inhibition

Answer 15

inhibition at the pre syn cell ( from a neuron that is synapsed on it) that prevents it from communicating with the post syn cell.

Question 16

presynaptic facilitation. HOw does this happen?

Answer 16

when the release of transmitter is enhanced through the persistent Ca2+ elevations in the presynaptic terminus, triggering vesicle release, or when another neuron contributes to the depolarizing events on a post syn cell, helping the pre syn cell execute its excitation of post syn cell.

Question 17

pre and post synaptic ____ and presynaptic ____ allow fine tuning control of the post synaptic cell

Answer 17

pre and post synaptic inhibition and presynaptic facilitation allow for the fine tuning control of the post synaptic cell.

Question 18

the __ ____ ____ is the total potential in the post synpatic neuron after the addition of all EPSPs and IPSPs that have occurred around the same time

Answer 18

Grand Post Synaptic Potential

Question 19

2 methods for EPSPs to bring a membrane to threshol

Answer 19

1) temporal summation: summation of multiple EPSPs from the SAME SYNAPSE.
2) spatial summation: summation of EPSP and IPSP inputs from more than one synapse. EPSPs from different synapse. the different inputs need to fire essentially simultaneous in order to get summated at the axon hillock together.

Question 20

Cancellation

Answer 20

when EPSPs and IPSPs get summated together from different synapses and essentially cancel each other out.

Question 21

why does the axon hillock have the lowest threshold?

Answer 21

because it has the largest density of voltage-gated Na+ channesl. the action potential originates at the axon hillock.

Question 22

convergence

Answer 22

many presynaptic neurons converge onto one post synaptic neuron

Question 23

divergence

Answer 23

axon terminals of one neuron can synapse with multiple post synaptic neurons.

Question 24

how do neurotransmitters work?

Answer 24

typically trigger the opening of specific ion channels to bring out membrane potential changes in post synaptic cell (EPSP or IPSP). Can also open 2nd messenger systems via metabotropic receptors.

Question 25

T/F Neuropeptides are larger than neurotransmitters

Answer 25

True . they are larger. around 10 AA-long chains

Question 26

T/F: neuropeptides are packaged in synaptic vesicles

Answer 26

false. They are packaged in DENSE CORE VESICLES which are released into the synapse.

Question 27

neuromodulators

Answer 27

messengers that do not bring about EPSPs or IPSPs themselves, but can bring long term changes that enhance or depress the actions at a synapse. Can bind at non synaptic sites and activate 2nd messenger systems

Question 28

Example of a neuropeptide. What does it do?

Answer 28

Substance P. It is involved with the delivery of pain perception. Substance P and glutmate is released from the afferent PAIN FIBER in response to a painful stimulus.

Substnace P and Glu bind to receptors on the DORSAL HORN INTERNEURONS which conveys the into to the thalamus for pain perception, as well as the RETICULAR FORMATION for awareness, and hypothalamus, to bring awareness and behavioral emotional responses to pain.

Question 29

how do endorphins affect substance P?

Answer 29

endorphins are amino acid chains that are released from the brain, spinal cord and pituitary and adrenal medulla. it blocks pain via PRESYNAPTIC inhibition of the afferent pain fiber.

It prevents the afferent pain fiber from stimulating the dorsal horn interneurons by preventing the output of substance P and glutamate. without the stimulation of the interneurons, the thalamus or reticular formation cannot be stimulated to bring on the awareness of pain.