The Synapse

Question 0

the synapse

Answer 0

• action at the junction

- presynaptic cell releases NT in the Synaptic Cleft which affects the postsynaptic cell

Question 1

Presynaptic cell

Answer 1

releases NT into Synaptic Cleft

Question 2

Synaptic celft

Answer 2

• tiny space (gap) between the presynaptic and postsynaptic cells
• typically 20 - 50nm wide

Question 3

Exocytosis

Answer 3

• 1)the release of Vesicles (packets) of NT from Presynaptic Terminal
• 2) when membrane depolarization reaches the axon’s Terminal, voltage-dependent Ca++ gates open,
• 3) extracellular Ca++ rushes into Terminal (per Electrical and Concentration Gradients) causing release of NT’s
• NT PASSIVELY FLOWS (DIFFUSES) across Synaptic Cleft

Question 4

NT binds to….

Answer 4

• … NT-specific Receptor Site on (usually) DENDRITES of Postsynaptic cell

Question 5

this prevents NT from continuing to affect Postsynaptic cell after message has been “sent”

Answer 5

NT is often then deactivated by enzymes or Glia in the cleft

- i.e. NT broken down, carried off, re-uptaken by presynaptic cell, etc.

Question 5

NT soon DETACHES from…

Answer 5

…Receptor Site and again floats in Cleft (most NT’s do NOT enter Postsynaptic Cell)

• NT binds to the post but doesn’t go in, floats back home to be used again

Question 7

binding to Receptor site triggers…

Answer 7

…reaction in Postsynaptic cell, which may lead to it firing its NT, etc.

Question 8

Exitatory

Answer 8

• Sodium gate

Question 9

Inhibitory NT

Answer 9

• Cl enter the cell

- polarity greater

Question 10

NT can have two basic types of effects on the POLARITY of the Postsynaptic cell:

Answer 10

EPSP & IPSP

Question 11

EPSP

Answer 11

• Excitatory Post-Synaptic Potential
• an increase that cell’s likelihood of releasing NT
• Post-Syn cell becomes HYPO-POLARIZED (less polarized, less difference between inside and out) and thus closer to its threshold for firing
  - excited when you say “O”
• Using a function of Na+ entering the cell

Question 12

IPSP

Answer 12

• Inhibitory Post-Synaptic Potential
• a decrease in the cell’s likelihood of releasing NT
• Post-Syn cell becomes Hyper-Polarized (more polarized, greater difference between inside and out) and thus farther from its firing threshold
  
  • when your inhibited you say “errr”
• usually a function of K+ exiting and Cl- entering the cell

Question 13

Spontaneous Activity

Answer 13

• absence of input, yet still firing
• firing at a base rate
• some Neurons show this spontaneous firing, in the ABSENCE OF INCOMING NT!
• these are usually graded potentials that release variable amounts of NT
• converging NTs increase or decrease such cell’s activity, modifying how much NT they will then release

Question 14

Summation

Answer 14

• The response of a given Neuron is nearly always the product of a SUMMATION OF EPSPs and/or IPSPs
• a neuron virtually never receives input from only one other cell, and can receive from 1000s of others

Question 15

Mechanisms

Answer 15

NT affects the Postsynaptic cells via one of two types of mechanisms:

Ionotropic and Metabotropic

Question 16

Ionotropic

Answer 16

DIRECTLY effects ion gates

e.g. NT binds to receptor site»_space; opens nearby Na+ gates

effects are RAPID, short-lived, esp good for conveying info about rapidly changing events

Question 17

Metabotropic

Answer 17

triggers METABOLIC CHANGES in Postsynaptic cell

e. g. NT alters receptor, releases G-Protein»_space; activates Second Messenger in cell»_space; may open ion gates, alter protein production, activate genes, etc.
- complex chain reaction requires ENERGY - Effects are SLOWER, longer lasting (up to hours!)
- typical of “Neuromodulators”

Question 18

TEMPORAL Summation

Answer 18

when one (or more) cells repeatedly stimulate another in rapid succession

Question 19

SPATIAL Summation

Answer 19

when multiple cells converge on a single cell at the same time

Question 20

• often both excitatory and inhibitory NTs simultaneously converge on a cell,…

Answer 20

…this summates their +/- effects

- if effects reach or exceed cell’s Threshold of Firing, triggering an Action Potential (in cells that have APs)