Synapses

Question 1

what determines the function of the synapse?

Answer 1

The RECEPTOR not the nt.

Question 2

what are the three morphological types of chemical synapses?

Answer 2

• axosomatic
• axodendritic
• axoaxonal

Question 3

what is axosomatic?

Answer 3

where synapses terminate on neuronal cell bodies and tend to be INHIBITORY

Question 4

what is axodendritic?

Answer 4

where synapses terminate on dendrites or dendritic spines (out pouching parts that make a connection with an axon) and tend to be EXCITATORY

Question 5

what is axoaxonal?

Answer 5

where synapses terminate on an axon, often close to synaptic terminals and modulate the release of nt.

They can modulate the release of nt by regulating the amount of Ca2+ that enters.

Question 6

What happens during a presynaptic event?

Answer 6

1. AP arrives at the terminal causing membrane depolarization
2. V-gated Ca2+ channels open (OUR GOAL)
3. Ca2+ enters the synaptic terminal
4. Exocytosis of vesicles filled with nt

Question 7

what are they two classifications of nt

Answer 7

1. small molecules

2. neuropeptides

Question 8

what are small molecule nt?

Answer 8

they are FAST

• elicit acute responses
• ex: Ach, NE, Dopamine, Serotonin, Histamine, Glycine, GABA, Glutamate, NO.
• these nt vesicles are typically “prepackaged and ready to go” that is why they are fast

Question 9

what are neuropeptide nt?

Answer 9

they are SLOWER

• effects are slower to be produced, more potent and do not need as much, and are more prolonged
• produced in the cell body and transported down axon
• LH, ACTH, GH, Vasopressin. oxytocin, angiotensin II, substance P

Question 10

how can a NT action be terminated?

Answer 10

• Re-uptake by the presynaptic membrane
• absorption by glial cells
• inactivation by enzymes in the synapse

Question 11

where do nt bind to when released?

Answer 11

• post synaptic receptors

- presynaptic membranes

Question 12

what happens during post-synaptic events if its an ionotropic receptor?

Answer 12

ionotropic receptors: directly affects the ion channels to directly open or close them

It can then do one of the following:

• change of a cells membrane potential
• stimulates muscle contraction/relaxation
• stimulate secretion
• act as a 2nd messenger to alter cell activity

Question 13

what happens during post-synaptic events if its an metobotrophic receptor?

Answer 13

nt binds to Gprotein coupled receptors

Question 14

How do ESPS occur?

Answer 14

• opening of Na+ channels
• closing K+ and/or Cl- channels
• depolarized graded potentials

Question 15

How do ISPS occur?

Answer 15

• opening of Cl- channels
• increased K+ conductance through and increase of all channels
• hyperpolarization of the membrane

Question 16

what is summation of EPSP

Answer 16

• it will allow for an AP to be fired if all 16+ synapses come together to depolarize a neuron. It is almost always necessary to have summation to produce an AP.

Question 17

What are the two types of summation

Answer 17

Spatial and Temporal

Question 18

Explain spatial summation:

Answer 18

simultaneous EPSP and IPSP from multiple pre-synaptic neurons
-can happen at different places but at the SAME TIME. Individually not enough but all together it will be.

Question 19

Explain temporal summation:

Answer 19

Successive EPSP or IPSP from a single presynaptic nerve terminal. One could be enough but will increase the amount of times it does it within one succession.

Question 20

excitability of a neuron can change in response to:

Answer 20

• synaptic input (due to axo-axonic synapses)
• prolonged activation
• changes in membrane permeability, ion concentration, or other chemicals

Question 21

What are the 3 ways a neuron changes excitability in response to synaptic input?

Answer 21

1. synaptic input
2. prolonged activation
3. changes in membrane permeability

Question 22

How can a post-synapse input change excitability

Answer 22

• an inhibitory nt (like GABA) produces an IPSP that decreases post synaptic neuron from reaching threshold
• an excitatory nt (like Glutamate) can cause an EPSP (depolarization) that increases post synaptic neuron from reaching threshold

Question 23

How can a pre-synapse input change excitability

Answer 23

a third neuron (axo-axonal neuron) can impact the excitatory neuron on how much it will release nt to the post synaptic neuron. It can decrease/increase the AP which then changes the Ca2+ entry which leads to more or less nt being released

Question 24

how can an axoaxonal neuron change AP for facilitation or inhibition?

Answer 24

facilitation: opening more Na+ channels
inhibition: increase Cl- conductance that reduces AP size

Question 25

how can an axoaxonal neuron change the nt release for facilitation or inhibition?

Answer 25

facilitation: increasing Ca2+ and more nt are released inhibition: decrease of Ca2+ because of the increased Cl- conductance

Question 26

how can the excitability of a neuron change in response to prolonged activation?

Answer 26

- synaptic fatigue - long term potentiation - long term depression

Question 27

explain synaptic fatigue

Answer 27

stimulus is identical but the response begins to get smaller because of a presynaptic change. Meaning that the presynapse will be constantly activating it could run out of vesicles or have less response which changes the excitability of the neuron

Question 28

LTP stands for what

Answer 28

long-term potentiation

Question 29

LTP and excitability of a neuron

Answer 29

the post synapse changes (having more receptors) that allows the synapse to be more active

Question 30

LTD stands for what

Answer 30

Long term depression

Question 31

LTD and excitability of a neuron

Answer 31

LTD decreases synaptic strength. The lack of use of a synapse can decrease the strength

Question 32

How can hyperkalemia alter neuronal excitability

Answer 32

if 6 or less: increase excitability | if 6 or more: decrease excitability

Question 33

how can hypo and hypercalcemia alter neuronal excitability

Answer 33

hypocalcemia: increase excitability hypercalcemia: decreaes excitability having more Ca2+ impedes Na+ movement through channels so decrease excitability

Question 34

How can caffeine alter neuronal excitability

Answer 34

increases excitability

Question 35

how can alkalosis and acidosis alter neuronal excitability

Answer 35

alkalosis: (up pH) so less H+ --> increase excitability acidosis: (down pH) so more H+ --> decreases excitability (acidosis happens to diabetic pts: too much H+ and can go into coma)