1/29: Synapses Flashcards
What do chemical synapses involve?
Neurotransmitters that are released from the presynaptci cell and bind receptors to excite, inhibit, or modify post-synaptic cell
What is a one-way conductor?
Chemical synapse
What determines the function?
The receptor, NOT the neurotransmitter
What is the largest known neurotransmitter receptor family?
serotonin
What are the 3 steps of a presynaptic event?
- AP arrival at the synaptic terminal causes membrane depolarization (whether it’s myelinated or unmyelinated)
- Voltage gated Ca2+ channels open and move out the cell
- Ca2+ enters the synaptic terminal
- Exocytosis of vesicles filled with NT
The amount of Ca2+ that enters dictates the amount of _______ released
NT
- different things (Ca channel blockers) that decrease amount of Ca entry
There is a synaptic delay of at least ______ between the pre-synaptic depolarization and post-synaptic response
0.5ms
What is the synaptic delay due to?
Time for calcium entry for exocytosis
Presynaptic neurotransmitter release
Diffusion in the synaptic cleft
Postsynaptic receptor activation
What does the synaptic cleft/space allow one to gauge?
The complexity of a reflex pathway (number of synapses) by looking at the speed of the reflex
What are the two classifications of neurotransmitters?
- Small molecules
- Neuropeptides
How do small molecule NT act?
Rapidly
- elicit acute responses
- ex: acetylcholine, norepinephrine, dopamine, serotonin (5-HT), histamine, glycine, GABA, glutamate, nitric oxide (NO)
How do neuropeptide NT act?
Larger molecules, slower
- effects are slower, more potent, and more prolonged
- fewer neuropeptides produced and released
- ex: LH, ACTH, vasopressin, oxytocin, angiotensin II, substance P
What does substance P do?
Connects with inflammation and pain pathway
What do NT bind to to cause a response?
receptors on a post-synaptic cell
What is NT action terminated by?
A. Re-uptake of the NT by the pre-synaptic membrane
B. Inactivation of the NT by enzymes in the synapse (ex: acetylcholinesterase)
C. Diffusion of the NT away from the synapse (and receptors)
What are post-synaptic events?
NT binds to receptor on post-synaptic cell
What are the two types of post-synaptic receptors?
- Ionotropic receptors
- Metabotropic receptors
What do ionotropic receptors affect?
Ion channels
Binding of the ligand and the opening or closing the channel can:
- Change a cell’s membrane potential
- Stimulate muscle contraction and/or relaxation
- Stimulate secretion
- Act as a second messenger to alter cellular activity
What are metabotropic receptors?
G-protein coupled receptors (GPCR)
Alpha and Beta adrenoceptors bind _______ and __________
Norepinephrine and epinephrine
All 9 adrenocoreceptors are what kind of receptors?
G-protein coupled receptors coupled to different G-proteins
When adrenocoreceptors couple to different g-proteins, this leads to production of different ________
2nd messengers
What are the resting membrane potentials for Na,Cl, and K?
Na = 61 mV
Cl = 69 mV
K = 86 mV
What are the two types of graded potentials?
- Excitation
- Inhibition
What are EPSPs due to?
Opening of Na+ and Ca channels
Closing of K+ and or Cl- channels
What do EPSPs increase the likelihood of?
That threshold is reached
What are IPSPs due to?
Opening of Cl- channels
Increased K+ conductance
What do IPSPs decrease the likelihood of?
That an action potential is reached
It is the _______ , not the ______, that determines the response produced
specific receptor; NT
Summation is almost always necessary to produce an ______
AP
What are the two types of summation?
- Spatial
- Temporal
What is spatial summation?
Simultaneous EPSPs or IPSPs from multiple pre-synaptic neurons
Spatial summation is added in _______
Space
- different spots on post synaptic neuron
What is temporal summation?
Successive EPSPs or IPSPs from a single presynaptic nerve terminal
Temporal summation is added in _______
Time
Can a spatial and temporal summation occur at the same time?
Yes
What is the duration of a postsynaptic potential?
Up to 15 msec
Excitability of a neuron changes in response to:
- Synaptic input (pre and post synaptic)
- Prolonged activation
- Changes in membrane permeability, ion concentration, other chemicals
What makes up the synaptic input?
A. Postsynaptic inhibition or excitation
B. presynaptic inhibition
C. Presynaptic facilitation
What makes up prolonged activation?
A. Synaptic fatigue
B. long term potentiation (LTP)
C. Long term depression (LTD)
What is presynaptic inhibition and facilitation due to?
Axo-axonic synapses
What does presynaptic inhibition and facilitation change?
The amount of NT released into the synapse
(how much Ca2+ enters the synaptic terminal)
What is an example of an excitatory neurotransmitter?
Glutamate
What is an example of an inhibitory neurotransmitter?
GABA
What is synaptic fatigue due to?
Less neurotransmitter available to be released
Each successive stimulus is ________, but the response is progressively _______, due to ______
Identical; smaller; presynaptic change
Long term potentiaion and long term depression occur in response to?
Repetitive synaptic activity and cause changes in synaptic strength that can last for days to weaks
What is long term potentiation due to?
Memory and hippocampus involved in learning/memory
Learn and develop things over time
Enhancement
What is long term depression?
Opposite of long term potentiation
Long term potentiation is best studied at _____ synapses
Glutamate in the hippocampus
Glutamate can bind to ______ and ______ receptors on the post-synaptic neuron?
AMPA and NMDA
LTD is the opposite of LTP as it _______ synatic strength
Decreases
What are changes that increase excitability?
- hyperkalemis (up to 6mM)
- hypocalcemia
- alkalosis
- caffein and theophylline
- up-regulation of receptors
What are changes that decrease excitability?
- hyperkalemia (above 6mM)
- hypokalemia
- hypercalcemia
- acidosis (can cause a coma, a coma depresses nerve excitability)(ex: diabetic DKA)
- anesthetics (ex: lidocaine (block VG sodium channel and puts it in an inactive state))
- down regulation of receptors
- hypoxia
- fatigue
Yes
Neurons A and B synapse with neuron X. If both neurons A and B release neurotransmitter in the synapse with neuron X at the same time, this is an example of _____.
Spatial summation
