Synapses Flashcards
What determines the function of a chemical synapse?
the receptor, not the neurotransmitter
What do chemical synapses involve?
neurotransmitters that are released into the presynaptic cell and bind receptors to excite, inhibit, or modify post synaptic cells
How many NTs have been identified?
over 100
What is the largest known neurotransmitter-receptor family?
serotonin receptor subtypes
What are the presynaptic events that occur within the presynaptic neuron?
- action potential arrives at the synaptic terminal causes membrane depolarization
- VG Ca2+ channels open
- Ca2+ enters the synaptic terminal
- exocytosis of vesicles filled with NT
What dictates the amount of NT released from the presynaptic cell?
the amount of Ca2+ that enters
What is a synaptic delay?
the amount of time it takes between pre-synaptic depolarization and post-synaptic response
How does synaptic delay alter?
the more complex the reflex, the more synaptic delay
What causes the synaptic delay?
due to the time for calcium entry for exocytosis, presynaptic NT release, diffusion in the synaptic cleft, and post synaptic receptor activation
What are the two classifications of NT?
small molecules and neuropeptides
What are characteristics of small molecule NT?
-rapidly acting
-elicit acute responses
What are some examples of small molecule NTs?
acetylcholine, norepinephrine, dopamine, serotonin, histamine, glycine, GABA, glutamate, and nitric oxide
What are characteristics of neuropeptides?
larger molecules
-slower
-effects are slower, more potent, and more prolonged
-fewer neuropeptides produced and release
What are some examples of neuropeptides?
LH, ACTH, GH, vasopressin, oxytocin, angiotenison II, and substance P
What is substance P associated with?
inflammation and pain pathway
What are the three ways to terminate the NT action?
-re-uptake of NT by the pre-synaptic membrane
-inactivation of NT by the enzymes in the synapse
-diffusion of NT away from the synapse
What are ionotropic receptors?
receptors on the post synaptic cell that directly affect ion channels
What can the binding of NT on an ionotropic receptor cause?
-changes in cell 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 on post synaptic cells
What causes EPSPs?
-opening of Na+ or Ca2+ channels
-closing of K+ or Cl- channels
What causes IPSPs?
-opening of Cl- channels
-increased in K+ conductance
-closing of Na+ or Ca2+ channels
Is only one graded potential needed for an action potential?
no, usually the summation of GPs are needed to make an AP
What are the two types of summation?
-spatial
-temporal
What is spatial summation?
when there are simultaneous EPSPs or IPSPs form multiple presynaptic neuron onto one post synaptic neuron
What is temporal summation?
successive EPSPs or IPSPs from a single presynaptic nerve terminal
What can cause a change in excitability of a neuron?
-synaptic input
-prolonged activation
-changes in membrane permeability, ion concentration, and other chemicals
What type of response of glutamate cause?
excitatory response
What type of response does GABA cause?
inhibitory response
What does an axo-axonal inhibitory signal cause?
causes less Ca2+ to enter the synaptic cleft and decreases the amount of NT released which causes a smaller EPSP
What does an axo-axonal facilitation signal cause?
cause more Ca2+ to enter the synaptic cleft and increase the amount of NT released which causes a larger EPSP
What is synaptic fatigue?
when each successive stimulus is identical, but the response is progressively smaller
-due to a presynaptic change
What is long term potentiation?
enhanced stimulation on the post-synaptic neuron after a brief period of rapidly repeated stimulation of presynaptic neuron
-becomes easier to cause an action potential
What is long term depression?
the opposite of LTP
-decreases the synaptic strength
What can cause increased excitability of a neuron?
-hyperkalemia (up to 6 mM)
-hypocalcemia
-alkalosis
-caffeine and theophylline
-upregulation of receptors
What can cause decreased excitability of a neuron?
-hyperkalemia (above 6 mM)
-hypokalemia
-hypercalcemia
-acidosis
-anesthetics
-down regulation of receptors
-hypoxia
-fatigue
