Synaptic Transmission Flashcards
Brain only understands…
Electrical signals
Membrane polarity
Separation of positive and negative charges
Na ions concentrated on the outside
K ions concentrated on the inside
Signals
Chemical to Electrical to Mechanical
Neuromuscular Junction
Always excitatory
Acetylcholine
Always stimulates muscular contraction
Synapse mediated by gap junctions
Electrical synapse
Gap junctions: formed by connexons/connexins
Purpose of Schwann cell
Production of myelin sheath
Cochlear connexins
Maintainin the fluid in the cochlea
Chemical synapse
There is a space called synaptic cleft
Bind to postsynaptic receptor
Ca ions
Essential for synaptic transmission
Neurotransmitter
If excitatory, binds with postsynaptic and opens the channel for the entry of Na ions
Blockage of Ca channels
Blockage of release of neurotransmitters
Will not open Na channels in postsynaptic terminal
(e.g. Pain will not be felt)
Direct transmitter : Ionotropic
Fast transmission dahil diretso na!
Indirect transmitter : Metabotropic
Slow transmission and modulation
Utilizes secondary messenger
Most common synapses
Axosomatic synapses
Axodendritic synapses
vs
Axo-axonic synapse
Inhibitory neurotransmitter binding to receptor
What happens?
Opens K and Cl channels
More negative
Hyperpolarized! (Not depolarized)
Signal will stop there
Voltage threshold for action potential to go to the next neuron
Must be reached
10-20 mV
Types of inhibitory inputs
Presynaptic inhibition - impt in pain
Postsynaptic inhibition
Temporal summation
Repetitive stimulation from one neuron can generate an action potential
Reach 15-20 mV
Presynaptic facilitation
Used in rehabilitation
With repetitive stimulation of the hippocampus..
Longterm potentiation
Impt in memory and learning!!!
Are EPSPs and IPSPs graded?
Yes! Summation of stimulation to generate action potential
Neurotransmitters
Excitatory or inhibitory?
Acetylcholine
In muscles, excitatory
In the heart (pacemaker), inhibitory (HOW?) —> bec. increase in Ca leads to inhibition and slowing of the heart
Biogenic amines BOTH
Glutamate Excitatory
GABA inhibitory (CNS, brain, spinal cord)
Glycine BOTH but highly inhibitory (excitatory, impt in the spinal cord, stimulates the NMDA receptor)
Opiates BOTH
Learn by heart and minds!!!
Second-messenger systems
Diff. systems
cAMP: norepinephrine
Phosphonolsitol: Ach
Archidonic: Histamine
Ach
Impt in control of movement, cognition, autonomic control
Deficiency in Ach esterase: Alzheimers
Binds with nicotinic receptor (ionotropic, in NMJ, bind with Na channels, less in autonomic)
Epinephrine (correlate: effect on asthma, allergies, breathing!!!)
Beta receptors - abundant in the lungs than in the heart
Noradrenaline
Alpha receptors - greater in the heart than the lungs
Dopamine receptors
D1 and D2 - striatum (smooth movement ~ Parkinsons disease); movement disorders
D3 - D5 - effect on the mood
Most D receptors are metabotropic
Synthesized in amygdala, arcuate nucleus
Serotonin
In the CNS, actions are different from peripheral serotonin
Found in limbic system
Inhibition (anti-serotonergic) : anti- depressant
Glutamate receptors
Ionotropic
NMDA (Na, Ca, K)- for this to open, sufficient voltage (comes from the opening of non-NMDA), ligand glutamate, glycine ~ related to vetsin! (MSG)
AMPA (Na, Ca)
Metabotropic
Excitatory transmission: glutamate binds to non NMDA
Bad side of NMDA (Pathological)
More Ca ions to enter the cell —> cell death
Excess stimulation may be detrimental
Opiate receptors
Mu High K conductance
Kappa Low Ca conductance
Delta Pure analgesic
