Chapter 8 Flashcards
Electrical synapse
Electrical signals or 2nd messengers transmitted from one neuron to another through gap junctions
Between neurons or glial cells
Adult brain
Raid conduction
Bi or unidirectional
Excitatory (Depolarize) or Inhibitory (hyperpolarize)
Chemical synapses
The release of neurotransmitters that activate signal transduction mechanisms in the target cell
Muscles and glands are effector organs
Unidirectional
Neuroeffector junction
A synapse between a neuron and an effector cell
Synaptic vescicles
Store neurotransmitter molecules
How are neurotransmitter synthesized
Synthesized in cytosol of axon terminal
Then store in vesicles until eventually released by exocytosis
Cytosolic calcium
Triggers the release of neurotransmitter by exocytosis
How voltage calcium channels work
1: calcium channels open when axon terminal is depolarized (action potential)
2: allow calcium flow down electrochemical gradient into axon terminal
3: calcium causes vesicles to fuse on inner surface of axon terminal
4: exocytosis, releases neurotransmitter to synaptic cleft
Amount of neurotransmitter factors
Concentration of calcium in cytosol
Frequency of action potentials in presynaptic neuron
Reuptake
Neurotransmitter molecules can be transported back into presynaptic neuron to be degraded and recycled
Channel linked receptor (ionotropic receptor)
Fast response
Ligand gated
Opens ion channel and changes mem potential
Postsynaptic potential (PSP)
Mem potential of postsynaptic neuron
Very rapid and terminates rapid
Channel closes as soon as neuron leaves receptor
Metabotropic receptors (G protein)
Slow response
Ligand binds to Metabotropic receptor activating G protein which excites or inhibits second messenger system
Second messenger affects state of ion channel
Seconds to hours
Excitatory synapses
Depolarize postsynaptic neuron closer to threshold for action potential EPSP
Excitatory postsynaptic potential (EPSP)
Graded potential, depolarizer as more neurotransmitters bind
Either a fast or slow response
Fast EPSPs
Strong electrochemical drives more sodium in than potassium move out, causing a net depolarization
Slow EPSPs
1: Neurotransmitter binds to receptor and activates a G protein
2: The G protein then activates the enzyme adenylate cyclase
3: which catalyzes ATP to cAMP
4: cAMP activates protein kinase A
5: add phosphate group to K+ channel
6: phosphorylation closed channel
*Take longer and lasts longer
Inhibitory synapses
A synapse that takes the membrane potential of the postsynaptic neuron away from threshold by hyperpolarization or stabilizes mem pot (-70mV)
Opens the channels for either K+ or Cl- ions
Inhibitory postsynaptic potential (IPSP)
Graded potential, Chloride channels are opened by neurotransmitters binding to receptors, chloride enter cell causing hyperpolarization
Chloride channels
Because chloride is an anion -70mV drives it out of cell
Chloride concentration is higher outside than inside cell, acts to me chloride inside
Chloride is not at equilibrium
Chloride equilibrium
The passive movement of chloride coupled with the lack of active transport allows chloride ions to be at equilibrium
Without active transport chloride simply diffuses through chloride leak channels to gain equilibrium
Clara equilibrium prevents the opening of chloride channels to cause a change in membrane potential
Divergence
The arrangement of the axon of one neuron having several collaterals that communicate to several other neurons
Convergence
Single neuron receives communication from many neurons
Neural Integration
Action potential occurs if mem pot at axon hillock is depolarized to threshold; below threshold nothing will occur
Divergence
Convergence
Temporal summation
Two or more post synaptic potentials are generated in rapid succession at the same synapse, causing the potential to not have time to fully dissipate before next potential
Generating a larger hyperpolarization or depolarization
Spatial summation
Two or more postsynaptic potentials from different synapses spreading to the axon hillock overlapping and summing
Frequency coding
Increases in the suprathreshold stimuli cause the frequency of action potentials to increase
Modulatory synapses
Axoaxonic synapses that Regulate the communication across another synapse
Presynaptic facilitation
The release of neurotransmitter is enhanced
Modulatory neuron
Presynaptic inhibition
The release of neurotransmitters is decreased
Modulatory neuron
Acetylcholine (ACh)
neurotransmitter Synthesized from the substrates acetyl CoA and choline, catalyze by acetyl transferase (CAT)
Released mostly from PNS but also CNS and efferent neurons
Stored in synaptic vesicles until action potential releases by exocytosis
Bind to cholinergic receptors or degraded by acetylcholineterase into acetate (diffuses in yo bloodstream) and choline(recycled)
Acetylcholine receptors
Nicotinic cholinergic receptors: ionotropic, 2 binding sites, opens k na channel causing EPSP CNS and PNS
Muscarinic cholinergic receptors: metabotropic receptors that uses G protein, causes opening/closing of ion channels and activate enzymes
Mostly found in CNS
Biogenic Amines
Neurotransmitter from amino acids (NH2), catecholamines, seratonin, and histamine
Dopamine, Epinephrine,Norepinephrine
Synthesized in cytosol—> Packed in vesicles
Adrenergic receptors
Receptors from epinephrine and norepinephrine
Two classes:
Alpha adrenergic
Beta adrenergic
Found in CNS and effector organs
G protein autocrine (Ca2+)
Catecholamines
Slow responses through G proteins
They are autocrines and bind to auto receptors
Can be degraded by monoamine oxidase and catechol-O methyltransferase
Amino acids neurotransmitters
Most abundant transmitter in CNS
Excitory: Aspartate and Glutamate (NMDA,AMPA,Kainate)
Inhibitory: Glycine and GABA
GABA and Glutamate are opposite effects
Glutamate
Most released in exciting synapses
Can bind to AMPA,NMDA, and kainate receptors
When binded to AMPA or Kainate receptors a fast EPSP is produced by sodium movement into cell
When binded to NMDA calcium channels open creating biochemical changes in postsynaptic neuron
Gamma aminobyutyric acid (GABA)
Most released in inhibitory synapses of CNS
Categories:
GABA a and GABA c (ionotropic)
GABA b (metabotropic) slow IPSP auto receptor
GABA a: binds sedatives
GABA c: found in retina
Purines
GTP, ADP,AMP (stored in vesicles)
Adenosine (releases by enzymes)
Receptor types:
P2X-ionotropic, allows cations, depolarize
P2Y-metabotropic, G protein, can bind adenosine, ADP, and ATP
Nucleotidases breakdown ADP and ATP
adenosine deaminase breakdown adenosine
Major in Enteric nervous system
Neuropeptides
Short chains of amino acids that are synthesized in rough ER and packaged in dense core vesicles in Golgi apparatus
Then transported down axon to terminal to be stored
Metabotropic
Hormones:
TRH- release TSH
Vasopressin-urine
Oxytocin-contractions, milk
Substance P-stomach motility
Cholecystectokinin-gallbladder contractions
Endogenous opioids=enkephalins and endorphins
Orexin-arousal and sleep cycle (narcolepsy)
Unique neurotransmitters
Nitric oxide- NO, catalyze by nitric oxide synthetase, The fuses to target cells and alter activity of proteins
Endocannabinoids-manufactored by membrane phospholipid, include anandamide (AEA) and 2-arachdonyglycerol (2-AG), stimulated by an increase in cystolic calcium levels
CB1 receptor that targets THC
Alleviates Parkinson’s disease, anxiety disorders, and post traumatic stress disorder
Acetylcholinesterase (AChE)
Enzyme that breaks, ACh= choline +!Acetyl CoA
Choline makes more Ach
Nicotine
Crosses blood brain barrier in 10-20 secs
1/2 life around 2 hours
Stimulate nicotinic acetylcholine receptors which stimulates dopamine (affects Heart rate, blood pressure, respiration, glucose levels
Tobacco MAO inhibitors
CB1 receptors (cannabinoid)
Medulla: nausea/vomiting, chemoreceptor trigger zone (CTZ)
Cerebellum: Movement
Basal Ganglia: Movement
Cerebral cortex: Higher cognitive function
Hypothalamus: Appetite
Hippocampus: Learning, memory, stress
Spinal cord: peripheral sensation, pain
Adverse Effects of Ecstacy
Clouded thinking
Hyperthermia
Disturbed behavior
Jaw clenching
Stimulants
Ritalin and Adderall
Acts like cocaine on dopamine cells
