5.3 Neurotransmitters Flashcards
Most neurons make _____ neurotransmitters
make two or more
*released at diff stimulation frequency
What are the classes of neurotransmitters?
- Acetylcholine
- Biogenic Amines (aka Monoamines)
- Amino acids
- Peptides (neuropeptides)
- Purines 6. Gases & lipids
Describe Acetylcholine
- Synthesized from choline & acetyl CoA by choline acetyltransferase (ChAT)
- degraded by acetylcholinesterase
– Released at neuromuscular junctions, some ANS neurons, & some CNS neurons
– Nicotinic receptors (N) (excitatory) on skeletal muscle, ANS ganglia & in CNS
– Muscarinic receptors (M) (can be inhibitory or excitatory) on visceral effectors & in CNS
How does Ach work
* 1st Coa A is released and binds to acetyl choline,
- binds to acetyl choline receptor and get an intracellular response
- Acetylcholinesterase can turn off Ach
What are Biogenic amines
*aka monoamines
drug calss: monoamine oxidase inhibitor (MOAI)
- derived from single amino acids
- play roles in emotional behaviours and biological block
3 Classes: Catecholamines (deopamine, norephinephrine, epinephrine), Indolamines (serotonin or 5HT), Imidazoleamine (Histamine)
What is dopamine
Biogenic catacholamine
- can be inhibitory or excitatory
- released from substantia nigra and hypothalamus
- important for motor pathways, motivation, reward and reinforcement
What is norephinephrine
- type of biogenic amine; catecholamine
- can be inhibitory or excitatory
- released from locus coeruleus, limbic system, cerebral cortex, postganglionic neurons in SNS & adrenal medulla
– Involved in mood, sleep and wakefulness, attention, feeding behaviour and SNS
What is serotonin
aka (5- hydroxytryptamine = 5-HT
- Biogenic amines - Indolamines
*mainly inhibitory
- Brain & spinal cord
– Role in sleep, appetite, nausea, migraine headaches, mood and digestion
describe histamine
Biogenic amines - Imidazoleamines
(can be inhibitory or excitatory)
- Hypothalamus
– Involved in wakefulness, appetite control, learning & memory, ↑ gastric secretions, in connective tissues mediates inflammation & vasodilation
What are the amino acid neurotransmitters
-
GABA (inhibitory) [Gamma (γ)-aminobutyric acid]:
- Principal inhibitory neurotransmitter in brain;
- important for axoaxonal presynaptic inhibition
-
Glycine (inhibitory):
- Principal inhibitory neurotransmitter in spinal cord
-
Glutamate (excitatory):
- Principal excitatory neurotransmitter; important in learning and memory
-
Aspartate (excitatory):
- excitatory neurotransmitter in some brain regions
What are the Neuropeptide neurotransmitters
-
Tachykinins (excitatory):
- Substance P, neurokinin A
- PNS = Mediator of pain signals
- CNS = respirator and cardiovascular controls and mood
- Also released by enteric neurons
-
Endorphins (inhibitory):
- Act as natural opiates; reduce pain perception
- Inhibits substance P
-
Cholecystokinin (CCK) (excitatory):
- Found in CNS & released by small intestines to encourage digestion
- Involved in anxiety, pain, memory; inhibit appetite
- Found in CNS & released by small intestines to encourage digestion
-
Somatostatin (inhibitory):
- Found in CNS & released by pancreas, stomach & intestines to slow down/inhibit digestion
Describe Purine neurotransmitters
-
ATP (can be inhibitory or excitatory)
- Released by sensory neurons
- Provokes pain sensation
-
Adenosine (inhibitory):
- Potent inhibitor in brain (Caffeine’s stimulates by blocking brain adenosine receptors)
- causes vasodilation to increase blood flow to heart & other tissues as needed
*Act in both CNS & PNS to produce fast or slow responses
describe gasotransmitters
Synthesized on demand
- Diffuse out of cells that make them (lipid soluble)
- Travel into target cell to bind to intracellular receptors
* Nitric oxide (NO) (can be inhibitory or excitatory)
• Involved in learning & memory • Smooth muscle relaxation
*Carbon monoxide (CO) (can be inhibitory or excitatory)
describe lipids as neurotransmitters
Endocannabinoids (inhibitory)
– Synthesized on demand from membrane lipids
– Receptors also activated by THC (tetrahydrocannabinol = principal active ingredient of cannabis)
– Involved in memory as a retrograde messenger to ↓ neurotransmitter release
– Also involved in controlling appetite, suppressing nausea & vomiting, & neuronal development
what are the types of neurotransmitter receptors
- Channel-linked (Ionotropic) receptors:
- G protein-linked (Metabotropic) receptors
Describe Channel - Linked Receptors
- Ligand-gated ion channels
- Action is immediate and brief (Direct action)
- Excitatory receptors are channels for small cations (Na+ influx contributes most to depolarization)
- Inhibitory receptors allow Cl– influx or K+ efflux that causes hyperpolarization
- Examples: ACh & amino acids
describe G protien linked receptors
Have an indirect action: Neurotransmitter binds to G protein-linked receptor & acts through an intracellular second messenger
- Responses are indirect, slow, complex & often prolonged/widespread
- Examples: biogenic amines, neuropeptides, cannabinoids & gases
What are Neuronal Pools?
- form of neural integration
functional groups of neurons that: Integrate incoming information & Forward processed information to other destinations
Describe the simplified version of a Neuronal Pool
Single presynaptic fiber branches & synapses with several neurons in pool
- Discharge zone: neurons most closely associated with incoming fiber
- Facilitated zone: neurons farther away from incoming fiber
what are the type sof circuits in neuronal pools?
diverging cirucit, converging circuit, reverberating circuit, parallel after discharge cirucit
describe diverging cirucit neuronal pool
One input, many outputs
– Amplifying circuit
– May affect a single pathway or several
– Example: A single neuron can activate 100 or more motor neurons in the spinal cord and thousands of muscle fibers
describe converging ciruit of neuronal pools
Many inputs, one output
– Concentrating circuit
– Common in sensory & motor systems
– Example: Different stimuli can elicit the same memory
describe reverberating (oscillaing) circuit in neuronal pools
Chain of neurons containing collateral synapses with previous neurons
– Involved in Sleep-wake cycles, breathing, certain repetitive motor patterns, etc
Describe Parallel after dischange cirucit
Signal stimulates neurons arranged in parallel arrays that eventually converge on a single output
― Impulses reach output cell at different times causes a burst of impulses (called after discharge)
― Involved in complex types of mental processing e.g. mathematical calculations
*get immediate output resonse
what are the patterns of neuronal processing?
serial and parallel processing
describe serial processing
Input travels along one pathway to a specific destination
– Works in an all-or-none manner to produce a specific response
– Example are simple spinal reflexes
describe parallel processing
Input travels along several pathways
– One stimulus promotes numerous responses
– Important for higher-level mental functioning
– Example: step on a sharp object
– serial processed withdrawal reflex parallel processing of higher order processing e.g. rub foot and seek first aid
