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 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
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
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
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
