Chemical Signaling Flashcards
What happens when Action Potential gets to Terminal Button
The neuron releases neurotransmitters into synaptic cleft/gap
Synthesis, Packaging, Transport, Release of Neurotransmitters
- Neurotransmitters are synthesized (made) in cytoplasm of the terminal button.
- Packaged into vesicles
- Stored near the presynaptic membrane
- Exocytosis = when stimulated by AP, the membrane channels open
- Calcium enters the button causing the vesicles to fuse with the presynaptic membrane and empty their neurotransmitters into the synaptic cleft
What happens when Neurotransmitters are released
- Neurotransmitters bind to post-synaptic receptors
- Receptors have binding sites for particular neurotransmitters
- Ligand = any molecule that binds to another (neurotransmitter is a type of ligand)
- There are both IONOTROPIC (ligand-activated ion channels, immediate, fast) and METABOTROPIC receptors (G-proteins, more prevalent, slower)
Amino-acids
Most fast-acting neurotransmitters are amino-acids
e.g. glutamate (excitatory), aspartate, glycine, GABA (inhibitory)
Define Hormones
Large-molecule neurotransmitters. They are slow acting and produce prolonged action
Define a Classic Neurotransmitter
- The substance exists in presynaptic terminals
- The presynaptic cell contains appropriate enzymes for synthesizing it
- The substance is released in significant quantities when action potential reach the terminals
- Specific receptors that recognize the released substance exist on the postsynaptic membrane
- Experimental application of the substance produces changes in postsynaptic cells
- Blocking release of the substance prevents presynaptic activity from affecting the postsynaptic cell
Acetylcholine
In the central and peripheral nervous system. Plentiful in the striatum and involved in movement. In hippocampus where involved in memory function, sleep/wake cycle and perception and attention. Involved in the periphery by helping with the contraction of muscles by releasing acetylcholine in muscles
Acetylcholine bind to 2 receptors…
- Nicotinic acetylcholine receptors are ligand-gated ion channels permeable to sodium, potassium and calcium ions (IONOTROPHIC = fast). They are ion channels embedded in cell membranes, capable of switching from a closed to open state when acetylcholine binds to them; in the open state they allow ions to pass through. Nicotinic receptors come in two main types, known as muscle-type and neuronal-type.
- Muscarinic (subtypes M1 through M5), all of them function as G protein-coupled receptors meaning that they are (METABOTROPHIC = slow). Thus slower than nicotinic receptors. Muscarinic acetylcholine receptors are found in both the central nervous system and the peripheral nervous system of the heart, lungs, upper gastrointestinal tract, and sweat glands.
Dopaminergic neurotransmitter pathway
- Mesostriatal = In the SUBSTANTIA NIGRA of the midbrain. Projects to the BASAL GANGLIA (part of the limbic system). Plays a role in movement. A loss of substantia nigra cells produces Parkinson’s disease (loss of movement)
- Mesolimbic = In the VENTRAL TEGMENTAL area of the midbrain. Projects to structures on the limbic system (hippocampus, amygdala, nucleus accumbens) and cortex. Plays a role in reward and reinforcement learning (drug addiction). Abnormalities in this pathway are associated with schizophrenia and depression
Types of Dopamine Receptors
At least 5 different types of dopamine receptors: D1-D5 all of which are metabotropic
The mesolimbic pathway projects to the limbic system (contains many D2 receptors involved in reward and reinforcement learning)
Many recreational drugs e.g. cocaine and amphetamines act on the mesolimbic pathway. They block a reuptake transporter so dopamine remains for longer in the synapse, increasing the ‘reward’ feeling of the drug/the addiction to the drug
Problems with dopaminergic neurotransmission associated with ADHD (can be treated with amphetamines)
Parkinson’s disease (slowing of movement) can be treated with levodopa (a precursor to dopamine) to increase dopamine in the brain (improves movement symptoms)
Noradrenaline and Noradrenergic receptors
NAd receptors are metabotropic (norapenepherine)
Acts as part of the ‘fight or flight’ response in situations of high stress/danger (mobilize the body for action)
Effects are mostly in the periphery (NOT the central nervous system) e.g. muscles, heart rate, respiratory rate, pupil response
In the brain, NAd can enhance sensory processing, memory formation (long and short-term), attention
Most NAd drugs are used for their peripheral effects (e.g. blood pressure) but beta blockers can reduce performance anxiety. Amphetamines also increase NAd
Serotonin and Serotonergic receptors
Serotonin receptors are ionotrophic AND (mostly) metabotrophic in the central and periphery nervous system (are excitatory and inhibitory)
Most of the body’s 5-HT is synthezised, stored in/acts on the gut, it seems to trigger peristalsis (gut movement)
There are 7 5-HT receptor families for a total of 14. 5-HT3 family is ionotropic (for Na+ and K+) the rest are metabotrophic
Many antidepressants act on 5-HT usually to increase its concentration in the synapse
Define SSRIs
Selective serotonin reuptake inhibitors.
A class of antidepressants e.g. prozac which blocks the 5-HT reuptake receptors keeping more 5-HT in the synapse to bind to the postsynaptic neuron. Can improve mood in depression
Neuropharmacology
The action of drugs on the nervous system producing effects on behaviour
Many drugs are neurotransmitter AGONISTS or ANTAGONISTS. Fit into a receptor like a lock and key
Effect depends on where they act in the brain and their dose (one drug can have MULTIPLE effects depending on these factors)
Define Affinity of drugs
How well a drug binds to a receptor
