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BIO 132

BIO 132. Lecture 34 Diffuse Modulatory System. Neurophysiology. Lecture Goals:. Understanding the advantage of having a diffuse modulatory system Understanding the differences between the four diffuse modulatory systems. Diffuse Modulatory Systems.

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BIO 132

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  1. BIO 132 Lecture 34 Diffuse Modulatory System Neurophysiology

  2. Lecture Goals: • Understanding the advantage of having a diffuse modulatory system • Understanding the differences between the four diffuse modulatory systems

  3. Diffuse Modulatory Systems • We will discuss four different diffuse modulatory systems in the brain: • Noradrenergic • Cholinergic • Dopaminergic • Serotonergic • Each has a different function but they all have certain common principles.

  4. Commonalities of the Diffuse Modulatory Systems • Each system has a small core of neurons (only a few thousand) • Most of the cores are found in the central core of the brain and brain stem • Each neuron from the core can influence more than 100,000 postsynaptic neurons spread all over the brain • The synapses are not terminal but rather run along axons (called boutons en passant) • Each system only modulates the actions of other neurons and does not turn them on or off. • Like adjusting the volume on a radio instead of the power

  5. Boutons en Passant • Boutons en passant is a French term meaning “buttons in passing”. • An axon terminal (“terminal bouton”) is what we normally think of as having the voltage-gated calcium channels and secretory vesicles but some neurons can have these areas strung along their axons like a string of pearls. • The synapses are not terminal but rather run along axons (called boutons en passant)

  6. Boutons en Passant • Neurons from the core meander through the brain, and when activated, release neurotransmitter from thousands of sites along the axon. • Any neuron in close proximity is affected. Cell body/dendrites Axon terminal (terminal bouton) Boutons en passants

  7. The Noradrenergic System • Neurons from this system release norepinephrine (NE) • The core of this system is called the locus coeruleus (meaning “blue spot”) and is located in the pons. • Each locus coeruleus (there is one on each side) contains ~12,000 neurons. • Destination: Nearly everywhere in brain (Cerebral cortex, cerebellum, thalamus, hypothalamus, spinal cord, etc) • A single neuron from this system can make connections with over 250,000 neurons.

  8. Noradrenergic System • Stimulus: Novel, unexpected, non-painful stimuli (has low activity while sitting quietly) • Effect: Thought to make neuronal signalling and processing faster and more efficient (increases the signal to noise ratio)

  9. The Serotonergic System • Neurons from this system release serotonin (5-HT) • This system cores are located in the nine Raphe nuclei (located in the brain stem). • Destination: Everywhere in the central nervous system • Superior Raphe project up to the cortex • Inferior Raphe project down the spinal cord

  10. Serotonergic System • Stimulus: Most active during active awake states • Effects: • Superior Raphe seem to be involved in regulating sleep/wake states. They have also been implicated in altering mood and certain emotional behaviors. • Inferior Raphe inhibit nocioception in the spinal cord.

  11. The Dopaminergic System • Neurons from this system release dopamine (DA) • This system has two cores: Substantia nigra (SN) and the Ventral tegmental area (VTA). • Destinations: • SN projects to the Basal ganglia • VTA projects to the Frontal cortex

  12. Dopaminergic System • Effects: • The Substantia nigra seems to facilitate the initiation of motor responses by environmental stimuli. • The VTA seems to be involved in “rewarding” behavior. Note this is not the same as feeling pleasure. The VTA pairs behavior or sensation with a feeling of satisfaction.

  13. The Cholinergic System • Neurons from this system release Acytelcholine (ACh) • This system has three cores: Medial septal nucleus (MSN), the Basal nucleus of Meynert (BNM), and the Pontomesencephalotegemtal complex (PC). • Destinations: • MSN projects to the Hippocampus • BNM projects to the cerebral cortex • PC projects to the thalamus

  14. Cholinergic System • Effects: • The effects of the MSN and BNM are unclear but there is evidence that they are involved in the laying down of memories • Damaged to these areas linked to Alzheimer’s disease • The PC seems to be involved in sensory filtering by the thalamus.

  15. Effects of Drugs on Diffuse Modulatory Systems • Hallucinogens (e.g. LSD) • Thought to stimulate the Serotonergic system. • Stimulants (e.g. cocaine, amphetamines): • Feelings of heightened awareness. • Evidence shows these drugs inhibit the reuptake of NE and DA, causing prolonged exposure of receptors to these neurotransmitters. • In the case of DA, this can reward drug use behavior.

  16. Effects of Drugs on Diffuse Modulatory Systems

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