Lecture 4- The Neuromodulatory System Flashcards
What is the neuromodulatory system
A collection of various types of neurons that produce specific neurotransmitters that act to modulate the level of activity of neurons at a distance
Neurotransmitters involved
Serotonin Acetylcholine Dopamine Noradrenaline Adrenaline
Neuromodulatory system characteristics
The origin is subcortical
Each system is the locus of a particular chemical transmitter that is projected to broad areas of the brainstem, thalamus and cortex
All systems are reciprocally connected with frontal cortex and parts of limbic system
The effects of these systems on downstream targets is similar
Functions of neuromodulatory systems
Cognitive abilities Developments and growth Levels of arousal Muscular activity Neuro plasticity Pleasure and pain Sleep/wake cycle
Serotonergic system
Located in the midbrain, pons and medulla oblongata (Brainstem), close to the midline
Consists of a rostral cluster in midbrain and pons and a caudal cluster in the medulla
Projects to the majority of the CNS
Neurons produce serotonin
Projections of rostral subsystem of serotonergic cluster
Strongest to striatopallidal complex, hippocampus and cerebral cortex
Functional correlations of serotonergic system
Inhibition in forebrain, specifically cerebral cortex, but can also be excitatory
Excitation in brainstem
Can induce co-transmission of other transmitters, especially hormones and neuropeptides
Modulator of neural activity
Cholinergic system
Location: mostly in striatopallidal complex, basal forebrain, hypothalamus, epithalamus, midbrain tegmentum, cranial nerve motor nuclei, spinal cord motor neurons
Projects to majority of CNS
Many subdivisions
Neurons produce acetylcholine
Functional correlates of cholinergic system
Neurons are interconnected at their distal dendrites, allowing correlated activity of groups of neurons
Continuous subsystems, therefore continuation of spinal cord to basal forebrain
Enhanced capacity to mediate behaviour and cognition
Can fire in correlation with wake and REM sleep
Contribute to complex motor programs, volitional behaviour, cog activity and conscious experience
Catecholaminergic systems
Include dopamine, noradrenaline, adrenaline
Up to 20 nuclei in CNS from olfactory bulb to spinal cord
Delineation of catecholamine system
Dopamine= Midbrain and forward/rostral Noradrenaline= Pons and rostral/upper medulla Adrenaline= Caudal/lower medulla
Hypothalamic DA neurons
Sexual reproductive behaviour
Feeding
Modulation of other hypothalamic functions
Midbrain dopaminergic system
2 main groups
- nigral
- ventral tegmental (substantia nigra/ A9/A10)
A9 nuclei
From the niggropallidal projection
Dopaminergic fibres project heavily upon corpus striatum, important for movement control
Loss of this input slows and impairs initiation of movement (parkinsons)
A10 nuclei
Form from the meso-limbic projection
DA neurons project heavily upon limbic system and cortex (meso-cortical projection)
Plays major role in modulation of limbic function, especially in reward behaviours
Other DA neurons
Retina
- released by amacrine cells
- role in transmission of info from photoreceptors to ganglion cells
Olfactory bulbs
- modulate olfactory nerve input to mitral cells which project to brain
Noradrenergic Pontine Neurons projections
Termed locus coeruleus
Projections
- Cerebellum
- Neocortex (including prefrontal cortex)
- Cholinergic basal forebrain nuclei
- Amygdala (hippocampus, thalamus, habenular nucleus, hypothalamus)
Role of noradrenergic neurons of locus coeruleus
Maintenance of muscle tone by projections to spinal cord and cerebellum
Neuroplasticity
Heat production in CNS via activation of glia
Growth of brain during development via uptake of thyroid growth hormones and conversion into neurotransmitter
Adrenergic Nuclei location and function
Location: Lower medulla
Function: Link visceral pathways of the brain with the sympathetic nervous system by projecting to hypothalamus and spinal cord (lateral horn)
Projections of caudal busystem of serotonergic cluster
RMg to posterior horn of spinal cord
RVL to intermediate horn
ROb to anterior horn
Serotonergic system D fibres
To striatum
Thin, vericose axon system
Diffuse, branching profusely
Small, fusiform boutons
Doubtful synapse contacts
Serotonergic system M fibres
To dentate gyrus
Basket axon system
Thick, non-vericose tract fibres
Short, thin branches
Large, round boutons
Extensive, repeated synapses
Enhanced capacity of cholinergic system to mediate behaviour and cognition
Neurons are interconnected at their distal dendrites, allowing correlated activity of groups of neurons
Continuous subsystems, therefore continuation of spinal cord to basal forebrain
