Summary
summary notes on circuits and oscillations- neuroscience
- Module
- Medical sciences
- Institution
- University Of Central Lancashire Preston (UClan)
This is the summary notes on circuits and oscillations- neuroscience
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Circuits and oscillationsNeurons in circuits
• Although neurones are (mostly) discrete and independent, they do not act in
isolation.
• “Neuropil” – dense tangle of axons, dendrites, and glial processes
• Vital for organisation and information processing
• Circuits are complex & coherent; although diverse, show many commonalities.
Volume activity
• Neurones usually act in volume
• Neurones may form multiple synapses with same target neurone
Excitation and inhibition
Odd number of inhibitory pathways = inhibition
Even number of inhibitory pathways = excitation
Knee-jerk reflex
simple reflex that causes the contraction of the quadriceps muscle when the patellar tendon
is stretched.
Feedforward
Feedforward excitation
Allows one neuron to relay information to its neighbour.
Feedforward inhibition
This is a way of shutting down or limiting excitation in a downstream neuron in a neural
circuit.
Recurrent excitation
Creates an excitation loop. In this pathway the activity is reinforced
Recurrent inhibition
This circuit can limit excitation in a pathway.
Convergence: allows a neuron to receive input from many neurons in a network.
Divergence: allows one neuron to communicate with many other neurons in a network
Convergence: coincidence detection: Activation of 1 or 2 alone insufficient to activate
output neurone
Activation of 1 AND 2 however will activate output neurone.
, Reverberating circuit: Pathway of excitation with positive feedback such that activity
continues throughout the network; stays on until switched off.
Parallel after-discharge: Single input leads to prolonged output (up to ~15ms). Thought to be
involved in complex conscious thinking.
Each chain is made up of a different number of neurons but their signals converge onto one
output neuron. Each synapse in the circuit acts to delay the signal by about 0.5 msec so that
the more synapses there are will produce a longer delay to the output neuron
Disinhibition: usually an inhibitory cell is tonically active; must be suppressed to facilitate
activation of the output neurones.
Central pattern generators:
Basic model of circuit for alternating system (e.g. walking)
• Many of the circuits regulating common actions which circuits to turn on and off.
• Activity of the two interneurons alternates because they inhibit each other via
another set of interneurons, which are inhibitory.
Topographical representations:
• How one area in the somatosensory cortex represents the different areas in the
body.
• The whisker is represented in the exact same position in the cortex than in the rat
head.
• Sensory homunculus
Hippocampus and memory: Lesion experiments suggest CA1 is most vital area for memory
formation.
Processing of data via convergence / divergence in DG and CA3; encoding of memory and
outputs from CA1
Major role for synaptic plasticity: strengthening of synapses to “store” information.
Thalamocortical circuit:
• Thalamocortical connections sensory perception and information about the
current mental state
• Dorsal thalamus excites CTX; CTX output excites thalamus.
• Feedback inhibition via GABAergic reticular thalamic neurones
• Basis of oscillatory activity
• (Second feedback inhibition in cortex via interneurons: “coincidence detection”?)
Basal ganglia pathway:
The basal ganglia pathway is a complex neural circuit involved in motor control, cognition,
and emotion regulation. It consists of a network of interconnected nuclei located deep
within the brain.
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