Optigentics And Oscillstions Flashcards
What is optigentics
Using opsins to positively or negatively modulate neuronal activity with high temporal resolution
How does optigentics work …
Forgin dna from algae expressed which codes for Opsin protein of interest in specific cell types
Promoter codes for expression of gene
What are the methods of gene delivery
Transfection
Electroporation
Viral infection
Types of virus used
Adeno-associated virus - doesn’t cause disease and onset of gene expression is fast
Adenovirus- can cause disease. Areas of virus genome deleted to prevent disease
Lentivirus - serviced from HIV but genomic deletions ensure inactivity. Enter nucleus of host cell and interstate into genome (stable and lasts months to years)
What are opsins
Light activated proteins
Name an opsin to activate neurons and what light activates it
Chr2
Blue
Name inhibitory opsin and colour
N PHR
Yellow
Why can’t you use gfp with chr2
The blue light used to stimulate gfp will activate and open the chr2 channel causing cations to enter and depolarise cell
Don’t want cell to be active during observations as it can cause extra cellular excitotoxicitu or plasticity
What is floxed
DNA sequences is flanked by two lox p sites. This means it’s needs cre-recombinase to delete or invert sequence
How to selectively express a gene in particular cell type
Breed mice that contain floxed gene in all cell types with transgenic mouse line that express cre-recombinase in one cell type.
Or inject virus into transgenic mouse line that express cre recombinase
What are some gluatamergic neurons
Pyramidal- found in all cortical layers
Spiny stellate- later 4
Purpose of feedforward inhibition
Acts as a break to liMit speed of excitation
Purpose of lateral inhibition
Prevent spread of excitation
Purpose of feedback inhibition
Prevent runaway excitation
Purpose of recurrent excitation
Amplify a signal
What is a neuronal oscillation
waves of electrical activity caused by synchronised brain activity
When neurons connect as groups they are simultaneously active and inactive together
What is a local field potential
Measure activity of lots of neurons within sampling radius of electrode
What is a wave phase
Angle representing a proportion of oscillation period
What are cortical slow waves
<1hz non rem sleep
Upstates - neuronal depolarisation (active)
Downstairs- hyperpolaristaion
Coordinate neuronal population activity in the absence of extrinsic input from environment
Properties of cortical slow waves
Input from thalamus
Propogate from rostral to caudal
Important in memory consolidation
Functions of theta oscillations
Spatial navigation and performance of cog task
Gamma functions
Higher cog processing e.g memory and attention
Properties of sharp wave ripple
120-250
Sleep and rest
Originate in hippocampus
Memory consolidation- reactivation of neurons that were previously active during wakefulness
Ca1
Functional connectivity
Relationship between anatomically distinct brain areas
Spatial memory- coordinated theta oscillations between pfc and hippocampus
Cog performance- tuning of pfc spiking to specific phases of hippocampus theta rhythm
Where does most spiking of hippocampus theta wave happen
Descending phase
Gamma waves and basket neurons
Inhibitory fast spiking basket neurons fire almost every gamma cycle in ca3
Basket cells respond maximally to gamma synapses so likely to fire ap when stimulated at that frequency
Basket cells and pyramidal cells
Fast spiking basket cells can control timings of pyramidal cell firing
Firing in basket cell drives IPSP of pyramidal
Only able to fire once IPSP had decayed and retuned to rest
How are gamma waves made
Through excitation-inhibition feedback and inhibition-inhibition feedback
Mechanism depends on functional properties of neuronal circuit which oscillation occurs
Gamma definition
Umbrella term that describes a variety of different oscillation subtypes in 30-120hz
What is the peripheral control of locomotion hypothesis
Sensory feedback from moving limbs drives rhythmic pattern of activity
What is central control hypothesis
Neural circuits drive rhythmic pattern
What are central pattern generators
Neural circuits that generate rhythmic patterns of motor behaviour even in the a sense of sensory feedback inputs. But feedback and sensory stimuli impact are useful to change patterns e.g if stood on a rock
Characteristics of cpg
Involved in motor behaviours e.g walking swimming breathing
Automatically generate motor rhythms
Activity modulated by sensory and proprioceptive movements
Brain also involved in coordination of voluntary activity
Why are CPGs in invertebrates good and bad to study
Good- small neuronal networks so are easy to study and manipulate
Bad- mostly inhibitory so not good for representing vertebrates which are mostly excitatory
Intrinsic membrane properties of invertebrates
Endogenous bursting- pacemaker activity
Plateau potential- bistability
Post inhibitory rebound- induce firing by inhibition then release
Spike freq adaptation - freq decreases with time
How are tadpoles cpg networks studied
Immobilise tadpole by blocking NMJ and create fictive swimming.
Electrical activity is recorded from roots or individual neurons
What creates very slow negative feedback
Isk (ca)
Slow oscillation bursts
What makes fast positive feedback
Ica, INa
Fast oscillations
How are oscillations produced by pacemakers
- Inward current quickly depolarise cell into active phase (positive feedback by L type ca channels) and open na and k channel
- During active phase there is a slow build up of ca in the cell
- When ca is high enough outward k (ca) current brings cell back to silent phase (negative feedback) channels close
- During silent phase the cell slowly removes ca and mp returns to baseline
What is in and out phase for synapses
Coupling of oscillators to synchronise them
In phase is excitatory
Out of phase is inhibitory
How do tadpoles swim
Post inhibitory rebound
Recurrent excitation and contra lateral inhibition
dIN stimulation results in spiking
(Group of connected din which are exciting each other are stimulated which causes spiking but doesn’t go back to rest)
Because NMDAR have slow decay so cells stay depolarised but don’t spike because Na channels are still inactive and k active
Then din are inhibited because NMDA current string enough to excite neurons which results in swimming
How can different cpg pattens be made
Coupling and different oscillation freq produce variation of patterns
Switching between different types of coordination can be achieved by excitation or through neuromodulators
How does modulation of freq of cpg unit work when running
High freq - lowered time of foot on floor
Low freq- longer time with legs swinging
Where do spinal nerves convey sensory info from and to
From peripheral receptors (soma found in dorsal root ganglion) to synapse with neurons in the dorsal horn of spinal cord
What is a dermatome
Area of skin innervated by dorsal root on the left and right side of each spinal segment
What are the 4 spinal segments
Cervical- head and shoulders
Thoracic- torso
Lumbar- front legs
Sacral- back legs
What is somatotopic organisation
Orderly representation and transmission of sensory information from the periphery of body to brain along topographically organised nerve tracts
What is the dorsal columns tract
Axonal projections of dorsal horn to skin are organised into the tract
Located between dorsal horns of spinal cord
Dorsal columns tract neurons
1 order neuron- dorsal horn to dorsal Columns
2 order- columns to thalamus (here projections becoming the medial leminuscus synapse with 3 order)
3- thanks with primary somatosensory cortex
Where do dorsal columns decussate
Dorsal columns nuclei to contra lateral Side
Trigeminal tract
Sensory information from face tongue mouth and dura matter follow this tract
1- Trigeminal nuclei decussate
2- thalamus
3- primary somatosensory cortex
Function and location of thalamus
Found in diencephalon
Relay station for sensory info (except olfactory)
First step in processing sensory info and functions in screening irrelevant info according to behavioural demands
Function and location of p.somatosensory cortex
Post central Gyrus in parietal lobe
Receives projections from vp nucleus
Processing of body positions and texture and shape
What is the sensory homunculus
Areas represented according to density of innervation
What are the types of cortical connectivity
Association fibres (short and long range)- connect nearby regions of cortex
Commisural fibres - connect corresponding regions of hemispheres to coordinate activity of both sides of body
What areas are involved in planning of movement
Pfc- integrate of sensory info and evaluate need for motor action
Posterior parietal cortex - spatial relationship of body and environment
Motor cortex
Lateral pathways
Control voluntary movements
Corticospinal tract
Rubriospinal tract
Corticospinal tract
Upper neurons -cortex to ventral horn
Lower neurons - ventral hormbgi muscle fibre
Decussate at mudullary pyramids
Rubrospinal tract
Upper - originates in red nucleus in midbrain
Lower- neurons in ventral horn
What is a myotome
Group of muscles innervated by all lower motor neurons in a single spinal nerve
Phototransduction
Light sensitive photo pigment on outer retina triggers membrane potential change in receptors in response to light
Decussation in vision
Light decussates at level of optic chiasm
Only temporal visual field
Cells of retina
Photoreceptors -convert light into info
Bipolar
Ganglion
Horizontal
Amacrine
What is receptive field
Area of retina where light stimulation induced a change in mp of a cell
Created by direct and indirect input
Bipolar cells
Each bipolar cell receives direct synaptic input from a variable number of photoreceptors and indirect input from horizontal cells
They can be on or off
On- depolarised
Off- hyperpolarised
What is visual field
Region of space seen by both eyes
What is visual hemifield
Region of space seen by individual eyes
Binocular
Overlapped space seen by both eyes
What are the ganglion cell types
M-type
P-type
Non m and non p
Function of fova
Used to position visual objects that need to be anyalsed in greater detail
Central retina is more represented in V1 than peripheral due to fova
Pathway of info from retina
Retina
Optic nerve
LGN
Primary visual cortex
Where are cell types segregated
LGN
Magnocellular - m type 2,7 (upper layer IV)
Pavocellular - m tyoe 6,5,4,3 (lower layer IV)
Koniocellular - Non m and non p
Properties of V1
6 layers
Visual info is segregated by eye and cell type forming ocular dominant columns in layer 4
What makes 3D vision
Binocularity occurs in layers of cortex
What do simple cells do
Found in layer IV and converge inputs from IV cells which create elongated receptive field. They have centre surrounded organisation
Function of complex cells
Receive inputs from simple cells
No centre surrounded antagonism
Has elongated receptive field
Purpose of elongated receptive field in V1
Underlies ability of cells to selectivity respond to stimuli which different orientations and directions of movement
What are blobs
Groups of cells outside layer 4
Important in object colour
Have opponent centre surrounded receptive fields
Respond to different wavelengths of light and some depolarise and some hyperpolersise
Act antagonisticly
Monocular
What are the what and where pathways
Where - dorsal
What- ventral
What are the connections of cortical areas
Feed forward- lower to higher areas- transmission of info
Feedback- higher to lower- modulation
Horizontal- across same area- output command generation bro higher order areas
How is shape perception possible
Upper level of V1 neurons respond to like segments (edges) of objects that’s are aligned with the orientation of their receptive fields
How is depth perception possible
Originates from binocular disparity
V1 neurons respond to images on and behind plane of fixation
How do we perceive motion perception
Visual system integrates local motion signals to determine direction of movement
Analysed by MT neurons
How is colour perceived v
V4 neurons add main determinates of colour perception
