Organizing Principles Flashcards
What are the embryological parts of the brain that developed from the neural tube?
What structures develop as the emryological proceed? From which one will thalamus derive? How about retina?
- Thalamus will develop from the diencephalon (prosencephalon)
- The same is true for retina (via optic cup) -> thus retina is a part of the brain
Find thalamus in the picture. What else can you see?
What is thalamus comprised of?
- 20 or 30 individual nuclei -> represent discrete pathways of inputs/outputs to cerebral cortex
- Anatomical framework
- Divided by white matter (“Y” shaped)
- At the head of “Y” sit Anterior nuclei => frontal cortex, cingulate gyrus
- Medial part => other parts of the frontal lobe, insula
- Lateral part => somatic sensory regions, motor, auditory, visual
- Intralaminar nuclei => modulatory function (rather than relying specific info)
Explain the schematic picture of thalamic relay system. What kind of nuclei innervate layers of the cortex (3) + what signals, function
First-order thalamic nuclei - from lateral aspects of thalamus
- Receiving ascending signals (often going to diff modalities)
Higher order thalamic nuclei - receive decending signals from the cortex
- involved in cortico-thalamo-cortical loops = distribution from one cortical regions to another via thalamus
Non-specific thalamic nuclei
- diffused connections, innervating different layers than the rest of the thalamus i.e. 1,2
- modulatory role e.g. attention, arousal
What is the proliferation? How does it happen during the embryonic development?
= process by which cells rapidly reproduce
- nuclei divide, DNA replicated -> when cells exit this neural cycle they become Neuroblasts
=> can further differentiate into neurons or glial cells
- While Progenital cell keeps dividing or differentiates into a stem cell
=> still possible to reenter the cell cycle
What happens to neuroblasts after they get created?
- Neuroblasts develop close to the wall of future lateral ventricle (in neural tube)
-> starts to migrate laterally away from it
=> developing cortex = cortical plate - migration is enabled by the radial cells on which neuroblasts can transport
How many layers do we find in neocortex? What can you say about them - describe them?
- Typically 6 (altough there may be structures with less e.g. hippocampus)
- Upper boundary = Pial layer
- 1st layer = mainly myelinated axons
- 2nd layer
- 3rd layer = broader, sometimes subdivided, zone of pyramidal neurons
- 4th layer = target of thalamic nuclei, populated by Stellar cells (NO large cells) = Thalamic recipient zone/Granular layer
- 5th layer = largest pyramidal cells, rish synaptic connectivity
- 6th layer = smaller, densily packed cells, gets small input from thalamus (but 4th primary) - Lower bound = white matter
Tell me a bit more about the 4th layer of cortex? How does the subsequent flow of info work?
- Primary recipient of thalamic connections
-> cells in the layer innerconnect with one another
-> send connections to upper layers 2,3
-> Broad distribution
- horizontal connections e.g. one region of layer 3 to another
- connections via white matter (e.g. corpus collosum)
- local connections within 2 and 3
- Infergranular layers (e.g. 5) - below 4
- Innervating inferior parts of the brain e.g. basal ganglia, spinal cord (5) or back to thalamus (6)
What are the functions of canonical microcircuit of neocortex?
- Amplification = distribution of the signal throughout the layers and the brain
- Computation = amplified signal can reach structures that provide more functions than the initial signal
- Communication = within/between cortical areas
Describe the cytoarchitecture of the cortex.
Notice:
- In motor c. - the 5th layer has prominant large cells
- In visual c. - the 4th visible while in motor c. diminished in thickness, density (provides more output than input)
What is Brodmann known for?
- Examined Nissl stained tissue slices -> noticed that different parts have sligtly different cytoarchitecture
=> these difference must have functional consequences- BUT do NOT imagine cerebral areas as indipendent => it is a network
How may we imagine a simple pathway of sensory neurons?
Neuron that receives peripheral signals from the environment (e.g. skin) = 1st order n. -> info gets to the CNS neuron = 2nd order n. -> received by 3rd order n. -> final destination in a huge network of neurons of the cortex
= set of neurons connected in a serial fashion
= Ascending
How does the output pathway work?
The output network in the cortex connected to the sensory network -> sends out an output neuron -> received by a local circuit cell -> alpha motor neuron that innervates e.g. skeletal muscles
- Descending
What is the principle of contralateral representation? How is it possible?
The body may be represented on the opposite side of the brain
- E.g. right hand = left hemispheres
There must be a mechanism for decussation = crossing
What is the sensory transduction? Provide an example how it may work with tactile information.
= process of converting environmental energy into neuronal signals
Tactile sensation may be mediated by Pacinian corpuscle = mechanoreceptor that includes a nerve ending
- contains ion channels sensitive to stretching of the P.c. => kations will enter e.g. Na+ = receptor potential exceeds the threshold => depolarization which opens voltage-gaten channels
What is meant by “labeled lines”? What othe principle is connected to it?
= the fact that neuronal response is shaped by the sensory receptor it is attached to (which focuses on certain quality of info)
- We can also see the principle of parallel processing
- E.g. in skin we have multiple receptors sensitive to diff things - vibration (Pacinian corpuscle), light touch (Meissner corpuscle)
Explain receptor fields in tactile dimension + center-surround?
= specific patch of skin may correspond to a specific neuron in the somatosensory cortex
- There tends to be a center-surround
- center is stimulated there is a rapid modulation of the neuron (rapid firing or ceasing to fire)
- surround behaves opposite
- if stimulation to center means firing = stimulation of surround will cease the firing
What’s the two-point descrimination?
= being able to diffrentiate two points of touch
- E.g. if we use 2 needles and touch the skin at different distances -> ask the person whether they feel 1 or 2 points
- Picture:
- green - falls within neuron b. (but just tips of a and c) => 1
- red => 1
- blue - falls in two separate neurons => 2
