Thalamus and Cerebral Cortex

which neuron type transmits intracortical processing info to other parts of the brain?

pyramidal (projection neurons)

2 major types of cortical cells

pyramidal and non-pyramidal (stellate/interneurons)

cells of layer V, where do they project to?

pyramidal, send axons mainly to layer III and V. Large pyramidal neurons in this layer project to basal ganglia, brainstem, or spinal cord

distortion of receptotopic maps

reflect behavioral importance of a certain part of the receptor sheet (somatosensory cortex - large representation of the index finger)

matrix thalamocortical neurons characteristics

small, receive comparatively weak and less well-organized ascending inputs. Project axons widely to layers II/III. Inputs to matrix neurons arise from collaterals of layer V pyramidal cells on their way to brainstem and spinal cord centers.

receptotopic organization

within sensory areas, there is a topographic representation of the receptor periphery in which adjacent areas of a receptor surface are represented by adjacent cell groups

2 types of thalamocortical neurons

1. core 2. matrix

characteristics of basic functional plan of cortex

1. motor areas in frontal, somatosensory in parietal, auditory in temporal, visual in occipital 2. topographic organization, receptotopic 3. receptotopic maps are distorted to reflect behavioral importance of a certain body part 4. map boundaries coincide with cytoarchitectonic boundaries 5. primary sensory areas receive major afferent input from a specific relay nuclei 6. each hemisphere contains multiple, separate, and more-or-less complete motor, somatosensory, auditory, or visual representations

3 functions of thalamus

1. process and relay info to cerebral cortex 2. regulate overall excitability of cerebral cortex 3. serve as integrative center for cortical function

thalamic nuclei corresponding to parietal cortex

pulvinar

core cells of thalamus project to layer ___. Layer ___ neurons project back to core cells (synapse weakly)

IV; VI

principle of localization of function

a given region of cerebral cortex is more involved with one kind of function than with others. Ex. right and left hemispheres are functionally asymmetrical in motor dominance and speech

thalamic nuclei projecting to cingulate gyrus

anterior

cytoarchitecture and Brodmann's areas

arrangement of cells bodies; areas are defined by cytoarchitecture and have very specific thalamic inputs. compositions of different areas reveal homology among mammalian brains. gyro pattern may be different, but cytoarchitectonically defined areas remain constant in relative size and location

cells in layer I

cell-sparse layer, cells are inhibitory

functional columnar organization

cells within a vertically oriented column form an elementary processing unit of interconnected neurons

parallel processing

different cortical regions perform different but related tasks at the same time

thalamic nuclei projecting to frontal lobe

medial

core thalamocortical neurons characteristics

large, receive strong, highly ordered ascending inputs and project their axons primarily to layer IV of cerebral cortex. Receive corticothalamic synapses from layer VI neurons

neocortex

largest expanse of cortical tissue, occupying approx. 90% of cortex in humans

from where do cells in layer V and VI receive input?

layer III, thalamocortical inputs

motor monitors

layer V corticothalamic inputs send motor commands and synapse with thalamic nuclei along the way, to inform them of the motor command

where do inputs to matrix cells come from?

layer V pyramidal cells, on their way to brainstem and spinal cord

cells in layer IV

mainly interneurons, receives most of cortex's afferent input from the thalamus. Project to layers II and III predominantly

type of cells in higher order thalamic nuclei

majority are matrix cells. project to association cortex (everything except primary sensory and motor). these nuclei receive inputs from and project to a number of different cortical areas, providing a means for integrating info via a cortico-thalamic-cortical pathway

Type of cells in first order thalamic nuclei

mostly core-type neurons. nuclei involved in primary sensation, transmit afferent information

areas 6 and 8

motor association cortex in frontal lobe

areas 5 and 7

parietal association cortex

receptive field of cell

part of receptor periphery which when stimulated causes a change in the electrical activity of neuron

how does thalamus regulate overall excitability?

neurons in intralaminar thalamic nuclei receive inputs from widespread regions of the brainstem reticular formation and spinal cord, then project their axons to widespread regions of cortex. these are thought to modulate the activity of large populations of cortical neurons Also...state-dependent thalamic firing modes

state-dependent thalamic firing modes

neurons in thalamus have a voltage- and time-dependent ionic conductance (T-current/calcium current) that enables them to switch between repetitive firing (relay mode) and bursting states. When thalamic neurons are hyper polarized for long period of time, T-current channels become primes, permitting the neuron to fire calcium-mediated bursts of APs. Synaptic inputs from reticular formation contribute to this switching with norepinephrine and ACh. Depolarization leads to switch to relay mode. In relay mode, cell's firing is determined, tightly coupled to sensory inputs.

areas 41 and 42

primary auditory cortex (Gyrus of Heschl)

area 4

primary motor cortex

areas 1,2,3

primary somatic sensory cortex

cells in layers II and III

projection cells, provide input to other II/III cells and to V/VI cells. Many layer III cells are corticocortical (project to other cortical regions in same hemisphere) or callosal (project to opposite hemisphere)

how does thalamus serve as integrative center for cortical function? examples

some thalamic nuclei receive inputs from one or more regions of cerebral cortex and send outputs to other cortical areas, notably association cortex in frontal and limbic regions. Ex. Medial dorsal thalamic nucleus receives inputs from the hypothalamus and amygdala. Also interconnected with prefrontal and temporal cortex. Ex. pulvinar receives visual inputs from LGN and is reciprocally connected with visual cortical areas in parietal, occipital, and temporal lobes

thalamic nuclei corresponding to somatosensory cortex

ventral posterolateral, arcuate

thalamic nuclei corresponding to motor cortex and motor association cortex

ventrolateral, ventroanterior

areas 17,18,19

visual cortex 17=primary visual or striate cortex (lingual and cuneus gyri)