The pathways
Cortex
CORTEX
Lateral view of brain
Development of cerebral cortex
Lateral view cortex
Cortical Divisions
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Anatomically the cortex is divided into lobes:
frontal, parietal, temporal, occipital.
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The insular cortex is also often considered as a
separate lobe, the insular lobe
The limbic lobe consists of regions of cortex such
as the cingulate and para hippocampal gyri.
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Functionally the cortex is divided into
numbered areas first proposed by Brodmann
in 1909
Brodmann’s areas were described based on
cytoarchitecture; later they were found to be
functionally significant
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Cortex: Coronal Section
Cortical Connections
Intracortical fibers
– short, project to nearby cortical areas
Commissural fibers
– Connect homologous areas
of the two hemispheres
– Corpus callosum
– Anterior commissure
– Posterior commissure
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Cortical Connections
Association fibers
– gyrus to gyrus and lobe to lobe in the
same hemisphere
– arcuate fibers connect adjacent gyri
– long association fibers connect distant
gyri
Projection fibers
– Projections from cortex to subcortical
neurons (e.g. thalamus, corpus striatum,
brainstem, and spinal cord
– Internal capsule carries most of these
connections.
Topographic organization of functional areas
Tonotopic mapping of auditory cortex
Homunculus
Ratunculus
Species comparison
The Ventricular System of the Human Brain
The Major Arteries of the Brain
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PN01202
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Types of Cerebral Cortex
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Neocortex
– Newest in evolution
– About 90% of total
– 6 layers, most complex
Paleocortex
– Associated with olfactory system, the
parahippocampal gyrus, uncus
– fewer than 6 layers
Archicortex
– Hippocampal formation; limbic system
– 3 layers, most primitive
Mesocortex
– Cingulate gyrus, insular cortex
– Transitional between archicortex and neocortex
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Histology of the Cerebral Cortex
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The neocortex has 6 layers designated I to VI
Pyramidal cells are the characteristic neuron
of the cortex and have axons that project to
other cortical or subcortical regions.
Cortical neurons such as stellate cells serve
as interneurons for local processing.
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Cortical Columns
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Run vertically across all six layers
Thousands of neurons in synaptic contact
Main input layer is layer IV which receives thalamic input
Are the basic units of the peripheral representation in the sensory cortex (e.g. retinotopy or
tonotopy)
Within a column neurons have similar response properties (e.g. characteristic frequency in the
auditory cortex).
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Cortical termination
Corticothalamic Thalamocortical afferents terminate in:
•Layer 4, spill into 3 and 5
•Layer 6
•Layer 1 spill into 2
Individual nuclei have projections to combinations of
layers, partly depending on cells size.
Thalamus
Thalamus
Divisions of thalamus
For the most part when we refer to the ‘thalamus’ we really mean the dorsal
thalamus. Most of the following material refers to the dorsal thalamus but
you should be aware of the ventral thalamus that consists of the:
•thalamic reticular nucleus
•ventral lateral geniculate nuc.
•zona incerta
.
The dorsal thalamus is divided into a number of nuclei.
A basic definition of a thalamic nucleus is “a circumscribed region of
cytoarchitecture receiving a particular set of afferent connections and
projecting within the borders of a particular cortical field or fields.”
Medial view
Massa intermedia
Medial wall of
thalamus.
Mammillary body
Hypothalamus
horizontal
Lateral ventricle
Corpus callosum
thalamus
Basal ganglia
Internal capsule
3rd ventricle
Human thalamus
The human thalamus
The rat thalamus
Corpus callosum
hippocampus
Nissl stain
Dorsal lateral
geniculate nucleus
Corpus callosum
thalamus
3rd ventricle
Myelin stain
Thalamic nuclei can be categorized on their location within the thalamus
Representative thalamic nuclei
Name
Afferents
Cortical target
Lateral geniculate (LGd)
Retina
Visual cortex
(Brodmann area 17)
Ventroposterior lateral (VPL)
Medial lemniscus (Dorsal columns)
Spinothalamic tract
Primary somatosensory cortex.
(Brodmann areas 3, 1, 2)
Ventroposterior medial (VPM)
Trigeminal nuclear complex
Primary somatosensory cortex
(Brodmann areas 3, 1, 2)
Ventrolateral (VLp)
Deep cerebellar nuclei
Vestibular nuclei
Globus pallidus
Primary motor cortex
(Brodmann area 4)
Medial Geniculate
Inferior colliculus
Auditory cortex
(Brodmann areas 41,42)
generalized scheme
Generalized scheme of thalamic circuitry including interneurons and
the thalamic reticular nucleus
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Topography
Somatotopy (VPL)
The thalamic glomerulus
•D thalamocortical neuron dendrite
•T1 principal afferent (Glu)
•T2 local circuit neuron presynaptic dendrite (GABA)
•G glial cell
The glomerulus
Tonic and burst mode
Basal ganglia
Basal Ganglia
Relationship of Basal Ganglia to descending motor pathways
Basal Ganglia definitions
Caudate
nucleus
Striatum
Putamen
Basal
Ganglia
Globus
pallidus
Corpus
Striatum
Pallidum
Substantia Nigra
Subthalamic nucleus
Basal ganglia
Basal ganglia
Basal ganglia: Coronal section
Basal Ganglia horizontal Section
Lateral ventricle
Corpus callosum
thalamus
Basal ganglia
Internal capsule
3rd ventricle
Basal ganglia circuits
The direct pathway
Direct pathway
GABA
GABA
Direct pathway
GABA
GABA
The indirect pathway
Substantia nigra
Basal Ganglia circuitry
Direct pathway facilitates movement
Indirect pathway inhibits movement
Cerebellum
Cerebellum
Relationship of cerebellum to descending motor pathways
Cerebellum
CEREBELLUM
Overall Organization and Subdivisions
Organization of cerebellar Outputs and Inputs
input
output
Functional Organization of the Inputs
Projections from the cerebellum
Input to the cerebellum
Open loop
Cerebellar Closed Loop
Primary Motor
Cortex
midline
Thalamus
(VA/VL)
Deep cerebellar
nuclei
PONS
(pontine nuclei)
Proprioceptive
(sensory) input
a-motor neuron