Last modified 1/7/08
Bio8020: Neuroanatomy
References:
- Kandel,
Schwartz and Jessel, Chapters 17-18, see
also figs. 52-2,52-5, Table 52-1
- Nichols et al., Ch 18 pp 355-366
- Nichols et al., Appendix C
Neuroembryology
of mammalian brain
- Three cranial divisions of
the cranial part of the central nervous system (CNS) become 5
- forebrain (prosencephalon)
- telencephalon
- diencephalon
- midbrain (mesencephalon)
- hindbrain (rhombencephalon)
- metencephalon
- mylencephalon
- Segmentation becomes apparent
and is controlled by hox genes
- Neural crest forms peripheral
NS: autonomic nervous system and cranial and spinal sensory ganglia
Anatomical
Organization of the Mammalian Nervous System – Preview/Overview
http://youtube.com/watch?v=CU9KBXHIObU
- Six principles of brain
organization
- Distinct Systems
(different sensory modalities, motor functions)
- Identifiable Pathways
- Topographical
Organization
- Hierarchical vs.
Parallel Organization
- Most pathways cross
the midline (decussate)
- Diffuse Modulatory Systems
- Terminology-
Planes of section
- Major divisions
- Spinal
Cord
- Segmented
- Four major regions
- Cervical - back of
head, neck, and arms
- Thoracic - upper
trunk
- Lumbar - lower
trunk, back, legs
- Sacral - lowest
trunk, back, legs
- Sensory and Motor
nerves
- Dorsal Roots-
sensory neurons
- Ventral Roots- motor
neuron axons only
- Gray matter (cell
bodies)
- Dorsal Horn -
sensory relays
- Ventral Horn - motor
nuclei
- White matter (myelinated axons)
- Dorsal
Columns: Ascending somatosensory axons
- Lateral Columns:
Ascending and descending axons
- Ventral
Columns: Ascending and descending axons
- Hindbrain
= Metencephalon + Myelencephalon
- Medulla =Myelencephalon: digestion, blood pressure and
respiration
- Pons = Metencephalon: relays between cerebral hemispheres
and cerebellum
- Cerebellum = Metencephalon: Sensorimotor
integration, motor learning.
Outside surface is termed cerebellar
cortex.
- Midbrain
= Mesencephalon: some motor control, relay for
sensory signals
- Tectum
(incl. sup and inf colliculus)
- sensorimotor integration
- Tegmentum
(incl. substantia nigra)
- link cerebellum, basal ganglia and cerebral hemispheres
- Diencephalon (from Forebrain = Prosencephalon)
- Thalamus: Relay
station for sensory input to cortex (also motor relays)
- 50 different
subdivisions (nuclei)
- Not a simple relay
- Under strong
cortical control: Most inputs are from cortex!
- local processing
within nucleus
- modulation from
brainstem inputs
- Hypothalamus:
Homeostasis, motivation, circadian rhythms, and endocrine regulation
- Telencephalon
(Cerebral Hemispheres, from Forebrain = Prosencephalon)
- Cerebral Cortex
- Sulci
- grooves
- Gyri
- bumps
- Early workers
believed that bumps were reflected in skull- Phrenology
- Localization of
function determined through inference from hospital patients, e.g. Phineas Gage
- Corpus callosum unites the two cortical hemispheres
- Ventricles are
fluid-filled cavities
- Cortex is separated
into 4 paired lobes (3 views in App. C)
- Frontal
- Parietal
- Temporal
- occipital
- Different regions
have different substructure for layers. Why?
- Basis for Brodmann's regions
- Different layers
have characteristic inputs and outputs
- Three main neuronal
types
- Projection
neurons
"Pyramidal"
in shape (layers III, V, VI)
Glutamatergic
- Granular
interneurons-small, round, "spiny stellate"
(layers IV and VI). Glutamatergic,
excitatory interneurons
- GABAergic
Interneurons -all non-spiny, non-pyramidal (layers II - VI) different
morphologies, types of inhibitory influence. These are generated in ventral telencephalon and migrate into cortex.
- Columnar
organization for circuitry
- Subcortical
telencephalic structures
- basal ganglia:
Movement control through motor cortex (interconnections with substantia nigra involve
it in Parkinson's disease)
- amygdala:
Emotions, social behavior, fear conditioning
- hippocampus:
Spatial learning and memory
- NOTE: neuroanatomical methods
- Six principles of brain
organization-Review
- Distinct Systems
(different sensory modalities, motor functions)
- Identifiable Pathways
- Topographical
Organization
- Hierarchical vs Parallel Organization
- Most pathways cross
the midline
- Diffuse Modulatory Systems
- Somatosensory
Pathway as an illustration of the six principles
- Afferent neurons in
dorsal root ganglia
- Submodalities
are arranged in parallel
- Axons ascend in ipsilateral dorsal columns to medulla
- Axons from lower
body run medial (Gracile fasicle),
project to Gracile Nucleus
- Axons from upper
body run laterally (Cuneate fasicle), project to Cuneate
Nucleus
- Neurons in Dorsal
Column Nuclei of the medulla (gracile and cuneate) have axons that project contralaterally
at the level of the medulla.
- Ascend in Medial Lemniscus fiber pathway
- Synapse on neurons
in the Ventral Posterior lateral nucleus of the Thalamus
- Thalamic neurons (VPl) project through internal capsule to Primary Somatosensory cortex (S1, Brodmann's
area 3b)
- S1 cortex has Somatotopic representation of body surface
- Arises from orderly
representation of axons at each stage of the pathway, creating receptive
fields that are topographically arranged.
- Cortical
magnification of sensitive areas, proportional to receptor density
- S1 cortical area
connects to other cortical areas
- Combines information
from submodalities and then from different
modalities
- Motor
Pathway
- Primary motor cortex
is also somatotopically organized
- Layer V neurons
project to motor neurons and interneurons in spinal cord via corticospinal tract
- Project through
"Medullary Pyramids" and decussate,
therefore also named pyramidal tract
- Extrapyramidal
system
- Complicated system
of feedback loops involving basal ganglia, cerebellum
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