october 5 - neuroanatomy
TRANSCRIPT
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COGNITIVE SCIENCE 107A
Neuroanatomy:Basic Principles
Jaime A. Pineda, Ph.D.
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Neurons
“The mysterious butterflies of the soul, the beating of whose wings may some day – who knows? clarify the secret of mental life.”
Santiago Ramon y Cajal(Father of modern neuroscience)
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Neurons• Functional units of
communication• About 1011 (100 billion) cells
in the brain• Independent units (Neuron
Doctrine)• Bioelectrically driven
(Functional polarity)• Categorized in terms of
Function (sensory, motor); Location (cortical, spinal); NT (cholinergic);
Shape (pyramidal, stellate)
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Dendrites
Cell body orperikaryon
Axon
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Variety of Multipolar Neurons
Differ in genes expressed,chemicals, shape,arborization, connectivitypatterns…
Structure function
104 connections per neuron
1015 total interconnections
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INPUT (convergence)
INTEGRATION
OUTPUT
Cajal formulated Law of Dynamic Polarization Dendrites generally receive synaptic input (i.e. are postsynaptic) and axons generally send synaptic output (i.e., are presynaptic)
Dynamic polarization (processes of input, integration, output, distribution) maybe considered “neurocomputation.”
However, DP is NOT independent of the neuroanatomy and can occur in both directions.
DISTRIBUTION (divergence)
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Cell Body
Nucleus (DNAmRNA)Endoplasmic reticulum (smooth proteins, rough lipids/steroids)Golgi apparatusCytoskeleton (microtubules, microfilaments)Mitochondria ATP
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SpinesDendrites may be spiny or aspiny
30,000 – 40,000 spines on the largest pyramidal neuronsIncrease receptive surfaceThey receive most of the excitatory inputUndergo morphological changes; regulate synaptictransmission
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Cytoskeleton
• Formed by 3 types of proteins– Microtubules
(tubulins)
– Microfilaments (actins)
– Intermediate filaments
• Microtubules (> 10% of total brain protein): intracellular transport, determine cell
morphology
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Protein conformation governed by quantum effects – Roger Penrose and Stuart Hameroff
Quantum states believed to be too sensitive and fragile to disruption by thermal energy (environmental decoherence) to affect the macroscopic nature of proteins and other macromolecular structures.
Microtubule lattice – computational quantum machine?(Orchestrated Objective Reduction) noncomputability
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Myelination
• Insulates axon
• Speeds up conduction without increasing diameter of axon
• Saves energy
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Synapses
Asymmetric: excitatory (Type2) Symmetric: inhibitory (Type1)
Pre- and post synapse
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Organization of pyramidal cells in cortex
Layers of distinct cells; radially organized.Layers allow for separation of inputs and outputs.Unique apical dendrite allows for distribution of information to/from other layers.
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Neuroglial Cells• Physical and metabolic support
• 90% of cells in brain
• Four types in CNS– Astrocytes (maintenance/support)– Oligodendrocytes (myelin)*– Microglia (macrophages) – Ependymal (line ventricles)
*Schwann cell is the major neuroglial cell in PNS
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Glial Functions
• Astrocytes• Constitute 20-50% of the volume in most brain areas• Originate from radial glial cells – migration/guidance• Source for CAMs (N-CAM, laminin, fibronectin), growth factors, and
cytokines (signaling proteins involved in immune function)• Regulate neurotransmitter uptake/inactivation (contain ion channels)• Detoxification of CNS• Astrogliosis – response to infection/disorders
• Microglia• 5-20% of total cells in the mouse brain• Mediators of immune response (macrophages)• Secrete cytokines and growth factors• Constantly moving and analyzing the CNS for damaged neurons,
plaques, and infectious agents
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Oligodendrocytes/Schwann cells
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Einstein’s Brain
Greater number ofneuroglia
Larger inferior parietalcortex
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Principles of Brain Organization• Subdivided into 3 primary
and 5 secondary regions
– Forebrain• Telencephalon (endbrain)
• Diencephalon (interbrain)
– Midbrain• Mesencephalon
– Hindbrain• Metencephalon
• MyelencephalonNeural plate > neural tube
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Principles (cont.)
• Brain contains an interconnected system of ventricles
Interventricular foramen
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Choroid Plexus
• Each ventricle contains choroid plexus
• 60-80% of CSF comes from CP; rest from extrachoroidal sources
• Total CSF=130-150 ml
• Rate = 20 ml/hr
Blood-Brain Barrierendothelial cells (lining of blood vessels)Ependymal cells (lining the ventricles)astrocytesrestricts passage of substances from bloodstream
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Functions of CSF
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Brain contains a protective covering
Principles (cont.)
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Hydrocephalus
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Principles (cont.)
• Brain is composed of two hemispheres connected by a set of fibers (corpus callosum)
• 200-250 million fibers
• Monotremes and marsupials do not have a corpus callosum
• Agenesis and split brain patients
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Topography of CC
spleniumgenu
truncus
rostrum
isthmus
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Principles (cont.)
• Cortex is subdivided into four major external lobes (plus the internal limbic lobe)
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Limbic lobe
Found only in the medial view of the brain.Its major responsibilities include olfaction and emotions
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Principles (cont.)• Cortex is subdivided into areas of specialized function
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Principles (cont.)
• Some areas of cortex (primarily sensory and motor areas) are topographically mapped.
V1 (retinotopic) A1 (tonotopic) M1 (mototopic) S1 (somatotopic)
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Principles of Neuronal Circuitry
• Long hierarchical neuronal connections (macrocircuits)– Sensory/motor pathways– Point-to-point connections– Long axons (myelinated)
• Local circuit (microcircuits)– Interneurons (unmyelinated)– Short axons
• Single source divergent– Modulatory systems– Global reach (unmyelinated)