Neuroanatomy - UCSD Cognitive Science

COGNITIVE
SCIENCE
107A
Neuroanatomy:
Basic Principles
Jaime A. Pineda, Ph.D.
Neurons
“The mysterious butterflies of the soul, the
beating of whose wings may some day –
who knows? clarify the secret of mental
life.”
S. Ramon y Cajal
Neurons
•  Functional units of
communication
•  About 1011 (100 billion)
cells
•  Independent units (Neuron
Doctrine)
•  Bioelectrically driven
(Functional polarity)
•  Categorized in terms of
Function (sensory, motor);
Location (cortical, spinal);
NT (cholinergic);
Shape (pyramidal, stellate)
Dendrites
Cell body or
perikaryon
Axon
Variety of Multipolar Neurons
Differ in genes expressed,
chemicals, shape,
arborization, connectivity
patterns…
Structure  function
104 connections per neuron
1015 total interconnections
INPUT
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) may
be considered “computation.”
However, DP is NOT independent of the neuroanatomy and can
occur in both directions.
Cell Body
Nucleus (DNA)
Golgi apparatus
Endoplasmic reticulum
Mitochondria
Cytoskeleton
Spines
Dendrites may be spiny or aspiny
30,000 – 40,000 spines on the largest pyramidal neurons
Increase receptive surface
They receive most of the excitatory input
Undergo morphological changes; regulate synaptic
transmission
Cytoskeleton
•  Formed by 3 types of
proteins
–  Microtubules (tubulins)
–  Microfilaments (actins)
–  Intermediate filaments
•  Microtubules (> 10% of total
brain protein): intracellular
transport, determine cell
morphology
Protein conformation governed by quantum
effects – Roger Penrose and Stuart Hameroff
Microtubule lattice – computational quantum machine?
(Orchestrated Objective Reduction)
noncomputability
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.
Myelination
•  Insulates axon
•  Speeds up conduction
without increasing
diameter of axon
•  Saves energy
Synapses
Pre- and post synapse
Asymmetric: excitatory (Type1)
Symmetric: inhibitory (Type2)
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.
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 glial cell in PNS
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
Oligodendrocytes/Schwann cells
Einstein’s Brain
Greater number of
neuroglia
Larger inferior parietal
cortex
Principles of Brain Organization
•  Subdivided into 3 primary
and 5 secondary regions +
spinal cord
–  Forebrain
•  Telencephalon (hemispheres)
•  Diencephalon (thal/hypothal)
–  Midbrain
•  Mesencephalon (sup.colliculi)
–  Hindbrain
•  Metencephalon (cerebellum)
•  Myelencephalon (medulla)
Neural plate > neural tube
Principles (cont.)
•  Brain contains an
interconnected system
of ventricles
Interventricular foramen
Choroid Plexus
•  Each ventricle contains
choroid plexus (ependymal
cells)
•  60-80% of CSF comes from
CP; rest from extrachoroidal
sources
•  Total CSF=130-150 ml
•  Rate = 20 ml/hr
Functions of CSF
Principles (cont.)
Brain contains a protective covering
Hydrocephalus
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
Topography of CC
truncus
genu
rostrum
isthmus
splenium
Principles (cont.)
•  Cortex is subdivided
into four major
external lobes (plus
the internal limbic
lobe)
Limbic lobe
Found only in the medial view of the brain.
Its major responsibilities include olfaction and emotions
Principles (cont.)
•  Cortex is subdivided into areas of
specialized function
Principles (cont.)
•  Some areas of cortex
(primarily sensory
and motor areas) are
topographically
mapped.
V1 (retinotopic)
A1 (tonotopic)
M1 (mototopic)
S1 (somatotopic)
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)