1. Neurohistology

2. Neuron Components Two parts of the neuron Dendrites
Cell body (soma)
Neurites
Axons (one)
Dendrites (many)
Dendrites
Some have dendritic spines that receive some types of synaptic input
Sensitive to type and amount of synaptic activity
Sensitive to quality of early environment
Research by Purpura
Mental retardation (MR) is from failure of normal circuits to form in brain
Dendritic spines of children with MR look like those of human fetus
Impoverished environment in critical period can lead to less dendritic spine formation
deprivation-induced changes in brain can be reversed if intervention occurs early
From: Bear, Connors, Paradiso. Neuroscience Exploring the Brain, 2007.

3. Classification of Neurons
Based on number or neurites extending from soma
Unipolar (1)
Bipolar (2)
Multipolar (most neurons)
Based on dendrites, e.g. in cerebral cortex
Stellate cells (star shaped)
Pyramidal cells
(pyramid shaped)
From: Bear, Connors, Paradiso. Neuroscience Exploring the Brain, 2007.

4. Classification of Neurons
Based on connections
Primary sensory
Primary motor
Interneurons (connect only with other neurons)
Based on axon length
Golgi type I extend from one part of brain to another (e.g. pyramidal cells)
Golgi type II are more local (e.g. stellate cells that never extend beyond cerebral cortex)
Based on neurotransmitter
Cholinergic, i.e. cells that release acetylcholine
Used in the motor system to command voluntary movements

5. Glia (support cells) Astrocytes Role of astrocytes Most common glia
Fill most of brain space not occupied by neurons
Role of astrocytes
Regulate chemical content of extracellular space around neurons
E.g. envelop synaptic junctions thereby limiting spread of neurotransmitter
Can remove neurotransmitter from synaptic cleft
Possess neurotransmitter receptors and can trigger electrical and biochemical events (new discovery – not sure of exact function yet)
From: Bear, Connors, Paradiso. Neuroscience Exploring the Brain, 2007.

6. Myelinated Glia Myelin spiral around axon to form the myelin sheath
Myelin sheath is interrupted periodically by nodes of Ranvier
Oligodendrocytes (in CNS)
Can myelinate several neurons
Schwann cells (in PNS)
Only myelinates one neuron
Cross section of optic nerve myelinated fibers
From: Bear, Connors, Paradiso. Neuroscience Exploring the Brain, 2007.

7. Other Non-Neuronal Cells
Microglia
Function as phagocytes to remove debris from degenerating neurons and glia
Ependymal cells
Line the fluid filled ventricles
Play role in directing cell migration during brain development