Neural Cells

Question 1

What are the types of neural cells?

Answer 1

1.) Axons:
 Have higher numbers of neurofilaments than dendrites
 In VERTEBRATES, some axons may be covered by myelin
2.) Neurons:
 Conduct fast information through the brain
 5 types of neurons:
Inhibitory local circuit neurons
Inhibitory projection neurons  projection neuron = projects outside the cell
Excitatory local circuit neurons (interneurons)
Excitatory projection neurons
Neuromodulatory neurons
3.) Microglial Cell:
 Immune cells of the brain e.g. clear dying neurons

4.) Synapse

5,) Oligodendrocyte

6.) Astrocyte

Question 2

What are the different ways to classify neuronal subtypes?

Answer 2

1.) By morphology

2.) By connectivity
 Local circuit neuron (interneuron) vs. Projection neuron
 By brain regional location of the cell body, and where it projects (if outside that region) [from:to – e.g. corticostriatal]  the corticostriatal has projections from the cortex to the striatum

3.) By neurotransmitter released
 Excitatory e.g. glutamate, aspartate
 Inhibitory e.g. GABA, Glycine
 Modulatory e.g. Dopamine, Serotonin  equal probability of being excitatory or inhibitory, depends on the neurotransmitter

Question 3

What are the 5 specific examples of neuronal subtypes?

Answer 3

A.) Inhibitory local circuit neurons – GABAergic interneurons of the cerebral cortex
B.) Inhibitory Projection Neurons – Medium spiny neurons of the neostriatum
C.) Inhibitory Projection Neurons – Purkinje neurons of the cerebellum
 Contain the inhibitory neurotransmitter GABA and the calcium binding protein calbindin
D.) Excitatory Local Circuit Neurons (interneurons) – spiny stellate neurons of the cerebral cortex
 Small multipolar neurons with local dendritic and axonal arborizations
 Provides asymmetric synapses and uses glutamate as its neurotransmitter
 Resemble pyramidal cells in that they are the only other cortical neurons with large numbers of dendritic spines, but they differ from pyramidal neurons in that they lack elaborate apical dendrite
E.) Excitatory projection neurons – pyramidal neurons of the cerebral cortex
 Use glutamate as excitatory transmitter
F.) Excitatory Projection Neurons – Spinal motor neurons
 Use acetylcholine as their neurotransmitter
 Have their cell bodies within the spinal cord and send their axons outside the CNS to innervate the muscles
 α-motor neurons innervate skeletal muscle
 ƴ-motor neurons innervate the spinal organs of the muscles
G.) Neuromodulatory neurons – Dopaminergic neurons of the substantia nigra
 Parkinson’s disease  inability to move
 Contain the catecholamine – synthesising enzyme tyrosine hydroxylase as well as dopamine as their neurotransmission
H.) Neuromodulatory neurons – Serotonergic neurons of the dorsal raphe nuclei
 Associated with moods e.g. SSRI’s

Question 4

What is the role of astrocytes?

Answer 4

• Clear neurotransmitters from synaptic/perisynaptic regions via specific transporters.
• Buffer extracellular K+ by maintaining high K+ permeability.
• Provide energetic/metabolic support to neurons.
• Can form networks connected by gap junctions and can be electrically active.
• Receive signals via neurotransmitter receptors.
• Comprise a large fraction of brain parenchyma
• Release neurotrophic factors to support neuronal survival
• Are connected together by gap junctions, forming a syncytium that allows ions and small molecules to diffuse across the brain parenchyma

Astrocytes are involved in the Glutamate Glutamine cycle:

Couples neurotransmitter re-uptake and ammonia detoxification with the synthesis of glutamine and provides neurons with glutamine as an energy source

Question 5

What are the characteristics of satellite cells (PNS)?

Answer 5

• Present in sensory, sympathetic, and parasympathetic ganglia
• Ensheath neuronal cell bodies
• Thought to have astrocyte-like functions, but many consider them to be a unique glial cell type
• Express Glutamine Synthetase, GFAP, S100, multiple neurotransmitter and peptide receptors and glutamate and GABA transporters.
• Glutamine Synthetase is thought to be best marker

Question 6

What are the characteristics of microglia cells and what are their markers?

Answer 6

• Comprise the brain’s immune cells (macrophages of the brain)
• Present antigens to T lymphocytes
• Rod-shaped soma
• Surveillance cells
• Pronounced activation due to disease or injury
• Derived from mesoderm (not neural ectoderm)
• Help phagocytose degenerating cells that undergo programmed cell death
• Secrete cytokines and growth factors that are important in fiber tract development, gliogenesis and angiogenesis
Microglia markers:
• CD11b
• CD45
• CD68
• CD40

Question 7

What is the role of the Cerebral vasculature and the Blood Brain Barrier (BBB)?

Answer 7

• Solute transfer is limited by a specialised organisation comprising endothelial cells with tight junctions (zonula occludens).
• Endothelial cells and pericytes are together encased by a basement membrane.
• The basement membrane is surrounded by astrocyte foot processes, which probably contribute to the specialisation and maintenance of the BBB.

Question 8

What are the Additional specialised cell types with important roles in nervous system function (though not strictly ‘neural’)?

Answer 8

 Ependymal cells – line the outside of the brain
 Cells of the choroid plexus – produce the CSF
 Brain endothelial cells – form the blood brain barrier

Question 9

What are the roles of Ependymal Cells and Choroid plexus?

Answer 9

• Cells of the ependyma and choroid plexus are derived from immature neuroepithelium. The ependyma, a single layer of ciliated cuboidal cells, lines all the ventricles of the brain, helping to move cerebrospinal fluid through the ventricular system.
• At several places in the lateral and fourth ventricles the ependyma is continuous with cells of the choroid plexus, which covers thin blood vessels that project into the ventricles.
• These choroid plexus epithelial cells filter plasma from the blood and secrete this ultrafiltrate as cerebrospinal fluid. C