Histology of the Nervous System Flashcards
What is the key cell of the nervous system?
Neuron
What are the types of glial cells?
Astrocytes Oligodendrocytes Schwann cells Ependymal cells Satellite cells of ganglia
What are the immune cells of the CNS?
Microglia
How many glial cells are there?
Almost as many as neurons
How many layers of neurons are there in grey matter?
6
What colour does the cell body stain with H&E?
Pink
What colour do the processes stain with H&E?
Pink
What is highlighted with a silver stain?
Processes
What does the ventricular system do?
Form and provide passage for CSF
What is the choroid plexus?
Vascular structure arising from ventricles
What does the choroid plexus do?
Form CSF
What cell type are ependymal cells?
Low columnar or cuboidal
Where are ependymal cells found?
Line central canal of spinal cord and ventricles in brain
T/F: Ependymal cells in some areas have cilia. If true, why?
True, to help CSF flow
Are ependymal cells epithelial or glial?
Neither, but they’re more glial than epithelial
How are ependymal cells attached to underlying tissue?
Via long processes anchoring cell in tissue
What are some characteristics of neurons?
Morphologically distinct Electrically active Rapid communication Long distance Specialised; eg: - Retina - Cochlea High level of protein synthesis Metabolically limited Terminally differentiated
Where are Purkinje cells found?
Cerebellar cortex
Where are pyramidal cells found?
Cerebral cortex
What are the three components of a neuron’s cytoskeleton?
Actin
Intermediate filaments
Microtubules
What is the role of actin in a neuron’s cytoskeleton?
Dynamic assembly/disassembly
Allows shape changes and movement; eg:
- Spines grow during learning
- Growth cones
What is the role of intermediate filaments in a neuron’s cytoskeleton?
In all processes
Permanent
What is the role of microtubules in a neuron’s cytoskeleton?
Dynamic
Made of tubulin
Axon transport
What does the soma do?
Metabolic centre of cell
What are the two types of neuronal processes?
Dendrite
Axon
What does a dendrite do?
Receive information from other neurons
= Input
What does an axon do?
Main conducting unit for carrying signals to other neurons
= Output
Where is a high proportion of total cell volume?
Axons (and dendrites)
Why is axonal transport critical?
To supply cell-body derived elements to long axon
Which part of the neuron does random damage often involve?
Axon, not cell body
Describe graded membrane potentials
Unequal distribution of positively charged ions on either side of membrane
Membrane has Na-K-ATPase pumps and ion channels - sets up charge distribution across membrane
What type of signal is sent via dendrites?
Passive spread of current - local signal
What type of signal is sent via axons?
Action potential - travels long distances
Describe the synapse
Pre-synaptic cell talks to something
- Synaptic vessels contain neurotransmitters
Synaptic cleft = space between communicating processes
Post-synaptic cell receives information > change in membrane potential > responds to information
What is the high level of protein production in neurons needed for?
Ion channels
Receptors
Cytoskeleton
How do you identify a highly synthetic cell in cytology?
Large pale nucleus
Nissl bodies
What are Nissl bodies?
Organelles that make proteins
- Rough ER
- Free ribosomes
Where is protein made in a neuron?
Cell body only
What is another name for glia?
Macroglia
Where are glia derived from?
Neuroectoderm, like neurons
Where are microglia derived from?
Bone marrow, like other immune cells
What are the passive support functions of astrocytes?
Neurotransmitter uptake and degradation K homeostasis Neuronal energy supply Maintenance of BBB Injury response and recovery
Why is neurotransmitter uptake and degradation important?
Otherwise signal continuous
What does too much K in the ECF mean for the neuron?
Overstimulation
How is glucose transported across the BBB?
Blood > astrocytes > neurons
How do astrocytes contribute to the BBB?
Wrap around blood vessels
What are the active functions of astrocytes?
Modulation of neuronal function
Modulation of blood flow
Why can astrocytes carry out their active functions?
Electrically coupled
Send signals
What type of neurotransmitter is glutamate?
Excitatory
What type of neurotransmitter is GABA?
Inhibitory
Describe the cycling of glutamate across the synapse
- Glutamate released into synapse
- Glutamate detected by glutamate receptor on glial cell
- Glutamate enters glial cell
- Converted to glutamine - toxic otherwise
- Glutamine shunted back to neuron
Describe the cycling of GABA across the synapse
- GABA released into synapse
- GABA detected by GABA receptors on glial cell
- GABA enters cell
- GABA shunted into Krebs cycle
- Glutamine also shunted to neuron for GABA synthesis
What happens when glutamate transporters on glial cells are inhibited?
Neurons depolarise more
Increase in signal strength and duration > too metabolically active > neuronal death
What is the intracellular ion that changes in concentration in astrocytes?
Ca
What does modulation in IC Ca allow a glial cell to do?
Release of neuronal modulatory substances
What initiates Ca modulation in astrocytes?
Neurotransmitters like: - ATP - Glutamate Trauma Spontaneous Inflammatory mediators
T/F: Glial cells have synaptic vesicles and show exocytosis
True
How does an increase in IC Ca in glial cells affect neurons?
Inhibited by Ca wave
Mechanism involves release of ATP from glia
How do astrocytes regulate vascular tone?
Ca wave in astrocyte causes vasoconstriction/vasodilation
What is the predominant glial cell of white matter?
Oligodendrocyte
What do oligodendrocytes do?
Myelinate axons in CNS
What do Schwann cells do?
Myelinate axons in PNS
Why is myelination important?
Provide electrical insulation
Speeds up conduction
What else other than myelination speeds up conduction?
Increased axon diameter
How many axons do oligodendrocytes myelinate?
Several
How many axons do Schwann cells myelinate?
One
What breaks up the myelin sheath?
Nodes of Ranvier
What is the role of the nodes of Ranvier in signal transduction?
Signal jumps from node to node
Rapid propagation of signal
T/F: CNS is immune priveleged
True
What is the role of microglia
Surveillance
Local defence
Brain development
Disease
What happens to microglia during inflammation or injury?
Change rapidly
Resemble macrophages
Describe the histological structure of a peripheral nerve
Made up of nerve fibres
Each nerve fibre and Schwann cell surrounded by loose vascular supporting tissue = endoneurium
Fascicles = one or more bundles of nerve fibres
Each fascicle surrounded by collagenous tissue = perineurium
Bundles of fascicles wrapped in epineurium
What are ganglia?
Aggregations of cell bodies outside of CNS
What are the types of ganglia?
Sensory
Autonomic
What are sensory ganglia?
House cell bodies of sensory neurons
Eg: dorsal root ganglia
What are autonomic ganglia?
House cell bodies of post-ganglionic neurons
What makes up ganglia?
Cell bodies
Nerve fibres
Satellite cells
What are satellite cells?
Supporting cells in ganglia
