Cell Types In Brain And Spinal Cord Flashcards
Neurons
Specialised for electrical signalling
What inputs to neurons
Dendrites
When are axons mainly formed
During development
What do action potentials propagate along
Along the axon from the axon hillock
2 types of synapses
Chemical
Electrical
Chemical synapse
Majority
Via neurotransmitters (glutamate , GABA, dopamine, serotonin, etc)
Electrical synapses
Less abundant
Via direct flow of ions- enable synchronised electrical activity eg brainstem (breathing) and hypothalamus (hormone secretion)
Chemical synaptic transmission
Axon potential depolarises synaptic terminal membrane
Opening of voltage-gated calcium channels leads to calcium influx
Calcium influx triggers neurotransmitter release
Where are excitatory synapses often concentrated
Dendritic spines
Neural plasticity
Changes in neuronal/synaptic structure and function in response to neural activity
Basis of learning and memory
Dendritic Spines
Dynamic structures- number, size, composition
Spine remodelling linked to neural activity
How do neurones differ
Size
Morphology
Neurotransmitter content
Electrical properties
Eg neocortex
Electrical synapse structure
No synaptic vesicles
Connexins found in both pre and post synaptic membrane
Form a gap junction to allow passage of ions
Betz cells
Upper motor neurones
Large excitatory (gluatmatergic) long projections, pyramidal cells
Vulnerable in MND
Medium spiny neurones
Striatal interneurons
Small, inhibitory (GABAergic)
Vulnerable in Huntington’s disease
Which neurons are vulnerable in MND
Betz cells
Which neurones are vulnerable in Huntington’s disease
Medium spiny neurones
Oligodendrocytes
Myelinating cells in the CNS
Unique to vertebrates
Provide metabolic support for axons
Myelin
Insulates axon segments
Enables rapid nerve conduction
Nodes of Ranvier
Gaps in myelin sheath
Saltatory conduction
Myelin sheath
Formed by wrapping of axons by oligodendrocyte processes (membranes)
Highly compacted - 70% lipid, 30% protein
Myelin specific proteins eg. Myelin basic protein (MBP) can be used as markers
Arborisation
Fine branching structure at the end of a nerve fibre
How do oligodendrocytes provide metabolic support to axons
Transferring lactate into neurones (can be used as an energy source)
Functions of microglia
Immune surveillance
Phagocytosis- debris/microbes
Synaptic plasticity- pruning of spines
Bad (M1) and good (M2) microglia
What percentage of myelin in lipid
70%
What percentage of myelin is protein
30%
Microglia
Resident immune cells of the CNS
‘Resting’ state - highly ramified, motile processes survey environment
Upon activation (eg by ATP) retract processes, become ameoboid and motile
Proliferate at sites of injury- phagocytic
Where do microglia originate from
Yolk sac progenitors that migrate into the CNS
At what rate do microglia survey environment
2-3 um/min
What can activists microglia
ATP
Which form of microglia is ‘bad’
M1
Which form of microglia is ‘good’
M2
Astrocytes
Highly heterogenous - not all star-shaped
Common marker glial fibrillary acidic protein (GFAP)
Most numerous glial cells in CNS
Why are M1 microglia ‘bad’
Linked to chronic inflammation
Astrocyte functions
Structural- define brain micro-architecture (contribute to blood-brain barrier)
Envelope synapses- ‘tripartite synapse’- buffer K+, glutamate etc
Metabolic support- eg glutamate-glutamine shuttle
Neurovascular coupling- changes in cerebral blood flow in response to neural activity
Proliferate in disease- gliosis or astrocytosis
Specialised astrocytes
Radial glia
Bergmann glia
Müller cells (retina)
Radial glia
Important for brain development
Bergmann glia
Cerebellum
How do astrocytes contribute to blood-brain barrier
Processes of astrocytes envelope capillaries in brain
Müller cells
Retina
Motor neurone disease
Adult-onset neurodegenerative disease characterised by loss of upper (motor cortex) and lower (spinal cord) motor neurones
Multiple sclerosis
Autoimmune demyelinating disease where immune cells attack the myelin sheath of oligodendrocytes
Commissures
Tracts that cross the midline
White matter
Contains abundance of myelinated tracts and commissures
Grey matter
Abundant in neural cell bodies and processes
Neuropil
Contains few cell bodies
How are axons gathered in the CNS
Into tracts
Nuclei
Abundance of neuronal cell bodies in CNS
Ganglia
Cell bodies and supporting cells in PNS
eg dorsal root ganglia
Nerves
Axons bundled into nerves in PNS
MND spinal cord shows pathological changes in
Motor neurons
Microglia
Astrocytes
MND symptoms are due to loss of
Motor neurones
Pathological CNS lesions in MS involve
Neurones
Oligodendrocytes
T lymphocytes
Acute symptoms in MS primarily reflect dysfunction of
Neurones
Myelinating cells of the PNS
Schwann cells
Origins of Schwann cells
Neural crest derived c.f. Oligodendrocytes- derived from CNS- resident neural progenitors
What forms the blood-brain barrier
Endothelial cell tight junctions
Basement membrane (few fenestrations)
Astrocytes end feet
Pericytes (contractile, aid blood flow)
What is the blood-brain barrier sensitive to
Inflammation
Hypertension
Trauma
Ischaemia
Ependymal cells
Epithelial-like, line ventricles and central canal spinal cord
Ciliated- facilitates flow
Functions of ependymal cells
CSF production, flow and absorption
Allow solute exchange between nervous tissue and CSF
Choroid plexus
Frond-like projections in ventricles
Formed from modified ependymal cells- villi form around network of capillaries—> highly vascularised with a large surface area
Function of choroid plexus
Main site of CSF production by plasma filtration drive by solute secretion
Gap junctions between ependymal cells
Form blood-CSF barrier
Which cells myelinate axons in CNS
Oligodendrocytes
Where is CSF reabsorbed
Arachnoid granulations
Ependymal cells
Produce CSF in choroid plexus of lateral ventricles
Choroid fissure
Attachment site for choroid plexus
Above hippocampus
Which pigmented hormone is present in the skin and what type of cell is it produced by
Melanin
Melanocytes
