Neurons- Different Cell Types In Brain And Spinal Cord Flashcards
Neurones
• Specialised for electrical signalling
• Inputs via dendrites
• Action potentials propagate along the axon from the axon hillock
• Mainly formed during development
Neuronal communications
Neurons communicate via synapses - 2 types
• Chemical – majority – via neurotransmitters (glutamate, GABA, dopamine, serotonin,
etc.)
• Electrical – less abundant – via direct flow of ions
- enable synchronized electrical activity, e.g. brainstem (breathing) & hypothalamus (hormone secretion)
Chemical synaptic transmission
Axon potential depolarises synaptic terminal membrane
This leads to Opening of voltage-gated calcium channels leads to calcium influx
The Calcium influx triggers neurotransmitter release
Exciting synapses are
Clustered and concentrated on dendritic spines
Spines and neural plasticity
• Neural plasticity
- changes in neuronal/synaptic structure and function in response to neural activity - basis of learning and memory
Stronger carry more current, weaker carry less current
• Spines are dynamic structures – number, size, composition
• Spine remodelling linked to neural activity
• Relevant to disease – e.g. schizophrenia & Alzheimer’s - ↓spine density
Neuronal heterogeneity
Neurons differ in their
Size
Morphology
Neurotransmitter content
Electrical properties
Eg neocortex
Arborisation of axons and dendtrites
Neurones can branch and give multiple terminals
Oligodendrocytes
These are Myelinating cells of the CNS
• Unique to vertebrates
• Myelin insulates axon segments, enables rapid nerve conduction
• Myelin sheath segments interrupted by nodes of Ranvier – saltatory conduction far more faster and efficient
• Provide metabolic support for axons
Myelin sheath
Formed by wrapping of axons by oligodendrocyte processes (membranes)
• Highly compacted – 70% lipid, 30% protein
• Myelin specific proteins, e.g. myelin basic protein (MBP) can be used as “markers”
Microfilm
These are the Resident immune cells of the CNS
• Originate from yolk sac progenitors
that migrate into CNS
• “Resting” state, highly ramified, motile processes survey environment (2-3 μm/min)
• Upon activation (e.g. by ATP), retract processes, become “amoeboid” & motile
• Proliferate at sites of injury - as they are phagocytic cells
Functions of microglia
Immune surveillance
Phagocytosis- debris/microbes
Synaptic plasticity-pruning of spines
Good and bad microglia
Bad- when the microglia become over reactive
Astro cytes- type of glia cells
Most numerous cells in CNS
Highly heterogeneous service
Common marker glial fibrillary acidic protein
Astrocytes contribute t the blood-brain barrier
Anti-GPAF immunostaining for asrocytes- cell bodies and processes coating capillaries
Dual immunostaoning with second astrocyte. Raker AQP4 reveals more of the vascular network:
GPAF
Aquaporin 4 water channel necessary because of blood brain barrier
Atrocities functions
Structural-n define brain micro-architecture
Envelope synapses- tripartite synapse- buffer K+, glutamate
Metabolic support
Neuromuscular coupling- changes in cerbral blood flow in response to neural activity
Proliferate in disease= glossies or astrocytes
Specialised astrocytes
Radial glia- important for brain development
Bergmann glia cerebellum
Muller cells
Abundance of neuronal cell bodies in nuclei
Axons gathered into tracts
Commissures
Tracts that cross midline
Grey matter abundant in neural cell bodies and processes- neutrophil contains few cell bodies
White matter contains absence of myelinated tracts and commissures
Cell bodies and supporting cells located in ganglia eg dorsal root ganglia
Axons bundles into nerves
Many PNS are enveloped by Schwann cells (myelinating cells of the the PNS- neural crest derived c.f. Oligodendrocytes, derived from CNS- resident neural progenitors
Dyes injected into blood penetrate most tissues but not the brain
Dyes injected into the CSF brain stains —> specialised blood-brain barrier
Formed by endothelial cell tight junctions, basement membrane (few fenestrations), astrocyte end feet and pericytes (contractile, aid blood flow)
Sensitive to inflammation, hypertension, trauma, ischaemia
Circumventricular organs lack normal blood brain barrier
homeostatic and endocrine functions
Pineal body
Secrets melatonin hormone into blood
Area postrema
A chemoreceptor trigger zone that initiates vomiting in response to chemical changes in the plasma
Post pituitary
Secretes hormones into blood
Organum vasculosum of the laminate terminalis
Osmoreceptor controlling vasopressin secretion and thirst
Subfornical organ
Circulating angiotensin II acts here to increase water intake
Ependymal cells
Epithelial like line vertices and central canal of spinal cord
Functions: CSF production, flow and absorption
Ciliated: facilitates flow
Allow solute exchange between nervous tissue and CSF
Choroid plexus
From like projections in ventricles
Formed from modified ependymal cells- villi form around network of capillaries
This leads to highly vascularised with a large surface area
Main site CSF production by plasma filtration driven by solute secretion
Gap junctions between cells from blood-CSF barrier