3. Cells of the nervous system Flashcards
Neurone
Info. processing unit.
Responsible for generation and conduction of electrical signals
Communicate with one another via chemicals released at the synapse.
Supported by neuroglia
Cellular structure of all neurons is similar.
Large nucleus Prominent nucleolus Abundant RER Well developed Golgi Abundant mitochondria Highly organised cytoskeleton
How is diversity is achieved by neurones?
differences in number and shape of their processes.
Why do neurones have abundant RER and Golgi?
For producing, processing and packaging proteins
Describe DENDRITES
Major area of reception of incoming information
Spread from cell body and branch frequently
Greatly increase SA
Can receive more inputs and from more locations
What are the protrusions coming out of dendrites called?
Dendritic spines
Describe the arrangement of primary, secondary and tertiary dendritic spines.
Primary dendritic spines come off the vertices of the pyramid
Secondary dendritic spines come off the primary
Tertiary dendritic spines come off the secondary
Why are dendritic spines described as ‘plastic’?
Can withdraw/ produce/ destroy spines
Excess alcohol, schizophrenia = destruction
What are dendritic spines full of? Why?
Many mitochondria
Indicates requirement for a lot of energy production
Describe AXONS
Conduct impulses away from cell body
Emerge at axon hillock
Usually 1 per cell
May branch after leaving cell body and at target
Prominent micro-tubules and neurofilaments
Size of axons vs dendrites
Axons are much smaller
How does the diameter axons and dendrites change as it moves further from the cell body?
Axon: Doesn’t: diameter is constant the whole distance so the conduction velocity remains the same the whole way
Dendrite: Diameter tapers
Why do Axons contain abundant intermediate filaments and microtubules:
IFs: Needs to maintain tensile strength over long distance, play critical role in determining axon calibre
Microtubules: To transport proteins, vesicles, mitochondria from cell body to synapse
What are the 3 domains of an axon? Describe them.
Node: No myelin, Site of Na+ channels
Paranode: next to node; site of tight junctions between the ends of the myelin sheath and the axon
Juxtaparanode: next to paranode, underneath the myelin sheath, site of K+ and Ca2+ channels
What are the 2 forms of axon terminal?
Butons
Varicosities
Where are varicosities found?
Along smooth muscle where 1 axon will stimulate the contraction of several smooth muscle cells (multiple swellings synapse onto different cells)
Describe a bouton
Swelling at the end of an axon, where synapse is present
What is responsible for synaptic density?
Increased number of proteins in that area responsible for the machinery of releasing vesicles
What happens to competing inputs? (excitatory and inhibitory)
Neuronal integration
Integrated in postsynaptic neurone to produce a single digital output
What are the 3 types of synapse?
Axo-dendritic (often excitatory)= majority
Axo-somatic (often inhibitory)
Axo-axonic (often modulatory): modulate action already passing down axon
What determines how fast an AP is transmitted?
Axon calibre
What is a key feature of fast axonal transport of vesicles of neurotransmitter?
Vesicles of neurotransmitter are carried along microtubules
Microtubules are unidirectional because they are polarised.
Retrograde transport occurs along other unidirectional microtubules.
What happens when the axon is damaged during multiple sclerosis? What is this comprised of?
Swelling due to compression of axon/ axon transected
Swelling= vesicular protein build up
Name 4 morphological subtypes of neurones
Pseudounipolar: single axonal projection that divides into 2
Bipolar: 1 axon, 1 dendrite projection
Golgi type I multipolar
Golgi Type II multipolar
Describe Golgi type I multipolar cells
Highly branched dendritic trees
Axons extend long distances
Most metabolically active
Most vulnerable to degeneration
Describe Golgi type II multipolar cells
Highly branched dendritic trees
Short axons
Axons terminate quite close to cell body of origin
Main output neurones
What is the difference between Golgi Type I cells and Golgi Type II cells?
Type I have long axons
Type II have short axons
Functional classification of neurones
Sensory neurons: Take input into brain
Motor neurons: Main output to skeletal and smooth muscle
Interneurons: Links neurones: responsible for modification, coordination, integration, facilitation and inhibition of sensory input
What are neuroglia?
All cell types in CNS that aren’t neurones
Support cells
Name 7 neuroglia
Astroglia Ogliodendria Schwann cells Microglia Ependymal cells Immature progenitors Satellite glia
Describe astroglia
Multi-processed star shaped
Most abundant cell type in brain
Numerous IF bundles in cytoplasm of fibrous astroglia (GFAP)
Signal to one another via Gap junctions
2 types of astroglia
Proteoplasmic (grey matter)
Fibrous (mainly in white matter between axon bundles)
List 11 functions of astroglia
Support cells of CNS Formation of blood-brain barrier Facultative macrophages Homeostasis: soak up neurotransmitter Scaffold of neuronal migration and axon growth Transport substances from blood to neurones Segregation of synapses Synthesis of neurotrophic factors Neuronal-glial signalling K+ ion buffering Glial scar formation
What forms the glia limitans?
Packed dense layer of astrocytes (layers of end feet)
Forms barrier between brain and CSF
How are astrocytes involved in the removal of neurotransmitters, K+ and H2O?
End feet on blood vessels involved in transport of K+ and H2O
Processes close to synapse involved in removing neurotransmitter
Astrocyte end feet are wrapped around…
Blood vessels or Neurones
What are the 2 forms of ogliodendroglia?
Interfascicular
Perineuronal
Describe ogliodendroglia
Small spherical nuclei and small cell body Dense nucleus and cytoplasm Few thin processes Prominent ER and Golgi Metabolically highly active
Functions of ogliodendroglia
Production and maintenance of myelin sheath in CNS
Each cell produces multiple sheaths (1-40)
Continually degrade protein to make new protein to maintain membrane
What is myelin?
A lipid rich insulating membrane
Up to 50 lamellae
Name 2 myelin disease states
Multiple Sclerosis (MS) Adrenoleucodystrophy
Describe microglia
Derived from bone marrow
Resident macrophage population of CNS
Involved in immune surveillance
Present antigens to invading immune cells
1st cells to react to infection/ damage/ change in microenvironment
Role in tissue modelling
Describe schwaan cells
Perform functions of astrocytes in PNS Myelin producing cells of the PNS Each Schwann cell produces only 1 myelin sheath Surround unmyelinated axons Promote axon regeneration
Where are Golgi Type I and Golgi Type II cells found?
Golgi Type I: pyramidal cells of the cerebral cortex, purkinje cells of cerebellum, anterior horn cells of spinal cord, long axons
Golgi Type II: short axons, stellate cells of the cerebral cortex and cerebellum
What is the normal morphology of sensory neurones?
Pseudounipolar
2 branches
1 to the CNS
1 to the sensory receptor
