3. Cells of the nervous system Flashcards by Georgia Leggett

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

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Cellular structure of all neurons is similar.

Large nucleus 
Prominent nucleolus 
Abundant RER 
Well developed Golgi 
Abundant mitochondria 
Highly organised cytoskeleton

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How is diversity is achieved by neurones?

differences in number and shape of their processes.

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Why do neurones have abundant RER and Golgi?

For producing, processing and packaging proteins

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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

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What are the protrusions coming out of dendrites called?

Dendritic spines

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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

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Why are dendritic spines described as ‘plastic’?

Can withdraw/ produce/ destroy spines

Excess alcohol, schizophrenia = destruction

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What are dendritic spines full of? Why?

Many mitochondria

Indicates requirement for a lot of energy production

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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

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Size of axons vs dendrites

Axons are much smaller

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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

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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

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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

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What are the 2 forms of axon terminal?

Butons

Varicosities

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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)

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Describe a bouton

Swelling at the end of an axon, where synapse is present

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What is responsible for synaptic density?

Increased number of proteins in that area responsible for the machinery of releasing vesicles

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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