cells of the nervous system Flashcards
what are the 4 major compartments of the neuron
- cell body, soma, perikaryon
neurites: - dendrites
- axons
- presynaptic terminal
where does the axon begin?
the axon hillock
features of axon
- no RER and no free ribosomes (no protein synthesis)
- membrane composition different to some membrane
- <1 mm to >1m in length
- 1 microm - 25 micom diameter (in humans)
what are the branches of axons called?
axon collaterals
what is the end of the axon called?
axon terminal or terminal bouton
what happens at the axon terminal?
it is a site where the axon comes into contact with other neurons and passes information on to them (synaptic terminal)
what is the segment after the axon hillock?
axon initial segment
what are specializations of the presynaptic terminal cytoplasm?
- no microtubules
- synaptic vesicles
- specialised proteins
- mitochondria
what are neurons?
excitable cells that conduct impulses
what is the purpose of neurones?
to integrate and relay information within a neural circuit
what are glia?
supporting cells, the ‘glue’
what is the purpose of glia?
maintain homeostasis, protection, assist neural function
what are the components of the soma?
- nucleus
- organelles for protein synthesis and processing
- ribosomes
- RER
- golgi apparatus
- mitochondria
what is Nissl staining?
- applying positive dye to distinguish between neurons and glia
- nucleolus of all cells stained
- neurons also have nissl bodies
- nissl stain binds to RNA
- also used to determine cytoarchitecture
what is a neurite?
any processes that come off of a neuron e.g. dendrites and axons
what is a golgi stain?
- silver chromate applied to brain tissue
- small percentage of neurons appeared but they were in more detail
- led to neuron doctrine (gaps between neurones)
what are the features of the cytoskeleton in neurites?
- microtubules
- microfilaments
- neurofilaments
features of microtubules
- composed of polymers of tubulin molecules
- longitudinally down neurites
features of microfilaments
- polymers of actin
- longitudinally and membrane associated
features of neurofilaments
- long protein molecules, wound together
- very strong
what is immunohistochemistry?
- used to located protein of interest e.g. voltage-gated sodium channels
- primary antibody specific to protein of interest
- fluorescent secondary antibody specific to primary antibody
- used on fixed tissue (not live)
what does it mean if an axon has many collaterals?
it has a high level of divergence, it can contact many cells
what are specialisations of the presynaptic terminal cytoplasm?
- no microtubulues
- many synaptic vesicles
- specialised proteins in the membrane
- mitochondria
what do many dendritic branches form?
dendritic trees / dendritic arbours
what do dendrites allow?
convergence of signals, can receive inputs from many neurons which they process and converge into one cell
what is live fluorescent imaging?
- technique to visualise neurones
- microelectrode with fluorescent protein inject fluorescent protein into neuron
- live imagine - in a live tissue
- can be genetically encoded
what are the functions of dendritic spines?
- increase surface area
- plastic - can be absorbed or grown to increase or decrease activity
- isolate chemical reactions
how are proteins transported from soma to presynaptic terminal?
- fast axoplasmic transport
- microtubules act as roads along axons
- kinesin attach to microtubules and walk along them
- this process is ATP dependent
- anterograde transport
- retrograde transport by dynein is when proteins move from terminal to soma (opposite)
what are retrograde and anterograde tracers?
- radioactive amino acids
- retrograde used to locate cell body
- anterograde used to locate cell terminals
how are neurons classified?
by structure and by gene expression
how can neurons be classified by structure?
- number of neurites
- dendritic geometry
- connections - where do they project?
- axon length
how can neurons be classified by gene expression?
- underlies structural differences
- defines neurotransmitter expression (excitatory or inhibitory)
features of unipolar neurons (pseudounipolar)
- dorsal root ganglion cell
- one central process that splits into two peripheral processes
- small are for receiving synaptic input = highly specialised function
- reliable relay of information
features of bipolar neurons
- e.g. retinal bipolar cells
- small area for receiving synaptic input = highly specialised function
- reliable relay of information
features of multipolar neurons
- e.g. purkynje cell
- majority of neurons in the brain
- large area for receiving synaptic input
- high levels of convergence
what is a stellate? (multipolar neurons)
star shaped dendritic tree
what is a pyramidal cell? (multipolar)
- basal dendrites that come out of cell body
- long dendrite that becomes an apical tree at the top
- pyramidal shaped soma
how can neurons be classified by their projections?
- sensory
- motor
- interneuron
what is an interneuron?
- connect one neuron to another neuron
- largest class of neuron
what are the two types of interneuron?
- relay/projection neurons = connect brain regions
- local interneurons = short axons, process info in local circuits
6 functions of astrocytes
- control environment surrounding neurons (maintain homeostasis)
- act as fuel suppliers
- regulate neurotransmitter activity
- buffer extracellular potassium
- form part of blood brain barrier
- couple neuronal activity to blood supply
features of astrocytes
- found in spatial domains - processes that extend out that dont over lap
- unique marker - glial fibrillary acidic protein (GFAP)
what are ependymal cells?
type of astrocyte that lines the ventricles and central canal
how do astrocytes act as fuel suppliers?
- glycogen stores in the brain
- glycogen converted to lactate when needed
what is a tripartite synapse?
an astrocyte is in the synapse and acts as a third element
what is the role of an astrocyte in a tripartite synapse?
- terminates neurotransmitter activity
- recycle neurotransmitters to presynaptic terminals
- astrocytes have receptors too so can respond to neurotransmitter
what are microglia?
macrophages of the CNS
what is the function of microglia?
- tissue surveillance and phagocytosis (they engulf and break down debris from cells)
- neural development
- synaptic pruning (remove unwanted dendrites)
what are oligodendrocytes?
form myelin sheaths in CNS
- unlike schwann cells one oligodendrocytes myelinates many axons
what are schwann cells
form myelin sheaths of PNS
- one schwann cell provides one myelin segment to a single axon
how is the myelin sheath formed?
- oligo cytoplasm wraps around many times around the axon
- cytoplasm squeezed out of layers by compaction
- myelin sheaths maintain contact with glial cells for nourishment
