module 2- cells of the nervous system

hierarchical structure of the brain (bottom-top)

• molecules

• cells

• circuits/systems

• behaviour

• cognition

Golgi

• invented the silver stain

• allowed him to pick out individual cells & see them in detail

• reticular network/theory: saw that neurons had processes & that they were fused together

  • THEORY IS WRONG

Cajal

• used Golgi’s silver stain

• made drawings of what he saw

• neuron doctrine: each neuron is a discrete cell (not joined together in a continuous network)

  • THEORY IS CORRECT

• principle of dynamic polarisation: neurons transmit info in a particular direction

• principle of connectional specificity: structure of the nervous system isn’t random

electron microscopy

• electron microscope

• highest resolution (1mil x more than human eye)

• can see cell ultrastructure (can see synapses)

limitation of using electron microscopes

can’t use living specimens

4 steps for immunofluorescence labelling methods

1. get an antibody/drug that has a fluorescent label which is selective for the part of the cell you want to look at

2. add the antibody/drug to the tissue (allow it to bind)

3. wash off any free antibody/drug

4. shine light on the wavelength that excites the fluorophore to see where fluorescence is coming from

strength of immunofluorescence labelling methods

can do it on living cells

limitation of immunofluorescence labelling methods

limited by the range of antibodies available

what antibody are microglial cells stained with

antibody for coronin (glial-specific protein)

what is confocal microscopy

combining fluorescence techniques with lasers

3 steps for confocal microscopy

1. laser is focused on different levels of a tissue labelled with fluorescent probe

2. see where fluorescence is coming from

3. use high sensitivity cameras + imaging software to create a 3D images of cells

2 strengths of confocal microscopy

1. can use in living cells

2. can see how the distribution of a molecule may change during a process

limitation of confocal microscopy

only has modest resolution (same as light microscope)

what is the brainbow technique

• genetically modifying an animal so that its cells produce combinations of up to 4 fluorescent dyes

• cells will end up being different colours

• used to trace the pathways of individual neurons

2 major types of cells in the nervous system

neurons & glial cells

why are glial cells needed

the nervous system doesn’t have internal connective tissue for support

function of glial cells

• structural/physiological support for the nervous system

• mediate some signalling in the brain

  • each type of glial cell has a different function

6 types of glial cells

• ependymal

• oligodendrocytes

• schwann cells

• astrocytes

• microglia

• satellite

difference between glial cells & neurons

glial cells can divide

astrocytes (star-shaped)

• majority of glia

• fills space between neurons

• regulates composition of extracellular fluids

• role in directing the multiplication & differentiation of neural stem cells

oligodendrocytes/schwann cells

• myelinates neurons

• oligodendrocytes = CNS, provides insulation for many axons

• schwann cells = PNS, each schwann cell insulates a single axon

microglia

• brain scavengers

  • phagocytic cells that have an immune function

• they are mobile (move to different tissues)

ependymal

• found in brain ventricles

• produce CSF

• during development = direct the migration of cells in the brain

• can turn into neurons so act as a backup of cells for regeneration

huntington’s disease

• autosomal dominant → due to genetic abnormality in huntingtin gene

• if polyQ repeat = >40 person will get huntingtons

• 27-35 repeats = unstable during cell replication so more copies can be added

• mutant huntingtin protein isn’t broken down properly (accumulates in neurons & kills them)

what areas of the brain are sensitive to the effects of huntingtin gene

• basal ganglia

• astrocytes (changes cause neuroinflammation & neuronal death)

• microglia (changes cause neuroinflammation & neuronal death)

what types of glial cells become activated in alzheimers + how

astrocytes & microglia → attaches to amyloid plaques

difference between neurons & nerves

• neurons = cell

• nerves = bundles of axons from different neurons

neural polarity/differences table (draw)

8 organelles found in the cytosol & dendtrites

• peroxisomes

• mitochondria

• nucleus

• ribosomes

• ER

• vesicles

• golgi

• lysosomes

3 organelles found in the axon hillock

• synaptic vesicles

• mitocondria

• smooth ER

ion/ion channel differences in axons & dendrites

• axon: Na & K channels, Ca channels (terminals), G-protein coupled receptors (terminals)

• dendrites: Ca channels, ligand-gated ion channels (glutamate receptors), G-protein coupled receptors

3 functions of neuronal cytoskeleton

• structural support (shape/diameter of axons & dendrites)

• transports cargo to & from axons/dendrites

• tethering (anchor) of components at the membrane surface

3 components of the neuronal cytoskeleton

• microtubules: role structure via (de)polymerisation & transport, run longitudinally down axons/dendrites

• neurofilaments: mechanical strength, filamentous

• actin (microfilaments): mediate shape change, tethered to the membrane

why are neurons only rarely repaired in the CNS

damaged areas are colonised by glial cells to stop regrowth of axons

what do schwann cells do when theres damage in the PNS

promote regrowth of axons