2. NEURONS & GLIA Flashcards
What is the human brain comprised of?
- The human brain is comprised of neurones & glial cells
What is the reticular theory?
- Reticular theory suggests that neurones fuse together & form a continuous network
What is the neurone doctrine theory?
- The neurone doctrine theory suggests that neurones are individual units which communicate
Describe the process of fixation & sectioning of neural tissue?
- Brain tissue can be fixated & sectioned for visualisation
- Fixation = freezing the tissue or embedding it in paraffin wax
- The tissue can then be sectioned with a microtome
- Different orientations e.g horizontal, coronal, saggital
What is the Nissl stain & what can it show?
- Nissl stain can differentiate between glial cells & neurones
- Cresyl violet
- Stains nuclei & Nissl bodies (cell bodies)
** What is the Golgi stain & what can it show?
- Golgi stain can differentiate between structures better than the nissl stain
- Silver chromate solution
- Stains neurones & their projections (neurites)
How did discovery of the electron microscope provide insight about neurones?
- The space between neurones is 0.02um but light microscopes only had a resolution of 0.1 um so there was a lot of disagreement about whether neurones were connected
- Electron microscope -. resolution was small enough to see between neurones
- Conclusion = Neurone doctrine
What are neurones?
- Neurones are specialised cells in the nervous system involved in the transmission & conduction of electrical & chemical signals
What are the three parts to a neurone?
- CELL BODY
- AXON
- DENDRITES
What are the properties of the cell body of a neurone?
- The cell body of a neurone contains the same organelles as those in other cells
Define the neuronal cytoskeleton
- The neuronal cytoskeleton is the internal scaffold which provides the neurone with shape
What three structures make up the neuronal cytoskeleton?
- MICROFILAMENTS
- NEUROFILAMENTS
- MICROTUBULES
- Ordered smallest -> largest
*What are the properties of neuronal microfilaments?
- MICROFILAMENTS - Smallest fibre
- Length = 5nm
- What? Polymer of the protein ACTIN
- Where? axons & dendrites
What are the properties of neuronal neurofilaments?
- NEUROFILAMENTS = intermediate fibre
- Length = 10nm
- What? Bound together in a rope like structure to provide strength
- Where? Axons - regulating axonal shape
What are the properties of neuronal microtubules?
- MICROTUBULES = 20 nm
- Length = 20nm
- What? Polymer of the protein TUBULIN. Involved in axoplasmic transport
- Where? Axons & dendrites
Define axons & the three parts of axons
- Axons are highly specialised neuronal projections that are involved in transporting nerve impulses over long distances
1. AXON HILLOCK
2. AXON PROPER
3. AXON TERMINAL
What is the axon hillcock?
- Initial segment of an axon
What are axon collaterals & recurrent collaterals?
- Axon collaterals are branches of the axon proper
- These axon collaterals will branch out to different areas but if they return to the same cell, they are known as recurrent collaterals
Define dendrites
- Dendrites are highly specialised neuronal projections that receive synaptic input from otehr neurones
- dendrites form dendritic trees with dendritic branches
What are the two main types of neuron classification?
- NEURONAL STRUCTURE
- GENE EXPRESSION
- But these two broad categories can be subdivided
What are the four types of neuronal classification by structure?
- Neurones can be classified by structure:
1. NUMBER OF PROJECTIONS
2. DENDRITES
3. CONNECTIONS
4. AXON LENGTH
How can neurones be classified by the number of projections?
- Neurones can be classified according to teh number of projections or neurites
- UNIPOLAR = one neurite
- BIPOLAR = 2
- MULTIPOLAR = many
What two ways can neurones be classified by their dendrite structure?
- Denditic tree structure (pyramidal/stellate)
2. Dendritic spines
How can neurons be classified according to the structure of their dendritic trees?
- PYRAMIDAL = Pyramidal cells
2. STELLATE = Stellate cells
How can neurones be classified according to the structure of their dendritic spines?
- Neurones can be classified based on the absence or presence of dendrites
- SPINY = presence of dendrites
- ASPINY = absence of dendrites
How can neurones be classified according to their connections?
- Neurones can be classified according to their connections as: SENSORY, MOTOR, INTERNEURONE etc
- SENSORY = skin to CNS
- INTERNEURONE = neurones synapsing with each other in the CNS
- MOTOR - CNS to gland/effector
How can neurones be classiifed according to axonal length?
- neurones can be classified into two types based on axonal length
- GOLGI TYPE 1 - axons extend from one region of brain to another (Pyramidal)
- GOLGI TYPE 2 - axons don’t extend to other regions (Stellate)
How can neurones be classified according to gene expression?
- Classified based on neurotransmitter produced
- E.g glutamatergic, serotonergic
What are glial cells & the 4 types of glial cell?
- Glial cells = support cells of the nervous sytem
1. ASTROCYTES
2. MICROGLIA
3. EPENDYMAL
4. OLIGODENDROCYTES/ SCHWANN CELLS
What are astrocytes?
- Astrocytes are star shaped glial cells
- Most numerous in the human brain
- Found in extracellular space between neurones
What are the functions of astrocytes?
- Regulate the extracellular environment in the brain by:
1. Actively removing neurotransmitter in the cleft
2. Covering & enclosing the synaptic junction
What are microglia cells?
- Microglia cells are found in the spinal cord
- They phagocytose neuronal & glial cell debris
- Ramified & ameboid
What are the two types of microglia cells?
- RAMIFIED (inactive)
- AMEBOID
- The ramified microglia contract their processes becoming ameboid
- Ramified microglia don’t phagocytose but identify threats
- Ameboid microglia are active & carry out phagocytosis
What are 3 functions of microglia cells?
- Phagocytose neuronal & glial debris
- Synaptic remodelling - microglia scavenge & remove unnecessary synaptic connections
- Direct neuronal migration during devlopment
What are ependymal cells?
- Ependymal cells are glial cells that line the ventricular system of the brain
- They act as a physical barrier between the tissue & CSF
What are 3 functions of ependymal cells?
- Osmotic regulation of CSF - controls osmolality by taking up ions & water
- Flow of CSF - ependymal cells beat to contribute to flow of CSF through ventricles
- Direct cell migration during brain development
What is a hydrocephalus & why does it occur?
- A hydrocephalus is when there’s severe pressure in the brain characterized by the accumulation of CSF in the ventricular system leading to enlarged lateral. 3rd & 4th ventricles
- Hydrocephalus occurs as a result of deficits in differentiation, maturation & function of ependymal cells
What are oligodendrocytes & schwann cells & what do they do?
- Oligodendrocytes & schwann cells are a type of glial cell that myelinate neurones
- OLIGODENDRICYTES = CNS, myelinate MANY neurones
- SCHWANN CELLS = PNS, myelinate SINGLE neurone
