OCB03-2003 Flashcards
What are neurofilaments? Describe their structure.
Intermediate filaments found in neurons that maintain cell structure
Coiled coil of polypeptides
Where is the action potential generated?
Axon hillock
What are other terms used for a neuron cell body?
Soma or perikaryon
What makes up the axon?
Axon hillock
Axolemma
Axoplasm
What are Nissl bodies?
RER
What is a multipolar neuron? Give an example.
Multiple processes leaving cell body
Motor neurons in ventral horn
What is a bipolar neuron? Give an example.
Two processes leaving cell body, one with dendrites and the other with terminals
Bipolar neurons of retina
What is a unipolar neuron?
One axon extends from cell body with a dendritic tree in the middle of it
In what kinds of organisms are unipolar neurons common?
Insects
What is a pseudounipolar neuron? Give an example.
One branch leaves the cell body and splits into two
Primary somatosensory neurons in dorsal root ganglia
What cells myelinate axons in the periphery?
Schwann cells
What cells myelinate axons in the CNS?
Oligodendrocytes
What are the gaps of non-myelinated axon called?
Nodes of Ranvier
What factors will maximise the speed of action potential conduction?
Large diameter
Myelination
(Increased temperature)
Which conducts impulses fastest: Aδ or C fibres?
Aδ fibres
What is the difference in nomenclature for fibres which are sensory/motor and sensory only?
Sensory/motor = capital letters (and sometimes a following Greek letter)
Sensory = Roman numerals (and sometimes a following lowercase letter)
What is the fastest sensory/motor nerve fibre type?
Aα fibres (eg α-motoneurons)
Are pain neurons myelinated?
Typically lightly or not myelinated
Is the nucleolus of a neuron prominent? Why?
Yes as neurons are transcriptionally and translationally active
What are the monomers of microtubules?
α and β tubulin
Which part of the cytoskeleton is associated with axonal transport?
Microtubules
In which direction does anterograde transport describe?
Towards plus ends (terminals)
In which direction does retrograde transport describe?
Towards minus ends (soma)
What molecular motor is used in anterograde transport?
Kinesins
What molecular motor is used in retrograde transport?
Dyneins
Describe the polarity of microtubules.
Plus end = terminals
Minus end = soma
How does kinesin move?
Two “heads” of the complex detach and reattach sequentially in an ATP-dependent manner
“Walking”
How does dynein move?
ATP-dependent “sliding” movement
Describe the properties of anterograde movement.
Fast via kinesins, 100-400mm/day to move mitochondria and vesicles to terminals
Slow via unknown mechanism, 0.5-10mm/day to move structural and metabolic elements
Describe the properties of retrograde movement.
Fast via dyneins, 50-250mm/day to move aging mitochondria and vesicles
What is the importance of retrograde transport?
Only way for soma to know if there is any damage to the nerve terminal (to change gene expression and start repair)
Also enables pathogens/viruses to spread easily along nerve pathways from the skin
Which type of axonal transport is generally faster?
Anterograde
What is Diffusion Tensor Imaging (DTI)?
Type of MRI
Allows visualisation of water movement in axons using “seed points” and “voxels”
What is convergence?
Many presynaptic neurons ending on a single postsynaptic neuron
What is divergence?
One presynaptic axon dividing into many branches to end on many postsynaptic neurons
How many inputs does the average CNS neuron receive?
10,000
How many inputs does a Purkinje cell of the cerebellum typically receive?
~300,000
What is the significance of convergence and divergence in the CNS?
Many multiple ways of getting from one point to another in the brain
Each with their own neural consequences
Brain is like a super computer!
What is the ratio of neuroglia to neurons?
10:1
What are the two types of astrocytes?
Fibrous
Protoplasmic
What are the functions of astrocytes?
Homeostatic:
- regulate ionic environment (esp K+) and water
- take up neurotransmitter (esp glutamate) and convert to glutamine
- glycogen energy reserve for brain
- regulate blood-brain barrier (glia limitans)
Structural:
- bond axons together to give strength and stability
- inhibit axon regeneration
- myelination
Which compound do astrocytes use to inhibit axon regeneration?
Chondroitin sulphate glycoprotein
Which type of astrocyte clusters around synapses?
Protoplasmic
Describe a protoplasmic astrocyte.
Greater number of shorter extensions
Largely confined to grey matter
Describe a fibrous astrocyte.
Fewer number of longer extensions
Largely confined to white matter (for stability and support)
How many axons can an oligodendrocyte myelinate?
Up to 40-50
What functions do oligodendrocytes have?
Myelination
Inhibiting axon regeneration
What is the function of the microglia?
Main cell responsible for removal of cellular debris and immune defence
What prevents normal immune surveillance of the brain?
Blood-brain barrier
How do microglia detect damage and react?
Normally have multiple processes expressing ATP receptors
ATP from damage or inflammation binds P2Y class of receptors causing a conformational change
Processes retract and the microglia becomes phagocytic
What are the three types of ependymal cell?
Ependymocytes
Tanycytes
Choroid plexus cells
Which type of ependymal cell is most abundant?
Ependymocytes
What is the function of ependymocytes?
Form epithelial lining
Have cilia to circulate CSF and microvilli for absorption
Describe a tanycyte and its function.
Elongated cell mainly associated with third ventricle
Acts as a sensor for secreted hormones (hypothalamus) and other small molecules in CSF
Describe choroid plexus cells and their function.
Specialised cuboidal epithelial cells
CSF production in all ventricles of brain
How many axons can a Schwann cell myelinate?
1
What are the functions of Schwann cells?
Myelination
Promote axon regeneration
How do Schwann cells promote axon regeneration?
Upregulation of permissive ECM components
Rapid removal of myelin debris by phagocytosis
What is the function of satellite cells?
Structural support, homeostatic and metabolic support to neurons (similar role to astrocytes)
What are satellite cells associated with?
Sensory neurons in dorsal root ganglia
Sympathetic ganglia
