Structure of the Nervous System Flashcards
How many neurons in the cerebellum?
68-86 billion
What is the axon hillock?
Controls what moves between the cell body and axon
What glia are present in the PNS?
Schwaan cells
Satellite cells
What do Schwaan cells do?
Produce myelin sheath that coats the axon
Have a role in the repair process
What do satellite cells do?
Surround cell bodies in ganglia
Regulate concentration of neurotransmitter, nutrients and dissolved gases (O2 and CO2)
What glial are present in the CNS?
Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
What do oligodendrocytes do?
Produce myelin sheath that coats the axon
What do astrocytes do?
Regulate concentration of nutrients, ions, neurotransmitter and dissolved gases
Form scar tissue
Maintain the integrity of the blood brain barrier
Recycle neurotransmitter
What do microglia do?
Absorb pathogens and waste products
What do ependymal cells do?
Produce CSF
Line the ventricles and spinal canal
What are the steps of neural tube formation?
- Start with flat, neural plate
- Morphogens cause the plate to fold, forming a furrow at the medial hinge
- Neural folds move towards each other and fuse at the neural crest, forming the neural tube and epidermis
Neural crest cells delaminate and migrate to form what 4 things?
Peripheral nervous system
Melanocytes
Chondrocytes
Smooth muscle
Exit/entry point of sensory/motor neurons
Sensory neurons enter the spinal cord through the dorsal horn
Motor neurons exit the spinal cord through the ventral horn
What are rhombomeres?
Rhombomeres are the subdivisions of the neural tube that will go on to form the hindbrain (brainstem and cerebellum)
Regions R1-R8
What are Hox genes?
Hox gene expression controls the head-tail organisation of the embryo body
Hox genes are found in the genome in the same order that they are expressed in the body
First discovered in fruit flies
What is sonic protein?
A type of morphogen that controls the structural formation of the spinal cord
How does sonic protein work?
Sonic protein is secreted by the notochord, which runs parallel to the neural tube on the ventral side
High concentrations of sonic protein lead to development of motor neurons
Lower concentrations of sonic protein lead to development of interneurons
What is a morphogen?
Chemical agent that controls morphogenesis - the development of new structural features
What is combinatorial control?
The type of neuron that develops is dependent on the concentration of many transcription factors
How is the direction of axon growth guided?
The axon terminals contain growth cones, made up of many tiny filopodia
Filopodia is made of actin and microtubules
Attraction cues cause polymerisation
Negative cues cause cytoskeleton collapse
Define chemotatic
Direction of growth influenced by chemicals
Define haptotatic
Direction of growth controlled by adhesion sites
What are commissures?
Regions in the brain where the two hemispheres are connected
Caused by horizontal axon growth that crosses the midline
5 commissures in the brain
What is midline crossing?
During axonal growth, axons grow parallel to the midline
At some point they cross over the midline, and then continue growing parallel again
What are the attraction cues/receptors for axon growth?
Receptor = Robo
Repulsion cue = Slit
What mutants have been made with drosophila that prove the mechanism of attraction cues?
Robo mutants have no receptor, so never detect repulsion cues. Nerve fibres just grow in circles
Slit mutants produce no repulsion cues. Axon tracts collapse down the midline
Another example of a receptor/guidance cue pair
Receptor = Neuropilin
Cue = semaphorin
can be attractive or repulsive depending on specific type
What is topographic mapping?
Axons map their output in the same configuration as it was received
Example of where topographic mapping is found
Retinotectal system
Axons from retina map on tectum in order of image
