Question

Cell Biology Tutorial: Cells of the Nervous System.

Answer 1

\({\bf{Basic~Terminology:}}\)

- Central nervous system (CNS): nerves/glia of the brain and spinal cord
> basic components: spinal cord, brainstem, cerebelllum, cerebrum
- Peripheral nervous system (PNS)nerves/glia in other parts of the nervous system
- Neuron: a bundle of cells/circuits that transmit information via electrical signals
- action potentials: electrical signals that travel along neurons
- sensory neurons: receptors that convert signals from the environment into electrical signals
- interneurons: transmit information between neurons via chemical/electrical signals
- motor neurons: neurons that stimulate other cells
- afferent neurons: sensory/receptor neurons that transmit signals from receptors towards the CNS
- efferent neurons: carry signals away from the CNS

- excitatory signals: increase transmission of electrical signals
- inhibitory signals: decrease transmission of electrical signals
- neuromodulatory: hormone receptors that activate GPCR's to increase or decrease electrical signals
- synapses: junctions between the axon of one neuron and the dendrite of another
- synaptic vessicles: carry neurotransmitters between the synapse
- presynpatic/postsynpatic cell: the cell that releases/receives the neurotransmitters

Answer 2

\({\bf{Glial~Cells:}}\) do not directly transmit signals but compose other cell types/structures that facilitate the transmission of electric signals
- oligodendrocytes: synthesize myelin sheaths for the CNS
- Schwann cells: synthesize myelin sheaths for the PNS
- astrocytes: produce growth factors and extracellular matri proteins, are often located around synapses and dendrites to change the conc. of ions via channels
- microglia: transmit signals to the astrocytes and are part of the CNS immune system

\({\bf{Neural~Stem~Cells:}}\)
- neural tube: layer of ectoderm that rolls into a tube shape; gives rise to the other CNS cells
- venticular zone: forms from the neural tube, region where cell divsion takes place
- general steps of neurogenesis:
embryonic neuroepithelial cells (NEC, yes, that's the abbreviation, not ENC): ---> radial glial cells ---> progenitors --> move to the SVZ (subventricular zone) ---> differentiate into neurons
- adult SVZ: may give rise to new neural stem cells

Answer 3

\({\bf{Action~potential~basics:}}\)
1. resting state: nongated K+ channel is partly open to generate the reseting potential, but the Na+ gated channels remain closed. cystolic face is negatively charged.
2. depolarized state: gated Na+ open, reversing the potential and negative charge distribution.

depolarization of membrane --> increased probability of one channel opening --> opening of the gate --> excess positive charges on the cytosolic face diffuse (passive spread) depolarize adjacent regions of the membrane --> opening of more channels and increased Na+ influx --> approaches ENa (equilibrium potential of sodium)

\({\bf{Functioning~of~Na+~Channels:}}\)
four positively charged voltage-sensing alpha helices around central pore + channel-inactivating segment

resting state: helices are attracted to the negative charges of the cytosolic side --> small depolarization changes the attraction towards the exoplasmic charges --> gate opens --> flow of Na+ stops after the channel-inactivating segment enters the channel --> re-establishment of negative charge distribution --> inactivating segment exits the pore and the process returns to resting state

firing is unidirectional and limited in quantity b/c the Na+ channels are inactivated after depolarization

\({\bf{Functioning~of~K+~Channels:}}\) similar to the Na+ channels with a few key differences:
1. they remain open after depolarization
2. only close when the membrane potential has returned to the original negative charge distribution

Answer 4

\({\bf{Brief~Notes~on~Myelination:}}\)
- for un-myelinated aons speed of action potential is proportional to the diameter of the axon which is why myelination is needed to keep neuron sizes reasonable
- influx of Na+ only occurs at un-myelinated nodes: the cytosolic charges spread through the cytosol to the next nodes, inducing action potentials down the next node
- oligodendrocytes are made of MBP and PLP
- Schwann cells are made of lipid and protein; P0 and MBP

Answer 5

\({\bf{Ca2+~Channels:}}\)

- action potential in presynpatic cell --> opening of Ca2+ membrane channel --> influx of Ca2+ --> fusion w/ vesicles containing neurotransmitters --> release of neurotransmitters
- astrocytres/schwann cells: release protein signals to form/preserve synapses, ex. thrombospondin (tsp)
- active zone: area of the plasma membrane where proteins involved in synaptic vesicle fusion and docking
- postsynaptic density: similar to the active zone just at the postsynaptic cell region

\({\bf{Neuromuscular~synapses:}}\)
- acetylcholine: neurotransmitter made by motor neurons
- AChR: receptor for acetylcholine
- MuSK: receptor tyrosine kinase localized in AChR regions, involved in the acetylcholine/AChR process
-Agrin: glycoprotein which is secreted near the myotube, stimulates interactions between LRP4 and MuSK --> activates signaling pathways

Answer 6

\({\bf{Ca2+~Vessicles:}}\) 3 subtypes
- small pool near active zone
- recycling pool
- reserve pool, most vesicles are here, most distant from the active zone, only released after strong stimulus

- synapsins: attach synaptic vesicles to cytoskeleton, which can be acted upon by kinases to release the vesicles
- before release, the synaptic vesiclce and the membrane are bound by alpha-helices made of v-SNARE and t-SNARE proteins and binding of complexin to the complex
- synaptotagmin: Ca2+ binding protein: ccauses exocytosis after Ca2+ influx
- after the vesicles are released, they are endocytosed via clathrin coated vesicles, then de-coated and refilled with neurotransmitter

- shibire (shi) mutation in Drosophila that prevents vesicle recycling (interferes with dynamin formation)

Answer 7

Anyway that's it, hope it was a helpful resource.

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