Neurons and Neuroglial Cells Flashcards
This covers ion channels and Donnan equilibrium as well.
Neurons are unique because they have the ability to precisely & rapidly communicate with other cells at distant sites. State the two traits that enable this.
(i) High degree of morphological and functional asymmetry.- receptive dendrites at one end and projection by axon.
(ii) Neurons are both electrically and chemically excitable: - express many transport proteins and ion channels which allow movement of ions and molecules. Alter neuronal excitability.
Why is a neuron like a minicomputer?
It integrates the processes of reception, integration and transmission, akin to a computer.
(a) State three criteria used in the classification of neurons.
(b) Diversity of neuronal cell type can be explained by ____________________. “Each cell is the set of molecules it expresses.”
(a) Criteria used in the classification of neurons:
✓ Dendritic morphology and the pattern of dendritic tree
✓ Pattern of axonal projection
✓ Electrophysiological properties of the neuron
(b) different patterns of gene expression
Neurons can be classified depending upon the length of axon into ________ neurons and ________ neurons.
Other than naming, compare the length of axons and state where they are found.
Golgi type I neurons:
✪ long axons
✪ cell body situated in CNS and their axon reaches remote peripheral organs
✪ usually sensory and motor neurons
Golgi type II neurons:
✪ short axons
✪ present in cerebral cortex and spinal cord
✪ usually interneurons
State the four functional neural zones.
- Zone of signal reception: dendrites and the cell body (soma)
- Zone of signal integration: axon hillock
- Zone of signal conduction: axon; some wrapped in myelin sheath
- Zone of signal transmission: axon terminals
(a) Neurons engage in energy transduction. TRUE or FALSE?
(b) Dendrites don’t have the property of plasticity. TRUE or FALSE?
(c) Dendrite have tapering shape and may increase surface area by having ____________.
(a) TRUE
(b) FALSE
(c) dendritic spines.
Axoplasmic transport:
Transport of small and large molecules along the axon is bidirectional. State the difference between anterograde and retrograde flow.
Anterograde flow:
☑ kinesin dependent
☑ from perikaryon towards synapse
☑ towards (+) end of the tubule
Retrograde flow:
☑ dynein dependent
☑ from synapse towards perikaryon
☑ towards (-) end of the tubule
[Remember from your cytoskeleton knowledge that kinesin and dynein are motor proteins/cytoskeletal motors beside myosin.]
Anterograde flow transports macromolecules and organelles synthesised in the perikaryon at 3 distinct speeds. State these speeds and the structures/substances transported at each.
(a) Slow stream: proteins and microfilaments (less than 10 mm/day)
(b) Intermediate speed: mitochondria
(c) Fast stream: substances contained in vesicles that are needed in the axon terminal during neurotransmission (50-400 mm/day)
NOTE: there must be a mechanism that designates particular vesicles for anterograde or retrograde transport.
State the functions of axoplasmic transport.
☑ Delivers proteins, mitochondria, vesicles to synapses
☑ Removes recycled proteins and organelles to cell body for destruction by lysosomes
☑ Carries intracellular chemical messages from synapse to cell body
☑ Delivers neuron-specific viruses (herpes and pox viruses) from peripheral sensory nerve endings to cell bodies in the CNS [not necessarily a function but more of a consequence]
State consequences of interfering with axoplasmic transport.
(a) Interruption of axoplasmic transport causes a traffic jam on the proximal side of the interruption and Wallerian degeneration of distal parts of neuron.
(b) Anticancer drugs targeted against microtubules have neuronal toxicity.
Further notes:
☑ Wallerian degeneration refers to the well-orchestrated morphologic and biochemical changes that occur in axons, Schwann cells, and macrophages distal to a site of nerve injury, resulting in the establishment of a microenvironment supportive of axonal regeneration.
☑ Some of the characteristics of Wallerian degeneration include:
(a) Reduced or loss of function in associated structures to damaged nerves.
(b) Gradual onset of numbness, prickling or tingling in feet or hands, which can spread upward into legs and arms.
True or False: Oligodendrocytes and Schwann cells constitute 20% of macroglia.
False.
Oligodendrocytes and Schwann cells constitute 50% of macroglia.
Further notes:
➤ Non-myelinating Schwann cells promote development, repair and maintenance of neurons.
➤ Both neurons and neuroglia develop from a common neuroepithelial progenitor cells in embryonic nervous system
Channel mediated transport allow much faster transport than carrier proteins. Ion channels are such examples. State the properties of ion channels.
☑ Membrane-spanning protein
☑ Hydrophilic ion conductive pathway; Water-filled; Traversing ion must lose hydration shell
☑ Selective; charge screening and size
☑ Gating properties; Exist in open and closed states
☑ Substrate is charged and the conduction can be measured very precisely, as opposed to water channels
[Jog your memory: What type of membrane proteins are ion channels?]
Classify ion channels into 2 major classes.
☑ Non-gated ion channels
☑ Gated ion channels
a) What are gated ion channels?
b) State the types of gated ion channels.
a) These are proteins that allow ions to move in and out of cells in response to a stimulus.
b)
(i) Stretch-gated: respond to mechanical stimuli
(ii) Ligand-gated: respond to an extracellular molecule (ligand)
[Note, most ligands are extracellular. Some may cross through the cell membrane to be intracellular]
(iii) Signal-gated: respond to intracellular molecule (this channel is coupled to a neurotransmitter receptor via a G-protein)
(iv) Voltage-gated: respond to changes in the membrane potential of a cell.
Further important points:
☑ (ii) and (iii) are located on dendrites and soma.
☑ Changes in channel permeability create electrical signals.
☑ Mechanically gated ion channels are usually found in sensory neurons.
In simple terms, what is the difference between hydrostatic and osmotic pressure?
Hydrostatic pressure is due to the force of gravity on a fluid, while osmotic pressure is due to solute concentration differences across a semi-permeable membrane.
