Cell Biology of Neurons and Glia Flashcards
What determines passive membrane properties of the neuron?
Conductance of non-voltage gated ion channels, membrane capacitance, and resistivity of the cytoplasm.
What determines the active membrane properties of the neuron?
All of the passive determinants as well as concentration and distribution of ion channels controlled by voltage, neurotransmitter or ligand binding, or a second messenger system.
What are the four structural compartments of the neuron?
Dendrites, cell body, axons, synaptic terminals
What are the three forms of axoplasmic transport and what purpose do they serve?
Fast anterograde transport: transports organelles and vesicles towards the synapse and is mediated by kinesin Slow anterograde transport: transports cytoskeletal proteins by bulk flow Fast retrograde transport: transports trophic factors, signaling molecules, endosomes, and lysosomes back to the cell body via dynein
What can disrupt axoplasmic transport? What symptoms does this cause? What foreign agents can also be transported this way?
Fast axonal transport is compromised by a lack of oxygen or microtuble destablizing drugs (i.e., colchicine) which can lead to neuropathy. Viruses can also infect the neuron and be transported to and from the cell body by these mechanisms.
What type of current flow (active or passive) is required for action potential conduction?
Both–voltage gated ion channels are opened in response to passive depolarizing current flow down the axon.
What two features of action potential firing are important for signaling?
Number of action potentials and the time interval between them (rate)
What are the roles of glia in the CNS and PNS?
Regulation of cell migration and axon guidance Formation of the blood brain barrier (astrocytes) Trophic and insulating functions (oligodendrocytes myelinate axons in the CNS, Schwann cells myelinate axons in the PNS) Modulation of synaptic function Mediate response to injury (microglia serve phagocytic and inflammatory functions) Maintain extracellular environment (astrocytes)
What is the difference between myelination in the CNS and PNS?
Oligodendrocytes myelinate axons in the CNS and have many processes that wrap around segments of different axons. Schwann cells line up along the axon and wrap around it entirely, therefore a single axon is myelinated by many Schwann cells.
What is saltatory conduction?
Conduction along a myelinated axon that jumps from node to node. Only the nodes contain ion channels that regenerate action potentials and the space between nodes has very low capacitance
What two properties of the axon impact the speed of transmission?
Myelination and diameter–increasing both increases speed
What is Charcot-Marie-Tooth disease? What mutation causes it?
Charcot-Marie-Tooth disease is a peripheral demyelination disorder caused by autosomal dominant mutations in peripheral myelin protein 22 (PMP22). It is characterized by progressive loss of muscle tissue and touch sensation.
Describe synaptic transmission of PNS synapses. How many synapses are needed to affect the postsynaptic cell? What neurotransmitters are involved? How are they eliminated?
The main synapse in the PNS is the neuromuscular junction. When an action potential reaches the terminal, voltage gated calcium channels are opened and initiate vesicle fusion and ACh release into the synaptic cleft. ACh binds postsynaptic receptors which open cation channels resulting in an end plate potential (depolarization). A single synapse is responsible for changes in the postsynaptic cell because ACh always depolarizes the postsynaptic membrane and always causes muscle contraction. ACh is eliminated by acetylcholinesterase which is located in the basal lamina.
Describe synapse transmission in the CNS as well as the two types of responses NT’s can induce and whether this response is dependent on properties of the NT or the receptor.
Presynaptic action potentials similarly result in calcium influx and vesicle fusion. Neurotransmitters bind postsynaptic receptors and initiate different effects depending on the properties of the receptor. Postsynaptic potentials are graded by the amount of NT binding and can be either excitatory or inhibitory. Excitatory synapses tend to be located on the dendrites while inhibitory synapses tend to be located on the cell body. Action potentials are not always elicited in the postsynaptic cell. Many EPSPs are usually required to generate a postsynaptic action potential. CNS synapses are more plastic than PNS ones.
What conditions affect the functioning of the presynaptic terminal?
Congenital myastehic syndromes that impair endocytosis or membrane recycling Lambert Eaton myastheic syndromes (affect presynaptic calcium channels) Botulinum and tetanus toxins impair vesicle fusion.
